The Stovebolt Site Forums The Shop Area Engine Shop Rumble exhaust....rich or lean?

Rochester B is starting to give me trouble. Runs fine for first run of day. Stop for 10 minutes and it misses and stumbles at anything less than half throttle. Also has stared to rumble like a split manifold with glass packs going down a hill. Can't remember if that's a rich or lean condition. Might be heat soaking as I only have 3/16" heat spacer on carb base.
1964 C10 230c.i. Timing spot on, tried new condensor. Increased ballast resistor value to get proper voltage to coil (has ni-chrome ignition wire). Plugs look great.
Thanks.

The rumble is too lean on aircraft pilots lean out their fuel for better performance at altitude for fuel savings then forget to adjust to a richer mixture in lower altitude. That's why you will hear small airplanes fart and rumble on landing approach. The spacer under our Rochester is 3/8" in thickness. You might be boiling gas also we wrapped our fuel lines with heat resistance jackets. Gas filter maybe dirty and air filter? I was once told that 99% of all DIY mechanics go to the carb as ther first choice for trouble it turns out it's 99% chance that its not the carb but elsewhere...go figure.

Does it run better once it cools back off?

Is the fuel tank vented properly?

Is the intake / exhaust manifold bolts tight and not leaking?

Is the vacuum advance working?

Is the fuel line right up next to thermostat housing?

Tank not venting could be creating vacuum in tank, starving the engine,
Manifolds cold be letting in air where it's not supposed to be once they heat up,
Vacuum advance can play havoc on the mixture,
Fuel lines are close to the high heat of the cooling system on these engine creating vapor lock.

I spent part of today running through some of the above.
Gas cap is vented type
Manifold bolts are tight (checked them).
Pulled top of carb to look for trash and verify jet size per manual. All OK.
Fuel lines look orginial and in correct place.
I have one of the newer timing lights, so I'll check operation of vacuum advance this weekend.
One thing I want to do is change plug brands. I've had bad luck with ACDelco on a 250 inline several years ago. Went to NGK and problem was solved. Heck, there isn't much left to check.
Thanks.

Depending on what kind of choke, could be choke. I have been fooled by saying "gas cap is vented type". Meaning: it was that type but not working properly. To be sure it's OK , leave it loose awhile. If you feel like it is fuel rather than electric. Start at tank and vent and think thru/check lines, filters, fuel pump, carb.
I try not to start adjusting things in a case where it was running great then something happened. Things get all out of whack so that you can't find original issue.

Bartamos, good advice. "If it ain't broke, don't fix it." Just bugging me...truck runs great then after a few minutes for a cup of joe, it runs like crap. I also don't like just throwing new parts at it. Heck, a dealer could do that for me.

You could have a coil overheating and going bad, or the condenser in the distributor. I have read stories of those causing lots of problems. I suspect something is heating up and opening a gap or breaking down and working correctly.

Joe

You are right on. Just drive some more and see if you detect any clues or it gets worse. Try gas cap loose and check the choke to be sure it's not closing after hot.

I had the same problem last summer(it was hot like this year). Made me nuts. After some failed fixes, this is what made a difference. Point gap was a bit small. A dwell meter helped find that. The needle was sticking a bit(some 600 paper polished up the sides and let it work with modern fuel) and last.. the power valve was sticking. Again some 600 paper polished it up and made it free. After that was done the timing was different so I needed to retard it just a bit. Problem gone. You might have different issues, but this worked for me. The above posts are good ones. That "new" B is very much like the old one I have. And, the 64 230 runs a bit hotter than my 235 so the tips on fuel heat matter. Let us know what you find and what works. Lots of helpful folks in here.

I think I got it but time will tell. I changed to NGK plugs from the ACDelco #4's. For some unknown reason I have never had good luck with ACDelco plugs. Also installed new ACCEL coil. As time permits I'm going to tear down and clean the Rochester B.
Before someone notices it, the ACDelco #4's are long reach plugs as are the NGK plugs I installed. Manual calls for AC46N which is a short reach plug. Scratched my head on this till I looked at the side profile on the 46N's. Behind the threads is a unthreaded barrel. When you hold the #4 and the 46N side by side the crush washer is the same distance from the threaded end of the plug. What, can I say, it works.