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There is a port smoothing goo out there, normal epoxies get dissolved by fuel, I have some of the special stuff, had to import it from the states.
I will dig it out and post a link later. its a 2 part thing, applies easily and sands easily, turns black with the fuel eventually but crucially doesnt dissolve.
This is a more involved solution but may work a lot better, primitive tuners/ port attackers often remove too much material particularly where the port turns down at the approach to the lowest part of the valve,this should be a large radius which has no sharp turn at the valve seat, if its been removed/ attacked , you will see big improvements in flow and carburettion if it is rebuilt.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
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The stuff you want for porting is " Kneadatite A/B Epoxy putty." from PSI Polymeric Sytems , inc.
The data sheet has an EU contact.
Whitford Plastics Ltd
10, Christelton Court
Manor park
Runcorn
Cheshire
WA7 1ST
tel, (44) (1928) 571000
email, [email protected]
website: whitfordww.com

i used this to reshape the butchered ports in my A65, its surprisingly easy to use , make sure the ports are fully degreased with an aggresive solvent before applying. most /all of it went into filling the port floor and rebuilding the bottom turn to the valves. Obvs, the head and valves will need to be removed for this work, . Allow 24 hours to cure then sand / file to shape.
[Linked Image from i.postimg.cc]

Last edited by gavin eisler; 04/17/21 4:43 pm.

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Wow. Seems there is a product for everything out there. Thanks for that. I will email or call on Monday to find out where suppliers are should I need some.

I've just had 10 minutes playing with the colourtune kit.

Tickover is good, nice and blue.

All rpm above cough and stall are blue or orange depending on throttle position. Settles on blue when the rpm is steady, whatever the rpm is.

During the cough and stall area, which I now know is probably between 1/16 and 1/8 throttle it is very yellow. As I very gradually apply the throttle from tickover, there is initially a very bright yellow, and if I then hold the throttle it steadies to a not quite so bright yellow, but definitely yellow all the same. I did try winding the mixture screw out, and it did make a slight difference, but after 3.5 turns (one turn out from standard) it didn't seem to make any difference.

If I blip the throttle there are two scenarios. 1) she coughs and the colourtune goes yellow then instantly black and she dies. 2) she coughs, there is a huge yellow flash but this time she survives and after that split second the revs build and blue running is resumed.

So this may have proved quite quickly that I'm not looking at too weak, I'm probably looking at too rich.

A couple of days back I started suspecting this, so I ordered a number 4.5 slide and a number 20 pilot. Hopefully they will be here early next week for further testing.

I remember further back in this thread I said things seemed slightly better when I screwed the mixture screw in, but I'm now wondering if I did this before sufficiently warming the engine. In other words, it was happy with a bit more fuel when cold.

Progress perhaps?

Last edited by Douglas Clark; 04/17/21 9:32 pm. Reason: Spelling.
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Originally Posted by gunner
. It wasn't unusual for BSA to miss stamp some of the timing wheels which means your timing may out one tooth advanced or retarded. This is mentioned in the rupert ratio unit singles manual so could be a possibility.


A lot of these parts got thrown back into a different parts bin during its time on the assembly line then 50-60 years later get sold on eBay as NOS.


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it is many summers since I last used colourtune, and then on a car, so I must admit I watched a Youtube vid, and it confirmed my memory.
The "huge yellow flash" is to be expected, or even desired, as the mixture is momentarily rich as the throttle opens, it needs to be.
What I find interesting (from what you wrote) is that when it isn't "huge" the motor dies on transition between pilot and slide.
What is also interesting is that this doesn't happen every time.

Now this might be barking up the wrong tree in entirely the wrong forest but ...... all machines are made by human hands, there isn't a bit of swarf rattling around under the pilot jet is there?? sometimes restricting sometimes not ?

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Hi Dave.
To be perfectly frank I've not studied the pilot jet in much detail, so I've no idea if there is something in there restricting flow. I assume though it would cause a week mixture if there was a restriction, and I'm inclined to think now that it is over richness causing the issue.

Just to repeat something I said earlier:
"As I very gradually apply the throttle from tickover, there is initially a very bright yellow, and if I then hold the throttle it steadies to a not quite so bright yellow, but definitely yellow all the same."
I believe under normal circumstances when rolling the throttle on very gradually, I shouldn't be getting that bright yellow followed by a steady yellow when the throttle is being held still. I think what you are describing is a more normal throttle opening speed where you would indeed expect an initial richening, but my concern is that it remains yellow on a steady throttle at that particular point, but nowhere else in the rev range.

Also, it has always been hit or miss as to whether she coughs and stalls or coughs and recovers, even with the old carb. I think some of it depends on the speed the throttle is opened. The faster (and wider) it is opened the more likely it will stall.

I will however take a close look at the pilot jet in case there is something going on in there. I'm not intending to try much else before trying the new weaker slide and/or the weaker pilot jet. Hopefully both will arrive within a couple of days.

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An update.

Dave: no swarf visible in or around the pilot.

