Hello.
Have rebuild the carb after it has been sitting a few years with no use at all.
The bowl was covered in a green coating.
Changed all jets and cleaned it well.
Have 140 main jet and 40 pilot jet.
Needle at 4. groove from top
Float height set to 14,7mm

It did run ok with sputtering idle when hot.
From time to time it wont rev up with half tank of fuel.
Changed te air filter a week ago and its worse than ever.

Bogs when applying trottle, high idle for i while and returning to normal after a bit.

Removed air filter box and it runs fine.


As far as i can see the carb is clean and i have blown trough all jets.


Any tips to do next??
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Needle clip needs to be in the 2nd position from the top,but probably not the problem.Plus check the tank vent hose to see if it's open and not kinked. Could be vapor locking if it is. Just take the fuel cap off and blow through the hose. Should be able to hear air hiss in the tank. One other thing you can do is to disconnect the reverse limiter module black wire from the terminal board as it too can limit in forward gear if faulty. Item#42 on the parts break down. Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse If none of this solves the problem then pull the valve cover and check the exhaust cam lobe. the 98 model was still in the model years that had cam lobes that could wear down. Worst case ones looked like this and would idle ok,but just back fire through the carb or act like it was limiting.Bad Cam Pic - ATVConnection.com ATV Enthusiast Community

 

Thanks for the advice.
Checked te cam, but it looks ok.
The exhaust rocker arm has a little groove after the actuator ball in the compression relase.

 

Exchaust rocker.
A bit worn after compression release ball

Cam looks ok

 

Checked cam and rockers
Cam looks ok, but exhaust rocker has a little groove from the compression release

will ceck teh other tips when its back together

 

Ouch.
Doublepost.
😳

Put it together,
Checked valve adjustment ok, disconnected limiter module, needle in second clip.
Bogds and almosr dies on alf trottle.
Without air filter box , runs fine

 

choke stuck maybe?

 

Look over this fuel section from the manual and see if you've overlooked something when you went into the carb.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA Plus as mentioned check that the choke is functioning properly. Pull the carb top cap and slide. Choke plunger is visible and should open and close the circuit. Here's a video on a different Mikuni cv carb,but same principal on how it works.

 

Have suspected the choke myself, but i have replaced the plunger.


Maybe a channel inside the carb is clogged up.

Is it any way to test choke function with the carb in the shop?

 

Best way other than visually checking that the plunger works is on the machine running. Choke when pulled should kill it or at least bog the engine down. If it only runs good with the air box off still sounds like a carb problem,air intake restricted or a dirty air filter if you haven't cleaned or changed it. Best way to really clean a carb is soaking in carb cleaner such as Berrymans B12,etc then make sure all the passages are blown out and open. Jetting you posted is correct for the 6x6 as well as the float height.At this point I'd go through the trouble shooting sections of the manual to see if it may be an electrical breakdown also that cause it to bog. You've eliminated the reverse limiter for one,but could be elsewhere. One old way of telling if spark is breaking down is to hook a timing light to the spark plug,run the engine until it starts to bog or limit. If it's an electrical problem the light will flash in unison with the limiting. If the spark is good the light will be continuous.