GS 750 Problems Anybody have any ideas

[twykle]

Hey everybody, Thanks for having me to the board, Just got back into riding after borrowing a freinds 97 Magna 750 It gave me the bug back. I went and picked up this 1980 GS 750L on the cheap at first it started when you would shoot starting fluid in the carbs now it doesnt even do that. The guy I bought it from said it hadnt been run in a year but the tags on it are 3 years out of date so I am guessing longer. All in all it is in pretty good shape except for the annoying thing about not starting. I cleaned the Carbs and the Plugs the pet %%%% switch was broken off, I checked for spark getting to the plugs and it is. I found out the hard way that the petcock is open LOL and not in the off position, So it appears to be getting fuel and spark but isnt starting, That has me baffled, Maybe I need to go get new plugs instead of cleaning the old ones. The bike has 19K miles on it.

Anybody have any ideas please let me know I cant wait to get it going and go for a cruise.

Thanks,

Troy

[AZRyder]

is this a 16 valve or 8 valve motor? Does it turn over or just crank. How did you determine if it was getting spark? One thing you want to verify is that you have the right plug wires on the correct cylinder. I've mixed em up before.

[twykle]

I'm not sure if it is the 16 valve or not It is DOHC I imagine with it being a 80 that is probably is the 4 valve head. I used a screwdriver in the spark plug wire and grounded to the block to see if the cylinders were getting spark. I of course woudnt know if the wires were mixed up I know I did them one at a time to avoid confusion, I dont think they are mixed up though because it did start with starting fluid before. Just wouldnt stay running when it started.

[midas6t6]

If you don't have a shop manual, get one. Replace the spark plugs; be sure to set the gap per specs. I prefer to gap on the tight side if a range is given. Make sure the spark plugs wires are on the correct plugs. Take the piolt jets out and clean them until you see daylight thru the holes. Replace them if you can't get them clean. Set float height, making sure they move freely. Make sure air screws are properly adjusted and when you reassemble everything make sure there are no air leaks around the manifolds or carb boots. Adjust the idle scew so the idle will be a little higher once it starts, then readjust once it's running and warmed up. Synchronize the carbs once it's running. My bet is the pilots are still clogged - the holes are miniscule and don't clean easily. It's much easier to just replace them.

[Aussie Steve]

Yes the carbs are probably the culprits after sitting so long. I would suggest to check the plugs to see if they are dry when you have cranked the motor to confirm no/little fuel situation. other points to check are the float needles themselves...not likely they all would stick but you never know. If the carbs are out of sync badly a temp setup will have to be done...by feel. Check also that the exhaust is not clogged with debris etc... as this can cause the symptoms you are experiencing.

Good luck

[twykle]

Hey I got it running, kinda it will even start without starting fluid LOL. But it runs for a few seconds then the idle comes down and it stalls out. Im thinking the carbs need an adjustment and while I am hell on wheels adjusting a Holley 1050 Dominator. I dont know S#!T about adjusting a quad Mikuni set up. Is it the Same premis? Any help would be appreciated. The Exhaust is not clogged though as a matter of fact the baffles are drilled out so it is pretty much running straight pipe and man is it loud.

Thanks

Troy

[AZRyder]

Originally Posted by twykle

Hey I got it running, kinda it will even start without starting fluid LOL. But it runs for a few seconds then the idle comes down and it stalls out. Im thinking the carbs need an adjustment and while I am hell on wheels adjusting a Holley 1050 Dominator. I dont know S#!T about adjusting a quad Mikuni set up. Is it the Same premis? Any help would be appreciated. The Exhaust is not clogged though as a matter of fact the baffles are drilled out so it is pretty much running straight pipe and man is it loud.

Thanks

Troy

Sounds like it could be a timing issue then or even a carb sync issue. Another thing you might check is the carb boots. If you can get it running for a bit, spray around the rubber boots with carb cleaner while it's running. If the idle goes up, then you have a leaky boot and it probably needs to be replace.

Oh, and to tell if you have a 16 or 8 valve engine, the camshaft covers on the ends of the valve cover are round on an 8 valve, rectangular on a 16 valve. I had an 81 with the 16 valve engine. I loved it.

Definitely look for a shop manual, not the aftermarket manuals, but an actual shop manual put out by Suzuki. Check ebay. If you can't find the actual shop manual then settle for the others.