I have now tried a number 5 slide and a 20 pilot, both weaker than standard. Despite my confidence, I appear to be totally wrong. It was noticeably worse using these two items. I tried them together and individually. With the smaller pilot it was harder to start, and with the slide I was getting popping or backfire from the exhaust on the over run. And plenty of cough and stall.

So I went back to standard pilot (25) and the 3.5 slide which is richer than standard number 4. This time, I started with the mixture screw just 1 turn out. With this richer slide and mixture setting there is no detectable cough and stall, but, the idle is all over the place. I gradually weakened the mixture adjusting for tickover as I went along, and found a reasonably steady (far from perfect) tickover at 2 turns out, but at that point the cough and stall had returned.

So all those that said cough and stall was from being too weak do appear to be right. So maybe a 30 pilot, or number 3 slide? Maybe a better air filter? I'm sure mine does nothing to restrict air flow like a normal filter would. I'm at a bit of a loss!

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There's a bit of info on the Trials Central website Here (third post down), where someone mentions they have all but cured the cough and stall on their C15 trials bike.

Apparently the fix involved adding 2 thick tufnol spacers on the manifold and also using a 35 pilot jet. The poster mentions the airway behind the pilot/air screw has been drilled out in order to allow a bigger pilot but doesn't know how it was done.

Don't know if this will fix your problem but I thought it was worth sharing.

Last edited by gunner; 04/24/21 5:51 pm.

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Originally Posted by Douglas Clark
So I went back to standard pilot (25) and the 3.5 slide which is richer than standard number 4. This time, I started with the mixture screw just 1 turn out. With this richer slide and mixture setting there is no detectable cough and stall, but, the idle is all over the place. I gradually weakened the mixture adjusting for tickover as I went along, and found a reasonably steady (far from perfect) tickover at 2 turns out, but at that point the cough and stall had returned.

Pardon me if you're already answered this but are you testing and adjusting with the engine at normal operating temps? Most engines like a richer mixture when cold but this should improve as the temps come up. I'm assuming that this behavior continues to occur even at operating temps but correct me if that is incorrect.

One simple test for me would be to take the air cleaner off and, using your left hand, place the tip of your finger in the airstream, blocking part of the cutaway. With your right hand, give it throttle and see if there is any improvement. This will mimic a different slide cutaway and help you narrow down whether a different slide would help.

If it does, doubly ensure that there isn't an air leak at the mounting surface before changing anything. You want to be certain that you're not leaning out the mixture elsewhere. If it all checks out, start with a richer pilot jet and that's likely cheaper than another slide.

I hope that helps.

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Thanks for that Gunner.

I don't know how he got 40mm worth of spacers in. Couldn't do that with mine, not enough room! I'm guessing as it's a rltrials forum his bodywork is gone. What would the spacers do? An area I have zero knowledge of.

I was also interested in the guy further down that said the conical filter he bought made his run too weak. If that's the case, my virtually straight through air filter won't be helping. I think I need to get this area sorted before playing around with jets and slides any more. I'll look into getting a decent filter.

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Hi Marc.

I turned the air screw in to 1 turn out before starting the bike, but I then fully warmed her up before trying to make further adjustment. I've learned the hard way that warming up is essential.

I tried blocking part of the air flow before, but I think I was not being careful enough to not overdo it as the engine would cut out. I will try it again being a bit more careful. I think I was blocking too much.

The mounting surface (to the barrel) is the one area I'm very confident I've got sealed. No amount of squrting carb cleaner in that area affects the running. Although sometimes it can be hard to tell when you have a tickover that's up and down like a yo-yo.

As I mentioned earlier, I think my air filter is doing very little and probably letting too much air through. My friend has a screw on type of filter. I might see if that will squeeze in the gap to see what difference that makes. That's assuming the thread size is correct.

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Regarding the air filter, I would avoid fitting a foam one as pictured in the link I posted earlier.

I once used a similar looking filter on my B44 and one day when restarting the engine, it kicked back and spat back through the carb. To my horror I saw flames appear and the filter was on fire. Luckily with gloved hands I was frantically able to extinguish the flames before the whole bike went up.

After that experience I've never used foam filters and rely on the K&N style with metal gauze or original pancake type which I believe are designed not to catch on fire.


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Wow, that must have been a scary moment. Thanks for the heads up.

I was indeed looking for a similar foam filter, but luckily I found nothing that would fit in the minimal space between the carb and air filter/battery box, so I didn't get one.

Instead, I have decided to upgrade the original air filter. I have bought a section of foam manufactured and sold by "Ram-Air" filters. Ram-Air have been supplying filters for motorcycles and cars for many years, so I'm guessing this foam is both fuel and fire resistant. It is a rectangular section that I'm planning to cut down into a circle to fit the original air filter cage thingy.

Perhaps I should try and find out a bit more about the safety features of Ram-Air foam before proceeding?

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I use Ramair foam in my Commando as the OEM foam filter disintegrated, its oiled as the oil tank breather opens out above the filter and copes well.

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That's reassuring thanks Kommando.

I won't oil mine initially as it might restrict breathing too much. I can always add oil later!

