Off-throttle hanging revs

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Off-throttle hanging revs

Post by Cocker Cox » Fri Jul 31, 2020 8:11 pm

Hi, All,

I’m looking for suggestions as to why my B25SS takes a couple of seconds to fall back to tick-over when with a warm engine the throttle is blipped.

There is no air leak at the inlet nor in the exhaust, and the bike ticks over strongly when warm. So, I’m wondering whether an incorrect fuel height in the carb. bowl might be the cause? Alternatively, might it be the auto-advance not closing quickly as the revs drop? Or is there anything else might cause it? Thanks in advance....

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Re: Off-throttle hanging revs

Post by kommando » Fri Jul 31, 2020 8:26 pm

Auto advance wears and then jams advanced which keeps revs up until it frees.

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Re: Off-throttle hanging revs

Post by Cocker Cox » Fri Jul 31, 2020 10:59 pm

The auto-advance was seized solid when I first checked the ignition timing. I freed it, but maybe it’s still not operating correctly. I just wondered if that might give the symptoms I describe....

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Re: Off-throttle hanging revs

Post by SteveS » Sat Aug 01, 2020 8:06 am

.
If you mark the points plate before removal so you can put it back in the same position, hopefully you will then be able to lubricate the auto advance in-situ, saving you re-setting the timing. I've had success with WD40 using the spray tube they supply with the can so you can direct it to the right spot and then working the AA back and forth to work the oil in. Also used a cotton bud with some copper slip in the past but it took longer to work its way in. Whatever you use make sure you use it sparingly
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Re: Off-throttle hanging revs

Post by Cocker Cox » Sat Aug 01, 2020 8:43 am

Cheers, Steve. I’m pretty sure now that the problem is with the auto-advance unit taking its time retarding as the revs drop. I’ve ordered new bob-weight springs and will lubricate cautiously as you advise....

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Re: Off-throttle hanging revs

Post by Momus » Sat Aug 01, 2020 12:19 pm

Try a stiffer carby return spring and see what happens brother <205
If you love it, lube it.

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Re: Off-throttle hanging revs

Post by Cocker Cox » Sat Aug 01, 2020 12:40 pm

No, it’s definitely not the carb slide sticking. I always make sure on all my bikes that the throttle twist-grip snaps back when released. New cable, good routing, clean, well-lubricated slide....

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Re: Off-throttle hanging revs

Post by Momus » Sat Aug 01, 2020 2:28 pm

Cocker Cox wrote:
Sat Aug 01, 2020 12:40 pm
No, it’s definitely not the carb slide sticking. I always make sure on all my bikes that the throttle twist-grip snaps back when released. New cable, good routing, clean, well-lubricated slide....
You lube your slide Cocker? With KY? :laugh That's a newy.

Sometimes, and with all due care, the last bit of slide travel is slightly compromised by the idle adjustment screw and a stiffer spring fixes it.
If you love it, lube it.

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Re: Off-throttle hanging revs

Post by Jeff K » Sat Aug 01, 2020 3:58 pm

Be aware that they had at least three different AA springs, Strong, med and soft. I used to have a few boxes of them and sometimes it was a combination that worked best. One strong, one medium etc.
Jeff

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Re: Off-throttle hanging revs

Post by Cocker Cox » Sat Aug 01, 2020 6:35 pm

Thanks, Jeff. No idea what the ones I’ve ordered are... but the description did mention B25s! It might not prove to be the answer but at least it’s another possibility crossed off the list. Not sure why a sticking auto-advance would only be apparent with a hot engine though....

