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Sooty #3

  • Thread starter Thread starter Livy
  • Start date Start date
L

Livy

Guest
Hi
Can any one help with a problem I have with #3 running rich? Thirty odd years ago I bought a GS 750 E , 1979 reg. I?ve spent most of my life moving around so have not really had a chance to work on her, until now. When I first bought her she was standard apart from a 4 into 1. The mists of time prevent me from recalling if there was a standard air box or K&N filters. If I had to stake my life, I would have to say there was an air box. Any way, I do know the engine ran as sweet as a nut and all four plugs were a nice tan colour.
Then came that fateful day when I decided to grow the engine up to an 850! The following is my shopping list from 30 odd years ago: GS 850 block, head gas flowed, slightly wilder cams, those pesky mists of time again, I can?t remember what type/stage of cams they are. I do know I was told I should be able to still use standard timing. And K&N filters. The carbs are the standard VM 26mm round slide Mikuni. The exhaust is a 4 into 1 Eagle. The setup of the carbs is as follows: the needle is fourth notch down from the top, pilot jet #10, main jet #110, fuel mix screw 1.5 turns out, pilot air screw 1.5 turns out. I junked the points for Dyna S and new Dyna coils, 3 ohms
I?ve balanced the carbs with mercury gauges, blown all air ways with an air line, checked valve clearance : but have not degreed cams, the fuel tap diaphragm (which has been replaced) is still operated by the breather tube from number 3 carb. The other breather tubes from 2 and 4 are not connected to anything as there is no air box. The state of the plugs are: #1,#2,#4 are just about a tan colour, #3 very sooty, not wet just very sooty. I?ve swapped HT leads for 2 and 3 still no joy. The old girl fires up pretty much first stab of the button, once fully warmed settles down to a steady idle. Here?s my problem, from idle if you blip the throttle the revs hesitate to pick up, almost like she?s being swamped with fuel, then she clears and the revs pick up nicely. On the odd occasion if you grab a hand full of throttle from idle she can die altogether.

From reading the threads on your site I guess I?m just going to have to bite the bullet and degree those cams. I just wonder if I might be better off re-fitting a standard air box as well.
Livy
 
You may be sucking fuel through the petcock through a leaky diaphragm.
 
Isn't the vacuum line from the petcock supposed to go to #2 carburetor or am I thinking of a different engine?
 
Isn't the vacuum line from the petcock supposed to go to #2 carburetor or am I thinking of a different engine?
Let's make sure we are numbering the cylinders correctly.

Livy, #1 is under your clutch hand, #4 is under your throttle hand.

Which plug is "sooty"?

.
 
Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. Livy,

(One moment while I mention this to Mr. 1948man) said:
Isn't the vacuum line from the petcock supposed to go to #2 carburetor or am I thinking of a different engine?


With the VM carbs (generally '79 and earlier), the vacuum is taken from the #3 carb. With the CV style carbs (Mikuni BS3xSS, generally '80 and later), the vacuum is taken from the #2 carb. Count the carbs and cylinders starting from the left as you sit on the bike.

Anyway, a leaking petcock diaphragm was my first thought too. Did you say you had set the float heights? It could be a leaky float valve needle or seat.

Now let me dump a TON if information on you and share some GS lovin'. :D

I just stopped by to welcome you to the forum in my own, special way.
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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!"....
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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...

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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! :D

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff
 
Last edited:
Put the petcock on prime and plug the vacuum line. Try it that way
 
Thankyou all

Thankyou all

Thank you to everyone who replied to my thread. I think it would be quicker if I answered all you questions in one hit.
I've already tried running the engine using prime only and blocking off #3 vacuum pipe (a .22 case just fits nicely): #3 still sooty. The diaphragm is new and is free from leaks. #3 pot is the one that's sooty. By #3 I mean the third from the left when sat astride the old girl. The float heights are 26mm. There is no fuel over flowing from the float bowls.
After reading the info on the bikecliff site I'm going to rip the carbs apart completely and clean with a good carb cleaner. I'm also going to look around for a stock air box. I must admit I will miss the roar of the carbs with the throttles at full bore!
To all you guys who run this site, you're doing an amazing job!
 
Hello and welcome. What part of this illustrious and poverty stricken isle are you from?

Are you sure of the numbers on your jets? Standard pilots on a 750 are 15 (or 22.5 or 27.5 depending on your carbs) not 10. And your mains look a bit light for K&Ns.

Have a check to see if your pilot is 100% clean. I've seen these symptoms before where there has been a bit of muck in there that acts like a flap - you blow through it one way and it looks clear and the other way it closes. You would think it would give you a lean plug but for some reason it gives you a sooty one.
 
Cold dark England

Cold dark England

Hi Hampshirehog

Sorry for not getting back to you sooner. As it turns out I'm not too far away, Houghton Regis, Beds. To be honest, my main concern is getting #3 the same colour as 1.2 and 4. Once I get that correct then I can work on the rest of the set up. I'm currently stripping the carbs apart, will clean with STP carb cleaner and replace all seals. Any idea where I can get a carb seal kit in England?

Livy
 
Any idea where I can get a carb seal kit in England?

Just pretend the war of independence never happened.....:) Get your seals from Robert Barr - he's a member here and his service is second to none:

http://www.cycleorings.com/VMkit.html

Nobody over here does the kit.

You'll need to dip your carbs as well - giving them a squirt of something doesn't work. Cellulose thinners works well (remove every rubber bit first) or boiling in a pan with a drop of Fairy Liquid.

Tutorial on how to rebuild your carbs here if you haven't already found it:

http://www.thegsresources.com/garage/docs/vm_carb_rebuild.pdf
 
Carbs like new (Hopefully!)

Carbs like new (Hopefully!)

Thanks for the info. I'm hopeing father xmas will get me camera for Xmas, some pics will follow soon.

Livy
 
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