Dellorto help

[Testarossa]

I'm generally happy with the way the T has been running since the rebuild, but there is a hesitation at 5000 rpm when I crack the throttle open -- at about 2/3 throttle I think. The plugs show it's running slightly slightly rich and I'm getting 47mpg in mixed around-town and highway travel. After the rebuild I changed the main jet from 145 to 142, and of course the bike lives at 5000 feet elevation. Pods, not oiled. At this stage in our life together we almost never run full throttle.

So I'm thinking I need to drop the needles a notch. What say the experts? 

[JoeW]

The VHB carburetors do not have a built in venturi. It's common practice to remove the aluminum fitting that connects the carb with the factory filter housing when installing pod filters. The problem is, now there is no venturi effect for proper air acceleration. When I change to pod filters, I have the outside ridges of the aluminum fitting machined down to the same outer diameter as the carburetor. Then I use UNI pod filters. I would do that before changing jets and needles.

[Testarossa]

Good point and I neglected to add that I have a set of short velocity stacks pulling from within the KN filters. Look like this: but I think I bought them from Mike Harper.

[guzzibob]

I gather that you are generally happy with the way it runs except for this hesitation at around 2/3 throttle when at around 5000'. If that is the case then that could be a needle issue. You think it is running rich at that point. If that is correct, then the symptom should be lessened and running improved, at least at that same throttle position, when at lower and leaner altitudes, worsened at higher/richer altitudes. Is it? If yes, then lowering the needle, which delays the point at which needle enriching begins  and lessens enriching at any given point up to max opening, would seem to be a good place to start. Certainly better than changing needles which is often a more complicated thing involving trade offs among the 3 needle parameters involved, esp since the needle design that you may actually need may or may not be made. At that throttle position, I would not expect idle, main or needle jets or slide cutoffs to be that relevant. 

[Fangit]

Good point and I neglected to add that I have a set of short velocity stacks pulling from within the KN filters. Look like this: but I think I bought them from Mike Harper.

They are strange looking velocity stacks. Looks like only a very slight taper in diameter. Are they like that so you can slip filters over them? True stacks would have a much larger air inlet diameter. Why is there a turned down diameter section on the air inlet end?

[ed.bremner]

This is interesting and goes some way to answering a question I have had for a while.

Maybe JoeW, you could shed some light :-)

I have a 77 T3 Cali and currently run pods directly onto the carbs.

My question is whether I should rather be connecting the pods to the aluminium connector pieces (as shown in the image - Not velocity stacks surely?), due as you say to the necessity for getting the venturi effect. 

I havn't done this in past due to two reasons:  First, and mainly because with both of them fitted there is not much (any) room for both the pods - they hit each other.  It would be OK on LeMans or others on which the carbs go more 'straight-back', but on T3 the head to carb connector pushes the pods back under the seat in front of battery where as I say, they hit.  (Sorry guess I am most probably teaching eggs to suck grandma here).

Second reason is that as Fangit says, they are strange looking velocity stacks....cos they ain't, and don't have any bellmouth at all, so didn't figure they would be doing anything??

So, reckon I could make em fit by cutting them down till pods just fitted?  But would this work?  Or mount the filter back over the top of connector, but this would leave a small gap between end of pod and end of connector and air would have to bend around and back before going through filter, which does not seem right.

Interestingly enough the big K&N filter which many people seem to like, also fits to carbs without the connectors:

http://www.thisoldtractor.com/mg_images/air_filter_kn_r-0642_2.jpg

So?   Does the connector have any real use as a velocity stack and if so how to you retain them when using pods?

eib

[Testarossa]

Bob, that's exactly what I was thinking.

[mtiberio]

They are strange looking velocity stacks. Looks like only a very slight taper in diameter. Are they like that so you can slip filters over them? True stacks would have a much larger air inlet diameter. Why is there a turned down diameter section on the air inlet end?

these are the vstacks from an early epa airbox model, not the stacks you see with loop frame airboxes or lemans. These are repops, and they don't seem to have the same internal profile as the stockers, but it is not significant.

[kevdog3019]

Yes... I would drop the needle one notch first and see what this does.  If it fuels well everywhere else (below 5000 rpm) I think this may do it for you. 

[rocker59]

It's easy to drop the needles a notch.

Drop 'em, then take it for a ride.

You'll know pretty quick.

Remember to change only one thing at a time!

[Testarossa]

Righto, folks. Thanks for the confirmation.

[Two Checks]

I would think at 5k ft 142s are still a bit rich. I'm at 500' and that's what I'm running now and ran in my T with pods.
What pilots are you using?

[Idontwantapickle]

My Eldo has K&N filters, runs much better with the filter adapters installed than with the filters directly on the carbs. Just look at the carb inlet, would you be happy rushing in there around all those edges and angles? Neither would the air.
Hunter

[Testarossa]

I've got everything sorted except for re-synching.  Needle was in the middle, is now at its leanest setting. FYI, my jets are 142 and 40. The "velocity stacks" are a straight 44 OD but the internal diameter tapers from 35 upstream (inside the pods) to 30 at the carb.

Will road test and report.

[Two Checks]

Your pilots are plenty lean compared to mine (50s) but your mains are the same. I imagine when you get into the main all that fuel bogs it down. My Cal III came with 130s and flat wouldn't run at WFO.

[Testarossa]

Two Checks, you're on the right track.

With the new needle position, midrange has improved a lot. Plugs are a lovely dry light tan and throttle response is good. It bogs now at full throttle and doesn't want to top 5500 rpm.

