Topic: CB750 F2 carbs on early CB750's are "the oil" mate, ha ha!

[Terry in Australia]

I thought I'd post this, I've been having all sorts of drama's with the slide carbs on my K1, so after I (eventually) determined that the high RPM miss was caused by some kinda blockage, (see Honda Man's transistorized ignition post, he explains what's the problem with them, he really is a "Wizard", ha ha) I decided to fit a set of F2 carbs, because, even when the OEM K1-K6, F/F1 carbs are at their optimum, they're still pretty average, in my opinion.

Here's what parts I needed to do the "conversion":

F2/F3 carbs with 110 main jetss, rather than the standard 105's (K7/K8 carbs will work too, they're pretty much the same and they come with 110 mains)
K7/K8 inlet rubbers (F2/F3 rubbers are too big ID at the head end)
F2/F3 cables (throttle cables and choke cable)
F2/F3 airbox (K7/K8 should be ok too)
F2/F3 or K7/K8 choke bracket (ground/filed to fit)
a new piece of fuel line and a new in line filter, and
a bolt and hose clip to block off your second fuel outlet, if you have a dual outlet petcock.

It's all a "bolt up" fit, and as you can see from the pics, it all fits without any clashes. The benefit of this conversion for me was much better accelleration with no "flat-spots" anywhere in the rev-range, and I can just twist that throttle and rocket off into the distance, rather than wait for the engine to catch up, as I do with the stock K1-K6 carbs.

I saw 100 Mph in 3rd gear @ approx 9000 RPM momentarily, before I remembered that I need my license for my continued employment. (with the 16 inch back wheel and 140/80 - 16 tire I'm running 18/43 gearing, which is a tad high, but may account for the rather high speed reading this morning) It'll be interesting to compare it to a stock K series bike (my engine is standard, rebuilt in January with just 2nd oversize pistons/rebore and Dyna S ignition and 3 ohm Dyna coils) in similar condition, to see if there's any real performance gains with this conversion. Cheers, Terry.

   

[bryanj]

Nice idea Terry, only problem is the lack of carb sets out there and the pushed in pilot jet!

[eurban]

Lack of carbs sets??  Honda made a bazillion cb750s in 77 and 78 (doesn't need to be the F model ones) and there seems to be an abundance of people out there who think that these "emissions" carbs are too much of a pain to work on and hurt performance.  I bet your could get them easily for cheap!  Oh, and Push . . . .Pull.

[Terry in Australia]

Yeah, I just looked on Ebay and there are currently 5 sets of K7/K8-F2/F3 carbs ranging from 9.99 to 124.99 (dreamer!) with no bids on them yet Bryan, so I doubt if that will be a problem, and the push in pilot jet comes out "easy-peasy" with a pair of vice grips, I had my pilot jets out, cleaned, and back in in minutes.

Only thing I didn't do was look at my manual and adjust the mixture screws to 1.5 turns out, they're on 2 turns out at the moment, but luckily another great SOHC4 member here, Sean Condon, sent me one of those fancy right angle screw-drivers for just that purpose, so I'll do that today, before I go for another ride, it's cooler today, only about 80 deg F as I type this at 0950, so it should be great ride, ha ha! Cheers, Terry. 

[mrbreeze]

I thought I'd post this, I've been having all sorts of drama's with the slide carbs on my K1, so after I (eventually) determined that the high RPM miss was caused by some kinda blockage, (see Honda Man's transistorized ignition post, he explains what's the problem with them, he really is a "Wizard", ha ha) I decided to fit a set of F2 carbs, because, even when the OEM K1-K6, F/F1 carbs are at their optimum, they're still pretty average, in my opinion.

Here's what parts I needed to do the "conversion":

F2/F3 carbs with 110 main jetss, rather than the standard 105's (K7/K8 carbs will work too, they're pretty much the same and they come with 110 mains)
K7/K8 inlet rubbers (F2/F3 rubbers are too big ID at the head end)
F2/F3 cables (throttle cables and choke cable)
F2/F3 airbox (K7/K8 should be ok too)
F2/F3 or K7/K8 choke bracket (ground/filed to fit)
a new piece of fuel line and a new in line filter, and
a bolt and hose clip to block off your second fuel outlet, if you have a dual outlet petcock.

It's all a "bolt up" fit, and as you can see from the pics, it all fits without any clashes. The benefit of this conversion for me was much better accelleration with no "flat-spots" anywhere in the rev-range, and I can just twist that throttle and rocket off into the distance, rather than wait for the engine to catch up, as I do with the stock K1-K6 carbs.

