Author Topic: Increasing Idle (Read 6962 times)

Harsh · « **Reply #25 on:** April 11, 2013, 02:54:17 PM »

Thanks for the replies. I wasn't going to use drill bets to set them I was just trying to get a guestimate at how far up the slides were from the bottom.

ekpent · « **Reply #26 on:** April 11, 2013, 04:15:49 PM »

That is a lot of thread showing on the adjusters. Think even the Clymers may mention you just want a couple threads or so.

Harsh · « **Reply #27 on:** April 12, 2013, 02:01:44 PM »

OK folks...as usually happens to me things aren't so easy. I decided to completely pull the carbs to make life a little easier for the bench sync and wanting to do it right. I read a number of threads on different ways to do a bench sync in an attempt to familiarize myself with the process and was ready for what I had in my mind was going to be a straight forward semi easy thing to tackle. One thing I noticed ready threads and looking at pictures is that the slide closed position should be viewed/measured from the engine side and not the airbox side. The previous picture of the slide was taken from the airbox side. Looking at the slides they do close all the way. 3 and 4 have just a tiny bit more light shining under the slide, but I don't think it is enough to cause my issue and could easily be adjusted during a vacuum sync. I also noticed that the return throttle cable line bracket was bent over pretty good. I put an adjustable wrench on it and moved it back to its correct position.

So I am once again at your mercy looking for some assistance on where to go from here?

flybox1 · « **Reply #28 on:** April 12, 2013, 02:11:03 PM »

looks like you are on the right track... when you actuate the throttle bell, do all the slides move in unison?
If they do, you should be golden and ready for your vacuum sync.
(I always do bench sync from the airbox side of the slides)

Harsh · « **Reply #29 on:** April 12, 2013, 02:26:08 PM »

Yes they do move in unison. However, I did not adjust anything. This is how they were set when they were running before which tells me the bench sync was done correctly.

I guess the only thing to really do at this point is to slap them back on run them up again to see what happens, which is likely going to be the same thing. That bothers me because the idle screw more than likely still won't do anything and I will still have an increasing throttle. I was really hoping something would be off that I could adjust.

crazypj · « **Reply #30 on:** April 12, 2013, 02:36:14 PM »

You shouldn't set the idle until bike is AT operating temp
Do vacuum sync at 900 rpm then re-set idle to 1,000~1,100
If everything in motor is good and set up properly, it's possible to idle down to 500 rpm or less (not a good idea to keep it there though as oil pressure drops so low but OK for a few seconds)

flybox1 · « **Reply #31 on:** April 12, 2013, 02:38:08 PM »

i think we needed to verify that the idle set screw allowed the slides to completely bottom out.
if idle still hangs , its a vacuum leak, or your cable routing/tension settings is lifting the slides slightly.
with the idle set screw backed out, it should choke out your bike.

thep1pe · « **Reply #32 on:** April 12, 2013, 02:41:50 PM »

Quote from: Harsh on April 12, 2013, 02:26:08 PM

Yes they do move in unison. However, I did not adjust anything. This is how they were set when they were running before which tells me the bench sync was done correctly.

I guess the only thing to really do at this point is to slap them back on run them up again to see what happens, which is likely going to be the same thing. That bothers me because the idle screw more than likely still won't do anything and I will still have an increasing throttle. I was really hoping something would be off that I could adjust.

Harsh you are not listening to what people are telling you about the excess threads showing. Get them to 1 to 2 threads showing, then the idle screw should do it's job and set idle speed.

crazypj · « **Reply #33 on:** April 12, 2013, 02:42:46 PM »

Too tight throttle cable is a major issue, don't understand why so many people do it, usual response is, 'takes too long to open throttle' (with correct slack)
I usually had to show customers how to open throttle as they had never been taught so learned all sorts of bad habits (particularly if father/uncle/brother/etc rode a Harley 30+ years previously)

Harsh · « **Reply #34 on:** April 12, 2013, 02:50:41 PM »

Oh I am listening, but have also read a number of times that the height of them isn't necessarily indicative to a poor bench sync as long as the slides bottom out and they move in unison. I am not discounting that they may very well be too high, but read below to my most recent find.

