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1985 virago 700 carb problems

PostPosted: Mon Jul 16, 2018 7:59 pm
Author: Vgo676
Ok I know this topic has been posted ad nauseum here, but I've had no luck. Was out riding the other day, was going faster than I should (>100mph) passing this car, and the bike suddenly lost the front cylinder. Limped 50 miles home on just the rear. Couldn't get front to fire, decided it wasn't getting gas, so I took the carb apart, cleaned it, put it back together. Still one cylinder. Ordered two carb kits, put them in, now it'll idle well on both cylinders, crack the throttle and it dies out. If I ease into the throttle, it will pick up high rpms and run well.
New spark plugs, very good spark, good battery, good compression in each cylinder. Searching for vacuum leak, I sprayed starting fluid on each carb intake boot, and it actually causes that cylinder to die down, which made no sense to me. Float bowl levels seem to be at appropriate levels when checked using methods on here. Any suggestions appreciated. I'm sure there's other things I've tried that I'm forgetting. Thanks.

Re: 1985 virago 700 carb problems

PostPosted: Tue Jul 17, 2018 12:06 pm
Author: bstig60
If the starting fluid caused a change in engine RPM, (either up or down), that's your vacuum leak. I recently had a vacuum leak on my bike that was causing an intermittent lose of the front cylinder, It turned out to be the O ring on that manifold had a piece missing... I would pull that manifold and check the Oring then add some wheel bearing grease on the head and manifold to make sure it seals.
BTW: If your engine is running rich, starting fluid will give it too much fuel and you will get the results you observed.

Re: 1985 virago 700 carb problems

PostPosted: Wed Jul 18, 2018 1:47 pm
Author: Vgo676
Thank you for the reply. I've tried two sets of boots/manifolds so far (neither brand new, but both in decent condition and both with o-rings intact) and they don't seem to make a difference. I think it's running rich because I've been messing with the pilot screws, thinking that had something to do with it. The brand new plugs turned black, confirming you richness diagnosis. It is such a pain to get the carbs on and off, and I feel like when they go back on, they're still not quite lined up perfectly, which would contribute to the vacuum issue. I am going to take them apart again today, reset the carbs back to stock recommendations, and then try the bearing grease. Do you apply the grease to both sides of the manifold (the rubber boot as well as the metal side that mates with the cylinder)?? Thanks, Brad

Re: 1985 virago 700 carb problems

PostPosted: Wed Jul 18, 2018 1:49 pm
Author: Vgo676
BTW I believe my vacuum leak is where the boot connects to the carb, not where the manifold connects to the engine, if that makes a difference in your answer.

Re: 1985 virago 700 carb problems

PostPosted: Thu Jul 19, 2018 1:25 am
Author: Flyingdog
JMO..if yer concerned with possible carb joint-to-cylinder mating surface leaks, specially "re-using" old joints, I'd be using a good RTV sealand on that 0-ring. Something like Permatex Ultra Copper sealant. Little more reliable getting a good seal than grease. Lot easier clean up if you have to remove these parts, too. Be mindful of the air/intake & A/F side of the carbs too. Can be..not always..pinched 'under' the clamps. Creating a open void/fold of the rubber. Check the mating surface with a mechanic's mirror, making sure everything is laying flat around the carbs flanges. Your last post, sounds like, maybe, the intake/boot isn't completely on the carb's flange. I've always had to use something to stretch this boot onto the back (inside) portion of carb. Seen where some people think it's on..go to clamp it down..and end's up being only 1/2 on the carb's flange. Last time you had the carbs out, giving the carb joints a good squeeze will also show the real condition of any surface cracks. Replacing those hex head bolts with socket/allen head bolts makes it little easier to loosen with a ball-end allen wrench.
Could you explain further why you don't think the carbs are lining up. This should never change. If it does, something is wrong. There is a correct sequence taking the carbs in & out. Everything (carbs to joint to cylinder) "should" line up, perfectly, everytime. If not, as in: having to force and/or tweak this alignment, to get the bolts-holes/joints to line up, something is wrong. Should just pop in or out perfectly every time.
There's an old adage here..."The slower you go, that faster you'll be".

Re: 1985 virago 700 carb problems

PostPosted: Thu Jul 19, 2018 8:07 am
Author: bstig60
I use grease because it will burn off over time and it won't be a deterrent the next time you need to remove the carbs. Put it on both the intake and head side of the carb holder....
There is a procedure on this site for removing and installing the carbs. Usually takes about 10-15 minutes. Do a Google Search on this site for it.... If you can't find it, PM me and I can send it to your email.
Set the pilot screws at 2.5 turns out from a soft seat. Bench sync the carbs before you put them back on the bike, do this by using a feeler gauge on the butterfly and match the rear carb to the front.

Re: 1985 virago 700 carb problems

PostPosted: Thu Jul 19, 2018 9:01 am
Author: Flyingdog
bstig60 wrote: add some wheel bearing grease on the head and manifold to make sure it seals.

Understand, but I read it as trying to seal. If it works for anyone...great. Whatever works for ya. Just something I wouldn't do.

bstig60 wrote:I use grease because it will burn off over time .


And if one has a leak here...and it burns off..I see the leak returning.

Vgo676 wrote:Searching for vacuum leak, I sprayed starting fluid on each carb intake boot


I'm reading the OP was having problems with leaks. Not about taking the joints on or off and what a pita it was. For him.
Grease on the cylinder side..just a new one to me.
Personally..I like using strawberry flavoured personal lubricant on the flanges. Gives ya that lovely aromatic bouquet going down the road.