SOHC.co.uk Forums > CB350/400

Air intake manifold

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Oggers:
Spent most of Saturday fighting to get the black plastic air intake manifold back onto to the rear carb stubs, and sad to report the manifold probabaly won. It is nearly correctly seated on the outer stubs, but certainly not on the inners. I'd say @ 5mm gap until it butts up.

Essentially I removed the blessed thing when refurbishing the bike. It was difficult to remove and I half expected it to be pig, but not that much! Intially I lubricated each carb stub and dunked the entire manifold in hot water to soften the plastic - no joy. Was not going on at all. Dressed off the innner bores of the manifold stubs a little - still no joy, then wrapped some abrasive papaer round a drill bit and took to the inner bores again removing more plastic. Smoothed it all off, lined up the dots, and tried again - better but not much, but at least it is on!

Some observations. The inner bore of the air manifold stubs appeared to be tapered not parallel. This is surely not conducive to clamping to the carb with the jubilee clip?  It cannot provide much of a clamping surface, and will have a tendency to slip off when the clip is tightened - which it did.

The collector - the large plastic box of most of the manifold is of course not rigid at all. Doesn't help when trying to push the inners onto the carb stubs. It just deforms rather than pushing the inners onto the carbs - hopeless!

Removing material from the inner bores means the wall thicknes is reduced, which means the jubilee clips "bottom out" for want of better words. I just got enough purchase to get them to clamp the manifold intakes properly onto the carb stubs.     

Tips for next time much appreciated - Can you fit the air intake manifold before offerring the carbs up to the head I wonder?   

billywingnut:
I had the same experience,  so last time I had the carbs off I fitted the airbox correctly to the carbswhile off the bike. Getting the assembly back on was an absolute pain but I did mange it. I wouldn't like to do this often as I'm sure it would damage the cylinder head rubbers as you have to force the assembly in place from the right side of the bike. Good luck.

taysidedragon:
Oggers,  a tip someone on here posted way back was to put a screwdriver handle or a piece of wood in through the large hole in the back of the air box and push the rubbers on that way. Worked a treat for me on the middle, hard to reach one's. 👍

Oggers:
Dragon

Yes tried that - no good. Just too rubbish a fit on the carb end to stay snug until I could get the clip tightened! The air filter stubs are also plastic not rubber - which doesn't help. No grip at all!

Bryanj:
If you mean the boots between air box and carbs they ought to be rubber

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