Starting Reassembled Engine

[Houseman39]

Thanks to all who helped me on my previous thread! (Reassembling the engine - check it out here http://www.xs400.com/threads/kick-start-locked-up.16804/). Now that I've got the new crankshaft and rods in and the whole engine reassembled I'm trying to breathe life back into my 1980 XS400 special.

I'm able to start the engine, but only with the throttle wide open. It stays running (both cylinders) at ~500 rpm as long as I hold it open, but as soon as I close it the bike sputters and dies.

I adjusted the valve clearances and cleaned the carbs out twice, but to no avail. Tried spraying carb cleaner in while running but no change. I have enough compression to blow my thumb out from the hole. Everything with my timing and camshaft looked proper when I adjusted the valve clearances, and I don't have points.

My brain is saying it could be:
1) Spark is too weak so gas only ignites sometimes (how weak is too weak). But on both sides at the same time? Battery is fully charged so that doesn't seem likely.
2) I did a poor job reassembling something in there and all the power is going into that friction, not into RPMs. The bike kicks over easily enough, so that doesn't seem like the issue either.
3) I adjusted the valves improperly. I can hear them in there tapping away when I listen, but these bikes are supposed to be loud, right. And I double checked every one. A problem on both sides at the same time? Maybe I just suck at adjusting them.
4) Carb is still dirty. Wouldn't spraying carb cleaner in there while running help in this case?

Any of the above problems I can probably rule out? Or that you think I should prioritize checking out? Or any ideas I missed? Or tests I can run to get more info? I'm an engineer so I love troubleshooting

I appreciate all the help I can get! I'm grateful to have the engine at least start after it was in pieces in the garage I've learned so much already, and I'm ready for more. Bring on the knowledge!

 

[spectra]

When cleaning the carbs where did you pre adjust things to ?

Just seems odd that it wont at least run.......I have had a few that I can get to rev high then have to tweak them to get to idle and run smooth.

 

[Houseman39]

I've had the floats at 26mm and at 32mm (I have the round brass ones) and the pilot screw at 1.5, 2.5, 3.5, and 4.5 turns out

 

[drewpy]

did you def check the valve timing is correct?

I've double checked on my fz and it was still out by 1 tooth, wouldn't rev either

 

[xschris]

I've had the floats at 26mm and at 32mm (I have the round brass ones) and the pilot screw at 1.5, 2.5, 3.5, and 4.5 turns out

Should be 26mm.

 

[Petew]

Should be 26mm.

That is where miine works best and starts easiest

 

[Houseman39]

Ok great I'll keep the floats where they are at 26 and won't experiment there.

did you def check the valve timing is correct?

I've double checked on my fz and it was still out by 1 tooth, wouldn't rev either

When I lined up the LT mark both left cylinder valves were disengaged every other cycle and slightly engaged every other cycle. Same on right side. If I was off by 1 or 2 teeth would It be enough to notice there, or is there a definitive way to check? Just uninstalling and reinstalling the camshaft?

 

[spectra]

I would think it would make a difference. Also when turning the crank you did go counter clockwise and also hold the wrench with something so it did not go clockwise? I know on all the ones I have done I needed to hold the wrench in place otherwise it would turn.

 

[Houseman39]

The bolt wasn't tight enough so when i turned ccw it came undone. Therefore I spun the crank clockwise to line up the marks (is that bad?). I continually checked the mark while I was adjusting and the crank didn't try to spin. You think that right there is indicrative of a problem?

 

[spectra]

The bolt wasn't tight enough so when i turned ccw it came undone. Therefore I spun the crank clockwise to line up the marks (is that bad?). I continually checked the mark while I was adjusting and the crank didn't try to spin. You think that right there is indicrative of a problem?

Tighten it and then turn it counterclockwise and adjust.......page 5 read it as it explains how its done. You can also put a wood dowel down the spark plug hole to verify you are at TDC. http://www.xs400.com/attachments/xs400_manual_part1_engine_clutch_gearbox-pdf.3894/

 

[Houseman39]

Got out there for an hour today in between rain...and I think I found the problem!! Valve clearances still looked good after spinning counterclockwise, so I pulled the head cover off. The cam chain sorocket definitely looked off by 1 or 2 teeth- check out the picture. When I correct that tomorrow I'll probably have to reset all those clearances, so good thing I'm a pro at it now!

Took this with crank lined up at LT

 

[xschris]

Looks like your cam chain is missing a rivet. All the way left in the pic and the last one showing.

 

[drewpy]

yep, like I said cam timing out.

I'd def check that cam chain rivet out

 

[Houseman39]

Good eye on the rivet! I replaced it and fixed the position of the timing sprocket/chain and it started up beautifully!! Interestingly enough I didn't have to change any of the valve clearances. Now I've just got to iron out the miscellaneous issues: Oil leak(s), exhaust leaks, and turn signals. Thanks for all the help hunting down and solving everything this bike threw at me!