Topic: Add accelerator pump to a set of 550 PD carbs?

[Bootlegger56]

I like the sound of this and definitely will follow.  My thinking is it would help the hesitation present on aggressive throttle opening that seems to plague the older style carbs.  But with my limited knowledge I could be way off mark.  I apologize for not having anything to contribute but look forward to being edjecated!!

[Flying J]

Mission has been aborted. I bought all the mill bits in the sizes i could but after drilling some test holes they are not the right size. With holes that small they have to be perfect or the little jets slip right out. It is absolutly possible i just lack the correct tooling. 

[crazypj]

probably need to drill undersize and ream?

[bollingball]

probably need to drill undersize and ream?

+1^
ffj You have come so close try again. The place for your tooling is a watch repair shop and they are pretty reasonable the old timers are few and the new guys are just like most bike mech. they just don't know how to work on them I will dig up a link. A used set is the way to go Most of the old timers took good care of there tools. Google watch repair tools I know this because my father in-law bought a set awhile back.
Ken

[Bankerdanny]

Accelerator pumps are usually found on 550F/750F models . Why not just get an F engine or carbs?

Could be a lot easier. I'd do that or get oversized jets.

Actually no. All years of the 550F have the same carbs as the 74-76 550k's (well, not exactly the same, but functionally identical), no AP. '77 was the last year of the F and it didn't get the PD46's that were on the K bikes that year.

[bollingball]

Even if you did all that is needed then you would have to go back over all of your jetting again and you may never get the right combo.

A complete waste of time.
Only the 1977-78 models had that feature.
A ll of the other models 1969- 1976 did nit need that.

BTW do not forget the restrictor tubes that go inside the rubber hose connecting all of the spray jets.

Really?

He did write this last year maybe he has learned something in that time. I sure don't see how the jet size has anything to do with this. Lucky if you read this could you come back and explain?
Ken

[iron_worker]

It won't affect your main jet selection, however, it will most certainly affect your idle jet size and probably neelde position too. You may even need to mess with your slide cutaway to get the transition just right.

As TwoTired pointed out, the idle circuits on carbs with no accelerator pump are *intentionally* set over-rich. This is so when you whack open the throttle quickly there is enough fuel there to maintain combustion. If the idle were set to a stoichiometric ratio of 14.7:1 then as soon as you whack the throttle, the vacuum in the carb throats drops off very suddenly. The differential pressure between the low pressure in the carb throat and the atmospheric pressure in the carb bowl (vented) is what drives the fuel up and through the jets. Thus as you quickly open the throttle the bike has a tendancy to go lean suddenly ... and if not compensated for it will hesitate due to a lean misfire.

The accelerator pump compensates for this effect by adding extra fuel whenever the throttle position opens up.

There would most definitelely be some trial and error in tuning the off-idle transition.

IW

[bollingball]

It won't affect your main jet selection, however, it will most certainly affect your idle jet size and probably neelde position too. You may even need to mess with your slide cutaway to get the transition just right.

As TwoTired pointed out, the idle circuits on carbs with no accelerator pump are *intentionally* set over-rich. This is so when you whack open the throttle quickly there is enough fuel there to maintain combustion. If the idle were set to a stoichiometric ratio of 14.7:1 then as soon as you whack the throttle, the vacuum in the carb throats drops off very suddenly. The differential pressure between the low pressure in the carb throat and the atmospheric pressure in the carb bowl (vented) is what drives the fuel up and through the jets. Thus as you quickly open the throttle the bike has a tendancy to go lean suddenly ... and if not compensated for it will hesitate due to a lean misfire.

The accelerator pump compensates for this effect by adding extra fuel whenever the throttle position opens up.

There would most definitelely be some trial and error in tuning the off-idle transition.

IW

IW Thanks for explaining that. So I guess when the EPA came in on the 77 lean setting of the pilot circuits of different bikes that is why Honda put on the pump. Would that be correct?
Ken

[754]

FWIW. I think it was Sudco sold an accellerator pump kit, mounts outside carbs , and you need a spltter for the added cable..