Motorcycle Repair Questions? Ask a Mechanic ASAP
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.
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.
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.
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.
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.
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.
Now you will want to adjust all of the air screws.
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.
You should now have a great running bike.
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.
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.
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.
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?
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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.
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.