missing

[Hershell Weaver]

I've got the Max running pretty strong now at wot to redline. Decided to see if there were any issues through the throttle range and there is a considerable miss or stumble between 5500-7000 rpms ( part throttle ) although it will jump over it at wot. The V-boost is working, stage 7 springs, stock needles, stock paj 1 and 2, 155 mikuni mains, and air correctors. I have my own version of Seans air box lid and UFO 4 into 2 pipes. Idle screws are out to the best idle ( 2-2 1/4 ) turns. It's about 62* out today and no humidity at sea level. Do I need to go up on the mains or add a shim under the needle or a little of both. Plugs look good although the center is white. Electrode looks good. Maybe another issue is the problem. What do you think/

 

[ninjaneer]

what do you mean by "part throttle"? 1/4, 1/2, 3/4?

 

[Hershell Weaver]

Just easing into the throttle until redline. Probable 1/2 to 3/4 is where the stumble starts. Not just whacking it to wide open.

 

[naughtyG]

I'm not quite sure you have a problem? What do you mean by miss/stumble? Of course when you're in the process of closing the throttle it can feel like it's stumbling. Do you mean it's actually feeling like it's missing some beats and not running smoothly when you try to cruise anywhere between 5.5 and 7k?

 

[Hershell Weaver]

what do you mean by "part throttle"? 1/4, 1/2, 3/4?

just easing into the throttle in 1st gear. Probably starts stumbling at 1/2 to 3/4 throttle. Will jump it if you whack the throttle.

 

[naughtyG]

I think this is normal. How does it go if you try cruising, say in 3rd gear, around 6ooo? Bear in mind the vboost starts opening at 5750, so from there it's kinda 'made to rush' with an open throttle.

Welcome to the site, btw.

 

[Hershell Weaver]

I think this is normal. How does it go if you try cruising, say in 3rd gear, around 6ooo? Bear in mind the vboost starts opening at 5750, so from there it's kinda 'made to rush' with an open throttle.

Welcome to the site, btw.

Yes, I did this in 1st gear. Imagine holding the throttle at 3000, every thing smooth and groweling, then 4th gear, hold the throttle still good but when it get's to just about where the vboost is kicking in the engine will start to break up if you hold it there but if you get into the throttle it will jump it and go on to redline.

 

[ninjaneer]

I am by far not an expert, but this is why i asked what throttle positions (i apologize if you already know): i've come to learn how to tune my carbs with the mindset that carburetor jetting is determined by the throttle position, not engine speed. Mains start becoming a factor at 1/2 and being a major contributor at 3/4 and then tapering off through WOT. Needles start coming into play at 1/4 and becoming most effective at 1/2 and then tapering off through 3/4. If the engine is having troubles from idle to 1/4 throttle, the pilot system the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the needle is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.

With that being said, it sounds like you are having issues when VBoost is kicking in. I'd entertain the thought of disabling VBoost with the butterflies closed and then running through the same steps of your procedures. If you try this, post your findings. And then the carb gurus will start chiming in.

 

[Hershell Weaver]

I am by far not an expert, but this is why i asked what throttle positions (i apologize if you already know): i've come to learn how to tune my carbs with the mindset that carburetor jetting is determined by the throttle position, not engine speed. Mains start becoming a factor at 1/2 and being a major contributor at 3/4 and then tapering off through WOT. Needles start coming into play at 1/4 and becoming most effective at 1/2 and then tapering off through 3/4. If the engine is having troubles from idle to 1/4 throttle, the pilot system the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the needle is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.

With that being said, it sounds like you are having issues when VBoost is kicking in. I'd entertain the thought of disabling VBoost with the butterflies closed and then running through the same steps of your procedures. If you try this, post your findings. And then the carb gurus will start chiming in.

Thanks ninjaneer. I was just sitting at the supper table thinkink about the same thing. If It's not raining tomorrow I'll give your idea a try.

 

[[email protected]]

I would try shimming the needles.

 

[Hershell Weaver]

Thanks ninjaneer. I was just sitting at the supper table thinkink about the same thing. If It's not raining tomorrow I'll give your idea a try.

Good idea Mike. Considering there isn't much of a load on it the way I was testing it, it could be lean at the upper end of mid range. Anyway, what got me started was trying to figure which was the best size main as I had read somewhere that it would be mostly on the main around 7000 and it would break up if it was lean.

 

[naughtyG]

Interestingly, I always thought that a more flowy exhaust (as in your UFO) would call for smaller jets? I may be totally wrong of course, but I noticed you're running 155s, and stock's 152.5. If I'm wrong, then yea maybe you're a little lean, but if not, it may be the other way?

Also it would be great if you could post a picture or better explanation of your personal version of Sean's airbox lid - does this mean you've shimmed the Y some?

