77 GS 750 - Need Help!! Smoke From PCV Breather / Running Rough When Hot

[Rustishacklefrd]

Need Help

1977 Suzuki GS750 - Pod Filters 4-1 Exhaust

I had low compression. Found 0 valve clearance. Sent head to machine shop to grind valves (thinnest shims were not enough) and replace valve seals / machine the seats.

After re installation I had a ton of white smoke with a combustion odor from the crankcase breather. Assumed it was worn rings (65k miles) and now that the valves were sealing it was now causing blow by.

Had shop gap rings and hone cylinders. Re installed everything and did proper break in procedure on first ride. (Ran well enough to complete break in before it started to run poorly) I still have a ton of white smoke from pcv breather. (Did not clean the two tiny filters under the pcv cover)

Also, Bike runs well once at temperature l. But within about 10-15 min into ride the bike does not want to idle, losses damn near all power and backfires from exhaust / pod filters.

It is currently 90+ degrees here.

I can hear the gas tank venting and when removing the cap it nearly blows off.

Any thoughts on the white smoke from pcv breather / excessive fuel tank pressure / runs poorly when hot.

As for the running rough / fuel tank pressure I am wondering if I could be dealing with a vapor lock situation but if it is due to the outside temps I dont know how to overcome that.

for the smoke. You would think rings or valves / valve seals but that has all been done. (Oil level checked and okay - not overfilled)

Appreciate your help!!!

[Rustishacklefrd]

Only thing I can think of is the Aftermarket O ring around the timing chain opening is thicker and not allowing the cylinder head / head gasket to fully seat causing combustion to enter from the cylinders. Other orings in this set were thicker than oem.

[Rich82GS750TZ]

There is no Positive Crankcase Ventilation valve. Just a vent for oil vapor to leave the the top of the engine and collect as a miniscule amount in the airbox, to be emptied out periodically or drain to ground. In lieu of an airbox, some pod runners have installed a small catch can or small pod type filter at the end of a short hose connected to the breather nipple on top of the valve cover.

"Also, Bike runs well once at temperature l. But within about 10-15 min into ride the bike does not want to idle, losses damn near all power and backfires from exhaust / pod filters............I can hear the gas tank venting and when removing the cap it nearly blows off."
This means your gas cap is not venting properly/has a blockage/ needs to be addressed. If your fuel tank is not letting air in the top, it can't reliably gravity feed the carbs and bike will struggle to run.

[unfocused]

If you're running VM26's did you install the much needed air correctors ?

My issues were similar as I rebuilt the top end on my 77 GS750.

The smoke coming from the engine breather isn't an issue as the motor still needs to seat in. This isn't something that happens on the first ride.