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01' XR not starting

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Hey guys,

 

Just got a XR400. Had the top end rebuilt with re bore and competition valve job, and got a Wiseco piston. Also Got a new T4 pro circuit pipe. Put a new Mikuni Tm36 pumper carb from XRs only on there too. I have everything on but this thing won't start! I have adjusted main jet to 135 and no change. What could be the cause of this? Timing? Valve clearance?

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Who put it together?

Changing the main jet won't do anything for starting. The pilot takes care of that and the 15 that it came with should be sufficient enough to get it started.

Is the stock air filter and cage still installed or is it aftermarket part? Underseat airbox snorkle still installed?

I'm guessing elevation is near sea level?

If the valve clearances are too tight it will cause hard starting. Same with timing.

Is this your first XR400 and/or first 4 stroke? It will not start like a 2 stroke, from anywhere in the stroke. You have to learn the start routine. Set choke to on, bring the engine to TDC and kick from there, every time.

Hopefully, whoever disassembled the head was aware of and didn't lose the plunger and spring that goes in a hole under the auto decomp cam and those parts got reinstalled on rebuild. If not, it's not going to start.

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Thanks for your reply bro,

I put it together. I made sure to check the plunger and spring for the decomp lever it's there. Yes I'm at sea-level, and I know how to get it to top dead center. I had the shop do a pro valve job so they must have not checked the clearance. I was able to start it, rode around and let it idle, then it would not start again. Didn't detect any pinging or knocking in the engine.It was able to start cold then after starting wouldn't run. I checked all other possible variables, the Carb is brand new never been used.

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Next time you get it started, keep it running and let it warm up. Check the tuning of the fuel screw.  Be sure idle speed is not set too low.

How old is the gas?

This is the tuning manual we use for the Mikuni. http://www.mikuni.com/pdf/hs40_manual.pdf

Be sure fuel is getting to the carb.

Unlike the stock carb, when restarting a hot engine, wicking the throttle open at the bottom of your kick works.

I recommend you turn the pump timing come on screw all the way in, at least for now until you get it tuned and running right. I find the 400 runs the best with it set there, but you can play around with it later if you want.

Go ahead and verify its valve clearances are right just to rule it out. Your problem is probably something simple that's being overlooked?

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Thanks for your reply man, I checked the valves and noticed when finding top dead center, there was no "play". I had to keep rotating the piston to get them to have wiggle room to use the feelers. Does that indicate the timing is off?

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No wiggle at tdc on compression stroke means your valves are to tight, and thats a good reason for it not to start, you want .004 clearance on the intake, and .005 on the exhaust valves. 

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