Help with carb adjustment please

[gdeangel]

Read the CV Tuning post, but I need a little more basic help. There used to be a tab on the old White Knight that explained when the various circuits kick in, etc. That's the kind of primer I'm looking to reference.

As I understand it, you've got a main jet (WOT), a needle jet, slow jet, idle circuit, and idle bypass. And somewhere in there is the pilot jet, which seems to be the only thing you can adjust (besides idle / butterfly position @ zero throttle) unless you rejet the carb or start clipping springs. I prefer to keep stock jets if possible, which I just cleaned.

Now my problem: when I set the idle screw cold so that the bike won't stall I get a stable idle around 1100 RMP. Then I start out running ok, but after the bike warms up / if I push it to 7K/redline, after I come back down, I get throttle surge at zero throttle / neutral / clutch in. I hit the 25MPH city street and end up riding in 5th gear, with zero throttle, going about 20MPH at 1800 RPM. If I clutch it, the engine surges to 4000K and I can't get it back down unless I close the butterfly / idle adjustment screw again. When I set it back to 1200 idle at this point, then it will start out running ok again, and the surging looks like it is gone... seems to be fine for a while... until I come to stop @ zero throttle and then it wants to idle down to 400 in neutral and stalls. I can goose the throttle to keep it alive till I start moving again, at which point I have smooth acceleration right up to reline, and no surging. But if I use the idle adjustment screw to get it back to 1100 RMP idle, the whole problem comes back. Problem seems to be related to whatever circuit starts kicking in around 2000 to 2200 RPM.

Can someone here with knowledge of the circuits on this carb please help.

Thanks!

[Blaine]

Check your slides for smooth operation (lift with your finger & should "snap" back closed) If not you have a diaphram leaking.

[gdeangel]

Pistons moved smoothly when carb was apart. Agree if piston not dropping smoothly that would cause problem. Good catch. I just hate to have to pull carbs again. If there is an air leak, it's going to come from ripping up the boots on the air box one of these times (still ok now). Maybe I put something in wrong / blocked the holes in the piston or something like that.

If it was an air leak in the diaphragm, the needle would fail to rise as the main kicks in. Slide would not be opening enough at WOT, right? At idle, shouldn't make difference because the venturi isn't generating any pressure differential anyway, UNLESS the butterfly is open too far when set at 1200 cold. Don't see why that would change when the bike warms up though.

Seems I have exact opposite problem. Possible the mid-range and/or main jet is kicking in but then not dropping the needles as the butterfly closes and the slide (should) drop. Let's say the idle position with the butterfly "open" to 1200 RPM cold is drawing only the pilot / idle bypass circuit, seems I can test whether it's problem with the slide / needle getting stuck open by warming up without going over 1/4 throttle. If the problem happens, I can rule out mid / main circuits. If not, then problem is that my idle mixture / levels are off causing it to be idling on the mid and not the pilot.

I found the rest of the CV Carb tuning instructions from factorypro's website, and they end saying that the idle should be under 1000 RPM to get mixture correct. What's up with that?

Also seems my problem could be caused by obstruction to vacuum port leading to lower diaphragm chamber (fail to maintain atmos. pressure), but I'm not sure where that is on the carb.

[eaglerider]

The idle info is probably for a different bike...idle on the 454 is 1150 - 1200RPM.

[gdeangel]

Inspected slide piston and found small ridge. Still moves freely though. Anybody have experience coating engine side of slide w anti seize grease?

Odd though b.c. bike didn't have this problem before i cleaned carb. These ridges didn't come from riding around in one afternoon.

UPDATE: buffed the slide smooth with some polishing compound and a Dremmel. Then coated lightly with anti-seize lube on both engine and airbox sides. With the carbs off the bike but reassembled, and my air gun about 6 inches from the carb, I shot compressed air into the semi-circle atmos. openning that connects to the lower diaphram chamber, simulating pressure differential. Slide rose fine. Shut off compressed air, and slide dropped in a slow and controlled manner - no catching or anything, just not too fast.

So I also figure my idle circuit might be requiring too much vacuum to hit 1200 with my floats set outside spec (was having flooding issue after I first reassembled bike). With new float needles, I set float height to 17.7mm, and checked fuel level with the homemade manometer (1/4 tubing and magic marker). Fuel level is now just up to the base of the carb, maybe .5 mm higher, depending on how thick the magic marker line is. With that I also leaned out the pilot screw from 2.5 back to 1.5 back.

