4hp not running

[caleb2003]

Got hold of a 4hp Mercury possibly 1978, cannot find the exact year on the serial number sites listed (s/n 8072749).

Won't start. Has spark, compression is 90 psi on both, seems to backfire when trying to crank and some smoke comes back out of carb (Carb has been cleaned and float seems ok etc).
Found a manual which states the rich/lean needs changing to be richer but this doesn't help.
The original model had a fuel tank which isn't there now so using a remote tank with primer bulb. After lots of reading on here, I checked the crankshaft key which is intact and not worn.

Anyone have any other ideas and also maybe any info on this motor serial.

Many thanks

 

[oldboat1]

should get your hands on an adjustable spark tester, and check the spark. Start looking at about 1/2 inch, and work backwards looking for strong spark. 1/4 inch or so should fire the motor. (Don't know what the plumbing is on your motor -- remote tank should connect to a fuel pump, then to carb. Do you have factory connections, or did you rig a remote tank to replace a missing integral tank?)

 

[tikki]

Is the engine running with high RPM?
Take out the spark plugs and clean or replace them. check for spark while you have them out.
Put the plugs inn and trie to start the motor a couple of times. Take out the plugs and see if they are wet or dry.
If the plugs are wet you have a spark problem if they are dry you have a fuel problem.

the idle screw on your carb should be 1 and 1/2 turn out.

 

[tommarvin]

Are you sure you have spark with a spark checker,Tiki has a perfect example of a fuel test,

If you have spark and fuel it has to run, My gut says you have a plugged jet.