4.5 HP Mercury won't start.

[ST]

Got this 1984 (s/n. 6428121) that the previous owner said he never started (not sure for how long), but seems to be in good overall shape. I see sparks when rotated the fly wheel manually (with a regular manual socket and ratchet) but unable to get it started. <br /><br />Then I took apart the carb and sprayed clean all the passages and crevices that I can took apart with Gumout Carb cleaner. <br />Put everything together, pump the bulb; pulled and pulled and pulled the robe: nada! Squirt some fuel in cylinder spark plug hole: nada; squirt some at the carb throat: still won't start at all! I even pulled the kill motor wire: no luck! <br /><br />I also tried to close/open the choke as well as rotating the throttle from Fast to Start to Idle position on any combinations; but never heard any sign of combustion at all. <br /><br />What else can I do to get this engine started? Please help, thanks a lot!<br />Sam

 

[joblo33]

Re: 4.5 HP Mercury won't start.

Welcome to iboats! <br />Check for spark by leaning a plug against the powerhead to ground it and see if its sparking when you pull on the starter rope.

 

[ST]

Re: 4.5 HP Mercury won't start.

Eric B,<br />Thanks for your prompt reply! But I already verified that it got spark, and I did it exactly as you described!<br />Any other things to check?

 

[joblo33]

Re: 4.5 HP Mercury won't start.

If you have spark it's unlikely it wouldn't start when you pour fuel in the carb. You'd have to have some really bad reed valves. try pouring fuel in the carb mouth then quickly choking it and cranking.<br />Eric

 

[ST]

Re: 4.5 HP Mercury won't start.

Eric B,<br />I took off the carb (again) and checked the "reed" valve beyond where the carb sits, (I am not sure what a reed valve is; but I see there's like a spring loaded shiny metal plate that is normally closed; but it opens with some sring resistance when I pushed the plate in). What's this reed valve for?<br /><br />Anyway, I went ahead and gave few sprays of fuel beyond this valve; and without reinstalling the carb back, I quickly pulled the starter rope again; and again and again...hoping to hear any sound of combustion; but still nothing happened, only the familiar sound of the piston going back and forth pushing some air...<br /><br />"Still hoping"

 

[joblo33]

Re: 4.5 HP Mercury won't start.

That means the reeds are working, which means they are sucking fuel, therefore there is fuel in the cylinder... I'd recheck spark, maybe something got bumped since you checked. Fuel, air and spark should cause combustion.

 

[Saskatoon2005]

Re: 4.5 HP Mercury won't start.

Here is what I learned about spark....it is not enough to remove a sparkplug and hold it up to ground to see the small blue spark jump the gap of the plug. The proper way to check for spark is to remove the spark plug and place a bolt into the "boot" of the spark plug and hold it 3/8 - 1/2 of an inch away from ground. If there is still spark coming from it, then there is enough of a spark to fully burn all the fuel/oil mixture you are presenting to it. I found out the hard way that just a spark is not enough. You need a real hard spark to get all the fuel burned.

 

[ST]

Re: 4.5 HP Mercury won't start.

Thanks for the tip Saskatoon2005, I will try your method and will report my finding later....

 

[JB]

Re: 4.5 HP Mercury won't start.

ST.<br /><br />Have you done the troubleshooting in Engine FAQs?

 

[ST]

Re: 4.5 HP Mercury won't start.

Saskatoon2005,<br />I put the 1984 4.5 Merc back on the stand, side by side with my 1986 Yamaha 9.9ELY; so that I can compare the sparks from both engines, using your method. After a few spins (Merc is manual; Yamaha is Electric) I honestly can't tell the difference of the intensity between the 2 Engine sparks; since my Yamaha is fine; then I could assume that my Merc's spark is okay too!?<br /><br />Now what? Well, I have to admit to JB (by the way JB; I've been following your valueble opinions from the Boston Whaler's Continuous Wave site as well) that I did not follow every steps you pointed out on the FAQ's "Awakening the sleeping outboards" and "Outboard won't start" topics. In particular; I didn't get the manual; no carb kit obtained; didn't replace the fuel pump etc. Seems that I am now going to need to go to this route, won't I?<br /><br /> Friends; You know, I am just trying to get this going with minimal expense and knowledge I obtained for being a week end family's mechanic at best. I guess, I will need to invest some of those now....<br />JB, if I may guess your signature rhyme: "Red sky at night..., then it will be fair tomorrow"?

