Carburetor rebuild

[Russell]

My 742B has always required a lot of pumping and full choke to start when cold, and even some choke to start when 'cool'. I just put a Walker rebuild kit into the carb . After re-installation, the engine started right up, but I have virtually no control over the RPMs. The engine races, choking it makes it worse, and moving the choke or throttle controls gives instant increase, but very slow or no decrease. In the course of the rebuild, I dismantled the components, cleaned them, and reassembled one at a time so as not to be overwhelmed by too many loose parts. Other than debris in the screen on the needle valve, there was no visible wear or damage. I replaced the needle valve and seat and checked the float level. I replaced the accelerator pump components with new, and the enrichment valve with new components. After removing the carb top, I dumped out the gas in the bowl, and saw the little weight in the pump discharge fall to the floor. I recovered it and noted how to reinstall correctly. I did not see the little ball fall out. In the reassembly I installed the ball that came with the kit. After the first experience with racing RPMs, I removed the carb and removed the ball thinking it wasn't intended to be in this model carb in the first place, but that didn't help. At one point I disconnected the throttle linkage from the governor, and that allowed the RPMs to settle down, but not correctly. If I manually forced the throttle plate closed, the RPMs declined more, but that isn't the solution. I believe I made an error with either the needle valve, accelerator pump or enrichment valve, since these are the only components which were replaced. Would greatly appreciate any suggestions about how to proceed. This unit is my snowplow, and there is more winter to come here in VT.

 

[Tazza]

I have never worked on a carb for one of these engines, but from the ones i have worked on....
The accelerator pump was mostly for starting i thought, not for general operation, so that shouldn't be the issue.
With the govenor disconnected, you don't have full control with adjusting the butterfly?
The only other thing i can think of is the float, if it's not fully seating it may be allowing too much fuel into the engine.

 

[[email protected]]

I have never worked on a carb for one of these engines, but from the ones i have worked on....
The accelerator pump was mostly for starting i thought, not for general operation, so that shouldn't be the issue.
With the govenor disconnected, you don't have full control with adjusting the butterfly?
The only other thing i can think of is the float, if it's not fully seating it may be allowing too much fuel into the engine.

Tazza--didn't see your reply, but here's an update. I tore the carb apart and consulted the Bobcat service manual in addition to the kit instructions. Replaced the little ball in the pump discharge, and put the original needle valve and seat back in. Some noticeable improvement, but still not correct. Visibility into and around the carb is almost non-existent--I have removed and reinstalled carb at least 6 times, searching for anything out of whack. Discovered that the throttle rod was hitting on the rubber vacuum hose coming from the rear of the intake manifold, so adjusted it as much as possible. That helped a lot. Problem now (and apparently all along since the rebuild) is that the throttle control from the cab and through the governor seems to be backwards. Opening the throttle plate is achieved by pushing the throttle rod up from below, but pushing the throttle lever in the cab forward(faster), causes the linkage on the governor to pull the throttle rod down. I had the engine idling pretty well with the throttle lever pushed all the way forward, but pulling it back a little caused the engine to race uncontrollably, not just increase in speed as you would expect from bass-ackwards operation. Referring to pages 7B-11 and 12 in the service manual the throttle lever (part 19) protrudes toward the engine, while mine points away. I tried changing it around, but the vacuum hose interference is even worse, and I don't believe that is how it was originally connected. I am disinclined to started filing the holes in the linkage to make small adjustments, since it was connected correctly before I started this project. Any thoughts ?

 

[[email protected]]

Tazza--didn't see your reply, but here's an update. I tore the carb apart and consulted the Bobcat service manual in addition to the kit instructions. Replaced the little ball in the pump discharge, and put the original needle valve and seat back in. Some noticeable improvement, but still not correct. Visibility into and around the carb is almost non-existent--I have removed and reinstalled carb at least 6 times, searching for anything out of whack. Discovered that the throttle rod was hitting on the rubber vacuum hose coming from the rear of the intake manifold, so adjusted it as much as possible. That helped a lot. Problem now (and apparently all along since the rebuild) is that the throttle control from the cab and through the governor seems to be backwards. Opening the throttle plate is achieved by pushing the throttle rod up from below, but pushing the throttle lever in the cab forward(faster), causes the linkage on the governor to pull the throttle rod down. I had the engine idling pretty well with the throttle lever pushed all the way forward, but pulling it back a little caused the engine to race uncontrollably, not just increase in speed as you would expect from bass-ackwards operation. Referring to pages 7B-11 and 12 in the service manual the throttle lever (part 19) protrudes toward the engine, while mine points away. I tried changing it around, but the vacuum hose interference is even worse, and I don't believe that is how it was originally connected. I am disinclined to started filing the holes in the linkage to make small adjustments, since it was connected correctly before I started this project. Any thoughts ?

Woo-hoo! If I leave these things for a little while, I can return to them with a fresh perspective. I had the throttle rod from the governor on the wrong side of the vacuum hose. Moved things around, and it runs like a charm. Amazing what a little visibility could do.

 

[Tazza]

Woo-hoo! If I leave these things for a little while, I can return to them with a fresh perspective. I had the throttle rod from the governor on the wrong side of the vacuum hose. Moved things around, and it runs like a charm. Amazing what a little visibility could do.

Glad you got it sorted out.
Having a clear head and attacking a problem sure can help. The frustration from when things don't go right take their toll.