Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: billdn on October 09, 2022, 12:10:39 PM
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The saga continues. I've refitted carbs after setting sliders using BrianJ's method, and others and seemed to achieve what was required. Bike starts fine and when warm ease off choke and all ok. But when revved up to say 3000rpm the throttles close properly on handlebars, but revs do not drop back to tickover 1200rpm. This can be achieved by using main idle screw, but when revved again the same happens meaning using idle screw again - could make for interesting riding! When revved higher say 4000rpm still won't drop back past 2000 without using idle screw.
I have fitted main air box to back of carbs but not yet connected up to filter box (suspected I'd be taking them off again!) and air filter not fitted but this shouldn't make any difference at this stage I believe. Carbs have been stripped/cleaned and replaced brass float rods and carb float height set.
Any ideas? Anyone? Please !
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Is the throttle cable lock nut thingy done up properly Bill? (I'm trying to remember the proper name for it...... But 🤔🤔🤔) It's the bit where the cable sits in a bracket and you lock the nut to stop the cable moving.
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The one on the open/ close butterfly thing or the handlebar ?
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The one on the open/ close butterfly thing or the handlebar ?
On the butterfly Bill.
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I'll double check but everything seems to open/ close OK but you never know bit fiddly at that bit .
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Reads like the throttle closing cable is not working as it should at the carb end - I made sure there was some slack in the cable so it closed off fully.
Could it be the heat of the engine is making the cables bind?
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Does sound like closing cable to me as well, if you twist the throttle the wrong way(forwards) after you let the throttle go do the revs come down, there is a spring loaded bit on the operating mechanism
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Try disconnecting the cables completely. Rev the engine using the butterfly by hand and see if it still does it. You'll need a remote fuel supply to do it though.
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Does sound like closing cable to me as well, if you twist the throttle the wrong way(forwards) after you let the throttle go do the revs come down, there is a spring loaded bit on the operating mechanism
Thanks Bryan , did think that too but doesn't make any difference. Also adjusted both cables but made little difference. Also made sure choke screw was not operating choke.
Incidentally though as I was pushing/ prodding stuff I did note that if I pressed on brass caps on sliders on 1 and 2 carbs revs did settle, almost if not quite returning down after operating.
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Try disconnecting the cables completely. Rev the engine using the butterfly by hand and see if it still does it. You'll need a remote fuel supply to do it though.
You don't like me do you 🤣
Worth a punt though. Given up Haynes manual (sorry Bryan) reference to 56mm distance on closing throttle to end .
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Try disconnecting the cables completely. Rev the engine using the butterfly by hand and see if it still does it. You'll need a remote fuel supply to do it though.
You don't like me do you 🤣
Worth a punt though. Given up Haynes manual (sorry Bryan) reference to 56mm distance on closing throttle to end .
Interesting, cables disconnected but still same issue and again could be resolved by pressing on top of sliders on 1 and 2 carbs.
Not quite sure what's incorrectly aligned but must be something of that sort 🤔
Carbs off again !
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Incidentally though as I was pushing/ prodding stuff I did note that if I pressed on brass caps on sliders on 1 and 2 carbs revs did settle, almost if not quite returning down after operating.
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That sounds like you have found the problem area.
Have you overhauled the carbs previously ?
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No, this first time off since I've had bike, only did it as waiting for rebore etc. And thought ideal time , any ideas Ted?
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Mine were seized up solid when I bought my 400. I had to soak the carb bodies in a series of solvents - Petrol, Acetone & ,carb cleaning spray to get them to move a mm. I suspect you just need to clean the sliders up properly by removing them fully - you could remove the slider top caps & use some carb cleaning spray if a full dismantle is too difficult or inconvenient.
There is a spring loaded mechanism that has ball cups at each end that can gum up as well.
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Just rebuilt comfysofas carbs and noticed that on the 400 set i had to start the bench sync with the adjusters screwed up a bit or the idle screw lever would not touch the bracket and the choke did not operate the high idle lever.
