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1978 Suzuki GS750 EC Mikuni VM26SS Part#

  • Thread starter Thread starter nickr234
  • Start date Start date
N

nickr234

Guest
I was wondering the Part Number for the carb body for my 1978 gs750 EC
 
im looking for the mikuni part number, not the suzuki one. sry
 
Unfortunatly they aren't an aftermarket carb. they are special carbs that were made specificly for the gs750 (and a couple other 4 stokes) and that is why the part # is so hard to find... but i guess i need to explain my situation. i just got some individual pod filters (K&N) and they call for a ~15% increase. i had a 1978 model so the carbs dont have needle possitions. i know the part for the main jet i need (witch is about a 120 from a 102.5) but i need the the carb body part # so i can find the right need jet (the seat that the needle slides into) and the carb body slide.
 
Just out of curiosity, was this bike running ok before you decided to go with the pods?
 
yes it is running just fine. it has a little bit of a rough idel because i don't have the carbs synced to the engine (they are benched synced because in my opion it givea better top end performance). the valves need to be shimed and i am also going to replace the piston head and rings. so that should fix the rough idle. im not racing the bike at all i just like to give it some gas every-once-in-a-while. my gs 750 came with the racing type of exhaust. It is the performance exhaust of the time which i think has more comprestion than the standard. you can tell the difference because the performance exhaust has just one big hole and the standard has 1 smaller hole in the middle with 6 smaller yet (maybe) holes around the center one. anywho im basicly just doing this for fun. thank everyone for your insight
 
Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. nickr234,

Check all the vendor links in your "mega-welcome", Sudco, etc. You might find a catalog with the number you're looking for. Otherwise, let me welcome you to the forum...

I just stopped by to welcome you to the forum in my own, special way.
big_hi.gif


If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....:)

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike! :D

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff
 
Have a look at the carb sticky on here to see your standard set up - there were 4 standards for the 8 valve 750s.

Plus do a search on running pods on your bike. Loads and loads of stuff on here about how to tune them in, what jets / settings to run at.

Your needle jet by the way is either a P-6 or an O-1 depending on engine number and your slides will either have a 1.5 or 2.5 cutaway, again depending on your engine number.
 
nickr234 said:
Unfortunatly they aren't an aftermarket carb. they are special carbs that were made specificly for the gs750 (and a couple other 4 stokes) and that is why the part # is so hard to find... but i guess i need to explain my situation. i just got some individual pod filters (K&N) and they call for a ~15% increase. i had a 1978 model so the carbs dont have needle possitions. i know the part for the main jet i need (witch is about a 120 from a 102.5) but i need the the carb body part # so i can find the right need jet (the seat that the needle slides into) and the carb body slide.
Click to expand...

The VM 26 carb does indeed have needle positions. Have you pulled out a needle (or better yet, all 4) to see where they are set?

It's unlikely you need different slides - the VM carb is very easy to tune and generally just needs rejetting and perhaps moving the needle clip down a notch

Also unlikely you need a new needle jet

A 4-1 exhaust (which has less back pressure and doesn't have any compression) and pods on your 750 should come out at about a 120 main, perhaps a 115 or 117.5 and possibly one size up on the pilot jet

I'm curious, if it runs well, why would your tear the head off?

And, yes, VMs run much better when they are vacuum synced. Much better
 
Holy Lean Batman.

Holy Lean Batman.

so last night i took apart a carb slide to see if there were any notches on the needles. it turns out that there are! i was lead to beleive by both K&N and the internet that all motorcycles 1978 and after didn't has ajustable notches for the needle on VM carbs... but also sumthing that is wird the carbs should not have fuel pilot skrews either because the epa made them illegal to tighten emission controll... i also read somewere (i can't remember) that the fuel pilots dont show up on any of the blowup schematics (which i just now conffimed)... im wondering if suzuki said to hell with the EPA and gave them boggus schematics so they could be sold in the USA (just a thought). anyhow so i put the notch down to were is should be for the filters. and since my orginal setting for the carbs were pilot 15, i thought the 17.5 i had in there would cut it (i dont' have any higher main, for now, so i just wanted to test the low end) and it wasn't even close. i have oval K&N pod filter and not cone so i think that has something to do with it. but i have a 20 and a 22.5 pilot coming and a 117.5 and a 122.5 for a main on the way. hopfully that will give me a good starting point. but we shall see.
 
Big T said:
The VM 26 carb does indeed have needle positions. Have you pulled out a needle (or better yet, all 4) to see where they are set?