Well folks I think I may have found the issue. I was thinking that it may be some sort of air/vacuum leak. Since I had trouble mounting the airbox I thought I might try and mount the trumpets to the carbs then figure out a way to finagle the airbox onto the trumpets once the carbs were installed. The airbox is difficult to mount because one of the tabs was bent and I didn't know it. I powder coated the frame and if I bend the tab into place it will crack the powder coat. I took a gander at the trumpets to pull them out of the airbox and what do I see...Three of them were like this. So even though it felt like they were nice and tight they actually weren't and were more than likely sucking in additional air. I will adjust the clamps, re-install and see what happens. Hopefully everything works out well. However, I still think the idle screw the idle screw will still cause me some issues.

flybox1 · « **Reply #35 on:** April 12, 2013, 02:56:05 PM »

cool...onto something there.
be sure your clamps are ALL the way backed out when you put the stacks on the carbs. I snug up and properly clamp #1, then move on to #4. get those on tight, and use a wooden dowel or a paint can stir stick to shimmy the stacks one at a time onto 2&3. check for creases/pinched lips/edges
snug them down well.
good luck

bjbuchanan · « **Reply #36 on:** April 12, 2013, 02:57:14 PM »

If you want to set those airbox clamps good, get everything back together and run it "fixed"

Slack them off a bit on that warm engine and tighten them back up. Not uber tight, that is a surefire way to create a leak just snugged

Hit it with some carb cleaner or wd40 now and see what's up it should be better

kghost · « **Reply #37 on:** April 12, 2013, 04:05:38 PM »

A leak around the bellmouths at the air box is not going to cause your idle problem.

It's caused by the fact you have the slides on one or more carbs set too high as indicated by your picture of the threads on the adjusters on the top of the carbs.

Do as fly box recommended or......

Set the carb adjusters all the same......about 1 - 1 1/2 threads showing.

Set the idle screw about 2 turns in.....

Vacuum sync.

Adjust the idle as required.

ekpent · « **Reply #38 on:** April 12, 2013, 04:21:57 PM »

You mentioned earlier that your idle screw was basically useless,that it wasn't even touching the plate. A little air leak does not cause that.If it were me I would back off the adjusters at the top of the carb and then I would move in the idle screw some so there was some useful headroom for its operation.That has to be able to function. Once you know that function will be available again than move on to a bench synch. Worry about air leaks after you solve that issue.

Harsh · « **Reply #39 on:** April 12, 2013, 04:33:06 PM »

OK...I am going to re-bench sync them.

I am absolutely not trying to be difficult here, but my mind is having trouble wrapping around the fact that the slides bottom out as they should and pretty much equally (3&4 have a pin drop of light shining through). Like I mentioned earlier I have been reading a few threads on the subject. I read a few by TT that have resonated with me about shining light through the carbs and looking to see how much light comes through. In there he also mentioned about the the number of screws showing not meaning a whole lot if the slides bottom out.

I guess I really have nothing to lose by trying and hopefully it will might fix the idle screw contact issue. I tried straightening the tabs on the straps, but it does no good. As soon as they make contact they start to bend up again. I am going to have to get some new ones (even though these were brand new from CB750supply). There is no way to stop them from bending once they are tightened.

Thanks for all of the help and I will let you know how things go.

ekpent · « **Reply #40 on:** April 12, 2013, 05:07:18 PM »

The way I visualize it when you loosen the adjusters at the top that will relax the slides to bottom + some. When you screw in the idle screw the arms at the top begin to raise the slides again. After you have turned in the idle screw a few turns without raising the slides that will build in the headroom you will need to use that function again.Then when the slides are synched again to the new idle adjustment spot the function should be there through its full useful range . Wish I had one of my bikes here to see how many turns it takes to get the idle screw off the plate. Maybe somebody has a rack off to check.

Harsh · « **Reply #41 on:** April 12, 2013, 05:08:45 PM »

Bench sync complete. It was a lot easier than I imagined. I have 1 to 1.5 threads showing and the slides still bottomed out. Now my mind is wondering how they bottomed out with all of the threads showing. I didn't take notice of where the idle screw was before all of this started, but it takes about four turns from being fully backed out to where it makes contact with the bar.

