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By Wheaters
I changed mine yesterday (actually about ten years ago). But the water supply pipework to the bath (and other long piping runs, including gas lines) remains the same as it was twenty years ago. The principle being the longer the run, the larger the diameter of the pipe needed to keep up the flow rate. Which is why we don't have a petrol pipe only the same diameter as the main jet.
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By Wheaters
This fuel starvation problem has never completely gone away.

In the interim period since I last posted I've gone over everything again, replaced the fuel tap with a different type and the inline filter again with packeted, RE branded items.

It recurred again with a vengeance a few days ago. I noticed that the in-line filter wasn't filling up properly; there was more air than fuel in it.

I stripped the carb again, everything was in very good order.

I unscrewed the float chamber needle valve seat and decided the diagonal drilling in the carb body was the only possible restriction. I poked the spray tube from a WD-40 can in as far in as it would go, from the inlet tube. I felt something "give" so I reversed flushed it . I found a sliver of carb body material (looked like a broken piece of thread) in the jug I used to catch whatever came out. I rebuilt the carb and refitted it.

The result was that the filter filled right up as soon as I turned on the fuel tap! The bike runs better than ever before; I went on the M1 yesterday and for the first time it just kept on going.

The most annoying thing about curing this is that a couple of days ago I'd actually lost all hope and had ordered a 26mm concentric carb to replace the this troublesome Mikcarb 24....

But anyway, for now I can meet up with Andy A and go to the classic bike meet at Crich Tramway Museum this morning, rather than take the big Honda.
By Adrian
I'm pleased it was an easy fix, even if it took some tracking down. Is your now redundant new concentric a premier or standard version?

Out of curiosity I've "invested" in a ludicrously cheap Chinese copy of a flat-slide Keihin PWK 34 (similar if not identical to the sort used in the JRC Amal replacements) to try on my 500 AVL hybrid. Current carb is a Dell'Orto. So apart from set-up/jetting issues I will remember to check for free flow of petrol through the thing!

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By Wheaters
The carb I've ordered is a 26mm one and it's not an AMAL at all, it's actually a Wassell branded one.

As it's slightly bigger than the present Mikcarb I intend to fit it anyway - I'd already opened out the inlet side of the head and gas flowed it to that diameter when I did a top end overhaul last year, to sort out the valve seat recession problem.

After our short ride to Crich today, Andy A said that he noticed the bike does nip along quite well now - he was following on his 500 Continental GT.
I had exactly the same problem on my Connie, and a change of fuel tap cured it. Can’t remember which one I fitted now, but it was from MrH and is a simple on/off job, and the description said something about high flow. Tickling the carb now produces a flood within about 5 seconds whereas before it used to take a minute!
Good luck!
User avatar
By Wheaters
The Mikuni doesn't have a "float tickler". If it had, I reckon I'd have narrowed down the cause of this problem sooner.

I'm looking forward to the Wassell carb, which does have one. It also has an equally useful drain plug in the float bowl. 8-)
User avatar
By Wheaters
The 26mm Wassell carb is now on the bike.

Thankfully it fitted straight onto the existing studs (lateral spacing on the inlet flange is 50mm). The existing throttle cable (Minda controls for the Mikcarb 24mm) also went straight on, with the adjusters at both ends wound right in.

The carb came supplied with a choke mechanism. I don't have a choke cable or a handlebar lever as per the Mikcarb so I decided to remove this and rely on the "tickler" for now. I found a suitably sized screw, washer and locking nut to block the aperture in the top cover, where the cable adjuster was fitted and used a little silicone sealer paste on the threads to ensure it was completely airtight.

The carb came with a 160 main jet and the fuel needle "out of the box" was on its lower (weaker) position on the clip (only two needle positions on this carb). I left everything as it came for the initial setup.

I never like running an engine on an open intake. I had a washable "cone" filter on the Mikcarb but this proved too small in diameter to fit over the short "bellmouth" type intake adapter on the Wassell and too big without it. I fitted a suitable foam one I already had, from another project, keeping the bellmouth in place.

The initial run proved that the mixture was too weak, with a lot of spitting back and poor power. The spark plug's centre electrode insulation after a full throttle "plug chop" was very white in colour, which confirmed it.

To remedy this, I fitted a 170 main jet. I just knew those old AMAL jets I'd saved from my old BSA C15 tuning days would come in handy one day - albeit it's now 46 years wife was amazed I'd got them to hand, some fourteen house moves (and two country moves) later but a man needs to prioritise such things.

I also raised the needle to it's richer position.

The float level seemed quite low, it was at the lowest position mentioned in the included instructions, so I tweaked the tab a little to raise it a couple of mm.

The bike then ran really well, it pulled noticeably stronger than with the Mikcarb at full throttle. There was absolutely no sign of the initial problem of the carb running out of fuel - BINGO!

However, another plug chop proved that the top end was now too rich, confirmed by a rather sooty exhaust. The original 160 main jet is now back in. Yet another test shows this is OK (I think it could really do with a 165).

The bike now pulls really nicely and idles well. I suspect for colder weather I might need to refit the choke mechanism so I intend to source a cable and air lever from Mr H. But for now, the bike starts first kick.

Although this Wassell "Concentric" carb isn't actually an AMAL, it's a relatively cheap pattern copy, I can certainly recommend this type of carb as an upgrade modification for a 350, as per the "OE" ones sold by our host.
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By Slappy
Good morning Wheaters

I have been reading this topic with great interest how are you getting on with the Wassell carb and if you don't mind me asking where did you get it from and what model, it would be going on a 500 bullet
User avatar
By Wheaters
The carb works really well.

I'm not going to mention exactly where I bought it due to our host's forum rules, but it was advertised as the last one the supplier had, however you might find another online. I bought a 26mm (right handed) one as an upgrade from the Mikcarb 24 for the 350. I think you would need a bigger one (28mm?) for your 500.

Mr H would be happy to supply you with an AMAL Concentric which is the "original" design; I presume that might be better quality still. The slight concern I have with mine is that the air slide might be on the soft side and wear quite quickly. The Mikcarb has an anodised slide for improved wear resistance.

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