My instruction were written for the 500 carbs which dont have thehigh idle so that could be a problem, sorry
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Aarrgh! 🙃 thought it was had to screw the bejesus out of adjuster to get slide down . 🤣😉
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In my defence comf's was the first set of 400 i have had where just about every screw possible was undone and i must give thanks to Nurse Julie and Oddjob for helping out with parts and once again appologies for the wrong instructions.
Iwould now suggest that on the 400 wind out the tickover screw, make sure that the choke lever is NOT touching the fast idle cam then starting with all the screw adjusters removed and nuts, links, washers etc removed screw down one adjuster keepin a close eye on the arm the big tickover screw pushes on till it just moves then back off 1/2 to 1 turn(i.e.screw up) then do same to each adjuster in turn.
Now fit washers, links and nuts as removed making sure the adjuster doesnt move as you fit the nut on each one.
Now fit the idle screw and screw in until your tiny drill shank just fits under the engine side of the slide on the slide with biggest gap and adjust the othe slides to that one.
This should give a good starting settup with all slides down.
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If you want a really in depth description of Stripping/Rebuilding Carbs which covers everything you need to know, have a look at ‘THE VINTAGE BIKE BUILDER’.
It’s an American site but one of the best I have encountered, having plenty of pictures to back up the written word so you shouldn’t get lost in the information.
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Or look at Classic Octane, he takes a set of 400 and 500 carbs to bits and rebuilds them fromscratch. MASSIVE HELP!!!
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I used this U-tube video - there is plenty of stuuf out there if you are a first timer like I was.://www.youtube.com/watch?v=JFTOfYl5BSc
.https://www.youtube.com/watch?v=JFTOfYl5BSc
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Thats the chap.
I am TAYLOR! :D
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Sorry to return to this but still having problems! >:(
I watched the videos mentioned and even carefully read the Vintage Biker piece on setting up the carbs- no joy still won't idle.
I've tried BryanJ's revised carb set up still no joy.
It just won't return to idle speed of 1200rpm. rev it to 2000rpm and won't drop, rev it to 300rpm drops to 2000, rev it to 4000 drops to 3000rpm. I've disconnected cables and it still won't drop, so can't be cables! and revved by hand.
I've adjusted air mixture screws to 1 1/2 turns out and nothing.
But again, press the top of the brass nuts on top of the sliders and you can get the revs to drop but then drops too low and stalls. it can be reduced by adjusting idle screw but continually doing that is not right, obviously!
Is it possible I've reassembled wrongly the sliders but they to be smooth enough in their action?
Is it possible to get the main spring the wrong way round but don't see how, it closes the carbs with a quick action?
Frustrated of Sussex
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How far down have they been dismantled? Sounds like a lifter arm problem, maybe one of the internal springs is missing or corroded to the extent it’s not pushing the arm down enough when it’s lifted. The fact pushing down on the top nut reduces the revs would make me suspect this.
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If pressing the brass nut down drops the revs then I suspect you have something not assembled correctly in the slider mechanism / links. There is a spring as well as the ball cups either side. Did you remove the lever bolted to the slider top that has the locking tab?
Even though the throttle return spring is quite strong the lever mechanism has to be working freely via the links to shut off effectively at all temperatures.
You have three links with spring & cups on each carb. One attached to the slider inside plus two external ones on the alloy body with the plastic cross links. If just one of the four sets of three links is not assembled correctly it could explain your issue. Twelve links in total that need checking.
Another thought have you removed the fast idle cam & lost the little ball bearing?
Update:- looks like my reply duplicates Kens thoughts.
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Cheers Ted and Oddjob,
Have stripped down and cleaned slider assembly, lubed etc and reassembled. Couldn't really see much wrong, no major debris and everything in the right place , thankfully. Did notice that the 2 springs in the slider arm although are same length were slightly different colours, so swapped them around , TTYL anything now.
Ted, still have little ball bearing in choke mechanism too.
Odd job, was full strip , everything apart including slider arm ..
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I'm trying to remember but I think one of the adjusters is quite critical if you overtighten it - I think it's the one in the slider itself. Mine was marked with yellow paint.
