Re: Desperate! Six weeks and 2 different mechanics?
Be careful of "mystery internal engine damage"<br />Your engine is basically a pump. Mechanically,<br />if it has good compression readings, you can probably look somewhere else for the problem.<br />All internal combustion gas engines require 3 things to run, fuel, ignition and compression.<br />rule out compression first. Blocked ehaust is probably not a factor either, since you say that the engine will reach 4500 in neutral. Make sure that you can run it for more than a second or two at this rpm. if the exhaust is restricted, the rpm's will slowly fall off, and the aforementioned spitting back through the carburetor will occur.<br />Cam timing is not an issue with these motors, unless the cam was improperly installed,<br />since it is gear-driven and teeth would have to shear off the cam gear to affect timing. This results in a no-start, because the cam stops turning.<br /><br />I would suspect one of three things:<br /><br />1) Weak ignition, or improper timed ignition. To test timing, simply use a timing light.<br />To test spark intensity, Take an extra spark plug and open the gap up to a 1/4" gap, or better yet, remove the ground electrode so that the spark has to jump from the center electrode to the shell.<br />pull any one plug wire off and attach it to this spark test plug. lay the plug on the engine block, or better yet, ground it with a jumper wire, and start the engine. (it will miss on one cylinder of course, but will cause no harm).<br />You should see ( and usually hear) a nice BLUE spark jumping the gap. If not find out why.<br />If so, repeat the test on all 4 wires. You have now eliminated all of the ignition system except for the plugs themselves.<br /><br />2)Not enough fuel.<br />This is a little more difficult to check, but basically, you need to have a mechanic install a test wheel in place of your prop, run the engine up, and somehow introduce more fuel to the engine<br />to see if it will accelerate past the 2600 rpm wall. I don't wan't to suggest that you mess with the fuel system while running the boat, for obvious safety reasons.<br />What can be done first, is to rebuild the carburetor to factory specs. I don't remember reading if you have done this or not.<br /><br />3) And this is my guess for the cause-<br />Boat is over-propped, not on plane, or not trimmed up once on plane.<br />I seem to remember that the problem supposedly started with a different prop being installed.<br />It all depends on whether or not you trust the person who you bought the boat from, but I have serious doubts about running a 19 pitch prop on that boat, much less a 23. The reason is, I own a 3.0 omc in a 17 foot boat, and there aint no way in hell it would plane out with a 19 pich prop.<br />My drive ratio is 1.7 engine revs to one prop rev.<br />I'm not sure what the Merc. ratio is. If it's numerically lower, say 1.5 to one, your engine would have to work even harder.<br /><br />My boat is a 4 winns 170 Horizon v-hull bowrider.<br />It needs a 15 pitch prop. The drive needs to be all the way down to get on plane. Once on plane,<br />it has to be trimmed up to exceed 30 mph-about 3200 rpm. Trimmed up just enough to get the front of the boat out of the water, it will top out at about 40 mph- about 4500 rpm.<br />It takes full throttle for about 8 seconds to plane.<br />Is your boat on plane at your maximum rpm? and how fast are you going?<br />Let us know. <br />John
