GS750 Purrs Like a Kitten-On 3 Cylinders :(

[Crescentius]

First of all, *wave* to everyone, and compliments of the nice forum

I'm the new owner of what is my very first bike, a 1978 GS750E. Overall it's in very nice shape, some minor surface rust here and there on the chrome, but a very clean bike overall, and EVERYTHING is original, save the paint.

So I listen to the thing idle, have a friend who has a license test drive it, everything is great, I buy the bike, good stuff. A few days later, as I am testing the tach after I cleaned and oiled it (it were a bit lazy) I reach down to tap the #1 pipe to make sure the bike isn't overheating yet. Then I touch the pipe. Then I grab the pipe with a full-on fist grip. Then I burn the ever-loving #$#& out of my hand when I grab the #2 pipe.

A few minutes and some ice later, I go back to scratching my head at the thing, and start wrenching over the next few days.

So far I've:

-Done a compression test, all cylinders OK.
-Replaced and adjusted the points (yes I used a timing light).
-P/O replaced the plugs and boots, I checked both, carbs appear to be running rich as most plugs were black, except #1, which had less black and was wet with fuel.
-Checked #1 for spark, looked OK.
-Swapped #1 and #4 wires, #1 still cold.
-Made liberal use of words like "huh" and "hmm" and "&%@*%*-%&$!(*"

So far my guts tell me that I have eliminated the ignition system (and here I thought they were only for digesting sammiches). This leads me to believe I have a fuel/air problem, what with those being the only other two things necessary for combustion and all.

Air box seems clean, I adjusted the air screws and the idle adjuster so it purrs nicely at 1000 rpm, compression test is good and no blowback "pop" so I gather the exhaust valve is working properly, and a wet plug leads me to believe that the intake valve is working properly.

I gather the carbs are running rich from the black plugs, don't have a vacuum sync tool, so I haven't adjusted fuel yet. Is it possible that #1 is running so rich that it isn't firing? Any other ideas?

 

[Guest]

Did you switch the plug and see if it ran until it fouled?

 

[Crescentius]

Removed all plugs, cleaned and gapped them, and mixed them up when I put them back.

 

[kelticsol]

I didn't see the obligatory "Clean the Carbs". Get some Orings for it and properly clean them.

I'm sure someone with be along shortly with a bunch of links for you that will lead to GS Bliss.

 

[tlepac]

If you are getting gas to Cyl # 1 then quit messing with the carbs until you have ruled out a plug wire problem. One quick thing you can do it clip off the end of the plug wire--about a 1/4 inch should be enough. Of course before you do this unscrew the old cap. Then get a brand new cap and screw it on and test the voltage at the plug to make sure there isn't a problem with it. (Probably not a bad idea to get all new caps---minimal investment)

Hope this helps

 

[Crescentius]

Plug boots were all replaced by the P/O along with the plugs, as stated in my post. I did unscrew them, and even cut 1/4 off the #1 wire. As I also noted, I swapped the #1 and #4 wires, and cylinder 4 still ran fine, and cylinder 1 was still stone cold :/.

Kelticsol: Will a dirty carb really cause a cylinder to not fire at all? Is it possible that I could get the cylinder to fire by messing with the adjuster screw to verify it's a carb problem? I had hoped to avoid rebuilding the carbs, as the bike runs like a champ on the other three cylinders

 

[kelticsol]

Kelticsol: Will a dirty carb really cause a cylinder to not fire at all? Is it possible that I could get the cylinder to fire by messing with the adjuster screw to verify it's a carb problem? I had hoped to avoid rebuilding the carbs, as the bike runs like a champ on the other three cylinders

Mine did the exact same thing when I first got it. I found out why after I took the advice of everyone here and tore the carbs apart. I was quite shocked at what I found. I should have taken pictures of it. My #3 carb was completely clogged. I mean completely. The rust and calcification that came out of it was really disturbing.

BTW, I am really shocked that BassCLiff hasn't made it over here yet with your own special mystical GS welcome.

 

[Crescentius]

Hmmkay. What's really bugging me is the wet plug in the cylinder, but fuel doesn't necessarily guarantee air I guess. I found bikecliff's collection of gs guides in my googlings, so I guess at this point I just need to start ripping and tearing . Thanks again for all the advice!

