The Stovebolt Site Forums The Shop Area Engine Shop 216 Rochester Carb Issue???

I just installed my professionally rebuilt Rochester single barrel carb from 1949 Chevy 1/2 ton truck with 216 engine. Tune-up went well - timing, dwell angle, idle speed, vacuum, fuel mix.... The engine sounds great.

Unfortunately, I'm having one problem. When accelerating or under light load, the engine stumbles, sort of like its not getting enough gas.

Is there an adjustment on the carb - perhaps with the accelerator pump, that can be checked or adjusted? Prior to having the carb rebuilt there was no hesitation when under load.

With the engine tuned so well, I'm sort of at a loss. Having only rebuilt the carb, it seems like this must be a carb issue. Any ideas what I might look for?

49TruckNut,

Curious to know what was wrong with the carb that it needed a rebuild?

Kurt

If you have one of the early Rochesters, the one with the thinner top, it may have a little hesitation. Maybe your carb waa flooding a little before the rebuild and that compensated for the problem. I am sure others will chime in but you can adjust the float level a bit and possibly with a higher setting you migh compensate for it being a bit lean.

Sure it is not a timing issue? Have you confirmed the vacuum advance is working correctly?

To check the accelerator pump look down the throat for a strong stream of gas to shoot out when you press the accelerator.

This is the classic Rochester complaint, there is another thread onging about a similar issue. I fixed my Rochester problem by replacing it with a Carter YF.

I did too Mike! My issue was I got tired of cleaning up the mess the Leak-chester left behind.

Works every time!

Seriously though, is there a modern replacement that is specifically designed for this? One that will accept the old air cleaner and look original?

I replaced my rochester with a carter and I am running the old filter. So all looks the same except Im not messing with it every day to make it run right. Here is the only pic I have of the carter with the old air cleaner.

http://talk.classicparts.com/picture.php?albumid=180&pictureid=1675

And my video of the swap



Good luck

I am restoring my truck and the carb was a total mess. Although it operated well enough I wanted to get all the parts cleaned and re-plated. Now the carb looks better than new but now I have this load issue. My intent was to keep the truck all original so I'm not sure if the Carter would have been original for my '49 1/2 ton.

As for the vacuum advance, I can not rule it out. Is there a recommended method to confirm it is operating properly? Its the only engine part that I have not specifically test, rebuilt, or replaced.

I've managed a lot of issues with this truck but the carb has always been sort of hands off for me. I'm going to check the float - sounds easy enough.

As for the vacuum advance, I can not rule it out. Is there a recommended method to confirm it is operating properly? Its the only engine part that I have not specifically test, rebuilt, or replaced.

"shoot out"??? When I pull on the accelerator linkage and look down the throat, I do see gas but its more like a slow flow, maybe 10 drops or so... not a spray or stream. This seems significant - while under load this doesn't seem like a sufficient amount of gas. Comments????

It was suggested that I check the vac advance too. If I disconnect the line at the carb and suck on the tube, what should I observe at the vac advance mechanism???

It should squirt a solid stream. These carbs are so simple I would pull the top off & check the pump piston. If it is leather it should be soaked in oil a little & softened up. If it a rubber type Make sure it is soft & fills out the cylinder. The float level should measure 1 9/32" from the gasket to the bottom of the pontoons with the air horn upside down. You might fudge alittle about 1/32 higher.
The vacuum advance is simple to check. Just watch the dist as you accelerate the engine. The whole dist should turn after you get above idle. You can fudge with the timing also by setting it a few degrees higher with the octane selector.

If you're not getting the stream into the carb throat you need to talk to your rebuilder and ask why. Sounds like the engine is starving for fuel under load, my gas shoots well into the carb throat when I open the throttle.

OK, I checked closer. I do have a steady squirt or stream of fuel. The first couple of pumps the line was not primed. The float measurement was 1 11/32". I adjusted the tang to achieve 1 9/32".

Now, measuring per the service manual, (float hanging down), I measure 1 15/16". The GM Model B carb service manual says I should measure 1 3/4". By my thinking, this would yield less gas in the bowl. Perhaps this 3/16" delta is enough to be significant?

Considering this discrepancy, what range of measurement would you suggest for your upside down measurement? Could a 1/16" make a difference?

One new development - the air horn screw that also mounts the choke cable bracket was snug but not as tight as the other three screws. When I tried to tighten this screw to be consistent with the others, the screw stripped - well, not the screw but the carb bowl casting threads for this screw. This might potentially explain the sluggish behavior I suppose - if there was an air leak there.

Perhaps my shop friends can repair this - maybe with an insert or maybe just a larger tap/screw. This is very frustrating - this is all that's keeping me from the road.

Also, the vac advance is working and the carb piston moves freely. So far, it looks like a float adjustment. I'm just not ready to believe it could be that simple... stay tuned, feedback welcome.

Forty9 - whats your experience with float levels? Could a 1/16" adjustment make any difference in this carb?

The float drop setting really doesn't affect performance. It needs to be large enough to allow a good flow and not too large so that the float and needle don't hang up. The float level on the other hand can affect performace. If the float level is set so the level is a bit higher, it tends to richen the mixture. However most of us set the float level to avoid flooding.

The stripped screw can cause a leak.

Haven't had to fiddle with the float levels. Mine are set according to specs and I've had no problems. You did note that float settings are made with gasket in place? Also need to be careful when tightning the cover screws as over doing it may lead to the cover getting warped.

My ‘51 has a Carter, and we will need to add different jets as since buying the truck and it now lives at 6200’ instead of sea level.