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Jet size poll

  • Thread starter Thread starter HiSPL
  • Start date Start date
H

HiSPL

Guest
I would like to hear what size jets people are using to get an idea of proper jetting for my ride. Also we'll have to post what other mods you've done to effect the mixture.....I'll go first,

81 750E
V&H Stg 3 kit
170 main jets
can't remember what clip
4 turns out
K&N pods
accell coils
Mac 4-1 with baffle in

My bike is running rich. The V&H stg 3 kit was designed to go with a V&H pipe and my mac doesn't flow that much air. It seems to be OK at idle, and in the cool weather the mid range was good, however, with summer approaching its gone rich. This kit jumped from 112.5 to 170 main jets so I'm wondering how much to go back to get close to right. I don't want to buy 8 sets of jets at $10 apiece to get it right.....knowhaddahmean? :wink:
 
FROM WHAT I HAVE HEARD FROM THE GANG ON THIS WEBSITE, THE MACK EXHAUSTS ARE NOT PERFORMANCE EXHAUSTS- I WOULD GO BACK TO THE STOCK MAIN JETS UNTILL THE TIME THAT YOU DECIDE TO CHANGE THE EXHAUST--ALSO THE K&N PODS MAY BE IN EFFECTIVE UNTILL YOU DO AN EXHAUST MOD ALSO. THE ADJUSTABLE NEEDLE IS THE THING THAT I WISH I HAD IN MY SETUP
 
hispl, why did you rejet the bike? was it to obtain more power or because of the exhaust? I have a mac 4 into 1, and when I changed the intake to a pod style filter it only opened a can of worms. I went back to stock breathing and the bike runs great. The 4/2 to 4/1 change didn't affect the performance nearly enough to warrant rejetting, but the change in intake definately did. Dominick........
 
Yes the mac exhaust is not that great but it does flow more than stock, plugs went lean after installing it, but not terribly bad. The coils were put in because my stock wires were falling apart.... A little leaner still..... needed an air filter after my uni split down the seam (35 bucks) found pods on ebay (40 bucks :D ) and forever lost the airbox :D :D :D .......Even leaner.....installed Stg 3 kit.......plenty rich..... tune :? tune :? tune......Ridable 8) ......weather gets warm...rich again in the top end :( but, its just the main jet, I can live with that. I can just come down a little on the mains. Now that I can pull my carbs in 5 minutes its not a problem. I just want to know how much to come down on the jets. 10? 20? 30? Who knows? Not me, thats why I'm asking the super tuners out there....
 
IF TOU CAN PULL THE CARBS IN SUCH A SHORT TIME THEN EXPERIMENT-COME DOWN 10 AT A TIME UNTILL YOUR COLOR IS CORRECT--I WISH I COULD GET MY CARBS OFF SO QUICKLY
 
My bike is a '78 wich has 102.5 jets as standard, I've had seperate K&N filters installed and they tuned it on the Dyno bench and installed 116 main jets and it's running great.
Your bike had 112.5 as standard and went to 170 ??? that may be too much I think, I would try 160 or maybe 150 mains.
(my bike has a 4-1 Marshall but the standard coils)
 
when i installed my dyna coils i didnt notice any diference in the plug coloring--perhaps it was because at that time the thing was running so rich that i just couldnt see it :?: :?:
 
jets

jets

170's are way out there My 1100 g had 140's for a while and the plugs read rich I went to 125's on 1and 2 and 127.5's on 2 and 3. The plugs read a medium tan and it hauls butt . I read about some one running different size jets several years ago because the center cylinders run hotter and leaner than the out side ones I dont know but it works great and the gas milage on a trip is in the mid 40's.
 
Say Richard
i am planning to use two diferent sized jets when i install my new carbs--While i was researching things i read that one of the later model suzukis ran hotter on the outer 2 cylinders--as researche by dyno jet kit company
this post of mine has nothing to do with the advice you are giving, I just thought that some folks might find the article interesting.

http://www.gixxer.com/cgi-bin/ultimatebb.cgi?ubb=print_topic&t=000014&f=26
 
I have read the article that slowpoke provided a link for. This rings true with some articles I have read. Basicly, if cylinders run hotter, richen the mixture. On my GS750 I am lead to beleive that cylinders #2 and #3 run hotter, so the thing to do is adjust the mixture. Maybe adjust the fuel screw 1/4 turn out. Maybe adjust the air screw 1/4 turn in. Maybe change the main jet up a size. I didn't do any of this and I must say that you have to decide what it is you want from this engine. Remember, these bikes are old. Solid stuff I must say, but old. They are not modern powrplants that we see in todays GSXR750's or R1's or Blades's. Just set up you bike as per factory spec, then tweak slightly with float hights, jet sizes, mixture settings to get it running good. Mine purrs when its setup correct, gives very crisp throttle response and pulls through all the gears right up to 8000. Sure, I can rev it harder but I don't need too. After all its 24 years old. If you want the type of performance a few people seem to be chasing, then by an R1 !! But remember, while the GS will never achieve 180mph and razor sharp precision handling it will always be one of the pioneers of the in-line 4 performance bike. Anyway, I best stop rambling .... Here is my setup.

1978 GS750
15 pilots
100 mains
needle set to 3rd clip (middle)
float height 26mm
fuel screws 2 turns out
air screw 1 1/4 turns out
splitfire plugs
boyer brandsen electronic ignition
timing as per factory spec

Runs like a dream, its sheer class on two wheels. (There I go again....)
 
I'm not looking for modern performance out of this. I'm not into going stupid fast. All of these changes took place because they were cheaper and more available than stock parts. My exhaust was rusted out and quite loud, so I bought the mac. my air filter split open, and I happened to get a good deal on pods. The plug wires were shot so I bought the accell coils with replaceable wires. After all this a rejet was necessary. I really didn't mind because the pipe/pods/jet route is an easy way to get more power without damaging anything. And theres nothing wrong with that! The performance gains are really fun. The carbs respond so much quicker than before its like driving a porsche instead of a volkswagon, both get you there but only one can do it in style.......
 
Didn't mean to offend, just wanted to point out the way I am trying to set up my bike. Sounds like yours is running well. Have you read the article on the theory of jetting the hotter cylinders slighly richer ? Anyway, a few things you can do to lean out your mixture. Firsly, try moving the clip on the needles up one notch. Try turning your fuel screws in 1/8 turn at a time. Try going down in main jet sizes one size at a time. Remember, only do one thing at a time and take it for a good ride after each change. I found that if a played with jet size or needle position then throttle response suffered greatly. I had better results with very small tweaks of the fuel screw. I bought a colourtune plug, its a real help when setting up mixture. You insert it instead of one of the plugs. It has a see through window and you can see the colour of the burn. Yellow is too rich and bunsen blue is bang on. This will help you I am sure. Good luck
 
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