89 rm 250 Loading up, hesitation, no idle, bogging bad

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#1
I have been trying to help a friend of mine get his 89 rm 250 to run right for a few weeks now. We have been trying to eliminate the simple cheap stuff but almost everything i do wont make any change. I will give a quick run down of the problem and what has been done to it. He bought the bike not idling and bogging. It will start on the second kick most usually but if you dont keep the throttle at about 1/8 open it will die almost instantly as if there is no fuel at idle. You can rev it and it will bog but clean out after 10 solid seconds of pinning it which i hate to do. It will run good for a minute and then back to bogging but it will never idle for even a second. I checked the compression and its at 200psi. I have taken the carb completely apart and used a can of carb cleaner and put it back together with new orings and set the correct float hieght at 14mm and stock jetting (have tried one step smaller on both jets). Crank seal on the left side looks good and has no play in the flywheel. The reeds look ok with no chips, no cracks in the boot, air filter is clean, spark looks ok but is not perfectly consistant when kicked but jumps a 6mm arc when tested ,silencer repacked, expansion chamber clean inside with no dents, has an NGK resistor plug in it with new boot, premix at 40:1 klotz and 91 octane, air mixture at 1 1/2 turns out (have tried everything from 0 turns to 4 and no change, choke will make no difference in idle and will only make it bog worse when pinning it. I think i could keep going forever but if someone has any ideas on something else i may have missed please let me know. We would greatly appreciate it. I have searched on here and got many helpful ideas but nothing has solved it yet. Sorry for the huge post.



Edit: I forgot to mention that otherwise the bike runs very strong when it cleans out but goes back within a minute of riding and we did check to make sure the linkage to the powervalve is moving freely.
 
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#3
If the bog is worse with the choke on, that would indicate a lean bog? No idle... clogged up pilot jet, and questionable main jet? However, you said you tried different jets. Were they new? Does it smoke a lot? White smoke? Any way it's dumping water in the cylinder through the head or base gasket?

200PSI? Seriously?

J.
 
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#4
check the float in the carb. it could not seal or the float may be damaged and not hold the correct height.
if you close the petcock gas and wait some time while the engine is running it will be better and the just run out of gas right?
 
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#6
julien_d said:
If the bog is worse with the choke on, that would indicate a lean bog? No idle... clogged up pilot jet, and questionable main jet? However, you said you tried different jets. Were they new? Does it smoke a lot? White smoke? Any way it's dumping water in the cylinder through the head or base gasket?

200PSI? Seriously?

J.
The bog is worse with the choke on. It will basically never rev out at all with it on. I have tried brand new jets a size smaller on the main and pilot and it did not change. It does smoke a little more than normal i would say and its white. I did a test to see if the idle circuit was clogged by having the boot off the carb , letting it run with my hand on the throttle just enough to keep it going, then letting off and spraying a touch of ether in there to see if it would keep it going to simulate the fuel it should be getting at idle and it still dies. In fact if i hold the throttle open just a little and spray a touch of ether it will kill it instantly. i have not checked to see if water is getting into the cylinder but i do know that the water level doesnt change. Plus the cylinder is reading 200 PSI with the wide open and kicking the crap out of it, that should be an acceptable. Usually anything over 190 is a descent cylinder
 
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#7
helio lucas said:
check the float in the carb. it could not seal or the float may be damaged and not hold the correct height.
if you close the petcock gas and wait some time while the engine is running it will be better and the just run out of gas right?
I did not turn the gas off and run it but that is a damn good idea. At one time we accidentally ran it out of gas and at the last second it idles way up just like usual when you run out of gas. With that being said maybe the float is sinking due to a tiny hole or something. i looked both of the floats over pretty well and didnt see anything. It has 2 floats and they are mounted on rods to where you have to remove some kind of epoxy on the ends to get them off. They are wierd and unlike anything ive seen. I wish we had another carb to try to see if that would fix it.
 
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#8
Badbowtie73 said:
It has 2 floats and they are mounted on rods to where you have to remove some kind of epoxy on the ends to get them off.
no, no, no. if i am understanding correctly, you take the floats from the metal arm? that arm is hold by a simple axle to let the float go up and down while closing or open the valve...
 
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#9
you can take the caps off the float rods without fear I know what your talking about 2 shafts the floats ride on...I have that carb on the rm125 1985.... go ahead and remove the "epoxy" you dont need it and clean the shafts to make sure thier not sticky
 
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#10
I would also recomend properly dunking the carb in the bucket style cleaner once you have removed everything you can from it and then blow it out with compressed air (use canned air if you must) the choke should make a difference.

yes turning the petcock off is a very good way to check for level problems
 
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#11
Ok i think I will go ahead and take it back apart and soak it. I will take the floats off and see if those might be sinking. I have read that you need to set the floats by measuring from the bottom of the float to the gasket surface, i have also seen where you need to measure from the casting line in the float to the gasket surface. i have done it both ways and it runs the same either way. Which one is the correct method? Thank you guys for your advice. Sometimes i overlook the obvious stuff. I once almost started tearing into the motor on my CR because it was running like crap and luckily i realized the choke was still on :laugh:
 
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#12
I got the bike out today and messed around with the petcock while riding the bike. I shut the fuel off and ran the bike out of gas. Everytime the fuel level got low enough it would run hard and idle perfect for 5 or 10 seconds then idle up real high and die of coarse. But i was able to shut the valve part way to keep the level low enough it would idle so i guess that eliminated a bunch of other problems i was looking into. I took the carb back off and dunked the floats to see if they would sink or bubble and they are fine. As far as i can tell it would have to be the viton tip on the float valve is not sealing up so i will get another one of those and let you know if that did the trick.
 
