I have a 1989 Yamaha phazer 480. It ran great for the past few years and now this year it's running like crap.

Compression is 110 in one cylinder, 120 in the other. Nice spark from both plugs. Changed gas. Checked both sets of reeds and they look fine! The sled runs but only one cylinder is working. Since one is working I assume the fuel pump is working plus both bowls were full of gas.

Now, I took the carbs out but I really suck when it comes to carbs. Both of the floats work and the needle valves work correctly. Also the main jet (big hole in the middle going to the top part of the carb) are clear. Other than that and the butterfly there are no other parts to the carb to remove and clean? What else do I clean? Also, there is only one screw on the top of each carb so how are these carbs adjusted? Does anyone know what the electric switch on the side of the carbs is for? The carbs are mikuni.

Is there any other reason only one cylinder would work other than the carb?

Thanks for any help!
Mark

What did the plugs look like?
When did you change them last?
Does it use 1 or 2 coils?
If 2, switch them to see if the other cylinder starts firing.
Although you say there's good spark, what is the color of the spark? Are both sparks the same color and intensity?
When you say one cylinder was firing and the other wasn't. Did you mean that you pulled the plug wires off while it was running one at a time and one of the wires made no difference?
I wouldn't have expected the carbs to be the problem. Thats why I'm asking all the ignition questions.

Plugs were light brown in color. I changed both plugs recently. I even swapped plugs and wires and the same cylinder still ran. There is one coil with a single power wire running to it. Both plugs fire all the time I think. The spark was bright blue and both the same. I pulled one wire, it stayed running the same, I pulled the other and the engine died. Also, one cylinder was hot, the other was cold which made me realize only one was firing in the first place. Anything else you suggest I check? I'm really stumped and my wife is getting mad because she never gets to go riding which means I never get to go for a ride

Thanks for the ideas!

my guess is you have a fouled carb. - no fuel. might check into a rebuild kit...

These guys claim to be experts
Link

There's a link at the bottom of the page just for questions.

that's just the thing, these carbs are strange. There is no rebuild kit because there is nothing to rebuild. There is one big jet in the middle that is changeable, a samll needle thingie for the starter enrichener thing, the float and needle valve, and the round flapper (butterfly) thing that opens when the throttle is opened. No slide, needle, blah blah, I don't know how this thing works?

I'll check out that link, thanks!!

Mark

The pilot and idle circuts are usualy tiny holes and passages, with a can of carb cleaner with the red straw on it, blast out each orifice and make sure its clear. Check the non firing cylinder for massive air leak, cracked rubber boot on the carb, etc. Just because you have compression, dont mean the cases or cylinder to block joint isnt leaking alot. Is there one common fuel line for each carb, or seperate? If seperate, check the bad side if being plugged or pinched. Is one of the floats sunk?