should I go bigger jets?

misiek93 · May 18, 2012

So me being me I just had to mess with my carbs and now I can't get it to run like it did before.

My set up is 4-2-1 header
stock airbox - with K&N filter
stock carbs
147.5 jets
A/F - 4 turns out
elevation is 758 feet.
brand new sparkplugs (installed yesterday) gapped per the manual.

My original spark plugs were a little black but not wet, tells me it was running a bit rich. I haven't looked at the new ones yet (ran out of time yesterday)

I was messing with the carbs all day yesterday, going anywhere from 3 turns out to 4 on the A/F screws and it seems to run the best with 4 turns out, BUT...
1. it has major popping on deceleration.
2. when I hold the throttle steady at 3-3500 rpm I get the popping sound as well.
4. at 4,000 rpm and up seems to be running fine.
5. when I cruise at 3,rpm and have the choke on 1/3 of the way the popping seems to go away but the rpms will not go gown when I let go of the throttle (think of cruise control)
6. WOT pulls fine with no popping that I can hear. I redlined it in first 3 gears and was pulling hard throughout the RMP range with no hesitation, at least none I can feel.
7. It hesitates a little when you start rolling but a bit more throttle solves that problem.

At this point should I got with 150 jets or should I go maybe 4.25 turns on the A/F to get the best performance? Everything I've read seems to indicate I should be around 3.0-3.5 turns out.

sdt354 · May 18, 2012

The 147's are run by a lot of people with that set up.I run 150's with the Y shimmed 3/8", A lot also shim the needles .030-,040. Although, I tuned my bike for milage yesterday, for an up comming long ride. I took the shims out(.032'S) and it still ran good. A little less punch.
You might want to shotgun, float height check, and sync the carbs. You might have a clogged air jet. Maybe a ,030-.040 shim on the needles will help out the midrange. I'm thinking decel. diaphrams and circuits dirty? My a/f settings are 2 1/4 to 2 3/4 out now, I usually run them about 1 more turn out. Some cylinders are a bit different. I'm sure I forgot something, but lots of good carb people here that will prolly chime in. That's what makes this site great.

mabdcmb@yahoo.com · May 18, 2012

Sounds like you are lean on the needles to me. Try to shim a bit.

gamorg02 · May 18, 2012

i'd do a shotgun make sure the low circuits aren't clogged. then go from there

that range, 3k/3.5k at low throttle is right between needle and a/f screws. might be a combo.

donnelly317 · May 18, 2012

Do the newer max's especially u being in California have a PAIR system?? Takes exhaust gases puts it int'l your intake. = retarded!! Its for emissions.. my old bandit 1200 had this problem when the holeshot exhaust was put on and went to a stage 2 jet kit.. removed the PAIR system and popping went away! Other than that it is to lean. I think its when your exhaust let'shott enough to cause any left over fuel/air to ignite in the exhaust. Its getting that hott because of the lean mixture. As fair as I read on it before!

misiek93 · May 18, 2012

Thanks. Where do I get the shims and how do I know what size to get?

One thing I noticed is that the front left A/F screw there was a lot of oxydation and the screw was not turing out easily. It took a while to get it to move so maybe some of that white stuff got knocked off? The other 3 are no problem.

Hhmm, maybe it's time for Morely muscke kit