Single carb conversion thread...

[TeeCat]

griz...

TC, the low speed issue you're describing sounds a bit like what sometimes happens under braking if the float level is set slightly too low (fuel level too high); depression of the front end causes fuel to slosh forward, richening the mix.

You know, I wondered about some inertia- or momentum-related issue like this. It stands to reason. I'll have to try your test and see if I can reliably reproduce the behavior. When I initially thought the carb was flooding on my early attempts to fire the bike up, I checked the float height when I had it apart to install the new needle and needle jet, and it seemed at spec. However, if you look at some pics of my configuration from the side, you'll see an ever so slight downward list in the carb position; this position seems to be a function of the construction of the intake manifold itself. I wondered if that might be a bit of a factor, but I think Mikuni recommends a carb "posture" of within... I want to say about 20 degrees... of level. Saw that in my reading somewhere. But yeah... we're dealing in thousandths of an inch here, so it's tricky!

Well... time and weather permitting this weekend, I'll try your test(s). (My neighbors adore me, incidentally... Well... the kids do. Parents... maybe not so much. )

And you remind me... one thing I do want to address is ease of carb tweaks. In a stock configuration, I recall your saying how easy roadside tweaks are. I have noticed, however, that in my carb's location, it's really tricky getting that bowl off without pulling the carb off the manifold, which can get old fast. So I need to either investigate a 90-degree phillips, perhaps, or do John's phillips-to-allen mod like I did on my BS38s. Being able to just drop that bowl in situ would be a boon.

TC

 

[XSLeo]

Just loosen the clamp that holds it to the manifold and twist the carb on the intake. Pull the bowl make your changes and twist it back and snug the clamp.

 

[TeeCat]

Why didn't I think of that?

I think there's enough room to do that if I have to. Still, the allens might be a good idea, though.

TC

 

[XSLeo]

Allens are always a good idea. On the 75 i had years ago that was how I did it. Just had to make sure the choke crossover tube was hooked right when yo turned the carbs back in place.

 

[TeeCat]

Well, in this case... no crossover tube to worry about. I think there's enough room between the throttle cable and the frame for me to rotate the carb without a problem.

Space-wise, this configuration has worked out surprisingly well. I do have to be a little careful where my left leg is when kicking (I straddle the bike... just can't kick off to the right of it), but once on the bike, things are ideal, even at stops. I still have to work out an O-ring for the very base of the air cleaner where it meets the intake tube. Cosmetically, I was originally noodling running a Hilborn-type V-Charger scoop, but it might be too big (long). So I may have to settle for this air cleaner; at least it meets the retro look I was envisioning. Got a cool little billet air cleaner retainer knob now too. Sorry... I get really excited about little stupid sh*t like that. I was thinking... it's neat how it's worked out that all of the intake assembly, from the carb outward, is all Spectre Performance, and that aspect really all came together by accident because, except for the air cleaner, I had the other stuff lying around when I started thinking about how I was going to clean up the incoming air.

Bad weather now. Hope to do some more testing this weekend.

TC

 

[TeeCat]

Update:

I took the TX out for a few miles today. It was sunny, but only managed to hit 49F. The bike took a good while to warm up to the point where it would idle stably, so I just used a bit of throttle and idle screw. Once I got it out on the road, it ran well at mid- and up-range, but still spits very occasionally off idle.

The idle is basically stable, except for the fact that the rpms will go up and down a couple hundred rpms or so maybe every 15 seconds, as if it's hunting, though return to idle from throttle blips is immediate. The left plug's electrode is quite tan, while the right one is slightly darker, but both are dry. The gently "wandering" idle makes me think that the 25 pilot may be a little small. I have a 27.5 that I might try.

I also made the mistake of putting 20-50 oil in there two weeks ago and she was hard to kick after sitting in the cold.

Impressions welcome!

The biggest issue I have now is that fussy clutch adjustment. Shifts like butter, but first is fussy at times, as is neutral, of course. I'm seriously considering going to a hydro clutch at some point, but I don't think I can manage that one without the help of someone who screws up less than I do.

TC

 

[5twins]

I would try an air screw adjustment 1st. Turning it in 1/8 or 1/4 turn may make things rich enough to cure the wandering idle. Easy enough to try and if it doesn't help then try the 27.5 pilot.

 

[TeeCat]

I would try an air screw adjustment 1st. Turning it in 1/8 or 1/4 turn may make things rich enough to cure the wandering idle. Easy enough to try and if it doesn't help then try the 27.5 pilot.

twins, you must be telepathic. I just a moment ago remembered what griz said about that, and came here to post that I'd try that first. Thanks, though, because your post would have reminded me to try that first!

