Topic: Why did the 77-78 cb750K get shafted?

[toytuff]

Good article, thanks for posting, Toy.

It's what I do.

tt

[Stev-o]

Good article, thanks for posting, Toy.

It's what I do.

tt

Yeah, that's why your Presidente of the K7-8 2 Cool Club!

Hope your stocked up on Tequila for your little rain shower over there.

[toytuff]

Good article, thanks for posting, Toy.

It's what I do.

tt

Yeah, that's why your Presidente of the K7-8 2 Cool Club!

Hope your stocked up on Tequila for your little rain shower over there.

Plenty. Buy by the case.

tt

[Jerry Rxman Griffin aka MuthaF'er]

Same valves as the other 392 engines Lucky, they weren't bigger...

The groove in the valve stem had to be different to accommodate the new style keepers.

Yes, that is correct Lucky. Grooves changed for newer keepers but standard size.

[Stoli]

^ekpent hit the nail on the head when it comes to the reason why the parts are harder to find.

3]http://forums.sohc4.net/index.php?topic=117106.73[/url]

You are showing bolt brackets.
QUOTE"As far as a bolt on bracket for rearsets, I think that is a bad idea anyways"

??

I guess I should have said "aftermarket bolt on brackets".The point I was trying to make was that the brackets that you buy, typically don't have an option as to where the peg goes, but if you fab your own, you can position it perfectly for your leg length, etc. Yes, mine "bolt on", but I adjusted the length of the bracket to fit me.

[750K]

To own a 77-78 you must be willing to modify things to fit. The only thing that really gripes me right now is no access to new carb insulator boots. We seem to be a small lost market.

+1 on the carb boots, if I remember correctly the cush drive rubbers are nla from Honda as well. Thankfully I've had some luck finding decent used set of both items for my K7

[Wobbly]

Number 1 and number 3 insulators are available new at CMS in the Netherlands. And I frequently see all four of them offered new on German EBay.
http://www.cmsnl.com/honda-cb750k7-four-usa_model14395/partslist/E02.html#results
Yeah, I know: they are too expensive, too much for shipping, can't pick them up locally, don't like the color, etc.
Not sure what you mean by "cush drive rubbers," but if you are referring to the rear wheel damper, they are available new: http://www.cmsnl.com/honda-cb750k7-four-usa_model14395/partslist/F11.html#results

[Djfob]

@lucky mentioned being able to use turbo silicone hoses as carb insulators. Anyone else try this?

[lucky]

To own a 77-78 you must be willing to modify things to fit. The only thing that really gripes me right now is no access to new carb insulator boots. We seem to be a small lost market.

+1 on the carb boots, if I remember correctly the cush drive rubbers are nla from Honda as well. Thankfully I've had some luck finding decent used set of both items for my K7

I bought brand new cush drive rubbers from Bike Bandit.

[BeSeeingYou]

Toytuff is correct. The -392 engine was used in the K7/K8 with a few changes. Even the K8 had a few changes over the K8. K7 used a different output shaft and cam is timed 5 degrees different then the K8 used the F2/F3 springs and keepers.

I looked for the link with the article but could not find it.

Senior moment. Thanks Jerry.

Edit<< I also remember reading that Mother Honda in fact wanted to drop the K model and just produce the F model. Honda did a detailed feedback program from Dealers as well as owners. What they found out was a great demand for the K model. Customers wanted a highway motorcycle that was comfortable for the long haul. This lead to the longer frame, increased rake and tire changes.

This is just from memory as I am still searching for where I read that. I can not verify. 

tt

The revised frame geometry first appeared in the 75 CB750F (28 Degrees and 4.5 inches).  The K6 retained the old frame geometry (27 degrees and 3.7 inches).  Did the 77/8 K adopt the better F frame geometry......I am assuming it did.  4th and 5th geat ratios are different in the F also making it run maybe 500rpm higher at highway speed so yeah the 77/8 K may make a better long haul bike.  The earlier K bikes not as good IMO...too twitchy.

[Stoli]

The K8 has 28 degrees of rake and 4.5 inch trail. The F3 has 27.5 degrees and 4.5 inch trail.

[BobbyR]

To own a 77-78 you must be willing to modify things to fit. The only thing that really gripes me right now is no access to new carb insulator boots. We seem to be a small lost market.

+1 on the carb boots, if I remember correctly the cush drive rubbers are nla from Honda as well. Thankfully I've had some luck finding decent used set of both items for my K7

I bought two sets of cush rubbers 2 years ago for my K8 from Honda

[750K]

^^^wierd, this spring I ordered a set for my wife's cb400t and wanted to check the price on mine. My Honda parts desk said it is no longer available oem, I hadn't checked aftermarket and in the meantime I've picked up two good used sets cheap. So I'm good for years.

[Black 750K8]

@lucky mentioned being able to use turbo silicone hoses as carb insulators. Anyone else try this?

I would like to see his or is this some more internet bull he just read?
Lucky how about some pictures and a link for the ones you know fit.

[BobbyR]

The cush drive rubbers are still available from Honda they are $9.42 a piece. I chose to go new rather than old and hardened. http://www.houseofhondaparts.com/fiche_section_detail.asp?section=2451907&category=Motorcycles&make=Honda&year=1978&fveh=131106 

[Terry in Australia]

@lucky mentioned being able to use turbo silicone hoses as carb insulators. Anyone else try this?

I would like to see his or is this some more internet bull he just read?
Lucky how about some pictures and a link for the ones you know fit.

People have been using various types of rubber hose to adapt carbs to CB750 engines for years, but it's not a smart move.

Whereas the OEM rubbers are designed to produce a smooth transition between the carb's venturi and the inlet tract of the cylinder head, shoving a piece of rubber (or silicon) hose over the carbs inlet stubs and the stubs on the cylinder head would not guarantee an air tight seal, and would also create a "step" between the carb's venturi and the cylinder head's inlet tract, which would cause turbulance in the fuel/air mixture, affecting the engine's performance. 

So yes, a piece of hose could be used, but even an old rock-hard set of OEM rubbers would work better. Cheers, Terry.

[lucky]

As usual, Lucky's research is flawed. The K7/8 engines are the same spec as the F/F1, not the F2/3, which has the bigger valves, slightly lumpier cam, etc. The K7/8 engine is probably the best though, as the F2/3 engines were a little more fragile.

The best thing to do with an "F/F1" or "K7/8" engine, is to install it in an early K bike, and then you've got the best of both worlds, the best engine, in the most popular (and easiest to obtain parts for) chassis. Cheers, Terry.

I did not do any research.
All I did was quote the CB750 chopper website that shows engine chart with changes for the different engine numbers. It is the same chart that was posted on this thread.

IF I did "research" I would actually tell you the diameter of the intake and exhaust valve. But all I was interested in was to let the OP know that the K8 was not deficient in comparison to the earlier models. It was actually improved in most respects except for the EPA carbs.

All of the carbs after 1970 were much harder to work on. They added those "lifter arms". They were added so that by turning one screw you adjust the idle on all 4 carbs but the price was all of the extra weight and complexity, and then if you wanted to work on them you had to remove them from the bike. Some people like them.

[Terry in Australia]

Actually, the lifter arms were added to the later carbs because it was difficult to keep the K0 carbs in synch with 4 separate throttle cables stretching at different rates.

The only time it was necessary to adjust the idle was when the engine was cold, and you could do that with the thumb-screw adjuster on the throttle assembly. Cheers, Terry.