Fat or lean

Im wondering what the symptoms are for each. After a couple hours of searching it seems like many of the indications are almost the same. Maybe its just my confusion with the termonlogy being used. Some say popping on deceleration is a sign of being lean and some say its completely normal.

So heres the deal. I have an 08 SM with about 3000 miles on it. I installed a SSW/MRD shorty system and a TT FCR kit with a Merge APS and extended fuel screw. The basic jetting guidlines told me that jetting I needed was exactly what came with the TT kit. Sea level with an uncorked pipe. The bike runs strong but it has a low to mid throttle hesitation. As in when the throttle is held constant while cruising and a lot of popping on decel. When I open the trottle further, it goes away. So Im thinking Im lean. I played with the fuel screw a bit today. When I close the fuel screw, the bike dies. But when I adjust it out with the bike running, there doesnt seem to be much of a change. To top it off, the hesitation seems worse when its hot and humid out, like today, which would make me think that Im actually running rich. So Im totally confused. Someone please school me before I throw in the towel and take the bike to someone who actually knows what they are doing. I would really like to learn myself. Thanks!

I am carbtarded... but it's Lean and RICH, not fat...

popping on decel is rich

fuel screw only effects idle fuel adjustments, nothing else

take off the cover for the air filter and ride around, better? or worse. If better then you are too rich (too much fuel)

if worse, then use tape to cover 1/3 of your 3"x3" hole (which you did cut right???) if it improves then you are lean

So what jetting are you running?

160 main jet

200 main air jet

EMN needle on clip 3

45 pilot jet

2 turns on fuel screw

pilot air jet removed

Merge APS

perfect 3X3

These are what is recommended for uncorked pipe at sea level and what Im running. However it doesnt account for it being hot and humid. I kept thinking that the constant part throttle hesitation was for sure a lean condition but the fact that it seems worse as the weather gets hotter has got me confused.

Air filter clean?... got good fuel flow from petcock on prime?

Try PhantomD's advice with the air door removal and report back....

Yep. New clean KandN filter. Wouldnt a fuel flow issue cause problems across the board? It rips all the way to the limiter besides the constant throttle cruise hic up. I'll try the air cover test.

The bike runs strong but it has a low to mid throttle hesitation.

you might try moving the needle jet clip down one notch and see what happens. at low to mid throttle, the needle jet is the primary player. hesitation can indicate a lean condition. lowering the needle jet clip raises the needle jet, thus richening the mixture at low to mid throttle.

before doing anything, though, i'd suggest reading your spark plug. pull the spark plug, put a new one in, ride at low to mid throttle (where you are experiencing the hesitation) for awhile, then pull the new plug, and read it.

popping on decel is rich

decel popping can indicate lean or rich...or decel popping can indicate an exhaust or intake air leak rather than anything to do with jetting. further, a little decel popping is perfectly normal on many bikes due to the way pilot jetting/carb vacuum works when closing the throttle.

in other words, the existence of popping on decel tells you about nothing in and of itself...though the tone/sound of the pop can tell someone with good ears and who knows what to listen for something.

Thought you could only accurately read a 2t spark plug.

Thought you could only accurately read a 2t spark plug.

you can read 4 stroke plugs also...heck, even on V8s. :smirk:

Yeah... ok..good luck with that..It's very hard to accurately read a 4t plug with modern pump fuels...

Some say popping on deceleration is a sign of being lean and some say its completely normal.

Popping on decel is normal. Loud backfiring is not.

I played with the fuel screw a bit today. When I close the fuel screw, the bike dies. But when I adjust it out with the bike running, there doesnt seem to be much of a change.

Did you have the idle speed turned down when adjusting the fuel screw ?

To top it off, the hesitation seems worse when its hot and humid out, like today, which would make me think that Im actually running rich.

Hot/humid climate means less oxygen in the air so that would cause a richer fuel mixture.

Make sure you haven't got any vacuum leaks.

Yeah... ok..good luck with that..It's very hard to accurately read a 4t plug with modern pump fuels...

it works. try it.

intentionally jet your drz too rich. read the plug.

jet it lean...read it.

jet it right...read it.

you will see a difference.

