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carb insulators NLA for CM 400A?

redlotus

Veteran Member
Joined
Jun 28, 2022
Total Posts
125
Total likes
22
Location
Columbus, OH USA
Hi guys. The latest news is not good. An update on the leaky carb mounts: just got a note from David silver that these are NLA for the CM 400 A - unless I'm lucky enough to find some NOS. If this is truly the case, only good used are the only option?

My first thought when I got the bike back in May and discovered the totally gummed up throttles was to think about a simpler single Mikuni setup that I'd read about on that other forum that shall not be named - before I saw the light and came over here :) So the carbs are cleaned, but with major air leaks at the mounts it's kinda dead in the water for now. Has anyone ever tried silicone to seal things up, as crude a solution as that is? I'd like to talk to that guy that put up a youtube video riding his CB 400 with a single setup -anyone here know him? I'll try to dig that up. Or see if EFI is possible somehow. Both seem like intriguing solutions once tuned properly. I know however that the devil's truly in the details of what some might refer to as the "nuclear option" (nothing to do with nutso Putin, BTW). Thanks for any input. Cheers, Ron
 
1) EFI should be doable IF you change the stator to the GL1000/1000 type which can be rewound to give you 350w of juice. Unfortunately you lose the the neutral timing function because you'll need to go with a different CDI, either Ignitech or using the EFI controller.
2) Weld a stub pipe to the original mounting flange and use a silicone sleeve with good clamps to connect the carbs to the stub.
3) Weld a long stub pipe to the original flange that will incorporate an O-ring to fit the carb into secured with a heavy duty clamp. This is more complicated than #2.
4) switch to the Mikuni carbs but the VM28's may be too large for the engine to produce proper power.
 
Thanks for the input Jim. I'll have to put this on the back burner for a while until I figure it out. Disappointing. Todd Rundgren comes to mind - "for the want of a nail...."
Cheers, Ron
 
BTW, here's a clip of a guy that made a single carb setup for a 400T: https://www.youtube.com/watch?v=GuOnOHi64EA I wouldn't mind dropping a few HP for a neat, simple setup like this. I like the look of his bike too. Anybody know this guy? A quick google didn't turn up a shop or anything. Cheers, Ron
There's 2 other video by this guy, Holt Works in British Columbia. Videos are 9 years old. I don't find anything useful on Google
 
Since no new mounts are available I'm going to try a careful application of silicone to seal up the leaks and then see where it's at. Very disappointing that new mounts leak like that. Also, hope all our FL and southern members here will stay safe, high, and dry - along with their bikes, of course! Can't imagine what that's like to go through. Gobs of silicone to seal doors and garages might come in handy. My younger brother in Orlando may be surfing in his front yard :) All the best, Ron
 
Cruzin Image does have ones for CB400A, should fit the CM400A. I believe I bought these indirectly from them on ebay a number of years ago. They do work, but they are starting to get cracks on the outer surface; however they still seal. If you get the CI ones just anticipate having to replace them every 5-10 years. Might be worth ordering a few since they are relatively cheap.
 
They didn't seal from new - leaked from both ends - so I smeared a bit of hi temp silicone on them yesterday and reinstalled. I'll try a spray test again tomorrow.
 
That's where I got them. Beautiful area there, BTW. Visited a music friend who used to live there a few times. Once picking up a '69 Alfa Spider there I towed home behind my '69 BMW 2002 - symmetry :)
 
The fit seems correct judging by the struggle to install the carbs, but they just leaked at both ends, both carbs. I reinstalled with a smear of hi temp silicone and will fire it up later today to see what the spray test reveals.Until/unless I can find some NOS Honda mounts I'll have to live with these I guess. Next task is to find some wintergreen oil to recondition the boots before I can really tell how it runs. I wrote Cruzin but no response.
 
Are the air box boots installed when you do the spray test? If not then the spray is still getting drawn into the carbs giving you a false reaction.
Also it takes a very light spray, a heavy spray can give a false also.
 
Thanks for the tip Jim. I'll be careful with the spray or just dribble. I need to do a wintergreen soak before I install the boots. Don't want to tear them as they are looking rather fragile and NLA it seems. Anybody fabricate something from auto radiator hose, etc? Cheers, Ron
 
Radiator hose is a no-go. Fuel vapors will eventually soften it and destroy it. Don't bother trying. Not sure how you'd make that work on the airbox side anyways since it's a custom shape.
 
Just speculating options. There's probably some sort of industrial hose out there of a more appropriate material if it came to that or maybe something a 3D printer could make?
 
Ron I have not tried it on intake boots but on some rubber parts I have had luck putting rubber parts in a plastic bag , spraying them with silicone spray and letting them soak for a few days.

Bill H
 
Thanks Bill. I was wondering about silicone myself. Thought I might look around for some in a quart size or something where you could really soak them. Just finished crawling out from under my 2005 Mini, replacing brake lines and trying to get all the air out. PITA! ABS makes it harder. Hope to get back on the 400A next week. Not enough hours in the day, sigh. Cheers, Ron
 
I've had better luck with pressure bleeding. The clutch on these Minis can be very difficult to bleed too, unlike my '71 2002 which gravity bleeds itself :) The ABS unit is full of air requiring an expensive trip to a shop for electronic bleeding, so not liking ABS anyway I'm going to bypass it with a couple of t's like some autoxers do, and remove it to unclutter the engine bay some and save a bit of weight. The KISS principle rules! :) Cheers, Ron
 
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