VM26 carb rebuild - missing pieces 78 GS750

[portdave]

I am in the process of rebuilding/cleaning/dipping my carbs. I am going to make some adjustments to the main jet size and e clip position based on what I have read here. Especially advice by Keith K and CK, Steve and others. I have K&N pods and a Mac exhaust. I noticed the stock Main jet size that is currently in there is still close to the original size. (105) I plan on trying 125 or 117.

In the process of putting them back together after dipping etc. I noticed that I am missing some parts on the slide mechanism. I do not have the 2 plastic spacers for the e clip or the spring. Not sure where the spring is supposed to go or what it does.

I have been driving this bike like this for about a year. The main issue has been a flat or sluggish spot between 4500 to 6500 rpm during a WOT run in first or second.

Any suggestions or does someone have some extra parts? I saw the parts on the microfiche but unclear as to whether they are the right ones or not based on the description.

Thanks

 

[portdave]

More info on plastic needle spacers

More info on plastic needle spacers

According to the microfiche, some of these carbs had spacers and a spring and some didn't. Not sure why but they show two different carbs on the listing. View attachment 7447 This one is without the spacers......

 

[portdave]

...and this one

...and this one

is with the spacers.View attachment 7448


Sorry for the small pics. Not sure how to make them larger. Still confused by all the posts talking about making sure the spacers are where they need to be and the spring but it looks like there were different setups.

 

[Big T]

Not sure how to make them larger. Still confused by all the posts talking about making sure the spacers are where they need to be and the spring but it looks like there were different setups.

Your confused because you've been reading about newer bikes with CV (BS) carbs and yours is an older bike with VM carbs.

You don't have spacers, you have adjustable needles.

For the mid range problem you are having, it's probably the needle position more than the main jet, altho I'm thinking you should have 112.5 or so, 125 sounds too big for your set up

I'd raise the needles a notch and see how it runs.

What do your plug chops show??

See here

http://members.dslextreme.com/users/bikecliff/

For photos and plug chops and everything nice

 

[KEITH KRAUSE]

I can't see the pics you supplied and can't zoom them on my computer.
Other members have made the same statements about the parts being there or not. I believe all the '78'/79 did use the spacers. Maybe the VM's used in '76/'77 did not.
The spring around the needle is necessary to stop vibration from shortening the jet needles service life. Vibration damages it and that's why the later carbs used this superior design. With the spring used, the thinner plastic spacer that goes under the e-clip is needed to eliminate any negative friction/contact between the spring and jet needle e-clip. The top spacer, which is thicker, goes directly on top the e-clip. Some have a small impression that should align with a dimple on the thin brass plate that goes at the inside/bottom of the slide. Some don't have this impression. This thicker spacer, actually called a ring, effects mixture because it sits atop the e-clip and effects how high the jet needle rises. The ring is also part of the later design that helps against vibration. I'm not sure why it has to be thicker.
Now if you're carbs should have the thicker spacer and they don't, then the jet needle circuit would run quite a bit richer unless someone has compensated by raising the e-clip position. Stock for '78 is the middle (3rd) position.
I can't be sure what year your carbs are. They may not be original. I do know that the later spacer/spring design is what I would want. Either way, 1/3 to 1/2 throttle position chop testing/general performance tests tests will tell you what you must do with the jet needle e-clip position.
As for your main, a 125 Mikuni main might work. I'm not sure how the Mac flows. The 117 has no chance unless something's odd with the bike. I'd probably go with a 127.5 or 130 if you've tuned everything correctly. Keep in mind the stage 3 DJ kit uses their own 138 mains which, due to different sizing methods, is the equivalent of 130 Mikuni mains.
You may not like the best jetting you can get out of the stock jet needles.
Don't forget to remove the two floatbowl vent lines.
You also must bench synch and then vacuum tool synch the VM's as part of the jetting and judging performance/test results.

 

[spyder2120]

mr. krause, could you contact me? i have a question about my carb adj. and they say you are the man. 79gs750l. my email is spyder2120@yahoo.com. thanks, bill.

 

[spyder2120]

i didnt want to tread on his question.

 

[portdave]

Your confused because you've been reading about newer bikes with CV (BS) carbs and yours is an older bike with VM carbs.

You don't have spacers, you have adjustable needles.

For the mid range problem you are having, it's probably the needle position more than the main jet, altho I'm thinking you should have 112.5 or so, 125 sounds too big for your set up

I'd raise the needles a notch and see how it runs.

What do your plug chops show??

See here

http://members.dslextreme.com/users/bikecliff/

For photos and plug chops and everything nice

Thanks for the info.

I am pretty sure all the carbs had the needle clip setup but most have the spacers and some dont according to all the posts I have read. That is what the microfiche show.

I am still trying to get the bike back together after the rebuild. I will try the chops when I get there.