Im running a SSW/MRD with the short muffler so everything coming out of the pipe is pretty damn loud. I wouldnt know if its "normal" popping or backfiring. But I honestly doubt the jetting would be that far off to cause backfiring. And like I siad, the slight constant throttle hicup/hesitation is my only issue. Give it a little more throttle and it goes away. Im going to carefully reset my idle and fuel screw tomorrow, check for vacumm leaks, and remove the side cover for a ride and go from there. Also going to factor in temp and humidity. I was also thinking of installing my quiet insert as a diagnostic tool. I'll let you guys know what happens.

I am not familiar with the short muffler set up with the SSW pipe...but I am thinking it is the factor influencing your apparent leanness on the needle...My bet is that it will be worse with the side cover removed...If lean running on the needle is the issue the install of the insert will improve it....

Thats what Im thinking too. Maybe the short version having less back pressure than most other after market open pipes, is giving me a slight lean condition using the basic jetting recommendation listed.

Well removing the side cover didnt change much. If anything it might have run a little better. Hard to tell. I also didnt get much out of the fuel screw. I rode the bike a bit to get it warmed up. It was running like crap. wouldnt idle and stalled at the lights. When I got home I realized the choke was hung on the pet cock. Closed the choke and it runs fine. Followed the fuel screw adjustment procedures but they are a little unclear. Heres what I did. Set the screw 2 turns out. Turned the idle down as far as it would go without stalling. Slowly closed the fuel screw. Bike dies at about one turn from being fully closed. Opened it to 1 1/2 turns and restarted the bike. Slowly opened the screw and the bike dies at at 3 turns out. So seems to me that 2 turns out is the sweet spot. The hesitation isnt as bad today as it was the other day so Im starting to think that its temperature/humidity causing a slightly rich condition. Looking at my head pipe and its blue for the first few inches and thats it so it isnt getting super hot. I was expecting a big change with the side cover off but I didnt feel it. So I just dont know. Its hard to duplicate one ride after another down here because the temp and humidity change so much throughout the day.

You keep saying rich condition,,from my experiance hesitation is caused by a lean condition, it hesitates because there is not enough fuel...

Take it back out and run it again with the side cover off then immediately after try taping off a small part of the 3X3. Does either way make a diffrents?

Heres what I did. Set the screw 2 turns out. Turned the idle down as far as it would go without stalling. Slowly closed the fuel screw. Bike dies at about one turn from being fully closed. Opened it to 1 1/2 turns and restarted the bike. Slowly opened the screw and the bike dies at at 3 turns out. So seems to me that 2 turns out is the sweet spot. The hesitation isnt as bad today as it was the other day so Im starting to think that its temperature/humidity causing a slightly rich condition. Looking at my head pipe and its blue for the first few inches and thats it so it isnt getting super hot. I was expecting a big change with the side cover off but I didnt feel it. So I just dont know. Its hard to duplicate one ride after another down here because the temp and humidity change so much throughout the day.

Sounds like you now have your idle circuit set correctly.

I had a rich condition at off idle, ie small throttle openings riding around town (hot humid climate). It got worse as the day heated up and improved at night when it was cooler.

My setup at the time was stock low hour motor, RS2 uncorked, 3x3, TT-FCRMX39, jetted to TT recommendations for seal level.

Eddie suggested putting the emR needle back in because this has a thicker straight/root dia than the emN needle. ( Did your FCRMX come with the emR neeldle ?)

That leaned out off-idle considerably with some overlap into the pilot circuit.

I then had to refit the Pilot Air Jet to richen up the pilot circuit, compensate for the overlap from the emR needle.

However this richened the pilot circuit a bit too much so I went down to 42 pilot jet to finally get it right.

Im in the same boat as you. When I first put the carb on I never really noticed the off idle hesitation. But is was cooler out and less humid. And I was running an RS2. Down here in the dirty south, the heat and humidity builds pretty fast throughout the day. I rode about 2 hours today and the bike ran well. I only noticed the hicup at off idle cruising in 4th gear mostly. And that was with my insert installed. So I still dont know if its a rich burble or a lean situation. Im going to play with it some more and hopefully get a night ride in when its cool out. I'll try taping off the 3x3 and see what happens.

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