Carb adjustment question

[Tmelita]

I recently cleaned carbs, installed new pilot air adjustment screws set at 3 turns out, did carb sync. I didn't fiddle with new pilot air adjustment and the bike is at a perfect idle, if I bip the throttle it returns nicely to 1000 rpm. When I took it for a ride, I noticed around 4000 to 4500 rpm or so that I have a flat spot (unable to tell if its rich or lean at that point) but as I continue the slow roll of the throttle it comes out of very quickly and I have no other issue. If I put the coals to her from idle I don't notice it at all. In the garage, I slow roll the rev up to 4000 rpm and I hear the interruption or stumble in the circuit. I'm not sure at this point whether it's a fuel issue or an adjustment issue. Does the pilot air screw (adjustment screws that were behind the brass plugs that I have set at 3 turns out) have any impact at the 4000 / 4500 rpm range. Any idea's how to determine whether it's a float or fuel issue verses adj issue. This weekend, I was going to try and adjust the pilot air screws a bit. I have no exhaust popping, it's an extremely smooth transition from idle. Wondering if it's really a float concern or something else. Any thoughts are appreciated.

 

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The AF screws and the needle have overlapping responsibilities in the range you are having problems. Throttle position has a lot to do with which circuit is the culprit.

What is your setup?
Air filter
Exhaust
Mains/Needles.....

Here is some info from Mark who knows way more about it than I do.

Originally Posted by maleko89
You should probably be able to accept WOT in any gear above 2K w/o any bucking or complaint.

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 leanness.

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.

As for your mains, I'd at least go to 147.5's. General rule is to subtract main jet size by 1% for every 1000 feet above sea level. So, need to decrease main jet size of 152.5 by 4.5%. 95.5% times 152.5 = 145.6. I'm thinking 145's would work best at 4500 feet above sea level.

 

[Tmelita]

Wonderful info. I'll do some testing this weekend. As I read Marks info, from cold start and engine is week, where is chokey setting, immediately turn down as soon as it's started cold?

Regarding my setup, my bike has stock exhaust and air system. I didn't check jet size or needle position as I never had and issue until bike sat after battle with leukemia. I'm thinking I'm rich on pilot air adjustment. Still fun stuff for an enthusiasts. Thanks, Tom

 

[Tmelita]

If needle is rich, which way do I move the clip? Guessing move it away from needle point?

 

[Traumahawk]

Move the clip towards the blunt end for the needle to be leaner.

 

[Tmelita]

Yhanks, I just made small adjustment to pilot air jets and just rode and it seemed like old vmax...I'm jacked. Thanks for all replies. Tom

 

[Jan Bee]

Yhanks, I just made small adjustment to pilot air jets and just rode and it seemed like old vmax...I'm jacked. Thanks for all replies. Tom

You made adjustments to pilot air jets or a/f mixture screws?

 

[Tmelita]

Mixture screws....

 

[Jan Bee]

Mixture screws....

With stock exhaust and airbox do you know how many turns out you are?

 

[Tmelita]

3.25 or pretty close on all 4 carbs. I turned all mixture screws in to bottom and turned out until I had slight stumble and then back in and then back out to what I thought was the best my hearing heard. I counted a marked screw driver and they all ended pretty close to 3.25 turns out, that's my best guess but it could be bit less on or more on each carb. Synchronized all 4 as well.. Idled perfectly and transitioned perfectly? Wot in fifth at 4000 r pm never missed a beat. From stop, smooth transition through throttle range. Raining today but as soon as I ride again I'll repot back. Test ride was in 55 degree outside air.

 

[sdt354]

3.25 or pretty close on all 4 carbs. I turned all mixture screws in to bottom and turned out until I had slight stumble and then back in and then back out to what I thought was the best my hearing heard. I counted a marked screw driver and they all ended pretty close to 3.25 turns out, that's my best guess but it could be bit less on or more on each carb. Synchronized all 4 as well.. Idled perfectly and transitioned perfectly? Wot in fifth at 4000 r pm never missed a beat. From stop, smooth transition through throttle range. Raining today but as soon as I ride again I'll repot back. Test ride was in 55 degree outside air.

That sounds too rich. I'll bet she fires right up without the choke? You should need choke to fire up a cold engine at 55 degrees. Try 2 -21/2. Be sync'd before doing the ear adjustment.

 

[Tmelita]

Just changed oil and filter, another test ride and perfect. Very pleased back to crazy fast with zero issues. Thank you for all the help. Tom

 

[Tmelita]

I didn't see the comment about starting without choke... she needs choke when starting cold otherwise coughing. Idles returns perfectly, once warm, instant throttle responce. Pulls continually in all ranges and throttle position. I'm very pleased