mix screws

[Carter Turk]

Fast 7

How's your ground clearance with all those mods? Does the thing corner like a champ?

Jethro, I had to lean my floats way out to work with my used jet kit and pods.

The Mac is probably mostly to blame.. The compromise is probably showing up right where your problem is.

I have a stock airbox if you want it.

[Anonymous]

hey Carter,

not much ground clearance, I scrape my pipe a bit over speed bumps, I do have my triple clamps down about an inch on my forks though. I could get a little more clearance if I was to raise it.

Corners pretty tight, I do need to get my forks rebuilt/set up though, the seals are leaking presently, it'll probably handle nicely once I do that.

Hey I see you're in Bellingham, I'm in Vancouver, BC, I've been meaning to get down and take a ride on Chukanut drive, we should hook up and go for a ride sometime.

take 'er easy

M.

[Jethro]

The Mac is probably mostly to blame.. The compromise is probably showing up right where your problem is.

For the record, this is not one of the late generation (read: crappy) MAC pipes. This is one of the last true performance MAC pipes when they were as high quality as anything out there. It's a true 4/2/1, ceramic coated, free flowing performance pipe. But it may still be the problem.

About richening up the floats, I don't know about that. The problem I am having is that I can't seem to find a pilot or air jet that makes my mixture screws do a damn thing. Here is what I have done- stock is a 45 pilot, I have tried a 40, 47.5 and a 50, but nothing affects how my mixture screws work- no matter what pilot or air jet I have in, the highest and cleanest idle I have is at 1/32 of a turn out from bottom. Even a 1/4 turn out makes the bike begin to stumble. So it would seem I have way to rich of a jet already, but when I tried the smaller than stock #40 the stumble seems a little smoother, only becasue the mix is a little thinner. When I had the bigger #50 pilot jets in there, the exhaust note was nasty, like it was burbleing. It just sounded rougher, so I assume it's too fat.

Tonight I am going a different route in an effort to aleviate the problem. I am gonna service the advance unit and I am buying a timing light. Anyone wanna tell me how to use the friggin' thing? I know nothing about the ignition system.

I still think I have a jetting problem, becasue my mix screws never make my idle increase, no matter what jets I have in there.

[KEITH KRAUSE]

Like I said before Jethro, your mixture screws are telling you it's lean.
If you check out jetting websites...or study a diagram of your carbs...then you'll see it must be the pilot circuit that's causing this IF the rest of the bike is adjusted correctly, such as valves, carb synch, clean carbs...
If you've tried many different pilot jets, then it's probably what I said in my first reply. The float levels.
This should come down to 3 things. Float level, pilot jet, and clean passage for the pilot air jet.
Sometimes you just can't get it right because of a particular set up. You may even have more than 1 problem. There's some jet needle overlap at small throttle openings too. That could cause a stutter taking off. But the needle wouldn't cause your screws to fail a highest rpm check at 1,000 rpm idle.
Have you tried any testing, such as partially bagging your pods, about 2/3 bagged, just to see the results? Use electrical tape to adjust the baggie. "Stuttering" can be taken both ways (rich/lean) and a positive test may help you figure things out.

[Jethro]

Have you tried any testing, such as partially bagging your pods, about 2/3 bagged, just to see the results? Use electrical tape to adjust the baggie. "Stuttering" can be taken both ways (rich/lean) and a positive test may help you figure things out.

I've been thinking of doing this, maybe tonight will be a good night to do that.

Tomorrow I have the whole day to try and get this taken care of. New chain and sprockets going on tonight, and tomorrow is a another carb tuning day.

I set the floats recently using the hose attached to the bowl drain, it was really close to the level specified in the manual. Is it possible that with my modified setup that I may need to alter the float heights from stock?

