Stutters in low throttle...not a very smooth pickup

[XSrat]

Been a while since i've been here, but pulled the bike out this spring and been having some issues. Im just going to lay out the symptoms and hope someone has some suggestions

First few rides were fine...a bit of stuttering and popping once in a while which I just attributed to old gas. Last night I got a few miles up the road and it started to spit and sputter at about 60mph...like alot. If i were to let of the throttle it would die completely but if i cranked on the throttle it'd come back, still missing and sputtering. I fought it for a while hoping it would smooth out, but it didn't so i gave up and let her die. It did this to me once last year too on my morning commute...soooo battery being next to dead I commenced kicking, and kicking, and kicking. I could get it to fire up on full choke but it would die soon after. After much fiddling like this I could get it to stay running by alternating the choke on and off...finally it smoothed out for the most part and I rode it home.

So. I was thinking there must be some dirt or something floating around which would work its way into the a jet and cause the problem. Tonight I pull them off and cleaned them out, checked all the jets etc. There was virtually no build up besides a bit of dirt between the main jet and the washer that sits underneath it on one of the carbs. But I did notice that one of the boots was a bit loose when I pulled it off...and upon further inspection found that both of the boots were weirdly deformed on the inside(i had put new boots from mikes on about 3 years ago when i bought it).
Anyway, put it all back together and it seemed to be a bit better, peppy, and responsive...took it for a ride and when i came back it was stuttering a bit again at low throttle...after revving it a few times to check its response it let out a large sputter/backfire and the left vacuum barb flew out.

That is where it sits...i know this is a book, but Im just wondering if i'd be correct in thinking that i might have been sucking in air around that barb if it was loose enough to fly out and also around the other potentially loose boot.
Could this cause these issues? Also where would I find better boots than the ones from Mikes?

Thanks!

 

[Grinder]

http://jbmindustries.com A lot of people don't buy anything rubber from Mike's.

 

[gggGary]

Yeah those mikes boots are known losers. JBM posted above are good.
What year, ignition, carbs? Why is the battery dead?

 

[XSrat]

Thanks for the link, I'll give those a look! It's a 1980 with the stock 34mm's...battery is dead from winter neglect and it doesn't seem to want to take a charge now...it's about time for a new one anyway. The more I think about it, it has to be an air leak in the boots...when I was messing around with it I found I couldn't really get a consistent idle...I could set idle, then rev, and it may or may not come back down to the same rpm setting...I'll have to give the Jbm's a try, thanks!

 

[XSrat]

I looked at Jbm's quick and they don't seem to have the vacuum barb fitting...isn't this something I need to run the vacuum hose up to the petcock?

 

[CDNTX650]

You could cap it, and leave it on prime. Mine dont have barbs either. I sync by ear now.

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[pamcopete]

CDNTX650,

The problem with leaving the pet cock in the prime position is that it uses the reserve pickup so you will have to keep track of your consumption because you will not have a reserve. Also, because the reserve pickup is down where all the junk gathers, you need to have an inline filter or you will be doing a lot of carb cleaning. Some of the finer particles that do gather in the bottom of the tank can actually get through the filter and accumulate in the smaller passages and jets of the carbs. If you use a filter that traps these ultra fine particles, the filter will get plugged up.

I agree with you about the syncing by ear method. You can do that if you have dual exhausts just by tuning the sync screw until both cylinders sound the same. All you have to do is start with a good bench sync.

 

[XSrat]

Ok, those sound like good options...just out of curiosity though, is there somewhere else I might look for good boots with the vacuum barb so I could get it back to normal operation? Or are the Jbm's accepted as the best method with the petcock on prime? I don't really enjoy cleaning the carbs often, and I do have an inline filter currently.
I guess I'm more concerned about the barb for operation as I have already synced them by ear so that wouldn't be too far from normal for me

 

[CDNTX650]

Or, replace tap with a non manual one. Im sure something else will cross reference for a tap.

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[5twins]

I think 650Central has alcohol proof barbed manifolds for the BS34s.

 

[XSrat]

So I guess(thinking out loud here) i could just seal up the hole where that barb came out and run it on prime to check whether that is the issue?
Is it just the crappy gas we have that wrecks those boots? I have to imagine that the deformities on the inside of the boot have to impede the flow of the fuel/air mixture running into the cylinder too...

 

[XSrat]

Alright, since I've been on here last I haven't had much time to tinker with the bike, but I did seal up the left vacuum port with some black permatex and tried running it on prime. It warmed up like normal and seemed a bit stronger, but there is still a flat spot at low throttle. When I snap the throttle relatively fast it will cut out momentarily and then recover...if I slowly give it throttle it will rev up normal. What could be causing the momentary stall?

 

[5twins]

A flat spot is a lean indicator. When a vacuum barb pulled out of one of my manifolds, I replaced them.