Vintage Dirt Bike Q & A

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 Post subject: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 7:59 pm 
I raced my bike one year ago and it sat till last week. I cleaned the carbs, put new points and condenser on it and fired it up. For the first 15 seconds, it bike revs nice and crisp, but then a series of back fires will drown it out until it dies. It will do this repeatably. Any ideas? Whenever I do keep it running to take off, it fails to reach power band. Thanks in advance.


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:00 pm 
Just thought of something. Check the sheer pin on the crank. I had one sheer once then it started to act like that.


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:01 pm 
I had one act like that too but it was a busted piston skirt. Jeez Barry... see what ya start with this stream of conciousness thing. ;>


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:02 pm 
Sounds like its out of time? check your timing marks. plus double check to see if you timed the points right!


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:03 pm 
Is there another way to set the timing without using a dial indicator?
Thanks, Keith


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:04 pm 
Hi Keith,

You really need a dial indicator. According to the Honda manual the point gap should be 0.3-0.5mm or 0.012-0.020in.

Here's another short list from their troubleshooting guide for erratic high end engine behavior.

1. Insufficient plug gap.
2. Retarded ignition timing.
3. Weak point arm spring.
4. Defective ignition coil.
5. Incorrect float level.
6. Clogged air filter.
7. Crankcase compression leak.
8. Short circuit in AC generator.
9. Broken or cracked expansion chamber or to much carbon deposit in pipe.

HTH,

Loren


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:05 pm 
Thanks Loren,

I'll see if my local bike shop will let me borrow one.


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:06 pm 
Hi Keith,

I don't know if you have the owners manual or not but it calls for 1.5mm BTDC. Some of the hop up guides say 1.7-2.3mm BTDC. I run mine at 2.0mm BTDC.

If you plan to buy your own dial indicator try http://www.goodson.com .

Good luck and let us know what the culprit was,

Loren


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:07 pm 
After rereading the original post I'm going to concur with Barry. I somehow misread the part about keeping it running but not getting full revs... mea culpa.


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:08 pm 
My first suspicion is the condenser. If you still have the old condensor and you didn't have any problems with it pop it back in there and try it. Have you taken the plug out, held it to a good ground, turned the engine over and checked the color and strength of the spark?

Have you looked at the plug? Is it dry or wet? Any signs of overflow from the carb? Just thinking out loud when you rebuilt the carb if something didn't get put back right or maybe clogged up one of the breather holes or somehow the fuel bowl is overfilling????


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:09 pm 
It was actually acting worse before the condenser change. I changed one thing at a time. Before the condenser, it would barely start and run at all in the first 15 seconds.


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 Post subject: Re: 73 cr 250 troubles
PostPosted: Sun Jan 25, 2004 8:10 pm 
Hi guys I'm back,

Sorry it took me so long, but when you work 60 hours a week, it's tuff to find time to do your hobby. Well, first thing first, the CR now rips!! This is what I did. I made a measure device to check my timing. It was made out of the body of a ball point pen with a xerox copy of a small MM ruler taped to it. That and a coupler fitting and a 1 X 4 finished it off. Anyways...I set my point gap, set my timing, and the rest is history.

I never set the timing on one of these bikes before and from now on, that's the first thing I'm going to check. Thanks to all who replied. I'm on cloud 9, so is the back of my leg.


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