Unfortunately I will have to wait on new clamps to test things out. I know my dealership doesn't have them (plus being almost $3 a piece) because I inquired about them before I bought the others.

kghost · « **Reply #42 on:** April 12, 2013, 06:19:18 PM »

Which clamps are you missing? The carb to engine ones?

If its the air box side ones you can still set them up without.

There's not a lot of light that shines thru the carb slides at idle.

When you have the adjusters on the carbs set......

Turn your idle screw in at least two turns after it makes contact.

You may have to turn it in further to get it to start and idle.

After you vacuum sync you can adjust the idle speed

Harsh · « **Reply #43 on:** April 13, 2013, 04:53:50 AM »

The clamps that I need to replace are the carb to airbox ones. The tang on them is bends every time I try and tighten them.

I have a lot of crap to do today, but I will try and find some time to get to work on the bike and fingers crossed put this animal to bed.

Killer Canary · « **Reply #44 on:** April 13, 2013, 09:22:36 AM »

I once had a problem with a changing idle that was caused by the bolt holding the bell-crank shaft halves together being loose. Just a possibility.

KB02 · « **Reply #45 on:** April 14, 2013, 06:00:08 AM »

Quote from: Harsh on April 12, 2013, 05:08:45 PM

... I didn't take notice of where the idle screw was before all of this started, but it takes about four turns from being fully backed out to where it makes contact with the bar.

When you started this thread, you mentioned that the idle screw was barely making contact before. Sounds like you have the carbs adjusted better now. Hopefully this all did the trick.

strynboen · « **Reply #46 on:** April 14, 2013, 09:48:14 AM »

Quote from: Harsh on April 12, 2013, 02:01:44 PM

OK folks...as usually happens to me things aren't so easy. I decided to completely pull the carbs to make life a little easier for the bench sync and wanting to do it right. I read a number of threads on different ways to do a bench sync in an attempt to familiarize myself with the process and was ready for what I had in my mind was going to be a straight forward semi easy thing to tackle. One thing I noticed ready threads and looking at pictures is that the slide closed position should be viewed/measured from the engine side and not the airbox side. The previous picture of the slide was taken from the airbox side. Looking at the slides they do close all the way. 3 and 4 have just a tiny bit more light shining under the slide, but I don't think it is enough to cause my issue and could easily be adjusted during a vacuum sync. I also noticed that the return throttle cable line bracket was bent over pretty good. I put an adjustable wrench on it and moved it back to its correct position.

So I am once again at your mercy looking for some assistance on where to go from here?

are this intake standart..or is there made some driling..to adlaud air gas/flow pass by..??overbore so it leaks asside the slides

Harsh · « **Reply #47 on:** April 14, 2013, 11:44:36 AM »

Engine and carbs are stock.

OK...finally got some time to tinker today. Bike was a little harder to start, but still started somewhat easily. It appears that re-bench syncing the carbs has proved to be successful. Idle stabilized at about 1500. Shut her down and attached the sync lines to the carbs. Now this is where I am unsure. All four carbs read something different. No surprise there. Do I adjust to the lowest or highest carb CmHg reading?
Lets say
carb 1 is at 20
carb 2 is at 25
carb 3 is at 30
carb 4 is at 22

When I adjust carb 2 to 20 (to match carb 1), carb 1 jumps to 28. Do I go back and adjust carb 1 back down or just remember it's reference point and adjust carbs 2-4 to carb 1's initial reading? Also when I make an adjustment the idle increases. Do I adjust the idle back down to 2500 during the sync process or just let it rise where it wants to. I think at one point it got up a tick over 2500.

crazypj · « **Reply #48 on:** April 14, 2013, 12:09:35 PM »

Numbers are irrelevant, just get them all the same
Do the highest one first as it's closed the most (causing higher vacuum and keeping the other 3 open)
Lowest is already open a bit (lower vacuum)
Keep adjusting idle to around 1000 rpm, lower is better as the ignition advancer wont be doing anything weird to timing

Harsh · « **Reply #49 on:** April 14, 2013, 12:17:10 PM »

Yes I understand the number is irrelevant. At the end of the sync all of them need to be relatively the same correct? So that would negate setting them to the initial reference of one carb, correct?

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Author Topic: Increasing Idle (Read 6962 times)