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Don't recall reading that Ted isn't that on the 500 or 550, hope so as all mine have yellow paint on 🤣
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Don't recall reading that Ted isn't that on the 500 or 550, hope so as all mine have yellow paint on 🤣
I did my best to return all the lock nuts to their original position on my 400 carb rebuild. I seem to recall that on one slider all the paint fell off so I had to fiddle with it a tad to make it return freely.
All 4 of my carb sliders were stuck solid. It took me several days of soaking the carbs in Petrol & other solvents before I freed them off.
It was a slow process as there was nowhere I could safely lever against to free them off.
It's anecdotal experience not anything I read. Looking at my post it reads as though it's down to one adjuster - bad phrasing - I meant the slider ones seem more critical than the external ones imho.
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Were all the little black rods fitted Bill, they slide inside the springs and are cupped on the ends to match the ball on the lifter arm. If those are missing the spring pressure would be reduced and allow it to remain raised.
There should be 3 in each lifter arm fitting.
https://images.cmsnl.com/img/partslists/honda-cb400f-england-engine-group-1j-1k-2j-2k_bigma000080e01-4_c702.gif
You can see them in number 96 grouping.
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Yep they're all there but one T cup bit in lower end of riser ( one on which brass cap fits) doesn't want to come out and didn't during strip down .
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Could be that's the problem, could be a spring under that which has rusted away and not forcing the T cup up enough for it to close the throttle riser.
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Yep they're all there but one T cup bit in lower end of riser ( one on which brass cap fits) doesn't want to come out and didn't during strip down .
I do not see that as a problem if its the unsprung static cup.
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With you on that Ted , also no spring below it.
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Did you number the sliders & put them back in their original carb body.
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No worries Ted on that score, been there before, isn't that what old takeaway dishes are for ? 😉🤣
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No worries Ted on that score, been there before, isn't that what old takeaway dishes are for ? 😉🤣
Yes indeed - so have you sorted it ?
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Not as yet. Got to take my dear lady into hospital for major surgery, so been a bit preoccupied. I'll let you know how it goes , the bike, that is, when I get time . 👍
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Sorry to return to this but have tried everything suggested to no avail. Watched videos suggested, did Bryan's revised bench sync . Air screw on carbs 1 and half turns out but still same problem.
Any more ideas, close to scrapping b****y thing. Even rechecked float heights again as per Nurse Julie method and all OK.
Someone suggested balancing carbs but as won't tickover seems to be bit early for that ?
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If the throttles are snapping fully closed, which is very easy to prove, I’d wager somebody else’s pension it’s a pilot jet/pilot jet route partial blockage.
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Im the last person to dispense carb advice as its all witchcraft to me, BUT my 500 would not run correctly until everything was on, and nice and tight.
Including the air filter and lid and the proper fuel tank, it did not like my aux tank.
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Bill, I'm down in Crowborough from Wed 23rd November for 5 days. If you haven't made any progress, I don't mind coming over and collecting the carbs, bringing them back to Lincs to check them out for you. But, by what you have checked already, I would really only be going over everything again.
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Just a thought Bill, did you fit the carb to manifold stubs in the correct orientation? If yours are OEM, if they are fitted correctly, they should read 1,2,3,4 from left to right whilst sitting on bike. The 2 middle ones, 2 & 3 are angled differently than 1 & 4, if not fitted correctly, air may be getting in.
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If the throttles are snapping fully closed, which is very easy to prove, I’d not somebody else’s pension it’s a pilot jet/pilot jet route partial blockage.
I'm taking them off ...again so I'll have a check but all were cleaned before reassembly but you never know 👍
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Just a thought Bill, did you fit the carb to manifold stubs in the correct orientation? If yours are OEM, if they are fitted correctly, they should read 1,2,3,4 from left to right whilst sitting on bike. The 2 middle ones, 2 & 3 are angled differently than 1 & 4, if not fitted correctly, air may be getting in.
I do remember checking that as they have a number embossed on them I recall. Have tried spraying them when running with carb cleaner and no pick up in revs. Thanks for the offer Julie, I'll persist in the meantime but if without success, may well take you up on your offer. 👍
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I've just finished rebuilding a spare set of carbs on the bench, here's my thoughts based on what I found whilst setting them up "static".
