The Stovebolt Site Forums The Shop Area Engine Shop Hesitation off of idle

1957 235 w/Rochester - completely stock except for Pertronix ignition. (I thought the Pertronix might cure it but made no difference)

Hesitated bad and flooded a lot so I rebuilt the carb. This helped quite a bit but it still hesitates just off of idle. Once engine revs a little it has very snappy response.

The carb has a fresh rebuild kit in it as of this afternoon along with a new set of plugs. I made sure the link between the butterfly shaft and the accelerator pump is bent so that the pump is actuated just off of idle. One thing I noticed is that the pump once depressed doesn't spring back firmly (almost like the spring is weak) but since it is directly tied to the carb linkage, it seems to go along for the ride just fine.

I have tried timing a few degrees advanced relative to the ball / pointer - seems to help a little but still not great. Distributor / vacuum advance seems to work fine (it dumps the vacuum and sets the distributor against the mechanical stop in the furthest retarded position when I first stomp on it).

Any ideas? Seems like after all this attention the motor shouldn't be such a slouch off of idle.

HAD a van do that once carb off twice finally pulled a lot of advance. End result was I replaced the timing chain. Try major advance

Hi Ken. Hope you and your family had a nice thanksgiving. My 48 dumper did almost the same thing. I would get a backfire and then sometimes go and sometimes die. I did all the stuff you did and in never helped much. My mechanic friend told me to adjust the valves 'cause one was too tight or loose i don't remember. Don't know if it's the same thing but what the heck. :-] fatboy

Hey Tim - went to my mom's place for Thanksgiving - no brawls, everyone avoided politics and religion discussions, we actually had a pleasant visit

Interesting comment on the valves. This is the first stovebolt I have ever had that didn't have some kind of ticking sound from the head when running - runs smooooooth and ultra quiet. Does occasionally pop back through the carby when I step on it (windshield wipers jump at the same time ) Perhaps the reason it is so quiet is that they are too tight! :confused:

Dont even want to think about the cam timing being off.

Check the size of the jet in the carb and cosider moving up a size or two. With one carb you might be starving a little.

Hey guys,
Might want to check the intake/exhaust manifold bolts. When I first rebuilt my 235 eons ago I had a problem with the bolts coming loose and losing vacuum. It took me a while to figure out that my truck wasn't supposed to whistle on acceleration!
Take care,
Bo

These carbs are very sensitive to float level. If you didn't move float during rebuild you might try raising float just a hair. I had the same problem and it took a few times to get it right. Can do with carb mounted, just take off top and adjust by bending tab on float. You have to do this with carb top upside down so remember that it is upside down and don't go the wrong way.

Ken, Take a look for vacuum leaks also.

I had a hesitation in my truck that was caused by a leaky vacuum wiper motor... I adjusted timing, points, valves, to no avail.. It wasn't until I removed the wiper motor to rebuild it that I found a cracked housing .. After replacing the motor the hesitation was history..

Looked for vacuum leaks - found none. Put fresh gas in it and that helped a little. Then I pulled the valve cover and did a very unscientific and imprecise thing. I backed off each of the intake valves about 1/4 turn on the rocker adjusters. This seemed to make the most difference. I didn't have the Racecarl guide to valve adjustment handy so I put the valve cover back on and drove it. Now an ever so slight hesitation still exists and the motor occasionally pops and farts back through the carb when motoring along at 45 in 4th gear.

I'll wait till I have some time in the coming week to see about a proper valve adjustment.

Ken,

Do you see gas leaking at the throttle pivot (or smell gas while running, or after shutting off the engine)?

I still have a similar backfire problem with my 261 with dual Rochester carbs. After doing most of the things mentioned above, the backfiring decreased but is still there when I back off (allow the engine to brake the truck).

My guess is that I have a bad float adjustment in one of my carbs (as suggested by Trapperschevy, above). After I shut off the engine, I can see a small amount of gas leaking out of one carb (my carbs have new bushings on the throttle pivot, so that is not the cause of the gas leaking). I have been too lazy to take it apart and check the float adjustment. If the float is set wrong, I think that gas can continuously dribble into the intake manifold (I have been told that this would result in excellent conditions for backfiring).

Good luck,

Tim

Ok Ralphy - I'll get a vacuum guage.

Tim, I rebuilt the carb and for once I think that I have a Rochester that does not leak inside or out. No dripping gas from the butterfly shaft and the tailpipe is not blowing soot. Looks good!

I won't get back to it till this coming weekend.