[twykle]

No Leaks, boots are all still soft on the carb inlets but there are a couple on the airbox that dont seem to be connecting really well and are hard and brittle Dont know if that maters. But I got it to idle for about 5 min, but it bogs out when I rev the RPM's up past 3500 or so and then if I let off it dies. Also there is the occasional back fire from the exhaust when I rev it up not all the time just sometimes. Does that sound like timing or Air or Vaccum leak I noticed there are two vaccum lines coming off the carb that aren't plugged into anything. It does have the rectangle covers on the side so it's the 16 valve then. Im just happy it's making progress. LOL

[AZRyder]

Originally Posted by twykle

No Leaks, boots are all still soft on the carb inlets but there are a couple on the airbox that dont seem to be connecting really well and are hard and brittle Dont know if that maters. But I got it to idle for about 5 min, but it bogs out when I rev the RPM's up past 3500 or so and then if I let off it dies. Also there is the occasional back fire from the exhaust when I rev it up not all the time just sometimes. Does that sound like timing or Air or Vaccum leak I noticed there are two vaccum lines coming off the carb that aren't plugged into anything. It does have the rectangle covers on the side so it's the 16 valve then. Im just happy it's making progress. LOL

I'd go with the vaccuum leak angle for now. Sounds like it works until it warms up then the vacuum leaks kill it. more than likely if there are only 2 vacuum lines coming off the carb, there's probably a T, or should be where they connect up to another vacuum line that runs to a diaphragm (I forget the technical term for it) usually mounted toward the front ( I forget where on the gs)...You may have to remove the gas tank and see if there is such a device.

[twykle]

Okay So I found the place to hook up the two vaccum lines off the carb there is one more nipple on there with no line and no place to hook it up and when I shot starting fluid on it the idle goes up. Anyway I put the two lines on and the carb started gushing gasoline into the airbox but the bike was running great and holding its idle not dying I had to jump up and turn it off. So I took the carbs back off and pulled off the float bowls on the bottom and all the floats look clean and none are stuck although there was a little screw in one of the bowls that I am pretty sure shouldnt have been there and by the amount of rust on it I would guess it has been in there for a little while LOL, I gave everything another real good cleaning and put back together I"m going to put them back on the bike without the air box and try again and see what happens.

[AZRyder]

The other vacuum fitting might just be for testing etc. get a rubber cap to put over it and see if that helps. you can get vacuum caps at Autozone or Checker pretty cheap. Sounds like your on the right track though. I'd be a leetle concerned about the screw in the bowl though. Might want to look into getting carb rebuild kits or usually you can get a carb set on ebay from a junker. Saves rebuilding time.

[twykle]

I must have done something wrong pulled the carbs back off. Made the mistake of trying to put the throttle cable on after the carbs were on LOL. Anyway I went and rebuilt the carbs and filled the tank with gas and that liquid gold started pouring out of the carbs could that be from the broken petcock? Again any ideas let me know.

Thanks again,
Troy

[midas6t6]

Check to see that you reconnected the fuel line to the carbs properly. If that's right you probably have a stuck float.

[twykle]

Well the place that I connected those two vacuum lines to was a T fitting that was also connected to the crankcase vent at the top of the motor!!!! Yikes LOL Im a Dip Stick so I guess that explains the fuel shooting out of the carbs. I took them back off and no more fuel leak but now back to having a vacuum problem. But now it runs starts I ran it for about 30 min today and let all the crap from it setting for so long burn off it smoked for about 20 min then stopped and cleared up, it also started running smoother once it cleared up with no more of the popping. But it still bogs down like it's to lean and starving for fuel once you rev passed about 4000 RPM and if you gun it and let it drop off to fast it stalls. So I am going to look for a Diagram on the Vacuum lines for that model and see where those two lines off the carb are supposed to go. Does the airbox have a hookup for Vacuum lines? I know on a car most of the times the lines from the carb are on the Air Cleaner. If the Airbox has vacuum hookups what do you do when you install Pods? Do you just cap the lines or what? The rubber boots on the airbox well at least two of them are shot so it might be easier to just go to pods for me, and with the straight pipes it might enjoy the better airflow but then I have to re jet too don't I? Sorry i know that is allot of questions I will wait for an answer.

Thanks again guys,

Troy

[midas6t6]

The airbox should have fittings for the vacuum lines. With pods you would just cap the vacuum fittings but they also open up new tuning problems. It sounds like the float valves are sticking or the floats themselves are set to low and need to be adjusted.

This link explains tuning CV carbs:
CV Carb Tuning Procedures

[superdave07]

somthing you might look at is to do a plug reading to let you know if you are running lean or running fat to me it sounds like your having a lean burn condition it sounds like if you can tune a holley 1050 you know how to do a proper plug reading. theother thing you may try is a partially applied choke and then throttle up and realease quickly. if the bike stalls check your base idle setting should be one screw for idle in the center of the carb rail on the bottom. let me know if this helps.

[JoelP79]

I just got the same bike with 2674 miles on it, almost brand new condition. Bike boggs down when ever it revs past 3500 ish, someone took the stock air filter off, put on 4 little air filters, and also the breather hose for the engine has one on it too, and what is really weird was gasoline i believe coming out of the crank case breather hose!

Thanks!
Joel