79 gs750E Carbs

[Anonymous]

I found a $75 miracle in this guys carport in northern Colorado. I took it home, cleaned it up, serviced the electrical, brakes, clutch, and cleaned the carbs (pretty gummed up after 10 years in the same spot). After I got it together and put a battery in it (along with an inline fuel filter), it started right up; but she stalls and bogs without choke. I can get her down the road with 3/4 choke. Talk to me about where I can get a manometer and how the hell I restore proper air/fuel mix. The facory set screws on the carbs have been messed with. I want real information beyond my clymer manual. I know how to use tools, but I want to get this girl cookin right the first time. Thanks from Fort collins, Colorado. elev.5500 feet

[Anonymous]

Mr. Collins...

How far into cleaning the carbs did you go? 10 years is a long time and gas will be good and hard by then. These carbs are pretty complex and having just succesfully, albeit an arduos task, rebuilt mine -- I found I couldn't just blow out the holes and put it back together again. I had to dismantle and dunk them one at a time to get all the passages cleared. Then and only then did I get the bike to run right after a 7 year slumber. Chances are if you can get them apart without breaking the bowl gasket, then you can just replace o-rings and clean the old jets. IF the bike has vacuum sliders, make sure you clean the needles up on these real good too, or they may not be moving.

There is a great step-by-step carb dismantle series on the Garage page on this site. Just be careful to remove ANY rubber parts if you dunk them, or you'll not have them when you pull them out of the tank.

And them maybe it's just that CO used up it's allotment of air to feed the fires this year and so at 5500 feet there isn't enough to run the bike now...

[Anonymous]

Thanks for the info/reply.. The carb teardown on this site is a good start, but I would love to find reliable/comprehensive info on my mikuni slides. Also, I know that i can adjust/sync. my carbs from the top (lock nut and screw under cap) using a manometer, but what about the air screws on the sides of the carbs? Do i have to have an exhaust gas analysis to figure the right settings for each? Talk to me. p.s. This site rocks!

[Anonymous]

The manometer is really only for the butterflies, and you can do a pretty good job of adjusting you air/fuel screws reading the plugs. I have a manometer to use, but haven't done so yet on this bike. You should consider one of those special screwdriver/wrench combo tools designed for this though. They're not that expensive and the aggrivation of not having them may cost you more.

As for detailed information -- good luck. You may get lucky and get a factory repair book off e-bay, but what I'd do (if I were to do it again) is to take specific notes and take photo's (and I had my digital camera and still forgot to do this myself). The Cylmer book I have is half-way detailed, but still leaved a lot to the imagination, which makes for a nervous rebuild. The carb kits don't tell you anything, unlike their automotive counterparts. Hate to say it, but it's just you and me and all these other fine folk on the GS, man. There is a lot of knowledge here, no doubt, but if you take your own precautions, you'll get it to go.

Cheers,

Roger Moore
81 GS750E
New Brakes
Rebuilt calipers
Rebuilt Rear Master Cylinder
New Electrex Regulator Rectifier
Rebuilt carbs
New chain and front sprocket
(Hand machined nut for said sprocket)
New shock oil
Cleaned/tighten electrical connections
Fresh oil
What's next?
Runs like a dream after 7 years asleep

[Anonymous]

What's next?

I can tell you whats next Roger Moore. We need to hook up for a ride with all of the Pacific Northwest GS owners. Got two more months before retiring from the USAF and I'm moving back home. Been gone for 20+ years. Hey......does it still rain all of the time up there?

[Anonymous]

We need to hook up for a ride with all of the Pacific Northwest GS owners.

Yeah, that does seem like a logical next step... Or, I could just cover it up and let it sleep for another 7 years and start the whole process over :roll:

We'll it's been OK here this summer so far. Being so close to the Pacific coast and on the leading edge of the jet stream, Seattle will never be considered a prime summer vacation desitination, but it sure has some nice motorcycle travel routes within a couple hours in any direction. My desire is to load up and go down the coast to California again. That was a most excellent adventure.

I saw a group trying to get together in the Portland, OR area, but I've been spending all my time trying to get it road worthy. I should add a post to the forum.

Cheers,

Roger Moore

[Anonymous]

I've been the highway 1 route, San Fran to Ocean Shores. Freakin' excellent. You would love it Roger. I hoping next summer to ride the Pennensula up there (101 all the way around). I'm from Shelton, by the way.

[Anonymous]

I didn't do Hiway 1 since I was heading south and needed to go to Sacramento. So I went through Central CAL down hiway 20 from 101 to Woodland and that was way cool. Nice twisty roads along a little river just in the cool of the day.

You're over in the Olympic side. The last "real trip" my bike got was to the Olympic hot springs with me and my (now ex) wife. She hated the ride and swore she'd never ride it again, and made it very hard for me to every ride it again. That's why it sat for so long. But I digress...

Hopping the ferry to the other side and going around the coast of Washington would be a good weekend trip even. Time... just need time, and fair weather -- I want to have fun while I'm at it -- not fight rain.

Roger Moore

[earlfor]

The factory pilot screw setting for a 1979 GS750 EN 1979 is
7/8ths of a turn out. Factory setting for the air screw I do not know, but you will find that idle will be smoothest and starting will be very easy if it is between 1 3/4 and 2 turns out. In conjunction with these settings and using mains within the 102 to 105 range with stock air box/filter and pipes you will get a nice even light brown burn on the plugs if you set the carbs to pull 24 inches of vacum at 2500 rpm. I am at sea level and youre at 5000 ft, so there will be some small change to make in the carb vacum settings. I expect you will be on the rich side with my settings, but better to start out rich and be safe rather than start lean and hole a piston first thing. I would set it up rich and run it to determine how much of an adjustment is going to be needed.

The very first thing you MUST MUST do is take the carbs apart and thoroughly clean them. All the set up info in the world isnt going to help if the carbs cant flow fuel. :-) :-) :-)

Earl

Also, I know that i can adjust/sync. my carbs from the top (lock nut and screw under cap) using a manometer, but what about the air screws on the sides of the carbs? Do i have to have an exhaust gas analysis to figure the right settings for each? Talk to me. p.s. This site rocks!

[Anonymous]

to rogermoore and earlfor..many thanks for the replies and info; like I was telling earlfor, I found some great technical info on mikuni vm carbs in a downloadable tuning manual produced by mikuni in california. all the charts + graphs plus some real practical info on how these babies work and what/where to look for when they're being dismantled/rebuilt. Yes, old Q+A does work for those of us looking for answers before we ask more questions...can't wait to get started! hopefully, I'll be posting a performance update soon.

[earlfor]

I would be very interested in reading what they have to say.
Whats the URL ?

Earl

[quote="GS750EN"] I found some great technical info on mikuni vm carbs in a downloadable tuning manual produced by mikuni in california.

[earlfor]

I would be very interested in reading what they have to say.
Whats the URL ?

Earl

[quote="GS750EN"] I found some great technical info on mikuni vm carbs in a downloadable tuning manual produced by mikuni in california.

[earlfor]

I would be very interested in reading what they have to say.
Whats the URL ?

Earl

[quote="GS750EN"] I found some great technical info on mikuni vm carbs in a downloadable tuning manual produced by mikuni in california.

[Anonymous]

Post the URL please

[Anonymous]

Mikuni VM carb

here's my first contribution to all you gs enthusiasts.. the MIKUNI VM CARBURETOR SUPER TUNING MANUAL published by mikuni can be found as a pdf file by going to mikuni.com; click on the carb. photo; click on "manuals" in left margin; click on "VM round slide tuning manual"; and there it is for you to download and print! let me know if this is helpful to anyone.