Can engine timing be good at one speed and bad at another?

[astampfel]

I'm trying to resolve my poor idling problem on my 1990, 90 Hp Johnson. It runs great at full throttle, but performs poorly at idle. I was wondering if timing could be an issue? If timing were an issue, I would think that it would run poorly at all speeds? But, is it possible that the timing could be set wrong, and the engine runs great at full throttle but not at idle? I only have one lever arm to adjust timing. If I move it to correct my idle, will it throw my full throttle performance off?

 

[Tim Frank]

Re: Can engine timing be good at one speed and bad at another?

Unless there is some reason to suspect someone has played with the timing, poor idle is more likely caused by something else....first thing I would suspect is dirty low speed jets.
Compression check would be the first troubleshooting step I'd do. (just 'cause it's easier than d/s the carbs.....)

 

[Dhadley]

Re: Can engine timing be good at one speed and bad at another?

Adjusting the idle timing does not change the wot timing stop.

 

[F_R]

Re: Can engine timing be good at one speed and bad at another?

I'm trying to resolve my poor idling problem on my 1990, 90 Hp Johnson. It runs great at full throttle, but performs poorly at idle. I was wondering if timing could be an issue? If timing were an issue, I would think that it would run poorly at all speeds? But, is it possible that the timing could be set wrong, and the engine runs great at full throttle but not at idle? I only have one lever arm to adjust timing. If I move it to correct my idle, will it throw my full throttle performance off?

There is more to timing than the spark timing. It has to be properly synchronized with the carburetors. If not synchronized, yes it certainly can affect certain speeds. The process is loosly called "link & sync".

 

[jtexas]

Re: Can engine timing be good at one speed and bad at another?

to answer your specific questions, if the timing is good at full throttle, then idle timing is ok. not sure what "lever arm" you mean; there's an "idle stop screw" for adjusting the idle.

If it's been like this since you got it, or if you've been messing with the linkages, it might need adjusting. If it was idling fine before, and this started recently, more likely you just need to do some basic maintenance.

back to basics.
1. compression test.
2. spark test (not a "spark plug" test): get an inline spark tester (couple bucks at autozone), set the gap for 7/16", clip it to the engine block, attach the plug leads (one at a time) and look for a strong blue spark while cranking. If it can't jump a half-inch gap in the open air without a spark plug, it's not firing in the hole under heat & compression.
3. carb rebuild, with new kits, followed by link & sync.

follow the "carb cleaning and rebuilding" link from the "top secret file" at the top of this thread.

need help, just ask.

a service manual would be a good investment, saved me countless hours and literally $thousands, I highly recommend the factory shop manual (find it at marineengine.com or outboardbooks.com).

 

[Dhadley]

Re: Can engine timing be good at one speed and bad at another?

You can change the idle speed with the low end timing but that has no effect on the wot timing stop. Motors that set deep in the water may well have to have a bit more low end timing than a motor that doesn't set deep at rest. They will both have 26-28 degrees at wot (on this model).

 

[F_R]

Re: Can engine timing be good at one speed and bad at another?

If I may add to my previous comment, at idle speed, the carburetor butterfly valves are completely closed and RPM is controlled by the amount of spark advance/retard as you move the throttle lever. At some point, just above slow idle, the carburetors start to open. If too soon or too late, you will get poor running at off-idle speeds. That is the synchronization part, and it is related to spark advance/retard ("timing").

 

[astampfel]

Re: Can engine timing be good at one speed and bad at another?

Thanks everyone for the good words of adivce. I bought the boat 1 month ago, and it has always idled poorly but very nice at full throttle. I did purchase a repair manual as a PDF file online, "Johnson-Evinrude Outboard Repair manual 1973 to 1991. I don't know if it is SELOC or Clymer or the actual factory. It has 11 chapters, an appendix, and wiring digrams (one of which they say is for my model, but my model better fits the wiring diagram on the following page in the book). I have rebuilt the carb, and no better idle. I put in a brand new VRO pump, and just replaced a fuel intake line 5/16" that had a hole in it and no better. I have done the carb linkage adjust according to the book and am now debating whether to fool with the timing.

The timing is adjusted by a thumbwheel screw that is attached to some kind of disk beneth the flywheel and the other end is attached to a cam that is linked to the throttle. I noticed that from about 1/2 butterfly valve open (1/2 throttle) to full throttle, there is no movement of the spark advance mechanism; the geometry of the cam is basically straight up and down so movement of the throttle does not produce an movement of the spark advance. It seems like the throttle will continue to open the carb, but nothing changes with the spark.

 

[mamm7215]

Re: Can engine timing be good at one speed and bad at another?

what you have is not the oem factory manual. You need to get the one for your model and year of motor. It is much simpler than the other manuals, they get some things wrong also because they're covering so many models/years. There's a lot of similarities but some differences as well.

 

[F_R]

Re: Can engine timing be good at one speed and bad at another?

Thanks everyone for the good words of adivce. I bought the boat 1 month ago, and it has always idled poorly but very nice at full throttle. I did purchase a repair manual as a PDF file online, "Johnson-Evinrude Outboard Repair manual 1973 to 1991. I don't know if it is SELOC or Clymer or the actual factory. It has 11 chapters, an appendix, and wiring digrams (one of which they say is for my model, but my model better fits the wiring diagram on the following page in the book). I have rebuilt the carb, and no better idle. I put in a brand new VRO pump, and just replaced a fuel intake line 5/16" that had a hole in it and no better. I have done the carb linkage adjust according to the book and am now debating whether to fool with the timing.

The timing is adjusted by a thumbwheel screw that is attached to some kind of disk beneth the flywheel and the other end is attached to a cam that is linked to the throttle. I noticed that from about 1/2 butterfly valve open (1/2 throttle) to full throttle, there is no movement of the spark advance mechanism; the geometry of the cam is basically straight up and down so movement of the throttle does not produce an movement of the spark advance. It seems like the throttle will continue to open the carb, but nothing changes with the spark.

DON'T mess with the timing unless you have good reason to suspect somebody already has. The throttle action that you describe sounds right. The carburetor butterflies open slowly till the timer base reaches full advance. Then the timer moves no more, but the butterflies open. THAT is all part of the synchronization I've been harping about.

 

[astampfel]

Re: Can engine timing be good at one speed and bad at another?

I just got back from a boat trip. I adjusted the timing and I think that was it. It idles perfectly (quiet and slow but strong) at 900 RPM (a little higher than the book, but I'm not going to complain). The timing was way off. I held the timing gun and walked the flywheel TDC mark into position at 6 degress before TDC. That was the trick. It even seems like it runs better at top speed. The timing thing really wasn't that difficult. The hardest part was keeping the sun off the flywheel.

I thank everyone for their input. I'm learning new things all the time.