One thing after another: Carb again
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
One thing after another: Carb again
Alright, got my transmission issue sorted thanks to your guys' help, and I rebuilt the flooding carb, per y'all's recommendations. Thanks again if I haven't already said so.
Anyway, the carb is suspect again:
At idle I'm still WAY rich, even after adjusting the idle screws on the front of the carb, I'm running far too rich; rich to the point that I can turn the idle screws all the way in and have the engine continue running rich. I'm seeing fuel coming out of what look like air-horns in the primary venturis, should I be seeing that? There's also a little fuel puddling near the secondary cam.
New needle and seat, new float, new gaskets, just cleaned it and rebuilt it 2 weeks ago.
It's not rich to the point where it won't run, but it IS rich to the point that at stoplights I can see black smoke and raw fuel vapor coming out the tailpipes.
I'm assuming that the float level is wrong, but if there are any other ideas that you guys have let me know.
EDIT: Fuel pressure is 3# after the inline filter between the pump and the carb.
Anyway, the carb is suspect again:
At idle I'm still WAY rich, even after adjusting the idle screws on the front of the carb, I'm running far too rich; rich to the point that I can turn the idle screws all the way in and have the engine continue running rich. I'm seeing fuel coming out of what look like air-horns in the primary venturis, should I be seeing that? There's also a little fuel puddling near the secondary cam.
New needle and seat, new float, new gaskets, just cleaned it and rebuilt it 2 weeks ago.
It's not rich to the point where it won't run, but it IS rich to the point that at stoplights I can see black smoke and raw fuel vapor coming out the tailpipes.
I'm assuming that the float level is wrong, but if there are any other ideas that you guys have let me know.
EDIT: Fuel pressure is 3# after the inline filter between the pump and the carb.
Instructor
Joined: Mar 2007
Posts: 223
Likes: 0
From: Henryville Indiana
I believe the carb is faulty internally.The Qjets had issues with the main well plugs leaking fuel and that leak is right over the baseplate.Take the baseplate off and look for fuel staining on the bottom of the main body.
It has been known to have been repaired by epoxy...EXTERNALLY,not inside the main well.
It has been known to have been repaired by epoxy...EXTERNALLY,not inside the main well.
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
I believe the carb is faulty internally.The Qjets had issues with the main well plugs leaking fuel and that leak is right over the baseplate.Take the baseplate off and look for fuel staining on the bottom of the main body.
It has been known to have been repaired by epoxy...EXTERNALLY,not inside the main well.
It has been known to have been repaired by epoxy...EXTERNALLY,not inside the main well.
I'm still thinking I didn't adjust the float right because (I did research for the terminology this time around) fuel is coming out of the main discharge nozzles at idle.
I'm thinking the float's too high, causing a mild flood (resulting in fuel on the secondary choke cam) and fuel out of the main discharge nozzles at idle.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
At idle I'm still WAY rich, even after adjusting the idle screws on the front of the carb, I'm running far too rich; rich to the point that I can turn the idle screws all the way in and have the engine continue running rich. I'm seeing fuel coming out of what look like air-horns in the primary venturis, should I be seeing that? EDIT: Fuel pressure is 3# after the inline filter between the pump and the carb.
This might be of some help:
http://books.google.com/books?id=DwU...ATIdIErOqUZskE
Last edited by TopGunn; Jan 29, 2008 at 12:35 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Check the height setting for the power valve. I had a similar condition which Lars determined was an improperly set power valve. Because of that problem, idle settings wouldn't work properly, etc., etc. After he reset the power valve, idle settings adjusted properly and carb runs well.
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
Initial advance is 8* (without vac)
I can't set idle speed because the idle mixture screws are unresponsive. It will idle at about 500RPM though.
I'll check out the power valve and the power piston. Thanks guys.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Carbs don't have both power valves and power pistons... If this is a Q-Jet (you don't state the type of carb you're working on...) it has a power piston and no power valve. Causes for the symptoms you describe are as follows:
- High Float
- Wrong float
- Float clip installed wrong
- Plugged idle fuel restrictor tubes
- Low power piston setting
- Lean jetting (jets or rods)
- Warped airhorn - not sealing against float bowl in idle fuel transfer area
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Instructor
Joined: Mar 2007
Posts: 223
Likes: 0
From: Henryville Indiana
My bad...I immediately assumed you had a Qjet....:bb
If you have a Holley,the boosters dripping is a sign of a float that is too high.Or a sinking float.That would cause the overrich condition and the smoke.
If the screws are un responsive,the powervalve is blown.
Replace the powervalve with the correct size for your application.
There are 2 schools of thought on powervalve selection:
1)use a valve that is 1/2 the manifold vacuum at idle
2)use a valve that is 2"below the manifold vacuum.
Item 2 is for RADICAL cams with less than 10"vacuum.
Most Holleys come shipped with a 8.5"valve in the primary.IME
If you have a Holley,the boosters dripping is a sign of a float that is too high.Or a sinking float.That would cause the overrich condition and the smoke.
If the screws are un responsive,the powervalve is blown.
Replace the powervalve with the correct size for your application.
There are 2 schools of thought on powervalve selection:
1)use a valve that is 1/2 the manifold vacuum at idle
2)use a valve that is 2"below the manifold vacuum.
Item 2 is for RADICAL cams with less than 10"vacuum.
Most Holleys come shipped with a 8.5"valve in the primary.IME
Thread Starter
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
Carbs don't have both power valves and power pistons... If this is a Q-Jet (you don't state the type of carb you're working on...) it has a power piston and no power valve. Causes for the symptoms you describe are as follows:
- High Float
- Wrong float
- Float clip installed wrong
- Plugged idle fuel restrictor tubes
- Low power piston setting
- Lean jetting (jets or rods)
- Warped airhorn - not sealing against float bowl in idle fuel transfer area
Took it apart last night and cleaned it thoroughly (some residual dirt from the old fuel filter found its way in) replaced the filter, set the float to 1/4" (as per the spec-sheet in my carb's rebuild kit) and it's working great at idle now.
Awesome.
Trouble is that now it starves itself of fuel at WOT.
So did I set the float level too low?
Would it be easier to just ramp the fuel pressure up by another 1-1.5 PSI (currently 3psi at the carb) so that it would have more fuel flowing in when the needle valve is open?