Topic: HELP!! about main jet sizes for my CB750 K8

[i2edman]

Hi everyone. Just need simple advice here. 'Need proper size main jets! I know it's an old topic. sorry
my spec.
1. 1978 CB750K
2. Stock internals and ignitions
3. PD42b Carbs. Mains 110's slows 35--stock carb setup
4. 4-2 exhaust baffled
--fuel screws turned out= x2 for now. runs good..fulls slightly okay..


HELP : Planning on installing Pods and baffles will be out. I'd like to create chaos around my neighborhood PLUS Livin' in L.A with all the idiot drivers who don't seemed to care joining your lane even if you are next to them..

125's or 130's too big?? and fuel screws settings anyone??


Thx in advance.

[SKTP]

is that the Cycle-X exhaust?

[climbingaz]

I'm a little confused.....if you are running stock size jets (which I believe are 110's) your bike should be running good as is.  If you plan to run pods, you'll probably want to go 115's or 120's but be warned - it gets tricky and time consuming jetting these things properly with pods.

[i2edman]

is that the Cycle-X exhaust?

Not sure what brand my exhaust are. I got them on ebay but it works for now.

[i2edman]

I'm a little confused.....if you are running stock size jets (which I believe are 110's) your bike should be running good as is.  If you plan to run pods, you'll probably want to go 115's or 120's but be warned - it gets tricky and time consuming jetting these things properly with pods.

when I first got the bike. it actually ran pretty lean from looking at the plugs plus too much heat from the headpipes with episodes of exhaust bogs..it over heated on me one point on the street good thing i had a small flat head screw and was able to turn the screws out a least 3 turns and it worked fine then...but now I decided to turn this bike into cafe styled with cool pods and willing to deal with pod issues.. so i plan to go bigger jet size plus i'll be taken out the baffles..i know my mid range velocity and few torgue will not be the same but I'm ready for that situation as well.

[climbingaz]

I'm a little confused.....if you are running stock size jets (which I believe are 110's) your bike should be running good as is.  If you plan to run pods, you'll probably want to go 115's or 120's but be warned - it gets tricky and time consuming jetting these things properly with pods.

when I first got the bike. it actually ran pretty lean from looking at the plugs plus too much heat from the headpipes with episodes of exhaust bogs..it over heated on me one point on the street good thing i had a small flat head screw and was able to turn the screws out a least 3 turns and it worked fine then...but now I decided to turn this bike into cafe styled with cool pods and willing to deal with pod issues.. so i plan to go bigger jet size plus i'll be taken out the baffles..i know my mid range velocity and few torgue will not be the same but I'm ready for that situation as well.

Have you cleaned the carbs yet?

[lucky]

So what happened? Are you gone?

[lucky]

I'm a little confused.....if you are running stock size jets (which I believe are 110's) your bike should be running good as is.  If you plan to run pods, you'll probably want to go 115's or 120's but be warned - it gets tricky and time consuming jetting these things properly with pods.

when I first got the bike. it actually ran pretty lean from looking at the plugs plus too much heat from the headpipes with episodes of exhaust bogs..it over heated on me one point on the street good thing i had a small flat head screw and was able to turn the screws out a least 3 turns and it worked fine then...but now I decided to turn this bike into cafe styled with cool pods and willing to deal with pod issues.. so i plan to go bigger jet size plus i'll be taken out the baffles..i know my mid range velocity and few torgue will not be the same but I'm ready for that situation as well.

Yes I bet it ran lean. QUOTE: "fuel screws 2 turns out"  LOL..lol
Make sure your accelerator pump and nozzles are working.
Before anything else.
Remove the air filter and with the engine off and the float bowls full look into the intake with a bright LED flashlight and turn the throttle. You should see a squirt of gas from the nozzle. Make sure that all 4 of them are working.

Stock air filter.
Exhaust 4 into 2.
Change to #120 main jets.
#42 idle jets. Push in style. Available at Sirius Consloidated.
Mixture screws 3/4 turn out.
You will be very close.

The stock air box and filter only has an opening 3.7 sQ inches! The four carbs
have a total intake area of 10.67 sq inches. The 1978 air box and filter act like a giant choke.

If you plan to use PODS I would get a set of 1977 CB750 needles first to make it easy on yourself.