Engine Miss

[cwmcobra]

For those of you that read my post in the New Members section, you've seen that I am trying to diagnose an engine miss in my '65 GS.  I need to get a compression tester and check cylinder pressures to be sure I don't have a cracked ring, but meanwhile, I have a question.  This engine had not been fired in about 14 years.  I am surprised that there's not external fuel leakage from dried out gaskets, etc.  When I pulled the spark plugs,  all are very black and smell like fuel.  One was wetter than others whice makes that cylinder suspicious.  For you carburetor gurus out there, do you think the rich fuel condition could be caused by something haywire in the main carb?  Something that perhaps a carb kit might cure?  I was going to wait until I rebuild the engine to rebuild the carbs, but will do it now if this could be a solution.

Here's my checklist for diagnosing the engine miss:

1.  Check/adjust timing (done)
2.  Check spark plug wire resistance (done & seems OK)
3.  Adjust points gap & dwell (not done yet; don't have a dwell meter.  Had one and gave it away years ago  >:( )
4.  Check distributor cap & rotor (not done yet)
5.  Check coil (how do you do this?  Take to Autozone?)

I've gotten myself focused on a fuel problem because of the black, fuelly plugs but perhaps that's not the answer.  Any experiences to share or other suggestions on potential solutions I've missed?

Thanks!

[Brian]

I have fired up engines that sat like that for a long time and had problems with rough running/misfiring.  I did all the normal diagnostics like you just described and everything checked out fine.  What it ended up being was carbon/junk in the cylinders.  I got the engine warm and fed a bottle of water through the carb air inlet while giving it throttle.  Blows all the carbon/rust/junk out of the cylinders and it purred like a kitten when I was done.  I have done that to several old Buick engines and it works great. 

[WkillGS]

If it is running rich, two things come to mind... first would be the choke not opening properly. That's easy to check.
The other would be stuck primary metering rods in the carb. That's easy to check too....there are two small sheetmetal covers on the top of the carb. Remove those and see if the metering rod assembly moves freely. It is held in the up position by light spring pressure. Engine vacuum pulls them down and leans the mixture.

Another common problem is a stuck butterfly valve in the right side exhaust manifold. It's at the manifold/pipe junction. It is closed when engine is cold. When closed, it forces the warm exhaust gasses thru the passages in the intake manifold, heating it. It should open as engine warms up. Check by rotating the counterweight on the outside of the valve to see if it moves freely. It's held closed by spring pressure.

[cwmcobra]

Thanks guys.  Here's my current status.  The metering rods in the carbs are free; nothing sticky there.  The butterfly valve at the exhaust manifold is a different story.  It's not stuck, but it has no counterweight on it and the pin that holds the thermal coil in place is badly bent.  Picture attached.  Can I buy a replacement or do I need to refurbish this one?  Or perhaps I should just wire it open and reinstall it.  At least for now.......

Before taking the butterfly valve off, I took the car for a short drive on our back roads here in the country.  It ran OK and didn't stall at all, but give it anything more than a feather to the throttle and it bucks and snorts and misses.  In any gear.  Seems to be very load sensitive.  I suspect timing is part of it, but I'm not confident that my high tech timing light is reading this right.  It only has an inductive pickup and I'm not sure it's compatible with the old small diameter plug wires.  I'll have to do more research on that.

I haven't tried Brian's water in the carb trick yet.  Thought I'd try to build confidence in the other areas first.  I also thought of a vacuum leak, but the only vacuum hoses that I can see are to the distributor advance and the EGR valve.  The only other path for a vacuum leak I can think of is at the intake manifold gasket.  Don't hear any whistling and haven't tried any smoke tests.  Looking for the obvious at this point.

[WkillGS]

give it anything more than a feather to the throttle and it bucks and snorts and misses. 

That could be the accelerator pump in the carb. With the engine off, open the choke, look into the carb and twist the throttle lever open....you should see a good shot of fuel come out. If not, the seal on the accelerator pump is probably shot. I think you can buy just it from NAPA.


As for the exhaust butterfly, I'd suggest repairing it. Remove the pin, drill a hole there, and insert a metal rod in its place.

[cwmcobra]

Thanks Walt.  I'll look into the accelerator pump in a couple of days.

Didn't you say there is supposed to be a counterweight on the butterfly valve?  I remember that from older days.  This one has none.  Will it function OK without?

[WkillGS]

You're right. The counterweight is gone!
I checked one I have off the car, the counterweight doesn't seem to keep the valve in one position, even with the spring off. Maybe the balance is not too critical. Hard to say if it will work properly with no weight.

You could just wire the butterfly open. Or remove it completely....to do that you have to destroy it, as the butterfly is spot-welded to the shaft. Then tap the shaft holes and plug them with set screws.

The valve assembly is pn 1377496 or 1377547 for 64-66 401-425.

[cwmcobra]

I haven't posted in awhile since I didn't have time to work on the GS.  I've spent some time on it this week and the result is it is running much better, although not perfect.  Here's what I've done:

-- Compression test:  lowest is 145 PSI, others in the range of 150-160 PSI.  I presume these are acceptable and don't indicate a particular problem.

-- Rebuilt the primary carb: with kit from Carmen Faso.

-- New distributor: with Pertronix ignition system from Carmen, including a higher energy coil.

-- New spark plug wires

-- New platinum tipped spark plugs

The bad miss I had is gone, but it still shakes a bit at idle.  Guess I'll have to try Brian's suggestion of putting water in the intake.  Brian, do I do it with a spray bottle, or just slowly pour it into the carb???

Do you recommend the factory spec for timing at 2.5 BTDC?  Or are there other thoughts?

Thanks for your suggestions.  It's almost roadworthy now!

Cheers!

Chuck

[richard65]

Hello Mr. Cwmcobra,
Not sure if this helps, but my 65 has a rough idle.  When I'm sitting at a traffic light the whole
car moves with the lope of the engine, you know the good lope. I was told that this is normal for a nailhead.  My car runs strong under a load with no miss, no upgrades, all stock igntion and single carb.
 Good luck, happy fathers day

[sjfd04]

Chuck

I had an idle problem as well, some things to look at:  Make sure all vaccum fittings are sealed with teflon tape and tight.  Power brake fitting, transmission modulator and any vaccum  fittings on the carb or on the manifold.  Also check to see if the throttle shafts are not worn and leaking.  Check manifold gaskets, anything on the intake side that would suck air into the combustion chambers. 

As far as timing, I would go with total advance setting.  I believe the 401 runs great at about 35-40 total advance, including the vaccum advance.  Should reach at about 3500 RPM.

After I went through everything possible, I gave up and bought a new carb.  Works great now.

Tom