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PHF 36 Accel pump

DanPez

DanPez

Cruisin' Guzzisti
Joined
Jun 27, 2010
Messages
488
Location
Hudson, Quebec
Hi everyone,
Just getting out from hibernation. :lol:

Started the LM3 last week and found myself in a similar situation like last May.
The right cylinder was lean and the left was rich.
Removing the K-N filters I found the right pump jet was not injecting fuel when giving throttle.
Took the pump housing apart and found the diaphragm worn so I got 2 on order at MG Cycle.
Looking at the dellorto manual guide a diagram shows the fuel flow and an explanation on how it works but no adjustment instructions.
I didn't touch the adjustments last year but found the screws all the way out. Thats most probably why my plugs were black. :pinch:

Do the pump adjusting screws start off all the way in, initially, then slowly unscrewing both RH and LH pump evenly till it accelerates smoothly on throttle?
Or is there a more scientific way to adjust the accelerator pump fuel dosage?
 
Greg Bender has the latest manual here: http://www.thisoldtractor.com/gtbender/ ... manual.pdf

The screw changes the stroke of the pump and therefore determines the amount of fuel. Clockwise makes more fuel. You can calibrate them by squirting fuel into a calibrated container - I'd do like five strokes and compare left and right.

The only other adjustable things are the ramp used (I think there are three different cutaways (40-50-60) with five different ramp profiles (1 through 5) ) which determines the timing and the pump jet size which determines the duration of the spray (i.e a bigger jet will reduce the time). The profiles are here: http://www.dellorto.co.uk/images/parts/Pumpramp.pdf

In practice few people bother fine tuning the jet or ramp - changing ramps requires a complete throttle valve and is expensive.

BTW sometimes the circuit needs 'priming' and can be a bit of a bitch - I think there is a ball valve that sometimes gets stuck leading to the pump not priming up properly so check it.

I'd start with the screws pretty much all the way out - a lot of racers fully totally disconnect the pump mechanism. If your jetting is correct - especially the size of cutout used which determines the - you don't really need much. If you twist the throttle relatively slowly and the plugs cut right in each transition then it is time to play with the pump. Wind it out and then in quarter turn increments, give it a fast twist of the wrist under load and see if it bogs down, add some fuel on both sides, and repeat until there is no more hesitation. Calibrate both sides as above as a final measure.

That is all I know.

Chris R
 
Chris R said:
In practice few people bother fine tuning the jet or ramp - changing ramps requires a complete throttle valve and is expensive.

BTW sometimes the circuit needs 'priming' and can be a bit of a bitch - I think there is a ball valve that sometimes gets stuck leading to the pump not priming up properly so check it.

I'd start with the screws pretty much all the way out - a lot of racers fully totally disconnect the pump mechanism. If your jetting is correct - especially the size of cutout used which determines the - you don't really need much. If you twist the throttle relatively slowly and the plugs cut right in each transition then it is time to play with the pump. Wind it out and then in quarter turn increments, give it a fast twist of the wrist under load and see if it bogs down, add some fuel on both sides, and repeat until there is no more hesitation. Calibrate both sides as above as a final measure.
Chris R
Click to expand...


I followed the advise of the guys here to size the jets and the bike is running OK https://www.guzzitech.com/forum/topic. ... =10#p42375

The set screw on both pumps are all the way out. The diaphram travels at it's max (too rich). I figure thats why the LH cylinder was cooler than the RH (And also because the RH pump wasn't working properly :blush: )..... and your right about the ball valve (check valve) on this fuel circuit I made sure it wasn't sticking.

If I got this right what your saying is to start off lean .... check the throttle response then slowly add fuel by turning the pump set screw by 1/4 turns on both carbs?
 
If I got this right what your saying is to start off lean .... check the throttle response then slowly add fuel by turning the pump set screw by 1/4 turns on both carbs?
Click to expand...

That is exactly what I am saying.There is no danger here from going too lean in the same way as for the normal jetting - the lean condition doesn't last long enough to cause any problems except for maybe a bit of hesitation. The fueling is dependent on how you drive - if you have a tendency to give a big twist of the wrist then you will dump a lot of fuel in one go. If you drive it dead gently it only makes it slightly richer at points.
 
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