Not Running Right When Hot

[65gto69]

Hey Guys,

Hope you can help me with this problem I justed having. Car starts up fine, idles great, great throttle response all when cold, once engine warms up to temp (190) she stumbles when you stab the gas peddle like it would be loaded up. Funny thing is, if you keep on reving the motor (like cleaning it out) the problem never clears up. After the engine cools down and you restart, no problem until it gets warm again. What do you think my problem is. Here are some specs, if you need anymore or have questions that I might help in figuring the problem please post here and I will answer to the best of my knowledge. Specs: 1968 400 30 over, stock crank, forged rods, trw 30 pistons, total seal rings, crane cam .560 lift w/ 1.65 rockers, 1968 #16 heads (ported if that matters), 1970 cast iron intake, new edelbrock 750 carb. Note: Engine has been running great for the last 10 years with a 2 four setup I had on it. Just within the last year I had taken off the 2x4 setup (sold it) and started messing with a single 4 setup (when problems started). Hope you guys can help, this has been a pain in the a$$ for the last year. If you need any othe info, please ask.

Thanks in advance for the help.

Mark

[65gto69]

Hey Guys,

Hope you can help me with this problem I justed having. Car starts up fine, idles great, great throttle response all when cold, once engine warms up to temp (190) she stumbles when you stab the gas peddle like it would be loaded up. Funny thing is, if you keep on reving the motor (like cleaning it out) the problem never clears up. After the engine cools down and you restart, no problem until it gets warm again. What do you think my problem is. Here are some specs, if you need anymore or have questions that I might help in figuring the problem please post here and I will answer to the best of my knowledge. Specs: 1968 400 30 over, stock crank, forged rods, trw 30 pistons, total seal rings, crane cam .560 lift w/ 1.65 rockers, 1968 #16 heads (ported if that matters), 1970 cast iron intake, new edelbrock 750 carb. Note: Engine has been running great for the last 10 years with a 2 four setup I had on it. Just within the last year I had taken off the 2x4 setup (sold it) and started messing with a single 4 setup (when problems started). Hope you guys can help, this has been a pain in the a$$ for the last year. If you need any othe info, please ask.

Thanks in advance for the help.

Mark

[russ467]

Is the choke opening up all the way after it warms up?

[65gto69]

Carb is manual choke, and is set open all the time. Choke is not closed at time of startup either.

Mark

[tikiklubracing]

Whats comming out the tailpipe when you tromp it warm???? http://forums.performanceyears.com/groupee_common/emoticons/icon_confused.gif

[65gto69]

It is a faint blue color.

[russ467]

Is there a chance your ignition module and or coil is getting weak when hot?

[Mo]

Seems like ignition to me. Perhaps a thermal vacuum switch. Do you have HEI with vacuum advance? If your advance runs through a thermal vacuum and your wires from the pick-up to the module are bad, you can have an intermittent stumble when vacuum is applied.
Check all your connections and grounds.
Other than the carbs/manifold what else was changed? Vacuum hoses and so on.

[Torment]

Since it ran well before you changed something, logic tells me the problem stand a good chance of being related to something you changed. If it runs good cold but stumbles warmed up the carb might just be too fat. I don't have much experience with the Edelbrock carbs but I do have a few friends that tried them briefly - likely for a reason. Anytime you have interchangeable parts availalbe it can be the easiest way to positively locate the offending problem - got another carb lying around? Short of a cracked manifold or a vacuum leak the manifold likely isn't the problem - and you mentioned it idles well so... I'd swap in a different and appropriate carb to see if the problem goes away.

[65gto69]

Thanks for the suggestions, I do have another carb, I will try that. I will also look for vacuum leaks, etc. Distributor is an original 65 points distibutor, advance not hooked up. Coil is basically new, bought when I got the car running 10 years ago. Note: car has been running for 10 years but I do not drive it much, I am lucky if I put 5,000 miles on it since it has been running. Maybe I just don't drive it enough?????

Thanks for the info, if there are anymore suggestions keep them coming, I will try mentioned suggestions and post results.

Mark

[tikiklubracing]

could be a vacum leak that doesn't leak till it warms up and the rubber expands. http://forums.performanceyears.com/groupee_common/emoticons/icon_smile.gif

[mrdan7]

http://forums.performanceyears.com/groupee_common/emoticons/icon_frown.gif Hope I'm Wrong, however the only time I ever had this problem as you described, it was the

HEAD GASKETS,
http://forums.performanceyears.com/groupee_common/emoticons/icon_eek.gif
easy enough to check though, Success 2-U

MRDAN7

[65gto69]

MRDAN7,

Man I hope it is not a head gasket. I will keep that on my list to check, but will make it my last resort.

Did find that my PCV maybe bad, and the hose was very dry, don't know how I overlooked that.

Will post as I find things.

Thanks

[george kujanski]

If it starts easy with the choke open, you very well may be too rich. Check the plugs for rich indication.

George

[felton thompson]

I had a similar problem and had to go up 2 sizes on accelerator pump squirters to get stumble out, with the 2-4 set up you were probably getting more gas when you punched it,could be worth a try!

[buwalda]

The cam you have must be fairly large, having 0.560" lift. Does the carb have a choke? If it does, the engine probably gets a rich enough mixture when cold with the choke activated, so that it idles ok with the large cam. With the engine warm & choke off, the carb probably needs idle circuit attention to run properly with that cam. I see you are not using vacuum advance, so your timing at idle is probably just the initial setting & that is probably insufficient. When the engine is warmed up, try advancing the initial timing a few degrees & see if that helps or fixes the problem. If it does, you need more timing [ did I say vacuum advance was a good idea? ], carb work, or both.

[65gto69]

Thanks kujanski, Thompson, & Geoff for your suggestions, I will be checking and trying those suggestions out this weekend and post how things went. Can't do it during the week because I live in a tight neiborhood. The car is quite loud and till I get home it is too late. Already had a run in with a neibor at 8:00pm telling me to shut the car down. So now when I tune, I do it during the weekend around noon time.

Thanks for all the help so far guys.

Mark

[johnta1]

Personally I would change to a Quadrajet or a Holley.

If the car has sat for a long time I would put some new points in. Also as was said, I would hook the vacuum advance up.

[tikiklubracing]

Faint blue is oil smoke http://forums.performanceyears.com/groupee_common/emoticons/icon_frown.gif......<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by 65gto69:
It is a faint blue color. <HR></BLOCKQUOTE>

[68lemans462]

read your plugs and dial in the carb. Also, try adjusting the pump shot. The AFB's are easy to tune and always work very well for me.

[65gto69]

I just wanted to say thanks for all the suggestions, and I will be trying them this weekend. I will post results when I get them. Neighbors don't like it very much when I am starting and reving the car after 8:00pm, so I have to wait till the weekend to work on it.

Mark