Pod Filters ? or stick a hot poker in your eye ?

[TwoManyXS1Bs]

Pouring through that thread linked by 650Skull reminds me that I forgot to address your report of a stripped bowl screw, in the one blind/cramped area where there's little room between the end of the threads and the carb body.

One of my carbs has the exact same problem. I was able to grind and fit a tiny nut in there, and snug that corner of the bowl using a slightly longer screw. I plan to make a threaded insert for that at some future time.

If the bowl cannot be properly snugged-up, either from warped surfaces or missing screw(s), there's a chance that the center area won't seal, and fuel mixing/delivery will be contaminated by unwanted air/fuel seeping through the slit/gap.

It sure screwed-up my carb adjustments until I did that temporary screw fix, straightened the warpage, and used new bowl gasket...

 

[peanut]

Pouring through that thread linked by 650Skull reminds me that I forgot to address your report of a stripped bowl screw, in the one blind/cramped area where there's little room between the end of the threads and the carb body.

...

I'd completely forgotten about that thread myself Twomany. When I read through it I felt such an ass . It was such a long time ago that I'd forgotten everything in the thread

Shortly after that time I couldn't get the idle right no matter what I tried so I put the bike in the garage and there it stayed there rotting for over 18 months ...such a shame to see all the rust and oxidation now on a previously pristine bike.

I think this probably happens a lot more than we realise. I actually bought the bike off the PO because he hadn't been able to work out how to remove one of the needle race bearings ! many owners fall at the last hurdle.

Anyways back to the fuel bowls.
I also worked out that you could fit thin nuts on all the fuel bowl screws and intended to do that, however in the event I fitted some brand new allen head screws and the new screw threads were sufficient to compensate for the worn carb threads and enable me to tighten down the fuel bowls evenly .

I'm hoping that the Ramair polyurethane pods I ordered yesterday will arrive today but if not, the weather looks fine so I'll do some tests with the modified K&N pleated pods to see if uncovering the vent holes make any difference to the hanging idle problem.

I have no other air filters at present and I'm reluctant to run the engine on a test run without some sort of filter so I'll have to make do for the time being with the K&N's for test purposes.

 

[TwoManyXS1Bs]

Yeah, it HAS been a while. Glad that the new screws worked.

One other thought. While it's doing the high-idle thing, and the filters are off, see what happens if you place your fingertips over the various bell periphery ports (air bleeds and diaphragm). And, check that the bowl vents are unblocked and vented to the atmosphere...

 

[peanut]

Yeah, it HAS been a while. Glad that the new screws worked.

One other thought. While it's doing the high-idle thing, and the filters are off, see what happens if you place your fingertips over the various bell periphery ports (air bleeds and diaphragm). And, check that the bowl vents are unblocked and vented to the atmosphere...

Yes I will try that . I cannot unfortunately run my engine at the house because of the close proximity of neighbours which makes testing very challenging

I might try starting and running the bike without any filters this morning to see how that effects the hanging idle. I'm a bit concerned about spitback and the excess fuel lying in the filters after every ride and the fire risk

The odd thing is that the last time I refitted the carbs the idle behaved perfectly 1 staying at around 800rpm for the whole ride.? It has to be something very simple that I'm overlooking somewhere ...very frustrating.

 

[TwoManyXS1Bs]

...The odd thing is that the last time I refitted the carbs the idle behaved perfectly 1 staying at around 800rpm for the whole ride.? It has to be something very simple that I'm overlooking somewhere ...very frustrating.

Well, THAT'S a good sign. Something changed. Maybe from heat, vibration, sediment shift, gasoline exposure? Silicone sealer will melt in gasoline. Vacuum lines and caps can move. ...etc...

 

[Brian902]

Peanut,
I ran the Uni-Pods on both my Mikuni VM (round slide 34 mm) carbs and my 2008 CVK carbs. Same size fits both, sweet.

5Twins runs Uni-Pods on his 1978 38mm Mikuni original carbs.

All have worked well.

The CVK's make starting my bike much easier than the seperate VM34 with two choke levers. Owner reports 42 mpg, we are still tuning.

My son drove the bike before I sold it recently and never had an issue with wind or air flow that he noticed.

We don't ride in foul weather, but some simple covers would eliminate the most of that issue.

