Topic: What’s Wrong with my Honda cb750K8?

[BenelliSEI]

Actually; nothing.

      I often wonder why these later versions don’t get as much love as the cb750K0-6 versions. I know they look different, but still a super good looking ride and they perform well. When new, their reputation was sliding. Kawasaki and others were well caught up and their bikes were easily outperforming the Honda cb750. The introduction of the cb750F bikes and the GL1000 didn’t help much either. But hey, nobody today buys a cb750 if they want the fastest bike on the planet? My K8 was actually the first SOHC cb750 I bought, probably +35 years ago, so definitely the bike I’ve had the longest.
     Several years ago, my buddy Gary and I restored three of them over a winter. We had a pair of well used K8’s so I snapped up the K7 when I spotted it on somebody’s lawn, thinking we might need parts. I played around with it for one afternoon (the tank and idle jets were plugged solid) and it ran so well we decided to do it too. Frames went to the powder coater and we started from scratch.
       We sent all three sets of carbs to Mike Nixon who returned them back looking and performing “better than new”. My K8 had an annoying head gasket leak, so I pulled off the top end. I think I did pistons and rings and recall the guides were shot too, so valves as well. I had Lester Wheels on mine, so we found some for Gary’s. Everything got cleaned, polished and painted and they turned out really well. Not long afterwards, I stumbled on a K3 (I needed a pre’74 for the first Ganaraska 250 event) and the K1 I’m still riding, so the K8 barely got “broken in”, then mothballed to the back of the shop.
       Thinking about this today, I’ve developed a NEW PLAN. One day, if I actually ever “thin the herd” without immediately buying another project, I’ll sell off the more desirable bikes and keep my K8. I might have been ignoring my favorite bike for a bit too long?

P.S. My son says I’m full of sh1t. He figures he’ll still have to clear out +10 bikes when I’m gone. Hopefully, he’s right!
   

[BenelliSEI]

And another good reason to keep it? Explain why I can buy a lovely reproductions set of pipes for this bike (we got a set for Gary’s) for HALF the price of the earlier pipes?

[denward17]

I don't know other than the size of the gas tank, but I've grown to love mine after it has been refreshed, nice riding bike.

[madmtnmotors]

Nothing wrong with mine either:

[BenelliSEI]

Great! I’m in your club.

[BenelliSEI]

I don't know other than the size of the gas tank, but I've grown to love mine after it has been refreshed, nice riding bike.

Den…. Think it’s too bulky?

[denward17]

I don't know other than the size of the gas tank, but I've grown to love mine after it has been refreshed, nice riding bike.

Den…. Think it’s too bulky?

For me, viewing from the side, the sharp angle where it goes in toward the neck, and the hump just over the fuel cap.

[seanbarney41]

Nothing wrong with mine either:

I just got a K7 running that has been sitting since 1997, although it had been stored well.  Still, the carbs needed cleaning.  I didn't have any success working with the PD carbs until this bike.  I am utterly flabbergasted.  This thing effing rips.  Just an RC 4 into 1 that sounds so tastefully brutal...or did a cam get snuck in there when the chrome valve cover got installed back in the day?  Sure idles nice.  I viewed the piston tops with a borescope and they looked stock?  I dunno...one of the rippingest sohc's I have ridden.  K7/8's are certainly underated...

...yeah, the gas tank shape s probably my least favorite thing about the bike too

[PeWe]

Good idea to sell the higher valued bikes if you get your money back plus more.

Ride your favourite bike.

I should not sell my K6 even if I should get the money back. It is not stock so value will be lower despite it is improved.
I have too many memories with it starting in 1979.

[gearsoup]

I have too many memories with it starting in 1979.

I as born in '79.... 

[beemerbum]

A more comfortable ride than my K1 or K2. One gripe: The side cover needs pulling off to check oil. Keep those grommets lubed

[BenelliSEI]

A more comfortable ride than my K1 or K2. One gripe: The side cover needs pulling off to check oil. Keep those grommets lubed

Nice to hear, I agree. My K7 has the best seat. It still a “log” I can move around on. The K8 is more of a saddle and restrictive, still very comfortable.

[beemerbum]

When I got the K7, it sported this abomination. I lucked out getting a near new K8. seat on eBay for a great price.

[69cb750]

I often wonder why these later versions don’t get as much love as the cb750K0-6 versions

When the CB750 came out in 69 it was smooth, powerful, reliable, better then what Harley, Triumph, Norton, BSA were selling.
The early bikes are desirable because of what they were in those years.
When the z1 and gs750 arrived the CB750 lost the prestiege it had.

[BenelliSEI]

My K8 was two years old when purchased by the first owner. I think he paid Cdn.$1200 for it. The dealer wanted it out of the showroom!

[grcamna2]

John,I know what's wrong with your cb750K8.
It needs to be ridden more 

[BenelliSEI]

John,I know what's wrong with your cb750K8.
It needs to be ridden more 

….so true!

