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PHF32 accelerator pump - Darmah

Posted: Fri Oct 11, 2019 8:19 pm
by pigmilker
Hi everyone, I was talking to an experienced bevel person and
he mentioned to me that I should to disable the accelerator pump.
His reasoning is you use a lot more fuel for very little gain, Any
unburned fuel can end up in the crankcase.

Opinions anyone?

Re: PHF32 accelerator pump - Darmah

Posted: Sat Oct 12, 2019 2:19 am
by Craig in France
Ok, let's start by going back to basics :) . Why do carburetor manufacturers install accelerator pumps?

Pumps are fitted to provide the temporary shot of additional fuel that is required under rapid acceleration. Without pumps, the engine may starve and falter. This Wikipedia description is pretty good:

"When the throttle is rapidly opened, airflow through the carburetor increases immediately, faster than the fuel flow rate can increase. This transient oversupply of air causes a lean mixture, which makes the engine misfire (or "stumble"), an effect opposite to that which was demanded by opening the throttle"

You might also reason that if pumps weren't needed, manufacturers wouldn't fit them. And it wasn't/isn't just Dell'Orto who do/did.

1. Yes, you can disable them, especially if you don't open the throttle quickly. Whether you notice a difference might depend on your riding style.*

2. Do they cause excessive fuel consumption?
Not in my experience. I get what I judge to be an acceptable 45mpg = 16km/litre = 6.3litres/100km out of both my SSD and my Laverda Corsa, both bikes running pumps. Of course the pumps have to be adjusted right - that's a given!

3. Will they cause excess fuel to enter the crankcase?
Now we really are entering the world of pure fantasy ... :roll:

* I do know of people - often Jota owners, it should be said :), who after disconnecting the pumps had to up the size of the idle jet. So a net loss all round ... ;)

Re: PHF32 accelerator pump - Darmah

Posted: Sat Oct 12, 2019 4:51 am
by gt94stang
I would find a different "experienced" bevel guy if I were you. The accelerator pump is there for a very good reason as stated above, and if you aren't accelerating hard, the pump isn't doing anything anyway. The pump is only activated after you twist the throttle far enough to activate it (assuming you have it adjusted properly). As the carb slide is raised by you twisting the throttle, there is a ramp like device that eventually presses on the accelerator pump to activate it. It doesn't just run continually. As previously mentioned, the comment about unburnt fuel is pure fantasy.

Re: PHF32 accelerator pump - Darmah

Posted: Wed Oct 16, 2019 5:02 pm
by BevHevSteve
keep it and make sure it is adjusted correctly.

20 pulls of the cable nets 5cc gas if correct

Re: PHF32 accelerator pump - Darmah

Posted: Wed Oct 16, 2019 8:51 pm
by Vince
My 350 Husky 4 stroke had a Delordo carby and it had a horribly knotchy throttle action, so I disconnected the accelerator pump arm and that made in very nice. BUT after it wouldn't pop a wheely to get over logs, snap open the throttle and it would fall on its face. Keep the pumps they have a purpose, especially if you ride over logs a lot. My little joke, they help you pull out of bends also.

Re: PHF32 accelerator pump - Darmah

Posted: Thu Oct 17, 2019 12:16 am
by ducadini
You could Always go with a different slide.
The reference on the slide : /1 to /5 is a indication of when the accelatorpump is activated, from low slide-opening to high slide-opening.
As for filling crankcases with fuel : that is an indication that the carbs are overflowing.
OR another reason could be that some kids are "racing" :vroom: Your bike while standing on the stand, spraying Your dash with moist broom-broom-broom, opening the throttle and spraying nice squirts of fuel down the pipes >:|!!! >:|!!! untill the carbs are dry.
If this happens : tell them :10-HUT: to pull the clutch 50 times with one hand : then they may have a go with the bike :-D :-D