1955/235 engine problems

[pkr]

I'm asking this for a friend This is his problem. When he starts his car and it is idling there is a slight pop. Unhooked #1 plug wire made no difference, unhooked #2 no difference,unhooked #3 made big difference run like crap At idle. if rpm is raised ,all plug wires attached it smooths out. on a drive it seems to have no power lose. compression on all six cylinders is in the 90's. The ign system has everything new, No water in the oil. this engine does have duel carbs but they have been on for years. Any suggestions would be greatly appreciated.

Edited March 15, 2010 by pkr (see edit history)

[Rusty_OToole]

Evidently #1 and #2 cylinder are not doing anything.

Possible reasons: He accidentally switched the wires, check your firing order.

Spark plugs not firing, take them out and inspect them. Attach the wires and see if they are firing.

Front carburetor bunged up and not feeding gas. This could be anything from dirt in the carb, float jammed, etc. Try tapping the float bowl, look inside and see if you get a shot of gas when you open the throttle. It may need to come apart for repairs. Could also be fuel not getting to carb although this seems impossible if the other one is getting gas.

Front carb might not be opening but if the linkage fell off I expect you would have noticed by now.

If spark is not getting to the plugs look inside the distributor cap for moisture or dirt shorting things out.

Could be lots of things, basically the questions are, is it getting spark? Is it getting gas? If it has compression then it must be one of those 2 things.

[pkr]

Rusty , Thanks for the quick response. My friend said the cap,rotor,points,wires,plugs have been replaced and he has fire to the plugs. He is a old time mechanic so i know things were installed right. He and his Friends are stumped and so am I. You might be right about the front carburetor not working properly. I'll also pass along what you said about taking the plugs out and grounding them to the block to see if they are firing. Once again thanks for your suggestions. paul.

[Guest DeSoto Frank]

Sounds like the idle circuit on the front carb is not working, or perhaps there is a vacuum leak.

Try gently spraying a small burst of starting fluid into the front carb while it is idling... if things smooth out for a few seconds, that indicates the issue is most likely fuel-related.

What kind of carbs are we running ? ( I presume this "235" is a Chevy six ?)

[Guest elmo39]

another simple solution is it could be faulty plugs , i know you said all the plugs were replaced , but it is possible for even new ones to be faulty , as a quick check change the position of the plugs to see if it makes a difference .

[Bill Harmatuk]

I had a '65 model, 283 that did the same thing.

Ran fine, very slight miss, till you accelerated hard. Then it popped back thru the carburetor.

Check to see if all your rocker arms are moving up and down correctly or the right amount.

You'll have to pull the valve cover and start it up with the valve cover off.

Always a mess, but you will be able to observe the action of the valves

You may have a lobe worn down or off your cam.

Just my 2cts.

Bill Harmatuk

[Guest DeSoto Frank]

That "slight pop", is it popping-back through the carb, or is it a subtle "puh"... "puh".... "pu-puh"... from the tail pipe ?

If it's the second "puh-puh", that might just be idle mixture vagaries. I've had a lot of Chevy sixes that did that at idle, but they ran fine under load and at speed, and I gave-up trying to make the puh-puh-puh at idle go away.

If it's popping back through the carb, then something's amiss.

When did this behavior start ? Cams don't wipe "overnight" (unless the oil supply fails), even then it's a somewhat gradual process as the lobes flatten-out.

While multi-carbs "look sexy", they can bring their own host of special gremlins to the picture, especially if they're "just dropped onto" an existing engine.

Try the starting fluid trick I mentioned in my previous post... ( or WD-40, if you prefer).

[Caballero2]

Like the man said, check your firing order. The most experienced mechanics will make this mistake all their lives, it just happens.

Dan

[Guest DeSoto Frank]

Like the man said, check your firing order. The most experienced mechanics will make this mistake all their lives, it just happens.

Dan

Good point !

For some reason, on the Chevy six, I frequently get # 2 and #4 reversed...

Heaven help me if I ever get a V-12 or V-16 !

[pkr]

Thanks All, My friend called and told me they found the problem. It was the front carburetor all the time, something with the idle circuit. I think the "puh" from the tail pipe is just a over rich mixture. Even though the plugs were new they turned black quickly. You guy's were a great help. Paul

[Guest Bob Call]

Chevy six firing order 1-5-3-6-2-4. Easy to cross 2 and 4.