RM 250 problem

[Stew312]

I have a good question for you Eric. I recently picked up a 1988 RM 250, and I can't figure it out. When I first picked it up, it had to be turned on its left side before it would start, you could kick it until you were blue in the face, but it wouldn't go until you leaned it on its left side. I rode it for a week like that and decided to fix it up. So I cleaned out the carb, blew out the jets, checked the float level, etc. (the jets in there were smaller than stock, so I put stock jets in, 370 and 20.). I put the carb back on, and now it won't fire. It only backfires (more of a weak fire than a backfire)every 3-5 kicks or so. I checked the carb, everything was still fine there, there is even small gas puddles on either side (air box flange, and intake flange) of the carb, but the spark plug is basically dry when you pull it out after kicking it. I checked the reed, which appeared fine to me (after all, I'm not an expert) and I noticed there is a gas coming out of the back of the carb (air box side) when you kick it 5-10 times. I replaced the intake flange gasket, between the flange and the reed, and all other gaskets seem fine (no leaks anywhere). Could I have an exhaust valve problem (causing intake from the exhaust pipe and firing out the pipe instead of down the cylinder)?? Could I have a reed problem (compression through the carb, causing the gas to flow towards the air box)?? What should I do?? Thanks alot.

 

[Stew312]

Also: the bike hadn't been run more than 5 minutes at a time in the past 3-4 years, and I rode it 3 times in 3 days for an hour each. Could this have caused the exhaust valves to heat up and cause me a problem now possibly from carbon buildup or anything?? Thanks.

 

[jmics19067]

Althouh not addressed to me and I feel kinda funny trying to answer for someone that is a lot smarter than me I hope I can help.
I would put the lean jets back in first and go from there. the reeds could definately be the problem as well as the float, needle and seat in the carb and the choke system. Have you changed the plug? all that gas and not starting the plug could be fouled on top of it.The reeds should sit flat on the reed block.

When you had to lean the bike over to start originally a lot of people do that to make even their new well maintained properly jetted bikes start easily. When you go back to square one and if you still have to lean the bike over to fire up check the choke and /or play with the airscrew a little to see if you can get an easier starting bike. I personaly turn on the gas pull up the choke and kick thru slowly 2 or 3times with my hand off the throttle to "prime" the cylinder. Maybe that way will be easier for you.

 

[Stew312]

Thanks for the help. I have been changing the plug to make sure that it is not fouling, but there is a small gap between the reed and reed block on one side, which is something i was worried about. The carb was also checked out by the local suzuki shop, and they said it was working fine as far as needle and seat, float, choke, etc. You mentioned "all that gas and not starting", actually there isn't enough gas getting into the cylinder, the plug isn't even wet when you pull it out. Thanks for the advice.

 

[Durt Cycler]

How is the compression? Could possibly a vacuum problem if the carb checks out fine. For the reeds I would definetly replace them if they show any wear, chipping, or gapping (might I suggest Boyesen Pro Series, they are the best reeds I have used).

 

[Stew312]

Compression's ok, no leaks or anything.. I'm getting new reeds this afternoon, and probably putting the bike back together without messing with the exhaust valves, because seriously, who wants to deal with that. Thanks for the help.

 

[jmics19067]

I f the reeds arent setting flat on the reed block the flow of air can and will be backwards at certain times during kicking. Which is why you have gas on the wrong side of the carberator<air boot>. But you also stated that you have a puddle of gas on the intake side and I find that a little wierd not fouling the spark plug if it doesnt fire. Not to say that it cant happen just that my luck it would.

 

[KTA]

is there enough gas getting to the carb? or is it just not getting from the carb to the engine? . . . check your gas tank valve

 

[Stew312]

There's plenty of gas getting in and out of the carb, after kicking it over a number of times, if you take off the carb the bowl will be full. So basically there is plenty of gas getting in and out of the carb, not enough getting through the reed into the engine (plug not wet), and no leaking gaskets.

 

[Stew312]

I checked out the reeds and they are fine, but my exuast valves are definitely stuck. I'm in the process of working on those, but I still don't have any ideas for the not starting, only backfiring problem. Any suggestions Eric??

 

[Durt Cycler]

Possibly electrical problem?

 

[Stew312]

It appears to spark fine, and plugs are not fouling.

 

[jmics19067]

if you have the proper flywheel puller for you r bike and/ or can borrow one make sure the woodruff key is not half sheared throwing off your timing or the timing wasn't advanced for more bottom end oomph

 

[Stew312]

Good idea.. I know that the timing wasn't advanced, cause the bike started fine before.. But the key might be sheared off seeing as how the bike doesn't seem to be sparking at TDC. Hopefully I can find a puller in the near future to check that out. Thanks.

 

[Stew312]

Well, I found a puller and as soon as I got the flywheel off the woodruff key fell out in 2 pieces, so I think I've found the root of my problem. All my parts should be in this week, so the bike should be back together before the weekend.. Thanks for the idea jmics.

 

[jmics19067]

well I am certainly glad that, that major problem of not having correct timing is atleast relatively cheap and easy to fix.
your welcome!