help diagnose with pic's

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#1
okay,
i have a 1993 rm125 that has become a project since i got my 250.
the bike has never seemed to run right. it has nothing from the bottom when you crack the throttle open and makes a bog sound. if you give it just a tad of clutch it starts to rip. i know 125's need allot of clutch but not like this. i have messed with jetting and still have had no luck. well i'm rebuilding the bike and my chick is going to learn how to ride. i took the head off today and examined the head, exhaust valve and piston. this is what i found.
the valve has zero tension and will not return on it's own. the rod seems slightly bent and there is carbon buildup on the head and piston.
see the pic's and tell me what you think.
thanks,
jackdrinker
 

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MWEISSEN

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#2
It's tough to tell what's up, but here are a couple of my opinions:

1. The carbon buildup on your head and piston aren't bad at all. In fact, I'd expect more on the head than what is there.

2. If the exhaust valve isn't closing, then that's most likely why you don't have any low end. The bent linkage MAY be bent stock (?).

3. The best bet would be to rebuild the top end and make darn sure the exhaust valve is working freely. Then deal with any jetting issues after all else is nice and tight. A bike with bad rings/piston/exhaust valve won't repond to jetting issues.

4. If it hasn't been running for quite awhile, I'd wonder about the crank seals too.... see if there's blow-by on the ignition side to check that side of the crank. If the bike was losing transmission fluid mysteriously, the other seal may be bad. More than likely a fresh top end will do wonders without messing with the seals.
 

woodsy

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#3
Hi Jack:
THe shot of the top of the piston seems to show some exhaust and intake side lean signs (from what I can see). You couldvery well be pulling air creating a lean condition. If it were mine I would remove the flywheel cover and the clutch/right side cover. I would then stuff the crankcase opening (where the jug meets the bottom half) with rags around a short piece of 3/4 inch conduit. Now, lite a cigarette and blow smoke into the crankcase (do like Bill and dont inhale) with as much pressure as you can push - if you can't keep the smoke from seeping around the rags - dampen them!! Turn the crank and try to move the crank ends both in and out and up and down while you do the smoke check. If you get ANY smoke of ANY amount from either end of the crank or center seal you are in for a split... Next check the roller that pushes the power valve open. If memory serves me correctly that valve is not checkable for "return" without the motor running (it works off centrifical force) but you can at least examine the components to make sure they are still intact and not worn to badly. You said youtried unsuccessfully to jet the bog out, did you jet via the needle? Moving the clip up the needle will lean and down the needle will richen - where are you in this adjustment and does the bog decrease as you richen? ANother item to consider when jetting is fuel level in the bowl. The amount of fuel avaliable has a DIRECT affect on how your jets perform - I know a TON of mechanics that doent agree with this and thats OK - IT STILL DOES!!!! Make sure that your float level is SPOT ON!! Also, the seal on the pipe (I believe that bike is new enough to use a set of rubberized "o" rings on the pipe) has to be good as it is possible to suck air back into the jug from this area! Of course, the intake manifold and base gasket are suspect also.. Reed valves can also attribute MAJORLY to a condition as you explained - what are the condition of yours? Can you see air under them? Have you miked your piston and cheacked clearances yet? I see your piston is stock size and that particular bike has an IRON cylinder - unless someone NEVER rode it or changed jugs on it recently it should have been bored a couple times by now just to freshen it up.. I would suspect that a 1st over bore with a new piston and rings would REALLY help you out with your bottom end needs!!! Final jetting should be done thru plug chopping!! It is the ONLY way to tell if your jetted correctly! Jetting to get rid of the bog is a questionable practice and should really be done only to diagnose problems IMHO.. NOW - have you checked your ports for port work? It was customary a few years ago for anybody who could afford a $15 die grinder to cut their own ports - I HAVE SEEN UNBELIEVABLE THINGS DONE SO DONT LAUGH!! I remember vividly a bike coming iinto the shop for repairs that was cut so badly that it ran at WOT or didnt run at all simply because of this BLUNDER!! Take a close look and MAKE sure that yours have not been altered!!
My 2cents
Woodsy
 

woodsy

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#4
Sheesh Mark, I want you to know that I didnt read your response before I shot him my answer... We seem to think ALOT alike :) I cant wait to see if we ere even close on this one :)
Scott
 
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#5
man you guys are great... cant wait until i need help doing a street legal conversion. you know i purchased a clymer manual hoping it had in-depth information, but, it doesn't. i need to know things like " how much the travel is in the power valve ".. what is the measurement between full open and full close. i'm just going to split the cases have them matched and do bearings and seals. it funny you brought up the home porting.. it has Marks, looks like it was to remove carbon build up. i asked in another section of the forums about the cylinder type and no one responded. so it is an iron sleeve and can be bored, ok cool. the reeds look good no chips although who knows how old they are, so there getting replaced. i'm heading to the auto parts store to pick up some parts was and i'm going to clean the carb tonight. everything is going back to stock on the jets and we will work from there. i'll call a dealer on monday about the bent rod. it doesn't appear to be bent in the book or on the microfiche.

thanks,
jonathan
 
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woodsy

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#6
Hey Jonathan: OOOPPPPPSSSS - STOP THE PRESS!!! I was wrong about that bike having an Iron bore.. I misread my Wiseco book - SORRY - and I hope you get this message before you go to a bike shop and make a complete fool of yourself because of me.....
SORRY!
Woodsy
 
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#7
woodsy shame on you........ ya i caught it. just got back from the hardware store.. well that kinda sucks...

if there is damage i wonder if eric gorr can fix it.
 

MWEISSEN

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#8
Wow Woodsy! I never heard of the smoke check for bad crank seals, that's a good one!

You're right about the float level. So many people ignore it, but it's so important to make sure the jetting is correct. Fortunately it seems this problem is a lot less prevalent since the days of the old brass floats.

Jackdrinker, you're on the right track. I'd venture to bet you're cylinder is OK unless you see gouges or other marks, but still check roundness (a machine shop can do it if you don't have the tools). If it's out of spec you could get another used cylinder or do a sleeve.
 
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#9
ok, time to reopen this thread for an update:
first the exhaust valve> i took the cylinder and stripped out all removable parts and the power valve would not budge at all. i tried and tried to pull it out, finally i took oven cleaner and tried that. nothing.... went and bought a dental pick set and chipped for what seemed five hours, a pound of carbon later, still not an inch. so about mid-night i grabbed a screw driver to pry it out.. i cam with the attitude of " it's coming out now or i'm going to break it out... a few forceful prying motion, it cam right out... what a mess. it took me about three hours to clean the valves themselves and the ports, now they slide great.

there was what i believe to be "blow bye residue " on the ignition side... no fear all new bearings and seals will be in today. one quick question for ya:
on the ignition side of the crank it has a spot that is blue ( like being heat tempered ) is this a sign of being lean or a less than fit seal?
thanks everyone..
jonathan

i know i should not be putting money into this bike, but i'm not a moto star and never will be. a non-current class seems fun...
 

woodsy

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#10
Those cranks are heated before the pin is is pressed - you are probably seeing original (or possibly it has had a rod kit installed) heat blueing from the factory..
Sounds like you are having a great winter!!
Woodsy