1985 yamaha moto 4 200 power surges

did you replace all diaphrams in carbs and fuel pump ? balanced the carbs ?

Is there an air fuel mixture adjustment screw? I'd try lookin for one and adjust it a little and see what happens. Sounds like your mixture is way too rich. A more lean mixture won't bog down, but too lean of a mixture will bring your idle speed up too high

Could be a bad temp sensor. The bog is a rev limiter to keep engine from running full throtle when hot or when there is another problem. You can bypass the temp sensor and see if that takes care of problem. The parts about 100.00. I disconnected mine a now run a temp gauge which I mounted on the right side just above oil gauge.

I have the same problems with my 1999 TTR 250, were you able to find out anything?

Walt
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Why mix thev gas ,your problem could well be down to a carb or air problem.

This sounds like water condensation. Drain the carbs and a cup of gas from the tank and see if that solves the problem. If no joy, check the filter screen (inside the gas tank) mounted on the gas valve. A plugged screen may not let the gas flow freely to keep up at higher speeds. If still no joy, clean the carbs.

hey,
Maybe your break calibars could be sesede.

Unhook exhaust pipe,check port for blockage. if it is clear try to rev up with pipe off.If exhust is clear you will need to check high side of carb. good luck

Whatever your problem is, I would guess that it happened after you began to drive it. I would consider looking for a vacumn leak. Plus, it would be helpful to know how the carb change affected the problem, as it does seem like fuel.

There are inline fuel filters under neather the truck body that may cause a problem, as well.

But I still feel that based on the limited amount of information, I would look for a vacumn leak. For example, if it has power brakes, a leaking hydrobooster can leak vacumn and throw of your air/fuel ratio. Vacumn pressure at idle should be 14.2, and at a higher idle should drop to about 12 or 11 inches of vacumn.
Bill