Wildguzzi.com
General Category => General Discussion => Topic started by: Mayor_of_BBQ on May 04, 2023, 12:50:46 PM
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Hello all,
I have an extensively modified CX-100 that I bought from a former member on this board. Tho I love a great many things about the bike, I have come to learn that a lot of the work done on the bike was shoddily completed and generally 'off'
I had the chance to briefly put it on a dyno at a bike show this week, and tho it was a quick couple runs up to WOT, It was immediately clear that I have EXTREMELY lean running condition on the bike, and the HP is probably nearly 30% under what I should be getting (@40hp)
couple quick things about the bike before I get to the question:
1. 1979 CX100
2. PHF 36b carbs
3. Lafranconi pipes
4. K&N pod filters
5. bike is said to have a hot cam (no I don't know which one)
6. bike is said to have had 'head work' (assumed polished but unsure of extent) I believe the valves are stock
7. The bike starts flawlessly (on choke) and idles perfectly (maybe a little cold blooded for a min or two), it's pulls smoothly thru the range, never coughs/surges/sputters or anything like that.
The guy running the dyno is a well regarded local vintage wrench/tuner/restorer/machinist. His specialty mostly Brit bikes, but he is known quality with BMW, Guzzi, and Ducati as well.
His comment was "way, way too lean! Go up 4 sizes at least on the main jets. She's got a LOT more to give"
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Now, I have always been confounded and a little disappointed in the performance of this bike, mostly because it was marketed as a hot rod.
Honestly, I've never ridden any other Tonti 850/1000/1100, and I have nothing to base it off of. My other Guzzi were a very strong running v65, an good running rebuilt Ambo, and my Breva 1100.
This CX100 is faster than the Ambo by a fair bit (ambo weighs a ton tho), but it's barely faster than the v65, and my Breva would absolutely blow its doors off.
Ever since I got it, I ended every ride thinking "huh, I really thought this thing would be faster" but it's not a dog or anything... I keep telling myself "the small block was much lighter, the Breva is much more powerful, and the CX100 was never a race-derived bike, it has a touring bike 949cc motor and it's 45 years old- so whatta you expect??"
But yet with the stated mods and this supposedly 'built' motor, it just doesn't have the sauce I thought it would.
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SO after that sprawling preamble (we are here for campfire discussion, right?)
* I pulled the main jets- they were 140 -I ordered a set of 145 mains and hope to get them tomorrow
* I checked the needle (no idea which needle it is) and it was clipped at the lowest groove (richest possible setting)
* I am not going to mess with the idle jets at this time, as I said it starts, idles, and runs great at low engine speed
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At long last, THE QUESTION:
Assuming the 145 mains wake this thing up, what should I do about the needles?
1. run the 145's and leave the needle where it is?
2. run the 145's and move the needle to the middle?
3. run the 145's and drop the needles all the way
4. replace the needles with something else (and set them on what clip?)(how/where would I measure the needle to determine what I have currently?)
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If you read all this, thank you. Please let me know what your thoughts are. This guy drags the dyno trailer to a handful of events over the summer, so I hope to make some changes, check it with the butt dyno, and then get back somewhere I can put it on the dyno again.
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A few thoughts...
First, is everything tight and leak proof (manifolds, etc.)?
Are petcock screens or or any other fuel filter flowing a 100%. Air filters clean?
Change needle for more flow.
My T-3 has the 949cc kit, 36mm, cam for the old V-7 Sport and heads ported and cleaned up. Valves are stock. K&Ns and cheap Emego mufflers. My mains are either 130 or 135s. Here is the dyno chart. The low RPM dip was intentional.
(https://i.ibb.co/XFkctX8/Screen-Shot-2022-10-10-at-2-52-40-PM.png) (https://ibb.co/XFkctX8)
GliderJohn
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Needle chart on This Old Tractor https://www.thisoldtractor.com/dellorto_slide_needle_specifications_for__phbe-phf-phm-phsb-vhsb_carburetors_-k_slides-.html
I believe Guzziology mentions that double digit needles were made as concessions to emissions regs.
Numbers are stamped on the side of the needles.
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As above, make certain everything is in order with the fuel delivery and air leaks. Having the valves adjusted is also important.
