RM 125 no power at full throttle

[PCMAX]

My '81 RM started playing up last weekend it runs great into the start of the power band but then as you hit peak power its like it is running out of fuel or spark particularly if I jam it full open.

I have done the following but the problem persists:
*Replaced the spark plug
*Replaced the plug cap
*Replaced the stator coil assembly
*Cleaned the carby & jets & needle valve & set the float level
*Tried a bigger (270) and smaller (250)main jet
*Pulled the barrel off and checked the piston, rings & reeds

Has anyone had any similar problems or does anyone have any suggestions???
 

[Lozza]

Have you completed a few plug chops when the problem is occuring?

[vandy010]

My '81 RM started playing up last weekend

so it was running ok before then?
and now it's just started to play up?
and you've replaced the stator/coil assembly with no change?
a blown main seal perhaps.
does it blow smoke when its playing up?

[DOK]

hi max
sounds like ignition coil.
runs ok down hill and revs ceanly
uphill is a bag of poop coughing and spluttering.

ignition coil will breakdown under heavy load.
being high revs and uphill

Thanks
DOK

[Curly3]

Blocked exhaust?

[Tex]

Blocked exhaust?

Took the words right out of my mouth, er, keyboard. Check the muffler first, and then the rest of the pipe.

Tex

[asasin]

How about a partially blocked feul tap/filter. Cheers

[TT5 Matt]

wasp love to build nest in exhaust pipes at this time of year and their good at fully or partly blocking bike exhaust,get a piece on wire with a small hook and go fishing for worms/spiders

[PCMAX]

Thanks for all the replies, I will try swapping out the ignition coil today and checking the internals of the expansion chamber and muffler. Will let you know how it goes after that.

[PCMAX]

Checked the ignition coil today and found that I have 50,000 ohms resistance from the coil (black/white wire) to the plug cap. The book says I should have 10,000--11,000 ohms so I guess ths could be the problem. Unfortunately I don't have a similar coil to troubleshoot with, all the spare ones i have only have one wire and a plug lead.
Does anyone know what the other wire (white/blue) that runs from the ign coil does??

[RMJJ]

One wire is the supply to the coil the other is earth back to the engine at the stator end.
You can use the later z d e f g coils. They all have near enough spec but they are internally earthed so earth to the frame where the bolt on.
Just try the one wire coils you have as a test and only connect the supply wire in the plug, leave the other connector in the plug empty

[TT5 Matt]

on the h/t side of the coil did that test/specs include the resistor plug cap?

[PCMAX]

Well another day of blasting up & down the street anoying the neighbours..... Cleaned the pipe (internals) and muffler, checked the crank case breather was clear, tried a mates ignition coil, same problem. Put another 32mm Mikuni on, same problem. Tried another CDI, same problem put another old stator on, same problem. Will pull the barrell off again tomorrow and check the reeds again just in case they are any different from last time I checked.

It runs fine until just before peak power then coughs & dies, if I hold the throttle wide open and keep rolling it eventually fires back into life and then dies again, if I then close the throttle and coast it will become responsive again at low reves and then the whole scenario repeats as I get to peak power.

If I cant fix it tomorrow I'm probably going to do the unthinkable, something I have never done since I started playing with bikes in 1973.....Take it to the bike shop (probably Gunters in Woollongong) and ask/pay them to fix it. A sad day indeed !!

[reg]

Pete check your fuel delivery, sounds like its starving

[bazza]

crank case seal?