Chef1366 or Kieth....help!

[txironhead]

Jgordon said that Chef1366 or Kieth could help me out, but any expert advice would be appreciated.

Here's the bike:

1981 GS750E, carbs from a 1000 or 1100, Vance and Hines 4-1 w/no baffles, stock ignition, pod filters. Mechanically stock otherwise.

Here's the questions:

Will the carbs work? I noticed that they're slightly off center and slightly larger than the stock carbs (which were trashed beyond repair, the idiot that tried to rebuild/repair them probably had two screwdrivers and one brain cell). Would I be better off trying to get a good set of 750 carbs? Will I have problems with air leaks from the intake boots?

If the carbs will work, what jets do I need? I'm assuming that a stage 3 kit for the 750 will work, but I'm by no means a carbuerator expert (obviously).

Do I need to get a baffle for the V&H? I'm trying to get this bike on the road as cheaply as possible. Also, is it possible to get a glasspack insert for the megaphone?

Thanks in advance for any/all help!

[jgordon]

Jgordon said that Chef1366 or Kieth could help me out, but any expert advice would be appreciated.

Here's the bike:

1981 GS750E, carbs from a 1000 or 1100, Vance and Hines 4-1 w/no baffles, stock ignition, pod filters. Mechanically stock otherwise.

Here's the questions:

Will the carbs work? You should have 32's and the one's off the 1100 are 34's. Probably not worth the effort unless you pump up the ponies

I noticed that they're slightly off center and slightly larger than the stock carbs (which were trashed beyond repair, the idiot that tried to rebuild/repair them probably had two screwdrivers and one brain cell). Would I be better off trying to get a good set of 750 carbs?bThis is probably the best bet.

Will I have problems with air leaks from the intake boots? You could make some adapters if you really wanted to use the 34's but I would go with some VM's.

If the carbs will work, what jets do I need? I'm assuming that a stage 3 kit for the 750 will work, but I'm by no means a carbuerator expert (obviously).

Do I need to get a baffle for the V&H? I'm trying to get this bike on the road as cheaply as possible. Also, is it possible to get a glasspack insert for the megaphone? Bike Bandit

Thanks in advance for any/all help!

................

[chef1366]

I'm going to start you off with some links. I don't know about fitting the 1100 carbs on the 750. 1100 carbs are 34mm and 750 carbs are 32mm. Someone will probably tell you that you can but I wouldn't know.

http://cgi.ebay.com/ebaymotors/suzuki-gs750e-gs-750-carburator-carbs_W0QQitemZ110047090449QQihZ001QQcategoryZ10066QQrdZ1QQcmdZViewItem

Ask the seller if the diaphragms are good on these carbs. If they aren't don't buy them because they are too costly to replace. If the seller doesn't respond don't buy them.

http://cgi.ebay.com/ebaymotors/SUZUKI-80-85-GS750-Dynojet-carburetor-jet-kit_W0QQitemZ4627527056QQihZ002QQcategoryZ35597QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

This is a dynojet kit. It is the easiest way to jet your carbs with the mods you have. It comes with all the jets you need except the pilot jet. I personally went up one increment on the pilot and we have similar mods. Mikuni jets go up and down in 2.5 icrements. My stock pilot jet was 45 and I went with a 47.5.

http://www.thegsresources.com/gs_carbrebuild.htm

http://www.cycleorings.com/

http://cgi.ebay.com/ebaymotors/SUZUKI-80-83-GS750-CARB-KITS_W0QQcmdZViewItemQQcategoryZ35597QQihZ008QQitemZ180044195129

This a great step by step for rebuilding carbs with pics. Buy the o-ring kit and and use it. Use the K&L carb kit for the gaskets and float assembly. Don't use the jets cause they come with the Dynojet. Be careful with the float adjustment and don't break the float post when removing float. (brace the post while tapping the float pin out)

http://www.factorypro.com/

This site provides a good step by step on jetting you carbs and helps give you a better understanding of your CV carbs.

I am not an expert but I do know these CV carbs. I've had these babies off so many times it would make your head spin.

When and if you take these steps feel free to ask questions about the final tuning process using plug chops and synchronizing the carbs(I use mecury sticks)
Plug chops teach you how to read your spark plugs at certain throttle positions to adjust each carb circuit. These carbs operate on throttle position and not rpm.
Pilot circuit= idle to just open throttle
Needle circuit=1/8 throttle to 3/4 throttle(or more)
Main circuit= full throttle.

Synchronizing the carbs make the throttle plates open up at the same time so all the cylinders work together.

[txironhead]

Um......what are plug chops? Thanks for the links, I'll definitely look into them.

