Is it Carb?

[usin13]

I have a 1977 GS750. In a past post I mentioned I have a small gas leak, and it was mentioned that it was either a bad petcock or a stuck float. That turned out to be that I had it on prime all the time. I had however tested the Petcock and it was fine. I thought the leak was gone, but it is still there. It seems to be mainly from #1, but I can't tell if it is from others as well. I have no problem taking the carbs off and cleaning them, however, I do not have a carb synch tool, nor will have the money to purchase one for a while. If I clean the carbs and don't sync it, I'm afraid that I will make matters worse.

I do have other issues which I believe are carb related (but could be wrong). If I pull plugs 1 and 4, it probably doesn't even go down 100 rpm's. I am however getting nice spark from both. Also, all 4 pipes are getting hot. Seeing how that doesn't seem to be electrical (good spark) and the pipes are getting hot, the only thing I can think are the carbs. I tried to find some info on this by searching but I am striking out. If this is not carb, let me know and I'll create a new thread for it.

Basically what I'm asking, is if I clean the Carbs, am I going to do more harm then good if I don't have a carb sync tool to finish the job?

As always, thanks for the help I know I'll receive.

[Tarbash 27]

you dont need a carb sync tool to clean the carbs. they will run fine if everything is cleaned. as for gas leaking out of carb 1, there is a curtain height the floats have to be. if its not the right height, the carb will leak. you should not ride with the bike on prime, keep it on the "on" position.

[usin13]

you dont need a carb sync tool to clean the carbs. they will run fine if everything is cleaned. as for gas leaking out of carb 1, there is a curtain height the floats have to be. if its not the right height, the carb will leak. you should not ride with the bike on prime, keep it on the "on" position.

I haven't been riding with it on prime. I did when I originally bought the bike, as that was what the PO had it on and I didn't know what it was, as I had never had a Suzuki before. Ever since the original post, I have NOT been riding with it on prime. In fact I don't even use prime at all.

Just to clarify, if I clean the carbs and set the floats appropriately, then I do NOT have to sync the carbs? I knew I did not need the sync tool to clean it, but I thought that once I put it back on the bike I had to sync it, and need the sync tool at that time. If not, then I will just start to cleaning them.

Is that correct becaue just about every other post I read says I have to sync it?

Thanks again.

[Tarbash 27]

i have had my carbs on and off my bike over 30 times since i got it and never synched it. clean all the jets and adjust float height to spec. get the bike to run and adjust air screws to highest idle method. the bike will run fine. synching does help the bike run smoother and more evenly on each cylinder. but its not like the bike wont run because of it.

[usin13]

What I wanted to hear

i have had my carbs on and off my bike over 30 times since i got it and never synched it. clean all the jets and adjust float height to spec. get the bike to run and adjust air screws to highest idle method. the bike will run fine. synching does help the bike run smoother and more evenly on each cylinder. but its not like the bike wont run because of it.

Thanks for the quick reply. That's what I wanted to hear.

Tarbash, I see that you have a 78gs750. Can you tell me what kind of speed/accelaration/pep that it has? This one seems to be doggy. I have a little Ford Escot for a car, and it feels like that. Basically, it gets up to speed, but takes its time doing it. I don't know if that makes sense. Basically, when I roll on the throttle, it accelarates, but slowly. I don't have a flat spot, and have no problem doing 70 - 75 on the highway (never tried faster). I'm hoping that the carb cleaning helps that. Of course, I don't know what a 750 with 33,000 miles should do, so that might be normal. Any insight you can give into that, I'll also gladly take.

Thanks.

[Cyg]

I have one too. you should get in first gear around 0 to 20 second at 6k rpms 20 to 40, third gear cruising speed at 45 5k rpms. 4 th, gear it should ride fine at 60 too 65-70 around 5.5 k.rpms. 5 th will get you in the top speeds 70-85. If it vibrates at top speed then back off the throttle till it settles down.
Now a bike will run on three cylinders but act doggy. I suggest you do the water bottle test. Take a water bottle fill with water and spray your exhaust pipes
If you have a problem like i had look for my gs 750 thread. Then you only see usally one, two and four sizzle and three be cold as ice. Now if all four sizzle the same. Then you know it's hitting on four cyclinders and not just three. Some of these older bikes need a shut off valve in between the fuel line and the tank. Its only 12 bucks for a decent one. Also make sure your gas in clean in your tank. older bikes have rusty tanks. The best way too trouble shoot a bike is thru process of elimanation. Fix one thing first then attack another.. Plugs are the life line of your bikes perfomance dont forget too read what they are saying to you.

