https://www.youtube.com/watch?v=U_CosKihFlI (https://www.youtube.com/watch?v=U_CosKihFlI)
Had this problem once, with time it stopped, never knew what it were..
something in the carbs?
Valves?
Loose Exhaust ?
How should be named this type of failure?
You can actually see like a grey smoke and pulverized fuel going backward with a hollow pop very dry sound.
Too lean or too rich mixture
Lean or rich can cause backfiring. You can see that it is a backfire and not an afterfire, (popping in the exhaust). Perfect video :thumb:
Things to check:
Valve clearances
Timing! (doubt it very much on these, but worth a check it's quite easy to do if you're checking the valve clearances)
Carb balance
Needle settings
Float height
fuel/air mix screw setting.
Quote from: Armandorf on February 20, 2019, 08:38:05 AM
You can actually see like a grey smoke and pulverized fuel going backward with a hollow pop very dry sound.
I saw this same phenomenon with mine while I was getting the carbs dialed. I have a theory but it's only a theory. It could just be a delusion, I'm not that sort of engineer.
During the intake cycle, air is drawn through the carbs, a mist of fuel is added and so on to the combustion chamber. Then the valve closes but the air is still in motion. So the air compresses slightly under it's own inertia then bounces back through the carb body and because it contains fuel vapor, you see it as a little cloud at the intake of the carb. Of course that little cloud then gets drawn back into the carb at the next intake cycle which is only a tiny fraction of a second away. At speeds faster than idle the pressure wave of air doesn't have time to escape the confines of the carb and if the air box is on you can't see it anyway. This is why we can see fuel deposits to the rear of the jets which never made much sense to me before. The popping sound is the diaphragm slides going up and down which can be seen and heard at idle with the air box off but are not visible and the sound is muffled under normal conditions and they don't hit bottom at speed.
I think you are close.
Something very strange i noticed in my carbs is that the needles have a greenish oily gas residue. nothing to worry, clears easily but its strange.
thisresidue is in the plastic needle clip above diapragm, like it is vapor residue of gas.
I retract what I said earlier. Hadn't watched the video until now. :cool:
I think the list of possibles from Numewsm is legit. Though maybe not in that order. I'd start with checking float height using the slack tube method, and save the valves for last (unless they're due anyway). In other words, do the simpler stuff first.
Your green goo is likely a bit of copper corrosion from the brass bits in the carb. Maybe there's something I'm overlooking but that's what seems most likely to me.