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Doug E.
Doug E., Kawasaki Master Technician
Category: Motorcycle
Satisfied Customers: 2885
Experience:  Professional motorcycle mechanic since 1978. Vintage motorcycle restorer.
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I have a 1982 Suzuki GS750T. HISTORY I bought this bike

Customer Question

I have a 1982 Suzuki GS750T.

HISTORY:
I bought this bike about 6 years ago.
I know very little about it before I owned it.
I had the starter replaced and had the carbs rebuild and tuned at a local shop near whare I used to live (the shop is no longer there so I can not ask the tech who worked on it any questions)
At this point the bike ran great, I was told that the exaust system needed to be replaced and further carb tuning would be needed then. I held off on doing that as my budget was exausted for the time being.

I rode the bike for 3 years without problem.
I had a minor spill when I hit some gravel in a turn, I brought the bike home and it sat for a year.
The next next year I began to repair it, I replaced the bent handel bars, fixed a dent in the tank that was there when I bought it, painted it and bought a new Vanse and Hinz 4 into 1 exaust (I could not find the stock exaust) The gage cluster still needs plsatic replaced but all gages function.

I got it running and fairly well for sitting as long as it did, I had a slight hesitation when I opened the throtle but nothing to make it unridable. I parked it for the winter without draining the gas and this year am having problems getting it running right again.

I understand that leaving it sit with gas in the carbs over the winter will plug up the small passages.

Here is what I have done this year.
The bike would start and idle fine but would die if I tried to put it in gear and ride it, so I drained the gas and replaced the spark plugs.
This did not seem to help the problem.
I did a compression test and all 4 cylinders were very close around 120 (I did not right it down as I check so I am going from memory)
No change.
I then decided to do a good carb cleaning.
I fully disiabled the carbs and soaked them in cleaner (About 30 to 45 mins each) I got at my local NAPA auto parts store (the 1 gallon bucket with a basket in it), I cleaned out all the small holes in the jets and such with a small wire I use to clean my spray guns. I did not force it through if the hole was to small for the wire. I sprayed carb cleaner and air from my compressor through all the jets and passages and looked to see that all was clear where I could.

After reassemble It started fine and would idle nicely but would die if I tried to open the throtle with the air box off, I have the air box back on and I can now thrttle up a bit but think that I need to properly tune the idle and air mixture.

he air adjustment screw was 2 3/4 out on all 4 carbs before I dissambled so I started there, I have not touched the Idle sync adjustment screws.

The best I can get get it right now adjusting the air screw, The idle is to high with the idle adjuste screw all the way out (the one that move all moves all 4 at once) I am hoping that someone can give me detailed instruction on the procedure to tune the carbs from scratch.

Also will I need to rejet the carbs for the aftermarket exaust? if so how would I know what kit to buy.
If I am to rejet I think I would like to get 4 pod type air filters as I hate the air box on it, ( have to remove the gas tank to get it out of the way to pull the battery for winter charging.) so a recomendation an air filters and jet kits would be appriciated)

Thanks in advance for any and all help the experst can give.
I could get it
Submitted: 3 years ago.
Category: Motorcycle
Expert:  Doug E. replied 3 years ago.

Kawasaki Doug :

Hello

Kawasaki Doug :

Did you remove all of the jets when you cleaned the carbs? if not, you will need to do it again. The back sides of the needle jets (main jet holders) build up varnish and soaking or pressure will not remove this. The jets need to be pulled, then soak the bodies and jets and blow them out.

Kawasaki Doug :

For future reference, the Yamaha carb cleaner is the very best product on the market. It mixes with water and is designed to dissolve varnish from gas going stale. It's also much safer to use then the automotive stuff that will destroy your nervous system if if gets on your skin.

Kawasaki Doug :

Being you have an aftermarket exhaust you will need to rejet the carbs. After you have done that, then you can adjust the air mixture screws and idle and be all set.

Kawasaki Doug :

If you decide to remove the airbox, I would try and find some 29mm Mikuni smoothbore carbs. Trying to jet your stock carbs for pod filters is almost impossible, even for an expert. You will not be happy with the results.

