Musings over morning coffee: Dellorto off-idle stumble

[bmweuro]

Get rid of the accelerator pumps and by the cover plates for them from:
HANSON RACING TECHNOLOGY
4950 COHASSET ROAD #4
CHICO, CA 95973-9000
USA
530-342-8049 (voice or fax)

You can argue or listen to SS but there absolutely no one that has more Del orto experience than this guy.

The R90S sidecar rig I built had the same issue. I did this very same thing and it took care of the problem, mileage went up and it accelerated very smooth.

[supershaft]

Originally Posted by Rucksta

Probably because the adjustment range of the equivalent part on the Del is so fine and narrow it's usefulness is limited to little more than balancing the carbs.

The mixture is determined by the jet, the amount of mixture delivered is determined by the screw position paradoxicaly known as the idle mix adjustment screw.

Transitional arrangements on the Del are somewhat crude with an orifice immediately upstream of the closing edge of the slide.
Overuse of the slide screw ( Idle speed adjustment screw) of a magnitude indicating a increase in slide cutaway is required can lead to confusion of this primitive transitional mixture arrangement producing rough tranistions or flat spots.

This is one of the evils masked by the pumps.

SS chime in here if you have a different understanding of the idle & transitional circuts .
I've come to terms with it in this way and it has produced results but I'm open to alternate ways of thinking & tuning.

I think I already mentioned the mixture screws up above early on. It does seem to me the the idle jet size is more important versus the mixture screw adjustment than Bings with or without the pumps.

I don't know about Dell's being any cruder in design than the other carbs mentioned here but they are a bit tricky to set up at low throttle/high vacuum steady throttle. I don't think you can ever get them as good right there as some other carbs? At least I haven't. I have got them a lot better but it took some doing. Again, this part of the equation IMO has little to do with the pumps.

I have tried to stay away from the 'looks' issue but I do like the looks of Dell's more than Bings or Mikuni's. The main reason I like Dells is that the airbox snorlels work right with them. Keeping dirt out of my engines is very important and I have worked with enough Mikuni setups that were letting a lot of dirt by.

I have never gotten around to putting cover plates over my pumps. I have known of them since I was a kid. I get my parts from Herdan's.

Argue or listen? Some of us discuss the topic of the thread. It's rare around here but it does happen.

[Rucksta]

Originally Posted by bmweuro

The R90S sidecar rig I built had the same issue. I did this very same thing and it took care of the problem, mileage went up and it accelerated very smooth.

Best economy for me is midrange lean past marginal and pumps kicking in at 1/4 to 1/2 throttle.
Economic crusie and instant throttle response OK for hard surfaces but lacks 100kph top gear power in deep sand.


I like the look of the pump bodies even if I'm not using them right now.