RM 125 no power at full throttle

[TT5 Matt]

fill the tank and see just how much comes out of the hose going to carb coz its sounds likes it running out of fuel,had a 185 do that till i drilled the passage ways and fitted a bigger needle and seat.fuel filters on taps block up as well maybe try removing it or at least cleaning it,do a test of how many secs to fill a stubbie with filter fitted then another without full tank both times.the hose from tap to carb isnt to long and vibrates too much as had a briggs stationary motor do that and it stopped fuel getting to the carb,no dout its something simple like too small of a needle/seat off of a less powerfull motor maybe

[micks]

pc max i think they mean the breather on your fuel cap see if that is blocked.

[Husabergpete]

Pete sounds like fuel issue to me. But I had an 83 Husky years ago that would die or break down at high revs. Local Husky bike shop said to check that a piece of quartz crystal was not stuck in the main jet as it had happened before and when put to light it was see through. bugga. That was not it. I farted about till late one arvo till I started it in the dark and found a big fat blue spark jumin from the plug cap to the expansion chamber. Simple fix was chuck out the black rubber cap and install a NGK red silicone sucka. $5 fix..............

Pete # 100%

[PCMAX]

Thanks for all the suggestions guys.
*Bazza, i'm really hoping its not a crank case seal, is there any other way I can check this without splitting the motor?

*TT5 Matt, I will give you flow check theory a go today have put a new filter in & tried 2 different carbs but did not check if the have the same needle/seat.

*Micks, I ran the bike with the fuel cap off, same problem, so its not the breather there.

*Pete Ringo, tried a couple of alternate plug caps but not a silicone one. Might buy one tomorrow

Thanks again to all for your suggestions, will let you know how it goes.

Peter

[Montynut]

This is going to sound really really silly but are the engine mounts tight. Lose engine mount - vibration high rpm - bad earth -bad spark - bad miss - head scratching. A 125 may not be easy to detect a lose engine mount unlike a open class bike.

[Lozza]

Thanks for all the suggestions guys.
*Bazza, i'm really hoping its not a crank case seal, is there any other way I can check this without splitting the motor?

*TT5 Matt, I will give you flow check theory a go today have put a new filter in & tried 2 different carbs but did not check if the have the same needle/seat.

*Micks, I ran the bike with the fuel cap off, same problem, so its not the breather there.

*Pete Ringo, tried a couple of alternate plug caps but not a silicone one. Might buy one tomorrow

Thanks again to all for your suggestions, will let you know how it goes.

Peter

Check the air gap the spark will jump. Also check your float level, set that so it's just before fuel runs out the overflow.

[DOK]

Hi PCMAX
can you try a down hill run at peak revs.
To me it still sounds like ignition coil.
Fine one day shit the next.
David

[PCMAX]

Update #5 checked the fuel flow per TT5 Matt's suggestion. 16 sec to fill 200ml with filter in line, 8 sec without so I just ran a new hose without filter. No improvement. Also removed the fuel cock and opened it up a bit with a 5/32 drill.
*Montynut--check tightened all of the engine mounts and have cleaned all the elec connectors and earths.
*DOK my street has a bit of a downhill but at peak revs she just dies. Tried a mates ignition coil from his 1978 RM125 same part number but it didn't make any difference.

After another disapointing run up/down the street I took the oil filler cap of and shone my torch in to see if I could see any evidence of gasses from a bad crank seal per Bazza's suggestion.

No wisps of fuel fumes but I had a eureka moment when i spied a garter spring on the R/H crank seal. I presumed that the idiot (me) that had put it in last time the crank was out (just before it started playing up) had installed the seal back to front and that was going to be the answer to all my problems. I convinced myself that at peak RPM/crank case pressure the gas was dumping past the seal and into the clutch casing causing it to die.

I removed the clutch cover, clutch and primary drive/water pump gears and popped the seal out only to find that it had a garter spring on both sides and was installed correctly (manufacturers numbers to the outside). However in carrying out this procedure I must have damaged the seal during the remove/install process as she now blows blue smoke like a Singapore mosquito fogger. That really impressed the neighbours......

So I will order another seal tomorrow and look forward to replacing that (NOT!!!) the weekend after next as I am up at Coffs at a mates 50th next weekend. Dissapointed about missing HEAVEN round 3 at Canberra but he's only 50 once i guess, and has booked and paid for my accom.

Anyhow i'm now kicking back now with a very fine Barrossa Valley shiraz wondering where my weekend went.

To be continued...............

[kitakitsune]

Howdy pcmax,
                    my '79 rm125 developed a "bog, rev, bog, rev,bog, rev" symptom after 1/2 throttle. Even in neutral.
Turns out, the boost bottle hose spigot which was drilled ( by previous owner ) into the right side crankcase at the transfer port wall was not air tight.
The clue was oil residue around the pipe/crankcase interface.
Anyway, sealed the leak and engine runs sweet.
Check for leaks around and about.
Cheers, kitakitsune.

[bazza]

PGMAX it might not be soon BUT YOU WILL LAUGH ABOUT THIS ONE DAY !!! I like the way your keeping at it

[Slakewell]

My Dad a small motor mechanic for years once showed me this trick , you remove the exhaust, carb air box etc , you then tip raw fuel into the inlet and start if the bike hits full revs as it SHOULD then you replace one at a time till it doesn't.

[TT5 Matt]

ok you know theres plenty of fuel TO THE CARB but is it getting into the carb fast enough?has someone put a little needle and seat in there?is there a partial blockage the the fuel inlet passaages going to the n/seat like abit of fuel hose,try some fuse wire through them and of  course compressed air.as a final check fire it up again and get it to do whats its been doing and turn the fuel tap off at that moment its cutting out and remove carb off bike and remove carb bowl and see how much fuel is in there.

[Montynut]

blocked carbie breather tubes. They are not just overflows but also allow air out of the carbie. If they block it can force the level of fuel in the carbie to be very low and also fill slowly. A bloody wasp taught me that once

  Not the WASP on here the winged/stinging version

[pancho]

 I agree reg, sounds like a classic case of very low flow of fuel.
Pancho

[GMC]

It does sound like fuel but sometimes it’s hard to distinguish between fuel and spark problems.
As already mentioned the carby vents are worth a check.
Also wondering if the flywheel has spun upsetting the timing.
Coils and stators can work but break down under heat and demand.

I know this sort of thing can be frustrating but if you give it to a shop they will double check all the same things you have looked at and charge you for it.

You can send the whole ignition away for testing, flywheel, stator, coils etc and they will test it in a running scenario.
There are a few places around that do this for around the $80.00 mark plus postage.
Sometimes it can be worth the 80 odd dollars just to rule out electrical problems