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RM250 troubleshooting

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Hi,

trying to figure out why my 1993 RM250 is having a hard time starting, seems to be fouling plugs (well, it started with a new one off a kick and ran for a couple rides), it will roll start if I get a big enough hill, still locks the tire quite hard, did a compression test and it got to 180 PSI (after about 10-12 kicks though, not sure how many it should take?) so I'm thinking it's electrical.

Ordered a manual from the interwebs but it won't be here by the time I need to get it fixed, just wondering if anyone knows whether the section for testing the electricals from the 04 manual would be in any way accurate for as old a model as mine. . .

It says:

Magneto :

Red/white ---- black/red 25V+

Green ---- Red 2V+

Black/white ---- white/blue 200V+

Coil:

Primary circuit : 0.17 - 0.46ohms

secondary : 13-20 kohms

Stator : Red / White ---- Black/red 28-46 ohms

Red - ---- Green 78-122 ohms

One other thing I'm thinking is that I've got the idle circuit completely set wrong, how many turns (from fully turned anticlockwise) should the choke knob be set on, and does a 62 pilot and 190 main jet sound a bit rich for running mainly a bit above sea level (~1000 feet - 3000 feet at times), could just be flooding the crap out of it? Went to the bike shop and they only had a 48 pj that would fit, hesitant to make such a big jump without being certain its the carburetor...

Also, previous owner had retarded the spark timing slightly, for more overrev, I'm not sure how much as I don't want to order new gaskets just yet and open it up (poor at the moment) how much would this affect cold starting / plug fouling?

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If you are getting spark then there's a very good chance that the electrical system is ok. It could be weak, but still ok. And with the compression at 180 you do not have any issues there either.

So that leaves the carb. A 62pj and a 190mj sound huge. And if my memory is correct the choke is either on or off, there's no setting (clockwise or counter clockwise), it's either on or off. FMF and Boyesen both have jetting spec's on their web site, compare with them but I'm willing to bet that you are running very rich.

Here's a link to FMF: http://www.fmfracing.com/RiderSupport/JettingCenter

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OK, so as I'm mixing fuel at 32:1 at the moment, and am not a particularly aggressive rider, but was mixing at the ratio recommended by the previous owner, could I be fine with swapping for the 48 PJ and mixing at 40:1 or even richer? FMF says stock is 178 main 55 PJ, don't really want to buy another PJ as the bloody bike shop charged $22 for a $6 jet. Gonna have to get another main I guess though.

This'd also be the reason the previous owner was so adamant about never backing off downhill, cuz you'll just foul plugs.. pilot circuit hugely out?

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Boyesen specs say 200 main jet and 45 pilot for stock reeds... My reeds are just sorta clear plastic, no boyesen written on em... So I might get away with the 190 main and just swap the pilot?

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Pick a mix ratio and stick with it. Jet from what you have chosen. Sounds like the pilot would be your next change, but FMF and Boysen specs that you listed are way different. I would double check the specs again to be sure of which is the correct one you need. Also read the sticky at the top on FAQ for jetting help. It helped me a lot.

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Boyesen says theres a huge difference in main jets from stock reeds vs their reeds... How would I tell which reeds I have? Could probably take a photo and post later on. . There's no Boyesen stickers on my bike though, and the previous owner stuck every other sticker of everything he ever bought for the bike on it, so I'm going out on a limb and guessing I've still got the stock reeds in my bike, so the 190 main may still be fine. .

Worst thing is I spoke to the previous owners son (mates with him) and he said it was a bike shop who screwed with the jetting and put it like this. . .

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Are the reeds you have one solid piece or is there two pieces on each side? If it's two, they are not stock. If they are one piece, change the pilot and test from there. If it's still too rich, it may need a smaller main. Be sure to set the float height too. If the pilot is too small, it will not want to start, but I'm guessing the "shop" messed it up. Rocky Mtn ATV/MC has decent prices on jets, but I don't know what it would cost to ship to Australia.

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They were just one piece reeds, so I guess stock, I have a 48 PJ in it now and it starts quite easily with one lazy kick from cold.. Cannot believe how much difference a tiny hole can make. Still think it might be a bit rich, haven't played with the air screw that much yet, will wait til I go riding on the weekend.

I was also told, that people jet the pilot circuit far too rich for jumping, so it doesn't stall in mid-air? Is this correct? 'Cuz my mate who owned the bike did used to let his son race it and do some freestyle, so that would make sense....

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A properly jetted bike will not stall, unless you have the idle set too low. Of course if you hit the rear brake in mid air without pulling in the clutch it will stall too no matter what jetting it has! Be sure to read the FAQ at the top of the forum to get the jetting sorted out.

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OK, so there was absolutely no reason for there to be a 62 pilot in there? *** then..

Oh well, I'll play with it some more once I order some jets, it's running for the moment, that'll do.

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