81 RM 125 problems

[Jibbercrap]

Lately my '81 rm 125 has been having problems starting. It used to start first or second kick and then one day my brother took it out and it completely died on him. the reason it died was because the spark plug has a piece of carbon lodged between the contacts. Ever since that its been taking like 10-20+ kicks to get it to start everyday. But the weird thing is, once it runs, it will start first kick from then on. We tried replacing the spark plug and its done nothing. So for now we are just dragging it behind an ATV every morning to get it going. Anyone have any ideas on what to look at or what needs to be replaced or fixed.

Thanks

 

[David Trustrum]

Yeah clean the carb, I suspect the choke cct is blocked. Failing that the plug cap needs replacing or ignition could be weak or the fuel tap leaking (try leaving the hose disconnected overnight into a jar & see if it is).

Failing that chronic wear, reed valves etc.

 

[Jibbercrap]

This weekend im gonna give the carb a good cleaning to see if it does anything, what could be causes for weak ignition?...Im also gonna check to see how worn the plug cap is, it does look old, but it has always worked fine. A friend also suggested to replace the reed valves.

Thanks for the info, i'll get back when i clean/test everything with an update to whats wrong

 

[David Trustrum]

Broken reeds can cause hard starting, but I doubt this is your problem, try the simple stuff first. You have to pull the barrel to get to the reed valve on those early RMs. Believe they were steel reeds which don’t tend to crack so often. Course they could have been replaced with aftermarket, however I wouldn’t expect it to start so easily after it was warmed. Plug Caps fail all the time.

Check that fuel tap (assume you DO turn it off every night yes?). Weak ignition could be a bad earth, the ignition coil (under the tank), maybe the CDI, or the stator coils (flywheel coils). They are known to have a limited lifespan & old RMs are weak sparkers at kickover speed. However weak stator coils would tend to get worse with heat & possibly break down at high rpm. Try the simple stuff first, including yet another plug, but disassemble & blow through the choke cctry do not poke wire through anything.

My 2000 model GasGas has spark so weak at kick over you would swear it has a problem & will not start from cold until you learn how to turn the choke on fully, then it starts 2nd kick.

 

[Jibbercrap]

Heh, thats assuming i remember to turn it off every night...i have bad history of forgetting to turn the fuel tap off :whiner:

I think i left it on the last i was using it, and now im not gonna see it till this weekend...AHH CRAP!...why is it one of the times i forget to turn it off its bad time.

But anyways, how come RMs have such weak sparks at kick speed?...and ever since that 'day' when it died on my brother, it doesnt start with the choke pulled out, so im gonna have to clean that all out to make sure its not clogged.

I'll have to get back to you this weekend

 

[David Trustrum]

Yeah what might be happening is the fuel tap leaks or is left on & overnight/week it dribbles a little into the crank case & some evaporates & leaves the oil, then when you first kick it the stuff in the cases is thrown at the sparkplug fouling it up. Maybe.

The early ignitions were a bit miserable but that was technology vs cost & Suzuki’s weak area was always the electrics, the rest of the bike was class leading at the time.

 

[Jibbercrap]

If it does turn out to be a fuel tap leak, is there cheap inexpensive way to fix it?, ive never had to replace a fuel tap. Does it require I buy a whole new gas tank?...heh

My brother leaves the fuel tap on all the time on his '83 Yamaha DT-125 and it still starts first kick.

Is that because his isnt premix?, it has a tank under the seat labelled "2-stroke oil" and thats where you put the oil instead of mixing it. I find that a lot more logical if you ask me. It mixes everything for him im assuming. So im guessing that his probably leaks gas into the crank case, but theres no oil to be left behind when it evaporates?

 

[David Trustrum]

It’s only a problem leaving it on (or it leaking) if the float bowl jet leaks as well, which considering the age is quite likely.

You can get fuel tap rebuild kits quite often, got one for my old KDX for, um ~$10 I think.

 

[langston7]

Check the exaust vlaves...check carb isnt gunked up...the float might be stuck.

 

[David Trustrum]

Check the exaust vlaves...

Good one!

Best check the fuel injection & the flux capacitor while you are about it.

 

[Kenya-640]

Better check and see what voltage you're getting at the vortex genetators as well.

 

[jmics19067]

Time to wring your brothers neck? just kidding I can see in a worse case scenerio that your brother ,who doesn't have to use premix, adding straight gas to what you had left in the tank. Depending on the possible combinations of ratios, blah blah blah, there wasn't enough oil in the premix to protect your rings and piston. And now you have low compresion.

I unfortunately have seen a few blown up small bikes <and family fueds> from this type of situtaion.

 

[Stew312]

If the voltage at the vortex generators gets too high, the power band will come off.

 

[cr25096er]

sounds too low on compression to me.

 

[Rockey5000]

Compression is what I would check first. I had the same problems with a CR125.

 

[Jibbercrap]

Alright, this weekend, which is almost here...YAY!, im gonna check the compression, clean the carb, check the fuel tap and try to get to the local dirt bike shop and pick up a new spark cap.

What is the vortex generator?(sorry i dont know a lot of terms)...is in the alternator area?

Thanks everyone for your feedback

 

[David Trustrum]

The vortex generator is next to the Smurf tube. Which is located where the exhaust valves would be if an ‘81 had exhaust valves.

Sorry we’re just taking the Michael out of the other poor chap who failed to notice the bike was pre powervalve.

 

[Jibbercrap]

Yeah...well...I took the carb out...was clean as a whistle...adjusted the floats since they werent sitting properly, rewired everything (cause my brother burnt some wires by accident), put a new spark plug in...started first kick. Then today we were riding it. It ran perefectly...never had it run this good, then BAM the engine seized...and we were all like "yeah..........this sucks"...so we pushed it back and now im gonna have to take apart the whole engine. We have pretty much narrowed it down to the berrings in the crank case, but it could be the piston rings

 

[David Trustrum]

Ain’t that a drag!

But it’s always a risk with old bikes, especially old competition bikes is they were designed to put out peak performance but the trade off is you are supposed to rebuild them regularly.

‘course when you have a bike that old you can’t afford to do so. Add to this the age & the crankseals were probably leaking etc. Obviously you were running the correct grade plug. When you rebuild, check the condition of the airbox & seal any suspect joints with weather strip & if the filter has any tears replace it. You might wish to check the mainjet size is conservative (std) when you get it going again & go from there.

Good luck.