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Re: Off-throttle hanging revs

Post by Jeff K » Sun Aug 02, 2020 10:12 pm

Check that the little oil felt on the points that lubes the cam is not too tight and causing it to drag. It should be just touching enough to let the oil get on the AA cam. Then take a little screw driver and move the AA to full advance. Then let it snap back, it should snap right back, If it does not, you found your problem. Try this again when the motor is hot to be sure that it is still working. You can fit the screw driver to the little notch that is under the AA mounting bolt. I have seen many where the springs were loose and could not snap the AA back. You can bends the spring tabs to adjust them on the AA unit.
Jeff

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Re: Off-throttle hanging revs

Post by eebtr7 » Sun Aug 02, 2020 10:46 pm

YES! What Jeff just said! And...if you do decide to tinker with the spring tension on the advance unit, do not get them too tight, or else the advance won't advance leaving you with a top speed of about 48 mph. I did that back in 1979. Then after a whole bunch of readjusting the tension prongs back and forth, they finally got a bad case of metal fatigue and fell off.

You tadpoles out there might just benefit from the battles we old toads have fought over the past half century with these wonderful unit singles.

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Re: Off-throttle hanging revs

Post by Jeff K » Mon Aug 03, 2020 12:48 am

If you have to bend the tabs, use a pair of needle nose pliers and just bend them enough to remove any slop in the spring, do not use them 'pre tension" the spring until you have tried all of the different springs and combinations 1st!

Fewer coils and thicker wire = Strong spring, more coils and thinner wire = weaker spring.

From some of my old notes---

Lucas AA Springs
54415638 67-70 singles
54415640 65-66 models with side points
54415642 triple cylinders 69 and BSA 650
54415641 ??
54417992 Twins including Norton? -- Strong springs. Also used on 69-74 BSA/Triumph singles
54412229 73-74 Norton twins * Norton was having trouble with the AA sticking and in 73 started using the 54425656 AA unit


VW
Some from the old air cooled beetles fit.

Twins need stronger springs due to double the tension on them, 2 points sets.

NOTE, your bike should have the stronger LUCAS 54417992 springs.

Be very careful of the AA units they interchange but are not the same! They can be 5, 10, 12 or 15 degrees advance, actual advance is times this by two. ET units like to use the 5 degree to stay with in the maximum field strength of the moving magnets. A 15 degree used in a system with only 32 at full advance means that you are only playing with 2 degrees at idle to adjust to. Not bad on a side point model, but a nightmare with an older distributor model. All the slop "extra" in the drive gears can eat up that 2 degrees fast.
And be aware that Norton AA units spin the opposite then BSA or Triumph unit. That mistake can put you in the hospital.
Also be aware that there are now many aftermarket parts out there of questionable quality, and this includes AA spring.

You could also hook up a timing light and see what is going on when you back off the throttle. This will clear it up right now. A timing light and tach will pin point what your AA is doing.
I must be getting old, I still buy timing lights at garage sales and actually know what the are. I had a kid at a estate sale ask me once "what is that? A flashlight" . I told him that it was a "death ray gun". If used improperly it will KILL your motor!
Jeff

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Re: Off-throttle hanging revs

Post by Cocker Cox » Mon Aug 03, 2020 7:02 am

Fantastic advice... and stories! I spent all day yesterday, firstly on the auto-advance. It snaps back with no sticking at all, and I couldn’t get it to ‘hold off’ from full retardation no matter how gently I lowered the bob-weights and rested the cam manually. I also carefully lubricated the mechanism anyway with silicon spray lubricant, under the bob-weights and around the pins; also the felt washer and a single drop of engine oil in the cam notch to lubricate the cam. I strobed the timing and checked that it fell to full retardation when the throttle was released. All good. So, I turned my attention to the carb.. I blew carb cleaner down every orifice to check my previous deep clean of it... all clear: carb. cleaner blowing through the float bowl passageway, through the pilot jet bush and out through the primary and secondary ports and pilot air intake. Cleaner squirted down the front pilot airway exited out through both the ports and the float bowl passageway. Float height bench-checked... petrol 6mm below float bowl lip as recommended. Float bowl lip perfectly flat (done when I rebuilt the carb. first time). But... here’s the thing... the needle was in the middle notch. It was in this position when I first got the bike and I put it back there when I rebuilt the carb.. But the manual gives the first (top) groove as the standard position. So I put it back there and initially it seemed that I’d found the problem. However after a few short runs to fully warm the engine, the bike wouldn't tick-over... it was all over the place. I’m now suspecting a worn carb.. Is there a way of physically checking how worn the slide is? I don’t have enough experience myself to know. The bike itself has only done a genuine 8000 miles according to the PO and circumstantial evidence (standard bore, original case fixings, OEM primary and drive chains, tyres and Champion N3 plug), but who’s to say it hasn’t been swapped?

