engine starts HOTTTTTT> carbss? please help me!!!!

[axeugene27]

So got some new mikuni vm30 carbs and put them on my cb350 set ignition timing measured and installed my throttle cables (they are perfect). I have the air screw set to 1 1/4 turns out and set the idle screw so that there is barely an opening on the slide. Here is the issue--> When i get the bike to fire it has to have choke on. When it does fire it goes into this high rpm state. If i try to back off of the choke it bogs down. I can rev from the high rev state but this motor hasn't run in years and i don't want to get it revving so high. Here are the needle/ jet settings. they were supposed to be set up for a cb350 but idk what is going on.

220-30-6f4-159 p-5

any help would be awesome.

 

[rockcitycafe]

barely an opening on the slide may translate to redline on an engine with no load. adjust the carbs again so the slides are fully bottomed out, it should keep it running on the idle circuit only in that case. also... there's no such thing as the carbs are set up for a 350 unless you set them up for your 350, engines this old and in such varied states of wear are not going to have all the same settings

 

[Sonreir]

220 mains is HUGE for CB350 without any mods. Drop that down to 180 or 190. Also, try a 20 or 25 pilot jet instead of the 30. Also, the 159 needle jet is really designed for two strokes. Use a 176 needle jet, instead, as it will help atomize the fuel a bit better and the fuel delivery will better match what your engine wants.

Also... check for air leaks. Even with the jetting as far off as it is, the bike shouldn't be revving too high unless the idle is set too high or there is some extra air getting in there somehow.

 

[axeugene27]

Thanks guys the bike still runs really hard with choke on but after syncing the carbs and dropping the main to 190 I got the engine to purr nicely on idle for about 15 min. Just let her run since it had been a long while i'm sure. Engine got really hot though and was smoking considerably not sure if that's normal if the carbon is just burning up or what. Rechecked compression and wasnt too impressed. 150 on the left and 135 on the right. Im gonna readjust the valves and see what happens but pretty sure the motor will need overhauled. Hopefully i can make through the summer though. Gonna order some smaller main jets. I have seen alot of folks using 150 is that a better place to start the lowest i have is the 190 The only mod is the k&n pods.

 

[djelliott]

Air cooled motors don't like to sit and idle. Probably why it got hot. Also, I'm willing to bet you're still running way to rich. I dicked around with the VM30's for about a year and a half. They were fun when you wanted to rip full throttle and cane the shit out of the bike but any sort of stop and go commuter riding was not so good. I put the stock carbs back on and have had way better results. Go figure.

 

[axeugene27]

IDK damn thing wont idle today. GO figure. I took the carbs off and resynced them not so sure that the hell the problem is. AM I CORRECT IN THINKING THE MAIN JET SHOULD HAVE NOTHING TO DO WITH GETTING IT TO IDLE>?? i am thinking the pilot jet should be completely responsible so i am not so worried about the main jet. You think that 30 is too big of a pilot jet. It looks like those dcc carbs come with a 50 so i figured i should be able to get the damn thing to at least idle. As soon as i cut the choke off the bike just dies again. Not sure what is going on.

 

[kopcicle]

plugged pilot circuit . not necessarily it jet but the circuit complete . make sure air , smoke , stale coffee is free to move between the idle mixture screw , the jet , and the discharge to the venturi .

~kop

 

[surffly]

Ah the joys of putting to big a carb on a motor....

What was wrong with the stock carbs?
Always a good idea to get the bike running 100% factory stock before moding things, and even then try to do mods that will improve the performance of the bike

 

[axeugene27]

when i lit my bike on fire the carbs got pretty charred. I also marred a needle that i can't get out of one of the carbs. I was thinking of getting a pair of used keihin carbs but they pretty much cost the same as the mikuni's. Seems like alot of guys use these carbs with plenty of success. These are really alot easier to dissemble and tweak as well. I just don't know what i'm doing yet. I don't know why it won't idle though. I had it idleing the other day and replicated my steps exactly and now it wont idle at all. I have the air screw out 1.25 turns. I used a 1mm round wire to sync the slide lift with the thumb idle screw there is plenty of slack in throttle cables. Idk what the hell is going on. Would the bike not run if it was too rich. Is the pilot jet the only one to worry about with idling? would the size of the pilot cause it to not idle. It's pretty tough to get it to idle at all so it's not like i can tweak the air screws while idleing. is 1.25 turns out a good place to start for the air screw. All signs point to a rich condition but when i choke it (doesn't this just enrich to mix) the engine reacts not bogs. Geez i really need a carb leprechan or something to sit in my garage and feed me advice and green beer.

 

[rockcitycafe]

1mm opening at idle is a lot. when you sync carbs like that, you sync them by taking up slack in the throttle cables, not the idle stop, you can use a 1mm wire to sync them, but the slides should be more closed than that at idle.

 

[axeugene27]

yeah rock city I am pretty sure you are right about that. The only time i did get it to idle the slides were pretty much closed. So do you think i should just barely crack the slides with the idle screw. The manual says to sync with the idle screw and then sync the cables. No biggie i took a break from carb tuning today so my head didn't explode. I glassed up a cafe seat. Only took me 10 hrs...... literally. and it looks pretty just ok. SHould have called you roc city. are you pretty backed up with seats right now?

 

[axeugene27]

back to carb talk though I am pretty sure I am gonna just crack those slides then half turn with the idle screw at first i'll leave the 30 pilots and just see if i can work the air screw. Do you think I am need to enrich the mix with the air screw> (do i enrich by closing the screw?) I only ask because when i give it choke (enricher) it idles .