Topic: What is normal for a CB750A Hondamatic?

[CBdave76]

I recently picked-up a 1976 CB750A and have worked on getting it running.  I replaced the points with a Dynatek ignition and coils, replaced the wires and plugs, changed the oil and filter, used Syntek 10-40, cleaned out the frozen carbs and replaced the lower half (seats, jets, etc).  I adjusted the carbs with the sync gauges as best as I could.  The bike runs and I rode it for the first time last Saturday.  I was just getting familiar with the automatic and adjusting the idles.  I dove the bike about 8 miles on the road and noticed the "L" seamed to have high rpm's at about 45 mph, much less than the 60 mph referred to in the owners manual.  Also the "D" seamed to have high rpm's at about 60 mph.  I took the bike up to about 75 mph to see where it's limit was, but back off quickly because of the rpm's and speed limit.  When I parked the bike the engine lower case and transmission were too Hot to leave your hand on.  Is this normal?  If not, should I have someone look at the transmission?  I'm not experienced with transmissions, I don't look forward to watching the gears and springs go everywhere!

[mlinder]

What were your RPMs at 75 in D ?

Also, these are fairly large air cooled engines, They do get hot.

[Alan F.]

And don't forget that bikes like to be ridden and not left to sit still, the more you ride it... the better it will run in general.
Welcome.

[Sam Green Racing]

I've not got round to riding mine yet but it sounds like the overall gearing may have been changed on your bike.

Perhaps someone who rides one can coment on what sprockets are on them as standard, you can then count the teeth on yours.

Sam.

[bgrave1]

Part of the high rpm issue is due to the rear sprocket size. The factory is like a 46 or 48 tooth. It is great for get up and go, but crappy for freeway cruising rpm.

I did some research when I got my 1977 CB750A and decided to replace the rear sprocket with the smallest one available. 38 tooth. The rpm in D is seemingly half of what it was with the stock gearing. I did have to get a new chain also though. As far as the L gear, I would say that 60 is a stretch unless you are racing. If you downsize your rear sprocket, not only does the rpm drop, my mpg went up and my engine temp lowered. Also check to make sure you are running synthetic, or at least a blend. I noticed a big temperature difference when I changed mine also.

Thanks by the way for the saddlebag pics.

[bucky katt]

I've not got round to riding mine yet but it sounds like the overall gearing may have been changed on your bike.

Perhaps someone who rides one can coment on what sprockets are on them as standard, you can then count the teeth on yours.

Sam.

+1 what sprockets are on there?

[Spanner 1]

If you compare the ratios, the ' Matic only having 2, they translate to 1st and 3rd gear on a K bike ( or close to ). So, yeah it revs it's head off at 75 mph...what rpm, don't know these bikes have no tachometer. If you choose to change the final ratio ( rear sprocket ) you will sacrifice power, which is diminished compared to a K due to lower compression, smaller carbs and an auto transmission...torque converter eats h.p.....feels like a 400 stock, IMO...but !

[CBdave76]

Thanks for all the replies! 
I haven't checked the sprocket yet, I believe it's stock.  I bought this bike from the original owner, and everything looks original (excluding the bags and fairing).  I am using Valvoline synthetic blend in the oil pan.  I am thinking of adding an oil cooler, if I can figure out how to hook one up.  I also thought about mounting a 12 VDC PC fan to the bottom of the pan.  I want to add a small tach gauge to the handle bars just so I have some idea of how close to death I'm flirting with. (Mine, the Bike's or Both!)