Smoke back through carbs

[Ben Coyle Racing]

Is it normal for exhaust smoke to come back up through the carbs at high revs ?

[cargo]

No
Please do explain further

[Ben Coyle Racing]

Well basically, when the bikes revving at about 10,000 rpm+ smoke comes out from the carbs ? Alot of it tbh, its exhaust smoke..

There is not much smoke coming from the exhaust though either, there is some but no where near as much as what it should be...

Would it be the exhaust camshaft ?

[cargo]

Cant imagine that it's the exhaust camshaft that is allowing "exhaust smoke" to find it's way out through the inlet valves.

I would question if this "exhaust smoke" is actually exhaust smoke and I also am wondering how your seeing this @ 10,000 revs

A fully warmed engine wont actually produce that much visible exhaust smoke out the exhaust.

The only way for exhaust smoke to get out of the cylinder and out through the carbs is if the inlet valves are open on the exhaust stroke so much so that I doubt the bike would start or run under such circumstamces...............because the inlet valves would be closed on the induction stroke and so no fuel would be drawn in no fuel means no start ????

Confused I am

[Ben Coyle Racing]

Yeha its definatly exhaust smoke coming back up through carbs

Its ok i'll pull engine to bits and take a closer look

[cargo]

have fun

[Dolts]

I would have thought it was pretty impossible for smoke to come out of the carbs due to the vacuum created drawing the air in to make it run in the first place? Is it a possibility that it is fuel vapor?

[Dolts]

Did you ever get to the bottom of this?

[Mori Man]

How about small exhaust valve gaps and chambers aren't clearing so once inlets start opening it's escaping but that even sounds bonkers

Burnt out valves badly seated with small exhaust valve gaps and its being pushed out through what should be closed inlets

Both combinations sound like it would never start , never mind reaching 10K with out going bang

Got to be vapour , even after running the bike and pulling the carbs "smoke" will come out of the inlet tracks - you smell it but it's not 100% petrol smell as its been atomized

Cause I run strainers on the TMR's after a good howl my jeans reak of stale fuel yet it's fresh - videoing them with me giving it big hand fulls reveals the vapor coming out plus the fact the strainers become very brown after a while. However the dyno showed it fueling near perfect so nothing untoward is happening.

Let us know how you got on,

MM!

[noelb]

If its appearing out of the airbox it could possibly be knackered rings allowing it to breathe heavily through the breather pipe (should still be sucked into the inlets though... would have to be bloody heavy). If its a fog appearing at the carbs as the engine is revving it might just be fuel stand-off. Just a phenomenom caused by positive pressure pulses causing atomised fuel to appear outside the bell mouths at certain revs. Its more of a fog than exhaust smoke though......Cryptic!

Noel B.