Author Topic: High Idle?? (Read 6936 times)

jstfkndi · « **on:** May 29, 2012, 10:39:59 AM »

So I am very close to getting this 350F back on the road

Have gone through a lot of items and addressing them. Had a local (very good) mechanic got through the carbs when they were off the bike and he adjusted the float bowls, cleaned and set carbs best he could to go back on bike. All well and good, as I have put the carbs back on and the bike runs! Problem is...it idles crazy high, around 4K Rpm. I made some adjustements and set the idle mixture to 1 3/4 out on each carb, adjusted valves and tightened down carb boots to make sure there were no leaks. Points on it looks brand new, so I haven't messed with them, but that is next. So I start the bike up and it idles nicely until I pull on the throttle and it responds, but then won't idle down. The large idle speed screw will be all the way out and not even touching the contact bar for the carbs! I guess my question is: Are there any othe factors I may be overlooking? Cables seem to be right on and I want to do a synch (as I have the synch kit) but is that pointless until I figure out this idle issue OR could it be that not being synched is also a factor? I have the Haynes manual and have gone through it several times in the fuel and carburetor section with out really any clear answers. Maybe someone here has had the same issue? Thanks!

iron_worker · « **Reply #1 on:** May 29, 2012, 10:48:19 AM »

I just went through my carbs on my 750 and my best guess is that when he was benching sync'ing the carbs he left the sync adjusters too far open. Your slides are probably not completely bottoming out even if it appears it is from the outside.

I'm not sure what type of carbs are on the 350 but on the 750 the sync adjuster not and locknut are visible poking through the top of the carbs. They should be adjusted such that adjuster and locknut are very near to the top of the available threads.

However, you may have the type of carbs with the enclosed top and internal rocker arm and I'm not sure how to adjust that type though I'm sure it's a similar principal.

IW

flybox1 · « **Reply #2 on:** May 29, 2012, 10:51:12 AM »

if it idles nice before you blip the throttle and it hangs, then your slides might be ok.

pull cable installed? use it....does it bring the idle down?
return spring installed and working? it should snap closed when you release the throttle.

if both of these are ok, then loosen all your carb boot holders and re tighten all of them.
probably on is not seated correctly and sealed causing a vacuum leak. be precise with all of them.

jstfkndi · « **Reply #3 on:** May 29, 2012, 11:35:58 AM »

Ok, thanks! I checked the cable and it lets the cable rocker (guess that is what it is called) close all the way. When I think about the carb boots, they are pretty old and I had a hell of a time getting the carbs back. I think I may try and start it up and shoot some carb spray around that area it to see if I get a reaction. I'll keep you posted and I will have to research the slides. I pretty much just trusted this guy to do what he does as I was a bit intimidated by all the linkage and adjustments with four carbs. This thing is so close to being on the road that it is making me nuts!!

TwoTired · « **Reply #4 on:** May 29, 2012, 01:14:48 PM »

Quote from: iron_worker on May 29, 2012, 10:48:19 AM

... best guess is that when he was benching sync'ing the carbs he left the sync adjusters too far open. Your slides are probably not completely bottoming out even if it appears it is from the outside.

^^^^^this.

lucky · « **Reply #5 on:** May 29, 2012, 01:34:19 PM »

Quote:
"through the carbs when they were off the bike and he adjusted the float bowls, cleaned and set carbs best he could to go back on bike."

You need a new mechanic.

Best he could?

?

flybox1 · « **Reply #6 on:** May 29, 2012, 01:45:11 PM »

Quote from: jstfkndi on May 29, 2012, 11:35:58 AM

I'll keep you posted and I will have to research the slides.

you are your own best mechanic

when you take your airbox off, you can look into each carb intake and see your slides. if they are all the way down(with your idle set screw turned all the way out), its your old and dry carb boots not sealing as they should.
get new boots and vacuum sync asap.

jstfkndi · « **Reply #7 on:** May 30, 2012, 06:10:05 AM »

Good info. I will check to see if they are up or down. As far as the mechanic who did it, he came recommended and has many good references, but he could have messed up. I guess I'll find out. So if the slides are up and the idle screw is out, it is the slide adjustment? And if they are down and the idle screw is out I have a leak? Again, this is my first time with a bike like this, so it may take me some time. I have had this thing off the frame and cleaned every part I could and bought new what needs, so I'm not afraid. I just want to do it right

Thanks!

flybox1 · « **Reply #8 on:** May 30, 2012, 06:54:49 AM »

Quote from: jstfkndi on May 30, 2012, 06:10:05 AM

So if the slides are up and the idle screw is out, it is the slide adjustment? And if they are down and the idle screw is out I have a leak?