[chef1366]

Sorry, I didn't see you already had the dynojet kit. First do a bench sync(do a search)
Using tape mark your throttle at full, 1/2 and closed. Then mark 1/4 and 3/4.
A plug chop is the process of jetting each circuit by reading spark plugs. To test the main jet find a good stretch of road preferably uphill. The main works with the full throttle so run through the gears and hold the throttle at full for as long as you can and kill the engine and pull in the clutch. Coast to the side of the road and pull the plugs. Tan is good. White is lean. Black is rich. If white you need to richen your main(bigger) and if black you need to lean(smaller)
Do the same with 1/2 throttle which is the needle circuit. This uses notches on the needle instead of jets. With lean plugs you lower the needle by going up notches. With rich you raise the needle by going down on the notches. (Dynojets suggested setting on the needle tends to be on the lean side so I'd start a little richer by raising the needle 2 notches from their suggestion)
Do the same with the pilot circuit during idle. Set your idle adjustment screws with the highest rpm method. Screw in until the rpms begin to drop and then take them out until the engine hits its highest rpm. (If you take them out too far the rpms will start to drop)
After you get the carbs tuned in do a vacuum sync with Mercury sticks, a Morgan Carbtune or whatever works. (some here have even made their own)

[KEITH KRAUSE]

If the carbs are off center compared to stockers, it sounds like there will be a fit problem that will lead to or cause an immediate intake leak. I can't see them but it sounds bad to me. I wouldn't use them. Having said that and if you insist...
For your mods, I wouldn't go with these particular larger 34 carbs but 34's can work on your bike. After all, you've increased intake flow and exhaust flow. No reason the larger carbs won't work, if they seat correctly into the manifolds.
What you would need to do in order to find a starting point to re-jetting, is compare the specs of both carbs by reading a factory manual. I would use the 32's jet sizes when deciding how to change the jetting. If there are only main jet, pilot jet, pilot air jet differences, then you can most likely find a combo that works, besides jet needle adjustments. If the jet needles, needle jets, or any "fixed" primary air jets are different, then keep in mind they are designed for the larger motor and they'll have to be changed too. Then the larger carbs will probably not work well with the 32's different jet needles and needle jets. You won't be able to change any pressed in jets. That could mean trying to find a combo could be very difficult and may not work without issues. I'm not saying they won't work, but you could go nuts trying to find a combo of jets that work.
If you have a DJ jet kit(?) their jet needle is designed to work with a specific needle jet and primary air jet. Without knowing true differences, I can't say how difficult it may be. I'd look for some 32's. If you can't find them in good shape then I suppose you have to make the 34's work but only if they fit into the manifolds as they should.
As for the pipe, I'd try to get the baffle and re-pack it.
And as for vacuum synching advice, I suggest vacuum synching BEFORE taking plug reads. Synching is part of the jetting. Without a synch first, you'll have an increased chance of seeing uneven plug reads because of uneven vacuum. What different colored plug reads/cylinders will you base any jetting changes on? Which cylinder do you choose? Makes jetting even harder.
Keep in mind the bike needs to be in good tune before the synch. Compression, valve clearances, spark quality/timing, mixture screws adjusted for highest rpm, must be correct first. If you run pods that need oiling, be sure they aren't over oiled. Run the bike before the synch to suck out excess oil. Synch on a completely warmed up motor.

[jgordon]

1981 GS750E, carbs from a 1000 or 1100, Vance and Hines 4-1 w/no baffles, stock ignition, pod filters. Mechanically stock otherwise.

Here's the questions:

Will the carbs work? You should have 32's and the one's off the 1100 are 34's.

Probably not worth the effort unless you pump up the ponies

I noticed that they're slightly off center and slightly larger than the stock carbs (which were trashed beyond repair, the idiot that tried to rebuild/repair them probably had two screwdrivers and one brain cell). Would I be better off trying to get a good set of 750 carbs?

This is probably the best bet.

Will I have problems with air leaks from the intake boots?

You could make some adapters if you really wanted to use the 34's but I would go with some VM's.


Do I need to get a baffle for the V&H? I'm trying to get this bike on the road as cheaply as possible. Also, is it possible to get a glasspack insert for the megaphone?

Bike Bandit

Thanks in advance for any/all help!

Txironhead...Read this reply very carefully....

[txironhead]

Will any 32mm Mikuni CV carbs work on my bike, or only carbs off of a GS? What other year/size carbs will work? Is there any difference between the carbs on different models (ie: E, L, G, etc.) other than jetting?

I really appreciate the help I've recieved so far. I've decided to try and find some 32mm's and either sell, trade or hang on to the 34's.

[chef1366]

Will any 32mm Mikuni CV carbs work on my bike, or only carbs off of a GS? What other year/size carbs will work? Is there any difference between the carbs on different models (ie: E, L, G, etc.) other than jetting?

I really appreciate the help I've recieved so far. I've decided to try and find some 32mm's and either sell, trade or hang on to the 34's.

Any Suzuki Mikuni CV 32mm carbs from 80-85 will work. (With the Dynojet kit) I know Kawasaki used the CV carbs but you'll have to research that one. I think the spacing with the pre 80 VM carbs are different but I know JGORDON will know what to do with that one. He probably even has the carbs you need for the right price!

[txironhead]

Okay guys, need your help again.

Quick update: Apparently PO did NOT install a DynoJet Stage 3. According to the DynoJet website, there is a "Main Air Corrector" (?!?!) that is supposed to be installed and glued in OVER the air jet. The carbs that came with the 750 had nothing over the air jets. However, the bike was running at one time with pods and a V&H open header. From looking at the jets I took out of the carbs, they are not stock size. Is there a jet kit that does not utilize a "corrector"?

