Vintage Dirt Bike Q & A

I almost completed my '74 CR125M restauration, but I have problems to make it running fine.

When I try to start it, I put the choke on and it start after only 2 kicks. But it run only for 5 second and die. I kick it again 2 or 3 times, and it does the same thing all the time.

I did a complete engine rebuild. New bearings, new seals, new oversized piston and rings.

The carburator was completely clogged. I did a soda blast and a complete cleaning.

I didn't found the basic setup for the carb. How many turn the fuel screw (slow jet)? For the air screw, they said to start at 1 1/2 turn, I did the same with the fuel screw, 1 1/2. The jet needle, it was at the second groove. I tried at the third also.

The rubber boots are hard, It look ok but I wonder if it can suck air? But I can't try to spray some cleaner to see if it affect the running since it doesn't run for more than 5 seconds every time.

I looked at the spark plug and it look a little bit wet.

Any idea of what can cause this kind of problem?

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1974 Honda CR125M - 1977 Honda CB750 - 1982 Yamaha XT550 - 1986 Honda TLR200 - 2016 Honda CRF1000L Africa Twin- 2012 Ossa TR280i

You put the choke on, start the bike, then immediately turn the choke off and it runs for 5 seconds? Or is the choke on for 5 seconds (too long)? Does this bike have the original carb, with '005A' stamped on the body behind the choke?

Can you start the bike without the choke, maybe by push-starting it?

Try running the air screw at 2 or 2.5 turns out for now. The idle speed screw (large one on left side) is adjusted to get the idle speed you want - there's no fuel screw on this carb. 1.5 turns on the speed screw isn't even close; I believe mine's turned in over 6 turns. Try backing out the speed screw completely, then turn it in 5.5 turns and start the bike, and if it still only runs for a short time, turn the speed screw in another 1/2 turn and try again.

Jetting for the original '74 carb is 125 main, 60 pilot, 200 air, and 3.5 throttle valve.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Rayivers, you're the man!!!

Yes, this is the original carb, 005A. And also yes, when I tried to start it, I let the choke on. I didn't remember that from 40 years ago!

So I did the adjustment you wrote, put the choke on, start it, put the choke off and gived a little bit of throttle, and it worked!!!

I will now have to adjust the idle once warm and it will be very good I think!

Thanks a lot Rayivers!

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1974 Honda CR125M - 1977 Honda CB750 - 1982 Yamaha XT550 - 1986 Honda TLR200 - 2016 Honda CRF1000L Africa Twin- 2012 Ossa TR280i

No problem - I'm glad it worked!

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric