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CRF 250 won't kick over after being warmed up

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Hi I'm new to this forum, new to four strokes and new to fuel injection so hoping someone can help me out. I've recently bought a 2010 crf 250 it starts first few kicks when cold and runs lovely, but it won't kick over after I've warmed it up and have to bump it and again runs lovely after a bump, the parts I've changed are:

Spark plug

Fuel filter

Coil

Coil lead

The valve clearances have been checked and valves re shimmed and then rechecked again after a ride

Timing checked and is ok

All plugs have been pulled apart and cleaned.

Tried a technique which I was told about for when shutting off, where by you blip the throttle 3 times before hitting the kill switch.

All this and I'm still in the same place as when I started, really stuck as to where to go from here, any help with where to go from here would be much appreciated.

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Let's work on your terminology. 'Kicking over' the engine is your foot, pushing the kickstart lever down. So when you say it won't kick over you are saying the kick lever is seized in the cases or the piston is seized in the cylinder, etc.

But from your description, it seems as though you are saying that the engine DOES kick over but won't start when you are kicking it over warm. This is a classic symptom of a leaking exhaust valve- hard to start warm, needs pullstart and then runs well. Typically caused by tight valve adjustment.

You need to do a 'cylinder leakdown' test to see if you have a slightly burned valve or worn/misshapen valve seat which is in this area, I suspect.

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Hi Sandlvr69, ok sorry, yes what I should have said was that it won't kick start once it's warm. When I checked the valve the exhaust valve clearance was on the high side of the tolerance for valve clearance but still in spec, 0.012".

Is the leak test something I can do easily myself and will I need specialist equipment? I'm trying to build up the equipment that I'll need to service the bike and do all the various checks myself, rather than have to rely on someone else. And also is a pretty easy fix if this does turn out I be the problem?

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You need a cylinder leak detector for this test, they are somewhat expensive at around $200 USD. Your local bike shop will have one and should perform this test quite reasonably. You could provide access by removing the tank and etc. before taking to shop.

 

If your piston is old or of unknown hours you should replace it as a matter of course. You can then inspect the cylinder head.

Cylinder head and piston replacement is very straightforward on the CRF250 but rebuilding of the head is best left to a professional, too many tools required. Stainless aftermarket valves are a good idea for future longevity and complete aftermarket heads can be purchased for just a bit more than having the old one rebuilt.

Of course, ebay usually has used cylinder heads for sale much cheaper. I scored a stock head for my 06 CRF450R for less than $100 USD and it looked like brand new when disassembled, maybe 10 hours on it.

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The piston was replaced and the engine rebuilt before I bought the bike, it's done about 15hours since. I've found out how to perform the test it seems pretty simple, I've also spoken to a friend who has a leak down tester but I'm going to have to wait a day or two to get it from him, as he's away. So I'll perform the test as soon as I get it off him and let you know how I get on. If I do find that this is the problem and I know it would have to be done correctly but is it just a case of replacing the valves? I've also be told about titanium valves, is there any point in fitting these or wouldn't I see any difference? I want to eventually tune the bike and intend on keeping it for a good while.

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Ok, so at least you don't have a tired piston also. It's hard to recommend a repair when you aren't sure of the engine's state. So now I'd like to know if they just replaced the piston (which is the most common) or split cases, etc. Did they attempt a poor head repair as well? It's moot until you have checked leakdown.

Stainless valves are the way to go for longevity. Titanium valves rely upon a coating to prevent rapid wear and Honda had a problem with this for a few years which badly hurt their reputation.

To rebuild the head, you need to grind the seats and check fitment or replace the guides and seals. Stainless valves come with heavier springs.

People DO just install a new valve without fitting it properly and it never lasts long.

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I believe it was more than just a piston and ring change, he did show me the parts that were changed, can't remember off the top of my head but I'll try to find out.

On top of this I've got another problem now as well as the starting issue, so, gave the bike to someone who has had motocross and enduro bikes for years to have a look at. He wanted to try and find out if it was a fueling problem, said the fuel pump seems to be working fine. Part of his process was to take the air filter off and spray fuel down the intake and kick stat the bike. He said that it started no problem even after being warmed up, but all of a sudden when he was doing this the bike started to idle high and the revs won't come down, adjusting the idle screw doesn't make a difference to the revs, but if you pull the idle screw out the bike does rev faster. When started the MIL comes on and goes off as it should without giving a code. Anyone got any idea why this would be?

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The 2010's had a lot of problems with the fuel pump.  The filter would solve the problem but if not we would replace the pump.  I would try and swap tanks with someone that has a good running bike.  After starting the pump would slowly loose pressure.  An engine in poor condition, IE low compression usually won't start easy when cold or hot unless the valves are near zero clearance.  We always start troubleshooting with a leak down test first and then for correct valve lash to determine engine condition.  The Motion Pro leak tester works good on bikes.  I think we sell it for $150. You may want to check your heat sensor but we haven't seen any of those fail.  See if the throttle position sensor has been moved.  As far as ignition problems its usually the stator in most MX bikes.  They have a tendency to give a weak or no spark when hot.  I haven't seen this on the EFI models.      

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Thanks fastheads, The filter has been changed but it made no difference at all. The next step I intend on carrying out is the leak teat, what do you mean by valve lash and where is the heat sensor could this be anything to do with the starting issue or is it the high idling issue that you are speaking about?

Edited by jamesturler

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Ok so I carried out the leak down test. The gauge showed that I had 80% cylinder leakage, weather this gauge is reading right or not I don't know but I could here air escaping from somewhere.

First I carried out the test on a cold engine at TDC, the compressor cut out when the gauge was reading 40%, I then read through the instructions again and it said to warm the engine to operation temp.

So this time I warmed the engine up, removed the spark plug and rocker cover, set it to TDC and tried again and got a reading of 80% cylinder leakage. I was able to hear air escaping from the top of the engine but not sure where from.

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Hell no, I checked for leaks on all of the joints but couldn't find any, read everything a few times:

Fit pipe and fitting to spark plug hole

Adjust the regulator all the way anti-clockwise

Connect the air line to gauge

Set gauge to zero

Connect pipe from the spark plug hole to gauge

Watch where the gauge comes to rest

Seems pretty straight forward

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Ok so after last nights leak down test I thought that I must have done something wrong, so I've checked everything and done it again (a few times), this time with a cold engine and I got readings about 7%, if what I've seen is right this is good. So I'm wondering where I go from here and if there is anyway of checking that the pump is in good working order before ordering a new one, I don't know anyone with the same bike, so I'm afraid that swapping tanks with someone is not an option.ImageUploadedByThumper Talk1392394808.805840.jpg

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Mechanic's basic 101 philosophy is to check frome easiest to hardest, most likely to least, etc. In your our case that was cyl. leakdown first. Next I'd check for good, clean, blue spark with the engine at it's hardest starting mode (warm). I'd use a new plug, removed from engine.

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Ok so finally got a chance to get back and do more, went to check the spark today but I wasn't able to start and warm up the bike, I had a friend check the spark whilst I kicked it over, it wasn't consistent.

1st kick= 1spark 2nd= no spark 3rd= 1spark 4= no spark 5= no spark 6= no spark 7= spark

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