Definitely.
Most likely.

jstfkndi · « **Reply #9 on:** June 04, 2012, 05:42:32 AM »

Ok. I finally got around to pulling off the airbox and from what I can see, the slides have a gap existing that is about half an inch or so from bottoming out. So there should be no visible opening? I should see the slides completely and that is all I should see? Again, my manual doesn't explain this. I started it up and it did the similar high idle, but not AS bad.

lucky · « **Reply #10 on:** June 04, 2012, 05:52:25 AM »

Quote from: jstfkndi on June 04, 2012, 05:42:32 AM

Ok. I finally got around to pulling off the airbox and from what I can see, the slides have a gap existing that is about half an inch or so from bottoming out. So there should be no visible opening? I should see the slides completely and that is all I should see? Again, my manual doesn't explain this. I started it up and it did the similar high idle, but not AS bad.

1/2 inch from bottoming out!! WOW!!! Better find out what is wrong.

jstfkndi · « **Reply #11 on:** June 04, 2012, 11:47:52 AM »

I am going to have to take pics. I am not sure where the bottoming out is. Seems to me that completely closed, the bike would choke off? I can see the needle with the throttle just sitting as is. Should I not see it at all?

jstfkndi · « **Reply #12 on:** June 05, 2012, 05:20:54 AM »

Picks weren't as easy as I hoped with carbs still on bike, but the short is, they are bottoming out ok. I think I may just take it to the guy who set them off the bike since he has a better idea of what he did than I and see if he can't get them set. It went from starting and idling high to barely running now. Pulled the spark plugs and cleaned them and two of the four were smelling of gas. I knew this was going to be the pain in the ass part.....

flybox1 · « **Reply #13 on:** June 05, 2012, 08:33:30 AM »

Quote from: jstfkndi on June 05, 2012, 05:20:54 AM

... but the short is, they are bottoming out ok.

how did you get them to 'bottom out'?
are you sure you got them all to bottom out the same?
if you're doing it yourself, and you have made it this far, keep going. we'll help.
i think it would be best for you to now take the carbs completely off the bike so you can get at them properly.
cleaned properly. bench sync'd properly.
dont let it frustrate you. i've had this CB750 for 3 months now and already had the carbs off 6-7 times

we need to get you back to stock settings. the 350F is pretty easy. no accel pump.
PM me if you get stuck.
I miss my 350F

jstfkndi · « **Reply #14 on:** June 06, 2012, 10:01:53 AM »

Thanks Flybox! I guess I can try to take them off again and look them over. #$%*, I already took the airbox off, so just gotta undo the cables and clamps! I will take them off and at least get some proper pics of it, but I am pretty sure that they are bottoming out because the slides hit a stopper at the bottom. I think I need to clean them really well myself and at least check out the jets. Might take me a minute to finally get a chance to work on them, but when i do you will know! Guy was saying he is up to his ears in work now anyway and said he'd make room, but would rather he take his time. During the summer, that is hard for a bike mechanic!

flybox1 · « **Reply #15 on:** June 06, 2012, 10:23:50 AM »

Do a bench sync of your carbs before you reinstall them. PM me if you need specifics.

your main jet, in the center, underneath the butterfly spring, will pull out. under it, is a brass (emulsion) tube, you'll need to get that out as if it clogs with debris/varnish, it will prevent fuel from entering the carb in a fine spray. there are tiny holes along its length on all sides. clean them out with a bit of brass wire.
the idle jet, just to the side of the main jet, looks like a brass post with a screwdriver slot in the top. screw it out and check its tiny holes for debris, too. be OCD with the cleanliness of these. you should be able to see light through lengthwise as well.
set your float height at 24mm. double/triple check them.
button them back up.
AF screws out 1 turn (7/8 turn is stock, 1 is fine for now) you'll fine tune this later after running a bit and checking your plugs.

