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Discussion Starter · #1 ·
The 1976 Bonney has sat covered in the garage for about eight years during which time there were a couple of half-hearted attempts to get her running. Prior to that, the top end and the cylinders were done and have about 3000km on them. Now the old gas is out, the tank cleaned and the carbs rebuilt. A Boyer system is sparking reliably.

But we have a problem. the left cylinder is not firing at idle. In fact, it will not draw fuel at revs under 3000. When it does fire, it draws well and revs hard till it winds down after a few seconds. Covering the intake on the faulty cylinder eventually induces a few sporadic detonations but only while fully choked.

And there is blue smoke. During the storage years, I had oiled the plug hole and kicked her over a few times every year. The resulting oil load in the cylinders most likely the source of much of the smoke but, I still have doubts. The smoke was reduced after it ran a bit but comes back strong when it revs.

Looking back 8 years (yes its hazy) I seem to recall it was starting to smoke and the problem cylinder tended to cut-in/out at high/low revs, so this has been a problem for quite a while.

So here is my question. The smoke seems to suggest rings but the intake suction problem might be valves. How might I sort this out? Any ideas?
Thanks in advance
RR
 

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Discussion Starter · #3 ·
The carbs have been totally cleaned and rejetted. The problem seems to be related to a lack of suction at the intake and the fact it is blowing blue.
 

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Did you poke something through the pilot bush or jet?

Carburettor cleaners don't usually work on it and I seriously doubt that you renewed that jet.

As for a cylinder failing to suck through the carburettor, that can only be a simple fault. Is air
leaking into the manifold? Is the exhaust valve burnt or so badly adjusted that it's failing to close?

But the cylinder does suck when you choke the carb.
 

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Discussion Starter · #5 ·
Triton, you are right I didn't re-jet the pilot. I used a guitar string to clean it and the carb cleaner will blast through with no problem. I'm pretty sure its clean.

But the exhaust valve might be the issue. In your experience, do you think sitting for a long time could cause a valve to seize-up?

RR
 

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No I haven't seen that happen.

And the valve clearance would go funny.

Can you feel compression on both cylinders?
With smoking issues and rough running after a long sleep in the garage, a compression test should tell the story.
Blue smoke is likely rings or valve guides. It was stated earlier in the thread that the top end had been done up at some point? Was it properly run in to bed the rings?

A sticking exhaust valve or rusted valve face could easily explain the lack of vacuum on that barrel.

Compression test....
 

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I've been told that if you squirt a small amount of oil in the suspect cylinder, screw in the compression gauge hose, kick it over a few times and the compression goes up on each kick it is the rings. If it doesn't, it is the valves, I'm guessing the oil will momentarily seal around the rings/piston.
 

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I've been told that if you squirt a small amount of oil in the suspect cylinder, screw in the compression gauge hose, kick it over a few times and the compression goes up on each kick it is the rings. If it doesn't, it is the valves, I'm guessing the oil will momentarily seal around the rings/piston.
First off, the compression gauge will go up in steps incrementally with each kick on a sound engine until it reaches its maximum reading. He should take a reading before and after adding oil to the barrel.

if adding a few squirts of oil to the barrel in question results in a higher maximum reading on the compression gauge, the rings are suspect. Oil would have marginal effect on a bad valve seat.
 
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