They are well worth a try and I suspect other problems that show up after installation will not be cause by Uni-pod. MHO

Good Luck

 

[peanut]

They are well worth a try and I suspect other problems that show up after installation will not be cause by Uni-pod. MHO

Good Luck

Hi Brian
you probably missed my post 22

I ordered up some Ramair pod filters two days ago when I started this thread because Uni pod filters are not sold in England .
Ramair filters are effectively the same as your Uni's

I am not the slightest bit concerned about air flow around the filters as I never ride my bike in anthing less than perfect calm dry weather. I simply related what I had read of other peoples experiences on other forums for general information and interest.

 

[peanut]

well I took a chance and made a couple of short runs with no filters fitted.

It started immediately and settled within 30 seconds to a low 800rpm idle .
Within 4-5 minutes of riding the idle had crept up to 2500rpm !
The internal lip of the K&N style pleated pod filters does not in itself cause a hanging idle.

So I'm back to where I started really.
The first time I started the engin 2x years ago the idle hung at 2500rpm and only considerable pressure on the throttle shaft lever would bring the idle down to 1000rpm or less. On releasing the throttle shaft lever the revs immediately climbed back up to 2500+

Although I've centred the butterfly valves 4-5 times now and synced the carbs I'm starting to think the hanging idle problem must in some way be due to the throttle shaft and butterfly discs.

With the carbs on the bench and both the throttle stops backed right out, the butterfly valves snap back to fully closed smartly. (I've even increased the throttle valve spring pressure on both carbs).
The throttle cable has even been removed from the carbs with no effect on the hanging idle.

I even thought that it could be heat that is causing one or both of the butterfly valves to stick at the nearly closed position but if that was the case why does the idle immediately shoot back up to 3000+rpm when pressure on the throttle shaft lever is released ??

Heres my last test run. Engine had been run for about 2-3 miles and immediately on startup you can see the revs rise to 2500rpm at idle . pressing hard on the throttle shaft lever lowers the revs to as low as 800rpm but they simply shoot straight back up again when the lever is released. Sounds like I need to adjust the camchain tensioner and valves too

 

[TwoManyXS1Bs]

Long ago, mine would try to do that, so I cooked-up a temporary band-aid that works for me.

If you suspect that there's some looseness of the fit of throttle shaft to throttle bore:

(Excerpted from that other thread)

"An effective band-aid can be done by recentering the throttle valve disc with the throttle shaft displaced toward the worn zone. Tricky, can be done, that's the way my wore-out BS38's are setup now. Also, setting the idle ignition timing at its most retarded position helps, as this forces you to nudge the idle stop a little higher, avoiding the disc/bore interference and eccentricity near full close."

I don't play golf because I drive with a really bad slice, what my grandfather called "A Boomerang Slice", because he swore he could see my golf ball actually head back toward us.

Really handy on right doglegs.

So, he taught me to drive with an "anticipated slice" stance, knowing that it would curve.

This recentering of the throttle disc is similar, positioning it in anticipation of the throttle shaft eventually displacing upward, toward the "worn" zone.

Then, again, maybe it's just weak advancer springs...

 

[peanut]

golf ! don't talk to me about golf.... my neck went further than I hit the ball resulting in a torn neck muscle which was excruitiatingly painfull for months.

Luckily I have the Boyer Bransden micro digital ignition system whch includes advance. I wouldn't have the patience to mess about with points and mech advance these days . However it did occur to me that the auto advance might be susceptable to engine heat but I immediately dismissed that as the black box couldn't get warm in just a few minutes.

I am also coming back to the butterfly disks.. I have centered them several times now ,paying particular attention to the seal around the disks and making sure that the disks close completely.
The last time it seemed to cure the hanging idle so I did a short video .
but the hanging idle is back again. Perhaps I am still doing something wrong ?

 

[TwoManyXS1Bs]

...I am also coming back to the butterfly disks.. I have centered them several times now ,paying particular attention to the seal around the disks and making sure that the disks close completely.
The last time it seemed to cure the hanging idle so I did a short video .
but the hanging idle is back again. Perhaps I am still doing something wrong ?

In the 'basic' sense, your butterfly work looks fine. The "snap them closed" centering method works well for most folks on here, really can't criticize it, but that's not the way I do it. And, I can't figure out yet how to explain it. Eventually.

While it's doing its high-idle thing, try cycling the enrichment system, looking/listening for any subtle signs of plunger leakage.

And, during your 'filters off' period, did you observe anything out of the ordinary when individually plugging the periphery vent holes?

 

[peanut]

regarding the peripheral air intake holes I forgot to test that yesterday.
i'd really like to know what they all do and where they go but I cannot seem to find a reference anywhere so far.

