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Ski Doctor
Ski Doctor, powersports repair specialist
Category: Motorcycle
Satisfied Customers: 818
Experience:  over a decade of double time experience, excellent electrical and mechanical diagnosis capabilties
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My 2004 CRF250x wont start. This is after a rebuild of the

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My 2004 CRF250x won't start. This is after a rebuild of the entire engine from crankshaft to valves. It gets fuel from the tank to the carb. I have blown out the brass fitings in the carb. It has spark. Compression seem excellent. Timing can't be adjusted. It did run for about a minute last week, but the tail pipe was turning red and it was rough so I shut it off. I have installed new valve guides and valves since then. What else can I check?

do you know the compression? if so, what is it and how did you check it? you really need a gauge to check engine compression. make sure you hold the throttle wide open when you do check it to get a accurate test.

is the engine timed wrong, maybe 180 degrees out? it will still turn over and backfire, but not start or bend valves. if the timing is off 60 or 230 degrees it will bend a valve.

my suggestion is to check engine compression, and then also double check engine timing.

if the bike was sitting for a while, you should clean the carb out, just to be sure no debris built up from the carb sitting. blow out all the jets and fuel circuits.

do you have any aftermarket intake filters or exhaust pipes, and is the carb jetted for that add-on?

Customer: replied 7 years ago.

Thanks for the hints. I don't have a compression tester that reaches down the plug hole, but the piston and rings are new as is the cylinder and now also the guides and valves. Carb has been cleaned out. J&D jetting kit has been in the carb for years and works perfectly. I don't think it is possible to put the camshaft in 180 degrees out on this motor. It only fits in one way with all the index marks on the crankshaft and the camshaft lined up. Ignition timing is non ajustable. Factory setting of the ICM is electronic. Flywheel is set where it needs to be.

any other thoughts?

have you tried to use aux. fuel source(like carb cleaner aerosol can) and spray down the intake when you kick over the bike?

make sure you remove the air filter, then spray the carb cleaner down the intake while you kick over the bike...does it start?

what color was the spark plug when the bike did run for a short while? was it white all over? i think the bike might be too lean, which would explain the red hot head pipe as well. keep in mind that pipe will get hot, but shouldnt glow red.

Customer: replied 7 years ago.

I did try starting fluid sprayed down the carb throat - no luck at all with that. The spark plug color was dark brown or tan. No obvious sign of running hot on the spark plug. The motor does seem to catch - almost - when I pull in the "hot start" lever while cranking the engine. This would indicate a rich condition for the starting jets instead of lean. I tried changing the idle jet to leaner with no result.

The spark plug seems a bit wet on pulling it out, but it does spark, at least when out of the engine, but this could be because I pump the throttle a few times to use the accelerator pump to put gas in the cylinder. The bike has always started best when I do that.

Any other thoughts?



gas engines need 3 things to run(for proper combustion)


2: compression

3: ignition spark

even if you have all 3 factors, one might be off, like too much gas, or wrong timing.

if you are sure timing is good and the woodriff key is good, then it has to be a carb problem. i thing the engine is flooding out.

when you pull the hot start, it acually leans out the engine.(it allows a little more air into the throttle body)

when you pull the choke, it allows more fuel into the throttle body, causing a rich condition.

if you have an air compressor, remove the rear boot from the carb to the airbox(the rubber ducting) and spray air into the carb when you kick it over. i bet from adding all the air to the over rich condition, the bike will start. even removing the airbox might get it to start by adding a lot of air.

what are the jets you have in the carb now?

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