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Discussion Starter · #1 · (Edited)
Hello,
I just rebuilt the top end of my 91 trx250x. New piston, new gaskets, new rings, new sleeve, new oil seals, new carb, new coil, new wire harness.

I just put it all back together. Have fuel, spark, and compression, but no start. We pull started it. We got it to fire and run once. It sounded like the idle was too high, so I adjusted the carb down. Suddenly it back fired through the carb. The carb actually popped off the intake. No start since then. I have double checked the timing. T notch on the flywheel even with the notch on the crankcase. The camshaft sprocket has the two horizontal lines even with the head and one mark straight up. The lobes are down I believe....? I'm at my wits end... Please help!

Other pictures in my garage....
 

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Discussion Starter · #3 ·
The ignition coil.... I got it off of eBay. I tried both the old one and new one.... I have bought a good used voltage regulator. The "stator" tested within specs.... Both ignition coils tested within specs.
 

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Discussion Starter · #4 · (Edited)
I forgot to mention that I had replaced the pickup coil and "stator". I had the sleeve replaced at a machine shop and also had them clean up the valves since i did not know how to. The only thing that I have not replaced yet is the cdi box. I also cannot kick start it. Checked all the wires. Good connections. I have removed the key, but it still has the off run off switch and is operational.
 

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Don't put too much faith in "tested within specs". I have a friend who was trying to get his 200 running. The only part that tested within spec was the stator. The part that ended up being the problem was the stator.

Did you have the flywheel off? If so, you may not have gotten it tight during assembly and sheared the key the first time it started. If you didn't have the flywheel off, don't discount the possibility that the flywheel is out of time. Easy to check - take the spark plug out, use a soda straw to put in the plug hole and roll the crank to TDC of the compression stroke. Look in the timing hole to see if the marks line up. If it's in time and you have over 110 psi of compression, then it's most likely an ignition or carb problem.
 

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Discussion Starter · #6 ·
Nope, didn't have the flywheel off. I will check that though. By chance did you look at the pictures I posted? I'm not sure about the came. The rockers should have what clearance? What is a good starting point for the idle screw? I had it set at 2 turns out, but wondering if it needs turned out more.

I had tried pull starting it, but nothing acted as though it wasn't getting enough fuel. I tried to use starting fluid, but wouldn't ignite that way either.....
 

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The pic looks right as long as the cam lobes point toward the head. How about a new spark plug? Initial setting on the fuel/air screw is about 2 turns, but it's not critical till the engine is running and warmed up. Valve clearence is about .002 intake and .003 exhaust, however too little clearence is worse than too much. .008 intake and .010 exhaust is ok too. After it's running and such then the final clearence can be set before riding on a regular basis. You might have to service the carb. Don't forget to inspect the air filter and intake ducts.
 

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Sorry, I missed the new carb part, but I question where you got a "new" carb since it is not available from Honda.

Whether the lobes point up or down is not too relavent, but installation of the head cover is easier if the lobes point downward.

Let's start with the basics - how much compression does the motor have - checked with the throttle wide open and at least 5 compression strokes.
 

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Discussion Starter · #10 · (Edited)
I believe the compression was 190ish?

The carb was off of eBay like 2 or 3 years ago. It did have the same part numbers from the carb that was on it compared to the " new " one.

The spark, I was checking with an inline spark checker? The tool that goes between the spark plug cap and the plug.

Last night when I was putting it together the rockers felt loose. I didn't check the spacing with a feeler gauge, but they were moving a decent amount. Could that be my issue?
 

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The compression is exceptionally high, but it will not keep it from running - it just means you will need to use fuel in the 105 octane range.

The spark checker tells you that there is spark, but it does not tell you it is jumping the gap of the plug - use a new plug (something other than a Champion)

As long as the clearence between the valve and the rocker arm is marginal (not 1/4 of an inch) getting the motor to run is feasible.

Take the float bowl off the carb and inspect the parts for cleanliness and freedom of movement

Beyond these steps I am at a loss - I would need to have the vehicle in my shop for detailed analysis
 

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Discussion Starter · #12 · (Edited)
So I have tomorrow off I need to check: fly wheel is showing actual top ideas center compared to the piston, adjust the rockers to 0.004 inches, check that I'm getting spark across the spark plug gap, the carb bowel is clean and everything is moving freely?
 

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It should be the T mark and align the cam there - if the chain is worn, you might be 1/2 tooth off - in that case, the front cam mark will be slightly above the head surface and the back mark will be slightly below the surface of the head
 

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Discussion Starter · #16 ·
Well we got it running today. We adjusted the valves, double checked and set the timing. Had to adjust the throttle cable a little bit, but it starts within the first two kicks.... even when cold.

The exhaust valves were tight and the intake were loose. The piston was at top dead center but was on the f mark. Set the time according to the piston. Runs great. Pulled a wheelie within the first hour of having it running! Thank you all for your help! My 3 year project is finally running.
 
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