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https://forum.retro-rides.org/thread/187887/friendly-warning-foam-filters

Maybe I shouldn't have read the above?

Starting to look at ways to avoid foam use.

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Prior to foam, surgical gauze and then paper was used as the filter material, just as inflammable. Then you have the use of carb cleaner as a starting fluid.

Quote
The quickest way to get it going is to spray a small amount of carb cleaner into the body... just a squit... and it will fire up off that and then pull in fuel thereafter. Not ideal but it's what I'm working with at the moment.

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I guess using starter fluid on a vehicle prone to carb backfiring was a tad risky!

I've since read about some fires caused by using oil soaked filters (spray oil) before the propellant and/or solvents in the oil had been allowed to dry out.

My filter foam doesn't arrive for a few days, so plenty of time to consider my options.

I've also ordered a 30 pilot jet, so I'll give that a whizz when it gets here to see what difference it makes.

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I think that if you are using the original air filter housing with foam as Kommando has done then the risk is minimal since the foam is enclosed.

The problem that I had was that I wasn't using a housing and the filter was simply a foam body with a mounting to bolt onto the carb, similar to the one in the link. I think the filter became quite flammable after a while as it probably soaked up oil from leaks and etc. and without a metal body there was nothing to help contain the flames.

So I think you would be OK using foam as long as it enclosed in the original housing.


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Several of the fires I've read about have been with filters directly connected to the carb and also not enclosed. A few of the riders were able to grab the filters with gloves hands and tear them off to save the bike.

What I have in mind is using the usual 2' rubber tube from carb to air box and placing the foam sheet inside the original filter housing. So maybe that'll be safe enough. I'll give it some more thought over the next few days.

Who'd have thought that someone that has been riding for 50 years with undoubtedly all sorts of unseen dangers, would now be weighing up the safety of something that is generally considered safe and normal?!!

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Just wait until you get a leaking carb and a kickback lights the petrol, does not matter what the air filter element is made from or even if one is fitted.

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Perhaps I’m barking up the wrong tree, but its unusual to want more intake resistance to air flow.

Such increased flow resistance will have little impact at low flow (ie low rpm/low throttle) but will have richening impact at higher rpm/high throttle.

As you’ve got the foam on its way, I guess you’re gonna have to try it to satisfy yourself. I hope it has the desired result, and I will be eating my thoughts!

As the engine runs well in all other respects, there aren’t many other things to look at.
The scoured inlet is the only one I can think of.
The choke cable entry has been sealed?

From what we’ve heard so far, I’m unsure whether “cough and stall” was a usual problem with C15’s or not. (I’ve not had one).

If it was a usual problem when newish, then perhaps it’s a design problem with the inlet port?

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"its unusual to want more intake resistance to air flow."

I suppose I'm working on the basis that the engine was originally set up with an air filter that did actually provide some resistance, whether required or not. It was just an unavoidable consequence of wanting to filter the incoming air. So all I'm trying to do is achieve something similar to the original set up. My current air filter might as well not be there. It's just metal gauze with a very thin and moth eaten piece of cloth that only covers a small area.

When I've had running issues in the past with other bikes, one of the questions that crops up regularly is regarding air leaks in the air intake. Well I couldn't have a much bigger leak than my current air filter!

"As you’ve got the foam on its way, I guess you’re gonna have to try it to satisfy yourself"
If nothing else it will provide some basic filtration. I've really no idea if it will go any way towards fixing my problems. As you said, only experimenting will tell me that for sure. I take your point that it might cause a greater effect at higher rpm and could be detrimental.

The choke cable inlet is sealed from new on my old carb and new one. I'm told the C15 never had a choke fitted.

I'm keeping the scoured inlet in mind if all else fails. I have some Kneadatite in my sights just in case.

"I’m unsure whether “cough and stall” was a usual problem with C15’s or not."
I've definitely heard comments in the past about "the dreaded cough and stall" and there is some talk about it in the trials scene where a lot of these bikes have ended up. As someone mentioned before in this thread, maybe the scouring was a previous owner's attempt at curing it?

I've got the foam on order and also a 30 pilot. I'll see which one arrives first and have a play with it.

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Originally Posted by gunner
I think that if you are using the original air filter housing with foam as Kommando has done then the risk is minimal since the foam is enclosed.

Eh?

If the filter can be soaked with fuel and can be exposed to oxygen then it will ignite, regardless of what it is encased with. After having knowing someone who’s rocket 3 set on fire in this same way I think that is proof enough.

The foam filters should be covered/impregnated with filter oil. This makes them work efficiently and are ideal for dusty environments. They work better also when impregnated with oil than when dry.

Paper filters work well but will eventually get wet by fuel or water and work less efficiently.

The K&N filters are good also, TB-100 is the one that fits in the old
Pancake filter housing, folk often over oil them and wonder why performance sucks, they are also quite the premium these days. Any modern cotton filter will work just as well in a typical ideal environment (ie not dusty)


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I just had a look at K&N TB-0100 and it's not the filter that would fit my machine. Does it perhaps go in the screw on pancake type filter?

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