Return to dirt = CR125

[tigertim20]

Gday.
I started out on dirt when I was much younger, but havent been on a dirt bike for years and years.
My dad (back when we spoke) and I used to go and buy fucked dirt bikes and do them up, ride them a while and sell them. Went through about 15 bikes in 2 and a half years before I stopped counting, and soon found my way to big sportsbikes not too long thereafter.

As fate would have it, my mate recently got his hands on a very rough CR 125. about the same time his missus announced that he was about to be a dad - so wanting to start saving for the next 18 years of poverty, he offered me the CR. the princely sum of $400 seemed about right to me.

So Im back to dirt. The bike is rough as fuck, but complete. the guys that had it last clearly had little respect for it, but it does run - though not well. She is going to be a bit of a project.

Im wondering if anyone else on here has one of these (1991 CR 125) and can give me some info?
A manual would be bloody handy.

I tipped some gas in her and she fired right up and ran ok - ish. she idles nidely but will not rev out. Im thinking it may have fucked rings judging by the smoke, but thats just a guess. I guess forst step is find a manual, and do a compression test, then go from there.

anyway i have rambled but thought I should venture into the dirt section and say gday

[nzspokes]

Do they use an oil injector or pre-mix. Me and a mate fired up an old TS185 that had been sitting for 10 years outside, the injector had leaked and filled it with 2 stroke oil. Good thing as it now runs mint but took a good ride for the smoke to clear and for it to rev.

Good carb clean would probably be a good start.

Dirt bikes are fun and it doesnt really matter what you ride.

[tigertim20]

yeah the whole thing will be pulled apart, bout would like to have a manual to work from if possible. Honestly havent looked at it thoroughly enough to say much about it, a CR125 is not something I have owned before, but I think its just premix.
hoping someone will have a manual they can email me

[Crabby]

def premix, for mucking around id run a good oil at 40:1 which is 25 mls of oil per measured litre of fuel. change the plug, pull the carb apart and blow out the jets and see how it goes, you don't need a manual for that, just pull the bowl off it, remove float and needle valve, jets etc. I like to do it on a bench with a cloth on it, the cloth stops parts bouncing onto the floor if you drop them haha. white helps parts stand out too, just unscrew the jets and blow them out with compressed air and put them back, assemble it how it came apart and refit and test

[unstuck]

Good on ya TT. Dirt bikes can be so much fun.

[Taz]

It's hard to judge the condition of a 2 stroke engine by the amount of smoke if pumps out. But it is real easy to strip the top end down and check the condition of piston, ring and cylinder, while you're in there you may as well just replace the piston and ring, clean the power valve, check the rod for play and with some new gaskets she's all good again. Takes not much more time than it took me to type this.

[ktm84mxc]

Yes it's a premix a ratio of 40-1 wud be a good starting point. Excessive exhaust smoke can hide a multitude of problems eg leaking crankcase seals, leaking head gasket, worn rings etc. When was the muffler repacked chances are it's filled with carbon and oil.
Pretty sure Clymer do a manual for early CR's.

[tigertim20]

Yes it's a premix a ratio of 40-1 wud be a good starting point. Excessive exhaust smoke can hide a multitude of problems eg leaking crankcase seals, leaking head gasket, worn rings etc. When was the muffler repacked chances are it's filled with carbon and oil.
Pretty sure Clymer do a manual for early CR's.

no doubt they do, but Im a bit broke atm, so trying to save costs where possible!
Cleaning the carb will be todays job and i shall see how she's looking afterwards.
from what I can see so far, Ill be replacing wheel bearings front and rear, swing arm bushes, taking a look at the forks, the carb likely needs a good clean.
Ill do a top end as well, looks like I can source a full top end kit including gaskets etc for about $100 from the USA, oversize pistons are readily available too, so no issues there hopefully.

so nobody has an old CR manual laying around they wanna share?

[cheese]

What colour was the smoke? White is normally an indication of crank seal letting go and sucking in gearbox oil. A leak down test will let you know pretty quick though.

[tigertim20]

What colour was the smoke? White is normally an indication of crank seal letting go and sucking in gearbox oil. A leak down test will let you know pretty quick though.

to be honest I didnt really look at the color.
I pulled the carb apart tonight and gave it a clean.
the issue I have is I can kick her over, and she fires up, and runs okay in the lower rev range - will not rev up high, and will only run for a minute or two, then die. then it simply doesnt want to start again.

It does need a new plug no doubt - that may be affecting it too. I will pull the engine down later in the week, as I feel like its probably in need of a new piston, there isnt much resistance from the kick starter, I can quite easily push it down with my hand and it feels like it should be harder - Im guessing this may also be affecting why it runs for a minute or two, then dies.

[cheese]

Have you got a compression tester? 125s have not much compression, but it should be a bit more than that.

[nzspokes]

Sounds like fuel starvation. Not got a slightly blocked tank/filter thats slow to fill the carb?

[tigertim20]

the fuel in the float bowl should keep it running for more than 30 seconds - but pulling the petcock and shit apart will be part of pulling it down anyway.

When I take the top end off and check it, i might as well do the crank seals as well and replace any bearings etc I can see. I am asuming crank seals could cause leaks et etc?

I dont have a compression tester, but they arent too expensive, so I will buy one, since it appears that none of my friends have one.
I guess I will have to splurge on a manual since I cant find someone who wants to share, and hit a dead end on free downloadable ones.

[noobi]

I would just give the whole bike the once over, make sure everything is properly torqued, cleaned, connected and greased.
If you can easily turn the engine over quickly with your hand then the piston/rings are probably worth replacing, but 2strokes leak compression so they will turn over fairly easily anyway, 125 especially because the piston is tiny and the ports are huge.
Check for parts and stuff here www.454.co.nz and search 'cr125', you'll get heaps of hits and all those products are available through any dirt bike dealer.
Fresh gas, fresh plug, clean filter and carb. If it still doesn't want to run properly, you may have a dodgy electrical connection somewhere which can be a bastard to find.

You dont 'need' a compression tester, if you want to save money just put it towards a new top end and be done with it. Leaking LH crank seal will cause the bike to run super lean which is white smoke, if the RH side seal is gone the smoke will be darker due to burning gearbox oil.

[nzspokes]

the fuel in the float bowl should keep it running for more than 30 seconds - but pulling the petcock and shit apart will be part of pulling it down anyway.

That depends on how much fuel the idle circuit drinks and if there is a transition circuit that is not getting fuel.

I had this problem with a bike the other week. Was a slightly blocked fuel line.