larry harding

i purchased a 91 xr250 in late summer to get in some riding before i went to cambodia in november. the bike had only about 7000 miles on it. it ran great but always seemed hard to start especially when cold. i had to be towed off a time or two when cold, but ran great once warmed up. it has a mikuni w 6 flat slide carb instead of the original. after much difficulty i got it cranked last friday and decided to check the carb. every thing is clean including the enrichener passages(i prefer old fashioned chokes). last night i couldn't get even a poot or backfire out of it. i even tried squirting some gass in the intake boot behind the air filter, and tried squirting gass in the spark plug hole and putting the plug back in. i am getting good spark if i pull the plug out and lay it against the engine. i tried a different plug. i don't know much of anything about these electronic ignition systems. i am more aquainted with magnetos and battery/coil/points systems. could something be weak and not be firing under compression(ive seen this happen with mags.) the shop manual tells what to check if you have no spark at all, but does not mention weak spark. i would appreciate any suggestions.

MSchu

have you tried simply re-juicing the battery? set a trickle charger on it for a night and see if that gets you anything before you start going any further.
you could try a new battery, but the trickle is doing essentially the same thing

larry harding

yep! recharged the battery, rechecked the valve clearance, replaced the two month old gass with fresh, made sure the carb is clean, spent about two haours with it last night and all i got was one muffler backfire and a one second sputter never really catching. i may make something up to screw in ths spark plug hole and try to check compression. the compression release cable broke up by the head, but that shoudn't matter. i don't know why you would need a comp release on such a small engine anyway. when the engine would still start it did better without the comp release.

MSchu

the electronic ignition should be about as bullet proof as it comes... the main thing being, is it putting out a signal. you say you are getting good spark, so I might be inclined to rule out coil or ignition for now and concentrate on fuel.

is the petcock on? are the fuel lines plugged? is there a fuel filter and is it flowing?

how did you check the enrichment circuit? usually they have a diaphragm if there is more than a single cylinder. if that diaphragm is torn, it can cause the enrichment to malfunction.

larry harding

as i stated earlier the carb had been replaced with a mikuni flat slide carb, so there are no diaphrams and such. just slide ,enrichner floats etc. i have taken the carb apart, everything is clean including the enrichner passages. i tried squirting starting fluid(eather) in the intake, putting a little gass down the plug hole, couldn't get even a puff from it. i have worked on engines and bikes for most of my life,mostly older bikes with magneto or coil ignition, this thing has got me stumped and embarrased.

ifIexplode

If youre getting spark and fuel it should fire up. It sounds to me like the valve clearance is too tight. A friend had a similar problem with his RMZ. Try bump starting it with a tow.

MSchu

NOT CV CARB... enrichment diaphragm. flat sides can have them.

larry harding

problem solved.... sort of. i took time last night to make an adapter out of an old spark plug so i could check the compression. only got 50 lbs after several kicks. tried about three times and got ZERO. i now remember a few times when i had stalled the engine while riding it felt like there was no compression but then it started and ran o.k. and i thought no more about it. the top end always sounded a bit loud to me but i'm not used to honda dirt bikes and let it go.the valve lash is good so it looks like a top end job in my future. i'm goint to pull the exhaust and intake tonight and see if a valve is sticking or leaking. the odometer only shows 5000+ miles, so much for tough, industructibloe hondas.