one more Weber question

[dlampe]

Things are really shaping up. I have gotten very close to having a happy engine with Weber's. I had a lean stumble between 2000 and 3000 rpms. I went from a 60 to a 65 idle jet. I seemed to run great, no stumble and good acceleration but my LM1 was reading really rich like 10-10.5 to 1 a/f. I went back to the 60 and the ratio climbed to 12.5 to one at an easy cruise which was good. When I hit the gas to check acceleration, I'm back to the lean spike/stumble. I have a 40 exhaust jet in the bowls now. Should I just put the 65 back in and run rich or should I switch to a 00 bypass. I don't have any 00 exhaust jets so I need to order them if you think that is the issue.

My main jets are 160's in f7 tubes

[ENTDOC]

Dean, I finally came to the conclusion that webers just run better a little rich, so I would stick with the 65s. Play with the timing a bit, this can also improve things quite a bit. Mine really liked a lot of advance.

[dlampe]

Yeah, I can't even guarantee the LM1 is working exactly right. I have 20 degrees of mechanical advance set to 38 max all in early. I am still rich on the mains too. I am running 160 main jets so maybe I could try the 65 idles with 155 mains. This acceleration stumble is definitely late in progression circuit. I don't have the stumble at higher RPMs. Another way to attack the problem could be to bump the idle holder to 100 from 90 with the 65's. The acceleration circuit might not be as affected by the holder as it is the jet.

Any thoughts?

[SpyderMike]

Did you verify the acceleration pumps squirt equal? Have you tried adjusting you acceleration pump squirt to cover the lean acceleration stumble?

[Gaz64]

Dean,

You may find a custom pump rod length is needed.

If the stroke is already used up early then no amount of changing pump bleeds will give the added pump shot you need at that point.

You have the richest e-tube for low end already, maybe choke is too large for the engine?

Or run the 65 with a larger idle air jet.

[xb-60]

Originally Posted by SpyderMike

Did you verify the acceleration pumps squirt equal? Have you tried adjusting you acceleration pump squirt to cover the lean acceleration stumble?

I had some side draft Webers rebuilt by 'professionals' years ago. They fitted SW kits, and after many returns for stumbling at acceleration, and having the float levels progressively increased with no effect, I took the car to a real expert who stripped and rebuilt again with genuine kits. He found that the plungers on the accel pump diaphragms were short by 5 or 6mm.
Funny, it ran OK after that.

[Caprimaniac]

What I have found is that when going rich on the idle, the plugs get fouled and engine will stumble at least in the transition.

If it runs fine with the 65's with no troubles (engine fires at all cylinders, always..) I'd keep it. Although 10.5 AF sounds a bit high....

Some have said that you should run a 00 exhaust for "performance use". I have found a good AF reading & nicely running engine by using smaller idle jets and 00 exhaust. You might get identical results by using another pump rod as well. (I've no IDA technical expertise...)

Hope it runs well, soon- summer's arriving....

[dlampe]

I spoke to Peirce Manifold today. They are always very helpful. We discussed the exhaust jet and, in the end, I don't think that is the problem. If I go to a oo jet, it will just extend the shot not increase the intial volume. To do that I would need to increase the pump jet to a .45. After talking for a few miutes, we decided that the next step would be to open the holder to 100 from 90 and run the 65's. I'll give that a try before I start ordering parts.

[dallas_]

Have you talked to Jim Inglese?
He's not Inglese Induction Systems anymore (he sold it to Comp Cams).
He's pretty familiar with how these carbs work in Cobras.
http://www.jiminglese.com/index.html

[ENTDOC]

I think the problem probably lies in the F7 tube. I realize it is the best you have come up with and you may find no better, it is almost as if we sometimes need a custom tube for our 427 applications.

[vector1]

i wonder if that is something you can tune out with the length of the trumpets.

[dlampe]

I thought about the stacks. I have room for longer ones but they are pretty pricey! I tried the F16 tubes again and it runs better as long as I stay off of the accelerator circuit. I am going to go back to the 00 exhaust jet and see what happens there. Unfortunatley, I ruined the ones I had so I need to order another set tomorrow.

[Gaz64]

Dean,

Be wary that there are pump bleeds (exhaust jet) that have steel balls or plastic balls.

The plastic ones being lighter, seat faster.

The steel ones can still act as a bleed on very slow opening rates, until the pump pressure seats the ball.

[Caprimaniac]

Originally Posted by dlampe

After talking for a few miutes, we decided that the next step would be to open the holder to 100 from 90 and run the 65's. I'll give that a try before I start ordering parts.

Good for those who run IDA's. I have to struggle with the no- holder IDF's. But maybe that makes'em easier to tune?

Hope it'll run good in the end.

[Eljaro]

on my engine there was no way running the 48IDA's with pump bypass. I have 00 in there, tried with no good result the .035 and 50. Always had stumble when snapping the throttle open. With 00 bypass it eagerly goes forward, sometimes also sideways

[Eljaro]

Unfortunatley, I ruined the ones I had so I need to order another set tomorrow.

dlampe, no need for new bypass jets. Just solder the holes shut with tin solder

[dlampe]

I thought about that but they act as a check valve and I wasn't sure what effect closing them off would have had.

I went to the track for some testing and it was running rich, actually fouling plugs. I was running a 150 air corrector with a 165 main. I am going to try a 155 or a 160 main. I think that will fix the rich effect.

What was very interesting is that I had 2 spark plugs, 3 and 6, that where dangerously lean at the same time, I fouled 4 and 8. I initially thought that I had debris in the passage ways, choking the fuel supply. After some inspecting, I think it is a result of the hood scoop. It dumps air right into 2,3,6 and 7. I was running the float about a millimeter low on 3 and 6 to correct a casting difference between Spanish and Italian carbs. My guess is that if I put a baffle in the scoop like the 289 cars, this lean condition will go away. (after I re-adjust the floats)

Any thoughts on this?

[dallas_]

Originally Posted by dlampe

My guess is that if I put a baffle in the scoop like the 289 cars, this lean condition will go away. (after I re-adjust the floats)

Any thoughts on this?

I've heard the baffles do help. I'd be interested to hear if it solves your problem.

[Eljaro]

I have my scoop opening covered up. No holes in it. Air is taken from the engine bay. Did away with hesitation art part throttle