1979 GS750L project - PO had the carb vents blocked on #3 and #4 - for some reason

[Guest]

PO had the carb vents on #3 and #4 blocked on my 1979 GS750L project, wondering what effect that would have? the bike ran pretty well on it's three very short test runs, although mix appeared perfect on #1 and rich on the remainder. bike is up for winter storage so carb tuning will have to wait.

but i am curious as to the effect of the blocked vent tubes? lines were attached to the vent nipples on #3 and #4, then blocked with a plastic plug. items "C" and "D" on pic.

resized.again.jpg

[Big T]

To help clear things up, A&D are the vents. C is the vacuum port for the petcock

A&D should have hoses running up over the air box and down the back
C should connect to the petcock, or be capped

[Steve]

Big T is probably correct, but it's hard to tell with a small picture.

.

[standswithabeer]

thx mr t,
not sure why the PO had vents on carbs #3 and #4 blocked and petcock line on #2, but i'll install new lines as you describe. he also had a 6 inch crankcase breather line installed, and blocked with a bolt. that's been removed.
bob p

[KEITH KRAUSE]

The two float bowl vent ports at carbs #2 and #4 should be open to allow the bowls proper venting. Fuel wouldn't flow well with them blocked. If you have a stock intake, the ports should have lines attached and run under the seat. I'm not sure of the exact length on your 750 but the lines terminate right at the end (rear) of the air filter housing on a '79 1000. If you run quality pod filters the ports should be open but no lines connected. Running pod filters changes how the stock venting performs. If you run pod filters with the lines attached, you will experience fuel starvation to some degree, especially in windy conditions. Dynojet tells you to remove the lines in their stage 3 jetting kits for this reason.
The port at carb #3 is to provide vacuum for the stock petcock. If it was blocked, it must mean that bike used a fuel valve from Pingel or ? that didn't require vacuum.
If the crankcase vent line was blocked, the person who did that shouldn't work on a motorcycle.

[scratch]

Hillbilly float height adjustment.