Scooterotica

Have there been any further developments finding a solution to the 1/4 throttle weakness with the 30phbh?

diesel wrote:Have there been any further developments finding a solution to the 1/4 throttle weakness with the 30phbh?

65 idle..

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Cheers Andy,

I can't weigh up this quarter throttle weak mixture. For years I've been struggling to get rid of the rich spot I always get at 1/8 - 1/4 throttle. I reckon if the thing will adjust to idle properly with a 65 idle jet there's an air leak.

There should be no weak spot with AV266 and X13.

Special X wrote:I can't weigh up this quarter throttle weak mixture. For years I've been struggling to get rid of the rich spot I always get at 1/8 - 1/4 throttle. I reckon if the thing will adjust to idle properly with a 65 idle jet there's an air leak.

There should be no weak spot with AV266 and X13.

No air leak, after countless testing and dyno runs 65 idle is needed to eliminate the weak 1/4 throttle and the advise from Ron to myself and others is the fitting of said Jet, but of course as Ron will tell you himself please check plug colour..

Andy Pickering wrote:

Special X wrote:I can't weigh up this quarter throttle weak mixture. For years I've been struggling to get rid of the rich spot I always get at 1/8 - 1/4 throttle. I reckon if the thing will adjust to idle properly with a 65 idle jet there's an air leak.

There should be no weak spot with AV266 and X13.

No air leak, after countless testing and dyno runs 65 idle is needed to eliminate the weak 1/4 throttle and the advise from Ron to myself and others is the fitting of said Jet, but of course as Ron will tell you himself please check plug colour..

He will also tell you that every set up is different i.e. exhaust, filtered/un-filtered, ignition timing, that 65 pilot may not suit all engines. I only have a 55 in mine with a breathsweet filter and if anything I'd say it was a bit boggy at 1/4 throttle. Not been on a dyno yet though, just trying to find time to book a session with Al.

Making the mixture too rich at tickover isn't the right way to address weakness at quarter throttle. That's something a racer might do as he won't give a rats ass if it runs like a bag of shite on the road and in traffic but not on a road bike.
with a 55 pilot, 40 slide, X13 2/3 clip, AV266, 125 main, and no air leaks take it to Al's Dyno and it'll be rich from progression to WOT with a rich spike between 1/8 and 1/4 throttle.

Coaster, you're totally agreeing with me as you're saying you've got a feeling it's rich at 1/4 throttle. Very tiny difference in airflow between breathsweet and open carb and certainly none at all until at least 3/4 throttle.

Special X wrote:Coaster, you're totally agreeing with me as you're saying you've got a feeling it's rich at 1/4 throttle. Very tiny difference in airflow between breathsweet and open carb and certainly none at all until at least 3/4 throttle.

Not so sure about the impedement to airflow with the Breathsweet on my scoot as the elbow is squashed quite a bit with the panel on, it really needs a shorter carb (PWK) or a shorted manifold than the AF one that I'm using. I'm using a CHT and it reads around 150 degrees at sustained 1/4 throttle riding, might be a bit less and rises to around 175 to 180 at 60-65. The same gauge used to read 225 at the point of nip up on my previous Indain ally 225 set up and 190 or so at 50ish. What worries me are the spikes rolling off the throttle, I'd never see that with the CHT, I do have an EHT as well but have literally only just got it working again and have no meaningfull readings as such on the Avanti.

PS, Ron might be an old racer but he is genuinly interested in getting these kits sorted, jetting carbs to run on kitted engines is not an exact science especially where different setups are emplyed from one engine to another, mine has an Augusto and dented JL3 so will obviously have significantly different jetting requirements to standard ignition and a bow exhaust.

"Augusto", yes, this will change jetting considerably over what is needed for the same motor fitted with static timing.

What has cracked me up about recent features on advance retard ignitions is that statement that a good advance/retard ignition will allow a motor to run cooler throughout the range (!). This is not true, if a static ignition is set to 17 btdc and an auto advance/retard ignition is set to range from 20 to 16 dbtdc then the motor will actually only run cooler once the ignition has retarded beyond 17 and is working its way towards 16 (or less, depending on range and starting point). From 20 (e.g.) to 17 (same as static) the advanced spark will cause the motor to run hotter, which will need to be made richer to keep the temps down and stop it from getting too hot.

The benefit of the advance at lower revs is that torque and power will increase and help the bike to pull better at these lower revs, however, it will not result in the motor running cooler. Indeed, if you start at too advanced a setting, or have too great a range of advance/retard, then you could well find that your motor is considerably hotter at cruising speeds than it would have been with the 17 dbtdc static ignition!

Auto advance/retard is the way to go if you want a motor that pulls better under a wide range of conditions (so a big thumbs up from me) but running cooler across the range is not what it offers.

Adam

coaster wrote:mine has an Augusto and dented JL3

LOL im running an augusto and battered PM25 , the 65 idle came from Rons concerns at the weak 1/4 throttle after dyno runs at Als (diablo) and the last phone conversation I had with Ron he was explaining this to me and other characteristics of the Avanti kit and of course as Coaster says each and every scooter engine will defer in some way..