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  #1  
Old 03-29-2016, 02:32 PM
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Default Rebuilt 1982 CR125 - help with starting issue?

     

Hi all

I have finished rebuilding a 1982 CR125 - taken some time, but it was from the literal bottom up. I have now been trying to start it

The good(ish) news is that after about 20 kicks it starts and runs beautifully - but then the bad news - it runs for about 3 seconds and then just dies. Adjusting the throttle in that three seconds doesn't help / seem to change the revs. This is starting with the choke on and half throttle or so.

It then takes another 20 kicks for the above to repeat.

Is this a fuel issue? Or some thing else? Or both?

While I'm kinda proud of myself for getting it started, it's frustrating as it's not really done / not the full deal.

Many thanks
Rich
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Old 03-29-2016, 03:01 PM
Wolf's Avatar
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Maybe you need to be more specific on the fuel and air situation.
How's the jetting, airfilter, sparkplug, possible air leak, etc.
Did you clean the tank and carb etc.
And what did you not do so far?
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Old 03-30-2016, 06:34 AM
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Hi Wolf

I completely cleaned the carb having had it fully apart.

Plugs are new, gap correct and I have a spark, plus new HT leads.

New air filter

Tank cleaned out and fuel flowing.

Replaced ignition coil and CDI unit with 2nd hand items, but from buyers who say they came off working bikes.

Believe everything is assembled correctly and tightened up

As I say it sounds great for the few seconds it runs (nice and smooth), but it does take a fair few kicks to get it going and then as I say it just dies.

cheers
Rich
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Old 03-30-2016, 08:53 AM
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I see a couple of "Red flags" in your post.

Number one, cleaning a carb is not the same as rebuilding one. You're talking
about a 34 year old PJ that's probably been put through the ringer. If it works
at all, it would be a miracle. A rebuild kit replaces the hard, dried up O rings,
gaskets and other parts that have most certainly perished from age and use.
While rebuilding the carb, you can check the carb castings for wear. For
instance, over the years, the float perch holes can elongate due to dirt and
vibration causing the float to jam. There are several other areas of potential
problems to check as well. Once you have insured the carb is up to spec,
load it with new brass per the manufacturer's recommended baseline.

Number two, no two stroke engine rebuild is complete without a successful
leak down test. I didn't read where you performed one, so I assume you
didn't. If your engine is leaking air from any of a dozen potential sources
after a rebuild, it will run like crap if it runs at all. A successful test would
be a loss of no more than 1 lb/min., less is better. For some reason, folks
seem to think a leak down is optional after a build/rebuild, it's not.

This is where I would start. If the engine starts and runs after you address
these two issues, you're good to go. If it doesn't, I would turn my attention
to the second hand ignition components.
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Old 03-30-2016, 10:04 AM
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I would suggest checking the ground connection as well if you repainted the frame. Eliminate as many variables as you can.
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Old 03-30-2016, 01:33 PM
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Thanks both - will do a leak test and check the ground. I was a bit circumspect when I mentioned the carb - I did replace all the components I could with new. However, I will give it another look.

Will let you know!
cheers
Richard
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