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#14
the plug is pretty black within 5 mins of running it. I didnt see any bubbles in the radiator while running. I was kinda thinking that if there was water leaking into the cylinder that the plug would be very clean. I will run it one more time with the radiator cap off just to be sure im not seeing anything
 
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#15
I guess this thing is gonna have to go to the shop. We went to a local shop today to get a float valve so i took ours in to match it up and they said there was no way that thats our problem and the valve we had was fine. I put it all back together and set the float again and its doing the same crap its been doing. I dont know what else to try other than split the case, do a complete rebuild and buy a carb for it. It would be my luck that wouldnt even take care of it :bang:
 
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#16
The black plug could be water from a leak in the cooling system into the combustion chamber. A leak down tester can help, and it will check the crank seal condition. The right side is good for spooge. You can not look at a float valve and assume its fine. You do not even have a guarantee by leaving the bowl off and pushing the floats up, that it will work correctly. Just replace it yearly, or when you are having screwy problems. And stay with oem parts, keep it simple, you do not need more variables like crappier parts. An 89, does it have a power jet also? And for pete's sake, dropping the oil ratio to 40 is effectively increased the amount of gas! You made it richer yet? Premium fuel, factory oil ratio, factory jetting, replace the float valve, have a leak down test done.
 
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#17
whenfoxforks-ruled said:
The black plug could be water from a leak in the cooling system into the combustion chamber. A leak down tester can help, and it will check the crank seal condition. The right side is good for spooge. You can not look at a float valve and assume its fine. You do not even have a guarantee by leaving the bowl off and pushing the floats up, that it will work correctly. Just replace it yearly, or when you are having screwy problems. And stay with oem parts, keep it simple, you do not need more variables like crappier parts. An 89, does it have a power jet also? And for pete's sake, dropping the oil ratio to 40 is effectively increased the amount of gas! You made it richer yet? Premium fuel, factory oil ratio, factory jetting, replace the float valve, have a leak down test done.
I figured i would replace the float valve but the guy at the shop wouldnt even sell it to us, he said our valve was fine and we didnt need it. Probobly just wanted us to drop the bike off and pay him 70 an hour to look at it. As far as the fuel ratio goes its been at 32:1 to startup to 40:1 and back down to 32:1 again. The thing that i am having a hard time understanding is when i shut the petcock off the fuel level will run down and the bike idles perfect for 5 seconds so that is telling me that its a fuel level problem. I can think of anything else that will cause the level to be high when the float has been set and measured 4 times. Its at 14 mm to the casting line on the floats. You pull the plug and its very wet everytime. I dont have a leakdown tester on a compression gauge so it looks like it destined to go to the shop.
 
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#18
Uh. Replace the float valve? And stay away from that shop! You can order the right valve from sudco, but you'll need to make a 15 dollar order. Add in a couple jets larger/smaller than what you have now to make a full order.

I like your method of running the fuel petcock partially closed, that is a good hint that the problem is indeed overfilling the carb with fuel. Have you checked that all the carb vent hoses are free of obstructions? If it's overfilling that badly you should have some fuel running out of the overflow, assuming it's not clogged up.
 
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#19
The vent hose isnt clogged up. If you lay the bike over to about 45 degrees on the petcock side the fuel will poor out of the overflow as usual. I might try to mess with it again before i have my friend send it to the shop. Ill probobly at least order a check valve like i thought we should try the first time
 
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#21
Ive got one more question. Is there any way the cylinder could be taking water in and not cause bubbles in the radiator when running? I have a float valve ordered and ill try that when it gets here and let everyone know if it helped. Also im thinking of making a video of the bike idling and running if anyone here thinks that might help them diagnose this.
 
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#22
You tell me, does the 2 hoses come off the pump and feed the head/cylinder, or seemingly pumps through the cases, and up through the cylinder. Look in the book for the normal operating pressure, or the cap, and pressurize the system with air? If it feeds into the cases take your pick, center case joint, base gasket, or a cracked cylinder/head or case. A leak above the compression would be the only one that produces lots of bubbles, I figure. Are you loosing a lot of fluid? A black plug can be from retarded timing, or incredibly rich jetting, low compression, bad right crank seal, or its been ported and polished?
 
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#23
I guess this thing is gonna have to go to the shop. We went to a local shop today to get a float valve so i took ours in to match it up and they said there was no way that thats our problem and the valve we had was fine. I put it all back together and set the float again and its doing the same crap its been doing. I dont know what else to try other than split the case, do a complete rebuild and buy a carb for it. It would be my luck that wouldnt even take care of it :bang:
Hi did you solve the bogging down problem. Having identical problems with same outcomes ... the bike runs strong when partial turn off of fuel .. float valve etc all been done still no clean run.
Air cleaner element to replace next see if that alters anything
Thanks.
 
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#24
Hi did you solve the bogging down problem. Having identical problems with same outcomes ... the bike runs strong when partial turn off of fuel .. float valve etc all been done still no clean run.
Air cleaner element to replace next see if that alters anything
Thanks.
I just did my brass on my 89 cr-fiddy, I leaned em out 1 step, it seem to run a little crisper. I have a kehin on it so it was easy to change them out. Pull your plug, if it looks like a charcoal biquet its too rich, if it is white and blistered its too lean, if the center electrode is carmel then its jetted perfect!