not even a pop on 1973 mercury 4hp

[robert53a]

Hi, tried to get even a pop out of this motor, no go. has nice hot blue spark, but even pulling the plug and squirting a jet of premix in nothing. Help!!!

 

[lckstckn2smknbrls]

Re: not even a pop on 1973 mercury 4hp

Check the compression.

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

Pull the flywheel, check for a sheared key.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

Hi back after compression test. Using my battery drill I spun the motor for about 4 seconds, 3 times. each time I got 100 psi. should be a little higher pulling the rip cord, but couldn't get the hood on because of the gauge. would 100 psi sustain ignition? I'll check the fly wheel key next. Thanks

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

Just pulled the fly wheel and found key and key way intact. Every thing under the fly is like pristine. The motor has good harsh spark. still not even a pop, but thanks for the help.

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

100 psi is plenty. So you have spark, you have compression, and fuel. Is the plug good, have you tried a new plug? I don't know if there is a timing setup on that motor either.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

well, I guess I'll do a link and sync and I'll clean the carb while I'm at it. Hope fully it will at least pop. even out of time it should at least pop.? Thanks

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

Backfire is more like it. The one and only time I had this happen on me, albeit was my merc 6 hp twin, was when I reassembled the mag which had been take apart by the PO. I had the magneto cam on the wrong way, I removed the cam flipped it and then it fired first pull. The cam was throwing off timing because the cam bump was off due to position.


Have you confirmed the point gap is correct? The gap has everything to do with timing as well as the key, just cause you have spark doesn't mean it's sparking when it should.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

Bktheking, I think you nailed it. I put the crank on high cam and tried to fit an .020" feeler guage into the point gap and it wouldn't fit. I had to go all the way to .010 before a guage would fit. I'm cleaning and resetting now and I'll report back..Thanks!

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

That would do it, I suspect it's running now!

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

I'm throwing in the towel. This motor isn't going to run. It has nice hot spark good compression and I'm stumped. I'll put it back on the rack and mess with it another time. Thanks for all the suggestion.....Robert

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

Lol, if you were close i'd get it going.

 

[Wingedwheel]

Re: not even a pop on 1973 mercury 4hp

I'm with the king. Your close....Sometimes it helps to walk away for a little while, just don't give it up..

 

[CharlieB]

Re: not even a pop on 1973 mercury 4hp

Points?

Does this motor have the plastic insulator that cracks and shorts out the spark when under compression yet 'seems' to spark test otherwise OK?

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

It does have the insulator block, I just looked it up. You could try replacing it like CharlieB said. When I encountered the bad blocks I got ZERO spark but you are getting spark. You could pull it apart and inspect it for cracks/burns- it could be that simple.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

This is interesting. What part of the magneto is the insulator block? Is it the micarta block the point are in? I'll try anything to get it running. Thanks

 

[stackz]

Re: not even a pop on 1973 mercury 4hp

magnetos can go bad and you can still have spark at the plug. it may look nice and hot but actually be very weak.

for any of the car guys on here, its similar to the ignitors in 90's honda engines going out but still getting spark at the plug.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

Thanks guys, I need to replace this insulator block, but I cant identify it in the parts breakdown. I don't know which peice it is. Could you tell me the part number? Thanks again.....Robert

 

[bktheking]

Re: not even a pop on 1973 mercury 4hp

You won't be able to get them through a merc dealer, they are NLA. You could try calling a couple.

http://www.crowleymarine.com/mercury-outboard/parts/456_4.cfm

# 28 part # 336-4460

If you don't have luck at a Merc dealer, CDI sells them as well. The insulator block is under the flywheel, white plastic block with a screw through it that attaches to the point and goes to the coil.

 

[robert53a]

Re: not even a pop on 1973 mercury 4hp

Thanks so much for the information, i'll pull the fly wheel again and take this piece out and examine it and start my part seach. I'm at work now, but can't wait to get to it. Thanks......Robert ps. I'll report back.