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Author Topic:   Max engine RPM
Makaira posted 04-10-2002 08:11 PM ET (US)   Profile for Makaira   Send Email to Makaira  
My recently rebuilt 135 evinrude will only turn about 4400 RPM. The engine is mounted on a 19' outrage. All external components remain unchanged including the prop, carbs, power packs, etc. The boat has not gained any weight and the trim remains the same. Prior to the rebuild I was able to run it up to about 5600 RPM. What factors could be responsible? Timing? Mixture? By the way, I was dilegent to follow the proper break-in precedures recommended by my mechanic (10 hours at 25:1 oil/gas and varied RPM) Any suggestions would be helpful. Also, is it true that it is necessary to set the advance while the engine is under load?
jimh posted 04-10-2002 11:13 PM ET (US)     Profile for jimh  Send Email to jimh     
Check the setting of the mechanical limits on the throttle linkage. Perhaps the rebuilder has set the throttle limit slightly lower than Wide-Open-Throttle (WOT).

Setting a limit on the WOT throttle position would be one way to ensure the rebuilt engine survived the warranty period.

Clark Roberts posted 04-11-2002 06:42 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Jim has a great point! Take airbox cover off and look into carb throats to verify that you're getting WOT. Also check the timing linkage... I believe that it's linked directly to throttle linkage! Another thing that could cause/contribute is fuel flow. Check for fuel pump output and for any kinked fuel lines. If there is a fuel fitting on front of engine, check it out or get rid of it and fit incoming fuel line directly to fuel pump (that is unless you use fitting for switching fuel tanks). Even so it would be better to switch at tank end... Happy Whalin'.. Clark... Spruce Creek Navy
Salmon Tub posted 04-11-2002 11:10 AM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Take it back to the Mech., just to see what he says. You paid for the rebuild, and the rebuild should be complete. If he did take "precautionary" messures to asure that the engine would not be "abused" during break-in, he should fix them. I would say, there may be a timing issue because I have read numerous times that adjusting the timing for the break-in period is a good thing to do. Keep this and Jimh's recommendations in mind, go to the Mech., play stupid and just insist on the fact that part of his job for the rebuild was to bring the engine back up to specified power output, and it is not doing that. Don't fiddle with anything yourself yet, as it will give him the opertunity to say, you should have brought it to me, but you didn't and now you changed this or that, and broke it.
Bigshot posted 04-11-2002 01:26 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Ditto to ifs, ands or butts! keep us posted.
Makaira posted 04-11-2002 05:19 PM ET (US)     Profile for Makaira  Send Email to Makaira     
Thanks for the replies all of you. The mechanic is a close friend of mine and one of the first things we did was check for WOT which is fine. My guess is that the problem is either fuel flow (I'll eliminate the fitting at the engine) or timing. The mechanic advanced it slightly from it's previous setting and we gained about 400 RPM. However, he claims the only way to do it right is while under way at full throttle. That procedure seems a bit ominous. I can't imagine using a timing light at 30+ mph. But if that's what needs to be done, that's what we'll do. Does anyone have experience with setting max advance? Maybe we should also check the power pack to see if I'm getting the correct voltage to the plugs? By the way, the behavior is such that once the throttle moves beyond about 3/4 WOT there's no response in RPM. The butterflies move open but nada mas.
Bigshot posted 04-12-2002 12:21 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Timing is done like that....crazy huh!

Either gas or electrical. If you squeeze the ball or push in the choke real quick, will it pick up speed at WOT?

Makaira posted 04-12-2002 12:30 PM ET (US)     Profile for Makaira  Send Email to Makaira     
I'm heading out salmon fishing in the morning. I'll give that ol'ball a squeeze and see what happens.....I'll keep you posted on progress.
Salmon Tub posted 04-12-2002 05:38 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Makaira, I slept at a Holiday Inn Express yesterday, and can tell you for a fact that as far as I recall, that is not exactly how it is done. I don't even recall using a light. In my book, for my engine it says that in order to adjust the timing, you should find timing degree indicators under the flywheel that is connected to the throttle via a link rod. Also, there is a timing mark cast right into the block. The way it works is that under your flywheel, there are magneto(s). They supply the spark for plugs. It is different than the system in a car. In a car, remove the alternator, and it will run till the battery dies. Remove battery, and the alternator supplies electricity. On outboard, the battery acts as an electrical storage unit only. For my engine, the book specifies timing position at off, idle, and WOT. You check the WOT with the engine off. There is a trick, On mine, the 'disc' that the timing marks are on moves back a few degrees when engine is running, and forward when shut off. So, I have to move it to the rear with my hand against it's spring when engine is not running, push the throttle all the way forward, and check the timing. Make sure that the engine is not running or you will loose some fingers. I have a clymer book that is very helpful, but they must have boot legged the text from Japanese manuals because the grammatic errors are just too much at times. Remember, as in the words of E-Trade, Timing is everything, and maybe, spend a night at Holiday Inn Express, and soon you'll be teaching stuff to your mechanic.
DIVE 1 posted 04-12-2002 09:48 PM ET (US)     Profile for DIVE 1    
We time most OMCs at WOT running. You have 2 choices-be brave and time engine with boat underway or use a test wheel. I prefer the test wheel. Be sure to check your sync and link prior to setting timing with timing light.
Makaira posted 04-15-2002 11:49 AM ET (US)     Profile for Makaira  Send Email to Makaira     
I should clarify. My 135 is an early or mid-1970's vintage. I do have an original shop manual which specifies that timing should be done while "under load". DIVE 1, what is can you describe how the test wheel works. Thanks alot. By the way, the salmon bite was wide open so I didn't bother fussing with thing over the weekend.....we were busy limiting on 25-30# Chinooks.

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