My engine will break up at higher rpms and sounds like a popping noise. If i back out it stops and pulls good again. I just replaced plugs and wires today, I know my carb isnt quite right, left idle mixture screw doesnt do anything. any ideas on what this is. engine has been sitting for about ten years and has only been driving for a week.

 

wanted to ad that it doesnt only do it at wot. I thought it was plugs or wires but its not.

 

I could be too much fuel getting into the carb then backfiring, does it sound like a cam shaft popping ?

 

sounds like possibly fuel delivery issue possibly. If you timing is in spec and the dist. is advancing correctly and functioning properly then I would venture to say make sure the fuel pump is working properly and then get into the carb.


Now you say you let off and get back in it and it pulls good does it break up again and pop or pull clean ?

 

I'm thinking fuel pump too..er carb related. You might not be getting the fuel quanity up top with something this old and sitting.

If you feel like the ignition is ok and the timing is ok, then procede with fuel delivery issues or just old fuel for now.

 

It could be the carb is lean.

 

I did new plugs and wires, gapped the plugs set the dwell(31) and set the timing to about 7.5( supposed to be 5). It runs better then before but since I started driving it it had this pop sound when it got to a certain rpm and above. While just driving if I held a gear a little longer than normal it would do it. Like driving up a hill holding second once the Rpms got a little higher it would pop if I backed out it would start pulling again and clear up. I opened up the carb and it was pretty dirty in one of the bowls, edelbrock carb, so I took it off and cleaned it out.

 

Hmmmm If its an edelbrock carb and it is popping while cruising then be fine once you cleared it out and get on it. Might come down to a little tuning if its an edlebrock carb you might have to change the step up springs for the metering rods they might be closing while cruising and causing a lean condition.


Did you take the carb apart and blow all the passages out with carb cleaner ? I have done a few edelbrock carbs what model number is it ? Did it work fine before ?

 

Since it's been sitting you may still have some varnish in the tank which could be mixing with the gas and causing the valves to stick. You might add some marvel mystery oil to your gas.


You also may have a couple of weak springs as they were sitting compressed for a long time.

 

It's seems more like the opposite of that. Yeah I blew through the passeges with cleaner and air. Idk the model number, I also don't know if the previous owner had this problem or not.

 

You might have to go to a stiffer or lighter spring depending on weather if it's lean or rich. Go by the model number for example 1405 1406 etc, Then Go to edlebrock and look up the pdf file and find out what you have and a tuning kit cost like 30 bucks and it has a variety of jets and metering rods and step up springs and you can download the tuning guide from edlebrocks website. It's a pretty easy carb to mess with since going back to stock settings is very simple. The step up springs are easy and quick to change along with the metering rods.


I don't like old crusty carbs specially if I don't know the background. If you have a buddy with spare carb that worked well borrow it and see how that goes. I had an experience with an edelbrock carb that was so corroded many passages where leaking into other orifices.

 

I know the carb is funny cause the fuel bowl that was really dirty, I've never seen so much crud in a carb before this, is the same side that the idle screw doesn't work. My dad has two 500 edelbrocks, I'm going to try one tomorrow and see what it does. I'm not particularly a fan of edelbrocks but they are available and fit the intake.

 

I'm not sure if the fuel is the same down in the US but the 87 octane here after it sits for a bit will turn a green color in the carb bowl. It gums everything up in time. Good thing its not a cam pop. Hope you nail it down and have a smooth ride soon!

 

Have you tried new points and condenser and a different coil?.
I know you set the dwell correctly but tired points or an iffy condenser or a coil going bad will give you similar symptoms.
Of course with an engine not used in ten years it's entirely possible you have several issues all at once, just because you find one fault that doesn't guarantee you have fixed your problem.


Roger.

 

I did not try new points or coil. I know they could still be bad but the points look brand new. im going to try a different carb today and see if that helps. wondering if it could be incorrect voltage to the coil while running. also seems like every time i start it after its warm i have to hold the peddle all the way down or it doesnt start, dont know if this is relevant.

 

If I sat for ten years I would need a lot to get going myself lol. I would clean up as much as you can , then go down the line on replacing tuning parts. If the engine seems ok, timing chain etc, then your good to go on replacing the mechanical things that haven't moved over the years JMO.

 

My '59 Imperial did something similar. We replaced the condensor, it was fine.

