Motorcycle Club » Star 1100 Classic & Custom

Maxair screw adjustments

10 posts from 6 voices
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  1. gz2548

    Had the maxair system installed about a month ago. I've noticed a backfire thru the carbs from time to time. I think i'm running a bit lean. I had the pms
    screws added also. The screws were set (at) 3.5 turns. which way do i turn them to tweak the mixture? Thanks in advance for any help......

  2. Troober312

    Turning the pilot mixture screw (PMS) in makes the idle mixture leaner. Backing the pilot mixture screw (PMS) out makes the idle mixture richer. You bought the kit so you should have access to their forum. I installed mine and was having problems. You may want to read some of the posts there. I haven't gotten a chance to go through mine, but the forum has a lot of good stuff in there.

  3. gz2548

    i appreciate it trooper......thought that was correct, but wanted to make sure before trying to tweak.

  4. bkman

    The main problem people have with the Maxair kit is the float levels. These need to be right on the money, and it is the one thing that you should take the most time doing. You can try to tune this out with the PM screws, but you might have to go back in and confirm your float settings if that doesn't work.

    Before you do anything, make sure your carbs are synchronized. Then, make sure your idle speed is set correctly. If you set the idle too slow on these V-Stars, they will do all sorts of wierd stuff (like randomly stall on deceleration and backfire through the carbs when you crack the throttle).

    For some point of reference, I will tell you that my bike seems happiest if the front cylinder PM screw is just a wee bit richer than the rear. Also, my PM screws sit somewhere between 2.75 turns and 3 turns - depending on what time of year it is. I usually back them out to the 3-turn range in the Winter (because I ride all year) and the engine seems happier there when it's cold. In the summer, if I leave it there, it seems to be a little too rich in the first 1/4 throttle, so I turn them back in about a quarter-turn (maybe a little less). I pull my spark plugs about three times each year to check and re-gap them and they always look fine. I've seen no signs of too lean or too rich, although they do look a little on the lean side after I've been runnning the Interstate a long way. I think the Maxair kit just runs a little leaner on the top end, but I've never run out of steam up there - it just keeps pulling toward the ton (and probably beyond, if I wasn't such a chicken - or if I was a whole lot more stupid).

    Don't be afraid to tweak it a bit. It took me about a month of small adjustments one way or the other to find the sweet spot on my motor. Once I got it there, I put painted markings on the thumbscrews so I could easily reset them (if I ever had to change something down the road). The only thing I've done in the almost 8000 miles since then is wash the air filters.

  5. yodz

    Hey bkman, I'm sure glad you posted your pms settings.

    I have had mine set at 3 1/2 turns each since Predator Pro install and thought I could smell fuel every now and then (possibly being on the rich side). Then one day a friend was riding behind me and said I was probably running rich because he could smell strong gas smell also.

    After reading your post and me being from Dallas figuring we're probably about the same riding conditions as you are in Florida, I adjusted my settings the same as yours. OOHH BABY what a difference. 2nd gear to fifty, 3rd to eighty, I never would have imagined it would make that much difference! Thanks Man!

  6. Mige

    I was thinking that 3 1/2 turns seemed a bit much. Since I didn't know your setup I figured you went by the instructions. I also (triple)checked my float settings. I had bought the float gauge from MaxAir and determined it was a waste of money. You can't really get an accurate reading at the correct spot on the float due to the design of the guage and the shape of the carburator. I ended up going to Lowes and for $15 less got a digital Vernier caliper like what Max uses in his video. I'm glad I did as one of my floats was off using the other guage. Glad you did get it figured out.

  7. bkman

    yodz, you will probably notice a rather pronounced increase in your gas mileage, too.

    There are a lot of guys I know who think that, if you don't EVER need to use your choke, you are just right on the low-speed mixture. I just don't personally see how this makes sense. The enrichment mechanism is there for a reason and, with my PM Screws set where they are, I need some choke to get it going - even when the weather is warm. I usually have to turn the choke back off after about a minute - less than that when it's really warm outside - or the motor starts to load up and the idle starts loping real bad. The thing is, those PM screws DO affect the mixture pretty much up until you're wide open.

    To set my PM screws, I go to an empty parking lot or a street with no traffic and try riding in a low gear (usually second) at a slow speed, and try to maintain that speed. What I've noticed is that, if the low-speed mixture is too rich, the motor tends to load up and run rough. However, if I open the throttle ever-so-slightly, the engine will "clear it's throat" in a couple of seconds and then the RPMs climb rather rapidly (as does my speed). This makes it difficult to maintain a "parade pace" like you'd see in rush-hour traffic.

    I do this a few times, and make very small moves on the PM screws until it runs smoothly at a nice slow pace. It's not very scientific, but it seems to work. Also, I balance my carbs a couple times each year - usually right after completing the procedure I describe here.

  8. Mige

    That's good info bkman. I was wondering when to check your spark plugs after doing the Maxair jetting? I guess your way gives another indication of whether you're running too rich. Short of pulling plugs, what are some obvious symptoms of running too lean? Since rejetting and removing AIS my exhaust has no visible smoke and gas smell like before and idles better. I still have to sync the carbs and fine tune the idle. I'm just curious if there is a way to tell from the sound/feel/smell of the bike if it's running too lean or too rich?

  9. bkman

    Some of the "classic" symptioms I know of (for being too lean) are:

    Lots of popping / backfiring in ANY part of the throttle range would indicate a very lean mixture in the fuel circuit that is predominatly affecting that throttle setting. I'd say (though others might disagree) that a little burble and pop is normal once in a while. I am talking about consistent and very noticable popping, AFTER the AIS is disabled.

    Revs "hang" during up-shifts. In other words, the engine doesn't drop right back down to idle when you pull the clutch - it sort of "hangs" up there for a moment.

    Spark plugs that are showing signs of detonation and / or look extremely dry, white and sandy (I couldn't think of a bettr word than sandy - sorry this isn't real clear).

    Long warm up times - if you need to ride with the choke on for an excessively long time (more than ten minutes in the winter or more than a couple mnutes in the summer), you're probably too lean.

    I've read tht back-firing through the carbs when you blip the throttle is also a sign of a lean mixture. I think that, in many cases, this is more of a symptom of the idle speed being set too low.

    I always know when I've hit the sweet spot on my PM screws when, after the motor is fully warmed up, I hit the start button and the engine starts immediately - I mean like before I can even think about releasing the start button.

    I always use full choke for just a second or two in the morning, then pull the choke back to about half way (or slightly less) for another 10 seconds. After that, I just start to nudge it toward closed as the motor warms up. I can almost tell when the choke needs to be adjusted - the motor will start to sound different and begin to lope. Also, the exhaust gets smelly. In the winter, I do usually leave the choke on 1/4 for the first couple miles of riding.

    I hope this helps, and doesn't confuse anyone - like me!

  10. yohntoe1

    i just traded my vstar 1100 with the maxair kit .i had some popping thru the carbs too.i made the homemade carb tool and adjusted myself .it would pop back thru the carb once n awhile like when coming to a stop and your blipping the throttle.
    heard alot of dual carbed rejetted bikes doing this once n awhile so i figured it was the norm.?
    i bought the pms screws but never got around to installing them .


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