Honda CM400A (automatic) Carb swap help!!

[Rawgman]

Hello all! First post so I hope I'm in the right spot. I have a 1980 Honda CM400A and the insulators (boots, whatever you want to call them) are completely shot and I have them patched up for now. Unfortunately Honda no longer makes the part I need and I've ordered two sets that are for "CM400's", unbeknownst to me there is a big difference in the carbs for the A, E, and T models. From what I can tell, all the carbs are interchangeable for the bikes. The difference being the outlet that feeds into the insulator is about 4mm larger on the E and T models. I have the boots for the other carb models but I would like to know if anyone has done something like this before, how difficult it is, and what I should and should not spend money on. Currently looking at eBay listings for Cm400 E and T carbs to put onto my A. I have attached a photo of the listing I'm looking at and my current patch job on the insulator.

 

[LongDistance]

Yes the VB24 carbs used on the A model are smaller both in the throat fit to the boot and the venturi sizing, 28mm.
Do the insulators that you bought physically match up with the head as far a bolt spacing and throat mating? If so then I see no problem in changing to the VB22 carbs which are 30mm venturi and used from 1980 thru 1982. I wouldn't go with the VB21's, 32mm venturi's, since it'll be over carbed and run poorly

 

[Rawgman]

Yes the VB24 carbs used on the A model are smaller both in the throat fit to the boot and the venturi sizing, 28mm.
Do the insulators that you bought physically match up with the head as far a bolt spacing and throat mating? If so then I see no problem in changing to the VB22 carbs which are 30mm venturi and used from 1980 thru 1982. I wouldn't go with the VB21's, 32mm venturi's, since it'll be over carbed and run poorly

As far as I can tell the only difference between the parts that are on the bike and the parts I found are that the metal backing to the boot that attaches to the carb itself is bigger than the carb outlet, assuming that is the throat? I've noticed a slight angle on the rubber end on some of the boots but it's nothing extreme.

 

[LongDistance]

The boots do look identical at first glance. But do the manual boots mate to the automatic head properly? That mating area inside is referred to as the throat. There has to be a smooth transition from the insulator to the head

 

[Rawgman]

The boots do look identical at first glance. But do the manual boots mate to the automatic head properly? That mating area inside is referred to as the throat. There has to be a smooth transition from the insulator to the head

I will try and take it apart this week and post some pictures. I've had it patched for a few months so I need to re examine the parts I bought with the parts I have and how it's set up right now. I'm still very new to the do it yourself for motorcycles so bear with me! I appreciate the responses though!!

 

[Rawgman]

The boots do look identical at first glance. But do the manual boots mate to the automatic head properly? That mating area inside is referred to as the throat. There has to be a smooth transition from the insulator to the head

Here is (a piece of) the part in question, next to the only parts I can find. They are the same size except for the throat? On the engine itself the hole is the same size as the old boot but the only boots I can find are slightly bigger. The second pic is the size difference back to back.