Grrrr. another jetting post...

[keman]

That's my point... Another jetting post...

Ok, so I am going to be taking apart my carbs, cleaning them and re-jetting for my 4>1 pipes.

Problem is as I do the research for jetting, I see 100 opinions and lots of advice. more posts on the subject etc...

What I have not found is a table or list of any sort that shows what jets etc are actually right.. It seems pretty simple, but then I am no carbologyst.

If you are installing 4>1 pipes you need to re-jet to ... ?
If you are installing open air intaskes you need to rejet to ... ?
If you are doing both air and pipes, ... ?


I did much searching and researching. read umpteen million confusing posts on jetting, Best I can figure out is the 4>1 will need me to go up 2 on the mains. My BS32SS carbs are factory with 115, so I need 120 jets....

Yet I post that I am going to do this on another bike forum and am told I will end up with no top end, and a drunk rich bike... WTF...???

I trust the GSR far more than I trust the rest of the forums I read.

I have looked everywhere and ended up more confused with a set of 120s coming in the mail.

Can someone please just tell me what jets are right?? What other carb bits do I need to tweak or replace??
Or point me to the actual correct info source that has been hiding from me in my search?

1980 GS850G BS32SS stock airbox, stock filter, well sealed, new boots, new intake O-rings etc. 4>1 Kerker exhaust with the Kerker baffle stuffed mildly.

The bike runs lean from the factory, leaner still with the 4>1 Kerker.
It currently pops through the muffler at cruise and off throttle, more on downhill or heavy gear deceleration. Power is fairly good/strong all the way through from 0-85mph.

Some times too much information is not good, especially if it's not consistant.

[chef1366]

With just a 4-1 with I hope a baffle I 120 sounds like a good place to start. I would of started with a 125 or 122.5 so do some plug reads and make sure you aren't lean. Take out the idle mixture screws and shim the jet needle also.

[IanDMacDonald]

Jetting Guide

Fellas-

As noticed in my thread, I also have a '78 Yammie XS750E, which is my pride and joy! I have put many more hours into it than my GS, but, they will both be pampered over the winter-time.

Anyways, I belong to both the XS750/XS850 & XS11 forums. The Yammies used Mikuni MKII carbs, which are not much different than the Mikuni BS32SS'. One of the members whom I deem a jetting guru, wrote up the following. It is reprinted with permission from Denny of www.xs11.com. Please do not re-post on another forum without his permission. Thank you.

Jetting Recommendations
by Denny Zander

Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

3 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Colour Tune. (See "Colortuning Carburetors" in the Maintenance Section).

Make sure your carbs are in perfect working order before making jet changes.

Example from my '79 XS1100 F:
Stock main jets: 137.5

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Jardine)

1 size for single K&N

1 size for drilled air box

4 (main sizes) - 1 = 3 or 137.5 + (2.5 * 3) = 145.0
1 (pilot jet size) or 42.5 + (2.5 * 1) = 45.0

With this jet configuration I get 32-38 mpg on the open road, Smooth idle, very strong exceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 76K mile on it, of which I have put 44K with this jet configuration.

I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.

[keman]

Take out the idle mixture screws and shim the jet needle also.

As in take them out and leave them out?? I'm confused, that's the screw on the side of the carb under the factory plug right?

What shim do I use on the jet needle? Where does the shim go? This one right?... http://www.thegsresources.com/images...%20removed.jpg

Do I need to worry about air jet size?

This is my first attempt at this. I have done a ton of research ending in more confusion. I feel like I can still do it because everyone says it's cake. I will be using the carb rebuild guide from GS resources carb pages.

Too bad they don't make a dyno jet stage 1 for my bike! (stage three is the only kit available.)

The more questions I ask, the more I feel like an idiot. I want to do this right, and learning how is part of that. But I still feel like an idiot. There's too much information and to many opinions to sort it out in my old addled brain.

[keman]

Fellas-...


... I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.

THAT"S what I have been looking for all this time!!

So, since I went up only two I should be OK without changing the pilot jet. Still need more info on shimming and idle mixture... The carbs are coming apart sunday, and I plan on taking my sweet mary time cleaning them and putting them back together.

[keman]

If I read plug chops too rich, I can always drop in a K&N single. If I'm still too lean I go up one more on the main and one on the pilot. Yes??

[TheCafeKid]

Heres the deal fellas...

These "charts" are more or less a good starting point, or a ballpark.

There are many factors to take into consideration when jetting for different set ups.

For one, the overall state of tune, and general upkeep of required maintenance is an issue.
If you've not adjusted your valves, you're being silly to bother with jetting, as the bike isnt breathing properly to begin with. And if you adjust the valves after you jet/sync, you have screwed with all the work that you put into it to begin with.