 

[TheCafeKid]

Hmmkay. What's really bugging me is the wet plug in the cylinder, but fuel doesn't necessarily guarantee air I guess. I found bikecliff's collection of gs guides in my googlings, so I guess at this point I just need to start ripping and tearing . Thanks again for all the advice!

If your airjet is clogged, it may not fire. Remember, the ratio has to be correct to get ignition. If its getting fuel, then is it getting enough? Is it getting air? Id pull the bowl on number one and have a look. A lot of times, if a bike sits on the side stand alot, it will collect some garbage in there. Also, check your screw settings, both the fuel screw (on the bottom) and the air screw ( on the side) IIRC on a stock VM bike, its around 3/4 turn out on the fuel, and 1.5 out on the air as a baseline..

 

[ddaniels]

Yep, clean 'em up and go again. Might take some time, but once it's right, it'll be good to go.

 

[BassCliff]

Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. Crescentius,

Sorry I'm late to the party. Yes, following the maintenance lists in your "mega-welcome", including a proper cleaning of the carbs, will usher you into GS-topia. Now let's get to it.

I'm glad you found us. We'll lend a hand where we can.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

 

[Crescentius]

Thanks for the welcome! Wow, lot more info than I had found already in there, good stuff .

Little update on my carb problem: pulled the #1 bowl, and surprise surprise, it's clean as a whistle. No sediment, gummy fuel, nothing. "Hmm" I proceed to start poking at things, attempting to identify screws, and the little plug screw (with the hole in the middle) on the bottom of the main jet falls out just from me poking it. What does that do, exactly? I didn't see any description on the rebuild guide, should I just turn it all the way in? or is it an adjuster? any help would me much appreciated.

Also, I'll make sure to take some pics of the bike, she's not the prettiest, but I intend to make her quite a bit shinier as I can.

 

[tkent02]

the little plug screw (with the hole in the middle)

That IS the main jet. Screw it in until it seats. It is not the source of your dead cylinder, it is used for open throttle, not low speed stuff.

 

[gs road racer]

That IS the main jet. Screw it in until it seats. It is not the source of your dead cylinder, it is used for open throttle, not low speed stuff.

LMAO soo sorry... never said better kent!! Apologies to the thread creator but i was almost rollin on the floor...screw that sucker back in you might just have four kittens purring....you can take a free kick for my abusing you....

Randy

 

[Crescentius]

Heh, never been afraid of a little fun had at my expense .

Yeah, main jet definitely wasn't the problem, I went ahead and pulled the carbs (man, bike are so much easier to work on than cars ), stuck a flashlight down the intake tube for giggles and pulsed the starter; yep, valve's working fine, as far as basic functionality is concerned anyways. Carbs all look VERY clean, top bottom and center, will proceed to disassemble them further I guess.

Took a pic of the bike with it's new doughnut hole out of boredom:



Uploaded with ImageShack.us

 

[kelticsol]

That is clean. Very nice. I'm talking of the picture.

And yes it is quite humorous that your jet fell out.

 

[Crescentius]

Thank you! It actually looks much cruddier in person, oddly enough, but I've got plenty of metal polish and rust remover. Can anyone suggest the best way to polish all the little fins and crevices and whatnot, btw? Dremel, maybe?

 

[tkent02]

Not to polish, but to clean, I use rifle cleaning brushes.
Chuck them in a drill. Go easy.

 

[a747freak]

Not to polish, but to clean, I use rifle cleaning brushes.
Chuck them in a drill. Go easy.

Awesome suggestion tkent, they're pretty cheap too. I'm gonna try that one.

 

[Crescentius]

Welp, week and a half and ~$100 later, got the bike running again!

Tore down the carbs into all their bitty pieces, soaked, wire brushed housings, polished top covers, cleaned and reassembled them. Cleaned and resealed the airbox, which was a very, very BAD place, plus there was NO weatherstripping on the filter . Replaced the intake boot o-rings, which were pretty flat. Cleaned 32 years of road dirt and chain oil off the crankcase and the back of the head while I was at it too.

Started her up about 20 minutes ago, and she lives! On 4 cylinders! Well, almost. #1 pipe gets darn hot darn quick so she fires, but the left pipe (muffler) is still colder than the right and has less exhaust pressure. Makes this weird "puff" noise intermittently too, almost like a really really quiet backfire.

Haven't synced the carbs or adjusted mixtures or any of that happy horse manure yet (for lack of tools, mostly), so we'll see how it goes.

Anywho, thanks again for helping me get this far, absolutely fantastic little site you have here!