Twin Weber DCOE question

[ConreroGT]

Ok, I'm not sure which way to go with this symptom:

1) I have poor/weak throttle response below 2500 rpm, but above that it really breaths great up to 6000+ (I havn't gone above 6k yet) But it will hesitate usually when I'm shifting unless I keep the RPMs high. Especially going into 3rd for some reason.

2) Also, when I adjust my mixture screws, I know they should be roughly 2-3 turns out, ballpark, but it seems like I go as much as 4 turns out....is this ok?


(Or could this be from a vacum leak?? I have the carbs off and I'm replacing the softmount gaskets to try and fix.)


Setup:

2.2l top/bottom, good but not a real wild cam.

Choke - 34
Mains - 145
Air Cor. - 180
Emuls - F2
Idle - 55F9
Pump - 40

Thanks for any pointers...

~kyle

[nobody]

Well I run 190 airs on my 2.0. The chokes will determine where your power curve is and especially low end torque.

[baz]

moved to right section

[nobody]

I just reread and I was a bit vague. With 34mm chokes your power band is going to be starting around 3500 RPM and run till your out of rev range. I'd try a 32 or bored to 33 to get some low end back. Your mains are ok but your air correctors need to be more like 210 for that size motor. An F2 emulsion is on the rich end of the scale, I'd suggest an 11 or 16. Your idles are about right but you may want to look at a 60F9. Your pump jet should be more like a 45 or 50.

My suggestions would be change the chokes to 32, air correctors to 200, Emulsion tubes to 11 and pump jets to 45.

More than likely what your seeing is a loss of air velocity in the lower RPM range that makes the carbs stumble as they transition. Oh and be sure they are perfectly in sync or you will fight it forever. What linkage are you using?
HTH

[N61WP]

Everything "Nobody" said is accurate, but I think I'd start with trying the larger pump jets first. You might just need a little more squirt!

JHHO,
Jc

[nobody]

James that's the problem you get into with OEs. The whole thing works on air velocity, including the pump jet curcuit. It's replacement the OMs eliminated this with a mechanical pump to help it transition better. Even Weber knew there was an issue there it seems. On an OE it's criticle to keep your air speed up especially at low RPM. The OMs aren't quite as bad, and to answer your question before you ask it. No they were never made in a 45. Too big of a pump jet will make OEs puddle and spit gas. Given a big cam next is ignite.

[ConreroGT]

Thanks for all the input! This should keep me busy for awhile.

To answer the linkage question: I have the (Weber style) center piece that connects the two carbs together. My throttle is actually another minor issue, but it's doable for the time being. I'm about 3/4" or 1" short from WOT. ~grrr..~

~k

[N61WP]

Instead of starting a new thread......

I finally picked up a set of dual manifolds for the 45's. How about some opinions on using balance tubes between the intake manifold runners on a dual side draft setup. I have heard both pros and cons on doing this. I wonder if the "wildness" of the cam makes a big difference if this works or not.
Opinions?
jc

[nobody]

James, sister motors just got a bit closer. The cross link with a big cam is pretty much useless except for the brake booster. the 45s will need to be choked way down to get torque and air speed for them to work right. Which manifold did you get? Can we talk ignition? Now we can have some fun. Welcome to the world of Twins. Let me know how I can help.

[RallyBob]

Originally Posted by N61WP How about some opinions on using balance tubes between the intake manifold runners on a dual side draft setup. I have heard both pros and cons on doing this. I wonder if the "wildness" of the cam makes a big difference if this works or not. Opinions? jc

I have found the biggest difference is in the availability of vacuum for the power brakes. But there are other benefits, including stronger torque and a smoother idle. If you go this route I suggest at least 3/8" ID tubes to connect each intake manifold runner.

Bob

[ConreroGT]

Since the thread came back up, and I was meaning to thank some experienced parties anyway....here goes:

I had originally asked R-Bob some jetting questions about my twins. I took his advice...but I didn't get ALL the jets he suggested only because I had some that "were close" and decided to move slowly.

I was still having some slight tuning issues below 2500 rpm and asked specifically what direction I might need to go. Nobody spoke up with some specific jetting suggetions. Coincidently, these were pretty much the missing jets thet I DIDN'T use that Bob first suggested.

Turns out that changing the air correctors to 200 from 180 and the emulsion tube from F2 to F11 (note: I already had the idle jets and pump jets that were suggested after all in the carbs :o ) are probably right on the money. So with this change the engine is a real monster now. Completly different from before. I think I'm still running a bit lean too. Nobody: You're probably right about the 60F9's too. I probably WILL get those now.

Anyway, I'd like to thank R-Bob and Nobody for the precision advice! (and I should be suprised..?? ) Damn, you guys are good. That advice made clear a lot of my jetting questions and I think I can make tuning adjustments better with the carbs. Again, thanks for the schooling.

I'm getting some video capture equipment for my computer soon. I want to make some MPEG type audio/video of the motor and the car. (anyone have any server space I could borrow for an future upload??)

~kyle

[nobody]

Kyle, I love the way twins act and tune. There are only a handful of people on this site that seem to have taken this aproach. I'm glad it's working out for you. If you don't have a good manometer yet, you might want to think about one.

[ConreroGT]

You mean a sync tool?

[nobody]

A manometer judges the level of vacuum you pull on a given carb and does not restrict the inlet air to do it. You can also do both carbs at one time.