Carb vs. EFI Idle

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Jun 12, 2009 | 01:30 PM

FunkyFungus

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From: Atlanta, GA

Carb vs. EFI Idle

Hello,

I know this topic has been brought up, but I have another seemingly benign question.
Why do EFI Sporties like mine idle so much higher than their carbed equivalent? I've heard oil pressure needs to be maintained. How is oil circulated differently on an EFI bike? Are guys with carbs and the potato idle harming their motors? I finally got my Rush pipes on but wouldn't mind lowering the idle a bit when I get a SERT or SEST. Will the PC-V work on an '07?

- Sorry to be so random. Just daydreaming while at work. :-)

Thanks,
fF

Jun 12, 2009 | 04:56 PM

xFreebirdx

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From: Landrum, SC , elevation 986'

Its the computer that controls the idle on a EFI, its just a screw on a carb bike. You need to stay at least above 980rpms to be safe with the oil.

Sorry can't help yuh with the EFI...not a fan of them so I don't know much about them.

Jun 12, 2009 | 08:20 PM

diablo666

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I typed an explanation of how the idle speed works but when I posted it.Well it was gone.Not really into typing it all again.If you want it pm me at least I will know you are interested in hearing it.

Jun 12, 2009 | 09:14 PM

bustert

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first the oil situation. the newer engines use a gearotor oil pump and to put into a picture, think of a circle with a star pattern cut out in the middle and another star inside it turning in a circular path inside the cut out star pattern. oil is feed into the void and as the star teeth mesh, the oil is squeezed between the points and builds up pressure to overcome the restrictions in the oil circuits. the older pumps used meshing gears side by side to do the same. the gearotor pumps are not that effiencent at low speeds so an idle of 1k is needed. the gear pumps do well at slower speeds but are not as effiencent at high speeds in volume as the gearotor pump. however, the oil pump is not the problem! slow idle speed is hard on the rod bearings no matter what pump you use. if you use a single fire ignition, it will not sound like a dual fire ignition which is a little rougher. the second point is that on a carb engine, the vac pulse, temperature and etc all have an effect on idle as the carb has to mix everything just right to get a consistant idle. the carb can not do it 100% of the time so you get idle inconsistancies. the carb has to control the air in order to try to control the fuel but on a fuel injection, only the fuel needs to be of concern. depending on which system you use, the air flow is measured and the fuel is calculated to present a proper mixture. the computer uses a fuel map calculated by the designer for proper engine operation. that is why the injected engine is quite consistant in idle. the computer uses sensors to determine engine operation parameters and modifies the fuel map to adjust for proper operation. now if you are having a higher than normal idle, check for air leak into the system, the base idle air setting and for a bad temperature sensor. if the temp sensor is telling the computer the engine is cold, it will richen up the mixture and increase idle slightly.

Jun 13, 2009 | 08:22 AM

FunkyFungus

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From: Atlanta, GA

Thanks for all the info so far. There really isn't anything wrong with my idle, 1000rpm hot and about 1200 cold - I was just curious. I'm from the old school myself and my expertise is in Holley and Edelbrock 4 barrels. New to this EFI bike thing. Next step is some sort of fuel management; I'd like to richen her up and cool her down a bit.

Thanks guys,
fF

Jun 13, 2009 | 07:53 PM

bustert

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i hear where you are coming from! unfortunately technology has put us small guys at a disadvantage when it comes to modifying a computer controller engine. although programmers are coming down in cost, it still is an expensive hobby. kick in big brother and the situation becomes worse, all in the effort to control emmisions which is it really a bad thing. you can have you cake and eat it too because you can develope power and still have a smile from epa, it just take a little time and effort(and cash). before the "E" square prom, we use to add a little resistance to the temp sensor in order to fool the computer to enrichen the mix but now it's just a matter of playing with the fuel map and reprogramming the computer. however, the computers are getting so close toleranced that you can not even change a muffler with out upsetting some other system. only time will tell what's next!