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**tkent02** · 06-18-2012, 06:06 PM

Maybe someone changed the sprocket ratios, some folks don't like to listen to the engine sing and they change to a lower ratio.

What are you sprocket sizes, and what are the stock sprocket sizes?

Also something like a worn chain can slow you down that much.

You could be too rich too, what do the plug chops tell you?

**p_trice** · 06-18-2012, 06:32 PM

my rear sprocket is a 41 tooth. I believe that to be the same as stock. I'll have to get back with ya about the front sprocket. i haven't got to it yet. My chain is newer and is in perfect conditon. My brakes don't drag at all, they r all new. It's kind of hard to read the plugs, by the time i get back to my garage and shut it off to pull plugs, they r white on the tips from running lean at idle. If I rev the bike to 4-5 rpm in neutral, hold it for a bit, then kill the bike. the plugs have a wonderful tan color all over them, so i would say the midrange is about perfect. I'm just having trouble near the top of the rpm range. It raps out great in town, in like 2 or 3rd gear. its just when i'm trying to top it out in 5th. It seems like in 5th at high rpm, when i go from 3/4 throttle to full throttle it doesn't pull any harder, it's about the same.

**Gonzo** · 06-18-2012, 07:25 PM

If you're doing plug chops, find a place where you can hammer it, shut if off and coast to a stop and check plugs on the side of the road. A long country road with no traffic sounds good.

I'm no expert mechanic, but wouldn't an engine wrap out regardless of what size sprocket is on it? The first thing that came to my mind was the spark advance, but then again, I know nothing about rejetting so maybe you're on the right track already.

**p_trice** · 06-18-2012, 07:49 PM

I drove at full throttle in top gear for about a mile, pulled the clutch, and killed the bike. I pulled over and checked the plugs. The tip of the plugs were whitish gray, the base of the plugs were a bit sooty, and the electrode was a nice whitish brown color. Am i too lean at full throttle?

**Steve** · 06-18-2012, 10:49 PM

Originally posted by p_trice View Post

.... it has a dynojet stage 1 kit with DJ116 main jets ... Any thoughts?

I think it's running LEAN.

Let's just put it this way: stock Mikuni jetting in an '80 750 is 112.5. That is the same as a DJ 120. You are running 116s, which are two sizes leaner than stock.

You should be running Mikuni 120 or DJ 128.

.

**gearhead13** · 06-18-2012, 11:47 PM

Originally posted by Steve View Post

I think it's running LEAN.

Let's just put it this way: stock Mikuni jetting in an '80 750 is 112.5. That is the same as a DJ 120. You are running 116s, which are two sizes leaner than stock.

You should be running Mikuni 120 or DJ 128.

.

Yes, but the 750 kit comes with a main air jet corrector which changes things. If it was installed that is.

**tkent02** · 06-18-2012, 11:51 PM

Originally posted by Gonzo View Post

I'm no expert mechanic, but wouldn't an engine wrap out regardless of what size sprocket is on it?

No, it takes a certain amount of power to move the bike that fast. If the ratio is too tall, it ain't gonna get there.

**p_trice** · 06-19-2012, 11:15 AM

my stage 1 kit didn't come with air correctors. I believe the stage 3 does though. I will look into getting some bigger main jets. thanks for the advice everyone.