[KEITH KRAUSE]

Your float levels should have a range. You can choose to get right to the minimum or maximum. You just have to be more precise with measuring.
I've read where some people say if it's lean adjust 1mm richer and vice-versa and they don't mention if this adjustment would put their float levels outside of the factory range. I personally haven't had to go under or over the factory range to allow for typical mod's.
I don't know if changing the float levels 1mm will help your mixture screws or not. But as I said earlier, if carb related, it has to be float level, pilot jet size, or a dirty pilot air jet passage that's causing a rich condition. I hope that changing the float level 1mm won't effect the rest of the performance though. I think you said you were happy with the bike except for the stutter?? Did you ever take any plug reads at 1/3 and wide open throttle? It really depends on where they are set at. Your floats should have a range of about 2mm. The CV carbs are a bit more complicated and have more things to fiddle with than the VM carbs. Personally, I don't think they lend themselves to re-jetting well. The primary air jets, the vacuum port enlarging, the diaphragm assembly spring rates (lighter/stronger), all add more things to think about.
I know you're a bit frustrated over this, and I'm trying to help you out.
One thing I've learned is to take care of all the basics, THEN re-jet. If something's wrong, I know I can blame the jetting. It's more work of course (basic maintenance) but can save you time and even money by allowing you to focus on the jetting and the parts you're trying to make work, instead of trouble shooting.
I read posts all the time that start off saying the carbs were cleaned, the floats are good, synch is good...and of course the guy's complaining. But as the post continues, you read that this and that WASN'T checked. The guy spends so much time back tracking and trouble shooting, he gets nowhere.
Any re-jet I've done completely by myself, with the owner not "helping", I've started with the basics, even if there's no reason to believe this or that needs checking or adjusting. That means a compression test if there's any doubt, fix any cause of oil burning, valves adjusted, ignition timing/spark, fresh plugs, intake leak checks, clean carbs with good o-rings/rubber parts, floats adjusted, mixture screws set, bench/vacuum synchs, filters clean/oiled, new exhaust gaskets...
Pay attention if the stutter gets worse as the motor reaches normal temp or gets better compared to cold. It should change either way. Ride the bike in a way that makes the stutter most noticable. Then pay attention to any difference from hot and cold. If the stutter gets worse under the same throttle position as the motor heats up, then it's a rich condition. If the stutter goes away a little bit, it's a lean condition. Also, with the bike idling on the centerstand, in neutral, does the stutter change at all compared to riding (under load)? Do the cold to hot riding test first, then the neutral test. After these tests, then see what partially bagging the pods does.
Let me know what happens with the float adjustments (if you decide everything else is good with the pilot circuit). Just be sure of the basics first. If there's something else I can come up with, I'll let you know. I'm working Saturday 'til about 4, so I'll check in with you if I can after that.

[Jethro]

Man, I appreciate all the help. You should get an award for all the help you've given us! It must be frustrating for you too...

First off, I can say with total assurance that the engine is healthy. That part I have gotten quite good at- valves are adjusted, compression has been checked, I don't burn any oil, fuel economy is quite good (further indicating a healthy engine), exhaust is sealed well- the only engine related item I worry about is the timing. I've heard that my 83 doesn't have timing adjustments, but I think that is false. I also worry about the advancer, becasue that was a problem on my 81, but overall I'm pretty sure things are good.

Over the winter I cleaned the carbs as well as I could with compressed air and carb cleaner. I really don't want to dip them, becasue I worry about the black paint on the carbs, so that is a bummer. I'm about 90% sure the carbs are totally clean.

I think you said you were happy with the bike except for the stutter??

It's taken a while, but I am finally super happy with everything else except the stutter. The bike pulls hard and smooth all the way to redline, I got rid of the nasty bucking by leaning up the needle jet. This could further indicate that my floats were too rich if I had to do that to compensate??

Did you ever take any plug reads at 1/3 and wide open throttle?

My plug reads at 3/4 and WFO are really good- FINALLY! I'm not looking forward to having to check them again after leaning the floats a little.

Pay attention if the stutter gets worse as the motor reaches normal temp or gets better compared to cold. It should change either way. Ride the bike in a way that makes the stutter most noticable. Then pay attention to any difference from hot and cold. If the stutter gets worse under the same throttle position as the motor heats up, then it's a rich condition.

