GS750 poor acceleration

[KEITH KRAUSE]

And just a reminder. You spend the most time riding while on the jet needle circuit. Many try to install larger main jets only and call it good, but that's a mistake. Your pods/pipe will lean out your mixture a lot at all three jetting circuits. Lean mixtures will cause pre-ignition and hole your pistons and burn your valves.

[casimage]

Got the screws out

Keith;

I got the screws out of the needle jet assemblies on all four carbs. I was able to remove and inspect the jet needles. All of the e clips were in the second position down from the top of the needle, the sharp end being the bottom.

I replaced the 110 jets with 120's as I erroneously thought the Mikuni kit included 130s but only had 110, 110, 120 and 140s. I figure to start with the 120s and go from there.

I also contacted both Dynajet and K&N regarding jet kits specifically for my bike. I will be traveling next week so hopefully I will have an answer by the time I return.

Have you ever seen a "Dial a jet" kit,

http://www.thunderproducts.com/dial_a_jet.htm

I had posted an inquiry on the performance board but apparently no one has used this setup.

If I get some time tomorrow, I will put the clips on the bottom position as recommended. However, I am using the sharp end of the needle as the bottom reference so please let me know if you are referening the positions in the same way.

I will start from the being with a bency sync followed by using the Motionpro to see if the problem gets resolved.

Thanks again for everything.

[renobruce]

I looked around for a DJ kit for your bike.... didn't find anything. They only show making a kit for the 78-79 1000 with the VM carbs. You might need to buy that kit and also buy smaller main jets? I don't know what size jets go in a 750, but Keith will know. Also, if you already have the right sized jet, maybe you can just buy the jet needle? I think they are the same on all the VM carbs? The DJ jet needle part number for the 1000 is DN0304. The DJ stage 3 kit part number for the 1000 is DJ3304.

[KEITH KRAUSE]

Just read the latest as I'm going out for the evening.
I'll add to this when I get back late tonight. Hope it gets to you before you make any needle changes.

[KEITH KRAUSE]

Have heard about the Dial a jet but haven't read much about it yet. Are they claiming it replaces the factory jetting set up or is it actually assisting it? I can't see how it replaces it but I haven't bothered to read it yet.

Yes, when I describe the e-clip position on the jet needle, I mean counting the grooves from the top of the needle. Lowering the e-clip richens the mixture. Always replace the factory plastic jet needle spacers in correct order. Thicker spacer (actually called a ring) goes on top the e-clip, thinner spacer goes below the clip. Be careful of correct re-assembly of all slide parts. Make sure the thin brass plate with the dimple goes right side up. Don't let it flip upside down and screw you up. I re-assemble by placing a very small dab of grease on the thin plate and this makes it stick to the throttle arm base. Then I drop the screws through and slowly lower this entire assembly as a unit into the slide. For the needle assembly, you just pull down the needle and its spacers until they're basically flush with the bottom of the slide before lowering the slide assembly. Just be careful of pulling the needle too far down in its spring and the top spacer falling off. It can take a little tinkering for some to get it right. Just be sure the screws are going in right and uniformly snug and the tighten them. Don't over-tighten any carb parts. The throttle arm to throttle shaft bolts only call for 3 ft/lb and the throttle adjusting screw HOLDING NUTS only get 3.5 ft/lb. These bolts are often over-tightened.

The main reason for this message and hoping it gets to you before you adjust the needles, is that you mention your e-clips are in the 2nd position from the top. I thought the factory position was 3rd. This is actually a good thing because it gives you more richening ability if needed. The only negative thing is that it means more potential adjusting to see if the stock needles will work. I know I said earlier you shouldn't have to try more than twice to see if the needles will work. Now it could be three times. Of course, you may get it right the first time and that would be great.
I take this stuff seriously and don't like to think my advice is causing you work but jetting is infamous for trial and error, as I've tried to mention.
What I'm trying to get at is I'm not sure about placing the e-clip in the bottom position now. That would be three full positions richer. Based on past experience, I THINK two positions richer would work and because I thought your e-clips were in the 3rd position, that gave us those two positions richer to try and I suggested trying the bottom position. I have worked on 750 carbs before and their needles were in the 3rd position so this has thrown a curve at me a little. I looked a 750 carb spec sheet and it also said factory position was the 3rd position but that doesn't matter now. What we know is yours are in the 2nd position and the e-clips have never been moved since you're the original owner. I have adjusted needles three positions richer in the past to get good results but it's quite a jump. Your bike appears to be quite fuel starved though and part of me says to try the bottom position. This is where I'm hoping you did a good job on all the other basic tuning because it's easy for me to wonder if this apparent lean mixture/fuel starvation is truly a jetting problem. But having to make my own decision, I think it is jetting related and I have to hope my advice helps you get it right, preferably the first time. You can of course have your own ideas as to what will work.
The other thing that complicates guessing is I don't have any plug reads to see for myself after 1/3 tests and I sure can't ride the bike.
To make it simple, three positions just seems a bit too much richer and so I'm going to suggest placing the e-clip in the 4TH POSITION from the top. If you take my advice, I hope I'm right. 1/3 throttle plug/performance tests will tell.
I assume you're familiar with how to bench and vacuum synch these carbs? I have a detailed bench synch post somewhere here if interested. Don't forget to adjust the slides fully OPEN position too, not just the fully closed position which I also cover in that thread. The factory manual states the same procedure. I don't know what manual you're using. Pilot fuel screws should be around 1 1/4 to 1 1/2 turns out for starters from lightly seated. Fine tuning them will usually be necessary. Warm up and adjust the side air screws for best idle and then vacuum synch. Then test.
I'll try to look in here tomorrow and hope to hear good news.

[casimage]

Success?

Keith:

Wow, you really know your way around Suzuki GS's.

I moved the clips to number 4 position, installed the 120 jets, bench sync'd and put the carbs back on the bike. Followed your instructions to the letter incuding putting a dab of grease on the plate at the throttle arm base. Pilot jet and air jet screws are 1.5 turns out.

It started right up, I let it warm up and then played with the throttle. It is smooth all the way up to 9K rpm. No more hestiation or lagging. Starts popping around 8K but I can live with that until I get time to sync the carbs using the motionpro carb stick.

There is some popping on deceleration when I let go of the throttle

I will fine tune it when I get back from San Francisco next weekend but all the major problems seem to have been corrected.

Thanks again for all the help and advice. I could not have done this without your and other board members' assistance.

[KEITH KRAUSE]

I'm glad it's running better.
The carbs must be vacuum synched before you can get accurate plug reads and true performance results. I'll wait 'til that's done and read your test results. If it still pops at 8K which I assume was at 3/4 plus throttle (?) we'll have to get plug reads at full throttle. We'll need plug reads at full, 1/3, and minimum throttle positions regardless if it pops or not. The important thing here is throttle position, NOT rpm. We'll make changes according to the plug/performance results. You still have one needle position richer to use if your 1/3 tests are lean and we'll see what the mains say later.

Decel' pop is something that we sometimes have to live with when making intake/exhaust changes, but too much decel' pop isn't acceptable. Be sure your header gaskets aren't leaking though before richening the pilot circuit. You can first try adjusting the pilot fuel screws an ADDITIONAL 1/2 turn out and test. If no joy, you can try a 1/2 turn more. Be aware these richer screw adjustments may help with decel' pop but may create another problem. If no joy still, I suggest returning the screws to about 1 1/4 and installing 17.5 pilot jets. Be sure you get the exact same length/style of pilot jets if needed. But the pilot circuit is sensitive to good/uniform vacuum too, so fine tuning the pilot circuit will wait 'til the vacuum synch is done too.