The most important thing to remember about jetting, is change only one thing at a time. You can't know how much a larger main jet will enrich the needles if you move the needles at the same time as you increase the main jets. The tedious answer to how to get where you're going is to increase the main jets one size at a time and chop the plugs properly (ignition kill at WOT high rpm) until you get a little color on them. Whether the motor wants them light tan or medium brown is a question for the dynomometer but typically hemi head engines like to be on the darker side. After you get the mains right, then you can go back and ride around casually to find the best home for the needles. It is possible that along the way as you increase mains that you'll get a rich stumble in the needles in which case you sort of have to drop them a slot or two.
Don't be disappointed in the performance until you prove that proper jetting doesn't bring hoped for results.
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Ed Milich devised this recipe for a Sport 1100 which probably breathes better than your bike - how much depends on the heads and cam I guess...
Works great on my stock Sport - 40mm PHMs
K4 needle clip in lowest groove
128 Main
68 Idle
50/3 slide
265 Atomizers
Guessing your atomizer (needle jet) is smaller because 140 mains were too small.
Atomizer and needle establish the range in which everything else works...
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One trick that I was told, and appears to work especially for main jets which have the most effect at wide open throttle is to do a run on the road or dyno and see how it performs. Then pull the choke a small amount to open the enrichment circuit a little. If it responds better the mains are to small. It should respond worse if the mains are the correct size.
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A few thoughts...
First, is everything tight and leak proof (manifolds, etc.)?
Are petcock screens or or any other fuel filter flowing a 100%. Air filters clean?
Change needle for more flow.
My T-3 has the 949cc kit, 36mm, cam for the old V-7 Sport and heads ported and cleaned up. Valves are stock. K&Ns and cheap Emego mufflers. My mains are either 130 or 135s. Here is the dyno chart. The low RPM dip was intentional.
(https://i.ibb.co/XFkctX8/Screen-Shot-2022-10-10-at-2-52-40-PM.png) (https://ibb.co/XFkctX8)
GliderJohn
My SP1000 (same motor) ran this spec for a time and my recollection of the mainjet size is as GliderJohn says. Certainly not 140 or above.
How many miles has the engine done and what is the mechanical condition? Valve guides? Valve sealing? Ring condition? A compression or leakdown test might be a good place to start. Was the squish clearance set at a reasonable level?
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ASI recall that is a fine looking bike,it is faster than a couple of you other bikes that go 100,it runs great and is 44 years old.The old adage if it’s not broke don’t fix it may apply here.No guarantees that it wont run worse if you mess with it.I bought a78 T3 that supposedly goes over 100 but I don’t intend to find out because it runs just fine up to about 75 andI don’t ride it on freeways.
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Take the main jets out and ride it. See if the needle and needle jet are correct.
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What do the plugs look like? have you tried messing with the timing?
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My 36’s have a 145 main and run great. I wouldn’t hesitate to throw those in. There’s thinner/richer needles you can get, jets are cheap. I bought quite a few carb parts before I was happy with mine. Now I have a little carb tuning box with new jets and needles I can play with. The WOT run though is main jet tuning so start there
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My advice is to not take advice from online forums until you know enough not to need the advice in the first place. That is, you will find contradictory advice, and you need to know how to evaluate it.
My best recommendation is to study the Dellorto tuning manual. They built your carb, and they give instructions on how to tune it.
Once you have absorbed that manual, you will be able to appreciate the rare beauty of elliptical advice such as John Croucher’s. Until then you will be lost, grasshopper.
You can do it.
Moto
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145 mains actually sounds about right. My 850 LM runs 143 mains. Determined at the dragstrip giving best ET and top end.
Never had it on a dyno but would estimate close to 60 RWHP. Pulls over 8k RPM in fifth with more on tap.
Stock Cam, Raceco heads, K&N pods, Renn Sport exhaust.
Pete
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A few thoughts...
First, is everything tight and leak proof (manifolds, etc.)?
Are petcock screens or or any other fuel filter flowing a 100%. Air filters clean?
Change needle for more flow.
My T-3 has the 949cc kit, 36mm, cam for the old V-7 Sport and heads ported and cleaned up. Valves are stock. K&Ns and cheap Emego mufflers. My mains are either 130 or 135s. Here is the dyno chart. The low RPM dip was intentional.
(https://i.ibb.co/XFkctX8/Screen-Shot-2022-10-10-at-2-52-40-PM.png) (https://ibb.co/XFkctX8)
GliderJohn
Yes thanks John
I have just gone thru the exhaust, all is tight and right. When I got it the crossover was loosely installed, huge leaks.
The valves are freshly set per guzziology
Petcock screen and fuel filters are good
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As above, make certain everything is in order with the fuel delivery and air leaks. Having the valves adjusted is also important.
