Top End Rebuild?

Lifter · 06-28-2016, 09:14 PM

Hello Again Everyone!

I tried to troubleshoot by bike problem with no results...

I brought it into my local bike garage and got the following diagnosis and was looking for help with the next step.

PROBLEM:
After the bike has run for a couple of minutes, it begins to stumble and studders. This happens a couple of times before it eventually stalls.

SELF TROUBLESHOT (Work verified by garage tech)
- Adjusted Valve Gaps
- Checked Petcock
- Trouble Shoot Voltage Regulator
- Cleaned Carb

GARAGE DIAGNOSIS:
- Vales are both leaking a bit (Leak down is 10%)
- Can hear air leaking escaping from intake and exhaust
- Compression 140PSI (GOOD)
- EXHAUST IS DRILLED - Suspect this may have burned valves (see attached pic)
------------------------------
- Should do top end, Valves and Rings

NEXT STEPS?

I was hoping to get two questions answered:

1. Does this sound like a reasonable cause
2. Does this sound like the correct fix?
3. Any details on parts: What do i need to buy? Any article to
follow?

Thanks in advance again!!!!!

spldart · 06-28-2016, 09:21 PM

Drilling the exhaust will not, I REPEAT 'WILL NOT', cause damage to the exhaust valves all the way back there.
If you had no exhaust to 4 or 5 inches of pipe then open air... then yes.
If you had terrible seal from pri pipe to head itself then definitely possible.
But those holes at the end of the pipe will not cause valve damage if you have good seal pipe to head.

Is the 140 hot or cold?
When the bike warms up and starts going tango uniform have you done a leak down then?
If so what psi then?

At this point getting a full gasket set + exhaust seals then doing a tear down inspection may not be a
totally bad idea. But
I can't remember the other thread...
Swapping a used carb on the bike, after a clean of course, might be a cheaper next course of action.

blaine · 06-29-2016, 08:39 AM

I agree......Drilling the exhaust would not burn the valves.As stated if exhaust leaking at head than yes.

wacio · 06-29-2016, 10:05 AM

Your problem sounds like ignition problem. If it was valves leaking too much you would not be able to start it. I would recheck valve clearances just to be sure and than concentrate on ignition. Check if coil has right resistance on primary and secondary windings especially when hot. Also check if key under flywheel is undamaged. Make sure that you try to run bike with petcock on "prime" while diagnosing.

06-28-2016, 09:21 PM	#2
spldart Senior Member Join Date: May 2015 Location: Stafford, Texas Posts: 604	Drilling the exhaust will not, I REPEAT 'WILL NOT', cause damage to the exhaust valves all the way back there. If you had no exhaust to 4 or 5 inches of pipe then open air... then yes. If you had terrible seal from pri pipe to head itself then definitely possible. But those holes at the end of the pipe will not cause valve damage if you have good seal pipe to head. Is the 140 hot or cold? When the bike warms up and starts going tango uniform have you done a leak down then? If so what psi then? At this point getting a full gasket set + exhaust seals then doing a tear down inspection may not be a totally bad idea. But I can't remember the other thread... Swapping a used carb on the bike, after a clean of course, might be a cheaper next course of action. Last edited by spldart; 06-28-2016 at 09:34 PM.
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06-29-2016, 08:39 AM	#3
blaine Senior Member Join Date: Feb 2010 Location: P.E.I. Canada Posts: 3,784	I agree......Drilling the exhaust would not burn the valves.As stated if exhaust leaking at head than yes. __________________ If at first you do succeed, try not to look surprised. Login or Register to Remove Ads
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06-29-2016, 10:05 AM	#4
wacio Senior Member Join Date: Apr 2016 Location: Illinois Posts: 174	Your problem sounds like ignition problem. If it was valves leaking too much you would not be able to start it. I would recheck valve clearances just to be sure and than concentrate on ignition. Check if coil has right resistance on primary and secondary windings especially when hot. Also check if key under flywheel is undamaged. Make sure that you try to run bike with petcock on "prime" while diagnosing.
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