 

[Saskatoon2005]

Re: 4.5 HP Mercury won't start.

I should tell you that the intensity of the spark is not as important as how far it can jump. Did you get it to jump 1/4 - 1/2 inch gap? If you can then the spark is indeed good.<br /> Another idea to try, and this is only to troubleshoot. I also believe in a carb rebuild as well. It has worked wonders for me...but another idea to try is to just take the carburetor apart and clean out all the orifices with carb cleaner without a kit. If the motor starts but does not run smooth, then invest in a carb kit. It takes very little time to rebuild one and if you have a manual handy, it is even easier. Just be meticulous as to how you take it apart and you will have no troubles rebuilding it. Good luck and let us know how it works for you.

 

[bigbrownbuku]

Re: 4.5 HP Mercury won't start.

compression test that sucker. you need more then spark fuel and air for usable combustion in an engine. you have to squash it all together. you are looking for 100+psi, might get away with slightly less.<br />if you have good compression, the fact that it sat for a long period couldve damaged the ccase seals. preventing the postive and negative ccase pressures required for charge movement. dont flog a dead horse. establish good spark and move on. establish good compression and move on. clean the carb , WELL, and move on.

 

[ST]

Re: 4.5 HP Mercury won't start.

Saskatoon2005 and BenC, thanks for your input.<br /><br />SPARKS: I think it's okay; i compared them with another working outboard side by side, I couldn't observed the difference. I am pretty sure they can jump at least 1/4 inch.<br /><br />CARBURETOR: I like your idea; I've already taken the carb apart, cleaned all the orifices with carb cleaner. I even squirt gas in the carb throat and or in the spark plug hole; numerous times. But not a single combustion happened from this engine.<br /><br />COMPRESSION: I feel that it's got decent compression; just by the feel of pulling the rope. But to test it with a gauge; here I have problem. I have not found a way-yet; to spin the "flywheel" fast enough for it to register at the gage meter. This 85 4.5HP Merc starter rope mechanism is built into the engine cover. There is no provision for attaching a knotted rope. I read somewhere on this forum that if I can find a flat packing strap material, and wrap it around the wheel few times; will it work?<br /><br />Also in this forum someone mentioned the use of an electric drill; but my 1/2 inch drill is still not large enough to accept a 3/8 extension socket to turn a 5/8 inch senter nut on the flywheel.<br />Looks like I will need to sacrifice my 3/8 extension: cut it in half?<br /><br />Anyway; it's ashamed if I have to trow this engine away; seems like it's well built; and well preserved I might add; judging by the amount of grease/oil and lubrication everywhere.<br /><br />Still hoping.....

 

[bigbrownbuku]

Re: 4.5 HP Mercury won't start.

buy a cheap 3/8ths extension and sacrifice that one.

 

[ST]

Re: 4.5 HP Mercury won't start.

BenC,<br /><br />Thanks for your response and recommendation!<br />Okay, I followed your advise; cut my other cheap 3/8th extension; and use the "male" end to drive the 5/8th inch socket to turn the center nut; hooked up the compression gauge: it registered at 75 psi.Do you think this is the problem? If so, any hope or it is worth the effort (difficult?) and cost ($$?) to have this repaired? (crank case seals??).

 

[bigbrownbuku]

Re: 4.5 HP Mercury won't start.

75 is kinda low. at this point decide how much this engine is worth to you vs replacement cost and make a decision. if you like it and want it to run and you have some mechanical skills buy a genuine service manual and dig in.