Author Topic: General "improvement" tips for the 1970s inline four engines.  (Read 3691 times)

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Offline HondaMan

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General "improvement" tips for the 1970s inline four engines.
« on: February 09, 2006, 08:41:22 PM »
Okay, you've paid off Christmas and it's been too long since it was warm enough to ride, and you're planning for next season. Wanna ride faster or get better MPG this year? Here's some [higher-dollar] tips for those of you who want to "get into it"...  ;)

1. All inline fours have this in common: crummy metal holding the cylinders together. As a result, after about 5,000 miles of running, the bores are no longer parallel, nor are they round. Power is lost, almost 10% by our 1970 rear-wheel dyno tests. To fix this, have the cylinders bored one oversize from where you are now, and tell the machine shop to make sure they are in parallel. They "wander" as much as .010", in my experience. Simply boring one oversize and refitting recovers all that power again.

2. All Honda gearboxes have this in common: their teeth are hog-cut. These tiny steps on the faces of the gear teeth rob a considerable amount of power and smoothness from the crankshaft. Aside from a LOT of hand polishing work, you can do this: remove the gearshafts and spacers, bearings and shift forks. Apply lapping compound (like for valves) to the face of the teeth and set the shafts into V-blocks that are spaced like the crankshaft. Load the mainshaft shaft with a soft piece of pine wood (clamped onto the shaft) and turn the countershaft by means of the countersprocket, sliped onto the shaft in its normal place. Do this until you're bored to tears, and you'll soon see shiny spots on the teeth of the gears where they mesh. This will transfer as much as 10% more power through the gearset to the countersprocket. Now, clean them like your life depended on it, then dip everything into 20w50 oil and reassemble.

3. In the heads: all of the inline fours except the 400-4 had breathing issues. Grinding a "pocket" above the intake valve(s) and matching the ports to the carb tubes will improve them, especially at high RPM. Polishing the intake valve(s) helps, too. Don't back-cut the intake valves or you'll pop off a valve head - an expensive day, at best. (Backcutting exhaust valves will make them burn, and quickly - the CB650 malady). Trim (narrow) the intake valve guide bosses for a smaller profile, and polish it. Smooth, but don't polish, the intake tract. If you're good at heliarcing, raise a bead about .100" high along the bottom of the intake ports (CB750 only) in a half-moon shape, then smooth it off along the sides so it "restricts" (apparently) the bottom passageway about 1/3 of the way around. The floor of the port should ramp up to it, then be fairly abrupt in fall-off on the valve side. Do this at the point where the intake track bends down toward the valve (no, it's not easy). Although not obvious, this mod creates some "free turbocharging" at RPM above 6000, all the way to 16000 (lots of work), which deals more with fluid dynamics than I will put into this post.

4. Jetting. ALL of the inline fours came rich from the factory. At sea level, we started with a 10 size less than what it came with. Here in Colorado, it's not unusual to drop a 30 size main jet. The jet needles are almost always set too high (except the 500/550, too low). The cutaways on the slides were close for sea level, too low for high altitude by about .030". My 750K2 runs at 20 less than stock for general cross-country touring.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline scunny

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #1 on: February 09, 2006, 08:52:36 PM »
OK HondaMan, you have got me worried now (650 owner). What's this about 650 exhaust valves ? and should I do something since I'm rebuilding the motor.
cheers
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Offline ericstew

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #2 on: February 10, 2006, 04:41:16 AM »
Hi,
While you're stripping down the engine,you can change all the gearbox bearings (which are low quality)to high standart ones.My friend from SKF told me they have bearings which are made by measuring each internal parts in order to get less resistance possible...To him,I can get +200/300 rpm  on the stock 750 engine(?)
Anyway,he says that a set of new regular bearing is allready a good improvment as the quality exceed those made 30 years ago.
Any other tips?
cb 750 k2 950SS2 Japauto
cb 750 k6 1000VX Japauto
cb 750 F1 "cafe racer"
cb 750 k3 "cafe racer"
cb 750 k2
cb 750 k7 "cafe racer"

Offline eurban

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #3 on: February 10, 2006, 06:50:17 AM »

4. Jetting. ALL of the inline fours came rich from the factory. At sea level, we started with a 10 size less than what it came with. Here in Colorado, it's not unusual to drop a 30 size main jet. The jet needles are almost always set too high (except the 500/550, too low). The cutaways on the slides were close for sea level, too low for high altitude by about .030". My 750K2 runs at 20 less than stock for general cross-country touring.