[HondaMan]

The general 'buzz' we heard from the Honda reps in those days was:
1. The pipes were called 'ugly' in a cycle magazine (I think it was Motorcycling, British rag).
2. The K7/8 and F2/3, when fitted with the Vetter that decorated more than half of the 750s sold in the shops where I worked, reflected the extra 850 RPM into the rider's face on long, boring 55 MPH interstate rides.
3. After about 9k-10k miles, the K7 (in particular) started oozing oil out the header pipes because the valve guides were wearing out already They had been changed to simple cast-iron guides somewhere along the K3 model, but the more aggressive cam and leaner carbs of the later bikes (and higher RPM for a given touring speed) seemed to wear the guides quickly. The bike being [mis]labelled to use 10w40 oil helped speed up this wear. This latter item was an American Honda arrogance issue, not a design problem...
4. The K8 was labelled 'cold blooded' right from the start, due to the lean-burn PD42b carbs' idle circuit. The K7 wasn't as lean and didn't suffer it as much.
5. From several customers: "Why did they make that inefficient front brake SMALLER?".

Those were the things that were 'burned into memory' that I remember, despite being [still] in love with the breed, myself.

The K7/8 has more front trail for a steadier ride than the first chassis, smoother and more linear throttle response (when the accelerator pump is working right), more 'guts' in 3rd gear when riding in city traffic, and runs cooler than the F2/3 - if 20w50 oil is used. They are quite sensitive, however, to having the little carb bowl vent air vent hose removed (or misplaced on its end: some have 2, some have 1) at modern hiway speeds (80+ MPH here): if it is missing and you are on a freeway at 70+ MPH speeds in a crosswind, the bike will mysteriously drop HP when the air over the end of the bowl-vent is significantly disturbed, like from the side. For that reason, more than one of them got a 'bottle' of one kind or another added onto the end of the hose: I used pill bottle with a snug hole drilled into the cap for the hose and 4 smaller holes drilled around the bottle, extending the hose to fit in between the oil tank and the battery box. This was first trouble-shot using a Vetter fairing with Lowers: with the Lowers on the bike was more than 10 MPH faster (top speed) than without. The Pill Bottle Booster (as it got dubbed) solved the problem with or without the lowers, and the bike liked losing the Lowers on hot days (this was done in Colorado, at 6000 feet altitude: your results might vary?).

Today, judging from the comments I get about rebuilding their carbs, they suffer lower opinions because of the difficulty in rebuilding the PD carbs instead of the simpler roundtops. The PD carbs do make for cleaner sparkplugs than the roundtops, though.

[willbird]

When I got the K7, it sported this abomination. I lucked out getting a near new K8. seat on eBay for a great price.

the sickest part of that seat is that somebody wanted it, bought and installed it, and loved having it lol

Bill

[willbird]

The general 'buzz' we heard from the Honda reps in those days was:
1. The pipes were called 'ugly' in a cycle magazine (I think it was Motorcycling, British rag).
2. The K7/8 and F2/3, when fitted with the Vetter that decorated more than half of the 750s sold in the shops where I worked, reflected the extra 850 RPM into the rider's face on long, boring 55 MPH interstate rides.
3. After about 9k-10k miles, the K7 (in particular) started oozing oil out the header pipes because the valve guides were wearing out already They had been changed to simple cast-iron guides somewhere along the K3 model, but the more aggressive cam and leaner carbs of the later bikes (and higher RPM for a given touring speed) seemed to wear the guides quickly. The bike being [mis]labelled to use 10w40 oil helped speed up this wear. This latter item was an American Honda arrogance issue, not a design problem...
4. The K8 was labelled 'cold blooded' right from the start, due to the lean-burn PD42b carbs' idle circuit. The K7 wasn't as lean and didn't suffer it as much.
5. From several customers: "Why did they make that inefficient front brake SMALLER?".

Those were the things that were 'burned into memory' that I remember, despite being [still] in love with the breed, myself.

The K7/8 has more front trail for a steadier ride than the first chassis, smoother and more linear throttle response (when the accelerator pump is working right), more 'guts' in 3rd gear when riding in city traffic, and runs cooler than the F2/3 - if 20w50 oil is used. They are quite sensitive, however, to having the little carb bowl vent air vent hose removed (or misplaced on its end: some have 2, some have 1) at modern hiway speeds (80+ MPH here): if it is missing and you are on a freeway at 70+ MPH speeds in a crosswind, the bike will mysteriously drop HP when the air over the end of the bowl-vent is significantly disturbed, like from the side. For that reason, more than one of them got a 'bottle' of one kind or another added onto the end of the hose: I used pill bottle with a snug hole drilled into the cap for the hose and 4 smaller holes drilled around the bottle, extending the hose to fit in between the oil tank and the battery box. This was first trouble-shot using a Vetter fairing with Lowers: with the Lowers on the bike was more than 10 MPH faster (top speed) than without. The Pill Bottle Booster (as it got dubbed) solved the problem with or without the lowers, and the bike liked losing the Lowers on hot days (this was done in Colorado, at 6000 feet altitude: your results might vary?).

Today, judging from the comments I get about rebuilding their carbs, they suffer lower opinions because of the difficulty in rebuilding the PD carbs instead of the simpler roundtops. The PD carbs do make for cleaner sparkplugs than the roundtops, though.

