This is no choke

[dforster]

Hello,

I just completed a major tuneup of my '66 Dream, which included rebuilding the petcock and carburetor.

I was having trouble getting the bike to idle. The pilot jet is new and clean, so that wasn't the issue. I finally solved the problem by turning the air mixture screw almost all the way in, which suggests another problem.

If I understand this carburetor correctly, turning in the air screw restricts the air flow and therefore enriches the mixture.

Here's what's happening. I turn in the air screw until it's about half a turn out from being fully seated. The engine now idles smoothly. If I turn the screw in farther until it's fully seated, there's no change in the idle performance -- no better, no worse. If I back the screw out from that half-a-turn-out position, it starts to idle rougher.

I'm concerned that I have to have the air screw turned in so far. Plus, when the engine is warmed up and idling smoothly with the choke fully open, when I then close the choke as a test, nothing happens. I would expect the engine to start running really sluggish and die because the air-fuel mixture is now really enriched, but nothing happens -- there's absolutey no change in idle performance.

Again, if I'm understanding this carb correctly, this would seem to suggeest that it's running too lean. But if that were true, wouldn't closing the choke at idle cause the rpms to rise as the engine gets a richer mixture?

I was tempted to lower the position of the clip on the needle to enrich the air-fuel mixture in that way, but the main jet doesn't come into play at idle, right? So that wouldn't affect the problem I'm having.

I'm at a loss here. Does this mean I have an air leak somewhere? And if so, how I do I check for that?

Could this be related at all to float height? I adjusted that when I rebuit the carb. I measured the distance from the top of the carburetor body to the top of the float, which seems to be what the picture shows in the shop manual. However, I've seen on this forum that some owners are measuring from the recess where the gasket seats, which would change the measurement slightly. Any thoughts?

The strange thing about all of this is that because I live at an elevation of 5,400 feet, I was expecting to have just the opposite problem -- that the engine was going to be too starved for air, not fuel.

Thanks.

[48lesco]

Float height is measured from the gasket surface. 0-1/2 turns on the mixture screw is OK as long as it idles OK. Your choke may not be closing all the way, but if it is, I agree that it should affect your idle but all my experience with these engines is near sea level, maybe someone else can chime in. If it's running good, I would just ride it and check the plugs after a few miles to make sure you're dialed in.

[brewsky]

Hello,

Plus, when the engine is warmed up and idling smoothly with the choke fully open, when I then close the choke as a test, nothing happens.
Thanks.

The engine should die if you are warmed up and close the choke all the way.

Has the choke slide become disconnected from the lever arm? Look at the carb end to see if the slide comes al the way down as you LIFT the lever.

Have you cleaned the internal passages in the carb?

If you squirt carb cleaner or compressed air thru the small tube opening on the left side of the carb intake end, it should come out 3 different places......idle mix screw opening (screw removed), slow jet opening (jet removed), and the small hole from the slow jet opening into the carb throat. Close off 2 at a time to make sure the 3rd is open.

Float level should be 26.5mm

[dforster]

Thanks, 48lesco and brewsky for your advice.

The choke slide is connected to the lever, and it does close all the way when the lever is lifted.

When I get home from work today, I'm going to pull the carb to reset the float and blow out all the passages again, and see what happens.

I suppose as long as it's running smooth, I won't worry too much about how far I have to turn in the air mixture screw, and I'll just keep an eye on the spark plugs to see if it's running too lean, which I've read can be a deadly problem with these engines.

I'll keep you posted.

[dforster]

I pulled the carb and reset the float from the gasket seat, and blew out all the passages again. Now the engine idles smoothly with the air mixture screw out a full turn. I'm calling that good. However, closing the choke still has little effect after the engine is warmed up, which suggests I might have an air leak somewhere.

The engine is probaby due for an overhaul anyhow. Compression is about 135 on both cylinders with the engine cold, the choke open, the throttle wide open, the air filter off and the valves adjusted right at .004. So I guess I'll ride it until winter and break it down then. Maybe in the process I'll eliminate the source of any air leak.