Hey Hondaman-  I was under the impression that  with the increasingly strict emmissions requirements that Honda was forced to lean out the carb specs particularly towards the end of the SOHC 750s run.  Certainly a few period magazine reviews that I have read complained that the emmissons compromises made in the mid years (maybe 75/76)  lead to poorer engine performance.  Perhaps this was BS? I also thought that Honda introduced the accelerator pump style carb so that they could both lean out their mixtures to meet regs while keeping performance decent.  . . . With the stock airbox my 78K seemed pretty cold blooded but ran fairly well otherwise.  I honestly think that the #35 idle jets that are stock on the last 750s are just barely large enough. . . .
Dont get me wrong, I think that alot of people simplistically  assume that richening up the carb specs is the ticket to better performance.   I'm just a bit suprised that you found the carb settings to be so consistently rich as this seems contrary to the influences of the emissions regs.  Basically, why wouldn't Honda have made these changes themselves? 
« Last Edit: February 10, 2006, 06:56:45 AM by eurban »

eldar

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #4 on: February 10, 2006, 08:24:25 AM »
Well you must remember that these engines were designed and made in japan. Japan is barely above sealevel. So as you get to higher altitudes, you will need to rejet. This was common on older cars as well. Honda did lean things out and while the 77-78 are a bit more cold blooded, especially the 78, I prefer it that way. If you must though, you can tap the carbs to accept different low speed jets. I must also wonder though how much of this applies to the later 750s anyways.

Offline volz1fsu

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #5 on: February 10, 2006, 01:04:39 PM »
2. All Honda gearboxes have this in common: their teeth are hog-cut. These tiny steps on the faces of the gear teeth rob a considerable amount of power and smoothness from the crankshaft. Aside from a LOT of hand polishing work, you can do this: remove the gearshafts and spacers, bearings and shift forks. Apply lapping compound (like for valves) to the face of the teeth and set the shafts into V-blocks that are spaced like the crankshaft. Load the mainshaft shaft with a soft piece of pine wood (clamped onto the shaft) and turn the countershaft by means of the countersprocket, slipped onto the shaft in its normal place. Do this until you're bored to tears, and you'll soon see shiny spots on the teeth of the gears where they mesh. This will transfer as much as 10% more power through the gearset to the countersprocket. Now, clean them like your life depended on it, then dip everything into 20w50 oil and reassemble.

I want to hear more about this, I don't quite understand what to do.  How would the marks at the end of the teeth have anything to do with the contact points on the faces? Pictures would be good.

Offline n9viw

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #6 on: February 10, 2006, 01:51:08 PM »
I think that one is about a moot point for most of our machines, now that they have 30+k miles on them. It may have been an issue when they were new, but I would be willing to bet the trans gears in all my bikes, even the '83 CB550 Nighthawk, have shiny faces.
Interesting to note about the cylinders, though- I doubt most machine shops would be set up to measure something like this. Where could a person go to have this checked out?
Nick

'76 Honda CB550k
'73 Honda CB750k

cd811

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #7 on: February 10, 2006, 06:59:30 PM »
not trying to pop bubble or stir #$%*...I think this is the same guy who talked about how to improve clutch by drilling holes(which sounded really good), but would not respond to questions :o

of course I could be wrong :-[
« Last Edit: February 10, 2006, 07:01:07 PM by cd811 »

upperlake04

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #8 on: February 10, 2006, 07:14:24 PM »
Hey - leave Hondaman alone -  he's us newbys hero ;D   check his post 'Clutch Hub Modifications' from Feb5

Offline cbjunkie

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #9 on: February 10, 2006, 07:26:47 PM »
more reading...less posting. that's MY new motto...

 :-X :-X :-X
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cd811

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #10 on: February 10, 2006, 09:21:36 PM »
hey thanks upperlake...I missed that...I was wanting those pics and info bad ;D

hey junkie...800plus post...less posting????...right ;D

kaysystems

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #11 on: February 11, 2006, 04:44:46 AM »
Great post HondaMan

Are you suggesting to replace the Main Jet and the idle jet? How much smaller on the idle jet?

Thanks

David


Offline HondaMan

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #12 on: February 15, 2006, 06:52:27 PM »

4. Jetting. ALL of the inline fours came rich from the factory. At sea level, we started with a 10 size less than what it came with. Here in Colorado, it's not unusual to drop a 30 size main jet. The jet needles are almost always set too high (except the 500/550, too low). The cutaways on the slides were close for sea level, too low for high altitude by about .030". My 750K2 runs at 20 less than stock for general cross-country touring.

Hey Hondaman-  I was under the impression that  with the increasingly strict emmissions requirements that Honda was forced to lean out the carb specs particularly towards the end of the SOHC 750s run.  Certainly a few period magazine reviews that I have read complained that the emmissons compromises made in the mid years (maybe 75/76)  lead to poorer engine performance.  Perhaps this was BS? I also thought that Honda introduced the accelerator pump style carb so that they could both lean out their mixtures to meet regs while keeping performance decent.  . . . With the stock airbox my 78K seemed pretty cold blooded but ran fairly well otherwise.  I honestly think that the #35 idle jets that are stock on the last 750s are just barely large enough. . . .
Dont get me wrong, I think that alot of people simplistically  assume that richening up the carb specs is the ticket to better performance.   I'm just a bit suprised that you found the carb settings to be so consistently rich as this seems contrary to the influences of the emissions regs.  Basically, why wouldn't Honda have made these changes themselves? 

