Quick Dellorto help, please

Hey, all you Dellorto 40mm guys!

I've decided to do a springtime tweak of my carbs and discovered that my Thomlinson Dellorto book is up in Massachusetts. Not a lot of help 1,000 miles away.

I want to adjust the accelerator pump stroke but can't remember whether more acc pump flow per gas pedal stroke is turning the adjuster nut IN or OUT? When running on the idle jets, and at moderate throttle, I see it go lean when accelerating for a second or two until the jets catch up, so I want to increase the pump output a tad. (That's watching an air/fuel meter.)

Just went out and looked and I only have about 1/8" of threads left beyond the acc. pump adjuster nut, so they're out about as far as they can go. Is this about what you other Dell 40 guys have? If that's it, I'll leave them, but if they squirt more by running the nuts in a bit I could try that, too. What length of threads beyond the adjuster nut do YOU see?

Thanks, guys.....

gn

Usually, the longer the stroke more fuel is added

This is true, unless the nut isn't touching the accelerator pump arm in the closed position (which it likely is not, nor should it likely be). I've got mine adjusted so there is the slightest bit of clearance between the arm and the nut and it works well there. Turning it in more would reduce the volume of the "squirt", but it would bring it in more quickly. Turning it in too far will just make it dribble all the time, which is always bad.

I'll have to look at mine, doesn't mean they are correct. If you'd like to know the procedure from the book to test and set the pumps let me know. Each pump jet operating in dual carbs on a 1600 cc engine should deliver .4 to .5cc for every two throttle openings. Larger engines (yours) require slightly more.

Gordon -- that's one thing you won't find in Tomlinson (at least I never did).
All I can find for you is: "Delivery of the pump can be adjusted by turning the nut (reference 43 on page 55).

That's all you get -- it doesn't say turning it one way or the other will cause increased volume or decreased volume.

I just used the trial and error method. At one time the exhaust would pop when I jabbed the throttle. I don't remember which way I turned the screws but I turned them until is stopped doing that. That was done years ago and I haven't touched them since.

I just went out and looked at the carbs and they're set up about like Stan says. The pump lever actuates about the same time as throttles leave idle. I have 3/8" threads showing. I have Dell 48s, but I think the pump is the same for all, the only variance between carb sizes being the jet size.

Thanks, guys.....good info...and now that I think of it, Mark's right - Thomlinson doesn't tell you the correct adjustment, only that you have to adjust them!

Yes, I know the range of cc's that they should put out, but that also depends on the size of the accelerator pump jets, the arm stroke, yadda, yadda...

Besides, as Captain Barbosa always says in 'Pirates of the Caribbean'; "That's more of a suggestion, rather than a rule". You still have to dial them in.......

Anyway, good visual, Stan. I'll wander out and check and I think you're right - the charge eventually overcomes the initial lean-ness and recovers, but it just seems a tad late so getting the squirt started sooner would probably cure it.

Didn't seem to be too bad until after Chris' wedding when it died and 4 car guys (the MItsubishi Racing Club wedding party) were trying to figure out what was wrong so maybe one of them messed with something unrelated. They didn't know (Hell, they're all EFI guys!!) and it turned out to be a broken rocker arm shaft instead.

Thanks again!

gn