Studboy

Thinks he can ride
Dec 2, 2001
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OK,  I finally got the bike to fire a couple of weeks ago (Loose stator wire.)


The bike <91 RMX250>  does not run right at ALL.  It feels as if the choke is stuck on.  It blows smoke and oil like a mosquito fogger and the response and power REALLY REALLY suck.  I have tryed everything that I could think of,  but here is the list just in case there is anything I've missed.

New Topend.
New Reeds.
All new gaskets.
New plug.
Cleaned carb (about 15 times!!!, maybe I'm putting it together wrong???)
Repacked Silencer and cleaned pipe.
Replaced Right Side Crank Seal.  (I thought for sure that was the problem but it didn't help hardly at all, if any.)
Put new jets in carb. (1 size smaller main, same pilot.)
Bought new airfilter and installed it.
None of the above have helped significantly.
Any tips or ideas would be appreciated since we want to go riding tomorrow!!!

Thanks Guys,

Richard
 

Studboy

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Dec 2, 2001
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Like I said, I thought for sure that's what it was. The left crank seal wouldn't do anything like that would it??? I assumed that it would cause a lean condition. The bike pukes all over itself and I can't think of any reason other than a curse as to why the bike won't run. We have spent hours and hours checking and rechecking everything that we can think of!!!! This is getting REALLY frustrating.
 

Studboy

Thinks he can ride
Dec 2, 2001
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Is there any chance that the little O-Ring that seals the plastic holder that the float holder thingy (I'm not quite sure what to call it.) in the Mikuni carbs is culprit??? The bike also seems to cut out at high RPM's. The weird thing is, I forgot to turn the gas on one time when I was running it and it ran really good for a second before it ran out, which tells me that I'm rich somewhere...(obvious.) I just can't imagine my jets being this rich just because I put new reeds and a new topend in it.
 

TrackMaster

Member
Mar 15, 2001
212
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oh yeah the rmx is a fun bike isnt it?? haha it seriously has a mind of its own and moodswings like a teenage girl!

but seriously, check your piston. which way is the arrow pointing? if its towards your intake you found your problem. I know it sounds dumb, but my friend did that once and it ran similar to what you are describing. (i personally didnt even know it would go together that way)

but if that isnt it, which it probably isnt, you could try your timing, i had my timing plate vibrate loose and it screwed over my timing. Also you may want to check your pipe and silencer, if there is any hole or significant ding in the silencer it will rob lots of power. I dont know why, but i replaced the silencer on my bike and it woke it up amazingly with an exact same replacement. I think my pipe/silencer joint pipe thingy was dented, as i put a smaller pipe on it to replace it and it ran terrible.

One more thing to try is check your oil.. Every time i put too much oil in the bike, it would run exactly as you state, and spew transmission oil out the powervalves and the overflow tube. i dont know what hte problem was, i replaced everything i could think of including the powervalves and cylinder and all the gaskets and bearings in the bottom end.

well good luck!
 

TrackMaster

Member
Mar 15, 2001
212
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one last thing is your floats are foam or something and will start to absorb gas over time. they may be sitting lower than they should be and will need replaced or adjusted to float higher.
 

bclapham

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Nov 5, 2001
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to figure out if you have an oil leak, measure the vol of trans fluid you out in then run it for as long as you can then drain it and see the difference.

sounds like a buggered carb to me- is the idle connected to the choke- i am sure i read a thread whereby the owners were swapping out the carbs for some reason
 

RM_guy

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Damn Yankees
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Nov 21, 2000
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Did you put the right crank seal in back-wards? It will leak if you did.

I know you said that you cleaned the carb but I had a similar problem where dirt got under the choke plunger and was letting fuel pass through when the choke was off. Does it start without putting the choke on? That a sure sign that the plunger isn't sealing all the way from either dirt or a bad seal.
 

dthoms

Member
Oct 6, 2002
175
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Stud,
Is your float bowl set correctly? Also did you replace the float needle and seat in the carb. What kind of Oil and how much are you putting on the filter?
What plug are you using?
IF you have had problems in the past with the carb, did you make sure your pipe isn't full of gas/oil? How about your silencer is it plugged?
Are the holes on the stator sloppy enough to change the timing if it was put back in the correct place?
If all else fails I can hook you up with a friend of mind that has an extr RMX motor for just that vintage bike.
Good luck,
DT

P.S.
The RMX is one of my all time favorite bikes! and I've had a few.
 

Zerotact

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Dec 10, 2002
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Any chance you could get a real carb? If I remember correctly the rmx had a funky carb on it that didn't have all the adjustments.. you should be able to score a PWK and slap it in there.......
 

Studboy

Thinks he can ride
Dec 2, 2001
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The float level seems to be fine. The piston is in the right way. We do have a better mikuni on the bike (one WITH a pilot jet! :thumb:) The choke is clean and I even tryed the choke plunger/lever from the stock carb with no avail!!! I'm about ready to put in some leaner brass and see what happens.

The bike exhaust doesn't smell funny at all (like tranny fluid.) and I just put a new seal in, so I'm ruling that out for now.
 