The most important thing to remember about jetting, is change only one thing at a time. You can't know how much a larger main jet will enrich the needles if you move the needles at the same time as you increase the main jets.
Good points. Thats why I am only doing the mains at this time, tho I am due for airfilter cleaning/oil.
I am going to service the filters and swap the mains now, will leave the needles alone until I see where I stand.
Fuel delivery, valves, and exhaust leaks are all freshly checked and A-OK
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My 36’s have a 145 main and run great. I wouldn’t hesitate to throw those in. There’s thinner/richer needles you can get, jets are cheap. I bought quite a few carb parts before I was happy with mine. Now I have a little carb tuning box with new jets and needles I can play with. The WOT run though is main jet tuning so start there
:boozing: Nice, thanks
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My CX with 36mm carbs and a B10 cam has 130 mains and it runs perfectly fine, as Turin said, I would check the timing. Does it have points or electronic ignition?
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My CX with 36mm carbs and a B10 cam has 130 mains and it runs perfectly fine, as Turin said, I would check the timing. Does it have points or electronic ignition?
Main jets are all about WFO. Have you ever wound it out for a mile or two. My 850 came with 135 mains. It would barely pull 6800 in fifth after Manfred did his magic. I tried 138s, 140s, then 143s and now it will pull well over 8200.
If you are running ethanol fuel it runs even leaner.
40 HP seems way low. ‘60s era 650s could do that.
I think a better test would be to take to a dragstrip and see what it will do. LM850s were turning 13 seconds flat nearly 50 years ago. Built 950s should be able to beat that.
Pete
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My advice is to not take advice from online forums until you know enough not to need the advice in the first place. That is, you will find contradictory advice, and you need to know how to evaluate it.
My best recommendation is to study the Dellorto tuning manual. They built your carb, and they give instructions on how to tune it.
Once you have absorbed that manual, you will be able to appreciate the rare beauty of elliptical advice such as John Croucher’s. Until then you will be lost, grasshopper.
You can do it.
Moto
A lot of Chrysler Theromoquads were thrown in the trash after being messed with. There is a very precise procedure for setting one up. The plastic body was usually blamed for the problem, claims they warped is unfounded. Follow the manufacturer's procedures and recommendations.
kk
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My CX with 36mm carbs and a B10 cam has 130 mains and it runs perfectly fine, as Turin said, I would check the timing. Does it have points or electronic ignition?
Electronic, I've never had a points bike.
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Main jets are all about WFO. Have you ever wound it out for a mile or two.
Pete
I have wound it out and it probably could use a larger main. It was mostly used as a commuter in the past but now that I'm not commuting I should install a bigger main jet but it doesn't feel anemic, except on hills which I have always thought that it was due to the lightened flywheel. Maybe a bigger main will solve that problem?
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I have wound it out and it probably could use a larger main. It was mostly used as a commuter in the past but now that I'm not commuting I should install a bigger main jet but it doesn't feel anemic, except on hills which I have always thought that it was due to the lightened flywheel. Maybe a bigger main will solve that problem?
Easily swapped on the road given the float bowl nut and you will know right away if there is a change for better or worse.
Pere
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Easily swapped on the road given the float bowl nut and you will know right away if there is a change for better or worse.
Pere
Yes, and I have some larger mains around here, as soon as I finish putting the transmission back together I'll give it a go.
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With that combination it should be reasonably quick in third from 50 mph on up to 7k rpm. You’ll get there, it got so I would want to tweak something before I went for a ride even after I got it running the way it should. As you get closer, the small changes make more subtle differences. Make sure you get the ignition super tuned to start. I had to laugh at myself when I started looking at a spare 44 amp magneto from our funny car. They probably take sixty horse to spin up and will hurt you, but you could ignite anything!
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Guzzi (and probably most all other manufacturers) were known to publish horsepower ratings that at best were optimistic. Claimed horsepower as measured at the crankshaft at optimal controlled conditions were likely still unobtainable in the real world.
My 72 Eldorado and 73 V7 Sport were both tuned on a dyno and the rear wheel horsepower on a fully rebuilt Eldorado (all stock) was right around 44 hp and the V7 Sport could (also fully stock and rebuilt) just touch 48 hp.
Put a Norton Comando or Triumph Bonneville of the same period on a dyno and I bet one would struggle to see rear wheel horsepower of 40.
