Motor has a miss

[redleo]

I have a 1977 V6 carbureted Mercury thats has a miss like a elect fault. I have just come bac from 2 weeks on the lake and every couple of days the motor would give a miss , starting around 2000rpm ,then next time out it would be as sweet as a nut!! .have fitted new spark plugs ( no change)check for obvious loose wires etc but still no good.
Also what fuel to oil ratio .at the moment I'm running 50:1 in 91 unleaded as this is what the previos owner ran.
p.s I'm in New Zealand so fuels may be different here?

 

[crem1]

Re: Motor has a miss

50:1 ratio is correct, I would check out the compression in the cylinders if OK proceed to carburator adjustment, fuel pump, and timing

 

[Chris1956]

Re: Motor has a miss

A miss that occurs every few seconds is usually too lean of a mixture. If it misses each revolution, you have some other issue. Check spark to see that it is steady, with no arc over to the block.

 

[redleo]

Re: Motor has a miss

Thanks will check fuel pump etc then go from there.

 

[j_martin]

Re: Motor has a miss

Thanks will check fuel pump etc then go from there.

You have no idea what is wrong with the engine, right? So start at the bottom and verify the systems one by one.

Without even compression, nothing else you do will matter, so check the compression first. Otherwise you may waste time and money on a bone.

Next, check for spark on all 6. Do it right making sure you have a good long spark on each cylinder.

Then, you go to the fuel system.

Ask detailed questions as you go, and you will get detailed answers. If you accurately list all the symptoms at a particular step, you'll get direction either to the bad part, or to the next test to isolate the bad part. If you cut corners in your diagnostics, or miss details when you post results, you'll find yourself going around in circles, probably mostly alone.

hope it helps
john