1986 Bayou 300,symptons are will only idle with choke out and will not rev out.Clean fuel, float height is correct allfuel and air passages clear, float bowl vent is open.Compression is 150lbs cam timing is correct, spark is good and on time at idle cannot check advance marks because engine will not rev out.Help before i go nuts.Thankyou

 

Remove air cleaner and lid.
Stock air/fuel mixture 2 1/8 turns out.
Insure the idle screw is turned a little, then insure the slide is moving properly, I would remove it and inspect, the diaphram seal is inportant on the slide.

 

Pilot jet is out 21/8 turns out ,have tried it with out air filtr,i cannot find any defects in the diaphram,if the diaphram had a air leak would it effect the idle mixture, to cause it only run with the choke on.Thanks

 

did you just do work on this engine? My friends suzuki had to go up three jet sizes when he bored the cylinder and just happened to get a high compression piston. He could only run it with the choke on.

Also, I guess you checked for vacuum leaks, but that usually affects idel more than full throttle.

I kept accusing him of having the cam timing off, but he was just so far off on the jetting. We used start fluid to help veriify the lean condition.

 

The engine has had no work done to it, i have been thinking about a bigger pilot jet,but wonder what would cause it to need to be jetted richer.I cannot find any air leaks at the manifold.The owner of the quad said this problem started out intermittent.

 

I gather than this is a cv type carb, where the venturi is opened by the diaphram you mentioned, somehow it is being sucked open to early, too fast, or all the time.

I had a quad that had mud clogging the back vent hose to the venturi, and it ran really sucky.

Can you check that any gaskets, and hoses pertaining to BOTH side of this venturi actuating diaphram are not missing, broken, clogged, swapped to the wrong side or something?

you should be able to watch this thing stay closed while idling. It will almost close off the bore. You should see it open a little with a little throttle. If that doesn't kill it, you should see it open more with more throttle. It should back off just as fast too. If it opens too much it will lean you out like no tomorrow. If it is stuck. Bye Bye to any hope of running good.

I think you have a sticky venturi, leaky hose or bad gasket. Guessing hard here since I don't have that quad and I am guessing your carb is a little like mine. Since your idle is lean too, I am still leaning toward some kind of leak.

Good luck.

 

The slide stays bottomed until you start to accelerate,you can see it attempt to rise,just as the engine stalls.Carb is clean and assembled according to the service manual.If i can borrow a Mikuni carb off another quad, with the same spigot diameter i will try that.

 

Ok guy I believe you have some problems!
It sounds like you have checked everything.
thier are three jets in thier:
starter jet: 65--68--70
pilot jet: 35--38--40
main jet: 120--122--125--128--130

Now this many choices tells me the bike has to be tuned to the area you are in, something tells me you are in the mountains so far your only problem is in the pilot jet, Take a look at what I've listed and tell me what you have and what elevation you are at.
we can go from thier, sorry but all three jets need change, low cost fix

 

Pilot jet 38 no starter jet in a 1986 model,cannot remember main jet size i will check tommorow,i will also check exact height above sea level,the thing i can not figure out is without intake or exhaust modifications why should the jetting require changeing.i am going to work on it tommorow i will fill you in with what i find.

 

On a 86 the jet sizes are
main: 125, 128, 130, 132,135
Sory looked up a 98 earlier

Well it's in the idle circut, all the kawis mosty will start with the choke and die if you give it gas.
But this doesn't help you, I would go as far as geting a can of carb cleaner and boil the crab, but I can't tell fom here.