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Good thread & timing, Chad- no pun intended... All this info is good to know. finally getting my CX sorted & on the road is on the immediate agenda. The details of the nearly new engine were a total mystery and the combination still isn’t “right” at this point. I will be quite happy to have the engine tuned and performing as well as my V7 Sport. Having another spot-on Guzzi with no stumble or hesitation, even if it isn’t the absolute fastest & flickable road burner on the road, is all I want.
Im guessing you hit the Dyno at the Meltdown last weekend(?). We were camping at Table Rock with the in-laws, so I missed it. Was it a good crowd?
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My SP1000 (same motor) ran this spec for a time and my recollection of the mainjet size is as GliderJohn says. Certainly not 140 or above.
How many miles has the engine done and what is the mechanical condition? Valve guides? Valve sealing? Ring condition? A compression or leakdown test might be a good place to start. Was the squish clearance set at a reasonable level?
Some good advice here, along with the enricher test. Sometimes with altered cams you may find it cheers up with the baffles out, check your exhaust system for restriction. Also air cleaners etc for same. DonG
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Guzzi (and probably most all other manufacturers) were known to publish horsepower ratings that at best were optimistic. Claimed horsepower as measured at the crankshaft at optimal controlled conditions were likely still unobtainable in the real world.
My 72 Eldorado and 73 V7 Sport were both tuned on a dyno and the rear wheel horsepower on a fully rebuilt Eldorado (all stock) was right around 44 hp and the V7 Sport could (also fully stock and rebuilt) just touch 48 hp.
Put a Norton Comando or Triumph Bonneville of the same period on a dyno and I bet one would struggle to see rear wheel horsepower of 40.
Before getting hired at Barbers, Brian Slark was the Norton Club’s tech advisor. Along with Norton tuner Leo Goff they said a typical Norton Commando made about 47 RWHP. Race bikes might make 53-55 RWHP.
Pete
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With respect to the Dellorto 36mm carbs, I put a new pair of Dellorto 36 pumpers on my 1975 Ducati 860 last year as that was all that Bevel Heaven could supply as they no longer stocked the 32mm stock carbs. The bike did not as well on the 36’s. I called Wolfgang Haerter the Laverda guru who also distributes Dellorto. Wolfgang was a wealth of information, to begin with he was supplying the new Dellorto’s to Bevel Heaven and these new carbs are jetted by Dellorto for Guzzi twins with the bigger valves specified for the 850 LeMans. Wolfgang said he had the stock 32mm Dellorto carbs in stock and they were better suited for the Ducati. Wolfgang had the correct specs for the 36mm Dellorto carbs for a Ducati 860 and sent me new atomizers, needles and jets, totally cured the Ducati.
Wolfgang told me the 36mm Dellorto carbs were too much for small valve Guzzi’s and Ducati 860 motors, better performance came from a 32mm carb.
For a 36mm Dellorto on a Guzzi, bigger valves, larger port diameter, bigger manifolds and exhaust diameter are needed to make use of the bigger carbs. The Guzzi LeMans and Mark II LeMans heads have bigger valves, ports, exhaust and manifolds.
Contacting Wolfgang at Columbia Car and Cycle in Nakusp British Columbia may be wort a call.
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I’m thinking the phf 36’s are too big too, I think the vhb’s are all you should need
Pretty common to hear someone try bigger carbs as an upgrade
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My LM2 with 950cc/B10 cam/PHF 36 is running with 148 main jets and, whilst I've not had it on the dyno feels fairly strong to me.
Actually, when I bought it, as an 850cc, it was running the 148 jets. I fitted the big bore and left the jets as were, I did intend to get it on the dyno but never got round to it, it certainly isn't running lean though.
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Amedeo from Raceco UK said many moons ago that 34 mm carbs were optimal for the small valve heads in terms of power
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I have 36's on my CX and it's been fine and I never opened the intakes to accommodate the larger carbs.
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It all comes down to the combination of components. The first mod I did to my 850T was to install 36 Delortos with delrin manifolds. The results were disappointing. (nothing lost buy not much gained) Installing an X9 cam, increasing compression/.040 squish, and minor porting really make for a really sweet running 850.
If I it had a wilder cam and bigger valves, It would need 40's, but that's another bike.
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I’m thinking the phf 36’s are too big too, I think the vhb’s are all you should need
Pretty common to hear someone try bigger carbs as an upgrade
May very well be true, but I am not a tuner... And I'm not even a decent mechanic. I can do my normal maintenance etc.. But I bought this thing because I thought a knowledgeable enthusiast put it together, and everywhere I have looked, it's cocked up. I still like the bike, but wow have I learned a valuable lesson. Not only did I overpay by at least $1k, but my hopes of a turn-key custom hotrod have pretty much been kaput. I would have been better off buying a late model V7 or waiting 8mos and getting the V100 Mandello.