If you don't screw all the linkage balancing adjusters in far enough, the throttle slides can be held ever so slightly open. Also, the butterfly stop bolt can be set wrong and prevent the carbs closing off fully - with the throttle fully closed there should be a gap between the butterfly and the eccentric stop pin.
Having said that, revs hanging up on closing the throttle used to be a classic symptom of an inlet air leak somewhere.... but if you're convinced there are no leaks, I'd try screwing the balance adjusters all in by the same amount, say two complete turns? You may have to readjust the fully-open throttle stop afterwards, to achieve full throttle, without the slides rising up beyond the carb bores. Hope this is of some help.....
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Bill, I'm currently rebuilding a spare set of carbs and I'm reading this with interest (sorry I can help yet!) and I will be interested to see what the outcome is.
Matt
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Get them built Matt and lend them to him?
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Get them built Matt and lend them to him?
Ha! I have to admit that I could have chosen from 2 sets of spare carbs to rebuild and I chose the wrong set! Parts missing ,damaged or just wrong - still I'm almost there but I have to admit they are quite complicated compared to other carbs I have restored!
Matt
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Hey Scottish nadger. When you cleaned the carbs did you remove the air screws and float bowls? I’m sure you know, but it pays dividends to understand the three orifices in the pilot jet pathway. Eg carb inlet, air screw and drilling in the main Venturi on the engine side of the slide. By judicious use of your fingers it’s possible to block of the routes in sequence and thus force carb cleaner and high pressure air through the pathways. Have you tried that with the carbs off the bike?
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Er badger, not nadger🤔
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Going back to Bill's problem of the bike refusing to return to idle, I think I've read all replies to your original post (hope I didn't miss any!). I hope you will forgive me if I'm stating the 'bleedin' obvious' but is the FB spring in the middle of the bank between 2&3 present, correctly attached and not badly stretched?
Ian
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Good shout Ian.SB says the slides snap shut (closed). Worth checking again I suppose?
Are you back home from your jaunt? If so I’ll post the gods on Thursday.
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Not back just yet, was supposed to be on the boat tomorrow evening but due to adverse weather it's been re-scheduled for 13.15 - no chance of making that from Aberdeenshire, so have moved it to Wednesday. One of the joys of living on an Island! PM me with the total cost with P&P and I'll fire some brass to you. Hope Bill gets sorted.
Ian
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Going back to Bill's problem of the bike refusing to return to idle, I think I've read all replies to your original post (hope I didn't miss any!). I hope you will forgive me if I'm stating the 'bleedin' obvious' but is the FB spring in the middle of the bank between 2&3 present, correctly attached and not badly stretched?
Ian
Return spring between 2 and 3 carbs is in place and snaps back really fiercely, when operating by hand have to mind your fingers!
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That's good Bill,
It was just a 'clutching at straws' thought. I've recently done 2 sets (one 350/4 and one 400/4) right down to completely bare carb bodies without problems, so have been racking my (admittedly rather old) brains to figure what might be wrong with yours.
Ian
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Going to go for full strip down, re clean and reassemble. In meantime I'll recheck tappets and timing in case it's slipped but shouldn't be problem 😉
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Did you replace the o-rings in the manifolds Bill?
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Sesman, yes, fully stripped for ultrasonic cleaning and all ports blasted through with compressed air afterwards.
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Did you replace the o-rings in the manifolds Bill?
All new o rings everywhere in carb including manifold. 🤔 you can see why I'm confused , seem to have done everything right, obviously not but as to what it's a mystery!
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Sesman, yes, fully stripped for ultrasonic cleaning and all ports blasted through with compressed air afterwards.
Not sure if this is relevant but:-
When it does not return to idle revs does unscrewing the knurled main throttle screw adjuster reduce the idle to normal now or is it still as it was at the start of your post?
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Any chance of a small crack in the rubber insulator?
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Sesman, yes, fully stripped for ultrasonic cleaning and all ports blasted through with compressed air afterwards.
