I have a MC21 SP with TA22B carbs. Looking at the floats with the float needle at the top, there is a brass tube forward and to the right of main jet. This tube seems to be deliberately blocked with a compound judging by the hardness. On my R5k carbs, TA21A, this tube is clear and extends internally up into the bellmouth in at least 2 places. One immediately behind the slide and one at the top facing backwards next to a larger hole. Is this a modification ie one of the differences between the two models. The more obvious one is the, still there but not machined, breather opposite the air screw.
Any help would be appreciated.
Thanks
Alan
PS If this is in the wrong section please advise as this is my first technical query.

This can actually go in the public forum... so, as if by magic...

'Bing!'

It's only specific jetting/setup that I do not allow here (there is a specific area in the Members section for setup), but contrary to that statement, I'm going to ask you what size mains you have!

The tube you are referring to is the feed to the power jet (PWJ). It is common practice to fit PWJ blanks, or to make blanks by soldering up standard ones, but filling the tubes with epoxy is another option. It just makes it much harder to revert to a PWJ setup should you wish to.

The MJ should be somewhere around 185 as a starting point. If your mains are significantly smaller (say, in the 130's), then you run an extremely likely risk of seizure at high RPM.
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Andy.
NSR-WORLD.COM

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Thanks for the reply, Andy.
Just to clarify,the brass tube is between the main jet and alloy power jet cover screw. The main jets are non standard at 150,150. Since the PJ's (72,75) were still present, I opted for the nearest MJ size to the M-max set-up with PJ's(145,148, 75,75). I have increased the air intake areas into the air box, but could increase more, and done the splice etc. So, what you are saying is, the PJ's are now redundant ? My options are then, to re-open the tubes or use 185,188 MJ's. My preferred option, if possible, is to clear the tube. The reason is twofold, firstly I modify or manufacturer MJ's (bearing in mind warnings about the internal chamfer) and can only get drills in 0.05 increments. Secondly, I am only after a healthy increase in power, hopefully 60ish.
As an aside, you probably noticed I only became a Carbon member today. When choosing between that and Titanium, the only difference in the options, as I saw it, was the offer of discounts. So when I tried to enter the NSR discussion forum it then said Ti members only. Can I upgrade for an additional £15 ?
I look forward to you comments.
Thanks
Alan

One way or another, that setup needs serious reconsideration. The mains are far to small to safely run without the PWJ. Specific jet numbers are not something I allow to be discussed here though. I only asked so as to know whether to pre-warn you of almost certain high RPM failure.

It's not impossible to tune with PWJs, but it's difficult. They are progressive, so it's highly unlikely you will ever get the best possible fuelling.
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Andy.
NSR-WORLD.COM

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an other solution blanking power jets that worked fine for me is to find screws slim like a power jet but long enough to screw in where the power jet sit and close the hole with their head so no need for the alloy screws.