My dad used Standard Oil Sohio “QVO” 10W40 in everything including my K2 from the day it was new. older cars bought used he used a bulk 10w40 we bought in square metal 5 gallon cans from Andersons farm store in maumee, Oh. the K2 has 55857 miles on it yesterday. had head off about 45k and valve seats were still perfect, I did not know enough to check guides, exhaust guides of course do not have seals that year

Bill

[PeWe]

Strange that the K8 stock seat was not comfy enough, replaced it with a 2 seat sofa!

[willbird]

Strange that the K8 stock seat was not comfy enough, replaced it with a 2 seat sofa!

only thing I can think was their *ss got cold a lot before they bought that seat

[newday777]

Strange that the K8 stock seat was not comfy enough, replaced it with a 2 seat sofa!

only thing I can think was their *ss got cold a lot before they bought that seat

Actually the thing that drove those seat sales back in the 70s were for the Queen's comfort and for those that toured long distance. Not unlike the goldwing and HD seat sales of today. Everyone has a different butt and different comfort ratings for their butts.

[willbird]

Strange that the K8 stock seat was not comfy enough, replaced it with a 2 seat sofa!

only thing I can think was their *ss got cold a lot before they bought that seat

Actually the thing that drove those seat sales back in the 70s were for the Queen's comfort and for those that toured long distance. Not unlike the goldwing and HD seat sales of today. Everyone has a different butt and different comfort ratings for their butts.

So....are you trying to tell me there is an *ss for every seat :-).

[HondaMan]

The general 'buzz' we heard from the Honda reps in those days was:
1. The pipes were called 'ugly' in a cycle magazine (I think it was Motorcycling, British rag).
2. The K7/8 and F2/3, when fitted with the Vetter that decorated more than half of the 750s sold in the shops where I worked, reflected the extra 850 RPM into the rider's face on long, boring 55 MPH interstate rides.
3. After about 9k-10k miles, the K7 (in particular) started oozing oil out the header pipes because the valve guides were wearing out already They had been changed to simple cast-iron guides somewhere along the K3 model, but the more aggressive cam and leaner carbs of the later bikes (and higher RPM for a given touring speed) seemed to wear the guides quickly. The bike being [mis]labelled to use 10w40 oil helped speed up this wear. This latter item was an American Honda arrogance issue, not a design problem...
4. The K8 was labelled 'cold blooded' right from the start, due to the lean-burn PD42b carbs' idle circuit. The K7 wasn't as lean and didn't suffer it as much.
5. From several customers: "Why did they make that inefficient front brake SMALLER?".

Those were the things that were 'burned into memory' that I remember, despite being [still] in love with the breed, myself.

The K7/8 has more front trail for a steadier ride than the first chassis, smoother and more linear throttle response (when the accelerator pump is working right), more 'guts' in 3rd gear when riding in city traffic, and runs cooler than the F2/3 - if 20w50 oil is used. They are quite sensitive, however, to having the little carb bowl vent air vent hose removed (or misplaced on its end: some have 2, some have 1) at modern hiway speeds (80+ MPH here): if it is missing and you are on a freeway at 70+ MPH speeds in a crosswind, the bike will mysteriously drop HP when the air over the end of the bowl-vent is significantly disturbed, like from the side. For that reason, more than one of them got a 'bottle' of one kind or another added onto the end of the hose: I used pill bottle with a snug hole drilled into the cap for the hose and 4 smaller holes drilled around the bottle, extending the hose to fit in between the oil tank and the battery box. This was first trouble-shot using a Vetter fairing with Lowers: with the Lowers on the bike was more than 10 MPH faster (top speed) than without. The Pill Bottle Booster (as it got dubbed) solved the problem with or without the lowers, and the bike liked losing the Lowers on hot days (this was done in Colorado, at 6000 feet altitude: your results might vary?).

Today, judging from the comments I get about rebuilding their carbs, they suffer lower opinions because of the difficulty in rebuilding the PD carbs instead of the simpler roundtops. The PD carbs do make for cleaner sparkplugs than the roundtops, though.

My dad used Standard Oil Sohio “QVO” 10W40 in everything including my K2 from the day it was new. older cars bought used he used a bulk 10w40 we bought in square metal 5 gallon cans from Andersons farm store in maumee, Oh. the K2 has 55857 miles on it yesterday. had head off about 45k and valve seats were still perfect, I did not know enough to check guides, exhaust guides of course do not have seals that year

Bill

Yep, most of the K2 bikes got Stellite valve guides (like mine), which survived even 10w40 oils.  After about 3/72 production the Stellite disappeared, becoming cast iron. Since Honda regularly re-cycled heads (and other parts) that had some defect or other in production the Stellite guides pop up here and there in later engines, but on the whole it vanished until the F0, then vanished again.

In the later bikes the increased detergent in oils made after 1976 became quite an issue. After a hiway run you could pull the dipstick and find up to 1" of foam in the oil tank (Pennzoil, Quaker State). This was not good...