setting idle rpm/timing on a 74 evinrude 115hp

[kevinr]

I have a 74 evinrude (115493b) that is running, but not at correct idle speed. it runs smoothly at about 1150-1220 with timing marker at about TDC, but the book calls for 600-700 and a little BTDC. it dies at that idle.

couple of questions: 

where idle speed is concerned, where are the necessary adjustments made? I do know where the timing advance/retard is done.

If i loosen the shift and throttle arms (single big nut in the middle), there is a large spring between the arms. I'm guessing it provides tension one way or the other on the timing advance...at least that looks like what it would do. First, is that what it does? Second, when I reassemble, it seems like i need to put a little clockwise tension on it for the tabs on the spring ends to contact the arms...is this direction correct?

I bought this motor used. I've replaced coils, plugs, plug wires, stator (which it turns out was shorting), fuel pump, and all the fuel lines. I've rebuilt both carbs. Compression is dead on 125 all four cylinders. looks like it will be a good motor if i can get it timed/idled correctly so I can check WOT (which book says is 18-20btdc at 5000 rpm.

Thanks for any help. Kevin

[boatnamesue]

Ignition timing (TDC/BTDC) is not adjusted to tune idle speed, which is what you've somewhat eluded to above.  Ignition timing once tuned rarely moves out of spec.  Idle speed on the other hand will require adjustment/tune, especially after pulling/cleaning carbs.  So from what I understand, your motor will not idle at spec rpm 600-700. 

I'm not familiar with rude's, but I reckon the carbs have an idle speed screw and idle air screws.  Idle speed screw opens/closes throttle plate.  Idle air screws (1 per carb) allow for more/less air to enter the mix.  Idle air screws are adjusted to dial in the mix by turning each screw in or out (rich/lean).  Once the idle is dialed in you can fine tune rpm by screwing in or screwing out the idle speed screw.  Important to note, the idle speed screw should always be screwed in just enough to crack open the throttle plates, otherwise you'll have issues starting the engine. 

[fitz73222]

That engine has fixed idle and high speed jets that are not adjustable. Idle speed was set at the cam pointer just touching the throttle roller. There is a throttle pick up timing adjustment that should be on the antenuater box that tells you the timing degrees to set the engine idle timing. I thought there was a separate idle speed screw that simply adjusted the butterfly position to adjust speed. We sold these engines new but it's been many years since I've had the cowling off of one.

[kevinr]

I think i've had a DUH moment...

I'm running it on muffs and a hose in neutral. it has no backpressure or water to push against. nor was it in gear. From what I'm reading, 1100-1200rpm under those conditions is probably perfectly normal. Once i get it in the water (or a tank), it should drop the RPM and i can do a final adjustment.

does this make sense?

[boatnamesue]

Spec idle rpm does not change whether motor is under load or not....so "those conditions" you mention are erroneous.  Makes no difference whether you adjust idle when LU is submerged or on muffs...only that your adjustment comes once engine has warmed to normal operating temp.  And I'm not familiar with the spec idle rpm for your engine, but boy, 1200 rpms sounds WAY too high.

[fitz73222]

I think i've had a DUH moment...

I'm running it on muffs and a hose in neutral. it has no backpressure or water to push against. nor was it in gear. From what I'm reading, 1100-1200rpm under those conditions is probably perfectly normal. Once i get it in the water (or a tank), it should drop the RPM and i can do a final adjustment.

does this make sense?

You are correct, idle speed and/ or mixture should not be done on muffs. Engines run leaner and rpm's are higher on muffs at idle. All adjustments should be made with the engine in the water, warmed up and in gear. Set the idle speed, idle timing and whatever the idle speed is out of water, thats what it will be.

[kevinr]

...which explains why it runs great at 1100-ish on the muffs. No matter what I tried, i couldnt get it anywhere near 600-700, but it was high wide and happy at 1100. I've been banging my head for a couple of weekends.

so that I'm clear.  Put it in the water (not tied up), motor level, in gear, at idle - adjust until i hit the target idle range. If I get it right at idle, do i need to check it at WOT?

[fitz73222]

Tied to a dock or on the trailer at the ramp is fine, actually preferred, just don't block the ramp (LOL). We used to twist these engines at 5800-6000 rpm's obviously not at the ramp. Max timing can be checked at cranking speed, spark plugs out and grounded, throttle wide open, key switch on, timing light on number 1, jump the starter solenoid, There should be a cranking speed max timing number which is different than the actual max timing number if you were running the engine wide open with one hand shadowing the timing pointer and the other pointing the timing gun at the pointer with a 6000 rpm flywheel buzzing 10" from your head, trying to see the light flash at the pointer which is the way we used to time them. (not fun!)