[verticalroll]

Sorry for this post everyone. I looked at the archive on carb problems but could not find my problem. My 78' GS-750 is a complete rebuild. I took apart the carbs and cleaned the base units with a sonic cleaner. Installed new o-rings and blew out everything. When I place the fuel to on #1 carb leaks out of the hole in the side where the fuel rail is on the other side of the carb. I tapped the bowl with a rubber mallet and it still leaks. Any ideas. Second problem the bike will not start at all. If I spray fuel into the intakes the bike fires up. To me it sounds like the idle circuit is the culprit. The pilot jet is clean along with all other jets. Even if I spray fuel into the intakes and rev the bike to 1/3 throttle the needle valve should take over and run, maybe rough but run. Air screw out 1 3/4 Fuel screw out 2.0. Any ideas i am pulling out the rest of my bald hair LOL!

 

[TrialsRider]

"When I place the fuel to on #1 carb leaks out of the hole in the side where the fuel rail is on the other side of the carb. I tapped the bowl with a rubber mallet and it still leaks. Any ideas."
Float needle and seat is leaking
or the float height is incorrectly set
or the float is in upside down (that last one can happen on some but not all carbs)

it likely won't start very well until you fix that issue first.

 

[TrialsRider]

Can you switch carbs and carb parts around on that carburetor bank,
that might help in trouble-shooting the over-flowing carb issue

& does it have an accelerator fuel pump on one or more of the carbs?

 

[verticalroll]

No accelerator they are the VM type carb's. I will see if the float is upside down but pretty sure it is not. You cannot change carbs unless you remove all the bank and unscrew the mounting plate which I will do next. Won't start at all is my concern unless I prime with spray into the intake. It seems the idle circuit is not functioning Just my 2 cents. I will try to get a pic of the area I am talking about.

 

[verticalroll]

 

[woodsman]

I'm not convinced carbs can be properly cleaned while on the bike. This is a good step by step.

http://gsarchive.bwringer.com/bikecliff/images/vm_carb_rebuild.pdf

 

[TrialsRider]

I assume the carbs have been apart to paint them and that might have been some time ago because I also see black paint flaking off them.
Pull the bank, flip it over and clean everything you can access from having the float bowls off. I bet you find something in there, likely in the main jets. Carb #1 must be leaking past the float needle valve and seat, that's the part that shuts off your fuel delivery once the fuel level in the float bowl is correct.

 

[8ball]

Alright, let’s forget about float needles and jets for now. That port you are pointing to is the fuel rail casting. It should be blanked off on the #1 carb. If you look at the pics attached, you can see in the old junk carb body the drilled hole in the port, but in the one on my bike...no hole . Also, those vent hoses: on my 550, there are only two carbs that have the hose barbs and they are on #2 & #4. That could be different on your 750, but I’ll just use that as a clue to my line of thought. Where are the air/fuel screws on your carbs? Usually they face outward (1 &2 have them on the left side and 3&4 are on the right of the carb).

I think the carbs are assembled in the wrong order on the rack.

 

[8ball]

To be clear: The fuel rail on #2 & #3 should be drilled on both sides. 1 should be drilled ONLY on the right side, and #4 should ONLY be drilled on the right. #1 & #2 should have the air screws facing to the left, and #3 & #4 should have the air screws facing right.

 

[dirkchecken]

great looking bike. looks like you have some money and time invested. ever think about replacing the carbs? might be the lazy way of doing things. just that 40+ year old carbs, be they slide or cv's are a headache. lots of the new replacement parts are bootleg junk. call sudco and treat your bike to some keihin cr's (26,29, 31). they'll get the jetting pretty close.

 

[verticalroll]

8Ball you are so correct sir! I noticed that myself after I looked at each carb when I removed them again. Placed them in their proper location and Vrooooom. Ignition!! Now second problem. The bike will only run on choke. As soon as I remove the choke the bike quits. I believe it is not getting enough fuel I will adjust the mixture to 1.5 then 2.5 out what do you all think?

 

[8ball]

Start with the fuel screws (the ones on the bottom of the bowls) at 1 turn out. You did clean those and their passages too, right? And the air screws (the ones that should now be facing outboard) at 2 turns out.

you can make adjustments from there. If you have to turn the air screws in or out more than a turn and a quarter, go back and adjust the fuel screw a 1/4 turn. Put the air screws back at 2 turns and start over. Remember, turning the fuel screws IN leans the idle mix, and turning the air screws OUT leans the idle mix.