It's unlikely you need different slides - the VM carb is very easy to tune and generally just needs rejetting and perhaps moving the needle clip down a notch

Also unlikely you need a new needle jet

A 4-1 exhaust (which has less back pressure and doesn't have any compression) and pods on your 750 should come out at about a 120 main, perhaps a 115 or 117.5 and possibly one size up on the pilot jet

I'm curious, if it runs well, why would your tear the head off?

And, yes, VMs run much better when they are vacuum synced. Much better
Click to expand...


tear the head off? im sorry but i guess i dont know what you mean

the only thing that im taking off and replacing is the air box (and im still keeping it) and the jets.

the reason i wanted to get a new slide and a new needle jet was because i thought they were not adjustable (the needle position).

also with the bench sync vs. the vac sync, you get a better performance with lower end and mid range with the vac sync, but not when fully open. the reason for this being is because with these old vm carbs you sync them by adjusting the slides. this means that if you adjust to the 1st carb, when fully open the 2nd 3rd and 4th carb will be either above or below where it is supposed to be thusly decressing power.

sorry i didn't see your post b4 i posted that last one, and in the future i wil try to clean up my posts.

Thanks,
 
nickr234 said:
tear the head off? im sorry but i guess i dont know what you mean

the only thing that im taking off and replacing is the air box (and im still keeping it)
Click to expand...

Well, in post #7 (?) of this thread, you did say you were going to replace " the piston head and rings" , so most of us assumed you were going to tear the head off.
As for epa stuff, My bet is that suzuki had to dump the vm carbs to meet the CALiF idle requirements- the cv met that goal. But there are plenty of folks here who can explain it better.
 
nickr234 said:
also with the bench sync vs. the vac sync, you get a better performance with lower end and mid range with the vac sync, but not when fully open. the reason for this being is because with these old vm carbs you sync them by adjusting the slides. this means that if you adjust to the 1st carb, when fully open the 2nd 3rd and 4th carb will be either above or below where it is supposed to be thusly decressing power.
Click to expand...

I can see by your posts so far that you've become misguided on a number of issues so far, I guess you can't believe what you read on the Internet! (oh wait, um, okay, anywhere but here)

You sync VMs to standard amount of vaccum, so at that point, all of the carbs will be equally open. There's nothing to prevent them from opening further, just the cable stop

Since I've vacuum synced a hundred or more sets of carbs in the last 40 years, I've found that bench syncing is often quite far off compared to the vacuum sync. Vacuum synced bikes run better everywhere in the rpm range

There's no loss of horsepower on the top end by vacuum syncing.
 
The CV carbs came out in 1980 to meet the emission requirement. Prior to 1980 there were no emission standards. Regardless of your theory Vacuum sync makes a big difference in the way the bike runs, smoothness. You are cheating yourself if you think otherwise
 
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ahhh yes i did say that didn't I

ahhh yes i did say that didn't I

i didn't remember saying that i was thinking about replacing the cylinders:-\\\. lol anyways. yes i am because when this bike was sitting in my dad's garage for about 19 years and at some point the engine decided to seize up:eek:.

i put mavel mystery oil down into the plug holes and let it set for a week. that fixed it thankfully but at somepoint im sure the commpression related to cylinder heads probably suffered. i did a leakdown test so see where compression was being lost and it didn't sound like there was any leaking into the crankcase but im worried about it.

but there was alot of compression being lost from the valves. about 10-15 percent on cylinder 1,2, 4, and about 20-25 percent on 3. so there is no question my vavles need to be shimed.

and maybe if some of the rings and cylinders heads need to be replaced it is on 3 since that seem to have the most compression lost.

Thanks everyone for your insight.


:EDIT also since my breather tube no longer will have anything to go into should i plug it up? Or will that hurt the engine? EDIT:
 
Last edited:
You can leave the breather tubes off but don't leave the vaccuum one off (or at least blocked if you're running a non-standard fuel tap).

You get no advantage at high throttle openings by not synching. You synch at low slide opening to get a smooth slow run and transgression - at low throttle openings the disparity between slide heights shows up much more as a percentag of throttle opening. At WOT if you've done a good bench synch the percentage differences are insignificant.

I've been looking at another way of synching carbs without using the gauges and I've now tried it on a dozen different sets of Mikunis. Measure (using calipers) from the top of the carb to the top of the slide on each carb (same point on each carb). I've followed up with the vaccuum gauges and not needed to adjust anything. I was surprised at how accurately Mikuni manufactured their carbs and slides. I'm not sure if this will hold for all carbs as it's still only a small trial but it looks promising. Of course you can only use it on carbs where the vaccuum levels should be equal - there would be a bit of guesswork on those carbs where the outers are meant to have 'half a ball' more.

Do your valve clearances then ride the snot out of the bike. Check your compression figures again after a good few miles - could make all the difference if she's been stood.
 
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