1978 GS750 Cold exhaust pipe

[ZakDanger]

Nah, I read up on those carbs quite a bit on here and other resources. Definitely made sure that they are in the correct position. 1 no nipple 2 tube goes to airbox 3 tube goes to petcock 4 tube goes to airbox. I WISH my carbs looked like that Ha!

[ZakDanger]

Maybe clean the points?

[MisterCinders]

Check the No. 1 plug. You thought it was dry, but check it again after idling the bike with that cylinder failing.

If it is dry at that check, you have a fuel problem. Backtrack from the No. 1 cylinder to determine why there is no fuel getting through. If there is fuel in the bowl but your plug is dry, you might need to raise the float level so that your engine will pull that fuel in. If the bowl is dry, find the blockage in the fuel path. When you cleaned the carbs, did you synch them, at least a bench synch? If your slides are out of synch, your No. 1 slide might be too low to pull fuel, relative to the other three. Bench synch the slides, get the bike started and warm, then vacuum synch the carbs.


If the plug is wet, you have a spark problem. I don't know what a purple spark indicates, but usually timing and ignition problems show up in pairs -- 1/4 or 2/3 -- because the spark is delivered to the cylinders 2 at a time. If your problem is isolated to the No. 1 cylinder, it probably traces to the plug or connection.

This is easy to confirm. Swap the plug leads for 1 and 4. Start the engine. If the No. 1 pipe is hot and 4 is cold, then you know the boot connection or lead is the problem. If the cold pipe stays at No. 1, then you have a bad spark plug in that cylinder.

If none of this bears fruit, you can also check your compression. First, have you checked and adjusted your valve clearances? Get that sorted out, then do a compression test. If the No. 1 cylinder has bad compression . . .

[chuck hahn]

You can put a rag under the bowl and loosen the drain screw to check for fuel at least that far too.

[ZakDanger]

Got her running, idling, and rode her for a bit last night. Gonna need to vacuum sync the carbs but definitely a boost in my motivation hearing her run. Cleaned the points and I got a nice solid spark for my #1, flipped the float in #1 cuz apparently I put it in upside down (uh dehr). Thanks for all the help guys. Invaluable information abounds on this forum and its helped me not just with my GS, but my XS750, and a couple of my friends' bikes that they are working on. One thing that puzzles me, isn't an issue, just a curiosity. When I open up my drain screws to drain the gas out of my float bowls, the gas comes out of the drain screw hole instead of my overflow tubes. Not a deal breaker or even really an inconvenience, just... Huh?

[chuck hahn]

The overflow is just that..in case the floats fail. The drain isnt connected into the overflow, so all it will do is drip the fuel out from around the threads.

[allojohn]

flipped the float in #1 cuz apparently I put it in upside down (uh dehr).

LOL - I did the same recently, on 2 carbs!

[ZakDanger]

Yea I felt like a total dope. Third carb is overflowing a bit out the tube... Checked the float, she's within spec, the needle is brand new. Carbs are pretty out of sync. She idles and rides, but bogs down when going up hills. Syncing them hopefully this week. A buddy of mine has a brand new vacuum sync and we're gonna break it in as soon as he makes up with his wife. Replacing the tach cable, replacing the valve cover gasket and checking my clearances probably tonight. Gotta be honest I kinda hate the bars on it. I'm used to riding my xs750 hard tail bob with clubmans, and I've grown accustomed to a wider arm position. Maaaaybe cafe' it, but how bout we get it running right first?