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2005 CRF250R Starting/Running Issues After Rebuild

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I recently rebuilt the engine on my CRF. I have it back together now but im having issues with starting/idling. At first it would only start with the choke out after rolling the throttle to spray fuel in the cylinder and would only run if you continued to pump the throttle. This made believe I had a fuel issue. I pulled the carb and went through it again. In the process, I dropped the fuel screw and lost the small washer. I bought a Moose one that came with all the parts. The carb appeared fine, all jets were clear, passages clear and all moving parts were moving. I also checked the valves again as I originally shimmed them on the bench during the rebuild. They were .001" tight all around, so I corrected. I put it all back together with the same result. I rolled it in the corner for another day.

That day came over Christmas break. I pulled the carb off again, and went through it again. The only thing I found was the main jet was a little small (170,I migh hqve done this during an initial round of troubleshooting), should have been a 172 corrected and checked all screw settings and needle, all are in stock locations. Checked vales again, all are within .0005" of spec (1/2 thousandth). I did notice though that the timining marks don't look right. The cam marks are flush with the head, the crank mark is a hair high. For some reason I remember it being a hair low when it was new.

I left it as is and put it back together. Starting it is the same, but it will almost idle with the choke on. I think it almost idles because I ended up putting a 175 mqin jet in it is running fast enough that the main jet is suppling fuel instead of the slow/pilot circuit. The way it it is running reminds me of tight valves. Im wondering if it is a timimng issue? I am going to look at the crank/cam marks again and I may move the cam gear one tooth to get the crank mark back to where I remember it? Im looking for any other suggestions, this is really pissing me off. I used to go though this bike every weekend when I raced, and I used to tear down friends engines regularly and never had a failure, but i have been out of it for arou d 6 years.

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Check the timing vs the flywheel marks through the inspection plug, sure sounds like you're off a tooth. Be sure pilot jet and the entire pilot fuel circuit isn't blocked/clogged. Main jet has nothing to do with starting/idling.

I recently rebuilt the engine on my CRF. I have it back together now but im having issues with starting/idling. At first it would only start with the choke out after rolling the throttle to spray fuel in the cylinder and would only run if you continued to pump the throttle. This made believe I had a fuel issue. I pulled the carb and went through it again. In the process, I dropped the fuel screw and lost the small washer. I bought a Moose one that came with all the parts. The carb appeared fine, all jets were clear, passages clear and all moving parts were moving. I also checked the valves again as I originally shimmed them on the bench during the rebuild. They were .001" tight all around, so I corrected. I put it all back together with the same result. I rolled it in the corner for another day.

That day came over Christmas break. I pulled the carb off again, and went through it again. The only thing I found was the main jet was a little small (170,I migh hqve done this during an initial round of troubleshooting), should have been a 172 corrected and checked all screw settings and needle, all are in stock locations. Checked vales again, all are within .0005" of spec (1/2 thousandth). I did notice though that the timining marks don't look right. The cam marks are flush with the head, the crank mark is a hair high. For some reason I remember it being a hair low when it was new.

I left it as is and put it back together. Starting it is the same, but it will almost idle with the choke on. I think it almost idles because I ended up putting a 175 mqin jet in it is running fast enough that the main jet is suppling fuel instead of the slow/pilot circuit. The way it it is running reminds me of tight valves. Im wondering if it is a timimng issue? I am going to look at the crank/cam marks again and I may move the cam gear one tooth to get the crank mark back to where I remember it? Im looking for any other suggestions, this is really pissing me off. I used to go though this bike every weekend when I raced, and I used to tear down friends engines regularly and never had a failure, but i have been out of it for arou d 6 years.

Edited by Eddie8v

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Did you replace the timing chain and tensioner when you did the rebuild? If not, you should.

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All the timing components were replaced with factory parts. I checked the valves again today and they are good, the timing marks are dead on. I verified that the begin is at TDC with a dowel rod in the spark plug hole. Moving the cam chain one tooth each direction made it pretty far off so I put it back. I checked the carb and found the float set pretty low, it was at 11mm and is supposed to be at 8. I'll check it out later this week to see if it resolves the issue. If not I'm going to check for leaking valves. The head, valves, springs, etc are all new (Honda).

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TDC was checked with the timing marks on the case and crankshaft. The dowel rod was to confim. 

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Been working late all week, and working all weekend. Probably be next weekend.

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I just got the 2007 crf250. I just finished the rebuild. Top/bottom... Started first kick n stall.. Start, stall over n over... New to this bike.. I had fuel valve off.... Prob not ur issue,

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Wow, haha. I've done the same thing. Valve perpendicular to the fuel hoses is counterintuitive!

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Ok, back at it today. Here are picks of all the timing components. All line up well. Everything is new Honda parts except the piston and crank. I'm going to dig out the leak down checker and see if the combustion chamber is tight. If all goes well I guess I'll try putting back together again with the new float settings.

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1454272831560.jpg

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are u using a aftermarket pilot screw?,  had a no start/hard to start issue with my 2008, after a top end rebuild i had set my pilot screw to stock settings in the manual and found out after two weeks of checking everything two and three times that the pilot screw was to far out , stock setting called for 2 1/4 turns out with the type of jetting it had, would not start so i put it at 1 1/8 turn out and kicks right over. now she start within three kicks.   as long as u got spark its probably a fuel issue. (my pilot screw is a moose racing one.)

Edited by RANDY_OSOK

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Mine is the moose set at the factory 1 3/4 turns out. I have tried as far out as 3 turns and as little as half a turn.

Fixing to do the leak down. Didn't have a 8mm adapter so I made on from an old plug and 1/4 brass nipple.

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Well I think I found a decent issue. Leak down failed in a spectacular fashion. 76% leakage. I removed the cam to ensure nothing is pushing on the valves because I knew the pressure would force the piston down. Something is going on with the exhaust valves, you can hear air flowing through the exhaust. So much that it instantly starts to whistle when you put your hand over the end of the header. My guess is it valve seating from not lapping the valves. I made the assumption that new valve and head should seal with out lapping. I'm looking through the manual and lapping the exhaust is required, but not the intake because of their coating. I'll drain the fluids tomorrow and pull the head.

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