I installed a handlebar choke partially to allow me to fine tune the choke so I can move away from my neighbours houses smartly but also in order to allow some fine enrichment adjustment whilst I'm riding. Unfortunately one of the bracket broke the other day as I was tweaking its alignment so its out of action.

My next ride I'll test those suggestions along with a list of checks I'm compiling . I'm not going to be beaten by this . Its just making me all the more determined to solve it .
I could just go out and buy some VM34 but it would always nag away at me that I hadn't identified the cause of the hanging idle with my BS38's besides its a lifetime compulsion with me to understand how everything works

 

[TwoManyXS1Bs]

I completely understand the compulsion, similar disease here.

The top vent supplies atmospheric pressure to the bottom of the diaphragm. But, more importantly, that's also the air source for the enrichener valve. If that valve is leaking air into the manifold, sealing off that vent would confirm a non-fully-seated valve.

The smaller periphery ports are for the air bleeds, and, (I think for the bs34s), bowl vents.

Sealing off the idle/pilot air bleed vent should have a very pronounced affect on idle...

 

[peanut]

In the 'basic' sense, your butterfly work looks fine. The "snap them closed" centering method works well for most folks on here, really can't criticize it, but that's not the way I do it. And, I can't figure out yet how to explain it. Eventually.
?

The last time I removed the carbs and centered the butterfly disks I checked the operation minutely and noticed that when assembled the throttle shaft return springs have a tendancy to pull the butterfly disks axially to one side of the venturi (the throttle spring side)
On both my carbs there were some clear indications that the disks had worn the venturi walls around the throttle shaft bushes on one side of the venturi. However that said I shortened the springs by 5mm to compensate for the 35 years of weakening and I checked that both disks shut off the venturi completely using both light and air pressure.

There is simply no doubt about it those butterfly disks are in sync and shutting off the venturi perfectly on the bench

I'm convinced that the clue to this hanging idle is the fact that I can reduce the idle from 3500rpm to almost stalling speed by pressing down firmly on the throttle shaft lever ! yet it still maintains a 3500rpm idle with the throttle cable disconnected and both stops screwed out ?

 

[TwoManyXS1Bs]

During idle, there's about 10-15 lbs of force trying to suck the butterfly plate into the engine.
Think on that for awhile...

 

[peanut]

I completely understand the compulsion, similar disease here.

The top vent supplies atmospheric pressure to the bottom of the diaphragm. But, more importantly, that's also the air source for the enrichener valve. If that valve is leaking air into the manifold, sealing off that vent would confirm a non-fully-seated valve.

The smaller periphery ports are for the air bleeds, and, (I think for the bs34s), bowl vents.

Sealing off the idle/pilot air bleed vent should have a very pronounced affect on idle...

Ah I hadn't realised that the chokes have their own air intakes I assumed they only fed extra fuel to the venturi.

Both the choke assemblies have been removed last week and stripped, cleaned and checked . I couldn't obtain new gaskets so i used some Threebond after carefully flatting the choke housing flanges on some wetndry.

I know they cannot be leaking externally from the choke bodies and as I'm not using choke to start I'm prettyn sure that the choke valves cannot be unseating or hanging up.

This hanging idle is kinda like having one or both of the throttle slides hang up allowing the vacuum of the engine to pull fuel from the needle jets but even if that happened could enough fuel and air be drawn into the cylinders when both butterfly disks were closed in the idle position to increase the idle to 3500rpm ?

ha ha just seen your last post mmmmmm

 

[TwoManyXS1Bs]

...On both my carbs there were some clear indications that the disks had worn the venturi walls around the throttle shaft bushes on one side of the venturi...

One of the things I do when final fitting butterfly plates is to shove the throttle shaft back-and-forth, find the middle position, and lock-down there...

 

[peanut]

During idle, there's about 10-15 lbs of force trying to suck the butterfly plate into the engine.
Think on that for awhile...

Ok heres another thought then.

What if one of the valves were not seating properly ?............nah! then I'd surely see some popping backfiring and spitback and I never see any. just tinkin out loud without engaging brain

 

[TwoManyXS1Bs]

The enrichener valve connects 3 passages, the air inlet, the fuel inlet, the delivery port to the manifold. The bottom of the valve seals the fuel inlet, but the body walls seal the air inlet. Looseness there could leak air.

But, it's just something to check. The pushing on the throttle shaft is the big indicator...

 

[TwoManyXS1Bs]

One good sign of butterfly valves not closing properly, due to throttle shaft deflection, is slight rub marks seen near the transition (bypass) ports...