Hi Bill. That might not do it. The pilot jet pathways are threefold and blasting air down the drillings without blocking of the other two holes will allow the air to,take the path of least resistance. I had this problem with my 550 F2 and had to deliberately force air down each passageway. I found the smallest drilling entering the carb Venturi just after the slide was the problem
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Would a seized up advancer unit cause this issue?
I was just looking online about cleaning and greasing them up. One article said it can cause hanging idles.
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Good thought Steve, googled the video and maybe might be problem. I'll try that as well , once I've reassembled carbs. Cheers for tip.
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So carbs ultra sonic cleaned and all jet holes clear and reassembly about to begin along with new o rings etc.
A question has been put to me by a friend that after bench syncing I'd still need to balance carbs, the impression I gleaned from BryanJ etc al was that a good bench sync should be near enough. Is my failure to do carb syncing after causing my problem of not returning to idle?
Haven't got that far yet but maybe why.
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So carbs ultra sonic cleaned and all jet holes clear and reassembly about to begin along with new o rings etc.
A question has been put to me by a friend that after bench syncing I'd still need to balance carbs, the impression I gleaned from BryanJ etc al was that a good bench sync should be near enough. Is my failure to do carb syncing after causing my problem of not returning to idle?
Haven't got that far yet but maybe why.
No Bill, if you have bench synced them and all the slides close when the idle screw is backed off, that is always close enough to get the bike running very well. We rarely even have to vac sync carbs after rebuild and bench sync.
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The cause of the problem, No.
I always vac sync carbs after a rebuild, a bench sync is fine for getting the bike running but a vac sync is the difference between "This is how they should work and this is how they do work".
If you haven't got a set of gauges then that's ok, just trust in your work, if you have got a set or access to a set what harm can it do, it's reassurance if nothing else. If you put the gauges on and you don't need to touch the carbs then it's a nice feeling that you've done a good job in the first place.
Every multi cylinder bike I ever serviced always had the gauges thrown on just to check everything was working as it should, even bikes coming in for their first 500 mile service were vac gauged, it was surprising how many needed altering to get them balanced as they should be.
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Cheers Julie and Oddjob, that's put that idea to bed finally. .
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The big thing is vac sync is the LAST thing to do in the service, customers would get upset when refused to "just sync" the cards without checking tappets, point gap, timing and cam chain
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I had that at a bike shop I was service manager at in Farnborough, folk would just come in for a sync and baulk when we said we would only do it all not just the sync.
We mainly did new stuff but quite a few mid 70's Honda's and Suzies used us but some were a bit put out. It's not like we didn't explain, they knew best. There was realistically minimal risk to them but for them to moan when just a sync was done that it was still ropey put stress on my workshop time and productivity as we'd inevitablby have to put it right FOC after they kicked up to the GM. The risk was always ours.
Perhaps they didnt like young upstarts (38 at the time!) explaining an engine to them they'd owned for 25 years and how one process can effect the other in the service etc. On the other hand, we had some super clients that just came in, handed the keys over and said, " work your magic on that, she's just a bit under the weather and needs a tickle". They knew the bill woud be the wrong side of £100, but knew that their bike woud be cock on when it left.
We liked those customers ;) :D
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Hopefully this is the closing post on this episode. Splashed out on a new advance/ retard unit and new throttle cables. And when fired up and revved returns to 1200rpm.
Whether or not it was the cables, advance retard, points, (renewed them too), bench sync or thorough carb cleaning I don't know and to be honest I don't care.
Just needs a minor timing set up but otherwise we're good at long last. 👍😉
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Hopefully this is the closing post on this episode. Splashed out on a new advance/ retard unit and new throttle cables. And when fired up and revved returns to 1200rpm.
Whether or not it was the cables, advance retard, points, (renewed them too), bench sync or thorough carb cleaning I don't know and to be honest I don't care.
Just needs a minor timing set up but otherwise we're good at long last. 👍😉
Well done Bill, at least it gave you something to do 🤣🤣🤣🤣
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Congratulations, Bill. At least you get to enjoy it now.👏🤞
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Get in Bill, well done mate bloody enjoy it mate ;) :) 8)
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At last! Just in time for spring!!
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Pleased to read it's now sorted - always annoying when you are not sure what was the cause - might have been a bit of everything.