32mm PHF Dellorto stock specs for needle and jets?

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confusa
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32mm PHF Dellorto stock specs for needle and jets?

Post by confusa » Thu Jul 22, 2010 10:41 pm

Trying to find out what the stock setup of 32mm 860 GT carbs would be as far as the jets that came in them, pilot and main, as well as needle and clip position. Looked through all the info and books I have and couldn't find it.

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Steve Foster
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Post by Steve Foster » Fri Jul 23, 2010 2:32 am

Ian Falloon's book "Ducati Twins Restoration Guide, Bevel Drive 1971-1985", p.216, gives the carb specs for the 860 GT as follows: Needle- K6/2nd; Main - 122; Pilot - 60; Slide - 70/2; Needle Jet - 265AB.

Mick Walker gives the same info in his "Ducati Twins Restoration", p.228.

Steve.
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Post by Ray O'Donohue » Fri Jul 23, 2010 9:55 am

Whatever you do,be sure to use ONLY a 60-1 slide,with the pump set for 5cc per 20 squirts. Just do it,for any and all Dellorto applications.

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Post by BevHevSteve » Fri Jul 23, 2010 1:52 pm

Ray O'Donohue wrote:Whatever you do,be sure to use ONLY a 60-1 slide,with the pump set for 5cc per 20 squirts. Just do it,for any and all Dellorto applications.
well I agree with the "5cc per 20 pulls on the cable" setup for the pump adjuster, but bold statements like ONLY USE A 60/1 SLIDE FOR ALL DELLORTO APPLICATIONS is a completely useless statement to make without posting back to back dyno charts comparing stock slides to your 60/1 recommendation.
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Post by Ray O'Donohue » Tue Jul 27, 2010 12:13 pm

Dyno Schmyno: You do what you want. I don't care. I'm just trying to be helpful.I learned it from (dyno genius) C.R.Axtell,altho I doubt if he made that discovery via the dyno. It will fix your bike.So sorry I can't provide dyno charts.

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Post by Steve Foster » Tue Jul 27, 2010 4:34 pm

Hi Ray - I guess that the more general point that could be made (and perhaps this is what Steve was alluding to) is that it's always useful to have some sort of evidence or at least a reason or justification to support such claims. Do you know why a 60/1 slide would be better than a 70/2, and the sort of issues that such a change would address?

The carburetion requirements across the various models from a 750 GT to a 900SS will surely vary and the factory does have some credibility when it comes to standard specifications. That's not to say that improvements can't be made however and different jets and slides could lead to improvements for particular circumstances.

The difference between slides is the size of the cutaway (e.g. 60mm or 70 mm) and the pump control ramp characteristics (how steep and when it starts). A "1" slide pump ramp starts at 10mm from the top of the slide and ends at 20mm. A "2" slide starts and ends at 13mm-23mm so there is hardly any difference between these two. A "3" ramp is 2mm-30mm so it differs significantly from the 1 and 2.

Any further info that you could provide would be welcome. Regards, Steve.
1974 Ducati 750 GT

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Post by Ray O'Donohue » Thu Jul 29, 2010 9:30 am

Steve: There's a lot to unpack here,but just for the moment I would just remind you that there were dozens of things terribly wrong with every production run of 750GT's,stupid little things that could have been done correctly by the factory at zero cost,of which the continuing slide snafu was only one example.Why and how those things occurred is another topic. As to the slides,again,I'm not being pig-headed when I tell you that every carbureted Ducati bevel twin of every description,from a stock 750GT to a full blown racer with 40mm carbs will give dramatically better throttle response with the setup I have given you. I thought everybody knew this by now.

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Post by Ray O'Donohue » Thu Jul 29, 2010 9:57 am

This set-up was developed for the XR750 Harley w/40's,which is obviously why it works for a 750SS with 40's. Why it works wonders for a stock GT 750 with smaller carbs and stupidly low compression is another matter,but it certainly does. And if it works across that range of tuning

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Post by machten » Thu Aug 05, 2010 4:53 am

Hmm,

well I have a few roundcases and a few squarecases of various capacities, but all with PHF32s. I tune them myself and have done for many, many years, and I have to say a "one size slide fits all" defies some pretty fundemantal laws of physics.

I'd stick with the factory slide recommedations unless you change cams, valve sizes or ride at high altitude all the time.