No two bikes are alike. Even if they're the same model. Getting the jetting right requires both patience and an understanding of what the bike is telling you..

Even just using an aftermarket header will require some changes in jetting. No matter what their advert tells you. Almost, if not all, carbureted bikes come from the factory set up in a lean state. This is done to meet EPA requirements. So, even a brand new bike will run a tad lean. Now add in the mix 25-30 years of neglected maintenance. Worn out airbox seals, intake boots, airbox boots, orings...etc etc. Every one of these things pushes the bike leaner and leaner.

So to properly jet a bike, you need to start with a known good baseline. And that requires that all of the air leaks, valve clearances, etc be dealt with.

From there you can take your charts suggestions and work around them. But there are no "put these in on your bike and it will run like a champ" answers.

The closest you can get to that is perhaps using, in vacuum style carbs, a Dynojet or similar kit. And even then, depending on what you're doing, there will have to be some adjustments made.

For a pipe, just a pipe, you may get away with simply changing the mains to two sizes larger. But the bike, even in stock form, likely had a flat spot somewhere... Thats usually the fault of the needle circuit. Many people have "shimmed" their needles and found that they have a bike that is much more responsive in the mid throttle area. A pipe, even with larger mains, may only exacerbate the lean spots in the needle circuit.

Generally, its been my experience, guys who dink around with tuning their carbs for pods and a pipe get to a point where the bike runs...OK. But because they most times had no idea how the bike SHOULD run, whether the result of never having had it run great in stock form, or run at all, they've really no idea of all the power they're leaving on the table.

I ran into this when I had my 1100ES. It ran pretty good when I bought it. Had a Supertrapp pipe and pods on it. And supposedly it had been jetted for those enhancements.

Well, whomever had done it had tried to jet vacuum carbs by hand... And i found the bike was drowning up top, stumbled down low and just felt "wet" overall.
I tore into the carbs early the next season and found mains that were WAY too large, stock needles still in use, and pilots that were also WAY too large.

These were used as an attempt to counteract the fact that the stock needle was simply too fat, or sometimes referred to as "too slow", to properly feed the necessary fuel to compensate for the increased air flow.
To get the bike to run even close to well, the mains had to be so large to feed enough fuel in the needle circuit so that the bike didnt fall on its face, that once you got into the main, the bike was drowning in gas...and would fall on its face...

same with the pilot circuit..The bottom end of the throttle was also incredibly fat. Because the pilot to needle transition is also very sketchy when pods have been used.

I spent a good month trying to sort it out. I didnt want to spend money on a Dynojet kit. Id jetted and dialed in mechanical slide carbs before, and got pretty good at it. SO I figured I can do this...

Its simply not the case. After a month of wasted riding time, and headaches and pullin my hair out, I broke down and bought a DJ kit... Followed the instructions and IMMEDIATELY the bike was putting out more power than ever. And after moving the needle clip around a bit, doing some experimentation, i found the "sweet spot" and the bike simply ripped. It was like an entirely different machine. Power EVERYWHERE... arm stretching torque down low, and retro-rocket like rush above 5500K.

I thought the bike was fast when I first bought it...this was a new level of fast.

My point is, there is no chart or rule that is the end all be all of jetting. You've read hundreds of posts on it because there are hundreds of opinions on how to do it. Its as much an art as it is a science.
The best that any one person here or anywhere can give you, especially without being able to FEEL what youre bike needs, or hear it or whatever, is a ballpark set up. That will get you close. And for some people, thats enough. But for the bike to be set up properly, you need to experiment, and learn how to listen and read what the bike is saying. It takes time, experience, and patience....Some people dont have that, and are content to ride around on a bike thats leaving some on the table. Thats fine. And some people simply get frustrated and give up....

But like anything, it requires work and effort...

[keman]

Before I do any of this, I am going to run the coils through a relay and do some plug chops.

I really am fairly competent. Carb tuning just scares the hell out of me.

The valves are proper, there are no air leaks, I have done 90% to get the bike close to perfect.. the carbs are the last bit.

[TheCafeKid]

If I read plug chops too rich, I can always drop in a K&N single. If I'm still too lean I go up one more on the main and one on the pilot. Yes??

You need to figure out WHERE its rich or lean.

The carbs are broken down into different circuits. Marking off your throttle with tape in 1/4 throttle increments is a big help in figuring out where its having trouble.

RPM has little to do with it, its a function of throttle position...

Ideally you shouldnt have to increase the pilot at all..


If you want to make it easier and more sure...buy a DJ stage one kit...

[TheCafeKid]

Did you just say you're trying to jet the carbs and you havent broken them down and cleaned them yet???


Cmon boyo...youre spinning your wheels...You HAVE to take care of the basics!