Kawasaki Doug :

For your stock carbs, go two sizes larger on the main jets. Raise up the needles in the slides by 2mm. If you don't have adjustable needles, use a 2mm washer. You can get these at a hobby shop or from an Arctic Cat dealer. They have a plastic washer that is the exact size needed. Here is a photo of how and where the washer goes.

Kawasaki Doug :

Full Size Image

Kawasaki Doug :

The stock carbs were very lean to start with, so you might want to go up one size richer on the pilot jets. On most bikes you don't do that just for pipes, but the 80's Suzuki motors were very lean from the factory.

Kawasaki Doug :

Now you will want to adjust all of the air screws.

Kawasaki Doug :

Lightly seat them and back them out 1 turns. Start and run the engine and bring it up to operating temperature and adjust the idle. You will now perform what's called an idle drop procedure. It helps to have a shop tach that reads in 50 RPM increments.

Turn all 4 screws out 1/2 turn. If the engine RPM goes up, continue another 1/2 turn. Continue until the RPM does not increase. Adjust your idle RPM.

Turn the #1 air screw in 1/2 turn until the rpm drops 50 RPM. Turn out 1/2 turn. Adjust your idle speed and go to #2 and so on until all are done. Adjust your RPM when complete.

If you cannot get your air screws adjusted, it means there is dirt or varnish in the pilot jets or your valves need to be adjusted. I find that motor runs best at about 2.5 turns out in most cases.

Kawasaki Doug :

You should now have a great running bike.

Kawasaki Doug :

Do not buy any of the jetting kits if any are offered for your bike. They are way overpriced and most don't work. My jetting info is cheaper and better and has been tested by me.

Kawasaki Doug :

Let me know if you need more information. If that is all you needed, please hit the accept button so I get credited for my answer. Thank you.

Customer: replied 3 years ago.

Did you remove all of the jets ?

I removed everything with the exception of the dismantling the slide and needle assembles (I need to get new needle nose snap ring pliers to get in there) I did wipe them off with a carb cleaner soaked rag to remove debris, they felt smooth to the touch before reinserting.

I made sure that both spray carb cleaner and air went through all the ports and jets before reassembly

 

For future reference, the Yamaha carb cleaner is the very best

I have seen reference to this product in other answers and I will look for it in the future.

 

If you decide to remove the airbox

I guess I will have to live with the airbox as is, This bike is not a project I can afford to put the kind of money into that a new set of fancy carbs would cost, I am willing to buy some parts to tweek preformance but if I have hundreds or thousands to spend on this I would take it to the local shop and say go wild.

 

For your stock carbs, go two sizes larger on the main jets. Raise up the needles in the slides by 2mm

Where do I look to get new jets? Do I just take one of the old ones to my Suzuki dealer or is there a prefered shop online? How do I know what size jets I have acording to a manual I found online My bike had #112.5 main jets, #42.5 Pilot jets and #50 starter jets, does that sound right for this bike? If so what is 2 sizes would that be # XXXXX on the main jets?

 

Raise up the needles in the slides by 2mm

As I mentioned earler I have yet to disasemble the slide and needle assemble, The needles seem to have a spring or spring washer under them as I can move them a 1/8" I assume that 2mm washer in there will bring them up and I think I can figure that out just wanted to mention that thay are not completely rigid in there.

 

go up one size richer on the pilot jets

Same questions as about the main jets.

 

Now you will want to adjust all of the air screws

I dont have a shop tach, can I do these adjustments watching the tach on the bike or am I out of luck without a pro tool?

 

I think I understand the procedure described for adjustment of the air screws.

I currently have the screws at about 3 turns out, seems to idle well there and I can open the throttle without it bogging, but the idle seems is a bit high after reving then drops down a 1/2 second later, this makes me think my carbs are out of sync.

