Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Oggers on May 04, 2020, 09:27:47 AM
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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?
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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.
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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. 👍
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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!
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If you mean the boots between air box and carbs they ought to be rubber
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Pretty certain it is some sort of plastic onto the carb. It does however mate into a rubber trumpet located within the - for want of better words - the large collector. This is definitely a different material than what mates onto the carbs. Mine is the earlier US version by the by.....
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All the ones i have seen are rubber, has a po done some sort of frankenstein repair?
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All the ones i have seen are rubber, has a po done some sort of frankenstein repair?
The rubber may have gone very hard and brittle Bryan, therefore resembling plastic.
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Very true Julie, but if it is that bad they really need changing. Havent done a 400 for quite a while does DS do those for the 400 as well as the 500?
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Nope - looked plastic to me, and I doubt very much if PO bodged it. Alignment dots on the collector and these stubs suggest it is original. Looks and feels very similar to the collector material. Hard and fine particles when subjected to a spot of grinding. Some melted, and it did give off a melted plastic smell.
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Put up a pic of the offending article(s) for us to condem
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If you soak them in hot water they should become soft if they dont then.....
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They are rubber. over many years and heat they go very hard like plastic......yours are shagged, replace them.
Kevin
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Well let us say they exhibit plastic-like qualities. Tried the hot water trick and it did soften them- for about 30 seconds, Then went hard again. I assume from all your replies that they should not have plastic like qualities, and indeed they may be goosed. This in itself is good to know and that it perhaps wasn't all my fault that the blessed things did not locate as they ought to have done.
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There are products that will soften the rubbers long enough for you to fit them. Over time they will harden again this is normal due to age. I tried various potions: wintergreen and IPA worked but the smell lingers. Have a look on You tube. Just make sure your carbs a well sorted before re-fitting them
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I never faff around with these things, any sign of hardening i buy new and bin the old ones, it makes life so much easier and gives me a little more beer time.
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I had the same problem fitting mine onto the carbs. Problem as I saw it was the plastic body holding the trumpets pushed in and became concave when trying to push on the middle two trumpets, leaving them stranded.
I removed the four trumpets and because the body is plastic, I used a heat gun to warm up the face where the trumpets fit and from then inside, pushed the face outwards, focusing on the middle two trumpet holes.
When suitably convex shaped, I then dropped the plastic body into a bucket of cold water, to freeze this new shape.
Refitted the trumpets and then the complete assembly back onto the carbs which gave a better, longer fit on the middle two trumpets.
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Pretty certain it is some sort of plastic onto the carb. It does however mate into a rubber trumpet located within the - for want of better words - the large collector. This is definitely a different material than what mates onto the carbs. Mine is the earlier US version by the by.....
I think yours are like mine were before I bought new ones. Over time the heat from below, or perhaps just natural perishing transforms the texture. The new ones felt noticeably different. Last time I endured this ritual I fitted the rubbers to the airbox first and wrestled it all in that way, wasn't easy...but easier. Maybe it's Tojo's revenge!