[TheCafeKid]

BTW...A DJ stage three kit will have a DJ stage one kit in it....

[IanDMacDonald]

One more resource, taken from Factorypro.com. It is meant for CV carbs, but, the same principles may be applied to our carbs as well. Hope this helps:

• 1. Top end (full throttle / 7.5k to redline -
  Best Main Jet must be selected before starting step 2 (needle height)!
  • • Select Best Main Jet
    
    
  • To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the hardest pull at high rpm.
    • If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.
    
    
  
  

• • • If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small.
      • In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
        • Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.

        
        
      
      
    
    
  
  
• 2. Midrange (full throttle /5k-7k)
  Step 1 (Best Main Jet) must be selected before starting step 2!
  • • Select best needle clip position
    
    
  • To get the best power at full throttle / 5k-7k rpm, adjust the needle height, after you have already selected the best main jet.
    • If the engine pulls better or is smoother at full throttle/5k-7k in a full throttle roll-on starting at <3k when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
    • If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
    • If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
      • Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets (Step 1) that produce the best power at high rpm. You will deal with the low-end / cruise next.

      
      
    
    
  
  

• 3. Low end (full throttle / 2k-3k)
  Step 1 (Best Main Jet) and Step 2 (needle height) must be selected before starting step 3!
  • • Float height (AKA fuel level & how to..)
    
    
  • To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
    • Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
    
    
    • If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
    • If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
    • Example: change float height from 15mm to 14mm to richen up that area.
    
    
  
  

• • • REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
      • Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.
        • Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.
        
        
      • Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!
      
      
    • If there are low-end richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs. Click here
    
    
  
  
• 4. Idle and low rpm cruise
  • • Fuel Screw setting (AKA mixture screws)
      • There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs have no caps, but use a special "D" shaped driver, usually supplied in the carb recal kit. We do have them available separately, too. 800 869-0497 to order -
      
      
    • Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation. (pj tuning information)
    • Pilot fuel mixture screw settings, float level (but, you've "fixed" the fuel level in Step 3 - which you have already done!) AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
      • If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
      • Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
        • NOTE: A rich problem gets worse as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
          
          
        • NOTE: A lean problem gets better as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
          
          
        
        
      
      
    
    
  
  

[keman]

Like I said, carbs scare me. I figured I would do the recomended jet when I pull them to clean them out. Did not know that would be an issue?

[TheCafeKid]

One more resource, taken from Factorypro.com. It is meant for CV carbs, but, the same principles may be applied to our carbs as well. Hope this helps:

• 1. Top end (full throttle / 7.5k to redline -
  Best Main Jet must be selected before starting step 2 (needle height)!
  • • Select Best Main Jet
    
    
  • To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the hardest pull at high rpm.
    • If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.
    
    
  
  

• • • If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small.
      • In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
        • Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.

        
        
      
      
    
    
  
  
• 2. Midrange (full throttle /5k-7k)
  Step 1 (Best Main Jet) must be selected before starting step 2!
  • • Select best needle clip position
    
    
  • To get the best power at full throttle / 5k-7k rpm, adjust the needle height, after you have already selected the best main jet.
    • If the engine pulls better or is smoother at full throttle/5k-7k in a full throttle roll-on starting at <3k when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
    • If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
    • If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
      • Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets (Step 1) that produce the best power at high rpm. You will deal with the low-end / cruise next.

      
      
    
    
  
  

• 3. Low end (full throttle / 2k-3k)
  Step 1 (Best Main Jet) and Step 2 (needle height) must be selected before starting step 3!
  • • Float height (AKA fuel level & how to..)
    
    
  • To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
    • Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
    
    
    • If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
    • If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
    • Example: change float height from 15mm to 14mm to richen up that area.
    
    
  
  

• • • REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
      • Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.
        • Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.
        
        
      • Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!
      
      
    • If there are low-end richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs. Click here
    
    
  
  
• 4. Idle and low rpm cruise
  • • Fuel Screw setting (AKA mixture screws)
      • There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs have no caps, but use a special "D" shaped driver, usually supplied in the carb recal kit. We do have them available separately, too. 800 869-0497 to order -
      
      
    • Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation. (pj tuning information)
    • Pilot fuel mixture screw settings, float level (but, you've "fixed" the fuel level in Step 3 - which you have already done!) AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
      • If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
      • Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
        • NOTE: A rich problem gets worse as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
          
          
        • NOTE: A lean problem gets better as the engine heats up.
          • If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
          
          
        
        
      
      
    
    
  
  

His bike HAS CV carbs...

And some of this only applies to adjustable needles, which his bike likely didnt have stock, unless it was a canadian spec bike..or a jet kit in it...

[keman]

And so, I learn more. , I had read the factorypro thing , but it only confused me more.