New to me cafe

[DXHippie]

Hey all,

Just bought an '82 650 from a guy in Houston, and I took it home to New Mexico, and have some general carb questions. I have done a little bit of searching and have stumbled across a couple threads with good information, that show how to tune the carbs, and which jets are stock. My question is that I have brought the bike from sea level to about 3500 feet above sea level, and I haven't come across elevation information. Now I know with my 2-strokes, you have to change the needle and jets to make it run right after that kind of change, but is this required on these bikes?

Also, I have been reading, and am a bit confused as to which Mikuni's I actually have. They have the left side choke knob, which doesn't stay extended, the chrome flat top lids, and the fuel is split at the petcock and run into each carb separately. Both the carbs are tied together with a piece of angle strap at the bottom and with a cut out flat strap at the top. I was originally thinking it was the stock carb for the '82 year, but the choke is different, as well as the fuel intake. Any help would be appreciated in this regard. (I will try to post some pictures tonight to help verify)

Thanks in advance for all your help.

Garett

 

[weekendrider]

Maybe 78-79 maybe 80- 81. Does it have a drain plug(78-79) or a screw and spigot(80 on) on the bowl.
With the split fuel line I'd suspect the earlier. The schematics show the cross pipe that feeds both carbs with a single inlet.
The choke rod needs a ball and spring to hold tension against it. Those are probably missing and lost it happens frequently. Take an old grease zert, drill or grind the nipple hole large enough the spring and ball come out. These will be the replacement parts.
(tip provide by gggGary). Next to the mixture screw tower (on the head size) on the right is a hole that crosses the guide hole for the choke rod. The spring then the ball go in there. I hold them in with a tooth pick till I work the choke rod in. If you find the drop from full choke to middle to big, an additional "catch" indent can be drilled while you are replacing the ball and spring. (tip provided by XSJohn)

 

[5twins]

Yes, post up some pics. Those may not even be 650 carbs. Maybe the P.O. swapped on a set from some other bike. The later BS34s were the only 650 carbs with a pull knob choke but all BS34s had a single fuel line run to a "T" between the carbs (as WE said). Only the BS38s had separate fuel lines but none of those had a pull knob choke. They couldn't as the choke plungers pull up to activate. The BS34 choke plungers pull out to the side so a side pull knob set-up is possible on them.

Here's the BS34 fuel line/"T" set-up. Don't mind the alloy tops. I swapped them on from different carbs as an "upgrade" for the rusty chrome steel originals.

 

[DXHippie]

They look like those carbs you posted the picture of. What may have happened, is that the petcock and tank when added has a split fuel line system, and they removed the "T" and went with seperate spigots. Will be able to post pics for sure tonight after work.

Anybody have an ideas though about what I might need to do for the elevation change? It seems that it is mainly towards the top end range of the throttle, so I was thinking I could get away with just re-jetting the main.

Garett

 

[DXHippie]

And pictures..

And this is the adapted fuel intake, I think..

And general bike shot, don't mind the mess.

 

[5twins]

Yes, those appear to be 650 BS34s. Someone replaced the fuel "T" with those brass fittings is all. Someone went hog wild with the carb top screws, huh.

 

[gggGary]

What 5t says. The choke is missing the balls and springs for the detent stops, easily remedied. From the float bowls, best guess is they from an 1981 or newer, should have foam floats in them. I noticed those long screws too. Would probably be worth your time to do a full tear down and verify they have all the correct parts inside. The 82 Heritage (what your bike appears to have started as) would have had black carb bodies and a handle bar mounted cable choke. So the carbs have been swapped or the PO blasted them and put in the pull style choke rod but not the balls and springs. As far as rejet, hard to say, the carbs were pretty lean from the factory, the pods and that pipe will probably need richer jets, your altitude would usually mean leaner. How does it run? how do the plugs look?

 

[DXHippie]

Pulling the plugs is the next step for verification, but I can tell you that at idle and low speed I don't see any problems, but when I cruise at highway speeds, I notice that the shock tower gets a nice coat of exhaust residue. It leaves a brown layer across it. I also get a couple backfire pops coming from wide open throttle cruising, when I come to a stop. It is because of this, that my initial thought was to drop the main jet down probably 2 sizes. Will post what I find with the plugs tonight after work.

Thanks again for all your help.

 

[yamaman]

Not that we have any altitude in Western Aus. But aren't CV carbs supposed to self medicate for altitude?

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[DXHippie]

I am not sure, that is why I was asking, however, with the lack of elevation adjustments in the manuals that I was reading, that would make sense. At the same time though, if the air coming in at one tuned location was more dense than another, I would think that you would have to correct somehow. Diaphragms can only do so much, in my opinion.

 

[gggGary]

If you haven't I might suggest synching the carbs as a first step. Some brown, down stream of the exhaust exit seems about right. Are you planning on staying with that pipe? Just that if you are going to change the pipe you might wait on carb tuning 'til after. You might get a fatter power band @ lower rpm with a slightly longer pipe. There is some good reading on pipe length tuning tuning around here. Try a full blast run, kill the engine, coast and pull the plugs (plug chop) see where you are at on the mains.

 

[DXHippie]

I was planning on keeping the pipes, unless there is a good reason to change them out. For now though, they don't seem to be an issue. I haven't checked to see if the carbs are synched, but i am not seeing any issues that would lead me to believe that they are far off of each other, except maybe the backfire. For the plug chop, would it be wise to do this with a new set of plugs? Or would it be ok to use what probably have some miles worth of buildup? Also, if getting a new set is recommended, does everyone run the standard BP7ES or would the resistor type be wise to get?

 

[5twins]

You don't need the resistor plugs because you have resistor plug caps, probably NGK 5K Ω ones from the looks of them.

 

[gentlemanjim]

I'd drop the main jet 1 or 2 sizes that should solve the rich running.