 

[verticalroll]

Thx 8Ball I will attempt this.

 

[trepanned23]

Sorry for this post everyone. I looked at the archive on carb problems but could not find my problem. My 78' GS-750 is a complete rebuild. I took apart the carbs and cleaned the base units with a sonic cleaner. Installed new o-rings and blew out everything. When I place the fuel to on #1 carb leaks out of the hole in the side where the fuel rail is on the other side of the carb. I tapped the bowl with a rubber mallet and it still leaks. Any ideas. Second problem the bike will not start at all. If I spray fuel into the intakes the bike fires up. To me it sounds like the idle circuit is the culprit. The pilot jet is clean along with all other jets. Even if I spray fuel into the intakes and rev the bike to 1/3 throttle the needle valve should take over and run, maybe rough but run. Air screw out 1 3/4 Fuel screw out 2.0. Any ideas i am pulling out the rest of my bald hair LOL! View attachment 104213

Interesting looking bike. I like the color. Frankly though, I’d take one look at the painted carburetors and kinda go “whaaa?
I wouldn’t waste another minute trying to chase down what’s wrong. If it were me, id just jerk off those carbs and shitcan them. Call Sudco and get a new set. That’s just me, though.

 

[Maurice]

Hi verticalroll, heres my twopenceworth, take it or leave it.
I have just gone through what you have but with my gs550. I found the fuel needle screws (underneath) were broken off in their tiny hole. This happens when some jerk tightens them up too much thinking they know what they'r doing.Take one out and if it is blunt the rest of it maybe jammed in the tiny aperture which leads into the intake mouth of the carb. It should be as I say like a sharp needle. If its ok then shine a torch in the main mouth of the carb and look up the hole for the needle screw. you should see light coming through a tiny hole. this could be where you have a blockage of crap or as I say the tip of the needle broken off in there. If its blocked shine a torck up the needle valve hole while you look up there. You may see brass coloured dot blocking the hole. You could get a piece of fine springy wire , make a 90 deg bend 8mm from one end and poke it down the tiny hole from the main carb aperture. Then blow out with an airline in the opposite direction to the direction of travel of the fuel from the needle jet. Its no good blowing the other way as that will force any crap further in the funnel shaped tiny hole. I think some people do that and block it worse.That tiny hole is your idling mix bypassing the slide and also allows starting without opening the throttle.
You will of course have already taken the choke plunger assemblies out and blown all those out etc?
Good luck. See also my post on carb problem gs550 a few days ago.

 

[Maurice]

PS
the screw on the side is the air adjustment screw to be set at 2 turns out initially till you get the bike running and warmed up then adjusted. The fuel adjustment pilot jet needleis underneath in its own tube not in the float bowl. Sorry you prob know this, just wanted to be clear.You cant really adjust the needles on 550 so its a case of taking carbs on and of trial and error etc but maybe you can on the 750.

 

[8ball]

....You cant really adjust the needles on 550 so its a case of taking carbs on and of trial and error etc but maybe you can on the 750.

The needles can be adjusted on the 550 (as well as the 750). There is a plate inside the slides that is held in with two screws. There is a c-clip that can go in one of the 4 or 5 grooves in the needles.

 

[verticalroll]

Thx everyone for the help. Indeed maurice all jets are out again and I am stripping the paint and getting a sonic cleansing at the motorcycle shop. There’s is a better unit then the one I used before. I also bought all new jets with a kit and will once again rebuild them. If this does not work I will replace them with a racing set from Sudco

 

[Maurice]

The needles can be adjusted on the 550 (as well as the 750). There is a plate inside the slides that is held in with two screws. There is a c-clip that can go in one of the 4 or 5 grooves in the needles.

I was talking about the pilot fuel jet needles underneath, not the slide needles.

Verticalroll, I didnt ask but have you made sure the slides bottom out when you let go of the throttle? There is an adjustment mechanism which moves all the slides together at the cable pivot mechanism and if you get this turned in it will keep the revs high? Its there to set the lower limit. I am just thinking the engine must be getting air and fuel from somewhere to be able to red line if the slides are properly down. Check without the air filters on. Keep at it you will get there in the end as I did and become a better mechanic for it. Let us all know how you get on.

 

[8ball]

I was talking about the pilot fuel jet needles underneath, not the slide needles.

Ok, you meant that you can’t adjust the fuel screws with the carburetors installed on the bike. Gotcha! That wasn’t clear. And you are very correct about that. I have a right angle fuel screw tool, and even with that, you can’t get the center two.