Rough Idle 65 Buick 401 Carter

[wmsue]

Can't seem to clear up the rough idle on my Buick. Let me tell you what's new and what I've done thus far: The following parts are new:

Engine (not a rebuilt - has 4 hours on it since 1964.) , dist.,cap, rotor, plugs RJ14YC Champion, wires - delco packard, exhaust system (heater riser valve is working correctly and is closed when cold and opens freely at warmup.

I'm using 93 octane BP gas with lead substitute and Stay-Bil. I drained the tank before adding new fuel. (I'm using the drained fuel in my tractor and it runs fine). I had the card rebuilt by a local reputable shop. I used the original steel gasket and sandwiched it between 2 new carb base gaskets. I installed an electronic ign. system. I've had the engine running about an hour all told and get no smoke out the exhaust and I removed 2 plugs on each side a few minutes ago and they look fine.

I'm able to get it running fair with 900 RPM in park with the dist vacuum advance disconnected. The vacuum is 17" and very steady. The carb mixture screws are out 3 1/2 turns to achieve max rpm and vacuum. It will not run at the recommended 2.5 DBTDC - I'm at 12degrees to achieve max rpm and smoothness. It stalls out when I try to get close to 2.5 degrees. There is no backfiring and runs great at 1000 rpm and higher. It runs very rough at idle but settles out at 1200 rpm or higher. I forget how much power these old nailheads have. It spins the tires without me really trying. I have to keep the idle high to keep it running and then I spin the tires ( or stall out) when I shift it from park.

Do you disregard the dwell since I installed an electronic system? The meter says a steady 40 degrees. No variation at change of rpm.

I think that's everything.

Any ideas or suggestions would be greatly appreciated. What's the next thing to look at?

Thanks in advance for the help:)

[61-63]

Check the windings on the coil with a multi tester and if either is out of spec replace it. That may solve your problem.

[wmsue]

thanks

I'll check it out tomorrow evening.

I was ready to convert back to original points ign. to see if that was the problem.

[JohnD1956]

I had the card rebuilt by a local reputable shop. I used the original steel gasket and sandwiched it between 2 new carb base gaskets.

Is this the right combination? Seems like one too many carb gaskets.

I installed an electronic ign. system. I've had the engine running about an hour all told and get no smoke out the exhaust and I removed 2 plugs on each side a few minutes ago and they look fine.

Did it run okay before this ignition change? If so try a new unit or go back to points and condensor. Speaking of condensors, make sure the wire is run through the wire loop in there.

I'm able to get it running fair with 900 RPM in park with the dist vacuum advance disconnected.

Have you checked the mechanical weights to make sure they are free and able to function?

The vacuum is 17" and very steady. The carb mixture screws are out 3 1/2 turns to achieve max rpm and vacuum.

3 1/2 turns is extreme in my opinion. But unless you can get the idle down you probably are bypassing the idle circuits anyway. I'd check the base gaskets to make sure you need both carb gaskets with the steel gasket and then make sure you try to bring the carb tight evenly and thoroughly.

It will not run at the recommended 2.5 DBTDC - I'm at 12degrees to achieve max rpm and smoothness. It stalls out when I try to get close to 2.5 degrees.

If you are timing it at 900 RPM, you also have the mechanical advances coming into play. Almost sounds like the balancer has spun and the reading is incorrect relative to the TDC position. Remember too that the first cylinder is on the passengers side of the engine in a nail head.

There is no backfiring and runs great at 1000 rpm and higher. It runs very rough at idle but settles out at 1200 rpm or higher.

Sounds like the idle circuits in the carb are clogged. May be worth while to take the carb back to the rebuilder for a second look.

Do you disregard the dwell since I installed an electronic system? The meter says a steady 40 degrees. No variation at change of rpm.

I would think so. The dwell is the gap of the points, which you have eliminated.

Good luck and please post what you find as you go along.

