1978 GS750 carb adjustment ?'s

[Jesse002100]

i have a 4 in to 1 header and k&n pods the jets have been replaced as specified by the kerker specifications. the bike is a bit lean and needs to be switched to prime every couple of minutes to fill up the bowls. im wondering if i adjust the mixture screw it can solve my issue?? and ideas as to what it needs to be at or close to im at about 1.5 turns out now

Thanks, Jesse

[TheCafeKid]

K, if youre bowls are falling off, check your petcock FIRST, then move on to the jetting. It sounds like your petcock is faulting, and not flowing fast enough, OR your gas cap vent isnt working properly.

[Jesse002100]

can you explain abit on how to check my petcock and gas cap vent ill tear it all apart here in a few and look at what i need to figure out??
Thanks again cafe you seem to have loads of knowledge on these gs bikes maybe one day ill come out to take a ride with you after i get all my issues sorted out
Thanks again

[TheCafeKid]

Your bike, if its STOCK, (id need a pic to tell) uses a vaccum operated petcock. It requires vaccum signal from the motor turning in order to allow fuel to flow thru it in the RUN (or ON) and RESERVE (RES) postions. IF you dont have the vac line hooked up (on your carbs, it would be the small line running from the top of the third carb from the left if you are sitting on the bike [btw, they are numbered that way, 1-4 left to right sitting on the bike] connected to the small nipple on the petcock) it simply wont flow unless its on prime. The easiest way to test this is to attach a temp fuel grade line to the output on the petcock, set it to on, with the vac line properly attached to the carbs, and crank the motor...if it flows while the bike is running, its probably pretty ok. However, these things ARE 30 years old, and DO GO BAD eventually, no matter how well the bike was maintained. You can purchase, if you find yours at fault, a OEM style VACCUM petcock (please PLEASE stay away from a Pingel..they work great when YOU work great) from www.z1enterprises.com The gas cap vent is a little harder to test, because generally it will only show fault when you are running at a high speed, which requires a high flow rate. Its job is to basicly fill the tank with air to push on the fuel and prevent a vaccum lock in the tank. One way to check is if your tank makes a "wooosh" sound when you crack open the filler cap, its not venting properly.

So, in summary:

Check to see that your vac line is run correctly from the carbs to the petcock
Check to see that your petcock is flowing correctly
Check to see that your cap vent isnt blocked or fouled in any way.
If that doesnt seem to solve it, get back to us

[Jesse002100]

well i got this bike to fix it is a vaccume petcock and it seems to run on "on" and "res" but when i take it up in the rpms it struggles and then needs prime ill check the vaccume line and then see what happens in any event ill just get a new one if need be.
Thanks agian cafe
Jesse

[crapwacker]

what's wrong with the pingle(besides the asinine price)?

[TheCafeKid]

what's wrong with the pingle(besides the asinine price)?

If you're a forgetfull person, and you dont turn it OFF EVERY TIME YOU SHUT THE BIKE OFF, you'll eventually wind up with a crankcase full of gas...Thats not good in case you didnt know