The Stovebolt Site Forums The Shop Area Engine Shop Do 235s run like this?

Is it normal for a 'hot' 235 to run a little uneven and stumble at all RPMs in neutral? Both my 235s have done exactly the same thing: they run great under load, but randomly miss and stumble in neutral at any steady RPM.

thanks
chip

Do you have an ampmeter hooked up to your 235? I was driving mine at night a few times and i lost all power for a split second and i thought my engine was miss firing but it was just the ampmeter. I would also check your spark plug wires, cap and rotor and timimng. Other than that not sure what it could be. My 235 does not do waht you describe.

That definitely is not normal. They should run fairly smoothly even under no load. It probably won't idle absolutely perfectly. I have never seen one of those old Rochesters that didn't produce a litle stumble at idle. Messing around with the idle mixture can change the RPM that it occurs at.

I've got a '48 Jeep that stumbles a bit at idle when the timing is set properly. Runs OK though when under load. The only thing I didn't replace in the rebuild is the coil, cap, and rotor. Likely this is a good place to start looking.

-Boyo

Chip, do you have the vacuum advance hooked up? If so , disconnect it and see if the engine runs smoother in neutral. Depending on the engine,the vacuum advance may provide a bit too much for smooth running with no load on the engine.If you are running points, a wide gap will cause it, as will a slghtly lean carb condition due to low vacuum signal from a hotter cam etc.

My 235 ran a little rough after I fixed all the carb problems. I just richened up the idle mixture and it smoothed out. I think 235's like to idle extra rich. Gas was cheep back then so who cared.

This is the new motor that took an act of allah to build. Everything is new, so I'm hoping I've got a distributor or carb adjustment problem.

I'm running the Holley 390 and the mini HEI from a 2.8 V6. Ive got the vacuum advance hooked up to ported vacuum. Water heat intake, Mallory coil, plug wires for a 250, R45S plugs.

Its the same dist, wires, carb & manifolds I was running on my other 235. There is a good chance the carb isn't set right, or the distributor spark curve isn't ironed out. Have not had time to do any road-tuning yet.

Have noticed it gets a little worse as the engine warms up and the choke opens. Heck, this engine only has about 10 miles on it. Just don't wanna run dead lean or detonate.

The wierd thing is that it runs JUST like my other 235, except this cam is a little milder. It could be the plug wires, but they were new when the old motor blew. I figured they'd be OK in a box for a year. Stupid? Not?

thanks

Chip

Plug wires don't change when they get hot. It sounds like carburation.

You mentioned that it gets worse when the choke opens up.It sounds like you have a vacuum leak either at the intake to head and/or through the vacuum advance,,,,, Or does it have a vacuum advance?( I am guessing it does)

You might also look at your distributor, watch for slack in the upper bushing next to the points.

My worn out 235 does the same thing and the bushing on my distributor is shot. I would like to try a Pertronics module to replace the points to see if that helps.

Are you running manifold heat? My 216 did that when the heat valve got stuck.

I just had another thought. Did you check your fuel lines for damage? and your fuel pump? That might be something else to check. My 235 was missing and ideling all weird too. I finally figured out that the intake gasket was leaking and sucking in air. I rebuilt the motor before all this happened and 1500 miles later the intake manifold gasket slipped up slowly and began to suck in air. I came to realize about 4 months ago that i never put back in those itake rings!! :mad: that align up your gasket so they don't slip up or down and leak. I actaully threw them out cause i thought they were broken cause they were cut. Little did i know this is how they are supposed to be :mad: Oh well it was the first engine i ever rebuilt now i just have to find some intake rings or machine some.

Hey Chiphead
Sounds like everyone has great advice. I had a very similar problem with my 235 after bebuilding and finaly tuning. During all the tuning after getting it running it had carboned up the plugs real bad, I cleaned them off and it ran perfect. Didn't take long for them to carbon up when running to rich, an easy fix and an easy fix to overlook.

I'll check all the suggestions. I've got 15-16" inches of vacuum at idle w/ 4 bbl and the M4F cam. I gave the idle mixture screws another 1/4 turn out, and the idle smoothed out some. Still have to check spark curve, etc.

thanks

chip

Yep sounds like an air leak. I stick a hose in my ear and go around the carb and intakes and any place else it might be sucking or blowing. Good luck!
Adios, Kip

Looks like time for the starter fluid/carb cleaner tests. Sh@t, I hate pulling those manifolds apart. Will post back....

chip