Topic: 1978 cb750F factory jet numbers.

[waldowoc]

Can you guys tell me what jets originally came with my bike, '78 CB750F?
Also, any advise to tuning the bike for winter use, such as a better jet pairing, etc.?


Background: I am the third owner of this bike this summer. The original owner parked it in 2010 when he bought a new bike. He started collecting parts with plans of a full restore. He sold it earlier this summer a mutual friend, who was looking for a project bike, but decided he just didn't have the time or money and offered it to me.
By the time I got the bike, it was running, but "needs a tune up". All symptoms seemed to indicated it was sucking air. None of the pilot screws had any springs to hold them in, and it sounded like it was not properly synced. My friend told me he purchased a whole carburetor rebuild kit, but I haven't talked in depth about it yet to confirm part numbers and such.
Anyway, I decided to just start from scratch and learn as I go. The carburetor was a mess when I opened it up, lending a LOT of doubt to the competency of my friend on these matters. So, I have cleaned it all up, bench synced it, set the floats. I am currently waiting on new o-rings. In the mean time, I'd like to know if I have the correct jets. All rebuild kits have a 105 main, whereas I currently have #110 main with a #35 pilot. Other online sources indicate it should have #40 and/or #125 jets, with no distinction whether they are main, or pilot. That's three different sources indicating 3 different jets. Anyway I'm very confused about which jets would return the bike to original settings. If I can get to that point, then I can better diagnose any issues.
This is the first bike I have ever owned, and bought it for two reasons, 1. It was cheap enough that if I wreck it while learning to drive I wouldn't be out much, (I didn't by the way, turns out driving a motorcycle is way easy and fun); and 2. I'd like to commute to work with it this winter.

[750K]

With stock exhaust etc it should be 105 mains and 35 pilots, have a look at this chart.

http://www.hondachopper.com/garage/carb_specs/carb_specs.html

[madmtnmotors]

It was cheap enough that if I wreck it while learning to drive I wouldn't be out much

I went into this with the same philosophy. These are hardy machines and I have not been able to tear mine up yet...

and I've been trying for twenty-nine years! 

[flybox1]

if you're needing jets...dont buy 'kits'.  You'll be stuck with cheap aftermarket parts known to cause tuning issues.
Buy genuine Keihin jets at siriusconinc.com or jetsrus.com
all other 'soft parts' needed (orings, gaskets, etc.) can be purchased anywhere.

[waldowoc]

Thanks everybody, I'll go ahead and get those #105s ordered.

With stock exhaust etc it should be 105 mains and 35 pilots, have a look at this chart.

http://www.hondachopper.com/garage/carb_specs/carb_specs.html

Great! I've been reading forum after forum hoping to find this information. My bike is indeed the 4 to 1 stock exhaust.

Buy genuine Keihin jets at siriusconinc.com or jetsrus.com

Thanks for the advise, that is exactly what I plan to do. I just didn't know which ones I needed. I am also looking for pilot screw springs. I live 50 miles away from the nearest Honda shop, which means everything has to be ordered online.

These are hardy machines and I have not been able to tear mine up yet...

I have drove two bikes before buying this one. The first one, when I was about 11 years old (five or take a year) I took a wide turn through some tall grass, hidden in the grass, was barbed wire that snagged on the shifter and stripped it right out. That was the end of that bike. The second was a dirt racing bike I kept falling over on slow turns and stops.
This time YouTube exists, and I was able to watch videos on how to turn at both low and high speeds. Now that I understand that, the bike feels more like an extension of my body than anything else.

[flybox1]

Pilot jets dont have springs, but mixture screws do 

PM member harisuluv...he probably has some springs. 
He's the carb part/rebuild guru...

[Taelonorigin]

How do you set the floats in the carbs. When I try to do it on these cards I couldn't adjust the needle because there was no place to move the clip

[Stev-o]

Do you have the stock airbox and a clean air filter?

[flybox1]

How do you set the floats in the carbs.
Bend the float tang.  Float height should be the same as the top of the press-in pilot jet

When I try to do it on these cards I couldn't adjust the needle because there was no place to move the clip.
Washer 'shims' (M2.5 x 6mm x .5mm) are needed to make needle height adjustments.