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Re: Off-throttle hanging revs

Post by mlb50 » Mon Aug 03, 2020 8:02 am

Is the needle bent? I had this "hanging high idle" on a Trident and it drove me nuts until I found the culprit. Slide goes down, needle stays up a wee bit and totally messes with the mixture.
B50 @ 10:1 - what's a leg between friends?

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Re: Off-throttle hanging revs

Post by Cocker Cox » Mon Aug 03, 2020 8:51 am

Good thinking! Actually, the needle has three identification rings at the very top (above the three position grooves) which my research indicates a 2-stroke needle. Could it be the wrong needle?

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Re: Off-throttle hanging revs

Post by Cocker Cox » Mon Aug 03, 2020 11:21 am

To further my question, does my B25SS have the wrong needle fitted... the answer is yes! It’s a two-stroke needle and too long. So, to recount the problem and report my my progress so far:

I’m struggling to get my B25SS ticking over. Initially it did tick-over but the revs took a few seconds to fall to tick-over when releasing the throttle, resulting in much grating of gears. I’ve checked and sorted absolutely everything (timing, auto-advance sticking, air leaks etc) all to no avail. Then I noticed the needle was on the second groove not the first (top groove). I put it where it should be and the result was even worse... no tick-over, poor starting and throttle response. So I checked the needle again against specifications: it has three engraved rings above the position grooves, which makes it a 2-stroke needle; it is also too long (which may be why a PO put it on the middle groove to compensate!). I only have 1-ring needles which are the same length but for the 600-series Amal carbs. I wonder if anyone knows the difference and whether I may have found the problem? Thanks as always for any help....

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Re: Off-throttle hanging revs

Post by Jeff K » Mon Aug 03, 2020 3:57 pm

http://amalcarb.co.uk/contacts
I would email or try giving them a call. I am not sure what the differences are between the 2 cycle and 4 cycle needles. But they are different. Problem solving is a process of elimination, you are getting closer. I would replace that needle with the correct one, then you could at least blame it or clear it of fault.
Have you removed the slide, cleaned it and then using a black Marker pen, colored the whole outside. The re-installed it and run it up and down many times, removed it and checked the wear pattern yet?
How much slop in the cable? You need a little bit, but not too much. I have seen were there was just enough where the outer cable could snap back and catch on the fitting, causing a high idles and then it would pop back into the fitting and all would be good.
Jeff

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Re: Off-throttle hanging revs

Post by Cocker Cox » Mon Aug 03, 2020 7:03 pm

Hi, Jeff,

Thanks for all your suggestions. Fortunately CCM Britain is just a few miles away, so I got the proper needle and 0.106 jet from them. Mark also looked at the slide and confirmed that it had seen better days, having clearly been used in a dusty environment (which makes sense as it came from Canada with bleached paintwork. However, it made sense to fit the proper jets and try it (the main jet was a 200 and the thread snapped as I unscrewed it; it should have been a 190 anyway, but the nearest I had was a 180, which is the Starfire’s main jet size. And as my SS has a standard Starfire piston, it made sense to use it instead of a 190).