The stutter does get worse when hot, definitely. When I first start the bike, the stutter is not noticable. Due to the fact that the smaller than stock pilot jet improved things slightly, I am going to lean the floats a little bit today. Hopefully this will help things.

Thanks again Keith, you rock.

[KEITH KRAUSE]

Hi. I'm off to work in a minute.
Just for the heck of it, shoot some carb cleaner spray into the pilot air jets/passages while you have the carbs off. They're at the filter side, near the side/bottom of carb intake. They're the jet that's not removable. The other hole is for the primary air jet. Clean 'em both out real good. Then rinse the cleaner out with gas immediately. Not much extra work, and might help.
Hopefully, re-setting the floats 1mm (?) will fix you up. But if the stutter is something else, it could be just one carb messing things up. So be thorough with each carb. But as I keep saying, when your mixture screws operate the way they should, you know things are right again.

[Jethro]

Well, I'll report on todays tinkering.

I took the carbs off and leaned up the floats. It seemed to make a slight difference in the stutter, but it's the same story with my mix screws. 1/32 of a turn out is the best setting. I made sure the passages you talked about were clear (they seemed to be, I sprayed carb cleaner in there and blew them out with air) and took her for a test ride. It was still missing a little at the take off. I decided to put the #45 pilots back in with my leaner float height, just to try it. Again no change with the mix screws- 1/32 of a turn out is the only setting that doesn't make the motor bog down. Power through the upper range is still great, so I'm not touching the needles. Any higher and I think it will start to buck at full throttle- however, maybe with my leaner float heights, it won't do that this time? I may try and raise the needles a notch, that's an easy job anyway. Some folks say that higher needles help thier stutter on the take off, but I'm still concerned that the mix screws don't affect anything. The stutter seems a little bit better, but not tons. I tried to get a new set of plugs for some new plug reads, but the shop only had 3 D8EA's left. I'll see if I can get some Monday and do some 3/4 and full throttle chops.

Checked synch again today, it's quite good. All less than a cm of each other.

After my test ride, I lubed up the advance unit. The bike was still warm after I did that, and just by playing with the throttle in the driveway, it seems quite a bit better. Maybe this was the casue of my stutter? It probably hasn't been serviced in years. Tomorrows ride will really tell the tale, but I think I may have made progress. I'll let you know!

[KEITH KRAUSE]

Hey! You just leave me hanging with that ray of hope at the end?
Well, an advance unit sticking or not operating correctly would certainly cause the stutter too. The advance kicks in right above 1,500 rpm's or so and generally fully advances about 2,500/3,000 rpm. This would be right about where your stutter is. Hope you found the fix. Like I said, basics.
I'm at a total loss about your mixture screws not having an effect as they should. All I can say is check out some jetting websites and you'll see what I say about them. I know you've tried hard to fix it. I'm guessing if the stutter goes away you'll probably just live with it. If the bike runs good...
Usually, actually always, when something is not working correctly, like your mixture screws, but the bike seems to run fine, then there's a second problem you're not aware of and the two problems compensate for each other. They tend to cancel each other out, but you know something's not "normal". In this case, you know your mixture screws are not responding the way they should.
Something's causing this condition, and the mixture screws are telling you somethings wrong. The screws should be about 1 1/2 to 2 turns out for the "sweet spot". I just can't say if the stutter is related to the mixture screws problem, or a seperate thing. Anyway, I hope the stutter goes away with the advancer being lubed. You still need to check that the advance marks line up at about 2,500/3,000 rpm's. Let me know how it goes.
PS: is there ANYTHING else you can think of that could cause these problems? Did you get the EXACT length and design of pilot jets? They must have identical amount of holes and be exactly the same length. Mikuni makes more than one length of pilot jet. Did you replace the mixture screws? If so, are they identical? You replaced the rubber plugs that cover the pilot jets? What air jets came with your jet kit? I haven't noticed you say anything about them. I have to say that according to a diagram of carbs similar to yours, the primary air jet shouldn't have an effect at closed/minimal throttle positions, that's the pilot air jets job, but I don't actually have your specific model carb diagram and so I'm just wondering out loud here, trying to come up with something.

