Topic: Main jets 125's or 130's cb750k4

[killersoundz]

I'm trying to pick what size main jets I should order. I'm running pods (well going to be) either pods or velocity stacks with foam filters. And a straight 4 into 1 header. Right now I have 115 mains in with the needle clip moved up one clip from stock. I have to run the choke about 3/4 the way on for it to not lean out and misfire under WOT. It's ok through the midrange but it gets lean very quick. I'm wondering if I should order 125's or 130 mains. Don't really want to spend the money on both to try and looking for experienced advice.  Thanks

[flybox1]

both    order both. (they're cheap, and someone here would probably buy what you dont use)
you wont know which until you try them (I'd probably guess 130's)
I'd be more concerned with low and mid-range tuning, as most riding is done here.

[lucky]

Quote:
"I'm trying to pick what size main jets I should order. I'm running pods (well going to be) either pods or velocity stacks with foam filters. And a straight 4 into 1 header. Right now I have 115 mains in with the needle clip moved up one clip from stock. I have to run the choke about 3/4 the way on for it to not lean out and misfire under WOT. It's ok through the midrange but it gets lean very quick. I'm wondering if I should order 125's or 130 mains. Don't really want to spend the money on both to try and looking for experienced advice.  Thanks"

If the needle CLIP is moved up from stock then it is leaner than stock!
You move the clip DOWN to RAISE the needle thus richening the mixture.

With that set up you would want to lower the needle one notch from stock. What number are your carbs???

Others on this forum including myself have already figured this out and Brewsky (forum member) has kept very good records. We were working with the K8 but yours will be close.
BTW...tuning for stack or pods will be almost exactly the same.

Click on chart to enlarge.
There it is all laid out for you .

[Old Scrambler]

What about 120s...........have you checked the float levels.........WOT with the 1/4 -choke is effectively telling you that not enough fuel is getting to the pistons.....so LOWER the clip to raise the needle and make sure you have correct (or slightly high) fuel levels and good fuel flow from the tank to ALL carbs before going drastic on jets.........headers and pods usually support bigger jets than stock, but 125s and 130s are not always the answer if your running stock pistons and cam.

[talkingbird]

i have a set of 122 only screwed in and out once i'd sell you, shoot me an email if youre interested. cameronsblanchard@gmail.com

[killersoundz]

oh yeah sorry guys I did lower the needle clip one from stock. So the needle is higher. I did it the right way 

I do have my float levels set good. I exaggerated when I sad 3/4 choke. It's more like 1/2 choke from the riding I just did today.

[lucky]

oh yeah sorry guys I did lower the needle clip one from stock. So the needle is higher. I did it the right way 

I do have my float levels set good. I exaggerated when I sad 3/4 choke. It's more like 1/2 choke from the riding I just did today.

You need #42 idle jets for that set up to work right.

[killersoundz]

oh yeah sorry guys I did lower the needle clip one from stock. So the needle is higher. I did it the right way 

I do have my float levels set good. I exaggerated when I sad 3/4 choke. It's more like 1/2 choke from the riding I just did today.

You need #42 idle jets for that set up to work right.

Actually I bought carb rebuild kits and they came with 40's and 110's. I put the new 40's in but the carbs had 115 mains in I just cleaned those and left those in. I have the mixture screws out 1 turn and I have no popping on decel, maybe every once in a while but it seems perfectly fine on the low end. Maybe those 40's in the rebuild kit were a little bigger? I can't even start the bike with the choke on if that tells you anything

[Old Scrambler]

This sounds like more is wrong with fuel delivery to the carbs........or your slides are in backwards.......

[killersoundz]

This sounds like more is wrong with fuel delivery to the carbs........or your slides are in backwards.......

Nope she runs good mostly up until about 3/4 throttle then it leans out. Here's a video I made riding it around my neighborhood

CB750 SOHC Rebuild Ride Along Onboard camera

[DaveI]

I have a similar setup (pods and 4-1) and after doing a plug chop with 40 idles and 125 mains I was way rich. 118 mains seem to the the sweet spot for my 750k4 but the 120's were very close with the clip in the stock (mid) position

[lucky]

oh yeah sorry guys I did lower the needle clip one from stock. So the needle is higher. I did it the right way 

I do have my float levels set good. I exaggerated when I sad 3/4 choke. It's more like 1/2 choke from the riding I just did today.

You need #42 idle jets for that set up to work right.

Actually I bought carb rebuild kits and they came with 40's and 110's. I put the new 40's in but the carbs had 115 mains in I just cleaned those and left those in. I have the mixture screws out 1 turn and I have no popping on decel, maybe every once in a while but it seems perfectly fine on the low end. Maybe those 40's in the rebuild kit were a little bigger? I can't even start the bike with the choke on if that tells you anything

Weither or not you need the choke to start the bike has a lot to do with the outside air temperature. Some days you may not need the choke at all.

[scottly]

I'm trying to pick what size main jets I should order. I'm running pods (well going to be) either pods or velocity stacks with foam filters. And a straight 4 into 1 header. Right now I have 115 mains in with the needle clip moved up one clip from stock. I have to run the choke about 3/4 the way on for it to not lean out and misfire under WOT. It's ok through the midrange but it gets lean very quick. I'm wondering if I should order 125's or 130 mains. Don't really want to spend the money on both to try and looking for experienced advice.  Thanks

So what are you running now? Stock air-box, or open carbs with no filters or stacks? Don't base your future set-up on how your bike runs now. Fit the pods or stacks, then decide what jetting changes are needed.

[PeWe]

Why running the bike without filters?
It will be different settings with separate filters like KN style or OEM filter setup. Clean filter(s) make a difference compared with dirty too.

[killersoundz]

Hey guys I've had a chance to get to know my bike from riding it the past 2 weeks.

I got some cheap POD filters on it and honestly they made basically no difference from not having any filters.

To recap, it's a 74', with pods, straight 4 into 1 headers. 40 slow jet and 115 main. needle is up 1 notch from stock.

My idle jetting still seems ok. I have the mixture screws to 1.5 turns out. I tried 1 turn out and that was actually too rich that it would bog out and misfire when I would have the slightest bit of throttle on, like slow 5th gear cruising. I tried 2 turns out and the decel popping got a lot worse. Hard to believe that little bit of adjustment makes the difference but when you're paying attention like I have been it does.

I still have to run the choke 1/2 on otherwise it will lean out so much under 1/2 to wide open throttle that it misfires with the 115's.

Now I need a bigger main. I'm thinking I have two options (guesstimates) from getting to know it. I'm thinking 125 mains with the needle where its at (1 up) or 130 mains with the needle moved back to stock position. I'm willing to give both a try. I think that these needles I have might be different than the stock ones since they're from rebuild kits. They seem quite rich on the low end at least with them moved 1 up. If I up the mains and leave the needles 1 up it seems like my low to midrange throttle is going to be real rich. 125's with the stock needle position might even be the winner.