Yamaha Grizzly 80 Carburetor issue

My son has a Grizzly 80 with carburetor issues. The carb has been cleaned very well but still has a problem with the idle hanging. There are no air leaks, at least none that can be found with propane around the carb and intake. This in a small makuni carb with the throttle cable connected directly to the slide, i.e. there is no butterfly valve. The slide moves freely and both the slide and carb chamber are spotless. The idle speed adjustment screw comes in from the side of the carb and makes contact with a beveled slot on the bottom of the slide.

The engine starts easily, and initially idles correctly. However, when the throttle is opened and closed the idle hangs initially, but if left running it will eventually settle down. The throttle cable is clean and oiled and there are no kinks. After having worked on this several times, I am of the opinion that the fact that the idle adjustment screw comes in from the side is causing the slide to bind within the slide chamber and I don't know of any cure for this if it is what is happening. The adjustment screw has no imprefections and the beveled slot looks to be perfect.

Before I buy a new carburetor, does anyone have any experience with this problem and any suggestions?

 

Play with mixture 1 3/4 out to start with and double check float height is not too high

 

I'd also take a close look at the main needle jet (emulsion tube) to see of it is worn.

I'd also examine the slide and slide bore for slop that may be causing the slide to tilt and keep it from dropping.

 

That's about where I set the mixture and I've tried "playing" with it. The float is not adjustible if I remember correctly--sort of like the float in my Honda Rebel. But I'll revisit that issue.

The emulsion tube is clean as a whistle--one of the first things I dealt with. As far as the slop with the slide and bore, that's where I think the issue may be. Not sure how to check that other than visually. Personally, I think the way the idle adjustment screw comes in for the side is a bad design and leads to the slide possibly binding.

 

Is the throat of the emulsion tube perfectly round?


Pull the top off of the carb, remove the cable and spring from the piston, and perform a clunk-test. You can polish the bore just as with a Hitachi or Mikumi carb while you are in there.

I'd also make sure that the cable isn't binding in the guide.

 

Ok so it has a plastic float with no adjustment tang

 

Well, it turns out that the float is adjustable, so I lowered the fuel level but it made no difference. I throughly cleaned this carb about a month ago and today when I removed the bowl it was loaded with a gray mud like substance. The line has a filter and the gas is marine gas--at least my son says that it is. The float pin was pretty tight and I distinctly remember it being nice and loose when I cleaned the carb. So I cleaned out the goo with carb cleaner and let it dry. That's when I noticed a gray oxidation all over the carb--inside and out. The same color as the goo. When I reinstalled the carb the screw threads on one side came loose and pulled out with the screw. I could actually twist them off of the screw in a perfect coil. I've never seen anything like this--it seems that the metal is being eaten away. Anyone have any idea what's happening? In any case I ordered a new carb today. I'll let you know how it goes.

 

Have seen dishwasher soap can turn aluminum grey or black

 

Under some conditions ethanol blended fuel can damage aluminum in that way. Did he happen to buy E-85 and not use a fuel treatment in the tank?

 

He swears that he used marine gas (ethonol free). I assume he is correct since that's what he uses in his yard equipment and boat. It had the consistency of tooth paste and had settled to the bottom of the bowl, almost 1/8 inch thick is some places. But it seemed to effect the entire carb, outside as well as inside, but worse on the inside. I've been wrenching all my life, and I'm 72 now, and I've never seen threads come loose like these did. These weren't stripped or overtightened, they just came out in a coil on the bolt. Wierd. In any case, I ordered a new carb today. It is an after market carb sold by Zoom Zoom Parts but all the reviews I've read are very good. So I hope it works for us.

 

Got a new carb from Zoom Zoom Parts for $79.50, installed it and it started and idled fine .I may have it idling a little slow but it runs well. Have no idea what is wrong with the old one, but for the price it worth replacing rather than fool with it. Zoom Zoom Parts--funny name but good service.

 

Were they quick?

 

Very quick and very responsive to questions. While the carb works great the drain nozzle on the bowl is brass but has a plastic sleeve with a 90% turn and the small nozzle which the hose connects to was broken. I'm not sure if it arrived broken or if it happened after we removed it from the package. However, since a regular piece of tubing can be attached to the brass extension it's not really a problem. In any case, I let them know and sent a picture and told them that I was fine with the carb as it is. However, they responded and are sending me another bowl and gasket anyway. I'm impressed with them, even if it is an interesting name--ZoomZoom.

 

My son called today and told me that the Grizzly wouldn’t start again. I could get it running with starter fluid but only if I kept the throttle open. No idle and no starting without throttle and starter fluid. I removed the carb and found the same gray goo I found in the original carb, but not as bad. The emulsion tube was completely closed. Cleaned the carb and installed the clean emulsion tube from the original carb and it started easily. It was the same gas that was used in the first carb, so we drained the tank and carb and will use fresh regular gas. My question is what kind of gas would dissolve the aluminum body of the carb? He said it was marine gas, that is no ethanol. Can’t imagine that any regular or marine gas would do that. He swears that nothing was added to the gas. Anyone ever had this happen, or have any idea what Happened?

 

I would not assume that a Chinse-mad carb has an aluminum body. More likely to be a zinc alloy.

 

Goog point. But the original carb was a mikuni I think and it dissolved even more badly. Hope new gas solves the problem.

 

is the emulsion tube aluminum type metal or brass? the fuel valve might be the same metal, check that too.
i'm thinking it's something about your machine because outboard motors would be having the the same problems. lawn mowers would be dropping like flys