im at a bit of a dead end, any help would be great

[yamaha guy]

alright so heres the deal, my 85 ytm 225dr has been in the shop im dumb and put a 2 stroke muffler on a 4 stroke,so we thought that's the problem so i put a new 4 stroke muffler on and now its still causing trouble well heres the problem it will start up fine but you put the throttle in it revs but half throttle it starts to like slip or stutter and wont rev any higher, we have checked the carb and were sure that, that wasn't the problem so we were thinking the back pressure from the muffler caused a build up of carbon and got the valve gummed up but would that cause the motor to do that, another we thought it could be the coil getting to hot? so im wondering if you guys could help me out, maybe it is the carb but it seems to be getting gas fine or am i looking at some thing serious, well thanks guys any help will be appreciated greatly or any input, thanks:(

[QCR77]

unfortunately i cant offer up any advice. but i will be watching this thread cause i have a 2stroke silencer on my 4stroke.

[portland250r]

my 200x was having the same reving problem.
i bought a new carb.
if i was you i would get a shop manual and check out the top end of the bike and rebuild the carb.
have you checked the compression yet?

[yamaha guy]

yea the carb has been rebuilt already, but im going to check the valves and timing chain and stuff and see

[yamaha guy]

any other ideas any one?

[whyzee]

i would triple check the float height in the carb, and try swapping the mian jet 6 steps down and see if that helps. sounds like you are getting to much fuel and not enough air ? is there a rag in the air filter box from cleaning it out, is the filter over oiled? when was the last time it ran good

[yamaha guy]

alright ill see about that

[RodKnockRacing]

remember to also check your electrical a bad ground or cdi will cause it to spit and sputter

[yamaha guy]

alright heres whats happening it runs and idle fine but it is miss firing at high rev, any pointers here would be great

[350x'inNY]

Timing chain off a tooth? /stretched?

[yamaha guy]

timing chain is perfectly lined up

[yamaha guy]

any more ideas?

[darkestskydiver]

you could try a colder burning plug. i had good success with this on my 200x, and my fl250 odyssey

[yamaha guy]

true, i got a ngk in it

[RodKnockRacing]

i still put my money on a electrical problem

[Dirtcrasher]

Doesn't a colder burning plug merely disperce the heat into a larger area quicker? Meant for hotter climates I thought.............

I won't lie, it's VERY difficult to decide whether it's fuel or ignition on high speed missing. IF the carb is in good shape, and just rebuilt with the right jets, the airbox lid is on and the exhaust doesn't have a larger than stock output then your jetting should be ok.

I know jetting stinks, but have you tried getting a few new plugs and doing some chops - EVEN if it's blubbering?? You could still have a lean or rich condition.

OR, it could be electrical. I had an SX I SWORE was the carb, and it was broken wires at the CDI. Ran like a champ until mid,3/4 to WOT..........

Don't let it defeat you. See who else lives near you and may have a fresh opinion. If ANYONE lives near me, I'd try and help myself. I'm by far no expert but I usually do OK as do plenty of other 3WW members :beer

There must be a way to make sure spark is consistent at high speeds other than exposing some wire and reaching down :lol:

These things do happen, I have an ATC70 (The simplest of engines) that will just quit once in awhile for know apparent reason. Fuel caps/carbs/CDI now and I STILL have an issue so that gives you an idea of how tough it really can be to diagnose.

For them to consider that silencer as an issue seems like a money maker to me. There's plenty of back pressure in the header pipe itself...............

[Thorpe]

My vote is brand new sparkplug...

[portland250r]

i still put my money on a electrical problem

in what way do you fix a electrical problem.
and if you replace the ground wire is their a specific type to use?

[makeadeal19]

if it was running fine be for you did the exhust then i bet its that

[yamaha guy]

thanks dc, but i got my buddy looking at it and hes putting his money on electrical cause the carb was just rebuilt, so he thinks the coil is getting to hot and is sparking spontaneously or some thing in that range which in a way it makes sense, but i put a Japanese muffler on it heres a pic of what it looks like its off a 200cc atv.92223

[yamaha guy]

any other suggestions?

[Grizzlypeg]

How does a fresh plug look after the high rpm sputter run? lean or rich? carb alone would cause lean, electrical miss or carb could cause rich.

Also, if you stick a clear tube on the bowl drain, and open the drain, you can watch the float level with an open ended clear fuel line running upwards. The fluid in the tube will match the fluid level in the float bowl. Gives you a nice visual if its a needle seat problem.

[yamaha guy]

i think its electrical miss because the carb was always working properly

[RodKnockRacing]

in what way do you fix a electrical problem.
and if you replace the ground wire is their a specific type to use?

fixing an electrical problem is all about testing the wires and looking for obvious signs of a problem. Im not the best with electrical but if a ground had a break in it and was bad i would use the same gauge copper wire to fix it but most of the time it just the grounding surface not making a good ground.

[yamaha guy]

question is there such thing as a rev limiter on these 225dr? cause Ive been revving it in neutral