**gearhead13** · 06-19-2012, 01:38 PM

Jet Kit for 1980-1985 Suzuki GS750

http://www.dynojet.com/pdf/3102.pdf

Dynojet Jet Kits Whether you run a standard motorcycle, or a tuned sportbike, Dynojet Carburetor Jet Kits can provide you with a simple and affordable solution to all your carburetion problems. Dynojet Jet Kits increase power and smoothness throughout the entire rev range, while maintaining optimum fuel economy. Each Dynojet Jet Kit includes comprehensive instructions which show step-by-step installation and testing procedures to ensure a perfect setup every time. This is backed by free telephone and Internet support to Dynojet customers. Kit installation and Dynamometer services are available in many parts of the world. Please see the Dynamometer Center Search Page to locate your nearest dyno shop. Read Full Description Jet Kit Types Needle & Needle Jet Caps Many newer bikes have very flat power and fuel delivery curves when used with the stock exhaust and air-box. When aftermarket pipes are used, the power curve is usually not flat. You find the need to lean out for low speed and richen up for top end; or leaner on the top end and richer at the low speed. In order to achieve full function and driveability, Dynojet develops shrouds or cap style nozzles for adjusting the upper or lower top end. They also have an effect similar to fuel injection by breaking up the fuel as it enters the air stream. Fuel Needle The design of the needle is where Dynojet spends most of its R&D time. The needle is designed to give the correct amount of fuel throughout the mid-range and is also designed to allow adjustment from groove 1 to groove 6 with little or no effect below 3000 R.P.M.; then with the correct end dimensions, the needle will have little effect on the main jet regardless of needle position. This isolates all circuits from each other and ensures easy set-up of the midrange and driveability. Main Air Jet This jet allows air into the emulsion tube to mix with fuel being drawn up from the float bowl. It controls the amount of fuel which can be pulled from the float bowl into the venturi. The larger the size of the main air jet, the more air you get and less fuel. The smaller the main air jet, the more fuel you get and less air. Dynojet alters this only to achieve the flattest possible fuel delivery curve. Pilot Circuit This controls 100% of the engine idle and 25% of the transition onto the needle. Dynojet has found that the engine will idle with the standard pilot jet, with or without the air-box and with the slides and needles removed from the carburetors; therefore we never change the pilot jet. Doing so is proof that you are not using the other circuits correctly. Idle and off idle is controlled by the mixture screws and the float level which have the most positive effect below 4000 R.P.M. On some models the pilot air jet is changed to provide optimum fuel economy. Correct balancing of the carburetors also ensures a smooth idle. Main Jet We develop our main jets to correctly serve two functions; static load and dynamic load. The static load is the fuel received through the main jet in the upper gears, where the tachometer is moving very slow. The dynamic fueling portion of the main jet is the amount of fuel received from the jet in the mid-range potion of the power. For example, you have a GSXR1100 G,H with #130 main jets. You then install #125 mains. After running the bike you notice the top end has improved but the mid-range doesn't pull as well. You then install #135 mains and you notice the mid-range is great but the top end is slower. This is a common compromise when using stock main jets and needles. If you install Dy 93 Dealers Orders Dealer Orders "Dealer Orders Dynojet Research Inc. dealers much call in to place an order. Please call us at: 1-800-992-4993 (Toll Free)/Suzuki/GS750/1985

The .pdf file says it comes with DJ120 jets for an aftermarket exhaust, not much bigger but worth a try. Supposed to have a 112.5 Mikuni stock, maybe a 117.5 or 120 mikuni main?

**p_trice** · 06-19-2012, 04:03 PM

i went on the cheap and bought the jet kit off ebay. it didn't come with the DJ120 jets. I guess that's what i get. I'm just going to buy some genuine mikuni 120 jets. These should work right?

Error Page | eBay

http://www.ebay.com/itm/Mikuni-Small-Round-Main-Jet-120-Kawasaki-Polaris-Suzuki-Yamaha-BN-BS-Raptor-/140768520270?pt=Motorcycles_Parts_Accessories&hash=item20c675284e&vxp=mtr

**gearhead13** · 06-19-2012, 04:55 PM

Originally posted by p_trice View Post

i went on the cheap and bought the jet kit off ebay. it didn't come with the DJ120 jets. I guess that's what i get. I'm just going to buy some genuine mikuni 120 jets. These should work right?

Error Page | eBay

http://www.ebay.com/itm/Mikuni-Small-Round-Main-Jet-120-Kawasaki-Polaris-Suzuki-Yamaha-BN-BS-Raptor-/140768520270?pt=Motorcycles_Parts_Accessories&hash=item20c675284e&vxp=mtr

Those are small round, you need large round. The pic isnt right.
A 120 mikuni main is closer to a 130 DJ main

**p_trice** · 06-19-2012, 06:12 PM

so i need a large round jet. what size should i go with? 115?

**Steve** · 06-19-2012, 07:43 PM

Originally posted by p_trice View Post

so i need a large round jet. what size should i go with? 115?

Wouldn't it be nice if someone suggested a size?

From post #6:

Originally posted by Steve View Post

You should be running Mikuni 120 or DJ 128.

and from post #10:

Originally posted by gearhead13 View Post

..., maybe a 117.5 or 120 mikuni main?

.

**p_trice** · 06-19-2012, 07:50 PM

k, will do

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80 gs750 won't top out

80 gs750 won't top out

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