Well, actually, we do have some data ..

Matt provided AFR/HP/TRQ data for his 351 build here - https://www.kawasakiforums.com/forum...68-dyno-42399/

His setup gives a good starting point for fueling a 351..

 

What I do not get about those charts is that this is basically WOT, right? I mean there's not millions of data points to decide based on throttle angle, load, rate of throttle increase, temperature and a million other things. Everything that happens under that line, where the throttle is partly closed or the bike isn't accelerating on a flat plane is just a guess, isn't it. Dynos measure one state WOT under a specific load. Under that curve at the top is a tuning wilderness.

I never ever ride WOT so I am not sure what that information means to me. I am so much more concerned with my perceived performance in various situations. it's tempting to believe there is a right air pressure for tires or a correct amount of preload, or the right swing arm angle, but there isn't. You always give up something.


I had a bunch of trouble at small openings that I *think* I basically tracked down to the air jet. The .9 was better for me than the 1.0. That wouldn't ever show up on a dyno run.

Also, the needle jet I use is a P4, not the richer P6. But the needle jet also will not show on a dyno run.

Eventually, with a complex carb like the TM36-68 where the air screw, air jet, pilot jet, jet needle, needle jet, and finally the main jet, plus the accelerator pump and float level all interact it becomes guess work.

All carb tuning is a black art and there isn't any right setting, there's a lot of wrong ones but there's not a right one. You're always compromising. That's why they invented fuel injection.

 

Dyno runs on the CVK are more representative of carb operation across the entire RPM range due to its design I'd say. WOT isn't actually WOT on a CVK until a certain RPM as I understand it. Slide position is dictated by airspeed and vacuum.

Despite the flat slides being manually controlled in the Mikuni's I'm pretty certain they are designed to have a correlated fueling curve that is generally pretty close at other RPM's and loads. This means that under a dyno situation, you've got a good load on the engine in a taller gear and WOT. This is a max air & max fuel scenario from which all other scenarios stem from. If you get this dialed in, then all other part load, part throttle situations should be generally pretty close to the desired fueling. Obviously there are some discrepancies when we start swapping carbs and needles into different bores and airflow situations than they were designed for, but as a general rule this is the reason the tuning takes place at WOT under load on a dyno.

To add to this, that chart is a bit misleading. All systems work together at WOT under load. That is to say, when I switched between the P8, P6, and P4 needle jets on my bike, it leaned the bike across ALL RPM ranges and throttle positions. The chart is more of an indication of general areas of impact each system has, but is misleading in the sense that it indicates they have no impact outside of those throttle positions.

You also don't need to spend money dyno tuning. I bought my AFR gauge used for 80 bucks (AEM UEGO). I still had to weld an o2 bung on my header, so it's not for everyone and as you point out, it might not be worth the effort to eek out 1 - 2hp in an rpm range you don't usually see anyway. I like tinkering with these kinds of things and seeing how good I can get it. "Good enough" isn't my style. Ride whatever feels good to you though, just don't be afraid to experiment!

Also just as a point of reference. There is no air screw on the TM36-68's. It's a fuel screw as it resides on the engine side and not the intake side of the carb.

 

But it is like a princess and the pea effect, right? By the time the slow air jet is unburied from all the other circuits on top of it it'd be pretty hard to deduce from a dyno run. This is the most extreme example, but it serves to illustrate that AFR from a dyno run is pretty specific information.

Having more information is usually better unless it starts leading you to conclusions that don't benefit you, or simply cloud the situation by having too much going on.

The BB kit with a pipe and a TM produces more than enough power for my application. I pretty much want the bike to run clean, idle on the stand all day and start right up. I want snap in the bottom third of the throttle positioning and good power in the next third but not so much that it's unmanageable. I actually like the top third weak so that it runs out of steam before things get too out of control.

It's pretty good all around. Does it do that? Yes! Is it optimal, maybe or maybe not. But, it's pretty optimal for me right now.

In fact, the only thing I don't like about it is how much fuel leaks out of it when it's laying on it's side!

The internet tends to reduce questions like this into some sort of rubric based on data, when it's really a qualitative thing. For me the question is do I like it? If the answer is yes, I am done.

A lot of people have done great work on jetting, and I am more or less riding in on the coat tails of others. I made final adjustments for my preferences and called it a day.

 

Dash8, If you find out what the diameter is, be sure to post it here so we can search it in the future!

 

Will do! Apparently no one has measured it, and Bill has not gotten back to me yet..

 

So the BB 351 bore diameter is 3.366

 

Dash8, off subject, maybe you know a couple of AC Pilots I know. Paul Dainty, recently retired, and Ed Wight RIP, longtime retired, was a cottage neighbour of mine and flew his float plane around my Lake for years. Must have shut AC down for the day at his funeral, dozens of AC pilots were there. On subject, ring compressor may be overkill as it is easy with the Zip Tie method. See Dan888's install tutorial.

 

I think I've met/heard of Paul, but not of Ed... Mostly if they are not on my machine I would not know them, unfortunately...


I'll check out Dan888s' write up... don't really want to spend 100$ on tools I'll hopefully only use once lol..


would you happen to know of anyone around here that has done the 351?


Also, What carb did you throw in there?

 

if my math is correct the 351 is about 85.5mm bore. I used a hose clamp as a ring compressor-works just fine