Stumbling at 5k rpm.

[99 MAX]

Stage 1 needles, 170 mains, has air correctors, {I think, see pic down below} K&N pods, 4 into 1, needles currently on 5th from dull end, I've tried 3,4,and now 5th clip down, 4th seems best but why can't I get rid of that cursed stumble at 5k ? I'm stressing.

 

[99 MAX]

Maybe I should have added this to my "air corrector" thread, don't mean to eat up thread space.

 

[99 MAX]

Let me start here first. is that an air corrector on the left??

 

[Rhoy Carter]

Yes it is, I would suggest that you get some stage 7 needles to go with your set up and start with stock jets or down one size and 177.5 PJ-2 jets.

 

[99 MAX]

Thanks, the plugs have been showing lean, all this time I've been thinking not enough fuel to air, I have the 7 needles, just pulled them to try the 1s for some reason, but it was doing the same thing with the 7s, first I'll try the 177.5 PJ2 as they are the easiest to get to, if no change, I'll go down on the main jet as well.

 

[[email protected]]

Do you feel the stumble when you are running thru the rpms quickly or only when you are holding steady at 5K?

If the stumble is when you are trying to hold a steady cruise at 5K, try opening (counter clockwise) the A/F screws a bit.

Here is an excerpt from the carb notes I have gathered from the forum:

4) Verify you can cruise "nice and deliberate" at 5K .. if you stumble around and are OK everywhere else you don't have enough pilot.

Some more reading below if your interested.

BASIC CARB TUNING TIPS FOR VMAX



Raising the clip on the needle means same as moving the clip towards the blunt end= dropping the needle=less fuel=leaner

Going up to a numerically larger fuel main jet= bigger hole in jet=more fuel=richer

Going up to a numerically larger air main jet (or paj1 and or 2)= bigger hole in jet=more air=leaner

Float Levels: The smaller the dry measurement the richer it will be 1.115 is richer than 1.125 and there will be more fuel in the bowls at 1.115 than 1.125. Since you are measuring from the carb body you are measuring the height in the chamber ABOVE the float, not below. This is why a smaller # makes it have more fuel

Pilot Mixture Screws: Turning counter-clockwise,left, out, allows more fuel into the pilot circuit=Richer

You should probably be able to accept WOT in any gear above 2K w/o any bucking or complaint.



RIDING TESTS


Do the following tests.

1) Cruise at 4K in 5th gear .. hold RPM steady (count to 5) and then whack it WOT as quickly as you can. You shouldn't feel the slightest delay or hesitation. If you do, too rich. This does not work at 3.5K or 4.5K, only at 4K because the slides will start to retract at 4.5K even at the lightest throttle angle. 4K sets us up on the threshold and gives us a big jump when we whack it. there is no other RPM to do this where you will get as big a slide jump when rapidly moving to WOT.
This tests for too rich of needle.

2) Verify that starting cold .. that the engine is weak .. and will complain if you try to hold the RPM at 1800 rpms. Within 1-2 min or no later than when the temp needle touches the first mark you should be able to hold the engine between 1500 and 2K w/o complaint or popping back through the carbs. At the least you should be able to do this by the time the engine is fully warmed up but if you are more than 1/2 way between the dot and cold on the temp gauge your pilots are plugged or too lean... (clean or reduce the PAJ2). If you can hold 1.5-2K as soon as you start cold then your pilots are set too rich and you will suffer rich symptoms when it comes to operating temp (clean or enlarge the PAJ2). ONly change PAJ2 bigger/smaller if you mixture screws are out or in too far already.
This is how you set your pilot mixture.

3) Do a hard WOT pull in 2nd or 3rd gear from below 3K. Look for a smooth pull all the way up. If it seems to lag in the 4-5K range then too much needle. If we sputter going past 4.5K you don't have enough needle.
This tests for needle richness and leaness.

4) Verify you can cruise "nice and deliberate" at 5K .. if you stumble around and are OK everywhere else you don't have enough pilot.
Another pilot mixture test.

 

[grimmie]

I have the same issue with stock and stage 1 needles. I've never been able to get the upper crossover together, & I've tried everything multiple times. I'm at sea level and my setup is:

2000 Vmax
Full Kerker header with 2.5" baffle
Morley Jet kit & air box & all Mikuni jets
Vboost stock
160 Mains
stock PAJ 1 & 2
#40 pilot jets
Stage 7 Needles 3rd clip from the blunt end
Stage 7 springs
Air correctors

My bike runs great, like an EFI motor. I get above 40mpg on the highway always, with my best at 43.5mpg.

I would suggest getting some stage 7 needles and trying them. Sean Morley can get them for you. Tune it from the top down if you can.

My favorite needles are the stock needles. I just can't get the upper crossover together. It's always lean. The stock needles with the Morley kit are a beast in the mids though!!

Hope this helps,
Shane

 

[99 MAX]

Thanks guys, ordered a stage 7 today, so as we get into it, I will know everything I have and don't have, if it is still stumbling at 5k, will try the a/f turn out, it fly's every where else.