[Tarbash 27]

well mine is a 79 L model but im converting to an E/custom model. it pulls hard and you want to get sucked off the seat. i had it up to 125 mph. its has 47,000 miles. only major mods are pod filters and aftermarket exhaust i made. it did require some rejetting. im not sure how yours is running but it should definately move.

[usin13]

I have one too. you should get in first gear around 0 to 20 second at 6k rpms 20 to 40, third gear cruising speed at 45 5k rpms. 4 th, gear it should ride fine at 60 too 65-70 around 5.5 k.rpms. 5 th will get you in the top speeds 70-85. If it vibrates at top speed then back off the throttle till it settles down.
Now a bike will run on three cylinders but act doggy. I suggest you do the water bottle test. Take a water bottle fill with water and spray your exhaust pipes
If you have a problem like i had look for my gs 750 thread. Then you only see usally one, two and four sizzle and three be cold as ice. Now if all four sizzle the same. Then you know it's hitting on four cyclinders and not just three. Some of these older bikes need a shut off valve in between the fuel line and the tank. Its only 12 bucks for a decent one. Also make sure your gas in clean in your tank. older bikes have rusty tanks. The best way too trouble shoot a bike is thru process of elimanation. Fix one thing first then attack another.. Plugs are the life line of your bikes perfomance dont forget too read what they are saying to you.

Last night I started cleaning my carbs. Before I did that however, I checked the pipes. All 4 sizzle with water. So, as you said, it is hitting on all four cylinders. Also I did look in the gas tank yesterday with a flashlight and the gas is nice and clean. I can see the bottom of the tank through the gasoline and it looks in nice condition, almost too nice to be a 30 year old tank ;-)

After taking carb 1 apart, the float needle (Hopefully the right term) was stuck. Am I correct that this is what was causing my gas to leak out of that carb? I am partially through with number two and will hopefully get all 4 done tonight.

One thing I didn't mention previously is that the exhaust is also 4 into 1 and I don't know if has been rejetted. I have no idea what size jets are currently in it (how do you tell) or what size should be for a 4 into 1 setup. Could this be why it is doggy?

I appreciate the continued advice.

[rustybronco]

let me see, used vacuum gauge 3.00, 4-way aquarium valve 4.79, 25 foot plastic tubing 2.19, misc. 6mm bolts and plastic connectors 1.00 drill and drill motor i had =11.00
one syncronizer tool

the last set i bench synch'd only one carb was off by 1 inch vacuum

[ptm]

Yes, if the float needle valve is stuck it will leak gas which will either run out the vent line, make the mixture way too rich, or fill up the crankcase. Smell the engine oil, it shouldn't smell like gas.

If you're running a 4-1 exhaust and it hasn't been rejetted, it will run lean. Check your spark plugs. If they're white, it's too lean. #1 might be black from being too rich because of the leak. If they have good color it's probably been rejetted.

As far as performance, it is a pretty quick bike. Not so much below 3000 rpm, picks up significantly above 4000 rpm and once you get above 6000 rpm you'd better hang on. Magazine road tests of a stock '77 GS750 had it running a 1/4 mile in 12.75 sec @ 104 mph. That's better than most Porsche 911s, Corvettes, etc. It takes my Honda Accord 12 sec to reach 60 mph.

Other things that can affect performance or help find a problem - Are the valves adjusted? Ignition timing? Have you done a compression test?

[usin13]

Yes, if the float needle valve is stuck it will leak gas which will either run out the vent line, make the mixture way too rich, or fill up the crankcase. Smell the engine oil, it shouldn't smell like gas.

If you're running a 4-1 exhaust and it hasn't been rejetted, it will run lean. Check your spark plugs. If they're white, it's too lean. #1 might be black from being too rich because of the leak. If they have good color it's probably been rejetted.

