Delorto PHM40 tuning

[micmel]

I need advise concerning tuning my carbs. I have a Lemans IV with PHM40 carburetors and I'm trying to adjust and balance my carbs. I started with my mixture screws turned out 1 1/2 turns. When I try to adjust the mixture screws I can turn both sides all the way in with no effect to either side. Shouldn't I be able to lean them out to the point of not running? Any advise would be appreciated.

[pete roper]

Yes, but only if everything else is *right*. How much do you understand about how carburetors work?

Pete

[micmel]

Not as much as I thought I did. I'm use to bing carburetors and the more I read about the PHM40 the more I realize there are many variables. I do understand basics had have never had any problem with all of the air head BMW's I've owned. Do you have any advise?

[pete roper]

Firdt thing. Go and download and read the DellOrto tuning manual.

Secondly.

Closed to 1/16th or so of throttle opening is controllded by the pilot circuit.

1/16-1/8th is mainly slide cutaway.

everwhere from there right through to about 7/8ths opening is controlled by the needle and atomiser choice, (As long as the main jets aren't grossly small.)

The last 1/th or so is dependent entirely on main jet and manifold depression.

PHM's do not have a 'Choke'. They use an enrichener circuit witha jet closed by a plunger. Make sure the plungers are seating fully or the mixture will never respond to the screws.

Pete

[micmel]

Pete,

Thank you for the help, I down loaded the manual and will start over.

Michael