Author Topic: Fine Tuning (Read 3391 times)

Rocketjock · « **on:** April 03, 2007, 11:03:09 AM »

Lookin for a bit more advice on my 06 B12 2Bros. Ivan's Stage 1 setup. Now have the bike synced to the max. Running great in all ranges. The only annoying thing is a lot of decel pop. Screws are set at 4 turns out. Tried 3.5 for a definate worse performance and 3.75 for a little less worse. 4 turns is definately better. Do you think going for, say, 4.25 turns will help on the decel pop? I haven't done any shimming but I guess that would be my next logical step if it starts getting worse above 4 turns out. Oh ya, I have left the PAIRS system hooked up because I figured a little fresh air into the direct exhaust can't hurt still with the hydrocarbons and all. Ivan's instructions were to disconnect and plug the hole into the box. Maybe this is why I need to adjust the screws to just above 4 turns? Waddya think?

Red01 · « **Reply #1 on:** April 03, 2007, 11:28:13 AM »

I think the PAIR system won't have an effect on performance one way or the other, and this is verified by Dale @ Holeshot. The only things you gain from getting rid of the PAIR according to him is weight loss and easier valve cover removal. OTOH, if Ivan says his kit works best without it, I'd give that a try at least. You should be able to test that theory easy enough by just disconnecting the PAIR hose from the airbox and capping off the connections.

wiredgeorge · « **Reply #2 on:** April 03, 2007, 02:33:26 PM »

Spent a few hours this past weekend doing some minor tune up... The "pair" system is indeed similar to most reed valve systems and most folks with reed valves find that they get SOME decel popping with the throttle closed. Fresh air in the combustion chamber (actually the exhaust runner adjacent to the combustion chamber) is the reason. It would help to block off the reed valves and I suspect some plates with some Ultra Gray Permatex RTV to seal would be the answer. Then you could get rid of all those hoses and such. Make sure you plug the #4 carb vacuum spigot with a 7/32" vacuum cap.

If you are out 4 turns, this is dangerously close to the end of the thread on most any pilot mixture screw. They have a spring under the screw to add mechanical lock so the screw won't back out when vibrated. You might want to invest in a set of pilot jets one size up from whatever is in there so you can get the mixture screw back into the middle of its adjust range which is likely ~ 1.5 to 2.0 turns out from lightly seated.

I get no decel popping with a Two Brothers slip on and stock airbox/air filter which I will likely keep. I will probably pull the PAIR system off as it makes removing the valve cover something of a chore.

I also added 5" long vacuum lines to each sync port as these are miserably hard to get to without removing the carbs. I removed the carbs, added the lines and put straight vacuum fittings in the lines which can be capped with vacuum caps after sync-ing the carbs. The carbs were out of sync a bit which might have accounted for some of the blurred mirrors I have experienced. I haven't had much of a chance to ride since this weekend since the missus and I went out on one of our Kawasakis for a joy ride on Sunday after church. The Kaw has a better passenger seat and backrest.

Rocketjock · « **Reply #3 on:** April 03, 2007, 08:20:09 PM »

Quote from: "wiredgeorge"

If you are out 4 turns, this is dangerously close to the end of the thread on most any pilot mixture screw. They have a spring under the screw to add mechanical lock so the screw won't back out when vibrated. You might want to invest in a set of pilot jets one size up from whatever is in there so you can get the mixture screw back into the middle of its adjust range which is likely ~ 1.5 to 2.0 turns out from lightly seated.

Don't know if you own a 1200 06 Bandit or not, George, but your screw settings are way out for that bike. Mine came stock factory set at 3.5 turns. What most people call "way lean". Ivan's suggested start point is 4 turns. He did supply extra shims and suggested trying without first. Maybe instead of turning out past 4 I should drop a single set of shim washers in. I'm really not keen in takin those carbs off again, at least for this year. But popin the tops is doable.

Red01 · « **Reply #4 on:** April 04, 2007, 09:47:45 AM »

FWIW - folks with Holeshot kits usually run 3-3.5 turns out and folks with Ivan's kit usually run ~4 turns... but conventional wisdom does state when you have to run 4 or more turns out, you should be considering a bigger jet.

Rocketjock · « **Reply #5 on:** April 04, 2007, 11:12:54 AM »

Disconnected PAIRS, plugged airbox nipple and PAIRS hose and had same decel pop. Am now in the process of removing the whole damn PAIRS system and making up four little stainless plates to cover the holes. Have the origional gaskets as new so sealing them up won't be a problem. Reread Ivan's instructions and he says screw settings should be between 3.5 and 4. Needle clip position #2 to 3 from top. I may have it at 2. Supplied shims are for half step adjustment. So hopefully these will do the trick. Now, the big question is, can I get the tops off without removing the carbs again. It looks like I can. I DO NOT want to remove those carbs again!

Red01 · « **Reply #6 on:** April 04, 2007, 12:52:38 PM »

You should be able to. As I understand, the frame on the 06 is pretty much the same as the 01-05 except for the tail (even that is similar). Anyway, you can get the tops off on the earlier ones, so I'm guessing you can, too.

wiredgeorge · « **Reply #7 on:** April 04, 2007, 04:53:01 PM »

Air leaking into the combustion chamber will cause popping. The PAIRS system is a likely culprit but have you had the headpipes off? Most Japanese manufacturers use copper or mesh crush gaskets that can't be reused. If you do reuse them, some air leaks in and POP POP POP...

Rocketjock · « **Reply #8 on:** April 05, 2007, 10:56:23 AM »

Negative. Bought the slipon and the header remains untouched. I suspect plating off the openings will definately help with the decel pop. Trying one set of (supplied) shims between needle clip settings. Hope that does the trick. Find out later today. If it stops raining. (Bike's still too pretty to rain ride.Lol.)

wiredgeorge · « **Reply #9 on:** April 06, 2007, 09:29:14 AM »

The popping is a lean condition with the throttle shut or nearly shut. The reason might be an air leak in the pilot system. The pilot system is the idle circuit. Can be choke plunger pads leaking, vacuum caps leaking, the smog hose on #4 vacuum port leaking, poor seal on the intake manifolds, bad orings on the mixture screws or bad exhaust gaskets. That is about it as far as air leaks. The other reason for "lean" is that the pilot circuit is lean. Shimming the jet needle won't make a difference as the jet needle / needle jet don't meter gas till you transition off the pilot circuit. The pilot circuit actually meters gas the whole time but since it supplies so much less than the mid-range circuit, its effect isn't all that great. The effect of the needle jet/jet needle with the throttle closed is negligible since the jet needle is fully seated in the needle jets. To richen the pilot circuit, you can adjust the pilot mixture screw out. From what I have been reading, this is pretty much the standard practice but I would look at buying a larger set of pilot jets... one size up from whatever is there now and turning the mixture screws out somewhat less as the larger pilot size will not require as many turns out of the pilot screw. If there are replaceable pilot air jets, then you could also downsize the those a tad as well but I prefer to use a bit bigger pilot jets.

Rocketjock · « **Reply #10 on:** April 16, 2007, 11:10:40 AM »

Added Ivan's supplied shims and backed the screws down to 3.5. All is well. Decel pop is minimal. My ears are ringing, tho. Earplug on a bike are new to me but will now be a given necessity.