[kirk]

Hi, I've got a 72 cb350 w/cv carbs. It starts up and
idles ok in the driveway, but after I run it down the
road a few times it will quit every time I pull in the
clutch. It also kind of jerks and boggs down in lower
rpms, say below 3000 or so. but after it winds up it
really does run pretty strong. but I can't ride it cause
i have to kickstart it at ever stop sign! This much I know:
The valves are adjusted correctly, the timing according to
a light is good although when set staticly, the light says it
is 5 or 6 degrees off. everything I can inspect visually in
the carbs is clear. Does anyone have any suggestions?
Thanks

Kirk

 

[jbranson]

Three things,

Make sure the chokes are off.

Make sure the idle air adjustment is correct.

If you still have a problem pull the carbs, take out the slow jet and inspect it almost microscopically. The slow jet has very very small holes for fuel flow. I use one of those things that doctors look in your eyes with to check jets. It definately takes a magnifying glass of some sort to see through them. Don't try to clean them with wire or anything it will mess up the fuel passage. Try blowing them out with compressed air or brake cleaner.
JohnnyB

 

[kirk]

the chokes are definately off, the pilot screws, which on my carbs i believe meter the fuel, are within the recomended range. Can you describe which is the slow jet? is it visible after the bowl is removed? I just took it for a ride, and overall it goes pretty well, but after about 10-15 minutes starts to stall at idle again. Also, and I don't know if this is related, but there is a fair amount of white smoke billowing out of the crankcase vent hose that runs from the head down out under the frame. It definately seems excessive. Any ideas about that? thanks for the help.
Kirk

 

[UngaWunga]

quote:
and I don't know if this is related, but there is a fair amount of white smoke billowing out of the crankcase vent hose that runs from the head down out under the frame. It definately seems excessive. Any ideas about that? thanks for the help.

lol... thats nothing. ignore it. All 4-strokes do that when their rings aren't sealing...

 

[joe c]

is that one of the late model oil injected ones ive heard so much about??

it shouldnt smoke.

do what branson says

jc

 

[kirk]

Well, I'm glad everyones getting a kick out of my post...
I know it shouldn't smoke, what i don't know is why it is.
I warmed it up and did a compression test, and got a good
150-160 psi on each cylinder. I'm new to motorcycles but
that seems pretty good for nonsealing rings.

 

[jbranson]

If you are just taking it for intermitent rides it's accumulating a lot of condensation in the crankcase which will boil off as white vapor when it warms up.

The slow jet...same thing as pilot jet. It's the small, long narrow jet screwed in next to the main jet. Extremely small passages, very easily blocked by tiny debri from the float bowl.

I would kind of lean towards it being the idle air mixture. Runs when it's cold but when it warms up it gets too rich and won't idle. Idle air mixture adjustments are supposed to be done when the engine is fully warmed up. Many people don't do this and adjust them when it's cold, when the engine warms up it needs less fuel and ends up idling too rich which will make it run rough or not at all in some cases.

Those carbs also have issues with the diaphram, they get holes in them causing air leaks... you'd have to ask someone more familiar with the carbs about what symptoms that may cause.

Check the service manual for the proper initial position of the idle air screws and start them out there. Get the engine started, let it warm up and adjust again according to the instructions in the service manual.
JohnnyB

 

[joe c]

i had a 360 that had the same problems. it drove me nuts. i eventurally just put on another set of carbs and it fixed it. the jets on the 350cvs push in not screw in. that might clear that up for you. also, 150-160 is fine. that was with throttle open right??

sometimes these things are a pain in the ass to get settled. if i had another set of working carbs, id send em up, but im down to the bottom of the heap again.

jc

 

[panic]

Vacuum leak.

Need help with your Mikuni VM? Click here:
http://victorylibrary.com/MIK-BT.htm

 

[kirk]

a vac. leak was one of the first things i thought of,
but finally dropped it because it runs completely normal
in the higher rpms.

 

[UngaWunga]

quote:
a vac. leak was one of the first things i thought of,
but finally dropped it because it runs completely normal
in the higher rpms.

that means nothing. at higher rpms there's a ton more air flowing through the carbs, so a little vaccuum leak means nothing. But at idle its pretty major.

 

[joe c]

how about a condensor or coil?? although ive found a cooked coil craps out at high rpms. seems like an as you heat up problem.

oil injected models, i thought that was pretty good.

jc

 

[jbranson]

Maybe condensor, coils doubtful since the stock CB350 has dual coils...should be pretty obvious if it drops one cylinder.

As boring as it is the proper way to tackle issues like these is start at page one. With everything by the book, plug gaps, point gaps, valve adjusments, timing, cam chain, idle air mixture, idle speed, any part you are in doubt of test or replace.

Then...if it's still broke you look for a problem. Dirty carbs, faulty coil, condensor, plug wires.

Personally.... I still bet on the idle mixture adjustment.

Isn't long distance diagnostics fun?

JohnnyB

 

[kirk]

When air flow increases, it will generate
more vacuum.

 

[joe c]

always start at the begining.

jc

 

[kirk]

Well, I went to test ride it yesterday and the left side ignition
was kaput! So hopefully a faulty coil or wire has been the problem all along. I'll swap them out today and see what happens.

 

[jbranson]

JC,
Looks like you win the long distance diagnostics contest.

JohnnyB

 

[joe c]

you old guys all tought me everything i know!

jc

 

[UngaWunga]

quote:
you old guys all tought me everything i know!

Hey! FU buddy, i'm not old!

Oh, you meant Branson... yeah, he's old.

 

[jbranson]

Who's yer Daddy?

Remember ya bastards... it COULD be me!

JohnnyB