 

[portdave]

I can't see the pics you supplied and can't zoom them on my computer.
Other members have made the same statements about the parts being there or not. I believe all the '78'/79 did use the spacers. Maybe the VM's used in '76/'77 did not.
The spring around the needle is necessary to stop vibration from shortening the jet needles service life. Vibration damages it and that's why the later carbs used this superior design. With the spring used, the thinner plastic spacer that goes under the e-clip is needed to eliminate any negative friction/contact between the spring and jet needle e-clip. The top spacer, which is thicker, goes directly on top the e-clip. Some have a small impression that should align with a dimple on the thin brass plate that goes at the inside/bottom of the slide. Some don't have this impression. This thicker spacer, actually called a ring, effects mixture because it sits atop the e-clip and effects how high the jet needle rises. The ring is also part of the later design that helps against vibration. I'm not sure why it has to be thicker.
Now if you're carbs should have the thicker spacer and they don't, then the jet needle circuit would run quite a bit richer unless someone has compensated by raising the e-clip position. Stock for '78 is the middle (3rd) position.
I can't be sure what year your carbs are. They may not be original. I do know that the later spacer/spring design is what I would want. Either way, 1/3 to 1/2 throttle position chop testing/general performance tests tests will tell you what you must do with the jet needle e-clip position.
As for your main, a 125 Mikuni main might work. I'm not sure how the Mac flows. The 117 has no chance unless something's odd with the bike. I'd probably go with a 127.5 or 130 if you've tuned everything correctly. Keep in mind the stage 3 DJ kit uses their own 138 mains which, due to different sizing methods, is the equivalent of 130 Mikuni mains.
You may not like the best jetting you can get out of the stock jet needles.
Don't forget to remove the two floatbowl vent lines.
You also must bench synch and then vacuum tool synch the VM's as part of the jetting and judging performance/test results.

Keith,

Thanks so much for all you do around this place. The way you share your knowledge is commendable.

Sorry the pics did not come out but the basically show the two different types of carbs for 77-79 GS750s. One has the spacers and spring and one doesn't. I am trying to get another set with the spacers and order the parts. I am gonna try and see how this one runs.

Yesterday I did the bench sync and then followed the procedure by Paul Musser and did the idle adjustment and then used my new morgan tune. I started out okay but it kept getting worse. Long story short I forgot to plug the number 3 vacuum since I was running off prime with a longer fuel hose to my tank. I came to find out I was not the first to do that.

So I took the carbs back off . I decided to set the fuel screws to 1.5 like you said in another post and came to find out the fuel screw for carb 2 was messed up. It was not seated all the way compared to others. It is all stripped out on the carb body. Can you even tap those? I didn't have a tap that small. Looks like .5 mm thread. I am trying to find a replacement #2 carb body. I was able to get the screw in without the spring but I have not gotten any farther.

You mean the vent lines on the bottom of carbs 1 and 4? What does that do? Back pressure?

Did music at church tonight and then came home to find the AC at the house is out. Pretty hot in Florida tonight. I have to pick up a capacitor. It was swollen. Hopefully that does it.

I will look at the carb some more and see after I deal with the AC.

Once again I thank you for your help.

David

 

[portdave]

I forgot...

I forgot...

Keep in mind the stage 3 DJ kit uses their own 138 mains which, due to different sizing methods, is the equivalent of 130 Mikuni mains.
.

I didn't think I could get a DJ kit for this bike? Is there one from another model I could try and use?

 

[TheCafeKid]

No...no DJ kit. The only one is a Stage3 1000 kit, and that will very likely be too big for the 750...HOWEVER if you need some help with it..give me a call. 937-672-7684

Depending on what you're doing, i can give you a good base to start jetting from, and I did get your email about some carbs. I have a full set I would sell. They'd likely need cleaned and new orings, but they're complete...

Josh

 

[portdave]

No...no DJ kit. The only one is a Stage3 1000 kit, and that will very likely be too big for the 750...HOWEVER if you need some help with it..give me a call. 937-672-7684

Depending on what you're doing, i can give you a good base to start jetting from, and I did get your email about some carbs. I have a full set I would sell. They'd likely need cleaned and new orings, but they're complete...

Josh

Thanks Josh. I may give you a call one night this week if I can get my AC working at the house tomm. Plus it is one of my girls 6th B'day tomm.

I have one set of carbs I am looking at but I would love to get some that have the right spacers on them Do yours? How much would you like? You can email me a response if that is better. Email on name.

I sure am learning alot

 

[KEITH KRAUSE]

David, the two floatbowl vent lines are located at carbs 2 and 4 (left to right sitting on the bike.) When running pods, crosswinds and/or general turbulence can cause fuel starvation. Removing the tubes so the bowls can vent easier greatly reduces this problem.

 

[KEITH KRAUSE]

mr. krause, could you contact me? i have a question about my carb adj. and they say you are the man. 79gs750l. my email is spyder2120@yahoo.com. thanks, bill.

Not sure why but clicking your link does nothing.
Just ask here and I'll try to answer. If it gets involved then start a new thread.

 

[portdave]

David, the two floatbowl vent lines are located at carbs 2 and 4 (left to right sitting on the bike.) When running pods, crosswinds and/or general turbulence can cause fuel starvation. Removing the tubes so the bowls can vent easier greatly reduces this problem.

Do you mean that the same port that is used on Carb 3 for the vacuum on the petcock, on 2 and 4 is a vent instead? If so mine had no hoses on 2 and 4. Thanks again.

 

[KEITH KRAUSE]

Do you mean that the same port that is used on Carb 3 for the vacuum on the petcock, on 2 and 4 is a vent instead? If so mine had no hoses on 2 and 4. Thanks again.

Yes. They're float bowl vents. Each one vents two carbs.

 

[portdave]

Yes. They're float bowl vents. Each one vents two carbs.

Thanks Keith.

I hope to put the carbs on tonight or tomm. Lots of other things I have had to fix or work on at the house lately. At least the AC is working again thank God.

I will let you know.

David