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ajsm18

Fitting Mikuni - help required, please

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Hello,

I've decided to replace the original Amal on my M116, 325 Alpina with a Mikuni and have bought one from In-Motion, along with the manifold. I have just tried to fit it and there isn't room for the retaining nuts at the two studs are practically touching the rubber manifold.

I thought I'd ask in case anyone else has found the same problem and how they resolved it. I suppose I could cut the rubber away but don't really want to do this in case I damage it too much!

Also, should I keep the original rubber carburettor spacer or remove it as the new manifold is rubber? If that is the case, I assume I will need a paper gasket between the new manifold and the existing manifold bolted to the cylinder?

I hope I've explained the problem and will give In-Motion a call after the holiday but wanted to ask if anyone else had hit this problem and how they dealt with it.

Many thanks

ajsm18

 

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Hi, quite easy to resolve, actually. The studs in the manifold are M 8 , just remove and fit the rubber manifold with Allen head bolts. The studs may be quite tight, use 2 nuts locked together to undo, also head up the alloy in a tub of boiling water for 3 or 4 minutes, or use a heat gun. You may need to turn the heads of the Allen down a bit to get clearance to fit, maybe shorten them a sixteenth or so, different makers seem to have different specs for the sizes made. Also, a smear of copper grease or Vaseline will be a good idea on the threads to prevent seizing in the alloy manifold. Essential if using stainless Allen head bolts, the 2 different metals will corrode if fitted dry. Hope this helps...........

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You could alternatively fit a flat adaptor plate that fits the existing studs and has 2 holes in a vertical plane for a connector that has the mounting holes further apart. I've seen those adaptors for sale but would be very easy to make. Connectors with wider spaced mounting holes are easy to source.

Yet another option is to use the inlet connector piece from a later model Alpina or Sherpa T, which are made to suit spigot mount carbies. That's what I did on my M138 Alpina when I replaced the AMAL flanged carby with a Mikuni, then an OKO

Edited by feetupfun
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As for your other question, yes when you use a rubber connector for the carby, you no longer need the thermal insulator piece. To seal that joint, you can use a paper gasket or machine an O ring groove or use a sealant that stays soft

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Fantastic, thank you for the replies, chaps! I think I'll give the allen bolt idea a go first as I should have some M8 bolts around somewhere! They may be stainless...

The adaptor plate also sounds a good idea but I think the allen bolts will be an easier fix.

Thanks, again

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Hi,

I'm still working on fitting my new Mikuni carb and now a really, stupid question! I'm going to use copper grease on the stainless M8 allen screws to fit the manifold but what is the best sealant for the manifold gasket? I was just going to smear the paper gasket with grease on both sides as I done that with old brit bikes so assume the same. Or should the paper gasket be installed dry? I'm never really sure!

Thanks

ajsm18

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Grease or even oil is fine as both let the gasket let go if you have to pull it off again. Installing it dry means you have to buy a new gasket every time. Graham.

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On 4/4/2020 at 1:16 PM, bullylover said:

Grease or even oil is fine as both let the gasket let go if you have to pull it off again. Installing it dry means you have to buy a new gasket every time. Graham.

Thank you very much for your help, Graham.  I really appreciate having such experts to call on!

Take care and stay safe. We'll soon be out riding again.

Mark

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