Jetting for 1000SP with 36mm Dellorto & Lafranconi Competizione LM1000 exhaust

[perter]

Hi Guys
I recently fitted a used LM1000 Lafranconi Competizione on my 1000SP. It already has 36mm Dellortos and K&N filters.

I used to run 135 main, 60 idle, K5 middle notch and AB265 atomizer before I added the exhaust. It may have been slightly lean.

After I added the new exhaust, I raised the needle to 3rd notch and swapped main to 140 and then to 144. The plugs now have a partial black base ring and it pulls strong from 2000/min to 8000/m without any soft spots or popping, but I still would like to be able to find the point where it's too rich to go back from there.

Question: What should I try next? Even bigger main jet, another needle (which?) or another atomizer (which?) or a combination?

Cheers!

[Chuck in Indiana]

Hi Guys
I recently fitted a used LM1000 Lafranconi Competizione on my 1000SP. It already has 36mm Dellortos and K&N filters.

I used to run 135 main, 60 idle, K5 middle notch and AB265 atomizer before I added the exhaust. It may have been slightly lean.

After I added the new exhaust, I raised the needle to 3rd notch and swapped main to 140 and then to 144. The plugs now have a partial black base ring and it pulls strong from 2000/min to 8000/m without any soft spots or popping, but I still would like to be able to find the point where it's too rich to go back from there.

Question: What should I try next? Even bigger main jet, another needle (which?) or another atomizer (which?) or a combination?

Cheers!

FWIW, here's what I'm running on the 750cc Aero engine. It's the same jetting as the LMIII. Food for thought, if nothing else. 
  K18 needle, AR 268 atomizer. 60/3 slide, 130 main jet, 50 idle jet.

[Groover]

I love that SP. nice job. Sounds to me you found the carb mix happy spot.

Where is the battery?

[perter]

I love that SP. nice job. Sounds to me you found the carb mix happy spot.

Where is the battery?

Thanks - it's though not only me who made it. Bought it a year ago where it was build more like a scrambler. I added the 36mm carbs, another handlebar, Avon Roadrider tires and now the Lafranconis
Aug 2015




Battery is in a small stainless box where the center stand used to be.... not so practical when you need a centre stand but the sidestand is remarkable stable (made longer than standard and different angle)




I think I found the nice spot, it's though still very light on the plugs so I would think it's on the lean side. And it feels a little like it's starving when accelerating from 3-5000/min so it could be a slimmer needle or other atomizer would help? Carbs only have 250 float valves where I understand 300 are standard, maybe I should try this first? Issue was worse before I cleaned the tank fiters last night 

[Groover]

Found a chart here that may help. Maybe you do need to focus on the Atomizer as Chuck in Indiana hinted...

http://www.thisoldtractor.com/guzzitech.dk/gb_en_technical_carburetor.htm

That's gonna change all your other jets' behavior though, so this may be the start of going down the rabbit-hole of carb jet tweaking..

A little more homework on Dellorto Carburettors..

http://www.ducatimeccanica.com/dellorto_guide/dellorto_3_6.html

http://www.mopedarmy.com/wiki/How_To_Tune_PHBG_Carburetors

They'll be a test next Monday, at 8:00am sharp! Bring a pencil.

Good luck, and hope that helps!

[Chuck in Indiana]

That's gonna change all your other jets' behavior though, so this may be the start of going down the rabbit-hole of carb jet tweaking..

Yep. This may help.
carb_jet_circuits by Charles Stottlemyer, on Flickr

[perter]

Thanks for the advise guys. I know it's a risky thing to touch, on the other hand I have the current setup to go back to if everything else fails.

What I plan to do in following order
New petcock/filters. The old ones were heavy clogged and this really impacted the setting, especially with low fuel. I cleaned them but broke almost all treads on one of them so it needs replacement anyway.

Float needles valve upgrade from 250 to 300. Carbs were taken off a Ducati and it had the "small" valves

These 2 will give a more stable float level

Then try to fiddle with a new atomizer (AB268) and K18 needles similar to the S1000 specs with 36mm carbs. If it doesn't work stay with current needle/atomizer

[Chuck in Indiana]

I'd say you are on the right track. Where you are having issues is controlled mostly by the atomiser and needle. You'll have to go down on main jet size with the AB268, I suspect.

[rodekyll]

Thanks - it's though not only me who made it. Bought it a year ago where it was build more like a scrambler. I added [snip] another handlebar [snip]

I can't get past this part.  Where did you put it?


A goofy but relevant test of your jetting at any rpm is to use your hand to start choking the air from the carb.  If the engine revs up as you restrict air at a given rpm, the fuel mix is lean.  If it bogs down, it's too rich or just right, depending on just how boggy it gets.  The faster and more fatal the boggy, the richer you are.  If you're trumpezian rich, it will quickly die and never start again -- bankruptcy, as it were.  If you have any sputtering at the intake at any rpm that's also a sign of fuel starvation.  Sputtering from the exhaust end suggests raw gas in the pipes or continued combustion in the exhaust.

Hope this helps you ballpark it.

[ed@guzzipower.com]

You wont get much better than that atomizer and needle combo. Play with needle position slightly- should be around 2nd position from the top. If you drop needles down until you get poor part throttle running, you've gone too far. Mains should be around 140. Only precise way to check mains is on a dyno or with plug chops at WFO....

[perter]

Thanks for all your advise and encouragement guys, new pet cocks, 300 float needle valves and a set of K18/AR268 atomizers are ordered so hopefully I can play with them next week. and I got 135, 140 and 144 main jets to toy with too.

I would expect the new petcocks and correct float valves would stabilize the carbs so I don't get the feeling "whow, what type of  rase gas did I just buy" every time I fill it up. Just cleaning the old ones a couple of days makes it easier to start (no choke from cold, temp around 20c)

I knew the trick pulling the chokes, I did it when I ran mopeds in the 80'ies. I though have separate chokes on each carb so I'm not sure I would get the full benefit of it but will give it a try.

Dyno tests yes of course would be no 1 but I love to do things myself and would just try to see if I can get "on the rich side" and then lean out from there.

Anyway, I'll post my results here for other users.

[perter]

I want to update this for future readers: After I fitted new petcocks, the right size float valves (300) and the AR268/K15 combo I went back to 140 main jets.

The plugs looks much better now with a black base ring, clean side electrode and light tanned middle insulator. The engine pulls remarkable better in the mid range and let out a loud "growl" as soon I touch the gas. It also runs smoother at low speed in e.g 50km/hr zones in 3rd gear so I think I stay here.

One question though: how do you read plugs for main jetting? Should it be with full gas and almost redlining in high gear? Sounds dangerous for your license where I live. Or could I run it out in e.g 3rd and kill it with 130?

[guzzisteve]

 "with plug chops at WFO..." and at least 2mi on a strait.  I go out on the interstate here in GA cause the roads are curvey.
Mark your throttle for 3/4-full and go, keep it in high enough gear where you don't float the valves.

[Two Checks]

Try one size larger on the pilot and see wbat you get.

[perter]

Try one size larger on the pilot and see wbat you get.

I will consider but I already  run 60 pilot jets which seems rich compared to the charts above. I know mine is a odd combo but would think the 1000s with 36mm phf is the closest reference and that is listed to 50pilot and 130main with same needle/atomizer I use now.

 What size do you recommend to try? 62? Or 65?