Carbs

[richard mackay]

I am fitting a pair of dhla 40's to my RH,and i have some consern about the operation of the accelor pumps.When you operate the throttle lever there are conecting rods which go down to the pump levers.The rods move down the way,but in order to operate the pumps the pump levers have to move up the way,what actually happens is,the rods slide up and down through the holes that conect them to the pump levers

[Longboarder]

The accelerator pump diaphragm is in a flat relaxed position when the throttles are closed with the pump chamber full of fuel. The lock nut on the pump rod supports the pump lever and determines the position of the diaphragm. When the throttle is opened the pump rod moves down through the pump lever. The lock nut on the rod is thus pushed down below the lever end. The rod spring above the pump lever 'free end' then forces the lever down which being pivoted in the chamber cover and having a big mechanical advantage over the 'chamber end' of the lever puts upward pressure on the diaphragm, pressurising the petrol in the pump chamber. This pressure forces the inlet valve ball closed, and the only route left for the petrol in the pump chamber is through the pump jet into the choke to provide acceleration enrichment. The volume of extra petrol 'injected' depends on the lever stroke, the position of the lock nut on the pump rod giving an adjustable starting position for the pump stroke and the degree to which the throttle is opened determining the end position of the pump stroke.The flow rate of the extra petrol and also the duration of the enrichment is dependant on the size of the accelerator pump jet. (It's also dependant on the mechanical advantage of the pump lever and the relative strengths of the rod spring and the diaphragm return spring but these give a fixed pressure and are not adjustable) The overall result is that you can alter the rate and duration of the enrichment the DHLA's give you on opening the throttles and the carb will automatically adjust for the degree of throttle opening. Clever these Italians.

 

It sounds as if you might not have the rod springs in place. These should be fitted on the pump rods between the mechanism on the butterfly spindle and the pump lever end, with the lock nut being fitted below the pump lever.

 

Nigel

[richard mackay]

The accelerator pump diaphragm is in a flat relaxed position when the throttles are closed with the pump chamber full of fuel. The lock nut on the pump rod supports the pump lever and determines the position of the diaphragm. When the throttle is opened the pump rod moves down through the pump lever. The lock nut on the rod is thus pushed down below the lever end. The rod spring above the pump lever 'free end' then forces the lever down which being pivoted in the chamber cover and having a big mechanical advantage over the 'chamber end' of the lever puts upward pressure on the diaphragm, pressurising the petrol in the pump chamber. This pressure forces the inlet valve ball closed, and the only route left for the petrol in the pump chamber is through the pump jet into the choke to provide acceleration enrichment. The volume of extra petrol 'injected' depends on the lever stroke, the position of the lock nut on the pump rod giving an adjustable starting position for the pump stroke and the degree to which the throttle is opened determining the end position of the pump stroke.The flow rate of the extra petrol and also the duration of the enrichment is dependant on the size of the accelerator pump jet. (It's also dependant on the mechanical advantage of the pump lever and the relative strengths of the rod spring and the diaphragm return spring but these give a fixed pressure and are not adjustable) The overall result is that you can alter the rate and duration of the enrichment the DHLA's give you on opening the throttles and the carb will automatically adjust for the degree of throttle opening. Clever these Italians.

 

It sounds as if you might not have the rod springs in place. These should be fitted on the pump rods between the mechanism on the butterfly spindle and the pump lever end, with the lock nut being fitted below the pump lever.

 

Nigel

[richard mackay]

Thanks Nigel,had to read your replay a couple of times to understand it.What is actually happening is the rods are moving up and down but not moving the pump levers.Am right in saying then that i will have to ajust nuts on the bottom of the rods.By the way the springs are there.

Looking forward to your replay and ahappy new year.

 

Richard

[Bob Tucker]

Hope the attached pics help...

You have to tighten the nuts to make the rod pull the arm up first.

Then when the throttle opens the spring can push it back down.

HTH Bob

 

BUG**ER Ive named the pics the wrong way round.

 

There is a gap between the locknut & the arm when the throttle is OPEN.

[richard mackay]

Hope the attached pics help...

You have to tighten the nuts to make the rod pull the arm up first.

Then when the throttle opens the spring can push it back down.

HTH Bob

 

BUG**ER Ive named the pics the wrong way round.

 

There is a gap between the locknut & the arm when the throttle is OPEN.

[richard mackay]

Cheers Bob,off to sort that now

Happy new year

Richard

[Longboarder]

Richard, the pump rods are easy to break. Always give them a squirt of penetrating oil and use two spanners when unlocking the nuts. Don't be tempted to use only one or they snap. Racecar can supply spares.

 

Nigel

[richard mackay]

Cheers Nigel.

Got the job done and the carbs are fitted.Ordered trumpets from Eurocarb so hope to have her going soon.

Richard.