 

Change the distributor cap. I had one that was cracked that did the same thing your car is doing. Changed it and the car ran great. The spark was arcing around inside the cap causing misfire. It's a cheap way to eliminate that area that may be the problem too.

 

The condensor is basically a capacitor and unlike points they will break down over time if they are not being used. It is a cheap part to rule out a possible problem. Another thing to replace would be the fuel filter. If you had/have varnish in the fuel bowl, you probably had/have varnish in the fuel tank that would plug a filter rather quickly. A plugged filter would cause a high RPM lean-out.

 

I tried another carb didn't fix my problem but seems work better than what was on it. I replace the fuel filter as well. I forgot to ad the engine was completely rebuilt in 2000 and only ran about 2-3 years before it was parked. I would assume internals are all in working order. I have an extra cap I can try and can try another condenser. Thanks for the ideas

 

Give us an update when you fix it. Please.

 

If it sat for 10 years rule of thumb is make sure the fuel system is In check and ignition. I would just go ahead and do new dist parts like cap , rotor , condenser and points. When we dug my dads car out from under my uncles deck which it sat there for 10 years we did new plugs wires, cap rotor , fuel filter and we used a gas can since the stuff in the tank was probably gunk by that time.

 

Watch out for the banjo spring in the jet port. If it's been sitting that long it's probably fried. Help him out copper.

 

Why not throw new points in as well?. You say they look new, but you know they are ten years old.
A long time ago I tuned up a car including new points, condenser, plugs etc and the car ran fine. A day or so later it went into a police pound for 18 months. When I went to collect it I had to replace the points again as it refused to start. I didn't need to do anything else apart from use jumper cables.


Roger.

 

I'm not buying the varnish causing the valves to stick, but a weak valve spring from sitting maybe.Nick

 

Did you buy a car that was sitting that long or did you own it, drive it, then let it sit? If it didn't pop when you last drove it, some 10 years ago, you could rule out point float. Condensors are prone to electrolyte evaporation, after approximately 20 years of service

 

I've seen varnish gum up carburetors, intake valves, fuel pumps, etc to the point that when the engine cools after running, moving parts inside are glued together. This is after the tank was drained, I assure you it happens.


It happened with Keiths 35 Olds, actually glued the moving carb parts, and it happened with the 36 Plymouth I'm working on now, intake valves were hanging open.

 

Everyone is focused on the carb, but my money is on ignition, specifically the coil. I've had exactly this problem before, and high RPM breakup is often a sign of a bad coil.

 

Yeah, Joe. That was mean of us to hold back with our electrical suggestions, until he got through completely rebuilding his carb

 

I looked at the engine after my drive home from work and saw fuel dripping off the secondary throttle shaft, upon further inspection i heard fuel dripping into the hot intake sure enough the left rear discharge nozzle was dripping. a pretty decent amount of fuel was dripping out. Also the external appearance of the coil isnt pretty. I also noticed it seemed to get better the closer i got to home, warmer, vs when i left work.

 

Consider weak valve springs causing valve float. My original 350 would pop and loose power around 5,000 RPM, but ran great otherwise. HEI and Q-Jet were fine.

 

Yes i'm not saying varnish can't stick the valves open,i'm sure the old flatheads you mentioned more so,the op is stating popping at higher rpms,no mention of dead miss across the rpm band.That's why i said weak valve spring-s.Nick

 

checked and its not dripping while running

 

It can be either, I've had both happen. On the Plymouth it ran ok until we turned it off and then the engine cooled and the valves were sticking intermittently on all cylinders. It was tough to diagnose until we pulled it apart.

 

the only popping I have had experience with was a cam in a 1978 chev 350 , I hadv to replace the cam and chain it would pop like crazy when revving then letting off . jus sayin

 

I agree more so on the flat heads as the valves are upside down compared to ohv.Nick

 

He won't tell us if he had this problem before storage or not. Time is not a factor which would cause either contact point- or valve spring fatigue

 

He doesn't know as the car was recently purchased.

 

I do not know if it had the problem before i got it. If i have time im going to do a compression test and pull the valve covers to check the springs. after listening to the sound some more im not sure its an ignition problem. I might be able to get a video up so you guys can hear it for yourself.

 

I checked the valve springs and none looked or felt broken. I took my cap off to see if it had any obvious cracks or corrosion, didnt appear to but two terminals on the inside were covered in what seemed like oil.