Which Mikuni for Navigator

Give Motocarb and Allens performance a call, if I remember correctly one of them had the mikuni specs for a Navigator when I was looking for a carb for the jubilee.

dan

Previously Andrew Wibmer wrote:

Hello,

putting my Navi back together but have begun to understand the chances of my rebuilt Amal being upto scratch are pretty thin, feeling inclined to look at the an upgrade. Am I right in thinking the Mikuni VM is the best carb to opt for. Re size and jetting, well out of my depth other than I see that a 22mm or 24mm bore is an option, the 22 being nearest to the 7/8" or 22.25mm bore is the best choice, however how to sort the jetting? any one done this or any thoughts on best way forward?

Thanks

Andrew

I fitted a new Amal 1600 card a 25mm mark 1.5 with all the better bits--an anodised slide and a stay up float it cost about £120 from Amal brand new-all my other bikes run well with them bit I have yet to start the Navigator. It is technically too big but I have never been bother too much n]by such matters before--this could be one of those ominous statements.

Cheers

JPA

Yep ..... a too big concentric on my jubilee did not work well, ended up buying a new monoblock!

Previously Dan Field wrote:

Yep ..... a too big concentric on my jubilee did not work well, ended up buying a new monoblock!

Hello Dan,

Is there a way of telling which manifold I have?--I gather 250 and 350 ones differ and I seem to have all manner of different bits.

JPA

The casting number might give a clue Iâll have a look in the garage later!

The number on my Navi manifold is 22855. The number on my jubilee is 20843

not sure if they all had those numbers but it might help!

The bore size of the Navigator manifold is fractionally bigger than the Jubilee one - to match the larger carb. - but I don't know the precise measurement.

Me neither, but I think this is what got me the wrong sized carb, the jubilee manifold had been widened by a previous owner so the carb matched the manifold but not what was required from the engine hence the poor running.

I think the carb sizes are in the manual, Iâll look.

Previously Dan Field wrote:

Me neither, but I think this is what got me the wrong sized carb, the jubilee manifold had been widened by a previous owner so the carb matched the manifold but not what was required from the engine hence the poor running.

I think the carb sizes are in the manual, Iâll look.

Hello Dan,

Mine has 20843 written on it from what I can gather. According to the parts book the relevant monoblock listed was 375/47

According to AMAL the specs for it are http://amalcarb.co.uk/carbspec/carburettor/spares/id/5411/

John, I've just checked the Norton parts list from 1964 - the numbers Dan provided are one digit different, the Jubilee inlet manifold is listed as 20844 and the Navigator 22854.....I will check my 1964 Navigator tomorrow and see if the number compares. It could be a typical Norton pronting era or they might have changed the part number or manifold design but I doubt it! Which ever way it is almost certain the lower number is for the Jub'.

Nick

Hello All,

I have ordered a 350 one from the spares scheme. Thanks for all suggestions.

JPA

Previously Nick Clarke wrote:

John, I've just checked the Norton parts list from 1964 - the numbers Dan provided are one digit different, the Jubilee inlet manifold is listed as 20844 and the Navigator 22854.....I will check my 1964 Navigator tomorrow and see if the number compares. It could be a typical Norton pronting era or they might have changed the part number or manifold design but I doubt it! Which ever way it is almost certain the lower number is for the Jub'.

Nick

The number cast into a Norton part is actually the casting number which for some strange was not the same as the part number. Normally the casting number and the part number are close to each other. I would expect that the lower part number refers to the Jubilee but wouldn't guarantee this.

Patrick

Would you credit it?

I have just had a navigator manifold tern up in the post--it has 20843 written on it just like my old one. They must have used a common casting at some point as it measures 22mm ish (7/8) rather than 19 ish 25/32 for the Jubilee.

The really ironic twist--I could not be bothered to measure the old one--it is has been taken out to an inch--oh dear....mind you the carb is that--shall see--I do hope no one has altered the head-- as I have one new one.

I have just measured the heads and they are the same. I tore a gasket and had to cut two new ones out of very old gaskoid.

The two inlet tracts of my old manifold are larger than the new one but no bigger than the holes in the gaskets and indeed the ports in the head--I wonder if (the new one) it is a Navigator one at all. It would be easy to make the inlet tract near the carb bigger but no so for the bit near the head.

So far--not a good day--the cat has vanished the Triumph missed a few times on a short run--then started rattling heavily and then stopped doing it (it has done it before) and I have just noticed the back tyre is bald--on the eve of a 110 mile journey

Cheers

JPA

Hello john,

I have a 1960 Jubilee engine sitting on the bench so I just checked what manifold it has. It has the casting number 20843 and measures 19.78mm -pretty well identical on all three outlets. The inlets on the heads I make 19.6mm but they need a bit of a clean. That equals 25/32 which agrees to the Jubilee carb size.

This info might be of some use as it appears to confirm that the sizing of the whole inlet tract is pretty consistent. (And this is an engine which seems to have had a hard life with minimum maintenance but was still a runner.) So possibly the Navigator follows the same pattern.

Patrick

I have a Navigator on the bench, but wonât get to it for a few days but will measure it when I can!