When I got the bike (at sea level) it came with 145 mains. Maybe I should drop to 135 or even 130?  I'm concerned about how it will run at Cripple Creek in a couple of weeks (10,000 foot campground, 12,000 foot passes, two up).

On the other hand, as Lannis will confirm, she ran great two years ago coming back from Ouray over Monarch Pass, easily hitting 90mph on a few modest uphill stretches, solo. That was on the 142 mains.

On the third hand, as most of us have found, 90% of fueling problems are really ignition problems, so I'll re-examine the timing and especially the advance mechanism tomorrow. The advance is new to this bike, off a T-3, during the rebuild.

And on the fourth hand, the bike is 41 years old and I'm 66, so maybe an 80mph rev limit is Luigi's way of telling me to cool it.

[Testarossa]

VHB carbs have no pump. PHF and PHM carbs do.

[Two Checks]

Stop. Change the jets before you start changing other things. Elmiinate jetting as a problem first. You say changing the needles helped, so stay on that path until you establish whether its the problem.
Make sure your choke plungers are seating, also.

[mtiberio]

VHB carbs have no pump. PHF and PHM carbs do.

ahh, actually they do, just a different technology from the PH* carbs

[Testarossa]

Righto. I've ordered new jet sets at 130 and 120.  Onward.

[Testarossa]

Jetted down to 130 and it helps -- running a lot cleaner with the throttle wide.

Raining now. Will try the 120 jets tomorrow (weather permitting).

Please explain to me why installing stacks makes the bike run richer. It did fine for years with nothing to smooth the airflow but the KN pods. I speculate that we're getting the same volume of air at a higher velocity, thus pulling more fuel through the jets? But the whole point is to flow more air with the additional fuel, no?

Something else to consider: the stacks roughly double the length of the intake tract upstream of the carbs. Does that matter? I know the new EFI V7s use a long plenum.

[dsrdave]

As a general rule of thumb..... longer runners improve low end and torque short runners are for WFO  and racing applications where you're willing to give up some low range and torque for ultimate HP at high RPM.

[Testarossa]

Before putting in the 120 jets I thought I'd try a run with and without the velocity stacks using the 130 jet and needle in its leanest position.

With stack, KN filter: weak low end, poor idle, good pull 3000 to 4500 rpm

No stack, KN filter (but no neck): weak low end, poor idle, good pull 3500 to 5000 rpm

In both cases idle and low end are better with the enrichener ("choke lever") engaged.

Ordered a set of Uni pods which will function as a shorter stack, and meanwhile will try the 120 main. Don't know what to do about the pilot jet.

[Testarossa]

The Uni Pod filters arrived and I popped them on. Then readjusted the low-speed screws to get a dependable idle -- the mixture screw needed a full turn richer. Running pretty well now but there is a hesitation when I roll on below 3000, so I'll take BigJohn's advice and clean the accelerator pumps. I was ignorant about this piece and the pumps haven't been inspected in at least 40,000 miles.

[Testarossa]

Big John: one of the accelerator pump springs was broken and probably hanging up the action on that side. But the real problem was  the springs in the ignition advance -- both were stretched a couple of mm longer than they should be, and also appear to have been wound from heavier wire. This is a "new" used timing unit off a T3, which I installed during the post-flood rebuild.  As I understand it (thank you, Dave Richardson!) the longer springs allowed an initial rapid advance, and then the heavier windings probably flattened the advance at high revs.

I put on new springs, retimed the ignition, and the bike runs as Luigi intended.

Thanks for all the feedback, folks!

See you in Cripple Creek!

[rodekyll]

I have seen guzzi distributors with unmatched springs -- one heavier and one lighter; one longer and one shorter (can't remember which).  I don't know if the designers intended it that way to smooth out the advance or whether some person simply slapped in some springs without thinking about it.  So you might want to check yours against specs.

$0.02

[Testarossa]

Richardson explains this in his section on modifying ignition advance curves in the big twins (Guzziology 6-11 thru 13. Basically there are two different sets of springs for this distributor -- one set fitted to the loops, Convert, T3 and S3 has mismatched springs, one with a long loop at one end. This set limits advance to 28 degrees but gets to 25 degrees at 1500 rpm.

The second uses shorter but lighter springs and starts at 8 degrees advance up to 1500 rpm, then advances steadily to about 35 degrees at 4500 rpm.  My assumption that a T3 distributor is identical to a T unit was wrong -- but the only difference is the springs. I have the right springs in there now and the bike runs as it did before the flood.

[Testarossa]

The T ran pretty well up to Cripple Creek and back -- not like a new bike, but it hauled the two of us and our gear -- about 220 lb of flesh and camping gear -- up the hills to 10,000 feet and didn't hold up traffic. Got 52 mpg for the trip.

Still not happy with top-end power so this morning I installed the Dyna III that's been sitting on the shelf for four years. Much improved low and midrange, mild improvement at the high end. It still doesn't want to pull beyond 5000 rpm (80 mph). Maybe I never got all the mud out of the mufflers?  Will investigate that next.

[acogoff]

    When my nearly 40 year old bike (T3) gets me there and runs good up to 5000 rpm I am just very happy it is still on the road doing what I ask of it. Just my take on tuning the old slug, Never felt the need, it is what it is.

[Testarossa]

Yes, I hear you, and in fact reliability is all I should expect here. But I can't help thinking that if it did 90mph uphill before the flood, then I must have overlooked something in the rebuild.