Much of this had to do with Hond'a "philosophy". They persistently portrayed themselves as "moderate rider" types, while trying to keep their warranty costs down and image up. Bikes were not "cool" in the 1960s and 1970s like they are now. Performance was not really their big marketing drive: that belonging to Kawi.
The acceleration pumps were a necessary addition when the 'leaning out' got to the point where jerking the throttle open could stall the rider in traffic. This was a BIG problem on the CB550 and 750 K4. Honda was trying to help improve the MPG situation while paying less for warranty sparkplugs (there were some threatened lawsuits over plug fouling issues, but I don't know how far they got). Our shop gave a lot of plugs away during the 12-month warranty periods. The biggest problems seemed to be that the intake tracts on ver head were cast differently. So, the jetting in production must have been a headache for their engineers. Going rich made them run better in the humid sealevel Japan, but in drier climes it was an issue.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #13 on: February 15, 2006, 06:54:01 PM »
2. All Honda gearboxes have this in common: their teeth are hog-cut. These tiny steps on the faces of the gear teeth rob a considerable amount of power and smoothness from the crankshaft. Aside from a LOT of hand polishing work, you can do this: remove the gearshafts and spacers, bearings and shift forks. Apply lapping compound (like for valves) to the face of the teeth and set the shafts into V-blocks that are spaced like the crankshaft. Load the mainshaft shaft with a soft piece of pine wood (clamped onto the shaft) and turn the countershaft by means of the countersprocket, slipped onto the shaft in its normal place. Do this until you're bored to tears, and you'll soon see shiny spots on the teeth of the gears where they mesh. This will transfer as much as 10% more power through the gearset to the countersprocket. Now, clean them like your life depended on it, then dip everything into 20w50 oil and reassemble.

The hog-cut teeth don't engage well and lose torque while they rotate. Smoothing the faces transfers torque better.
I want to hear more about this, I don't quite understand what to do.  How would the marks at the end of the teeth have anything to do with the contact points on the faces? Pictures would be good.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #14 on: February 15, 2006, 06:55:09 PM »
not trying to pop bubble or stir #$%*...I think this is the same guy who talked about how to improve clutch by drilling holes(which sounded really good), but would not respond to questions :o

of course I could be wrong :-[

Check again, CD -- I tried to post pix, but ended up only being able to install links. They're in the forum, somewhere.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #15 on: February 15, 2006, 07:02:03 PM »
Great post HondaMan

Are you suggesting to replace the Main Jet and the idle jet? How much smaller on the idle jet?

Thanks

David



Your picture looks like a K0. I'm jealous....
If you have a K0 or K1, use this rule-of-thumb if the pipes are original type (straight-thru with fiberglass) and the airbox is intact: reduce the jet size on the mains 1 number per 1000 feet above sea level. Drill out the emulsifier tubes toe .040" holes (see that post around here, somewhere). Also, on K0, lower the jet needle 1 notch, especially if you have the 4-cable throttle type: on those, you might need to go 2 notches if it's an early one. All of these, taken together, makes the off-line start a little smoother (helpful on greasy streets) and the midrange throttle response quicker.

On K2 and later with chambered mufflers, reduce the main 1/2 number per 1000 feet, or just drop it by 5 to start.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

cd811

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #16 on: February 16, 2006, 03:32:52 PM »
yea thanks hman...upper lake pointed them out for me...I missed that post...now that's helpful to me ....thanks ;) ;D

kaysystems

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #17 on: February 16, 2006, 03:58:25 PM »


Quote

Your picture looks like a K0. I'm jealous....
If you have a K0 or K1, use this rule-of-thumb if the pipes are original type (straight-thru with fiberglass) and the airbox is intact: reduce the jet size on the mains 1 number per 1000 feet above sea level. Drill out the emulsifier tubes toe .040" holes (see that post around here, somewhere). Also, on K0, lower the jet needle 1 notch, especially if you have the 4-cable throttle type: on those, you might need to go 2 notches if it's an early one. All of these, taken together, makes the off-line start a little smoother (helpful on greasy streets) and the midrange throttle response quicker.

On K2 and later with chambered mufflers, reduce the main 1/2 number per 1000 feet, or just drop it by 5 to start.
Quote

Thanks

Yes, that's a January 1970 K0, that I paid $1000.00 two years ago. Totally original, except for 3 of the pipes, which are 300s. The paint is really faded that doesn't show in the photo.
You replied to me about the emulsifiers before. Thanks. I ran with the needles 2 notches lower this summer and was still a bit rich. After cleaning the carbs this winter I will startt again & see how it runs.
Should I lower the needles & see how it runs before I drill out the emulsifiers, or start with the emulsifiers?

Slowly getting it into shape, as the servicing & cleaning was neglected and it sat for 20 years.

David

Offline HondaMan

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Re: General "improvement" tips for the 1970s inline four engines.
« Reply #18 on: February 16, 2006, 07:52:44 PM »
Wow. $1k. What a gem!

I would start with the emulsifiers, then the needles.

The paint fade was a real problem on the Fours until about the "F" models or so.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com