cavi · « **Reply #16 on:** June 06, 2012, 11:24:07 AM »

as long as you are removing the carbs again swap out the carb boots so you know they are not a source of air leaks

jstfkndi · « **Reply #17 on:** June 07, 2012, 05:18:33 AM »

Ok, I will do all this when I get them off. Floats should be adjusted with the bottow facing up or down. I know it can be done on the bike as well, but if I have them on the bench, I will do them there. And Cavi, are you talking about the boots between the motor and carbs or air box boots? I have heard of people using guitar string to do this cleaning of the jets and all, but they are usually steel. Where can I find brass wire thin enough for this job? I really appreciate the help and I might become a pest with questions

flybox1 · « **Reply #18 on:** June 07, 2012, 07:06:17 AM »

Quote from: jstfkndi on June 07, 2012, 05:18:33 AM

I really appreciate the help and I might become a pest with questions

No problem. I'm just paying it forward

I think Cavi means the boots on both sides, if you can find them..

rip apart a chunk of phone cord/cat5/speaker wire to get your strand.

float measurement is done easier when carbs are off the bike.
prop your bank of carbs on the table with a towel. we want to position them so that the float tang (little square brass tab in the center of the floats) is just resting on the float valve needle(internal spring not depressed). take your float height measurement from this position at the center of the flat side of the float. gently tap the floats so they bounce against the needle, and re-measure.

lucky · « **Reply #19 on:** June 07, 2012, 08:20:42 AM »

Quote from: jstfkndi on June 04, 2012, 11:47:52 AM

I am going to have to take pics. I am not sure where the bottoming out is. Seems to me that completely closed, the bike would choke off? I can see the needle with the throttle just sitting as is. Should I not see it at all?

When the slides are bottomed out only the slide cutaway should be visible and you probably will not be able to see the needle at all.

jstfkndi · « **Reply #20 on:** June 07, 2012, 05:50:03 PM »

These are the carbs off the bike, and what the slides look like bottomed out.

TwoTired · « **Reply #21 on:** June 07, 2012, 06:11:09 PM »

The slides are not resting on the floor and they appear to be out of synchronization, too.

They must be able to rest on the floor when the idle knob is backed out. That way, the idle knob can adjust them as close as is needed for proper idle speed.

The individual slide adjusters have no limits built in to their adjustment travel. A knowledgeable rebuilder will know this, and make sure the slide adjusters are not ALL skewed so that proper idle can be set.

Keep your drill bits in their drill index holder.

lucky · « **Reply #22 on:** June 07, 2012, 06:18:33 PM »

The slide on #4 carb is obviously way too high.

The syncing of the carbs (adjustment of the height of the slides) is done through the top cover of the carbs.

Don't just start turning screws if you do not know what they do.
Your problems will just get worse.

Forget about that arrow going to that screw for right now.
Looks like it adjusts the position of the choke butterfly.

TwoTired · « **Reply #23 on:** June 07, 2012, 06:28:04 PM »

Quote from: lucky on June 07, 2012, 06:18:33 PM

The arrow points to a screw that may lower that slide buy I cannot tell from just that one photo. Leave that screw alone for right now. Could just be the idle screw.

No. The circled screw is for setting the choke plate position. It has nothing to do with idle setting.

Quote from: lucky on June 07, 2012, 06:18:33 PM

The syncing of the carbs (adjustment of the height of the slides) is done through the top cover of the carbs.

No again. These carbs have the slide position adjuster besides the carbs and top caps. The shop manual usually points these out with clarity.

jstfkndi · « **Reply #24 on:** June 08, 2012, 05:10:14 AM »

Ok, thanks. Right now, all I have done is adjust the float level on the one carb without the bowl on it and took out the brass jet with all the holes and sprayed carb cleaner through and the passages where it sits. Going to go over the manual this weekend to see how to go about gettingthe slides adjusted. Looks to me that it has a stopper that I might have to pull the tabs back from to be able to undo a bolt if necessary..? Not going to try and get above my head and I will try and post more pics from the side and screw adjustments before I start to do anymore. The bike ran.....just not well....

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Author Topic: High Idle?? (Read 6936 times)