stalls in idle

[StephenGwyn]

Until recently, my engine ran fine at idle. Now it will run fine at all speeds but dead slow idle. Below a certain rpm (and that point is above where I feel comfortable shifting) it will start to run fairly rough and a nudge below that it will stall completely. Also, no matter how long the engine has been running, it requires a full choke and throttle to start again. It used to be, when the engine was warm, not choke or throttle was required to restart.

I feel this is a fuel problem.

I have a largish fuel filter (Racor 320). After this started, I changed it: no obvious crud or water.

When push the lever on the fuel pump, fuel comes out generously.

I changed out the carb for my spare carb. No change. Took the original carb apart, cleaned it, made sure that carb cleaner sprayed in all the various orifices came out the corresponding orifices, There was some slight varnishing, but no obvious crud. I put in a new needle valve and seat. Put everything back together, put it back on the engine, no change.

Since it was the time of the year when I normally do it, I put a new condenser, points, rotor and cap on the distributor. Didn't help.

Playing with the idle mix changes the revs slightly, but I'm running it with the throttle slightly more open than where the idle mix really makes a big difference.

Any suggestions?

When the throttle is fully closed, it is supposed to cover one of the two little holes in the carb throat right?

[Marian Claire]

Do you have a PCV valve?
Have you checked for an air leak at the carb to manifold connection?
How is your idle jet adjustment set, how many turns off seated?

General idea is that if you are sure the carb is clean then an air leak could be destroying the carbs ability to create suction at low RPM and not allowing it to suction up the fuel.

Dan S/V Marian Claire

[hanleyclifford]

Have you checked the centrifugal advance mechanism to be sure it is free to move and both springs are present?

[JOHN COOKSON]

I've Been Down This Road Before

My A4 wouldn't idle correctly. I tried adjusting the idle mixture\speed. Nothing really changed. Finally the engine wouldn't start at all. Me, being a certified AFOURIAN, knew what the problem was: KRAP in the carb. I disassembled the carb, soaked it in the goop, reamed out the passages, and reassembled it. No change. The engine still wouldn't start. Anyway to make what could be (is) a long story short, the rubbing block on the points was worn away. I did two things: changed out the points and bought a dwell meter. The whole fisaco would have been detectable with a dwell meter. Live and learn.

So: Recheck the point gap. Then measure the dwell. If the dwell is not in spec with the point gap set correctly there is a problem with the points or distributor.
BTW #1: I pass a points file between the contacts before I install any points.
BTW #2: It is normal for an updraft carb to need brief full choke to start even when warmed up. The colder the engine the more choke you will have to use.

TRUE GRIT

[StephenGwyn]

Do you have a PCV valve?
Have you checked for an air leak at the carb to manifold connection?
How is your idle jet adjustment set, how many turns off seated?

General idea is that if you are sure the carb is clean then an air leak could be destroying the carbs ability to create suction at low RPM and not allowing it to suction up the fuel.

Dan S/V Marian Claire

I do have a PCV valve.

How do I check for a an air leak? Do I need a vacuum gauge? If so, where I do attach it?

The idle jet is 1.5 turns off seated.

[CalebD]

If you have been using E10 fuel you very well could have crap in your fuel tank.

[Marian Claire]

I am not a PCV expert, I do not have one. But my understanding is that if they are not functioning properly they can cause issues with fuel/air ratios at idle.
You can use a spray, WD 40 being the safest AFAIK, to spray around the suspect connection and see if you hear/notice a change in RPM.
From my experience you may have to actually see the liquid being drawn in to the leak.
You do not need a vacuum gauge for this.
1.5 off seat is .5 turns past "normal" IIRC. That makes you lean at your present setting.

Dan S/V Marian Claire

[zialater]

I have the PVC mod which I installed last fall. After running for a few weeks I encountered the same problem as you. I just cranked down all of the clamps on the PVC installation and "presto" problem solved. Hope that works for you.

[Mo]

I have the PVC mod which I installed last fall. After running for a few weeks I encountered the same problem as you. I just cranked down all of the clamps on the PVC installation and "presto" problem solved. Hope that works for you.

Thanks to you and Dan both. My friend has a boat with a PCV and same problem...I did the carb last year and couldn't get it to come right down nice and idle..had to leave it a tad high. The boat is a Pearson 30, tiller and he shifts with lever down low. It must be a nightmare to dock. I will concentrate on the PCV and see what happens when he puts it in this spring.