I saw 100 Mph in 3rd gear @ approx 9000 RPM momentarily, before I remembered that I need my license for my continued employment. (with the 16 inch back wheel and 140/80 - 16 tire I'm running 18/43 gearing, which is a tad high, but may account for the rather high speed reading this morning) It'll be interesting to compare it to a stock K series bike (my engine is standard, rebuilt in January with just 2nd oversize pistons/rebore and Dyna S ignition and 3 ohm Dyna coils) in similar condition, to see if there's any real performance gains with this conversion. Cheers, Terry.

   

Wow Terry.....thats some shiny paint on the oil tank cover. I can see your reflection in there!!!!

[Hockers Choppers]

Yeah, looks like you've got an idea about something.....OoPps, I guess thats the reflection off your head, My bad....

[Terry in Australia]

Ah, you guys are too kind, that's just an old pair of side covers that some "knob-head" filled in the badge recesses, so I gave them both a quick coat of Subaru Metallic Black 2k with a couple of coats of 2k clearcoat, and that's how they came out, "straight off the gun", I'm not into polishing, ha ha! Cheers, Terry.

[HondaMan]

Looks pretty Wizard-y to me, Terry.   

Here's a tip I forget to mention: when that popular keyswitch adapter (on the handlebars) appeared, we sold LOTS of keyswitches, due to fractured wires from the moving handlebars. Honda's original idea (burn your fingers while fumbling for key) never impressed me, either. But, I did find a "sweet spot" that is directly across from the fuel petcock, on the left side, under the tank, that will let you locate the key there with no moving wires.

But, I wonder: does this spot disappear with those (tempting) nice pump-equipped carbs?

P.S. - Still don't have the ignition yet? 

[chung]

DAMN Terry, 18/43? I've always called 18/48 "Bonniville gearing"

I guess I'll add 18/43 as "Oz Gears" You lucky bastard, room to use high gear

Better wear a helmet to protect you hair. LOL

[Terry in Australia]

Looks pretty Wizard-y to me, Terry.   

Here's a tip I forget to mention: when that popular keyswitch adapter (on the handlebars) appeared, we sold LOTS of keyswitches, due to fractured wires from the moving handlebars. Honda's original idea (burn your fingers while fumbling for key) never impressed me, either. But, I did find a "sweet spot" that is directly across from the fuel petcock, on the left side, under the tank, that will let you locate the key there with no moving wires.

But, I wonder: does this spot disappear with those (tempting) nice pump-equipped carbs?

P.S. - Still don't have the ignition yet? 

G'Day Mark, I just got home from work, and guess what was in my mailbox? Woo-hoo! I'll post something on your ignition thread shortly..

Re: the relocated switch, this one is really interesting, it's a NOS "Kit" that came with what appears to be an OEM switch (certainly the keys are genuine Honda) but the harness is longer than the one on my K2 key switch, so I don't know whether it came from the Honda factory like that, or whether the aftermarket "kit" supplier in the US made up another longer harness?

It certainly is a bit more "user friendly" above the tank than the OEM position, and due to our warm climate here in the land of Oz, gloves are optional, so there's not much protection from hot cylinder heads and header pipes for delicate Aussie fingers like mine, ha ha! Cheers, Terry.

DAMN Terry, 18/43? I've always called 18/48 "Bonniville gearing"

I guess I'll add 18/43 as "Oz Gears" You lucky bastard, room to use high gear

Better wear a helmet to protect you hair. LOL

Yeah mate, 18/43 seems really high, funny thing is that in 5th gear at 4000 RPM running the 16 inch rim and 140/80 tire, it's doing only 65 Mph? Now with an 18 inch rear rim, 120/90 tire, and 18/48 gearing, my K2 is doing 60 Mph at the same RPM?

But it does feel high, not really sluggish, but I do feel the need to change down a gear when passing in 5th gear below say, 5000 RPM? Don't get me wrong, it'll still pull ok from 4000 RPM in top gear, but if I drop it down a gear and "give it the berries", it takes off like a scalded cat!

I did try it with 18/48 gearing, but from memory it was a tad low, at about 5000 RPM at 60 Mph in 5th, so I might first try 17/43, (because I've got a nice new 17 tooth sprocket in a box somewhere) which would roughly equate to 18/45, and hopefully it'll give it a little more "pep" without too many extra RPM's, as much as this engine really loves to rev, I try to control my "manly urges" and cruise at (semi) legal speeds for the most part, ha ha! Cheers, Terry.      

[dpen]

No sense of adventure you blokes.

What's an ignition switch?

I don't need idiot lights so the light panel on the K7 has become a nifty switch panel for ignition & lights (with a hidden switch elsewhere of course)

On the carbie subject, I picked up a set of K7/8/F carbs complete, ready to bolt on for $A40

They're a pretty regular item on ebay