Topic: cb750k6 jet sizing for performance

[oldk6guy]

does anyone have any idea what jet sizes i should be using on a 750k6 with drag pipes and horned carbs? stock were barely usable. slow and no top end. i have a set of 120's. also would like to know what needle clip position to go with. Any help would be greatly appreciated.

[oldk6guy]

seriously? no one?

[Bailgang]

When you say "horned carbs" I'm assuming velocity stacks. If so then any time you take the factory air box out of the equation then you're in for a headache, Honda did a pretty good job of setting the carbs up with the factory airbox and any time velocity stacks or pod filters are used then all bets are off. There are countless threads on the subject on this site. It's not that tuning the stock carbs to work with velocity stacks can't be done but it can mean a tuning nightmare that involves trail and error which is probably why no one has responded to this thread ......... or the fact that your question has been asked so many times by others that every one else is tired of answering the question. No offense intended but it is a routinely asked question.

I myself can't give you any tips because after reading all the headaches others have dealt with I've decided to stick with the factory airbox. The best advice I can give is do a search on this site for the subject, you'll quickly see what I mean. Good luck.

[Jerry Rxman Griffin aka MuthaF'er]

It's not as easy as just replacing jets. Start with the 120's and see what it does. May be too much vs your 105 stockers. That's 3 sizes up. Usually you try one at a time. Your bike has a puny ass cam so that alone does NOT need bigger jets in all likelihood. Anyway get settled on mains first then play with your needles. I'm 'thinking' your stock is middle position. Keep in mind the needles overlap with the mains so do NOT do both at the same time. They MAY be fine where they are or you could end up lifting the needles one notch. Again only do one jetting at a time or you won't have a clue as to what did what.

[oldk6guy]

I've been on this forum for a while. I've seen the question asked countless times. I've even asked it before.....What i have never seen, even after hours of searching, is any kind of helpful answer or simple guide. Something along the lines of "okay, you've done this, this, and this....you need that, this, and that and you'll be running good....." There has got to be well over a thousand years of experience of honda tuning and modding on this forum. It amazes me that there is no carb tuning guide or list or layout for COMMON mods. I bought the bike with the air horns. Don't have the factory air box. So at least for the time being I'm stuck with this set up. I LOVE this bike. It's my first bike. I'd like to ride it....also, where I'm from, velocity stacks go between the carb and the filter. Air horns take the place of the filter. I have NO filter, just air horns with mesh screens on them. Kind of similar to a 60's ferarri race car. Since i can't find any useful information I am going to go with the 120's, even though i feel they might be too big, over the stock 105's. I feel the 105's are too small for the modifications on my bike and i guess I'd rather be rich on an air cooled bike. I'm going to try to lean them out using the needle clip. I'm going with the second from the top position. If anyone thinks this is wrong I would greatly appreciate some positive feedback. Thank you.

[oldk6guy]

update....one of my emulsifier tubes was almost all the way out and is warped and mangled somehow.....probably explaines why the bike was running like crap....

[martin99]

The reason you can't find a 'guide' on the forum is probably because there are just too many permutations of filter and exhaust set-up. All anyone can do is try to get you in the ballpark, and from then it is trial and error. Pod filter quality varies, tuning will be different if you have cheapy Emgos or the more expensive K&Ns for example. Whether they are oiled or dry will also make a difference. Velocity stacks (never heard them called horns before, learn something every day) vary in volume, length etc. Aftermarket exhausts also vary widely in specification.

If you've been hanging around a while, you will know there are a lot of people who are haters of this kind of mod, and also many who have successfully done it. I am in the latter category, but as my carbs are PDs and I'm running pods my mods are going to be of little help to you. I would also quantify what I mean by 'successfully done it'. My bike is close to what I would consider to be perfect tune throughout the range, but still not as good as a stock set-up can be made to be. I can only echo Jerry's advice - do one mod at a time. Raising your needles would seem to me to be a good place to start. My PD carbs are also 105 stock, and I settled on 130s, so 120 might get you pretty close on yours. But as said, it's like comparing apples and pears. I'm sure Lucky was compiling some sort of record of what others have done - maybe have a look and choose the settings closest to your set-up?

If you're not going for looks or performance, but rather using your stacks just because they were already on the bike, you would be well advised to look out for a stock airbox which will save you time and money. Best of luck.