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rpms drop with headlights off.

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Bobthebiker

rpms drop with headlights off.
« on: March 12, 2010, 06:06:29 PM »
what can cause my engine rpm to rise to normal idle speed with the parking lights, or headlights on.     any idea why this happens?     

with headlights or parking lights OFF, and the engine warmed up, it wants to idle at about 500 rpm or so.  with them on, it idles right at 1000rpm.
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Offline wildgoody

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Re: rpms drop with headlights off.
« Reply #1 on: March 13, 2010, 01:18:10 AM »
This is normal, engine RPM increases probably for more alternator output
under electrical loads
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Online fordem

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Re: rpms drop with headlights off.
« Reply #2 on: March 14, 2010, 10:12:21 AM »
Quote from: Bobthebiker on March 12, 2010, 06:06:29 PM
what can cause my engine rpm to rise to normal idle speed with the parking lights, or headlights on.     any idea why this happens?     

with headlights or parking lights OFF, and the engine warmed up, it wants to idle at about 500 rpm or so.  with them on, it idles right at 1000rpm.

What vehicle, what engine are we discussing here?  Since this is a Suzuki forum, I'd say it's safe to assume it's a Suzuki.

I've been a Suzuki owner for almost two decades and all of the vehicles have has some sort of mechanism to bring the idle speed up to compensate for the power draw of electrical and other accessory loads (just like wildgoody says), some have had vacuum operated "idle up" linkages, some have had vacuum "bleeds", others have done it using the IAC (idle air control) motor.

In all probability, your engine is idling too low, for whatever reason - most Suzukis seem to have a factory spec of 800~900 rpm and the idle up mechanism brings it up to the correct speed.
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Offline rascott

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Re: rpms drop with headlights off.
« Reply #3 on: March 14, 2010, 01:13:52 PM »
the hitachi carb may have an idle up vacuum pot on the linkage side (toward the distributor). it is activated by a switched vacuum source when lights,  a/c, and mabe other electrical loads.
you should be able to see it work when that happens.
if all else tuning-wise is ok you may just raise your idle a little. unless it's a nice 500rpm idle.
i remember right, there is another adjusting screw near the idle adjust screw that is involved with adjusting that pot idle.
kinda complicated linkage.
at least on mine.
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Bobthebiker

Re: rpms drop with headlights off.
« Reply #4 on: March 14, 2010, 02:07:00 PM »
well, the samurai carb is by far the most confusing thing ever to me.     
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Offline zukimoo

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Re: rpms drop with headlights off.
« Reply #5 on: March 14, 2010, 04:19:53 PM »
it should be set to 1000rpm's at idle with nothing on. When you turn something on then it'll go around 1500rpm's and stay there. The alt doesn't charge enough at 1000rpms so they added the speed up feature. Years ago my mechanic checked with meters at it wasn't turning fast enough.

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Online fordem

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Re: rpms drop with headlights off.
« Reply #6 on: March 15, 2010, 05:53:21 AM »
Quote from: zukimoo on March 14, 2010, 04:19:53 PM
it should be set to 1000rpm's at idle with nothing on. When you turn something on then it'll go around 1500rpm's and stay there. The alt doesn't charge enough at 1000rpms so they added the speed up feature. Years ago my mechanic checked with meters at it wasn't turning fast enough.



Are we talking a 1.3 here?  If you are, those numbers are WAY too high - the only time the idle should be over 1000 rpm is at a cold start.  With the engine warm factory spec is less than 1000 rpm.

As a matter of fact I have yet to see any Suzuki (or any other brand) vehicle that had a factory spec warm idle over 1000 rpm.
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Bobthebiker

Re: rpms drop with headlights off.
« Reply #7 on: March 15, 2010, 08:51:16 AM »
yeah,  I've got a 1.3  factory engine in my 87.
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Offline wildgoody

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Re: rpms drop with headlights off.
« Reply #8 on: March 15, 2010, 07:52:19 PM »
Warm idle should be 700-800 RPM

Wild
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Offline zukimoo

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Re: rpms drop with headlights off.
« Reply #9 on: March 18, 2010, 05:38:34 PM »
when mine are set at 7-800 they stall when coming to a stop...I know the carb is probably dirty but it runs fine for me at 1000. my 413K doens't go up with the lights on so it doesn't get to the 1500 unless my foot is to the floor and then it really gets high. specialy with low gears on the highway.
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Bobthebiker

Re: rpms drop with headlights off.
« Reply #10 on: March 18, 2010, 06:43:46 PM »
I had it idling at 800 rpm yesterday,  its going back to 1000.  800 is too rough and just feels choppy.
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Offline jaunty

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Re: rpms drop with headlights off.
« Reply #11 on: March 20, 2010, 10:59:59 AM »
yeah, its the "idle up solenoid" that causes the idle to increase when you turn on lights or accessories, this means its working properly.  It can develop a mind of its own though.. If you want to defeat this there is a green plug near the left side of the radiator (when looking at the engine bay).  This mechanism tended to make my idle too variable so i unplugged it.  you may find that this is the cause for all that variability.  If you're going to run your idle at about 1000 you can do without this thing.  I am now running at 800 rpms and max idle up is about 1100 so its not too bad. 
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Offline Skyhiranger

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Re: rpms drop with headlights off.
« Reply #12 on: March 23, 2010, 11:35:51 AM »
Quote from: fordem on March 15, 2010, 05:53:21 AM
Quote from: zukimoo on March 14, 2010, 04:19:53 PM
it should be set to 1000rpm's at idle with nothing on. When you turn something on then it'll go around 1500rpm's and stay there. The alt doesn't charge enough at 1000rpms so they added the speed up feature. Years ago my mechanic checked with meters at it wasn't turning fast enough.



Are we talking a 1.3 here?  If you are, those numbers are WAY too high - the only time the idle should be over 1000 rpm is at a cold start.  With the engine warm factory spec is less than 1000 rpm.

As a matter of fact I have yet to see any Suzuki (or any other brand) vehicle that had a factory spec warm idle over 1000 rpm.

X2.
The proper specs have been mentioned (800ish no electrical load, 1000ish with lights, blower motor, etc. on)
On the one carbed samurai I have had, I did set the warm idle to up around 1000, just because 7-800ish made it idle slightly rough.  And I had just cleaned and fully adjusted the carb, so everything was operating properly.
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Offline djlantis57

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Re: rpms drop with headlights off.
« Reply #13 on: March 29, 2010, 12:39:24 AM »
My warm idle is 800 RPM and my idle-up is about 900-1,000 RPM.  I was flabbergasted by it at first too when I bought my Tracker (a '90 w/ 1600 8v) because I was unfamiliar with it.  It idles up when I turn on the parking lights (and headlights too) and any heater/AC fan.  All my offroad lights don't activate it, though, so I figured it must be wired only into those select few circuits
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Bobthebiker

Re: rpms drop with headlights off.
« Reply #14 on: March 29, 2010, 02:58:08 AM »
oh welll, now that I'm actually DRIVING it, I never notice the tach so its not a big deal anymore. 
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