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Discussion Starter · #1 ·
Hi Guys.

I need to raze an issue I have picked up with the accelerator pumps on the PCIII. It does not always add more power, so be careful when you use it.

Let me explain where I am coming from.

I have tested a 700R the other day, plus I worked on a few Xt660's (two wheeler uses similar engine as 700R) and the accelerator pump might actually dropped the power output.

It all depends on the type of map you run and how much fuel it adds at the lower RPM.

Some maps don’t give you a 13:1 A/F ratio in the lower RPMS. For maps like this, the accelerator pump will work, but if you have a map that is set up to run 13:1 across the RPM range or supply that A/F ratio at 80% or larger throttle openings, the accelerator pump will add to much fuel and drop the power output. The engine can only burn so much, to much or to little and it drops the power output

Try the accelerator pump, but don’t just implement it because your mate tells you to do so.

From the dyno testing I have done, it can actually drop the power output by 2HP across the RPM range. This is with a map that was custom made for this bike and was running 13:1 at 80% or larger throttle openings.
 

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From the dyno testing I have done, it can actually drop the power output by 2HP across the RPM range. This is with a map that was custom made for this bike and was running 13:1 at 80% or larger throttle openings.
I do not see how it can drop 2 HP through out the range when the added fuel is for only 20 revolutions if you have it set at 80, 20, 20.
 

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blewbayou said:
I do not see how it can drop 2 HP through out the range when the added fuel is for only 20 revolutions if you have it set at 80, 20, 20.
I agree, that was my undersatnding of the accelerator pump as well. :3question:
 

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Discussion Starter · #4 ·
It does not sound logical I agree, but the dyno clearly shows I lost power all the way thru the RPM range.

I think what is happening is that because the dyno run is so short, any loss that happens at the start of the run, causes the motor to start at a lower HP output and it cannot gain that loss back by the time the run is over.

I have seen this happen on quads that use carbs. You change the needle clip position, which should only affect low and midrange power, but it also shows up as a gain at the very top RPM when the low down is better. The motor seems to carry the power it gets at the start and if it is good at the start it shows a gain all over, but drop it at the start and it drops the power all the way thru the rpm range. It might be possible that if you go thru the gears very quickly, like you do on a dyno or a drag race, that loss at the beginning might just effect your end result. It all depends on how quick you go thru the gears

In real life, top end power might not drop when you ride, but the point is that it can drop the power output instead of giving you a gain.
 

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its like momentum... if you start out with little to no power you have a hard time getting the most inthe end. but if you have a running start then your top out will be better. like freez said most wont see it in real world scenario but on a dyno w/ a short run then it shows up onthe sheet.. good point
 

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that along with an oil change, filter cleaning and I had them grease everything for me. I pay because I really don't have the time to do it myself. 8)
 

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Thanks Talljess! Its good to know somebody understands where I'm coming from. I have two jobs so my time is limited as far as doing what I love to do. Therefore, when I go home to ride, I try to ride as much as possible and thats it. 8)
 
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