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By Presto
#84122
I’ve never understood the idea that ‘A’ carburetter gives better performance than ‘B’ carburetter and even better than ‘C’ carburetter. Unless there is a mechanical fault I don’t see how one carburetter can give ‘better’ performance than another provided both are set-up correctly for the engine they are used with.

If the state of tune of one carburetter is correct and the state of tune of another carburetter is also correct then the engine performance will be the same. The engine doesn’t ‘see’ the shape, colour, or make of the carburetter. All it reacts to is the fuel mixture the carburetter supplies. If that’s correct then the engine performance will be the same, whatever make of carburetter.

One may be easier than another to tune but if both are tuned correctly then both will perform equally well.
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By Wheaters
#84136
Presto, although I don't disagree with the theory of what you wrote, I'm unsure what you are getting at here. If you read this thread from the beginning you would see that I finally decided to change the carb on my bike to a different type due to ongoing problems with the float bowl of the Mikcarb running low on full throttle and causing the engine to cut out - not a safe situation on a busy road.

I found the fault (a manufacturing/quality control fault inside the casting) just after I had ordered the new carb. However, as I had previously opened out my bike's inlet tract to 26mm the new concentric fits perfectly and gives scope for more airflow than a 24 mm one could.
By ridingdirty
#84150
Hi Wheaters,

I'm so happy that I stumbled upon this thread! I first encountered this problem when I did a long ride to France with my girlfriend last year. As I could sort of live with it by rolling off the throttle and riding for a bit at that speed, and usually able to return to full throttle (at least for another 5 mins!), I hadn't bothered to look more deeply into it. However, in the last month or so I've been riding a lot more and it's really started to bug me. Having to move around between 80% throttle and 100% gets really annoying when you're trying to cruise on a motorway, and downright sketchy when you're trying to overtake a lorry!

I really felt like it must be a fuel starvation thing, but just like you I did a lot of tests with the tap/tank and fuel line and there seemed to be no problem there. Also like you I had upgraded to a 105 main jet, and I was wondering if this was draining the float bowl too quickly. I was going to try dropping to a 100 to see if that helped, but since I found this thread I think I'm going to make a deep inspection of the carburettor casting to see if I'm lucky enough to find some rogue swarf or similar! Let me know if you've got any other practical tips not already covered. Will report back with progress.
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By Presto
#84155
Forgive me not reading through all of these posts. I was in no way intending any critical reflections on Wheaters findings.

I was only commenting on the idea that changing to a different make of carburettor will provide improved performance in and of itself.

I’m still not going to read through all 5 pages of this post but in my experience problems similar to what appears to be reported here are often caused by surface coating residue from the use of ethanol. This can be enough to marginally restrict the flow of fuel through the very narrow drillings in jets in particular. But it may also adversely affect other carburettor components. Spraying with aerosol solvent carb cleaner is the only effective way of removing this residue.
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By Wheaters
#84170
If you had read the thread, you would be aware that I'd cleaned the carb a number of times, with various solvents and everything flushed within an inch of it's life. I'd also blown the fuel inlet passage through with high pressure air and all the jets were replaced with brand new ones. ;)

Unfortunately, this wasn't enough to flush out the offending piece of casting metal stuck firmly inside the fuel inlet drilling.
By ridingdirty
#84212
Well, I did everything you described (plenty of little bits of swarf dropped out from the carb main inlet after hand turning a 2.5mm bit in there), and after being out for about 40 mins and having done a far bit of top speed running, I got all excited and thought I'd cracked it! Alas, on the last run back home on the A14 the dreaded jerking returned :x Back to the drawing board...
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By Adrian
#84213
Well you obviously managed to shift some of the obstructing material to get the improvement that you did, give it another go! My guess is that there was a loose but persistant bit of swarf from your first attempt. 3mm drill bit this time?

A.
By Lou E
#84237
I had a similar problem on my '66 interceptor custom (single carb) The carb had a float bowl extender on it and no heat insulator. The carb sits well out of the air stream, the extender gave the fuel in the bowl more dwell time to heat up and the lack of an insulator meant the metal transferred a lot of heat to the carb. Run the bike and feel the temp of the carb. If the gas is boiling it won't love you anymore.....

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