Kev

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Post by Ray O'Donohue » Thu Aug 05, 2010 5:29 am

As for"factory slide recommedations": it's obvious that there was rarely any such thorough tuning process going on or being applied consistently at the chaotic place that Ducati was in those days. What they usually sold you was what they had somehow managed to finance,acquire, and put together for a batch of bikes,and probably the next model would be a bit better. Thus the specifications list a # 70 slide because that's what was in the bikes.They also came such tuning niceties as 7.5 to 1 compression,a non-functioning squish band,and an ignition that set a record for low secondary voltage.Look,it's your bike.I don't care what you do.But if you want to enjoy riding your bike a lot more,just install that set-up.

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Post by machten » Thu Aug 05, 2010 6:03 am

Ray,

It's not my bike the question was about. I set my bikes up as I think best and I've had 33 years of doing so, soi I feel entitled to have some opinion.

I'm assuming here we are setting up a bike for road (not race use). You might feel that things are otherwise, but I'm afraid you can't argue with the laws of physics. The purpose of a slide in a PHF carb is purely to control the mix of fuel and air from the main jet after the idle jet has maxed it's job. The pumper adds it's bit to this. The mix of fuel and air required for the "best" result is dependant on many things including piston cc volume (the space to occupy), cam timing, compression ratio, fuel ocatane level, exhaust backpressure, needle setting, jet size, altitude, air density...(we could go on)

But one slide addresses all...sorry, i don't think so.

Kev

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Post by Ray O'Donohue » Fri Aug 06, 2010 5:30 am

Yes,yes,everything affects airflow,and I'm sure you guys are all fine tuners,and yes,I am taking an entirely empirical approach.You don't have use the set-up,which you might even be able to try for no cost by borrowing a set of slides. What I am a bit baffled by is this idea that the Ducati folks had any good reason for the multitude of idiocies that they routinely committed in those days. This was not la Japanese company.The secondary ignition voltage of those bikes was "X" (I don't remember the number,but it was half that of a Norton Commando which was in turn half that of most bikes in that era.) By you folks' thinking,that constitutes Ducati's spec/reccomendation for those bikes.Well those bikes wouldn't start and run with a plug gap above .024,and you could increase the idle speed by 200 rpm merely by swapping the ignition coils out with any available coil.Everybody did it.The slide situation was a similar phenomenon.

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Post by wdietz186 » Sat Aug 07, 2010 7:10 pm

I do feel I must jump in and defend Rays assertion as to the slides on Bevels.It does help and it helps alot. Most all the 750's and 860's I have dealt with have had a dead/flat spot right off idle even when fitted with the stock air filtration setup[Anyone remember riding a bike with those?]
Fiddling with the mixture screws,pilot jets, and to some extent the pump will lessen the symptom and most just accept it as an idiosyncracy of the bike and ride around it.But the richer mix provided at 1/8 + throttle the 60/1 slide provides improves the tractability 100% I've used them in my bikes for 30+ years.

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Post by Steve Foster » Sun Aug 08, 2010 6:06 am

Ray - I have to agree with you when you say that there were many things wrong with every production run of 750 GTs, and that Ducati was a chaotic place in those days, but fortunately the majority of those niggles (e.g. crap switches, poor generator, spaghetti wiring, rusty head nuts, poor paint, etc) were fairly inconsequential to on-road performance and the really important stuff (frame, brakes, suspension, wheels - Borranis at least - and engine) were among the best there was. Sure the coils were hopeless but I never saw a factory spec sheet saying that the recommended secondary voltage was the as provided "X" kV. Upgrading the coils was the first modification I made. Junking the standard air filters with the crushable concertina air hoses was the second. I'm glad they cut costs on the stuff that was easily fixed and got the basics right.

As wdietz186 points out, the 60 cutaway richens the mixture slightly compared to a 70 up to about one-quarter throttle. I can understand why this could be beneficial. Personally, I haven't experienced the dead/flat spot right off idle that he mentions with the 70/2s I use. And if it's throttle response we're talking about here then that wouldn't necessarily show on a dyno chart.

By the way, I got it wrong in my post of 28 July - should have been 6mm or 7mm for the cutaway, not 60 or 70mm. D'Oh!

For me, this has been a useful discussion with many valid points of view. As my bike aint broke I'm not going to try to fix it by changing slides but I would really like to try a set of 60/1s if I had the opportunity to do so at no cost.

Thanks to all.

Steve.
1974 Ducati 750 GT

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Post by machten » Mon Aug 09, 2010 12:40 am

For me, this has been a useful discussion with many valid points of view.
Ditto...and...
As my bike aint broke I'm not going to try to fix it by changing slides but I would really like to try a set of 60/1s if I had the opportunity to do so at no cost.
Ditto

Kev

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