Spent the weekend doing spring yard & garden prep.. I did get my jets and some other bits... Hopefully the rain stops and I will take it out for a rip with the new mains and see what it does.
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I’m thinking the phf 36’s are too big too, I think the vhb’s are all you should need
Pretty common to hear someone try bigger carbs as an upgrade
If you are happy with the performance with the vhbs fitted, that's fine, no point in expending time and money changing things.
But if you fancy a little more grunt then the larger carbs and ideally porting to match is a good start. You also need to remember that these engines are getting on in years so the condition of bores, rings. valve guides, cam, lobes and valve sealing may leave a bit to be desired and could impact performance whatever route you take.
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Turin & Blackcat have touched on the subject of timing & ignition. I'll throw in also sparkplugs. You're getting fuel but probably not a complete burn when the throttle is opened.
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I had one like that, it turned out that the squish band was too wide. Deleting the base gasket and using flange sealant cured it without any machining. It came out at .040”. So if everything else checks out, I’d try that. It didn’t ping , which was a concern.
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almost everyone thinks that bigger jets are the answer to more power. This is often wrong and is particularly wrong on an engine with good head work.
Conversely to what one would think, an engine with free flowing heads needs smaller jets (and even carbs at times) because it is now flowing fuel and air so much more efficiently. The better air flow actually pulls fuel up efficiently now as opposed to just burbling up from a bigger jet before the head work.
I used to roadrace a Sportster. When I made it a 1200 with Buell heads, I naturally put in a bigger main jet. It bogged on WOT. I put in the next size jet. More of the same. Repeat for every large jet I had. The same. I even took a jet an bored it out even bigger. The worst running yet. I was all set to buy new cams.
In desperation, I used the smallest main I had and went on the the track. It ran like a raped ape with zero hesitation when the throttle was whacked open. Power everywhere and a stupid amount of torque.
Where one has the accelerator pump set to activate also plays a role.
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I,m thinking cam off a tooth
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I,m thinking cam off a tooth
Didn't think of that, certainly worth checking if all else fails.
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almost everyone thinks that bigger jets are the answer to more power. This is often wrong and is particularly wrong on an engine with good head work.
Conversely to what one would think, an engine with free flowing heads needs smaller jets (and even carbs at times) because it is now flowing fuel and air so much more efficiently. The better air flow actually pulls fuel up efficiently now as opposed to just burbling up from a bigger jet before the head work.
I used to roadrace a Sportster. When I made it a 1200 with Buell heads, I naturally put in a bigger main jet. It bogged on WOT. I put in the next size jet. More of the same. Repeat for every large jet I had. The same. I even took a jet an bored it out even bigger. The worst running yet. I was all set to buy new cams.
In desperation, I used the smallest main I had and went on the the track. It ran like a raped ape with zero hesitation when the throttle was whacked open. Power everywhere and a stupid amount of torque.
Where one has the accelerator pump set to activate also plays a role.
I has a similar experience with my SP1000 but with the pilot jets. It picked up from okay from low revs/low throttle openings but not as well as I thought it should. Conventional wisdom was that the pilot jet was right and a smaller one wouldn't work. But a smaller pilot jet transformed it!
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OK!
I kinda put this out there and left it hanging for a couple weeks.... But I have a hellish work situation right now, and the first two weeks of May is when you put your garden in here- I had a lot of work to do- so no riding.
1. I am doing one change at a time so I can track results
First thing was a simple jet swap. I pulled the 140's and put in 145's
THE CHANGE IS AMAZING!
If you were paying attention, I said the bike starts, idles, and runs great at low and moderate speeds. Well, I put in the bigger jets and took it for a real romp around the mountains yesterday. It hauls ass. Really, like a different bike. I finally feel like it's doing what it should do!
I am going to do a couple other minor things like torque the heads, clean the air filters... I had just set the valves and changed all the fluids, fixed an exhaust leak.
If I can line it up this summer, I will ride out to another event where they set up the dyno and try it out.
I don't know if it's perfectly tuned... for sure you can't change one set of jets and proclaim it fixed. BUT it is running the best it has and I am pleased as punch. I'm going to futz with it more in the future, but just larger jets has really transformed the bike. A nice starting point at least!
