Exhaust Porting

[petejw]

Hey guys,
Was just reading a thread about exhaust porting.
Ive just finished doing mine
heres a few pics...

before


after

[petejw]

that time out edit sux

cont..

The engine that it went on had been sitting for years and burning oil,
this head was off my seized engine,
all valves were lapped and leak tested.

The result was that it pulled much harder thru out the rev range, especially at 6000rpm BUT ive got a buzz/vibration around 5000rpm
this improved when i removed the 4-2-1 and put back the 4-1 exhaust, but moved the vibration
down to around 3000rpm.

Im not really happy with it atm, im still trying to fine tune it, the buzz is annoying and
its no way as smooth running as it was before.

Im also running rich at off idle under acceleration, ive tried several things to correct this, the best being dropping
the float levels to 24mm this helped a bit but i lost acceleration,
i put the floats back to 23mm.

I beleive the vibration is caused by the fact i took to much out of the exhaust port, and
took out an uneven amount of material between the ports, i tried to keep the same profile of the ports.

hopes this creates some discussion,

[XJOK2PLAY]

ok... now I'm intrigued!
My question is, how would porting cause a vibration in a particular RPM range? By changing pressure somehow?

I can understand mixture change, (especially if combustion chamber "swirl" has been altered negatively,) but I'm having a hard time seeing how this could cause a vibration.

I could understand it if something was goin' on in the bottom end... like worn bearings, or something like that.

I'll stay tuned... this could become informative!

[XJOK2PLAY]

One other question, Pete...

You're sure it couldn't be from any of the engine mounting bolts or something else being loose causing the vibration?

I do know how it is sometimes - if you didn't have the vibration before you worked on it, and now you do... makes one think it has to be something that was just done...

But, I've also been fooled before, too!

But, don't get me wrong... I'm giving the benefit of the doubt here that all the obvious has been checked first.

If it is head re-work related... I'm gonna learn something... and that's always cool!

JAT.

[petejw]

Hey Xj,
Not sure why it would cause a vibration, i was thinking that
maybe it was caused by uneven material to be taken out of the ports, i tried
hard to keep the same profile as stock, other than burning oil,
this was a really smooth engine.

Im cleaing up the other head that came off, wont b porting it just polishing
the exhaust ports as best i can.

Ill stick up a vid of how its running.