Author Topic: How open should slides be on idle (PD46A)  (Read 1734 times)

Offline michtag

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How open should slides be on idle (PD46A)
« on: January 19, 2020, 12:30:51 PM »
Hi all,
I have been chasing gremlins on my 1977 CB550K3 and now, after a deep carb clean where I unplugged a couple of bowl breather holes and an overflow tube, the bike starts well (always has) but within 30 seconds from stone cold idles between 4.5 and 5k. When warm, just shoots up there straight away. No binding cables, the idle screw is fully off and the shaft rotates all the way to the "fast idle" screw (which I have not touched). Slides are not getting stuck anywhere.
3K miles tune up done and all the rest as suggested by this and other forums (or is it fora?), so I know it could be a series or a combination of factors that I have on a big list and will get to (it is mostly stock, but has paper air filter and 4 into 1 Delkevic exhaust, so some fine tuning will be needed), however, proceeding by elimination I wanted to check with the experts here that my slides are actually in the right position for idling. To be honest I thought they would much closer than this, but before I take the carbs off again I wanted to ask a wider audience.
The carbs have only been bench synced for now as I don't want to perform a proper vacuum sync at 4k RPM...

Are this simply too wide open for idling, meaning I must have messed up something when reassembling the throttle shaft? I have not taken the slides off their linking arms, so there is no chance that I put those back incorrectly (back to front, that is)

Apologies for the mini images...my usb camera is not the best, but it should give you an idea anyway. This is carb #2 viewed from the air box.
Many thanks for checking this out!!
Michele
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline heliwilly

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Re: How open should slides be on idle (PD46A)
« Reply #1 on: January 19, 2020, 02:10:33 PM »
Hi,

An educated guess , from the pics they do look high to me. Hopefully someone with more knowledge than me will be able to give you a more accurate method of reducing the height of the slides.  Bill W.

Offline Nurse Julie

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Re: How open should slides be on idle (PD46A)
« Reply #2 on: January 19, 2020, 03:27:18 PM »
Yes, far too high. They should be that low that a ⅛" drill bit shank should be a snug fit under the slide, when bench synced correctly.
« Last Edit: January 19, 2020, 03:30:29 PM by Nurse Julie »
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Offline K2-K6

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Re: How open should slides be on idle (PD46A)
« Reply #3 on: January 19, 2020, 04:45:56 PM »
As other's already indicated,  look too high to get near specification on tickover.

http://www.sohc.co.uk/index.php/topic,17769.0.html this link will help and give you a routine that should correct the mechanical positioning within their carb set to normalise their position,  and hence give to the adjustment that makes normal setup.

Offline michtag

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Re: How open should slides be on idle (PD46A)
« Reply #4 on: January 19, 2020, 05:17:43 PM »
As other's already indicated,  look too high to get near specification on tickover.

http://www.sohc.co.uk/index.php/topic,17769.0.html this link will help and give you a routine that should correct the mechanical positioning within their carb set to normalise their position,  and hence give to the adjustment that makes normal setup.

Thank you, but I think this specific procedure is not for PD carbs (which is what I have). I cannot set the height in n 2 carb.
I'll just see what other experts may think, but I am starting to think I may have reassembled incorrectly...
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline Nurse Julie

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Re: How open should slides be on idle (PD46A)
« Reply #5 on: January 19, 2020, 05:43:28 PM »
BryanJ or Oddjob will be able to advise more on the PD's I'm sure. I could be wrong but I think on those #2 carb is fixed and you bench sync the other carbs to the same level as #2. I can't help any more as luckily, I don't have PD's fitted to any of my DOHC/4's.
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Offline hairygit

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Re: How open should slides be on idle (PD46A)
« Reply #6 on: January 19, 2020, 05:54:01 PM »
BryanJ or Oddjob will be able to advise more on the PD's I'm sure. I could be wrong but I think on those #2 carb is fixed and you bench sync the other carbs to the same level as #2. I can't help any more as luckily, I don't have PD's fitted to any of my DOHC/4's.
Has Trig managed some incredible engineering and somehow fitted a second camshaft to your bikes???. (Sorry, couldn't resist!)

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Offline Nurse Julie

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Re: How open should slides be on idle (PD46A)
« Reply #7 on: January 19, 2020, 06:03:15 PM »
BryanJ or Oddjob will be able to advise more on the PD's I'm sure. I could be wrong but I think on those #2 carb is fixed and you bench sync the other carbs to the same level as #2. I can't help any more as luckily, I don't have PD's fitted to any of my DOHC/4's.
Has Trig managed some incredible engineering and somehow fitted a second camshaft to your bikes???. (Sorry, couldn't resist!)

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Well noticed Mr Hairy.... That's defo a TYPO and no twin cams in this house at all.... It should read SOHC/4 😊😊😊😊😊
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Offline Bryanj

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Re: How open should slides be on idle (PD46A)
« Reply #8 on: January 19, 2020, 06:24:40 PM »
PD's are one of those things that cause "sick days" among most mechanics. Yes one carb is non adjustable and i think it is No2, that one MUST fully close before attempting to bench sync the bank.
I do have some odd bits left over from a 550 set and NO I WONT DO THE JOB

Offline michtag

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Re: How open should slides be on idle (PD46A)
« Reply #9 on: January 19, 2020, 06:31:47 PM »
PD's are one of those things that cause "sick days" among most mechanics. Yes one carb is non adjustable and i think it is No2, that one MUST fully close before attempting to bench sync the bank.
I do have some odd bits left over from a 550 set and NO I WONT DO THE JOB

I am not surprised! I hope I don't need any spare bits for my carbs and don't worry, I won't ask you to do it :)
I guess it's time to take them off...again!
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline CB5501977K3

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Re: How open should slides be on idle (PD46A)
« Reply #10 on: January 20, 2020, 08:22:12 AM »
Hi Mitchtag
I have spent hours getting my PD46A's running well on my 550 and grew a beard trying to sort out an intermittent problem (which may cause the fast idle)?
I had a choke flap which was catching the carb body and sometimes didn't release as it should when closing the choke.
You can see the score mark on the attached image, just check the choke mechanism is fully moving freely by observing the choke linking rod.

