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Cause for concern? Seriously odd pipe discoloration...

11K views 47 replies 19 participants last post by  Stinky Pete 
#1 ·
Ok - so I've been screwing around with the shovelhead timing and finally got a good startup.

Here's the setup - '76 stock displacement motor, Andrews B grind, Super E carb (jets unknown), Morris magneto timed with a buzz box at the advanced timing mark with Autolite 4265 plugs.

My best start method to-date has been no primer kicks, no throttle squirts, no enricher. Trying to gas it just seems to wet the plugs.

Yesterday when starting the pipes got a crazy discoloration. I figured it was too advanced. I retarded it different amounts and but couldn't get it to fire.

Today I polished the heat marks of the pipe and reset timing to recommended and started it right up. Two kicks, no help with the gas. Let it run for about two min, no enricher and would idle on it's own.

Take a look at the pics and tell me what you can discern. The discoloration is exactly the same as yesterday. To me it's spooky how pronounced the cutoff in color is.

Front pipe:


Rear pipe:


Pipe design:


Plugs look good (for two min idle):


Thoughts?
 
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#39 ·
Yes on oil return to the tank.

Old Wrench - that's what I was wondering when the speculation is that it's running lean, but all you would think is running rich because if the set up (jets, air cleaner and pipes). I noted some high-temp RTV between the jugs and the manifold...maybe that was also to put down a leak.

I finished the blocking plate last night, but didn't test. I did a quick search, but didn't find what I was looking for...just put the piston to TDC to test?
 
#40 ·
...I finished the blocking plate last night, but didn't test. I did a quick search, but didn't find what I was looking for...just put the piston to TDC to test?
Pete!

Just kick the motor through until both of the intake valves shut,
your regulator will make up for leakage:
http://virtualindian.org/11techleaktest.html

Be sure to wash dish soap off thoroughly, as it is corrosive.

....Cotten
 
#43 ·
I watched the video of it running and heard it cutting out every once in a while and i'm assuming the idle is up so high to keep it from farting through the carb and dieing.

I think you have an intake leak, you said there was silicone on the intake at the head? Take the intake manifold off and clean everything, put it back together, then pressure test.
 
#46 ·
Sorry - to be clear I'm using a blocking plate with a rubber gasket on the intake manifold. Closing the intake valves, putting in 15psi air and spraying with soapy water to check for bubbles.

The leakdown tester was a recommendation from a friend to check the exhaust valves. It looks like (based on the literature) it will "tell" you you have an intake leak if you hear air escaping through the intake, however I tested my intake using the method above.
 
G
#47 · (Edited by Moderator)
The pressure test is only good from the face of the valves (Intakes) to the face of the intake manifold....Shows how well the O-Rings/Bands are sealing...Be hard to know about the seating of the valves on their seats in the heads... Outside of hearing air escaping from the spark plug hole.



A Leak-Down test shows this loss as a percentage on a gauge...
It only works on the combustion chamber.
This consists of the piston ring seal to the cylinder walls, both valves on their seats and the head gasket....



You will hear air from the carb if the intake valve has a problem ...Same for the exhaust..
A loss past the rings is called "Blow-By" if a high percentage is shown on the gauge, you can pull the timing hole plug and hear air ....

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#48 ·
Ok, after lots of delays I ran the leakdown test this afternoon. Also negative for leaks.

Yesterday I couldn't get the bike to start, today it fired right up first kick. Moody summa a .....

Anyway - running it a bit to warm it for the leak test, the discoloration continued to move down the pipe.



They're noticeably hot before the rest of the the bike warms up. It ran well (as in stayed running) and would hold an idle. The plugs now appear to be fouled...looks carbon fouled.



I still have timing per the factory instructions and haven't screwed with the carb. I'm wondering if I should reset the carb. I've never messed with it, I'm not sure if going back to the factory setting on it would help or hurt.

I'm stumped - this sure isn't my domain. Just want to go for a ride. Thoughts? Thanks.
 
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