These are the culprits (along with some SOHC rubber bits), below:
The black rubber/plastic donuts that sit between the carburetors and the cylinder head - AKA the "insulators' in Honda-speak. Over 30 years or so and a few thousand heat cycles, these dry out, get hard, sometimes leak leading to strange running conditions, and make installing and removing the carbs a larger pain in the arse then it needs to be.
You can buy replacements! Randakk's Cycle Shack will sell you really nice high quality replica parts for $110 for a set of 6, plus tax and shipping:
http://randakks.com/collections/honda-c ... master-kit
Or there are a few sellers on eBay that sell nice replacement sets for $70.00 plus tax and shipping, for example:
http://www.ebay.com/itm/BRAND-NEW-6PCS- ... 1c3d01f714
Or you can restore the ones you have, along with any other hard rubber bits you have, using 4 oz of wintergreen oil for roughly $20:
http://www.amazon.com/Wintergreen-Essen ... n+oil+4+oz
In my case I popped for the set from Randakk, but that's because I didn't know about the wintergreen technique. The active ingredient in wintergreen oil that is helping is called methyl salicylate, and this is how to use it, some cautions I'd take if I were doing it over, and how it can go wrong.
You need:
4 oz of the wintergreen oil.
A hot plate or a VERY UNDERSTANDING significant other that LOVES the smell of wintergreen lifesavers and wants to smell it for a while, in which case you can do it in your house on your stove.
A pasta pot that you may not intend to use for pasta again, WITH A LID!
Tongs.
A fan.
Instructions:
Clean the insulators well, get them nice and squeaky clean
Put your hot plate and pasta pot in a doorway or maybe just outside, or use a fan to direct fumes away and outside (see above).
Fill the pasta pot with a gallon of water, add the wintergreen, cover, and bring to just below a boil, roughly 200 degrees.
Toss in the insulators, lower the heat to medium give them a stir now and then, and simmer for 30-60 min.
Fish them out, rinse them off, declare victory. Your old rock-hard insulators are now much softer and more pliable, will install easily and make installing the carbs much easier too.
What, you ask, could possibly go wrong with such a simple process?
Take a look at this photo below, paying particular attention to the large rubber plenum>airbox seal (CB400F, BTW) that's just below the bottle of wintergreen oil.
See how it's looking a little ragged, punky? That gasket and the other airbox tubes off this set were all decomposing I think, felt slightly gummy to the touch before I dunked them. Not sure what happened to them, maybe some solvent got sprayed on them before I got them, but once they were in the pot WITH ALL THE OTHER STUFF (mistake) they commenced to falling apart, and gooey spooge was floating around and getting on the other parts. I stopped short of the full cycle, fished my parts out pronto and cleaned them off before the stuff cooled and hardened, and got them about half as good as they could be - still a huge improvement in just 15 min of simmering.
At left is one of the snorkels from the set that was half punky, at right is one from the other set that came out really well:
As above, plenum seal:
So - yes I think you can do pretty much any rubber part in this solution, but pay close attention when you do, and maybe do any suspect parts separately and watch carefully to see what happens.
I'd also suggest you do a better job of fumes containment and evacuation than I did, including maybe wearing a respirator. My sinus is still lightly infused with wintergreen today, and I bet my lungs are too, and it's not all pleasant. My garage and office on the other hand are TOTALLY infused with wintergreen, despite having the garage and side door open for an hour after I was through. It's not that pleasant IMO.
Last thought: I am betting I can reuse the solution, so I bought an unused paint can and saved it.
Good luck, and report back if you try it!
N.