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A dyno with a sniffer will give you a better idea of the mixture throughout the rev range. A WFO run on a straight road or one up a steep hill at a lower gear will give a seat of the pants feel on the main jet. If you do a dyno run take some jets with you a step larger and smaller to better tell the direction you need to go if any.
Pete
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A dyno with a sniffer will give you a better idea of the mixture throughout the rev range. A WFO run on a straight road or one up a steep hill at a lower gear will give a seat of the pants feel on the main jet. If you do a dyno run take some jets with you a step larger and smaller to better tell the direction you need to go if any.
Pete
yep,
Dyno with the sniffer was what indicated the problem in the first place
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If you read the tuning book there is a formula so the main jet is big enough to feed the atomizer/needle area.
I'll bet it will be closer
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If you read the tuning book there is a formula so the main jet is big enough to feed the atomizer/needle area.
I'll bet it will be closer
I'll never read that book. No way I could get thru that. Same reason I would drive 8hr round trip to have you do Guzzidiag on my bike. I just dont have the knack for this stuff, it doesn't land for me.
I'd more likely drop it off with someone to tune and pick it up completed. I dont find wrenching soothing or enjoyable at all. It's just frustrating and irritating. I have a ton of respect for the people who have the mind for it, but it's not for me. I already barely have time to ride 1-2 times a week.. Working on the bike or taking it out of commission to spend hours on it in the garage just sounds like torture to me!
The important thing is, the bike is running awesome and is hugely improved with a simple jet change. I doubt it's at peak performance and superbly tuned, but I don't care enough to agonize over it.
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...Working on the bike or taking it out of commission to spend hours on it in the garage just sounds like torture to me!
The important thing is, the bike is running awesome and is hugely improved with a simple jet change. I doubt it's at peak performance and superbly tuned, but I don't care enough to agonize over it.
So here's the easy path forward. Since it's a simple quick task, go up one size on the main jet and ride. If you feel an improvement, go up one more size next time. And again, until you make a change with no difference- then go back to the previous size main jet. You'll then be on the lean side of max power. Adjust the needles as necessary for drivability and enjoy. I've spent an enormous amount of time reading plugs, changing carburetors, and making dyno runs to discover at the end of the day that the 80/20 rule applies; you can get 80% of the benefit for 20% of the work, and on public roads you can't tell the difference. Unless you're racing or have a fever to maximize fuel mileage, there is no benefit to micro-tuning if you don't enjoy the tuning process itself.
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So here's the easy path forward. Since it's a simple quick task, go up one size on the main jet and ride. If you feel an improvement, go up one more size next time. And again, until you make a change with no difference- then go back to the previous size main jet. You'll then be on the lean side of max power. Adjust the needles as necessary for drivability and enjoy. I've spent an enormous amount of time reading plugs, changing carburetors, and making dyno runs to discover at the end of the day that the 80/20 rule applies; you can get 80% of the benefit for 20% of the work, and on public roads you can't tell the difference. Unless you're racing or have a fever to maximize fuel mileage, there is no benefit to micro-tuning if you don't enjoy the tuning process itself.
Excellent advice, I can work on these terms
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I bought a 79 1000SP last winter. I think a previous owner was trying to make it a LeMans. It has LeMans foot pegs and mufflers and 36mm carbs and it ran like dog poop! I'm sure the motor is stock. I went back to VHB30 carbs and it runs great. I think 32mm carbs would be a nice upgrade though. Bigger isn't always better when it comes to carbs. My LeMans 4 powered sidecar rig hit a flat spot at 4200 RPM with the stock 40mm carbs, it would not pull past it. especially with a head wind. It runs much better with 36mm carbs. You can put a dial indicator on the rocker and measure lift, you may be able to figure out what cam is in it from that.
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I bought a 79 1000SP last winter. I think a previous owner was trying to make it a LeMans. It has LeMans foot pegs and mufflers and 36mm carbs and it ran like dog poop! I'm sure the motor is stock. I went back to VHB30 carbs and it runs great.
A ‘79 1000SP would have ordinarily come from the factory with the same foot pegs and mufflers as a LeMans, except that the exhaust was chrome. If I recall correctly the SP pegs and mufflers (and seat) were made more touring oriented in 1981, with what some call the NT version.
My SP and my current CX100 both ran a lot better after 36-mm PHFs were installed, as much as anything because you don’t have to twist the throttle a long way to get a given throttle opening. Otherwise they were well suited to the engine and had/have no flat spots. Lack of power or other issues would not in my experience be due to using 36-mm carbs, if they were jetted correctly.