Topic: Hond -O- Matic woes

[grumburg]

New project fell in my lap. 1977 750a. 20k miles, one family owner, perfect seat, excellent orig paint and exhaust. Parked in barn for 10 yrs. Filthy and full on mice nests. Have taked it down and found out it's kind of an oddball. Little carbs with dashpot, Gold Wing rims, and you can remove the head in the frame! One big problem. Removed the parking brake cover and it looks like it had been soaking in salt water for 30 years. Totally ruined . WTF?  Could it be the steel parts in an aluminum case? Would never have dreamed I would own one on these, but have 2 people that want to by it when it's done. Can anyone enlighten me on the quirks and things to look for on these?

[stresssolutions]

I've heard that the parking brake can rust to pieces.  The transmission/torque converter likes fresh oil.  The wiring is different than all other CB750s.  It has a gas gauge.  Enjoy.  Post pics.

[05c50]

The transmissions are almost indestructible and trouble free, The carbs are very similar to cb550, except they use a throttle kicker that is activated when shifted into gear. It also uses a signal from the speedo (speed warning unit) to shut off the kicker above 20 mph. The park brakes seem to rust up pretty easily, but I was able to save the ones I have worked on. There's a neutral switch built into the trans to keep it from starting in gear and the trans should go into neutral whenever the sidestand is put down. Internally the engine is the same as a "K" except for the cam profile. It has a heavy chain and sprocket- I'm not sure why. The hardest thing to find are the carb boots. They're specific to the 750A and haven't been available for a while. Although it's not the quickest bike in the world, it does run pretty good and it's a blast to ride. hope this helps.

............Paul

[Dave Wyatt]

ebay is your friend when searching for 'matic parts.  It has helped me keep my ride on the road. 

The transmission runs on motor oil from the crank case, it is a wet sump system on the 'matics.  They use the same oil filter as the other SOHC 750's.  I've put over 30,000 miles on mine, with very little trouble.  I just keep the oil changed and ride the crap out of it.

[eldar]

The head part was a nice feature as the A engine is heavier. The carbs are smaller but as the motor is the same, at least the upper half, you can use K carbs as I think those openings are the same. The bottom has a lot of differences. You could swap the A cam for a K or F cam and get a little more out of it I would think. As the upper is the same, I would bet an 836 kit would work fine as well.

[mlinder]

I'm pretty sure the A was lower compression than a stock K, so there must be SOMEthing different in the top end, either pistons or head. So which is it?

[eldar]

Well it is hard to find the specs but 1 source says the comp is 8.6 but does not say why.

[mlinder]

I think one of my manuals lists it as even lower. But even then, 8.6 vs 9.0....
There's got to be a difference up there somewhere.

[05c50]

I'm not sure about the heads, but the pistons are the same. I've got 3 original pistons and 1 from a K in my 77 750A. Part numbers cross over.

..............Paul

[eldar]

Well I suppose since it uses smaller carbs that the combustion chamber might be a touch smaller with smaller valves. I would still figure that the A would be interchangeable with the K as far as the upper parts go.

[mlinder]

That would mean the head is different. Wouldn't mind seeing them side by side.

[eldar]

If I had to guess it is just the chamber. I thought someone here had swapped the heads but with so few A's around, it is hard to find anything. I sure would like the head removal part though!

[05c50]

I think that I have some pictures of the A head showing the combustion chambers. I'll check later and post them. Maybe someone more familiar with the K head can tell the difference.

..........Paul

[05c50]

Here's a picture of the combustion chambers on a 77 CB750A. Do they look any different then a K head? Other then the rust,crust and corrosion.


.....Paul

[eldar]

Difficult to say but they do seem a touch smaller. I have no picture to gauge them by though so I cant be sure.

[Ecosse]

Too bad someone can't cc these heads for comparison.

[dusterdude]

for a lot more info go to www.dragbike.com and join the forums.look for the hondamatic thread in the other bikes section and ask away.

[750mikeb]

Hi Ive got a 78 auto in my amen runs awsome It sat for 12 or 15 years till I woke it up I also have some doner parts left over give me a list and Ill check to see if I have them  mike