Long block wont fire (swap to my other motor and it fires right up so its not elec)

[yamasaki760]

Hello,

I have a weird problem here.

I have a motor i recently built that i've been wanting to run in my 200x. Its got a fresh paint job and nice, shiny new internals. I had it running for a day or two but then one of the valve adjusters backed itself out and I took it out, fixed the valve adjuster (checked the valves and saw no signs of piston making any contact at all with valves at any point), and put it all back together.

It just wont fire. Ive gone over the timing and valve clearances 100 times. I just can't figure out why it wont fire. I thought at first I had an electrical issue somewhere so I went through and tested every single component (i even changed stators, cdi's, etc). Spark is good. I can see a nice blue arc when i kick it over.

I pulled my other motor off the bench and threw it in the frame and it fired on the first kick.


What could cause a long block to not fire?

1. I tested continuity of yellow wire to body ground.. nice solid beep on the multimeter
2. I tested resistance of black/red wire to body ground.. it was somewhere in the 150's if i remember correctly
3. I tested resistance on the cdi and it was in the 94 range

not to mention i swapped all 3 of these parts with my spare motor on my bench and it still wouldnt fire



Anyways, Im running my "other" motor for now so I can at least ride and have some fun, but want to figure out/understand why this motor wont wire.

I'm guessing I did some kind of damage to the head when the valve adjuster backed out that I just can't see (nothing obvious/visible)?

I think I just convinced myself to test another head..... :-)

thanks for listening.. lol...

[Jmoozy27]

Have you tested the compression? You have fuel and spark, there is only one thing that your missing. Your cam timing could be slightly off. Does it have a decompression lever? Those have caused problems in the past.

[yamasaki760]

Have you tested the compression? You have fuel and spark, there is only one thing that your missing. Your cam timing could be slightly off. Does it have a decompression lever? Those have caused problems in the past.

tons of compression..

seriously has me stumped.

gonna tear it down again tonight and go over every nut and bolt again.

[barnett468]

.

What could cause a long block to not fire?

in your case, no fuel to engine, bent valve, jumped timing chain, spun flywheel.

I'm guessing I did some kind of damage to the head when the valve adjuster backed out that I just can't see (nothing obvious/visible)?

in addition to the compression test mentioned, you can put the piston on tdc compression/fire stroke, then remove carb and ex pipe and spray carb cleaner in the ports . . if it drains out quickly, you have a valve problem . . if it doesn't, i would not take the top end off if it has compression . . i would check the timing chain and flywheel position and just turn the gas off, drain the float bowl then spray flammable brake cleaner or starting fluid in it to see it it will fire.
.

[yamasaki760]

.


in your case, no fuel to engine, bent valve, jumped timing chain, spun flywheel.




in addition to the compression test mentioned, you can put the piston on tdc compression/fire stroke, then remove carb and ex pipe and spray carb cleaner in the ports . . if it drains out quickly, you have a valve problem . . if it doesn't, i would not take the top end off if it has compression

i see.. like a poor man's leak-down test.. i like it. i never thought of that.

. . i would check the timing chain and flywheel position

I swear i went over the timing 100 times. I changed the CDI twice to 2 of my spares from running motors. I swapped out the stator from a running motor.. The one thing i never checked was a "spun flywheel".. what is that? Like saying I sheared the woodruff key that mates the stator to the flywheel? This term I'm not familiar with. It would definitely explain the timing being way off and hte motor not firing if the flywheel sheared the key or something like that. The valve timing is perfect as well, did not skip any teeth on the cam sprocket or anything like that.

and just turn the gas off, drain the float bowl then spray flammable brake cleaner or starting fluid in it to see it it will fire.
.

I spent at least an hour doing the ether spray dance in the carb and kicking the starter like a madman.. choke on/off and all over the place.. nothing. when i bolted one of my spare motors up it fired up halfway through the first kick lol.

[HairyJR]

....then one of the valve adjusters backed itself out and I took it out, fixed the valve adjuster (checked the valves and saw no signs of piston making any contact at all with valves at any point), and put it all back together.

I'm guessing I did some kind of damage to the head when the valve adjuster backed out that I just can't see (nothing obvious/visible)?

when I first read your original posting the my first red flag thought was the cam shaft had been damaged due to lack of oil and you made the lash adjuster adjustment correcting for wear damage. Which valve adjuster came loose? You stated the adjuster was fixed, does that mean you removed the screw, cleaned/dressed/filed the mushroom end and reinstalled? Next you say you checked the valves to piston for contact none seen, does that mean you removed the Head assembly or did you just look thru the spark plug hole?

You mention it has kick starter compression and as the motor is out and setting on your work bench now you can't check it. An official leak down is the next option or the "poor man's " carb cleaner check as mentioned above. Hell even just using compressed air applied thru the spark plug hole and listening to escaping air in the intake/exhaust ports could work.