Good Luck

Chris

Offline michtag

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Re: How open should slides be on idle (PD46A)
« Reply #11 on: January 20, 2020, 12:06:54 PM »
Hi Mitchtag
I have spent hours getting my PD46A's running well on my 550 and grew a beard trying to sort out an intermittent problem (which may cause the fast idle)?
I had a choke flap which was catching the carb body and sometimes didn't release as it should when closing the choke.
You can see the score mark on the attached image, just check the choke mechanism is fully moving freely by observing the choke linking rod.

Good Luck

Chris
Thank you Chris, I had checked previously and all plates open and close correctly (I tightened them up only at the very end of the rebuild to make sure they move freely) off and on the bike. I guess the only way to make sure about the slide height is to take them off again.....but as I do not have a garage I have to make sure there is still enough light in the day, it does not rain and it's not freezing cold so i can still feel my hands. basically, any 2 hour job can turn into a 5 weeks waiting game :/
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline michtag

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Re: How open should slides be on idle (PD46A)
« Reply #12 on: January 20, 2020, 03:48:08 PM »
As said those look too high to me, would account for the high revving on startup and idling. As you haven't taken the throttle slides off their linkage arms it's unlikely to be that, saying that how do you know the previous owner didn't?  As Bryan says, one carb which I'm 99% sure is number 2 is non adjustable, if that sits high then the rest will too. The problem is most likely the linkage between the carbs, if you disassemble the carbs from the linkage plate look to see if the throttle slides now sit lower, especially number 2. If it does it's the linkage bar or the choke mechanism. Check to see if you can find the problem with them. Been a while since I had a set of PDs carbs apart so can't remember if it has butterfly adjustment screws like the 500 carbs, if so check those.

Thank you Oddjob; as I said I have been trying to get this bike running properly for a while and even a mechanic (which obviously over-stated his expertise on these bikes) could not settle it. It's a long story and i will probably write another post about it, but for now let me just say that the bike used to start off well and then hang around 3k rpm after warm-up, which pointed to weak advancer springs. I have been playing with those and timing but never got it solved, then I decided to tear the carb down again, change all throttle shaft seals (rubber and felt) just to rule out air leaks from there (despite reading that is really did not matter). Once I put it all back together, after cleaning again all jets and realising that 2 breather holes were clogged, it started just jumping to 4-5k rpm from the start (or within 30 seconds anyway).
I have done the usual air leak checks (I have new boots and new manifold o-rings) and found nothing so before starting to look at it as a possible electrical problem (next step is to try new points and condensers, to see if anything changes) I wanted to make sure I had not cocked up the reassembly of the throttle shaft in some strange way. Which I may well have done!
Regarding the butterfly adjustment screws, I am not sure what they are, so i am guessing these PD carbs do not have them.
Cheers
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline michtag

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Re: How open should slides be on idle (PD46A)
« Reply #13 on: January 23, 2020, 11:59:38 AM »
Just found some pics of the PD46A carbs abd you are correct, there are no butterfly adjustment screws on them. I presume you've unscrewed the idle adjustment screw as far as it will go?

The other possibility is the linkage which is on number 2 carb, looking at the pics it appears the butterfly (where the cables clamp) runs the cables down to the linkage where the cable nipples engage, this linkage appears to be attached to number 2 carb and if it's been disassembled it could have been put together again wrong or the return spring on it has broken. Have you tried running the engine with the throttle cables totally detached?

Oh yes, the idle screw is backed all the way and more, there are a couple of mm of clear space, even. The shaft rotates all the way until the fast idle screw butts against the choke shaft cam (choke IS off).
I have not tried running it with all cables disconnected, but I will take the whole thing off this weekend, hopefully and see where I may have done something wrong.
Cheers
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

Offline michtag

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Re: How open should slides be on idle (PD46A)? - SOLVED!!
« Reply #14 on: January 26, 2020, 01:38:56 PM »
OK, finally some progress.
I realised that even if I had not touched the "fast idle" screw the PO or indeed the mechanic who attempted to settle this bike a few months ago (attempting, failing and blaming worn-out carb's bushings) could have done that. After my latest deep clean, the carbs breathe much better to the slides can be closed more.
To cut a long story short, I unscrewed the fast idle completely and that pretty much did it.
Now I can use the main idle screw to change idling speed and after warm-up it settles nicely around 1000-1200 rpm (on the tach).
So, this problem solved, I am getting closer, I hope to smoothing out everything else that is either wrong or inconsistent about it (slow return to idle, mostly). I won't bore you with it now, I have plenty of suggestions gathered from reading the forum and a list of things to do and to try, but i will probably post a detailed report at some point to serve as a reference for anybody who found themselves facing the same problems.
For those of you not familiar with PD46A carbs, here's what the "fast idle" screw looks like, viewed from below (bottom of pic is airbox side, top is engine side). It should barely touch a cam on the choke shaft, where the 2 halves meet with the spring mechanism. For now I have retrieved it almost completely, but once I have synced the carbs and settled them properly I will reset this as suggested in the manual.
Thank you for your help!
-- I will fix it...or at least I will understand why I can't --
1977 Honda CB550K3

 

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