340 heartache

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VonCramp

VonCramp

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I am posting a new thread because I am convinced my issue is not fuel related as originally believed. So far, I have changed carbs three times. I put in a brand new distributor. I have a resistor that is one year old and tried two different coils. It also has a one year old orange box. No matter how I set the timing the 340 dies immediately if I don't constantly give it gas by working the throttle. She will start and run and can even be driven as long as I don't quit massaging the throttle. I put on a new carb base gasket as well. I did get a couple of small pops out of the carb, but nothing big. I checked all electrical connections, but haven't found anything out of the ordinary. Fuel pressure is a steady 8lbs out of Holley regulator and blue pump. I'm at my wits end here. The only things I haven't done is changed the intake gaskets or tried a new resistor. Please help.
 
I would say you have a vacuum leak. Timing mark could be off need to verify that its right. Be sure you have all the vacuum ports are plugged that can bite you in the ***.
 
67cudafb said:
I would say you have a vacuum leak. Timing mark could be off need to verify that its right. Be sure you have all the vacuum ports are plugged that can bite you in the ***.
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I would start with this...
 
I will back down on pressure. I am thinking a vacume leak at the intake is very possible because aside from the constant peddle work the engine runs great. The car sat for about three weeks with that stuff the government tries to pass off as fuel these days. That's why I started at the carb. I want to say thanks for all of you taking the time to help me. Y'all are a great bunch of guys!
 
I'd pull that front cover and check to see if the chain jumped a tooth. After checking the previous mentioned vacuum and timing suggestions. Just my opinion based on a previous experience. Good luck.
 
Do you have a vacuum gauge? Check the vacuum at the carb port , it will give you a clue if it is the intake leaking into the lifter galley.
 
Could be plug wires crossed up. My official guess is jumped timing chain.
 
funwithfuel said:
I'd pull that front cover and check to see if the chain jumped a tooth. After checking the previous mentioned vacuum and timing suggestions. Just my opinion based on a previous experience. Good luck.
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X2

This sounds EXACTLY how the 360 in my car was running the first week I got it running. It ran good for break in, but trying to drive it it would only run if I two-footed it. It was a dog. Fuel pressure, oil pressure, timing from with a timing light were all right on, and I was using a carb that came off a running engine.

After a week of going nuts looking for anything and everything, I pulled the front cover and saw I had installed the chain a tooth off.
 
Yes 8 psi is too much, but the issues with too much fuel pressure don't fit the symptoms. From this and your prior post, adding fuel (with choke, pumping, or carb cleaner) smooths it out; lower pressure will not increase fuel. Some vaccum readings would be very helpful.
 
rklein383 said:
I agree, 8 lbs is too much.
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Yes 8 is way to much. 4 is plenty with a blue pump and regulator because it is constant. You can always put a mechanical on it and adjust the carb as follows. The idle screw needs to be set until the throttle plates open a tiny bit. Then adjust the air fuel mixture at 2 1/2 turns if it's a edelbrock or carter and 7/8 of a turn if it's a holley. Hopefully the timing is adjusted, if not set it at about 9 degrees before top dead center, a happy place. Mopar small blocks love lots of vacuum advance at a idle but too much will ruin the engine and idle characteristics. Most say to set the total advance at 35 degrees no more than 36. Most of my mopar hot rods have run best at 28 to 32 degrees. This information is based on a mild street build. If you have a wild high compression (more than 11 to 1 ratio) and a high stall and big thumping cam, it will need to be all set by dyno unless you are a "wizard mechanic"
 
Here is a few things I would try. Put a vacuum gage on a manifold port. Disconnect power brake booster, vacuum advance and pcv and and plug ports to eliminate points that may be leaks. If your carb has a choke close it and see if it will idle if not cover with a rag or your hand. If it speeds up you have a vacuum leak. Basic trouble shooting and elimination is the only way to find problem. If you have a car club in your area find a old guy that knows how to tune old cars with carbs. Old hot rodders love to help others and pass on the knowledge they have. Good luck and keep at it and enjoy your A body. Is this a recent rebuild or did it run and start have problems?
 
67cudafb said:
Here is a few things I would try. Put a vacuum gage on a manifold port. Disconnect power brake booster, vacuum advance and pcv and and plug ports to eliminate points that may be leaks. If your carb has a choke close it and see if it will idle if not cover with a rag or your hand. If it speeds up you have a vacuum leak. Basic trouble shooting and elimination is the only way to find problem. If you have a car club in your area find a old guy that knows how to tune old cars with carbs. Old hot rodders love to help others and pass on the knowledge they have. Good luck and keep at it and enjoy your A body. Is this a recent rebuild or did it run and start have problems?
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It's an ongoing build! The car is a real big block 4-speed car. The person I bought it from thought it was a small block car. Self-proclaimed Mopar expert! A quick check of the k-member and vin verified that it was a true big block car. I managed to locate an a-body 18 spline 4-speed for it. The 340 was pulled from my 68 Barracuda that was totaled when it was hit from behind by a drunk 16 year old girl. I don't ever plan on selling this car unless I come across a real S/S project. I like to dream big, but hey I never thought I'd have a real 'Cuda either!
 
Nothing wrong with dreaming big. Good luck with the cuda. I had a few rare a-body's over the years and kick myself in the *** for selling for next to nothing years ago just used cars. Bill
 
nm9stheham said:
Yes 8 psi is too much, but the issues with too much fuel pressure don't fit the symptoms. From this and your prior post, adding fuel (with choke, pumping, or carb cleaner) smooths it out; lower pressure will not increase fuel. Some vaccum readings would be very helpful.
Click to expand...
I will purchase a vacume gauge today and get those readings. I have a Crane 509" cam but no power brake booster. Motor is .040 over with x-heads. Edelbrock Performer intake and Hooker Super Comp headers. Mopar distributor tuned advance with orange box. Mallory coil and Moroso 8.8 wires. A-body 18 spline 4-speed. As I stated in a previous post the car was running fine before sitting for three weeks. I went out and started it up and it wouldn't idle. Thanks again for the advice!
 
67cudafb said:
Nothing wrong with dreaming big. Good luck with the cuda. I had a few rare a-body's over the years and kick myself in the *** for selling for next to nothing years ago just used cars. Bill
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Looks like you got a cool project right now! I am a hot rodder not a numbers guy. So, I didn't want the car because I wanted to restore it, but instead just go fast and look cool. Still have that teenager mentality! What are you doing to yours?
 
try shimming the rocker shafts .030 see if that helps unless you have adjustable rockers.
 
VonCramp said:
I will back down on pressure. I am thinking a vacume leak at the intake is very possible because aside from the constant peddle work the engine runs great. The car sat for about three weeks with that stuff the government tries to pass off as fuel these days. That's why I started at the carb. I want to say thanks for all of you taking the time to help me. Y'all are a great bunch of guys!
Click to expand...

So when you parked it, it was running fine? Three weeks later it won't?
 
Bad Sport said:
So when you parked it, it was running fine? Three weeks later it won't?
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Running perfect! I don't know what's going on. It is something weird because I can't seem to isolate it. Maybe the filter at tank is clogged. I will check that after I do the vacume test.
 
This might be a silly question, but does it run good for a minute and THEN develop the symptoms you describe or is it right from the git go?
 
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