cb350 vm30 woes me

[axeugene27]

I know this has been brought up a gagillion times and i have read pretty much all of the posts. I just can't seem to find a straight answer. Here is the conundrum.....

I put vm 30s on my near stock cb350. stock pipes. K&n pods. (they look sick)
Got bike to fire up with these carbs on there. yay i was very happy.
Can't really get her to idle well though. I synced the carbs with a wire like the manual states.
Got her to idle well once i was so pumped.
Now i can't get her to idle well. I just want to get the idle in order right now.
Just a few simple questions...

1. If it runs with the choke and when i choke it slightly the engine picks up again and doesn't die is that an indication that i am running too lean with the pilot jet ???? My logic is that isn't the choke on these carbs and enrichening circuit??

2. I know this is dumb but when i turn the air screw out it leans out the mix right. I am starting with the air screw 1.25 turns out as i have read all over the place. my chilton manual says 3/4 turn but i am not sure if this should be applicable to these carbs. I have a 30 pilot in currently

3. should i tune the idle with the throttle slide pretty close to closed. as when i am syncing them i am using a 1mm round wire on the engine side of the carb the only time i got it to idle the slides were pretty much closed. My theory is that there is too much air rushing in through the venturi with the slides open that much and that the pilot jet isn't supplying enough fuel so the engine dies.

4. What is a good starting point with pilot jetting and air screw setting these are sudco carbs and were supposedly set up for a near stock 350 here is what i am running.
190 30 159p-4 2.5 cutaways 6f4needle
I am mostly concerned with the pilot jet right now i have a 20 a 25 and a 30 . From my research i see that alot of people are running smaller pilots. My conflict is that the dime city uses 50 pilots for their "set up" carbs. so what the what......

5. do i need to mess with the needle setting at all or is that for more fine tuning?

I realize all carbs need fine tuning but mine won't even run crappily with these right now. sigh.....


My bikes compression is 135 on right side and 150 on the left. so i don't even know if it should idle with those numbers but it did pretty damn well that once. I think i need to stick with one jet size and work the air screw and just set those thumb screws to a reasonable height and leave them alone until it purrs then back the thumb screw down if it's too high.

a few considerations
-my throttle cables have nothing to do with this they have been checked and are slightly slack so not an issue.
-I really do not think there is an air leak i spayed wd around boots when i had it idling and no change.
-I don't know my newer honda won't even idle well until it has choke for a minute or so but i am afraid to leave this choke on since it idles so high with choke.
- I don't think these are too big for this motor i know you are dieing to say this you do on every carb post i find.


Come on i know you carb nerds are just dieing to show off your knowledge...

p.s. : Wish i was a carb nerd. :-X

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By <a target="_new" href="http://profile.imageshack.us/user/axeugene27">axeugene27</a> at 2012-05-30

 

[Sonreir]

The compression does sound like it could be a problem. It should read within a couple of PSI of one another. If that was a cold reading you should be OK, but that's quite low if you read the compression on a warmed up engine. 155 PSI should be the bear minimum and you really want over 165 PSI. Time for a rebuild?

As for the fueling, I would drop the pilot to a 20 or so. Jets that are too large can exhibit lean symptoms because there just isn't enough vacuum to pull the fuel though the bigger opening. Not usually a problem with pilot jets, of course, but I digress...

As for the opening, 1mm is pretty big. Try half that. It's possible with all that air you're bypassing a good portion of the pilot system. You may want to invest in a decent vacuum gauge to get it working correctly. If I remember correctly, a good idle should pull about 20cm of mercury at 1200 RPM and the difference between the two carbs should be less than 2cm of mercury. Start with the mixture screws 3/4 out and leave them alone until after the sync is done. Leave the needle alone for now, too.

 

[axeugene27]

Thanks sonreir I Will try droping the pilot tomorrow. I know i am in for a top end rebuild i just was hoping to get this season out of it and then go delving into the engine. I just got the damn thing near together i guess that is how it goes though I knew from the start an engine rebuild was in the cards i think it always is sooner or later with these old motors. I bought this bike for an education and it will not be denied i guess. Just wish the lessons weren't so expensive. I wouldn't mind using vacuum gauges but don't i have to have the thing idling pretty good to use those?

 

[axeugene27]

tried to get it running again yesterday. No luck. I tried with the 30s/ the 20/s, Now it wont even try to start even with the choke on!!!!. I checked compression again was actually alot better not sure if i got a bad seal last time or what 160 on left 170 on right. so maybe it's ok? not sure why readings are so inconsistent thougH> ? I did everything to try and get this thing to go yesterday. Checked spark on plug was dead for some reason? Replaced it spark is good on both cyclinders. cleaned petcock it was kind of gunked as this is only the first tank of gas since i cleaned the tank. Flushed lines/ filters. fuel is flowing really good now. Opened carbs fuel dumps like it should. SOme of the fuel in the carbs looked a little murky so not sure if that has plugged up some channel in the carb.?? I am gonna go though with a spray carb cleaner and get all the passages i can find. That is the only thing i can think of why the dang thing wont turn over now. It does almost seem like an electrical short though as it won't even kick with starter fluid. Would there be spark at the plugs at all though if there was a short. I have this thing very basic as far as wiring goes so idk. Ugh well at least compression seems good for now so i will just have to sort this thing out.