 

[sdt354]

I would try shimming the needles.

+1, or using adjustable needles like the ones in the Morley kit. Stock needles were set up for stock air flow.
I have a set of Titanium needles, never used. pm if interested.
Steve-o

 

[Hershell Weaver]

Interestingly, I always thought that a more flowy exhaust (as in your UFO) would call for smaller jets? I may be totally wrong of course, but I noticed you're running 155s, and stock's 152.5. If I'm wrong, then yea maybe you're a little lean, but if not, it may be the other way?

Also it would be great if you could post a picture or better explanation of your personal version of Sean's airbox lid - does this mean you've shimmed the Y some?

I did try 150,s and took it out the eairlier in the week and it was a bit colder. The bike was doing the same thing only at 4,000 rpm's. I contacted Sean by email and he thinks I should go as high as 160 or even 162.5 before even shimming the needles. I will see what I can do about posting a picture of my air box lid. Looks pretty good IMOP. It flowed well enough to need the restrictors.

 

[Hershell Weaver]

+1, or using adjustable needles like the ones in the Morley kit. Stock needles were set up for stock air flow.
I have a set of Titanium needles, never used. pm if interested.
Steve-o

Thank's for the offer. I will keep it in mind. I actually had a set of DJ stage 1 needles and honestly the bike ran the best it ever has at one point. It would actually lift the front wheel from a roll on or break the rear tire loose when the vboost kicked in. Got great milage too. It was shortly after that that I started having problems with floats, idle passages ect. and started messing with all the settings and screwed everything up. I have recently cleaned them up good and am trying to find that sweet spot again. Should have kept records of every thing and tried one thing at a time. I may go back with the 1's or try a different needle. I'll let you know.

 

[ninjaneer]

Interestingly, I always thought that a more flowy exhaust (as in your UFO) would call for smaller jets? I may be totally wrong of course, but I noticed you're running 155s, and stock's 152.5. If I'm wrong, then yea maybe you're a little lean, but if not, it may be the other way?

Also it would be great if you could post a picture or better explanation of your personal version of Sean's airbox lid - does this mean you've shimmed the Y some?

naughtyg, i believe you are correct. more flowy exhaust = richer, which would theoretically would require leaner jetting and shimming--but not all setups and circumstances are the same. more flowy intake = lean, which would on the flip side require richer jetting and shimming--again not all setups are the same. mileage will vary. it may be that putting in a Morleyized airbox nullifies the need to lean out the jetting that would normally have had required leaner jets.

with that being said, look at what some folks have to do when they install a more flowy Marks system, which is just tweaking the mixture screws.

what HW may have done with his airbox is similar to what I am doing to maximize midrange performance, which is transitioning myself off of my S7 pods to the airbox velocity stacks by cutting in a K&N panel filter.

 

[Hershell Weaver]

naughty i believe you are correct. more flowy exhaust = richer, which would theoretically would require leaner jetting and shimming--but not all setups and circumstances are the same. more flowy intake = lean, which would on the flip side require richer jetting and shimming--again not all setups are the same. mileage will vary. it may be that putting in a Morleyized airbox nullifies the need to lean out the jetting that would normally have had required leaner jets.

with that being said, look at what some folks have to do when they install a more flowy Marks system, which is just tweaking the mixture screws.

what HW may have done with his airbox is similar to what I am doing to maximize midrange performance, which is transitioning myself off of my S7 pods to the airbox velocity stacks by cutting in a K&N panel filter.

You are right ninjaneer. I cut the top of the lid off and epoxied the sides closed where the Y used to be. Then cut a square hole in the lid and installed a K&N SU-7953 panel filter with black automotive sealer. I doesn't have quite the area as Seans lid but it works and looks great. Believe it was for an earlier Model Kawasaki. I'll try to figure out how to post a picture.

 

[ninjaneer]

You are right ninjaneer. I cut the top of the lid off and epoxied the sides closed where the Y used to be. Then cut a square hole in the lid and installed a K&N SU-7953 panel filter with black automotive sealer. I doesn't have quite the area as Seans lid but it works and looks great. Believe it was for an earlier Model Kawasaki. I'll try to figure out how to post a picture.

hehehe, cool. I'll post a pic of mine later tonight as well. i used K&N Air Filter that is billed for a Buick Rendezvous :rofl_200:

to post a pic:

in your "reply", click "Go Advanced" button undeneath your edit box, scroll down and click the "Manage Attachments" button



if you want, not totally necessary, you can place the pic "inline" (like what i did above) by clicking the down arrow next to the paper clip in the edit menu and select the attachment. if you don't the pic will still show up, but just at the bottom of your post in a "Attached Thumbnails" box

 

[Hershell Weaver]

 

[naughtyG]

Something's missing here.. ;-)