Replacing Carbs

[Anonymous]

I am new to forum. I have a 79' GS750 that I have had for about 9 years. I had sold it to a buddy, and he had recently given it back to me, for financial reason. In the interim he had changed the stock setup, putting on turn out exhausts as well as an open air air box. While he had it it seemed like spark went out on 2 cylinder, and quit running all together. So I replaced the coils, put on new condenses and points, cleaned the carbs, replaced the fuel filter, and finally put on a new Dyna electronic ignition. Well I have spark in all 4 cylinders now. But my buddy has messed around with carbs and I feel this is the culprit at this time. I am told have slide carbs on this bike and the different shops I have been to say they don't know how to tune them. The one guy that gave it a shot ended up charging me $300 and from all I can tell he just cleaned them again. So I am here, excellent on bolting on new parts, but no idea how to adjust these carbs. It was reccomended that I just replace those carbs with something more conventional. My question is should I try to tune these carbs (and how,) should I replace the carbs (and with what,) or am I going at this all wrong.

Any help appreciated,

Allen.

[Anonymous]

I don't know if I can help you, but someone here can. I would think the first thing that needs to be known is what carbs you currently have on the bike that you need help with. Can you be more specific?

[Anonymous]

Carbs

On the side of the carbs they say Mikuni Kogyo Japan. I didn't see any model or serial numbers on them. Hope this helps.

Thanks,

Allen.

[first timer]

maybe a picture?

[SqDancerLynn1]

What kind of air box does it have??? Open air air box???? will not work unles you re jet Try to find a stock air box on ebay

[Anonymous]

Slide carbs? Flatslide? Do the carbs have butterflies on the intake side? If they do then they are CV and the carbs could be off a GSXR, if not then they are RS. An easy way to check is to move the throttle and see if the slide moves when the engine is NOT running. I think RS carbs require a push/pull throttle cable also.

One you find that out then we can go from there.

Are you running any filters, pod or otherwise?

[Anonymous]

Air box carbs

Well the airbox currently is just a big rectangular chrome box. The carbs do not have butterflies, just look like plungers that go up and done when rolling on the throttle. Yes they do have a push and pull throttle cables. i.e. two cable coming off the throttle.

Thanks,

Allen.

[Billy Ricks]

They are most likely Mikuni VM series carbs. Try this link, http://www.lafishmag.com/CarbTuning.html.

[Billy Ricks]

If the slides are round they are VM, if they are flat and kind of rectangular shaped they are RS.

[Anonymous]

The throttle valve (slide) appears to be cylinder shape. I was looking at the website that you put it and didn't really give much instruction in my mind, it was more of a description. Is there more than two pages?

Thanks,

Allen.

[Billy Ricks]

Give this site a try, http://www.mikunioz.com. They have a page on tuning.

[Anonymous]

Billy, I couldn't get to that one. If you can't either, try this http://www.mikuni.com/fs-carburetor.html

The left side of the page has links to Manuals/Exploded views. Take it then go to the link for the VM tuning manual. It's in pdf format.

[Billy Ricks]

Copy and paste this into the search window, www.mikunioz.com. One of the results will be a "Welcome" page for mikunioz. Then they have pages for all the different types of carbs.

[KEITH KRAUSE]

Allen, you most likely have VM carbs, should be 26MM.
These carbs can be jetted for the changes to your motor.
Jetting is trial and error so you sometimes have to take the carbs apart several times. When you change the needle position, you should also synch' the carbs with a vacuum tool. I used a jet kit from Dynojet, but you can try to make the stock needle work. You will have to buy main jets and possibly pilot jets.
I'll give you my best guess how to set your jetting, but you need to give detailed info.
What are these "turned out" exhausts? What brand? Are they 4 into 2? Are they baffled and packed, or wide open?
Is your "open" air box just a stock box with the lid taken off or ? Any holes cut into it (other than the factory)? Is there a filter in it now?
Do you know if the carbs have the stock jets in them?
Are the needles in the stock position?
You say you have good spark with the new ignition, but you did'nt say what the problem is.
To be sure of the type of carbs you have, visit my website and check out my carb photo. Click the WWW below and let us know if you want help with your jetting.