Difficult hot/wam restarts...Ethanol?

[brown7373]

The Q-jet on my 72 Cutlass 7042250 is rebuilt stock, using new choke tubes and choke stove.  Restarts when warmed up are more difficult than I think they should be.  Engine temperature is 180-190.   Is it the 10% ethanol in the fuel?  I see zero evidence of any leaks.  The new float is set at 1/4 as per the spec. 

It starts perfectly when cold, idles fine, does not stumble and can be driven away immediately with no issues.  It is smooth and responsive, and I would say as close to perfect as possible...except when restarted warmed up.  The plugs were all drilled out, threaded and Marine-Tex used on screw in plugs to seal everything.  It has a new Cliff kit with float and all the good rubber parts.  It can sit for weeks, but once to the floor and it fires and runs just like it should.

Very recent tune-up with new everything set to specs.

[Cliff Ruggles]

Difficult hot restarts can be related to mixture screws set too lean or too rich.

If the carb is leaking someplace, you would notice vapor coming up out of it right after hot shut-down, something to check but a leak that big the carb would be empty by the next day.....Cliff

[429bbf]

i don't know if your doing this ,but this was my problem . i was stepping on the throttle on hot starts. it was a bad habit i had with my original cards. when i switched to quads i caught myself still stepping the throttle down about 1/2 way and was actually flooding the engine. once i quit the problem went away. hth

[brown7373]

I do put the pedal 1/2 way down, like it says in the manual.  I drove these cars back in the 60s and 70s when they were new and the gas wasn't laced with ethanol.  I used to just reach in through the window and twist the key, and it would always start unassisted.  I will take another look at the idle screws, as I might be a bit rich. 

[brown7373]

I adjusted the idle screws 1 full turn in from the initial 4 turns out.  At that point, the idle slow slightly and it ran just a touch rough.  It started fine cold, but a restart and it wouldn't idle and kept stalling.  I adjusted the screws out an additional 1/4 and the idle smoothed out.  The hot restart idled fine, but it was back to the previous condition of not starting as easily I think it should. 

I have no obvious vacuum leak, but if my throttle shafts are leaking, or some other vacuum leak, could that be causing this condition?

[Cliff Ruggles]

Just curious as to where you have the timing set at, and if the vacuum advance is hooked up to ported or manifold vacuum?

Does the engine require a shot of fuel from the accl pump on hot restarts, or just it just take several seconds to start instead of roaring to life at the turn of the key?.....Cliff

[brown7373]

8 degrees btdc, ported vacuum advance.  I have never given a shot of gas before, but the funny thing is, today I decided to try that.  It made it worse.  The engine feels like it is flooded, but the bowl is never out of fuel, and it doesn't appear low. 

[Cliff Ruggles]

Do you see any vapor coming up out of the carb after a hot shut-down.  Sounds like it is leaking some fuel into the intake after shut-down causing a rich condition for hot restarts.....Cliff

[brown7373]

I have nor specifically checked for that, but will today.  It has baffled me, because the cold start is immediate, and shows no sign that the bowl was low on fuel.  That applies if it is restarted after a few hours or a few weeks.  If it had a small leak when shut down hot (normal operating temperature), wouldn't it continue to leak over night or during a week or two of sitting?

[Cliff Ruggles]

I've seen a few set-ups have a pressure rise on hot shut-downs and push enough fuel past the N/S assembly to overflow a little fuel into the engine making restarts difficult, and the engine act slightly flooded.  This would happen with a mechanical pump set-up, and is easy to test, just loosen the fuel line right after a hot shutdown and see if it helps the problem.....Cliff

[brown7373]

So you are saying to loosen to release the pressure, to see if that helps.  If that does solve the problem, is there a permanent fix?

I did check the top of the carb after a hot shut down and saw zero vapor or evidence of leaking coming from the carb.

[Cliff Ruggles]

A few posts back you mentioned giving it a shot of gas and it acted flooded.

This would indicate that there is already plenty of, if not too much fuel in the intake. 

Since there are no indications of the bowl leaking down after sitting several days, and bottom plugs are sealed, unlikely it's leaking out the bottom of the carb anyplace. 

To have a leak higher up in the casting the fuel level would need to rise after shutdown.  This can be caused by a pressure size in the fuel line after the pump.

Another possible cause is a very slight leak at the gasket under the fuel inlet seat.  This problem isn't all that common, but does produce the exact symptoms that you have.  A very small leak doesn't effect the engine when it's running, provided the fuel being used by the engine is greater than the leak.  It can cause a problem after shutdown if you still have pressure in the fuel line, or on an electric pump set-up if the pump is left on after shut-down......Cliff

[brown7373]

I did have pressure in the line after shut down.  I noticed that when I removed the carb, not immediately after shut down, but within a half hour or so.  I am running a stock mechanical pump on a 1972 Olds Cutlass 350, but don't remember if it has a return line.  Would a return line relive the pressure after shut down?  Maybe I will remove the inlet seat and make sure nothing is causing a leak.

[von]

I had that problem with my '69 Malibu and it was caused by a parts store replacement mech fuel pump having too much pressure. When running the carb could keep up but after shutdown pressure would rise and overcome the needle and seat, then flood and hard starting.  Many of the off-brand parts store pumps nowadays are that way. A new AC Delco pump fixed it.

[brown7373]

Hmmmm.  Fuel pump pressure.  I DID replace the fuel pump a while back.  I think it is an Air-tex, which I never heard of.  I see no evidence like vapor in the carb when I shut it off, but it doesn't restart like I think it should.  This is on a 72 Cutlass 350 Q-jet.