The difference, not withstanding the worn slide, was immediate and the hanging revs are no more. Having said that, it still doesn't fall to tick-over as quickly as I’d like but quickly enough to avoid graunching the gears. It may be a matter of adjustment but I fear a new Amal Premier will be required before the issue is completely resolved. The idle screw is at 3/4 of a turn currently, although, having turned the screw in and out to find both rich and lean ‘falter points’, it could be that I’ve set it at the rich end of the adjustment. It’s funny, I went to bed last night lower than a sausage dog’s belly. Not only was the carb. issue a worry (I’d happily invest in a new carb. but was still uncertain about the reason for the problem), but a dribble of petrol down my newly-painted tank (with supposedly petrol-resistant clear-coat) lifted the lacquer. Today, everything seems brighter... I’m now sure that the tick-over issue is carb. related, and have approached a local car spray firm who will put a proper two-pack top-coat over my tank once I restore it again. This will inevitably involve rubbing it back to the silver base-coat and re-applying both the silver and the Flamboyant Red top-coat, re-applying the BSA tranfers and the white pin-stripe. So, perhaps another £100 that I haven’t got. Add to that £150 for a Premier Amal and I’m looking at the thick-end of £250. Altogether I’ve now spent over £4000 on a bike that I haven’t even restored, just renovated! But do I care? Not when I’m blatting down the road, showing the citizens of my part of the world what a sorted British bike sounds and goes like. The induction roar audible when I change gear is fantastic!

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Re: Off-throttle hanging revs

Post by beat » Mon Aug 03, 2020 8:36 pm

Cocker Cox wrote:
Mon Aug 03, 2020 7:03 pm
do I care? Not when I’m blatting down the road, showing the citizens of my part of the world what a sorted British bike sounds and goes like.
this is what really counts :!: :!:
:thumb :thumb

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Re: Off-throttle hanging revs

Post by Cocker Cox » Mon Aug 03, 2020 9:25 pm

When I think of the tens of £1000s I’ve lost on depreciation with cars and modern bikes, what does being a few hundred quid out of pocket matter?!

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Re: Off-throttle hanging revs

Post by eebtr7 » Mon Aug 03, 2020 10:50 pm

Can we get a BIG AMEN from the congregation? Here's mine...AAAAAAAAMEN!
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Re: Off-throttle hanging revs

Post by Jeff K » Mon Aug 03, 2020 11:05 pm

Be sure that when they paint your gas tank that they DO NOT paint the upper part where the gas cap/ gasket makes contact. This area needs to be bare! if it is painted, the gas will creep under the paint and work it's way down and ruin a good paint job! Any one who has painted a motorcycle gas tank in the past will know this, but a painter who has not done motorcycles will not.
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Re: Off-throttle hanging revs

Post by Cocker Cox » Tue Aug 04, 2020 7:18 am

Funnily enough, that’s exactly what I did! But fortunately the cork washer stuck to the top, giving me an early warning, so cleaned off the lip with thinners. It did also warn me that the clear-coat wasn’t petrol-proof, but by then the die was cast. I’ve been contacted by an auto-shop who will do the job but say they need it soon after I put the final candy coat on. But therein lies the problem as I need to put pin-striping and transfers on before letting them have it. I can’t see why they can’t give it a final light flatting before applying the clear coat, but am arranging to take the bike down and discuss. There has to be a solution. They are a crash repair shop so putting a clear coat over old paint can’t be new to them....

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Re: Off-throttle hanging revs

Post by JerryT » Tue Aug 04, 2020 4:59 pm

Where are you taking it for the paint?
I need my tank, side panels and mudguards painting in Flamboyant Red.
Would work out cheaper if my painting was bundled with yours.
I live in Dod'oth.
PM me if interested.

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Re: Off-throttle hanging revs

Post by Cocker Cox » Tue Aug 04, 2020 5:47 pm

Blimey, that’s close! I need to see the guy first but will report back. I used to have my paintwork done by a one-man-band in Wetherby. He was expensive but brilliant. I’ll contact him as well and let you know....
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