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Old 08-31-2012, 10:31 AM   #1
john479 OP
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Honda XL250S won't start

I am once again in need of some help.

I bought a 78 XL250S a couple of months ago and the seller said that they were finding it difficult to start but they had done nothing to try and fix the problem. OK I thought, blocked carb or similar maybe...

When I got it home I gave the carb a clean but it seemed that was not the source of the problem. I did eventually get it running, by kicking, not bumping though. It sounded like a mower to be honest. So I set about tearing it apart.

It was obvious that nothing had been done on it for quite some time. The oil was full of metal fillings and the whole inside of the engine was covered in them. The bad noise was a worn cam chain way out of adjustment and clashing with the cylinder (no holes in the side though) and also the intake valves had been hitting the piston at some point. I split the case and cleaned out all the gunk.
I put some petrol in the upside down head to see if the valves were leaking and sure enough they were so I gave them a lap and honed the cylinder. It seemed that the cam and all else seemed OK.

After reassembling I tried to start it and after about 10-15 kicks it started and seemed to run ok and sound really nice. I stopped it to put the seat on and a few other bits so I could give it a test. Came to start again but it won't go at all now.

I've changed plugs, cleaned the carb and it won't go. I've tried easy start fluid but it's barely firing - only occasionally.
Tried real good push starts and it doesn't really fire at all. It's got a spark and the plug it wet. I don't have a compression guage but tried the thumb test and it blows it off so I assume it's ok.

It does seem to have a lot of kick back though, if I don't get the piston at TDC before I kick it, it will spring back and give my left foot quite a shock.

Normally I'd say its timing but since it's automatic, what else can I do? It has no battery or lights, just powered off the generator.

Can anyone help?

Thanks very much in advance,

John
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Old 08-31-2012, 10:39 AM   #2
JeffS77
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the cam and crank timing are spot on when you put it back together? it is cdi ignition but your timing for the crank and cam got to match up ? valves adjusted properly ?
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Old 08-31-2012, 12:48 PM   #3
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Originally Posted by JeffS77 View Post
the cam and crank timing are spot on when you put it back together? it is cdi ignition but your timing for the crank and cam got to match up ? valves adjusted properly ?
I'm sure they are right. I will double check. One thing I forgot to say is that I did stop and start it a couple of times when I got it running that first time and it seemed fine, started with no extra throttle. It was just when it started to cool down that it didn't start and now nothing.

Valve clearances are set to what is says in the manual
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Old 09-14-2012, 11:27 AM   #4
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Checked valve timing and all is fine.

Gave the carb another really good clean and now I have it firing more often and had it running but only for like 3-5 seconds, taking choke off doesn't help so I just leave it on.

Also, if I don't get the piston perfectly at TDC and kick it over, I get horrible kick back if I'm not careful which certainly wakes my leg up Is this a cause for concern or normal?

Any ideas anyone?

Thanks

john479 screwed with this post 09-14-2012 at 03:17 PM
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Old 09-14-2012, 11:51 AM   #5
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hmmm still sounds like a timing issue to me....or maybe valves way out of adjustment....weird
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Old 09-15-2012, 04:38 AM   #6
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Originally Posted by JeffS77 View Post
hmmm still sounds like a timing issue to me....or maybe valves way out of adjustment....weird
Yeah I agree that it sounds like a timing problem but why would it have started up that first time and ran well with no misfires and even restarted a number of times whilst the engine was still hot?

Very strange, I wonder if it could be a carb issue still, not sure...
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Old 09-15-2012, 06:51 AM   #7
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Originally Posted by john479 View Post
Yeah I agree that it sounds like a timing problem but why would it have started up that first time and ran well with no misfires and even restarted a number of times whilst the engine was still hot?

Very strange, I wonder if it could be a carb issue still, not sure...

I cant remember but I would assume these bikes use a key on the crank to hold the alternator/flywheel from spinning...make sure that is in place and it is not spinning around the crank shaft

maybe change the plug out for shits and giggles and really make sure that carb is clean
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Old 09-15-2012, 09:07 PM   #8
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Is it possible he's 180 degrees out on his timing?
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Old 09-15-2012, 09:55 PM   #9
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Is it possible he's 180 degrees out on his timing?
thats what I was thinking..but he mentioned it was running fine then was not
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Old 09-16-2012, 01:43 AM   #10
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find a strobo light and check timing. I had similar problem with a husky te610 and turned out to be the magnets de-glued from flywheel that were offset from their original position.
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