The Stovebolt Site Forums The Shop Area General Truck Talk Runs rough when warm

Hi All,
I've searched through the posts and finally had to post my own question. Many of you have been through this before from what I read.
It goes like this - my beloved '49 with a 216 stock and Rochester carb has been running beautifully since I got it a year ago. I just drive it a little on weekends. Last weekend I ran it a few miles to the hardware store. On the way home it started sputtering and needed to pull the choke out a bit to keep it running, though it ran rough. From then on it runs great when cold, but as soon as it comes up to temp it starts running rough again. I tried adjusting the throttle faster but it didn't help the rough run. I pulled the inline filter between the pump and carb but still the same thing. The glass bowl on the pump is always full, so assume the problem isn't there. I thought maybe it was the ethanol gas I last put in, but the problem didn't start right away. I'm just befuddled. I want to smile while driving my truck again. Can anyone help?

Aloha,
Rich

I had the EXACT same problem with my 1952 Chevy Deluxe, and I had to rebuild the Carb.

Now she runs like a Champ.


Cliff59

What CLIFF59 said, plus check for vapor lock or similar problem. Possibly a failing fuel pump? Also make sure the insulator block between the carb and intake manifold is in good condition.

Mine did this suddenly last fall, and after I spent a couple of hours blaming the fuel system and tracking down possible problems, I ended up cleaning and regapping the plugs - I also had one bad plug wire.

I think that the guys have everything pretty much covered.

Personally, it sounds to me like it's a carburetor problem. Check your mixture.

Vapor lock happens when it's under load, but works okay at idle. Usually caused by a weak fuel pump.

When was the last time you did a tune up?

CLIFF59,
Did the problem develop suddenly like mine did? Did it run well until it came up to temp?
Thanks for the input.
Rich

Thanks Fred and Brendan.
Fred, cleaning and re-gapping did the trick for you? You mentioned that your problem came on suddenly as well.
As you asked, Brendan, I haven't tuned her yet. She was tuned before she arrived and only driven occasionally for short durations. I'm just puzzled about the sudden onset of poor performance as she warms to operating temp.
I will start with the simplest suggestion first and move on from there I guess.
Thanks again!

Perhaps the heat riser is stuck?

Thanks Phil. O.K. here's the confession - I'm not a mechanic nor do I know alot about engines. I'm learning as I go. Can you describe where and how to check for a stuck heat riser? What's the fix?

Rich

On the intake manifold, below the carb there is a 'flap' that opens when the engine is cold and closes once it warms up. All you will see is a rod with a spring on one end, and a weight on the other. Check to see if it turns. If it does not, spray some penetrating oil on it and tap it gently back and forth over time and it shall free up. The problem is if it does not close once the engine warms up, the carb gets to warm and the gas mixture 'evaporates'.
However I don't think that will suddenly happen.
Good Luck.
Colin

Thanks Colin.
The heat riser is stuck. I'm not sure what position it is stuck in. Perhaps someone could take a look at the photo
http://home.hawaii.rr.com/calabash/hrv.JPG
and tell me if it is stuck open or closed.
Thanks,
Rich

It would start up nicely and run for about 30 min and then "chug" she would shut down like you
had pinched the fuel line or something.

I checked on the "vapor lock" thing and It was not a vapor lock issue.

I checked for distr. problems and It had great fire. "ouch"

It turned out to be a BAD Carb. So I changed points cond. and plugs but ..... I would drive her about 30 min then "chug" shut down

I then totally rebuilt the carb. and SWEETLY she runs, and No more problems...


Glad to see that you got your problem under control
take care and keep her on the road.

Aloha
Cliff

point gap should be looked at when it gets warm points could be not hardly opening

Thanks to all you stovebolters for replying to my post.
I replaced my plugs today and took her out for a test drive. She ran awful! After spending some time pulling and pushing ignition wires at the plugs, distributer and coil she suddenly started running crisp again. I'm at a loss as to what the true cause was, but perhaps it is cured. I'm thinking of replacing the coil/resistor next. It's still an uncomfortable feeling to not "really" know what the problem has been.

Aloha,
Rich

sounds like you had a wire pulled a bit out of its socket.... go back an give each one a little tug.. just becareful about getting shocked.

Interestingly, a week after thinking the problem was solved I started her up and once out of the garage I couldn't get enough power to drive up the street. Everytime I gave it throttle it would die. About a half our after rolling it back into my garage I started her up again and she ran fine, though I didn't drive it but in and out of the garage. The next day I started her again and drove her around the neighborhood for awhile with no problem. My neighbor says it is surely crap floating around in my carb bowl and occasionally getting stuck in a jet or something.
This weekend I'm rebuilding the carb. I haven't done that in over 30 years. Hope I can pull this off successfully.
Aloha,
Rich

Before you dig into the carb, check your point gap, as others have said. It may very well be the carb, but it's a lot easier to see if you have a worn rubbing block causing the points to have a very small gap.

Another possible problem (one that I had on my Bolt) is worn distributor bushings. When this happens, you can set the point gap (dwell) and on the next revolution of the distributor, the adjustment can be out again. I finally went to an HEI distributor and haven't had a single point problem since.

On one of my old tractors once, it would run fine when cold, then start to cut out as it warmed up. Turned out to be a bad coil.

To answer your question....the heat riser is open to the exhaust when in that particular position shown in your picture. It is closed and directing exhaust gas to your intake when in the horizontal plane. It shouldn't be an issue at your location. Hope this answers your question.

Well, I though I would provide an update to my truck's performance problems.
I purchased a carb rebuild kit from CD and rebuilt it. She started right up but I was concerned about the gas weeping from the seam. I took it apart and applied aviation permatex to it and the fuel line connection. 24 hours later I started her up again, made some mixture/throttle adjustments and she purrs like a kitten.
Thanks everyone for all the great input. You guys are the best!
Aloha,
Rich