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Here's a problem for ya

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About 3 weeks ago, while I was at the track riding, my bike (2002 CRF450) got hard to start and did not want to idle. Having not checked the valves in a while, I checked them and they were at zero clearance(figured that). After measuring with the smallest shim in place, there was still zero clearance. Time for new valves. So I replace valves and springs. I try to fire it up and it will not kick over unless I twist the throttle as I kick. When it does fire, it will not idle. I double check the valve clearance - both dead on at .006 inches. Next step is to clean out the carb, right? I take the carb apart - clean EVERYTHING put it back together - same problem. Won't start without twisting the throttle, once it starts, will not idle, and if the choke is out, it dies.

At this point, I give up and take it to the shop. Shop does a new top end and exhaust valves – low compression and leaky exhaust valves. After this is done, bike still won’t idle, so they tell me I need the carb cleaned - ok, I did that, but no telling, so I say to go ahead and do that as well. They told me the bike was ready – but when I go pick the bike up tonight, same problem – won’t start and will not idle. There is definitely more compression since the top end, etc was done. It will not fire up unless you twist the throttle and it will not idle period. There is some minor popping, but nothing major. It does sound strong when it runs, but it will not idle nor kick over without a twist of the throttle. Shop thinks I need a new carb. Now, that might be a possibility, but at this point, I am out a lot of money so far (and dipping into my 05 fund) and do not want to spend and extra 550 for a carb.

The only other factor was that I switched from a FMF PowerBomb header to a stock header and did not rejet. I do not know if this would cause a problem or not. Ideas? We are not talking a major difference in pipe diameter - so I cannot imagine that the different headers would make THAT much of a difference.

As far as timing issues - between the mechanic and I, I think we would have got the timing down right, same with the carb and all other parts. Even if I screwed something up, I would expect the mechanic to correct what I could have messed up.

I just find it hard to believe that EVERYTHING - top end, exhaust valves and carb all went out at the same time. Anyone out there got any ideas? The bike is still at the shop and we are trying to figure out what it is.

Thanks!

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Having done my valves last night, and everything fresh in my mind, you should triple check that the timing is correct on the motor.

take the cover off the top of the motor, and the inspection hole down by your rear brake lever as per the valve adjustment write up in the manual. when you line up the marks correctly on the bottom and the top, look at the outer two cam lobes. they should be pointing rearwards and a little upwards. i'm just wondering if your timing is 180 degrees off, because if you make the assumption that all the new parts are correct and installed correctly with the correct shims, then the timing must be a little wonky.

oh, check your plug too.

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Get a new mechanic. Your guy sucks azz.

Does it really take trial and error part replacement to diagnose your bike? Only for a dumbass who isn't qualified for the job.

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That is the first time I've ever heard a mechanic suggest that the whole carb needs to be replaced. I think that your mechanic is a fool.

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Bringer over...i'll get her runnin like a crack head runnin after free crack for a small fee of a 12 pack of new castle.

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As far as only being able to turn the motor over with the throttle open, wouldn't that be a Decompression Release problem?

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My bet is on the slide too. Its probably in upside down, which is super easy to do. Ive done it, so dont feel bad.

Could be cam timing too, its either or, could be both....doubt it'd run at all with both being wrong though...

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Dude,

Fire your mechanic! After he fixes your bike though. 😢

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Definetely check the slide. The plate that has the rubber thing next to it is upside down. This creates a huge air leak. If thats not it double check the exhaust and make sure there isn't something stuck it somewhere that would create a large back pressure.

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The carb was swapped and the same problems still persist. So any problems related to or with the carb are eliminated.....

😢

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To all the folks that said timing - that's it. The chain was stretched to the point that the timing appeared on the mark. The sprocket was moved one tooth and it ran fine. However, the chain does need to be replaced to ultimately fix the problem as opposed to just putting a bandaid on it.

Thanks for everyone input.

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