Finally or maybe first and easiest could be to check timing for piston TDC in relationship to the generator rotor TDC marking located by the wooddrift key. With the spark plug removed stick a small round rod (maybe a straw/coffee stir stick) to the piston and rotate the crankshaft back-in-forth to find piston TDC. Now inspect to verify generator TDC marking. If its off then the cam and pulse rotor timing are out of sink to TDC as the key has sheared.

"HJ"

[yamasaki760]

Which valve adjuster came loose?

The intake

You stated the adjuster was fixed, does that mean you removed the screw, cleaned/dressed/filed the mushroom end and reinstalled? Next you say you checked the valves to piston for contact none seen, does that mean you removed the Head assembly or did you just look thru the spark plug hole?

Yes, I took the whole top end apart to inspect for damage. The piston still looks like it came out of the box, nice and shiny, not a scratch, dent, chip, etc.

The valves have no sign of making any contact with anything. no chips, dents, scratches, etc. They look good.

You mention it has kick starter compression and as the motor is out and setting on your work bench now you can't check it. An official leak down is the next option or the "poor man's " carb cleaner check as mentioned above. Hell even just using compressed air applied thru the spark plug hole and listening to escaping air in the intake/exhaust ports could work.

I'll try compressed air tonight and see if it's coming out somewhere. never thought of that.

Finally or maybe first and easiest could be to check timing for piston TDC in relationship to the generator rotor TDC marking located by the wooddrift key. With the spark plug removed stick a small round rod (maybe a straw/coffee stir stick) to the piston and rotate the crankshaft back-in-forth to find piston TDC. Now inspect to verify generator TDC marking. If its off then the cam and pulse rotor timing are out of sink to TDC as the key has sheared.

I've checked the timing 100 times and I even reset my air coil gap at .30mm to make sure there wasnt too much space there causing it not to fire. Last night I pulled the flywheel off and the key was still in there and looked normal as can be.

I'll try to post some pics tonight too so you know I'm not totally nuts.. I think I'm doing everything right (my spare motor I built myself runs just fine).

For my next test.. I'm gonna try to swap my head and cam on this motor for another stock head and stock cam just to eliminate any valve issues not obviously visible. It's gotta be something simple/stupid.. I just haven't found it yet.

The head on this block has HD springs and new oversize valves and the cam is a FST cam.. Maybe I did damage one or the other and just can't see it.

[yamasaki760]

Last show offy pic I promise

[oscarmayer]

the CDI, when the piston is at TDC, the cdi rotor is pointed where?

[yamasaki760]

the CDI, when the piston is at TDC, the cdi rotor is pointed where?

At TDC, the the line in the center of the pulse generator is perfectly lined up to the line on the pickup coil

The air gap between the two has been set/confirmed at .30mm

That said............ however....... comma.....

The one weird thing i did notice is that with this cam, at TDC, in order to line up the two marks, the pickup coil is almost at full retard.

With a stock cam, it's almost perfectly centered when they're lined up. I shrugged this off as this being somehow due to the custom cam grind and more complicated things about motors i dont know/understand? That is the only "weird" thing I've noticed.

My stock head/cam test should confirm this theory. Unfortunately I've been working later and later and havent had much time to dedicate to this project lately

[oscarmayer]

can you manually and easily wiggle the cam? also when you installed the cam, did you install it with lobes down or up? I have seem some cams that could be installed either way and if that is the case, you could have lobes up instead of down. lobes down means both valves closed.

take carb off. spray some carb cleaner into the intake and attempt to fire off motor.

[Jmoozy27]

You may need to advance the timing some.

[yamasaki760]

You may need to advance the timing some.

yeah i thought the same thing .. i kicked that motor 4,371.3 times with timing slowing getting advanced every few kicks.. changing out plugs in case they were fouled, flooded, etc... you name it , i tried it..

[yamasaki760]

can you manually and easily wiggle the cam?

yes, it doesnt appear bound up and i did put the thrust washer as well

also when you installed the cam, did you install it with lobes down or up? I have seem some cams that could be installed either way and if that is the case, you could have lobes up instead of down. lobes down means both valves closed.

i set it lobes down. ive thought about flipping it to lobes up but havent tried it yet

[yamasaki760]

Ok, here is that weird thing I was telling you about yesterday.

These two pics were taken within 1-2 seconds of each other. :-)

Note that at TDC, the pulse generator and pickup coil are lined up perfectly, however, its at full retard. That struck me as really weird, right?

Even if i advance the timing, it wont fire though. Is this the root of all my evils?

P.S. I swear I uploaded these pics upright. I don't know why they're getting rotated like that. WTF.