[Jethro]

With correct float levels, 45 or 47.5 pilot jets, clean passages, this shouldn't be happening.

I have 47.5's I havent tried yet. But we think this is a rich condition, so I don't know. I got another ride in, the hesitation is still there.

Did you replace the mixture screws? If so, are they identical?

I did, but they are all Identical. I was thinking of replacing them though anyway, maybe I will this week.

What air jets came with your jet kit?

I didn't install the jet kit, it come with the bike. It always had a little hesitation though. I have 160, 170 and 180 pilot air jets though, and have tried them all.

One thing I notice though Keith, my manual shows something other than you say in previous posts:

Just for the heck of it, shoot some carb cleaner spray into the pilot air jets/passages while you have the carbs off. They're at the filter side, near the side/bottom of carb intake. They're the jet that's not removable. The other hole is for the primary air jet.

My manual shows the removable air jet in the throat of the carb as being a part of the slow circuit. I wish I could scan the page, but I assure you, the manual shows that.

We'll see how the bike does tomorrow on a long ride, but the hesitiation is there, I am sure. All other carb actions are awesome, and work great. It's fast. Maybe I just am being to picky? I expect smooth, un-stuttering power right off the line with very little throttle. I might just need to live with the little cough off the line, and be the tough guy next to the Honda Accord can deal with it. I feel like an idiot when I have to blip the throttle a little.

Hey, is it the rich condition that causes the cylinder to load up with excess gas and stuff at the light? I don't know, should I buy a 135 pilot and see what that does? I'm thinking of trying the undrilled slides off my 81 carbs. Maybe that will work better with my pods and rich condition.

That's the wierd thing!!! I have pods, 4/2/1 performance pipe and I have a rich condition!!! With way smaller than stock pilot jets. Why is this happening???

[KEITH KRAUSE]

I don't know. But trying to find a problem that someone else created can be a PITA. Who knows what could have been done wrong?

[Jethro]

Another update:

Yesterdays ride went really well. I am so happy with the throttle response it's great. Off the line hesitation is definitely improved, so much that I can say I'm happy with it. It coughs a little bit but a hair more throttle and it's clean smooth power. I have no stutter or surge throughout the entire range of the throttle. Power is strong and hard everywhere. Great!!

The only issue is that it is definitely still too rich. I get puffs of dark smoke on hard acceleration and the folks behind me smell it. Strange, I get killer milage and awesome power. This machine is as fast I'd ever need right.

I tested the compression a few months ago, so I'm sure the smoke isn't coming from rings, but I will again tonight just to be sure.

Still too rich, but I don't really want to change anything. It's the best it's ever run right now.

[KEITH KRAUSE]

I'm not sure what you did, but I'm glad it's running better.
I know you said you might try different slides. That could certainly effect throttle response.
It's impossible to know what the PO could have done, if they did anything wrong. I was even thinking the piston springs could be changed, which changes throttle response and can also create a richer or leaner condition, depending on the spring tension. I read at a jetting website that some people install stage 7 springs that improve throttle response buy also richen the mixture. This mod' also "has adverse effects on lower throttle positions", according to the writer.
So I don't know what to say. Could be many things still.
You never said where the float levels are re-set though. You just leaned them some. If they were way rich, they could still use some leaning? I've never had to go over or under the factory min/max setting to make a bike run well, but you should measure if you want sometime and see where they're at. The float level definitely effects the pilot circuit and the mixture screws. You may still have some room to adjust.

[Jethro]

Yeah, I bent the tangs on the floats a lot, and measured off the gasket surface. They were rich, I may yet try and lean them up some more. With the way it's running, I kinda don't want to mess with it, but I don't want to be a smokey, stinky lead bike (which I always seem to be ).