3 replies to this topic

[Evo160K]

Couldn't believe my eyes when I came upon your remarkable website. I had no idea there were so many knowledgeable and enthusiastic Dell'Orto fans in one place. For the most part dellortos are not that popular on Harleys in the United States any more, perhaps they're too much of a challenge for most to tune. Admittedly, I had major problems for several years trying to use harley's traditional gravity fuel flow. From a full tank to a half tank or every 10 degrees change in temperature required an idle mixture screw adjustment. Finally, the very good people at Dellorto.uk put me on to the dellorto vacuum, pulse pumps and provided excellent advise and parts. Since that time I've had very satisfactory results. I've also used many of the tuning books, including Jack Wagner's book on tuning dellortos for harleys.

My question: since I'm always trying to learn and considering the topic of my post may not be appropriate to your website, are you able to direct me to a comparable site or source that is? Thank you very much.

Edited by Evo160K, 15 January 2012 - 12:12 AM.

[Evo160K]

Would you please help with a problem I'm experiencing? On sustained high speed runs to approx 4800-5000 rpm and brief WOT acceleration through the gears, the engine begins to stumble like it's running out of fuel. When I back off the throttle the engine will slowly pick up again. The engine details are

1606 cc (803/ cyl)
36 chokes
05 main emulsion tubes
155 main jets
190 air correctors
Grose jet (fuel needle and seat)
Dell' Orto pulse fuel pump - I calculate it will support approx 100 hp
03 idle jet holders
60 idle jets

Thank you very much.

[Nick Jones]

I'm not a Dellorto expert but it sounds to me like you are drawing more fuel that the supply can stand. I'd be wondering about things like

fuel line size
tank venting

Also, I don't know much about these pulse fuel pumps, but sounds like they are powered by manifold vacuum and at big throttle openings there isn't very much manifold vacuum.....

Cheers

Nick

[Evo160K]

Mr. Jones,

Thank you very much for your comments. I appreciate them.

The venting I can check by cracking the fuel cap when the stumbling presents. To check the fuel line size, (I believe it's a 1/4" id), I can bypass the fuel pump and static check fuel flow through the line by measuring the free flow. With that number I should be able to calculate how much horsepower that flow will support at wide open throttle rpm. I think that will tell me if the fuel line is sufficiently sized to the pump. Does that make sense to you?

Regarding flow through the pump, you're suggesting there may not be adequate pumping at wide open throttle to deliver sufficient fuel because the pump more or less stops working due to low vacuum. I hadn't thought of that possibility. Do you have a thought on how I can test to see if that is the case?

Thank you.