I have to pull the air cleaner assembly off, anyway, to make some fitment adjustments in that, so I'll richen the air screw a tad.

TC

 

[XSLeo]

Just a thougt, for air scew adjustment would taking the side civer off give you room to adjust the air screw easier?

 

[jackstraw650]

TeeCat......loved your persistence on this single carb conversion. Looks like it is finally coming together for you. I'm a newbie and am picking up my first 650 this weekend. It is a standard '79 and I plan on making it into a cafe bike. At the risk of angering everyone by changing the subject[I didn't want to start a new thread for one brief question] Where did you get that great seat on your bike?
Sorry about the hijack....
Phil

 

[5twins]

MikesXS and Phil, don't even think about changing your carbs. You've got about the best original set ever put on the 650, lol.

 

[TeeCat]

Leo, the side cover has to be off to do it, as well as the whole intake/filter assembly, because the screw is hidden in such a way that I still have to use a little precision screwdriver to get to it. That's one inconvenient thing about this set-up.

Phil... thanks and welcome to the forum. Hopefully all I need to do now is keep the idle from "hunting" a bit. We'll see how a slight tweak of the air screw did. And yes... got the seat at MikesXS.com.

And when it comes time for you to start working on your carbs, do yourself a favor: just cut right to the chase and work with 5twins, grizld1, and XSLeo (not to disparage anyone else, of course... it's just that these three seem to have the patience to deal with me in large dosages).

TC

 

[jackstraw650]

TC and 5twins....thanks for the welcome! Believe me, I have no intention of changing my carbs....everything I've read on several forums says just what 5 says...they seem to be the best of the stock options on the 650. Hopefully I won't need too much help; as the bike I'm buying has less than 8K miles on it and seems to run well.......on the other hand, one never knows.............I do know that after the obligatory bearing and bushing replacements, my first purchase is going to be a complete Pamco ignition set-up!
TeeCat, thanks for the info on the seat....does it fit on the stock hinges, etc.? Is it worth it from a comfort and quality standpoint? After reading all the various rants on two forums, I'm a little reluctant to buy things from Mike's.....I can't decide if he is the incarnation of Johnny Yam650seed or the Devil himself..................
Thanks again and I will post some pictures after I get my bike home.

 

[TeeCat]

Phil, my seat will fit '74 to '79 without mods. My bike is a '73 so I had to finagle a bit. I find that the seat is a nice one for the money.

Keep us posted!

 

[ugottalovewagner]

I just bought one of Wiseguys intakes and im excited to give it a try. i got the one that puts the carb forward on the left side. Just looking for a good carb to buy and ill be ready to give it a shot. I appreciate your Thread cause it will take alot of the guesswork out of it. its going on my hardtail bobber. ill try to get some pics up when i get it on.
Jeremy

 

[TeeCat]

I just bought one of Wiseguys intakes and im excited to give it a try. i got the one that puts the carb forward on the left side. Just looking for a good carb to buy and ill be ready to give it a shot. I appreciate your Thread cause it will take alot of the guesswork out of it. its going on my hardtail bobber. ill try to get some pics up when i get it on.
Jeremy

Jeremy, go for it! I hope my thread does indeed help you. If you tell us more about your motor and exhaust, maybe we can help you even more, though my extremely limited experience is with the Mikuni 36mm VM. But it definitely works a treat in the mid- and upper-range... I'm just needing to get my idle a little more stable now, I think (hunts just a tad).

TC

 

[ugottalovewagner]

i have a stock motor and im just going with some straight drag pipes with weld in baffles. im most likely going to go with a vm36 however ive had a few people tell me to go with a flatslide instead cause it will be easier to tune and have better response. If anybody has any ideas let me know. im sure ill be asking more questions once i get into it

 

[TeeCat]

Jeremy, I would guess that virtually any direct-pull carb would offer somewhat better response (when jetted properly) than one with a vacuum-actuated slide, but I can't speak to that with authority. Bet someone else will have good input, though. I chose the VM36 based on wiseguy's testing.

Incidentally, here are a couple of new pics... one with my new Spectre billet thumb nut that makes for firm retention removal of the air cleaner itself without a tool (sorry... little bits excite me ), and a shot from the right. I have an idea for a chrome or polished aluminum "shroud" that will fit into the right side cover's accommodation for the former right carb, and cup the right runner of the intake manifold to cosmetically close the space where the right carb was.

TC

 

[Jezuz]

Nice looking work!!

Im goingto use tm38 flatslide on my "racer" and similar manifold as teecat got, do anyone got any jetting advices, engine is stock!?

 

[TeeCat]

Thanks, Jezuz! Maybe we'll start a cult!

Maybe Wiseguy knows of someone who has done this conversion with a flatslide.