Here's the new situation: a member here is willing to trade my good 1100 carbs for his good 750 carbs, and he is willing to throw in whatever size jets/needles/etc. I need. The carbs are currently on a running bike and not leaking, etc. What parts do I need to compile my own "jet kit"? This is what is contained in the DynoJet Stage 3 kit:

(4) Main Jets DJ124 (stock exhaust)
(4) Main Jets DJ130 (aftermarket exhaust) (I'm assuming size is 130?)
(4) Main Air Correctors DC0302 (no clue)
(4) Fuel Needles DNT604
(4) Adjusting washers DW0001
(4) E-clips DE0001 (mine are still good)
(1) Tool DT002 (?????)
(1) Glue DA0001 (to glue in air correctors)
(1) Screw (to remove idle screw plug, mine's gone already)
(1) Slide drill DD#30 (assuming a #30 drill bit to enlarge hole for needles, bit sketchy about doing that)
(1) Plug Drill DD#5/32 (again, my plugs are already gone)

SOOOO........

I've also had recommended that I enlarge my pilot jet to 47.5. To recap, bike is an '81 GS750E, pod filters, V&H exhaust (currently open, I plan to replace baffle and repack with steel wool as per another post), stock ignition and otherwise original. Honestly, I don't have the money to buy a new jet kit and this member offering to give me whatever jets, etc. that I need is a godsend. I just need to know what sizes of each thing to get.

Thanks for bearing with me. It's rough trying to piece this bike together on a broken and frayed shoestring budget, and, honestly, it's a bit humiliating. I've actually had other people (on other sites, luckily) tell me that if I can't do it exactly as I should, then I shouldn't be trying to work on a bike at all. Disability checks suck. Oh, well, enough whining.

[chef1366]

Stock jet sizes for 1981 GS750 E
Pilot jet 42.5
Main jet 112.5
Pilot air jet 170

I suggested that you go up one step up in Mikuni land on your pilot jet which would be 45.
If you do not have a dynojet installed and you don't have notches on your needle you'll have to raise the needle by putting tiny washers under the clip. Two washers = one notch. You can get washers at Radio Shack.

On the main jet I'd start with 122.5 and also buy 120 just in case they are rich. Dennis Kirk and local shops do return jets.

On the pilot air jet I went up one step with the larger main. I'd go with a 180.

If you don't have dyno needles I would not drill your slides. You don't drill the needle hole but an air port which raises your slides quicker for faster throttle response.

Dynojet and mikuni jet sizes are different that Mikuni rates their jets on the amount of gas that flows through them and Dynojet rates them with their size. So don't assume that they are the same.

This is not going to be an install and go. It takes plug chops and synchronizing to get these carbs tuned to your bike and with patience you will be a pro and posting advice to newbies.

I understand you are poor but a Dynojet will cut your time in half.

If the bike was running well with the jets that were in the old carbs use them. If they work I'd be interested in how close I was on the jetting.

[KEITH KRAUSE]

I agree with chef about the main jet size choices. A DJ 130 would be right in between a 120 and 122.5 Mikuni main. I'd try 122.5.
45 on the pilot jet seems right.
Go up one size over stock on the pilot air jet.
Set mixture screws for highest rpm and vacuum synch.
If using the stock jet needles and if they're non-adjustable, I suggest raising them approx' the equivalent of two positions richer than stock. That would be about .090".
To improve throttle response, removing the air box makes drilling the vacuum orifice's necessary. Get instructions and follow them exactly.
REMOVE any float bowl vent lines and leave the ports open.
I don't like the idea of steel wool as a packing replacement. It would turn into a ball of rust and start to eat at the pipe too. Just my opinion, never tried it.
Keep in mind that re-jetting should only be done after the "basics" are done. Basics are good compression/no oil burning, valve clearances set, 100% fuel flow and venting, fresh exhaust gaskets, clean/adjusted/vacuum synched carbs, clean air filters, good spark/timing/connections throughout.
If the basics aren't done first, you can be in for a lot more of trial and error beyond the normal that re-jetting may require.

[txironhead]

I was actually thinking about using stainless steel wool, as per this thread:

http://www.thegsresources.com/_forum/showthread.php?t=91241&highlight=steel+wool+exhaust

Might just run it with the baffle alone, though. Gotta get the baffle and then see how it sounds without packing material. I wanted the glasspack sound but haven't figured out how to do it on this exhaust.

[txironhead]

BTW, the needles are adjustable (does that mean they're not stock?) but I think they only have 4 notches, not 6 like the Dynojet kit showed. I'll have to double check.

Where do I find instructions on drilling the vacuum orifices?

[chef1366]

Research and buy the drill bit you need for the slide #30? All you do is enlarge the air port with the drill bit. NOT the hole the needle goes through. What notch is the needle set on now? I'm not sure of the stock setting.
I drilled down towards the diaphragm side with if sitting flat on a table. Keep the drill straigh and don't push too hard. Let the bit do the work.