old 4.5hp mercury won't start

Emery · Oct 1, 2006

Hi and thanks for reading my post.

I have an old 4.5hp mercury that doesn't start.

I cleaned the carb, removed the spark plug and cleaned it. It gives a good blue spark. I put new fuel in it but it's not starting. The compression is also fine. I think the fuel is not getting to the cilinder but I am not sure how I can check this. My other guess is the timing and the gap between the spark plug.

Could someone please guide me through a few steps on how to get this motor started?

I would really appreciate your help.

Thanks so much from Holland,

Emery.

Laddies · Oct 1, 2006

Re: old 4.5hp mercury won't start

If you have spark and fuel and the compression seems OK then it probably has a broken reed its quite common on those little singles and not a big deal just remove the carb and the reeds are on the plate behind it simple pull out and check them

Emery · Oct 1, 2006

Re: old 4.5hp mercury won't start

Thanks for your reply. I'll take off the carb and take a look at them. how can i tell if it's broken and is it something i can replace?

I will post back how it went.

Emery · Oct 1, 2006

Re: old 4.5hp mercury won't start

sorry, double post.

Emery · Oct 1, 2006

Re: old 4.5hp mercury won't start

double post sorry

Laddies · Oct 1, 2006

Re: old 4.5hp mercury won't start

One of the petals will be chipped or in most cases broken off, if the whole thing or alarge chunk is gone you must get the peice out of the crankcase

Emery · Oct 6, 2006

Re: old 4.5hp mercury won't start

I checked that. Nothing was broken or chipped off. I changed the spark plug (don't know what gap this 4.5 hp needs). I gave it a few pulls and it gave me a more hopeful sound than it did before. I am pretty sure the gap is the problem now. I cleaned the carb entirely. Do you know what gap this spark plug has to be?

Thanks, Emery.

Laddies · Oct 6, 2006

Re: old 4.5hp mercury won't start

A 4.5 should use a L78V surface gap plug so it should fire a convention plug at .030 to .040 easily

Emery · Oct 7, 2006

Re: old 4.5hp mercury won't start

Thanks for your help.

I gapped the plug. Motor still doesn't run but I found another possible cause of the problem.

There's a fuel hose with a very small interior diameter. Both ends seem to attach to the motor block. This hose was rotten and fuel flows out of it when the flywheel turns around.

I am going to replace this hose today but I am wondering what its purpose is.

Do you know what this hose if for and what it does?

Thanks again.

Laddies · Oct 7, 2006

Re: old 4.5hp mercury won't start

If it's attached to the crankcase of the engine its the pulse line to operate the fuel pump and it should not have fuel in it if it does the fuel pump has a diaphram leak and needs to be replaced. That would flood the engine and keep it from running

Emery · Oct 8, 2006

Re: old 4.5hp mercury won't start

I replaced the fuel hose and I got the motor running. It doesn't start easily and I can't get it to idle. Is the timing messed up?

Could the timing be off? The motor backfires and runs poorly.

Is the timing easy to change?

emckelvy · Oct 8, 2006

Re: old 4.5hp mercury won't start

Has the flywheel been off? Backfiring could either be a problem with carb mixture or something like a sheared flywheel key.

Try adjusting the idle mixture and see if turning the adjusting screw in and out affects the way it runs. These motors are quite touchy and there's not a real broad range of adjustment on that screw in which the motor will idle well.

If turning the screw has no effect, the idle passages in the carb are probably plugged up and you'll need to take the carb apart and thoroughly blow/clean out the idle passages.

If it's not a carb-related thing, pull the flywheel and check the key to see if it's sheared. You might also want to clean and re-gap the points ( if your model has them) while you're in there. Points gap is .020".

HTH.........ed

Laddies · Oct 8, 2006

Re: old 4.5hp mercury won't start

Emery, one of the major problems with the Phazer point ign. systems and probaly the most over looked. When a engine has spark but misfires and in some cases will even kick when pulling the start is the nylon block the the stud for the points goes thru, the points are high voltage points and burn quite rapidly so we always want to change them as they look bad, but the little block shorts out and you can't see it the leakage when causes the engine to have random spark and misfires. When replacing points or the block don't over tighten the nut I think that adds to the cracking problem--Bob

old 4.5hp mercury won't start

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