I dont have access to a 4 port vacume or mercury gage but I do have a vacume pump with a gadge on it and a friend should still have a 2 port mercury gadge I lent him years ago, can I check vacume on each cylider with the pump/gage and balance that way or work 2 at a time with the 2 port mercury gadge? I am trying not to buy a lot of tools I will not use again as this is a hobby not a profession.

 

Do not buy any of the jetting kits

I am always pleased to take the advide of a pro over that of a online shop trying to sell parts but the jet kits (specificly dyno jet stage 3 Link: http://www.motorcycle-superstore.com/1/5/90/30239/15392/PITEM/Dynojet-Stage-3-Jet-Kit-1982-Suzuki-GS750T-Parts.aspx) I have seen for my bike are about 100 bucks, and come with drill bits, instructions washers, springs needles, ect. Do I need to drill out the ports? is that kit overkill, I like to save money how much will 4 each main, pilot jets and washers cost me seems like that would be almost 100 bucks anywhere.

Expert:  Doug E. replied 3 years ago.
Stock jets are $5 to $7 each, although if you buy jets from an aftermarket source they are about half that. Washers are a few bucks at the most.

The problem with the kits is that many I have seen just don't work. They have the wrong needle tapers or other issues and end up being a nightmare you spent $100 on.

If you want to get by on the real cheap, take your stock jets to the hobby shop and size them with a drill then buy the next size drill bit. A good hobby shop carries all of the micro drill bits for a pin drill. This is actually what I use. I always recommend buying jets to customers because once you drill it, that jet is no longer the size marked and if it's too rich you have to buy the jets.

A good hobby shop that sells lots of RC equipment will have a massive selection of drills and washers. You can jet a carb for about $5 if you know what to look for.

Doug
Doug E., Kawasaki Master Technician
Category: Motorcycle
Satisfied Customers: 2885
Experience: Professional motorcycle mechanic since 1978. Vintage motorcycle restorer.
Doug E. and other Motorcycle Specialists are ready to help you
Customer: replied 3 years ago.

Doug,

 

I have a couple follow up questions if that is ok.

 

I plan to buy main jets(not the kit) from dynojet (I can get 5 sets of 4 mainjets for $30)

 

In the instructions for there jet kits they tell you to drill the slide hole with a supplied drill bit either #30 or #40 depending on the kit installed.

 

Do you think I should drill this hole? I have a set of numbered bit, should I follow their size sugestion or do you have a recomendation as to how much larger this hole should be if at all.

 

next I have the carbs on the bike before jetting to do a little testing. I noticed that gas was leaking out of the airbox drain, so I took the airbox off to see which carbs was causing the problem,

None of the carbs were leaking gas back towards the airbox with the petcok on pri (fuel on bike off) but when the bike was running if I rev the engien with my hand behind the carbs I felt moisture. After doing some reading I am thinking that my floats need adjusted to keep the fuel level down a little but lower, does this seem like a correct assumption?

Expert:  Doug E. replied 3 years ago.
Hello,

I was out of town and just returned. You will need to correct the float problem before doing any jetting work. Here is how to check it.

Connect a clear hose to the bottom drain nipple on one of the float bowls and route it up alongside of the carbs. Level the bike, turn the petcock to prime and open the drain screw. When the gas stops rising, measure from the level in the tube to the top of the float bowl. Here is how that test looks.

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The level should be 4 to 5mm below the top of the float bowl.

I would not drill the main jet holder/needle jet at this time.

Doug
Customer: replied 3 years ago.

Thank you,

 

I wil get the parts I need to set the fuel level.

 

Just to be clear, the hole I was asking about drilling is refered to as the Slide lift hole, It is next to (off center of) the slide needle hole, I am guessing that a larger hole will let it travel faster.

 

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I am ok with not drilling it to start with if you still think that is best.

It is easer to drill it later than undrill it.

Expert:  Doug E. replied 3 years ago.
If you were going to try and use pod filters, then I would drill it. I wouldn't drill it otherwise.

Doug

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Doug E.
Doug E.
Vintage M/C restorer
2483 Satisfied Customers
Professional motorcycle mechanic since 1978. Vintage motorcycle restorer.