Author Topic: IT 175J intake manifold  (Read 319 times)

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Offline katostrom

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IT 175J intake manifold
« on: July 14, 2019, 03:19:16 PM »
Hi all
Just after some ideas or recommendations re ongoing problems with Yamaha IT175J intake manifold. Original was very cracked (appeared to be on outside only) so to be on safe side decided to replace with the current repro items. First one purchased had flaws/leaks in rubber to metal bond plus the rubber body itself, unnoticed at first, which possibly part contributed to a major engine failure, second one has just shown the same flaws after only 6 or so rides and with possibility of air leaks I have removed. Now I am back to resurrecting the original item which I have heavily coated on the outside with sikaflex sealant in the hope of sealing or preventing any possible air leaks. This I am hoping will be a suitable fix for next weekend ride, not sure if this will be a long term fix. Am reluctant to get a third repro item as quality seems very poor and they ain't cheap, am guessing this may be a problem for others so any current ideas other than the above (all searches only lead me to very old posts/info) can another model be adapted (don't know if this will solve the quality problem though), is there something else available (I only seem to be able to find the one USA source avail of the repro item - postage is mind blowing) and J model item seems very rare. Any ideas appreciated.

Offline James P

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Re: IT 175J intake manifold
« Reply #1 on: August 12, 2019, 03:50:22 PM »
If you are handy with welding and machining (or know someone who is), you could make an inlet manifold from aluminium plate and tube, welded together.

The tube can be machined to suit the internal ribs of a proper carb-mounting rubber, e.g. https://vintagetriumphparts.com/Carburetor_Mounting_Rubber_Spigot_MK2_Genuine_AMAL/p710.

If you have the standard VM34 carb, the Amal Mk2 (30-34mm) rubber should fit...or you can use car radiator hose as a bodge!
You can seal the joint (between the new manifold and the reed block) by making a gasket to suit, or lap the manifold surface flat after manufacture and use sealant. If the original rubber manifold has a reed block 'stuffer', you could make this as a separate part...or adapt one from another bike.

Regards,
James

Offline katostrom

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Re: IT 175J intake manifold
« Reply #2 on: August 13, 2019, 07:09:33 PM »
Hi James
Thanks for your reply and suggestions. That has given me something to think about. Am reluctant to get another new repro item as quality has been so bad on the two I have purchased but I do now have aluminium manifold plate that I could hack out of the repro item and maybe modify and adapt as you have suggested using the second unit as a template. The original does have a stuffer so will need to work on that aspect, its also got the boost bottle pipe outlet but all seems possible. Noted the Amal rubber mount - looks good. Cant machine or weld aluminium myself but am sure can find someone. Again thanks for advice

Offline James P

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Re: IT 175J intake manifold
« Reply #3 on: August 16, 2019, 02:13:16 PM »
If you want to avoid welding, an alternative would be to use a flat plate with a 34mm hole in it (best done on a milling machine, but can be done by hand), four M6 holes to secure it to the cylinder reed housing and two more (tapped) holes to mount a rubber adaptor flange like this:



These adaptor flanges are available from many sources in many sizes (you can start by searching for "Mikuni rubber flange"...). As you suggested, you may be able to utilise part of your original (or remade) inlet manifold to obtain the reed block 'stuffer' portion - just see how it looks once you've removed the outer portion of rubber. It may be difficult to obtain a nice smooth passage into the reed block, so you could possibly make your own stuffer (from Araldite or Devcon or something similar) which will give a uniform intake passage and fill any 'dead space'.

Regards,
James.