[Guest kaycee]

I agree with Johns comments. The carb should only have the metal gasket and one regular type base gasket, and idle screws only about 1/4 to 1/34 turns out according to the manual. It may be sucking air at the carb or intake manifold. I used to time my 401 -425's to as much as 10 advanced with good fuel. You might try (after you check for any air/ vacuum leaks) advancing the timing a little, assuming your electronic ignition is Ok. You may have to try points again or another electronic unit. I've only installed a Pertronix in a '65 Riv. 425 in the past, and it worked well, but I normally just replaced points and condensor in routine tune ups.

kaycee

[wmsue]

Hi

I checked the mechanical weights and they are free. I installed the extra gasket to ensure no leak at the carb base and because Cars Inc. recommends it in their parts manual. I don't recall ever using 2 gaskets before but I was listening to what other people said to try. I never remember having idle screws out 3 1/2 turns. I always started at 1 1/2 and went from there. Maybe I'm using the carb to adjust for a bad ignition system?

this car was my daily driver from 1973 - 80 and it's sat for the past 29 years. Little by little I've accumulated parts and installed them. So there are so many new parts (which I understand can be bad out of the box) that I'm baffled by where to look. I installed the electronic ignition a year or so ago but never started the car till a month or so ago.

Thanks for the great help. I think I'll start at the coil and work through the ignition system by checking each wire and going back to the original points. Then the carb.

Let you know what happens

Thanks

[carbking]

ASSUMING you have the original carburetor:

Maximum benefit from the idle mixture control screws occurs at 1 3/4 turn. Beyond that point, no additional fuel.

I would first remove the electronic ignition (simply because better than 90 percent of our prospective new customers with "carburetor" problems (particularly idle issues) have an electronics ignition installed). About 89 percent of these solve the "carburetor issue" by reinstalling points and condensor (and I lose a prospective new customer!).

If this does not solve the issue, then I would be looking for a vacuum leak.

Jon.

[wmsue]

I do have the original carb. A Carter 4453S AFB. I bought a pt/cond set yesterday and have the bag of original parts left over when I switched to electronic ign. Should find time this weekend to pull the dist. and switch back.

Thanks

[wmsue]

Coil checked out OK. I switched back to the original points/cond ign and the smoothness is coming back. It runs very well at 800 rpm in park with the mixture screws out 1 1/2 turns. It stalls when i put it in reverse or drive and the vacuum fluctuates between 10 and 15. I'm going to switch back to one carb gasket and the metal plate and then check the intake for leaks. I've already ruled out the dist, vac. modulator and the heater controls. I replaced the vacuum booster a few weeks when I installed disc brakes but I'll block it off to be sure.

Thanks for the help and I'll let keep you informed.

[wmsue]

Found the leak . Intake manifold has a leak near cyl #1. Now to order a gasket and replace it.

thanks to all forum members.

[JohnD1956]

Good work and thanks for letting us know.

[Guest kaycee]

Congradulations on your troubleshooting! Let us know when you get the intake gasket replaced, and of course tighten the bolts to specs (25=35 lbs. torque and in sequence) and readjust the carb. idle screws. They'll probably be about 1/12 to 1/34 turns out when the engine is'nt sucking air any longer. 'Should run great.

kaycee

[wmsue]

Success!

Intake gasket replaced and it runs like to day it came off the showroom. I did some painting of the intake and pushrod cover while I had the opportunity and replaced a few hoses. Did a compression check while double checking the gap on the plugs and had 200 psi per cylinder. No variation.

Couldn't find a torque sequence in the book so I tightened each one bit by bit (from the center outward) and finished at 30 ft lb. Carb screws are finally at about 1 1/2 turns out.

I can't believe how smooth it is running now. Thanks to all forum members for the help.

Now it's time to do some body work.

[JohnD1956]

Great. Drive it some too.

[Guest kaycee]

Congradulations again. Thanks for getting back to us. Now your car is running like Buicks should run!

kaycee