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2004 CRF450R Won't Start issues - open to suggestions

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Can't believe I'm posting one of these, but I'm almost out of ideas....

 

I bought a non-running 2004 hoping that it was just a quick valve adjustment that was needed. The guy I bought it from even got it to bump start once pushing it down the hill in front of his house. I figured "easy-peasy."

 

Here's what I've tried so far:

 

Day 1:

 

Brought it home and ripped out the carb. It had obviously old gas in it, so I soaked everything in carb cleaner and reassembled. 

 

Opened up the head cover and checked the valves. Just as I suspected, intakes were off by .10mm or so. Dropped the correct shims in and now they're a nice .15-.18mm.  The exhaust shims were so far off, I was thinking that someone got their inches and mm mixed up.  I removed 1.45mm shims out of each side and replaced them with 2.55 and 2.65mm. Clearance is now .28mm on both sides.  I then adjusted the decompression arm. .63mm total clearance (.28 and .35 combined).

 

When I go to kick, the compression is so strong that it felt like I was kicking a brick wall at first. Before I get 800 responses, I've checked the timing using the left side marks on the flywheel, and it's on.  I even tried adjusting back one tooth and forward one tooth, just to see what it looked like, and I know I'm on the right tooth on the cam.

 

Day 2:

 

I adjusted the decompression lever tighter (.50mm) and it made it a little easier to kick, but still doesn't start.

 

I then took it up the hill to bump start it. Usually the rear tire just skids (so much compression), but after 3 failed attempts, I decided to kick and behold: It started ... I rode it down the hill, around the corner, and then it died. Wouldn't restart, so I pushed it back to the garage.

 

I tore the carb down again and really got after it with the cleaner and the compressed air. I even replaced the pilot jet (42).

 

I checked and re-checked the valves and put the decomp back to its perfect .63mm.

 

 

Possible solutions:

 

1. I have another head from a 2003 crf450r that I know will fit. I may swap out the head, or maybe just the cam and camshaft holder first.

 

2. Is it possible that the cam chain is stretched and the timing is off because of that? to get the timing perfect, i feel like the mark of the cam sprocket is just slightly higher than the arrow mark on the holder.

 

 

I'm leaning toward #2, but would appreciate any opinions before I order the new chain.

 

Thanks,

 

Price

 

 

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I would try a new cam chain as that can and will stretch especially on an 04.  I just rebuilt an 03 top end and changed the cam chain due to it being stretched.  Also dont laugh but I had to re-do the spark plug gap on a brand new plug as it was nearly closed.  Between these two the problem was resolved. Good Luck.

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I just did the same rebuild and cam up with the same problem. I was told that if the sproket itself was turned 180 degrees it would cause that issue. I was skeptical but tried it and problem solved..

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I just did the same rebuild and cam up with the same problem. I was told that if the sproket itself was turned 180 degrees it would cause that issue. I was skeptical but tried it and problem solved..

 

The cam sprocket? I guess at this point I'm willing to try almost anything. You mean rotate it 180, right, not flip it. If you flipped it, the marks wouldn't be visible and it would be harder to set TDC (and I"m not sure it would line up correctly.

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Changed out the cam entirely and it's kicking over correctly. Also fished wire up into the carb and there was definitely an obstruction in the pilot port. Going to have to do more carb work, but the good news is that it fired up! (just won't idle and backfires like crazy.)

 

Thanks for the help!

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Backfiring can be caused by the vacuum plate in the carb being upside down.

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You mentioned that you cleaned the carb with carb cleaner. Apparently carb cleaner will destroy the seal for the vacuum plate, so when you are checking the plate is on the right way round you should check the seal as well. From what I have picked up on the forum the carb should not be cleaned with carb cleaner!!

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