New owner 79 gs750. Carb swap: vm to cv?

[Guest]

Got the bike and it ran ok, but rust in tank issues. Thinking of rebuilding the carbs, but if I'm going to put the time and parts into it, would it be worth putting cv carbs on? Dyno Jet makes the stage one kit for these, but not the vm's. I put the stock airbox back on 9I prefer how it looks) and have a Vance & Hines 4 into 1 on it now. Thinking about a Mac 4 into 2 , (again, an appearance thing, plus the V&H pipe is for '80 & up... hangs low and drags on right turns).

[salty_monk]

Mac pipes are not that great but it will work.... You can't fit CV's - the port size is different.

Dan

[Big T]

Plus, you can get all the parts for VMs to tune them however you want

[crapwacker]

Thanks and darn. Also, how about pipes from an 82 gs650 or an 80 gs750? Possible fitment or performance issues? When I replaced the foam pod filters, the throttle issues around 3500rpm to 4500 went away, but now it bogs around 5000. BTW, there's a K&N in the airbox

[Big T]

650 pipes maybe

By bogging at 5k, does it then rev up?

Raise your needles one notch

[nisom512]

Got the bike and it ran ok, but rust in tank issues. Thinking of rebuilding the carbs, but if I'm going to put the time and parts into it, would it be worth putting cv carbs on? Dyno Jet makes the stage one kit for these, but not the vm's. I put the stock airbox back on 9I prefer how it looks) and have a Vance & Hines 4 into 1 on it now. Thinking about a Mac 4 into 2 , (again, an appearance thing, plus the V&H pipe is for '80 & up... hangs low and drags on right turns).

plus CV's are hard to tune properly when you start changing your exhaust and air box. they are really picky

jake

[crapwacker]

It will but just barely. Backing out of the throttle smoother it out. It used to start to scream about there. A little backfire of sorts at mild throttle. Also, how important is it to vent the # 3 and 4 carb vac lines? They all are plugged, and the petcock is esentially open.

[TheCafeKid]

Sounds like you've actually developed an intake leak. On the 77-79 750s, behind the rubber intake boots/manifolds there are viton rubber orings..after time these get hard, brittle crack and break, thusly allowing air between the head and the boot. This will lean your mixture out, and cause the popping on deceleration that you are experiencing, as well as a host of other problems...failure to correct a lean condition will eventually result in expensive and extended mechanical failures, mostly in the combustion chamber. Valve heads, rings, pistons...the cost will rack up...

www.cycleorings.com sells the needed rings, as well as the orings for you to rebuild/refurbish your VM carburetors (I would strongly recommend doing this if you havent already. Even if they're fairly clean carburetors, the orings break down over the years, and allow air and fuel in uncontroled volume which will further compound your running issues) Also, valve adjustment SHOULD be checked and/or performed every 5K miles at the latest. Its not difficult once you get the hang of it, and Steve here on the board offers a very helpfull spreadsheet that will help you to keep track of what shim sizes youre currently employing, and likely which sizes you will need to order or source next. Shims are available new thru www.z1enterprises.com (although your local dealer can probably get them too, but for at least a few bucks more each) Some guys on the board, such as Steve and myself will even participate in a shim swap where we supply you with a needed size, you send us your old shim(s) back plus a dollar for each shim you required...Works pretty good, and if you only need one or two, its cake.

I have a pretty soft spot for those old late 70s 8v 750s and 1000s. they are bulletproof machines, alot of fun and will take to tuning well. If you have any more questions, please dont hesitate to ask, I will assist the best i can. Also, on your "vent" lines, Only ONE of the carbs (number 3) is the petcock vaccum hose to be attached to. The other rubber lines, between one and two, and three and four, are vent to air. If you are running pods and a pipe, it has been suggested, and I have followed and found it helpfull, to run NO RUBBER LINE from those vents. It has something to with barometric pressure and some scientific stuff that i cant even begin to understand

Also, I see that you have a 750 "L" model i think? If you need, i have a tank in decent shape, actually off of an 1000L but its slightly bigger (a plus no doubt) and will need a new petcock. The tank had recently been cleaned at a radiator shop, and has little if no rust inside (been a while since ive looked) no rot holes forming either. Its just sitting around, will need paint, but I cant recall it having any dents to speak of..maybe a ding or two. If you're interested, I would be happy to let it go for a reasonable price.

[crapwacker]

Thanks! BTW, how much do you want for the tank?

[Dan Ruddock]

Vm's have no diaphragm to go bad and YOU are in control of the throttle. Dan

[TheCafeKid]

Thanks! BTW, how much do you want for the tank?

I dunno, 20-30 bucks sound fair? You'll obviously want to get a new petcock for it of course. where in ohio are you? Might be cheaper to come pick it up...

[crapwacker]

That sounds good to me, and I need to get the RIGHT petcock anyhow, as the one that is on now has the fuel port coming out the back instead of the front. I'll prob be able to get down your way on the weekend, as i work 2nd shift.

[TheCafeKid]

Works for me sir.. Just shoot me a PM when you plan on makin it out, I will give you directions and what not... I might have a few other 8v 750 goodies you might be interested in as well and if ya need any help with that beast, let me know. Never to busy to lend a hand.

[crapwacker]

About that tank, it has the single mounting bolt, right? My work schedule is not showing any holes to make it your way, so let me know how much it might cost to ship. I live in Galion, near Mansfield. Also looking for the airbox boot clamps. Do you have paypay?if so PM me. Also wondering, when putting carbs back together, is there anything i should put on one surface of the gaskets to aid in the removal(s) for changing jets, needle settings, ect, as well as the valve cover gasket?

[TheCafeKid]

About that tank, it has the single mounting bolt, right? My work schedule is not showing any holes to make it your way, so let me know how much it might cost to ship. I live in Galion, near Mansfield. Also looking for the airbox boot clamps. Do you have paypay?if so PM me. Also wondering, when putting carbs back together, is there anything i should put on one surface of the gaskets to aid in the removal(s) for changing jets, needle settings, ect, as well as the valve cover gasket?

I can get you some pics, yeah its the single bolt in back. And, I dont mind shipping it either. I dont have any spare airbox boot clamps that I know of, but if i happen to find some (ive got a LOT of crap laying around) I will let you know. I have Paypal.

On the carb gaskets. Generally, i put them together dry. They dont get subjected to much in the way of heat, so really they dont get baked on like the motor gaskets do. If you're carefull when removing the lids and bowls, you can reuse those suckers for a good long while. Heck, on some of the carbs Ive got, *I* have NEVER replaced gaskets on em, and they still work just fine. On the valve cover gasket, some guys will soak the gasket with a film of oil before installing it. Ive seen others use liquid teflon and such. I just put a film of regular old motor oil on it, mainly to try to keep it from baking on because i HATE trying to clean burnt gasket off the motor. Its a PITA. I generally dont try to reuse valve cover gaskets, because every time i have, it works ok for a couple weeks and then it starts leaking like a siev. If you want to save money in the LONG run, get a "Real Gasket" its made of silicone and reuseable over and over. They arent exactly cheap on initial purchase, but if you do the math, and adjust your valves as you SHOULD, it saves you money in the long run.