Studboy

Thinks he can ride
Dec 2, 2001
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I guess we're not in a huge hurry to get this thing running now.

My riding buddy just broke his leg yesterday. :(

He overshot my 45 ft. double on his XR250!!!!! :scream: :scream:

He may have set a new distance record on a XR though!!! ;)
 

cyprice

Member
Mar 2, 2003
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Your 45ft double? It must really stink having your own track. My wife and I went for a drive this afternoon looking for land for a new house and backyard track. How much ground did you put it on? what do you do about water?
Cy
 

89rmx250

Member
Feb 10, 2000
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What size main do you have in it?

I bought a 89 RMX 250 from a friend in Arizona, but I live in Denver. When I first started cleaning it up I noticed it had a 320 main jet in it. He was doing wide open deserts. I went down to a 190 for summer riding in the mountains. If I had just went down one jet size I would have had the same problem. I think the stock for that year was the 230, just a thought.
 

Faded

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Jan 7, 2003
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Originally posted by dthoms
Stud,
.....Also did you replace the float needle and seat in the carb....

I second this idea. If the needle and seat is leaking then no amount of float level adjustment will keep it from filling the float bowl.
 

Studboy

Thinks he can ride
Dec 2, 2001
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We just bought a 310 to put in it, it had a 350 and we went down to a 340.
It runs so rich that it's not even funny. Do you think that the new boyeson power reeds that we put in it would affect it that much??? I need to look and see what the stock jetting specs were for the 91... although we have a little different carb. It looks the same as the stock except it has a pilot jet also.

Cyprice, the jump is out in Erda (Just before Tooele.) I've got a couple of acres designated for jumps and stuff but as of now I only have the 45 footer. As for water.... well, I don't have anything close to a sprinkler system right now, so I kind of made my own. I have a plastic 55 gallon drum that is tipped on it's side sitting on a trailer that I pull with an ATV up and down the runway to wet it down. I built a sprinkler arm system out of PVC.
I want to build some more obstacles but it is a lot of time and maintenance!!!
 

jmics19067

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Jan 22, 2002
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although we have a little different carb. It looks the same as the stock except it has a pilot jet also.

I think that is your problem. whatever the settings are in that carb they are probably not set up for the rmx.The needle jet and jet needle can be worlds off. If yousay it ran better right before the float bowl ran out of gas everything in that carb is probably way tooo rich. If it ran better for a little bit then ran lean before it ranoutof gas then the needle and seat could very well be a problem.
 

Rcannon

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Nov 17, 2001
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This sucks. I went riding with these guys. Honestly, the kid WAS making huge jumps on the XR.

 

Please wish him my best. I finally get my computer working to read this...crap, he is a good kid!
 

Studboy

Thinks he can ride
Dec 2, 2001
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The thing is jmics at one point the bike ran really good with that carb. so I assume that the needle and everything are OK. All of these jetting problems have happened since the new topend and new reeds. I think that the guy who had the bike before us kept jetting up and up because the old reeds were going bad, and when I put the new reeds in the bike went WAYYY rich. The stock main jet is supposed to be a 260, so I am going to start from there and see what happens. The bike has a RM250 head, Pro-Circuit pipe, Boyeson Power Reeds, and No airlid on the box. I just couldn't figure out why it would be so rich after the rebuild except for the reeds???? The old reeds were really worn, could that make that big of a difference?
I am going to try out the smaller jets tommorow and see what happens.

Thanks,
One Seriously Confused Person.
 

jmics19067

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Jan 22, 2002
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All of these jetting problems have happened since the new topend and new reeds.

sorry I missed that part. aside from something silly like maybe a shop towel still stuffed into the air boot while changingthe filter or the filter being rediculousy overoiled with something like grease your plan of attack sounds feasible.

possibly your smoke is antifreeze trying to burn? torn base gasket/kinked,knicked head gasket upon reassembley? I think though youwould definately know if it was antifreeze burning from the pungent smell you get.
 

placelast

Member
Apr 11, 2001
1,298
1
For novice jetters like myself, the Mikuni should be pitched; it's not worthy of even the recycling bin.

I have a PJ which came with my RMX - you can try it instead, and it wil be an improvement and get you in the ballpark, but that's only part way to a much better-performing PWK. Look into buying the latter, used.

Here's another twist, although this wouldn't be your problem if you are not burning trans oil: When I bought my son's '90 it was an oil burner. A shop had not only put in the RH side crank seal backwards, botched up the rubber o-ring on the primary shaft collar, but did not locktite the primary drive gear. Nonetheless as a consequence I became a better mechanic, and from henceforth didn't use a drop of oil.
 

490Dave

Member
Mar 18, 2003
316
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I can surely sympathyse with you man (are you sure it's not gotta YZ490 motor in it) you have described my past problems with the 490 to the T. I finally jetted down so far it was spooky. I went from stock 440 down to a 360 which seemed to work, but went back up to the 380 i also dropped about 3 pilot sizes too. I finally got it to run pretty decent but was still rich somewhere.
PS. Make sure everything is sealed up good on the exaust side.

Good Luck....

Dave....
 
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