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GS750E tuning

  • Thread starter Thread starter spwalker09
  • Start date Start date
S

spwalker09

Guest
I'm slowly but surely making progress on my GS. I installed a 4-1 system (MAC, I believe), and pods that I had sitting around. I had the standard MAC crushed-pipe baffle cut out, and a straight piece of pipe welded in.

I installed a Dynojet Stage 3, set to their specs, which from what I've heard around these parts, is way too rich. That was confirmed when I started it up, and wouldn't rev past 4-5k - it bogged down and wouldn't go any higher. I dropped the needle down (installed the clip 1 notch above the DJ spec) and she revs through the whole range, but backfires when the throttle is abruptly closed - sign of running too rich on the mains? I'm thinking instead of raising the needle up another notch, should I go ahead and order one size smaller on the main jets? The DJ kit comes with 130s, which are Mikuni size 122.5 - the next size down would be 120.

Nevertheless, I decided to try some plug chops and tune according to FactoryPro's method. I'm a noob when it comes to tuning, but short of installing an AFR, I decided to try go it old school. Trouble is, I'm not getting good readings on my plug chops (nothing is jumping out at me). I'm not about to jump on the highway during rush hour to do some WOT runs then to shut it down and take a plug reading at the side of the highway with all the inattentive sheeple racing by. So, I did some 1st and 2nd gear pulls on my street to see if I can get a reading. Any rec's on the best plug chop method?

Lastly, if anyone out there has gone through the pain and suffering, and has some better ballpark main/needle combination to try, mind sharing?

Thanks
 
Continuing the saga...still looking for answers.

I took the bike out yesterday to get some more runs in, again up and down my street. As before, it's stumbling at WOT, confirming I should probably go down a size on the mains. I have a set of DJ124 jets from my stage 3 kit, but they're a little smaller than I want to experiment with (don't want to run too lean)

The DJ124's recommended for just a 4-1 exhaust and stock airbox...isn't that stage 1? There's a whole separate kit (with different sizes) just for that, so I'm a little confused.

Continuing on, I stopped into my neighbor's house to chat for about 15 minutes, and after I hopped back on the bike, it would only run on 3 cylinders, huge loss of power (couldn't give it any throttle to start off in 1st gear) and wouldn't rev in neutral past 3-4k before it would backfire thru the exhaust because its obviously not running right.

From what I read on FactoryPro, symptoms of running too rich only get worse as the bike gets hotter (which it did) so, sizing down should be my next step. Am I going down the right path?
 
What cylinder fouled? It does sound like you are way rich to me as well. Main jet size shouldn't have any affect on idle though same goes for needle clip position. Have you checked to see if your petcock vacuum diaphragm isn't punctured and flooding the #3 cylinder? Does it pop when idling, or if you rev it does it drop below idle then return to normal? Those are signs of rich idle curcuit, so is loading up on extended idle, that makes the bike stumble when you give it throttle. I'd work on getting the idle circuit right then move to main jet then needle settings.
 
Ghost rider from exile land asks if you have replaced the orings in the float seats. These are the most common placefor fuel to bypass the float needles.
 
Posting an update....

First, I junked the pods I put on because I had them, and installed the correct K&Ns that the kit was designed for. Today, I had just enough time to get the bike hot and do some pulls up and down my street. Bike runs much smoother and pulls harder than before, but I still feel the slightest hesitation in the midrange. There's also an off-idle stumble that I'm more concerned about. I'm gonna need more time to do some plug chops to see where the tuning is now.
 
Bringing this back from the dead. I parked the bike for the last 2 years and dug out the carbs this past winter to go through them thoroughly. I dipped/cleaned them (they were all sorts of nasty), installed new pilot jet rubber plugs, and installed new o-rings from Robert Barr. Took my time and made sure the float settings were correct, the float needle springs were not sticking (they were gummed up) and that everything was set to DJ's recommendations.

Got the carbs back on the bike, with fresh oil and a new battery, and it fired up, albeit not idling very well. It'll die w/o the choke on, and it's very slow to return to idle when the throttle is blipped - classic lean symptom. The fuel screws are 3 turns out from seated - seems like a lot? That is the stage 3 recommendation. I'll try 1/4 turn out increments to see if the idle clears up.

I know they probably need syncing from being apart, as well as mid-range/full throttle tuning, but I'd like to get them at least be able to idle in order to warm up the bike and get some tuning in. Any other suggestions?

Plan of attack:
1) Adjust fuel screws to get an OK idle
2) Sync carbs
3) Tune full throttle (verify that the DJ 130 main is the right one)
4) Tune mid-range (needle)
 
Let's see if I follow this........So you were the original guest poster 2 years ago and now are Stevo12 with same gs750e ?

the carbs sat for long time, how long did you dip them? Sounds like your idle circuit passages are not clean enough- they might improve as it runs, but......
 
Try running the fuel screws in to 2.5 turns from seated.

How are the boot O-rings?
 
tom203 said:
Let's see if I follow this........So you were the original guest poster 2 years ago and now are Stevo12 with same gs750e ?

the carbs sat for long time, how long did you dip them? Sounds like your idle circuit passages are not clean enough- they might improve as it runs, but......
Click to expand...

Correct...sorry if I was unclear about that! MY original account was deactivated because I was inactive for a long time.

I dipped everything for ~1 hr at a time (each body, each bowl, all the jets, etc.). Sprayed cleaner through all the passages to make sure they were clear

78550GS said:
Try running the fuel screws in to 2.5 turns from seated.

How are the boot O-rings?
Click to expand...

Forgot to mention when I get home tonight I'm going to spray the boots to make sure there are no leaks.

If I'm not mistaken, aren't the fuel screws metering fuel? So I would need to turn them out for more fuel @ idle?
 
Stevo12 said:
Correct...sorry if I was unclear about that! MY original account was deactivated because I was inactive for a long time.

I dipped everything for ~1 hr at a time (each body, each bowl, all the jets, etc.). Sprayed cleaner through all the passages to make sure they were clear



Forgot to mention when I get home tonight I'm going to spray the boots to make sure there are no leaks.

If I'm not mistaken, aren't the fuel screws metering fuel? So I would need to turn them out for more fuel @ idle?
Click to expand...

Dip each carb 24 hrs. The fuel screws are too hot 3 out as soon as you get the pilots unplugged. I would actually start at 2 turns out when they are correctly cleaned.
 
Damn...back to the work bench these carbs go...

Those o-rings I installed, good as gone when I take them out to dip the carbs again? Is it recommended to get some more?
 
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