Initial start after rebuild --- Problems....

[bsdoig]

Initial start after rebuild --- Problems....FIXED 4-22-11!!!

Just got the rebuild done on my 77xs. Installed pamco ignition, dual coils, new pistons, rebuild head, all new gaskets, and carbs rebuilt by old school carbs.

When kick started bike cranked in less that 10 kicks. Ran on choke. And when taken of choke would idle down. However on the right side cylinder sounded like it was mis-firing as you could hear it through the exhaust. The intake would also spit/pop fuel out.

Checked:
Swapped plugs- no change
Swapped wires- no change
Checked compression- same on each
Checked valve lash- good
Cam chain tension- good
Cam Position- good
Timing- good
Intake boots- OK
Carbs- Appear OK

The right plug doesn't appear to have soot or fuel. What's weird is the bike will idle and doesn't appear to run awful. Just the off sound at the exhaust and spit at the intake.

Any ideas? Right now I'm thinking carbs but the idle appears to change when mix screw is adjusted.

 

[BigJimmyW13]

Gotta timing wheel and light laying around there?

 

[bsdoig]

Gotta timing wheel and light laying around there?

Yeah have a timing light handy, but the timing mark seems to be kinda erratic . I've got it as close as I can for now.

 

[cpt137]

Make sure you aren't off 1 tooth on the cam. It's an easy check and I had similar issues.

 

[bsdoig]

Make sure you aren't off 1 tooth on the cam. It's an easy check and I had similar issues.

I don't believe it is.... How would I check?

 

[Sundie]

pull off your pamco maget. the pin should be straight up every other tdc.

 

[bsdoig]

pull off your pamco maget. the pin should be straight up every other tdc.

Checked the cam position using this method and it appears to be spot on.

 

[bloodthirstysystem]

adjust cam chain, then check that the pin is straight up or down. after cam chain check valves again.
set timing with a light, if erratic timing marks with a pamco use the other plug wire.

10 kicks is bullshit. clean the carbs yourself, maybe they did a bad job

 

[pa23driver]

sync the carbs

 

[bsdoig]

Messed with it some more tonight. Confirmed the cam chain tension was correct, re-adjusted valves, pulled and checked carburetors, checked intake boots, and confirmed cam position. Still no change.

I also pulled the exhaust off and there appears to be carborn, so it is firing.

With the filters off it will mist fuel outward at the right side carburetor w/ throttle applied. I'm completely stumped....Any thoughts?

 

[CDNTX650]

did you sync the carbs?

 

[bsdoig]

did you sync the carbs?

No not yet.... Can carb sync really effect it that much?

He said the carbs were bench tested....is that the same?

 

[azman857]

Bench sync gets the carbs in the ballpark, but carb sync get your motor running smooth. Too many variables in each intake track that effect the air flow.
Are you sure the all the jets are the same? Floats swinging freely? Float levels in spec? If your timimg light is erratic, try flipping the timing light's sensor over and hook up that way. I wouldn't believe it would make a difference, but did it and the light smoothed right out and got good readings.

 

[bsdoig]

Well got my hands on a manometer, so i'm gonna try and sync the carbs over the weekend.

It still bothers me that I see air/fuel spit outward from the carburetor. Really makes me think the intake valve isn't fully closing. Visually with the carburetors removed the intake/exhaust valves appear to be closed at TDC, and the compression test shows the same on both sides.

Being a 30year old motor going through god knows how many hands, could there possibly be an earlier year cam in the motor creating this condition? From what I've read the earlier years have a longer duration cam? I'm gonna triple check cam chain tension and valves lash one last time as well.

Also, would a leak down test show something a compression check wouldn't?

 

[bsdoig]

Got home a did a little more investigating. It seems as though I've found the problem. The right side head pipe collapsed midway through the inner pipe. I have no clue how this could have happened, as there was no visual damage to the outside of the exhaust pipe!!! Guess what bike runs great now!



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[Ironriot]

Wow! I wonder how the hell that could've happened. Either way congrats on getting it running

 

[Gordon]

That is not the first time I've seen that on these bike's. It does happen quite often, but we don't see allot of it here anymore because most swap out the stock pipe's for a tuned pipe. The easyest way to tell, apart from taking them off and rolling a golf ball through them is feel for exhaust coming out the water vent in the bottom of the pipe. Use the bottom hole, because you can confuse normal heat as exhaust coming out of the top, unless you have a gas analyzer.
Anyway, real glad to read you found your problem.

 

[pa23driver]

thats pretty crazy, i'm still running the stock head pipes on my bike, got me thinking maybe its time for new pipes as well...

 

[XSLeo]

I think water gets down in there, when it freezes it crushes the inner pipe.