The result was the hesitation described in the CV tuning post, so dialed up the pilot to 3.0 back. Got the butterfly set at a nice 1100 RMP, and sitting in garage I can hit WOT and it's coming back down ok, although there is some hesitation where you can see around 4K and again around 2200K, when the slide is taking some time to drop. But the real interesting thing is how it rides. Trolling along at under 2000 RMP, it will idle right back to 1200. But if you run it up anywhere into the mid circuit, then it wants to stay there. Running at 3000, and clutch in, it will power shift to at 4000. If I hit 7000 +, it will come back down to mide range, 3k-4k, but won't switch back to the idle / pilot circuit. This makes for some adrenaline takeoffs, but not comes the REALLY REALLY intersting thing. If I make a controlled deceleration in gear, without rapid down shift, then as the RPM's drop down to the 2000-2400 range, the pressures will equalize again in the diaphram, the slide drops, needle seats, and I come to a nice quiet stop at 1200 RMP.

I don't know whether to keep messing with it or just leave it, since I don't mind the power shifts and knowing what to expect, I'm probably not going to end up wrapped around a tree. On the other hand, my main reason to keep this bike is to give to my kids, and so this kind of power shifting isn't ideal.

Anyone else have similar experience or know what might be causing this? As far as I can tell, there are no air leaks, and I even reseated the diaphram "inside out" to get it lined up with the little channel.

[gdeangel]

Alright, did some more road testing, here's what I found....

At around 1/4 throttle (2000-2200 RPM), that is where the problem is. I can ride around all day and night one the idle circuit under 2000 RPM. Clutch in, neutral, bike idles down nicely to 1100.

Go to the mid range circuit, over 2000 RPM, and at that point it wants to surge up to 3000-4000. Once you get it back down under 2000 again, it switches back to idle circuit and no problem.

And it drives fast, doesn't stall, and shifts cleanly this way. Problem is you have to power brake it to get back to an idle once your cruising.

At WOT, it will return to the mid range circuit and maintain a steady 3000-4000 RPM.

This doesn't sound like a stuck piston - which wouldn't cause the rise. It does sound like an air pressure issue, but for the life of me I can't find any air leak. Which leads me to believe it's a tuning issue, and somehow I've got the top of the idle circuit overlapping the mid circuit that the butterfly is too far open at 2000 RPM and it's lowering the pressure in the venturi so much that the slide opens wider than it should, and doesn't want to close.

Carbs are synch'd (check with a wire last night when I had it off the bike), and butterfly idle is set just behind the first indicator hole, as I read is spec. So that leaves me with nothing to go on except that this is just how the CV carb works. But still doesn't seem right to me. And I already know where it's going to mess me up - going up a curb in 1'st, rev to around 3000 RPM, then back off the trottle, and relax the brake, but the bike will surge on its own to 4000 and I'll be kissing the hood of somebody's car. Not cool.

[eaglerider]

I don't remember if you mentioned as to if you have checked/adjusted the valves.....have you? If not, stop everything, and do a good valve adjustment, following the directions that are in posts here on the forum. If the valves are not adjusted properly, everything else is useless....this engine requires a good valve adjustment about every 5,000 miles, in order to run right, and make all other adjustments effective.

[gdeangel]

Thanks eagle! Valve clearances were checked at the local "vintage" shop 2 yrs ago when it had a little over 5000 miles. They did something with the valves for sure as the bike came back noticeably noisier. Will find that post and get on it myself this time.

Just thinking a little out-loud, a poorly seating valve would affect power, and that's not an issue. A valve clearance above spec would not open "long enough", and the breathing cycle of the engine would be shortened, meaning chopping air flow in venturi, and a slide that's more prone to searching. Valve clearance below speck would open "too long", and if we're talking intake valve, the cumulative amount of time (for 1000x cycles) air is being sucked through the venturi starts to be affected. More air through venturi per second = lower pressure = bigger diff to atmos. = upward pressure on diahpram = mid / main circuits activated. That would explain a lot. Will report back when I have another weekend to take off the head.