Big idle, carbs, checking my work... Options

[VaccaRabite]

Weber 40, IDF carbs. Cable throttle linkage. They are NOT synched yet, and both carbs just had rebuilding work done. I've been working very slow due to time constraints. I fired up the car Friday night!!!

But it was idling at 3000rpm.

After an hour, I had the idle down to 1800 rpm. Both idle adjusters were off the stops. Using a snail, one side was drawing a 7, the other a 14. When I turned off the car, I got a backfire. My "work hour" was done, so I had to leave it at that until the next time I can work - probably next Friday.

So causes for the big idle that I need to investigate:

1. air leaks at base gasket between carb and manifold (reused, very possible)
2. air leaks at top between carb and air filter housing (do they even leak here?)
3. bent butterfly shaft (hope not, and don't think so)
4. slave cable from weak side to strong side needs to be loosened as it is possibly holding throttle open slightly?

Backfire causes:

1. exhaust leak? Fresh installed SSIs, I probably have one at the head somewhere.
2. big carb imbalance? Probably combined with the leak...

Did I miss anything?
Where can I get the good base gaskets? The ones I have are from Weber Carbs Direct and they are the ultra crappy tan cardboard. They took a set and I am sure they are leaking like a sieve.

Zach

[anderssj]

You might want to give David a call at Air Cooled Engineering (ACE, Art Thraen's place in Utah). He might have the gaskets you need or tell you where you could get them.

ACE
360 W. 6100 So. #A
SLC, UT. 84107
801-943-1234

www.aircooledengineering.com


I've also had good luck getting carb parts at Carbs Unlimited:

CARBS UNLIMITED INC.
727 22nd st NE
Auburn Wa 98002
Questions and Information (253)833-4105
Order Line 1-800-994-CARB (2272)

http://www.carburetion.com/index.htm

Hope this helps!

BTW, Dave and the other folks at ACE do GREAT WORK! (IMG:style_emoticons/default/smilie_pokal.gif)

Steve A-

[anderssj]

Just checked the Carbs Unlimited site and found this:

40 IDF Base Gasket
Dense fibrous, Anti-vibration paper
need 2 per carb
$3.67 ea

about 2/3 down this page:

http://www.carburetion.com/Weber/weberpartsjetkits.asp

Steve A-

[r_towle]

what "rebuilding work" did you do?

Its simpler to take off the carb linkage from both carbs and see if you can get them to balance at idle first.

Describe what you did on the carbs cause that may have some affect on the base idle settings.

Rich

[VaccaRabite]

Cleaned the jets and stacks. bored out the lead plugs that were weeping fuel, tapped the holed and put sealed set screws in place. Made a thread to tell folks about it here: http://www.914world.com/bbs2/index.php?showtopic=133490

I did not change float height or touch the accelerator pump. Carbs had a full rebuild 2 years ago, this was only oppertunistic stuff that I could so while I had the tops off to fix the leaky plugs.

The linkage is a cable linkage. Unhook one end and both ends are essentially free.

[jmill]

So causes for the big idle that I need to investigate:

1. air leaks at base gasket between carb and manifold (reused, very possible) I'd also check at the manifold to head.
2. air leaks at top between carb and air filter housing (do they even leak here?) doesn't affect idle speed. Just get dirty air
3. bent butterfly shaft (hope not, and don't think so)check to make sure your butterflies are in correctly. They are angled to fit bore tight. Are they in upside down?. Loosen screws and align on shaft to center.

[r_towle]

tighten them down at the heads and maniflod and remove the cable from both carbs.
No telling waht may have gotten twisted up in the linkage....just use both carbs only to see if you are idling right.
Cant rev the motor, but you can set them to match at idle first.

Then hook up the linkage cable again and see where the issue might be.....a twisted cable can cause issues....make sure they are happy with no twists.

Rich

[KaptKaos]

Are your air by pass screws all the way in?

[SGB]

My car (40 idf, tall manifolds w/ isolators) does this if my timing is off.


Other carb issues I've experienced (besides those same plugs popping out):
1-Backfire (popping) out carbs at high rpms was ntake valves too tight.
2-Erratic idle (could be your issue if timing is right) was gummed up cam drive between the barrels that drives the accel pump caused dribbles all the time
3-Too small idle jets gave better MPG but ran hot at high RPM

So, try dialing that diz back a degree. I have a mallory and when it is set up right it is almost about to run away- just a couple of degrees up and you you can tell the spark advances and RPMs climb right up to, um, about 3K... hmmm...

[VaccaRabite]

I was about to discount the advice about checking the seal between the manifold and the head - but I did have to remove that manifold when I took the tins off this spring. I had forgotten that! Another obvious source of a leak that I need to check.

I'll recheck timing too. Pulled the dizzy, but I think I retimed after I put it back.
Zach

[904svo]

Disconnect the throttle linkage, then using a flashlight look down the carb and see if the throttle plates are close all the way. Chances are the return spring on the carbs is not centered right which will hold open the throttle plate. This is what I found after I rebuild my carbs.