Rs125 engine saga, please help!

[colin_397]

hi, i'm new to the forum and will be very greatful for any help anyone can offer on my rs125 engine problem.
I bought a 52 plate rs off a mate at work it has only 4500k on it but had been stood for 6 years.
i got it tested up and have ridden it for around 100 miles.
the engine pulls well when its screamin, but it bogs down badly from idle and is really hard to set off on, sometimes gettin stuck at junctions unable to get the revs high enough to move!
However, i quickly noticed that if i pulled a little choke it allowed me to get the revs up and set off.
So i decide its a carburretor problem, runnin lean i guess. so i stripped all the fuel system (again) cleaned every thing and it still has the same symptoms, i bought a good second hand carb, still the same symptoms.
I now have to run it with the mixture screw right out, nearly falling out!! and the idle screw right in. it just about idles now, and it runs ok until its upto normall runnin temp, around 70-80 deg then the symptoms return, it bogs down from idle and you have too really feather the throttle to get above 2500rpm.
I have cleaned the powervalve, and checked the selonoid operates, which it appears to do so.
So eventually i did a compression check. it read 85psi, so yesterday i put a new piston and rings in, the new reading is 85psi, no different!!!!! it still runs exactly the same.
i recon the tester i used is nackered, or am i missing something? (i did the test with the throttle wide open and the tester was screwed in tight)

Help!!! if i knew what to fix i would fix it, but i just cant find whats up with it!!

[2stroke 2smoke]

hi mate, i had the same problem with my nsr a few days ago, it was a nackered crank seal, letting the fuel out and leaking air. i had to rev it up to about 6k for it to move, but as soon as it got going the fuel shot straight through the ports into the ewngin and it was fine, have a look at ur crank seals and check the engine for perished oil seals or air leaks, u can pick up leak detector spray wich bubbles when there is a leak, spray it on the gaskets and anywhere that could be leaking, if ur carb is okay then i'll say its a leak

hope this helps

luke

[colin_397]

nice one, i'll check it over today, can you do the crank seals without stripping the engine?

[Kickstart]

Hi

Compression should be a lot higher than that, and sounds like you tested it correctly.

Seems you have done a fair amount of playing with the carb. Idle circuits on carbs can block up easily (they are tiny), but seems odd that 2 give the same results.

Worn main bearing seals tend to result in a high idle speed (although very uncertain idle), with the revs tending to stick when the throttle is blipped. Possible that is the problem but I would expect other issues. You should be able to change the ignition side main bearing seal without stripping the engine.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[colin_397]

i know the comp should be higher, but i think the gauge is ballsed. i'm gonna get a new gauge sorted today and pull the side casings off and have a look at these seals!
____________________
rs125, cg125, atc70, fantic 201
and the missus' ybr125!

[Kickstart]

[colin_397]

i tried my mates snap on gauge, that reads 100psi and i bought a myself a new gauge, that reads just over 100psi, still not as high as i would have expected. engine temp doesn't seem to effect the pressure.
could the crank seals leaking cause this?
____________________
rs125, cg125, atc70, fantic 201
and the missus' ybr125!

[Kickstart]

Hi

Shouldn't think so. While it might have an effect on small throttle openings on mixture, doing a compression check on full throttle any small change to crankcases compression from a leaking seal would be drowned out by the amount of air coming in through the carb.

Did you use the right clearance rings? Is the barrel standard? Did you use the right thickness base gasket?

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[colin_397]

Yes to all of the above. Cheers, I've looked at the crank seals and it looks pointless changin them as they seem in great condition, still seating nicely and quite elastic with no perishing. I'm gonna return to the basics again. This is really doing my head in now! What's the float height supposed to be?
____________________
rs125, cg125, atc70, fantic 201
and the missus' ybr125!

[colin_397]

Well I seem to have got it runnin a little better. It'll get a good run out tomorrow as my mate has borrowed it to do a track day on at oulton park. Lol!!
____________________
rs125, cg125, atc70, fantic 201
and the missus' ybr125!