As far as performance, it is a pretty quick bike. Not so much below 3000 rpm, picks up significantly above 4000 rpm and once you get above 6000 rpm you'd better hang on. Magazine road tests of a stock '77 GS750 had it running a 1/4 mile in 12.75 sec @ 104 mph. That's better than most Porsche 911s, Corvettes, etc. It takes my Honda Accord 12 sec to reach 60 mph.

Other things that can affect performance or help find a problem - Are the valves adjusted? Ignition timing? Have you done a compression test?

I planned on changing my plugs after cleaning the carbs because I drove it with prime on for a while until I learned that was incorrect. Currently the plugs are sooty black, but I don't trust it. Once I get my carbs back together and installed, I will take a look at the other things.

Valves adjusted - No
Ignition timing - No
Compression test - No (I couldn't get my compression tester in the #2 and #3 holes, maybe I need one with a hose where this is basically a stub on the end of the gauge)

Remember I'm new at this, so don't be too hard on me for not doing those other things :-) I really wanted to clean the carbs to address the gas leak and then go from there. I'm sick of the brown stain dripping down the side and the smell of gas all the time.

I have no one local to give me a hand with these things, so I appreciate all the advice I've been given. It is a learning experience to say the least. However, I'm enjoying each part of it.

Rusty Bronco, I gotta say that I'm intrigued by your sync tool. How did it work? I plan on buying one when I can afford it, and don't plan on building one, but I just wondered if it did the job for you.

[rustybronco]

Rusty Bronco, I gotta say that I'm intrigued by your sync tool. How did it work? I plan on buying one when I can afford it, and don't plan on building one, but I just wondered if it did the job for you.

Perfect.
I looked at buying a motion pro or a vacuum gauge setup but they were too much money for my finances. my cousin has an oem suzuki tool and had offered to lend it to me but i need it more than 1-2 times a year and he is 40 miles away so i built it myself.
want pictures?

[ptm]

Remember I'm new at this, so don't be too hard on me for not doing those other things :-) I really wanted to clean the carbs to address the gas leak and then go from there. I'm sick of the brown stain dripping down the side and the smell of gas all the time.

I have no one local to give me a hand with these things, so I appreciate all the advice I've been given. It is a learning experience to say the least. However, I'm enjoying each part of it.

No problem. Sorry if I came across a bit harsh. It wasn't my intent. As RustyBronco says, if you do a careful bench sync you can get very close. And as Tarbash says, the syncing will mainly make it run smoother, especially at lower engine speed. More important to get the gas leak fixed so it isn't affecting the other tuning steps and overall performance.

Too bad there's no one nearby to give you a hand while you get familiar with the peculiarities of the GSs. And the fact even the newest ones are 20 years old. It will take some time, patience, know-how and a few tools to get it running well. You've come to the right place to get the know-how. It's amazing what this group collectively knows. If you haven't found it yet, I did a brief write-up on the VM carb rebuild that was based on info I gleaned from this site that might be of some help. It's in the garage section - look on the main page.

Glad you're having fun. It gets even better as you get it dialed in.

Good luck, and keep the questions coming - someone here can answer them...

[usin13]

Pictures, YEAH!

Perfect.
I looked at buying a motion pro or a vacuum gauge setup but they were too much money for my finances. my cousin has an oem suzuki tool and had offered to lend it to me but i need it more than 1-2 times a year and he is 40 miles away so i built it myself.
want pictures?

I sure would like some pictures. In reality, I could build one like yours before I could buy one. $10 here or there is a lot easier than $50 at once.

Progress tonight - I got all the carbs cleaned and reassembled. Tomorrow I'm going to see how much the tool to do a bench sync costs. If it isn't much I will buy one so that I can do the best bench sync to my abilities. Then I will put it all back together and see what's up. Hopefully I didn't make things worse ;-) At least I could ride it before :-)

Carbs 2 & 3 were the dirtiest with 1 & 4 being pretty clean. And just as a reminder, 1 & 4 were the two where I could pull the plug wire with very little affect.

I'll keep you posted tomorrow or Saturday on my progress.

[ptm]

No tools needed for the bench sync - except the wrench and screwdriver. Look in the VM rebuild guide for a brief description or do a search in the tech section for a more detailed description. It's mainly making sure that all the slides are in the same position when they are closed and wide open.