4hp Yamaha, problems.

Mercury · 29 June 2015, 15:18

I have a 4hp 2 stroke Yamaha, circa 1985. It refuses to start, can any one tell me how to check the ignition timing on this engine please. I have re built the carb using new diaphrams and gaskets, but it still has the face on. Any help in pacifying this little sod will be appreciated.

office888 · 29 June 2015, 15:24

Quote:

Originally Posted by Mercury

I have a 4hp 2 stroke Yamaha, circa 1985. It refuses to start, can any one tell me how to check the ignition timing on this engine please. I have re built the carb using new diaphrams and gaskets, but it still has the face on. Any help in pacifying this little sod will be appreciated.

Are you getting spark?

paintman · 29 June 2015, 19:08

Kill cord connected?

Mercury · 30 June 2015, 06:50

Quote:

Originally Posted by office888

Are you getting spark?

Hi, Yes spark is there, but about every fourth pull or so I get a little backfire, thats why I question the timing.

Mercury · 30 June 2015, 06:51

Quote:

Originally Posted by paintman

Kill cord connected?

Hi. No kill cord on this, so I checked kill button it's working fine..

paintman · 30 June 2015, 06:56

If you squirt a small amount of petrol into the carb intake does it attempt to run?
Has it ever run properly in your ownership?

Nightfisher · 01 July 2015, 00:07

after all the work..RUSH it in. Seriously. 20-40 pounds they'll set timing, start choke, ignition coils ohm tests. All kinds of stuff based on your work.

paintman · 01 July 2015, 00:41

Quote:

Originally Posted by Nightfisher

after all the work..RUSH it in. Seriously. 20-40 pounds they'll set timing, start choke, ignition coils ohm tests. All kinds of stuff based on your work.

Is this an ad for a company called RUSH in Ontario? If it is, it might be a bit far for the OP who's in England.....

Fenlander · 01 July 2015, 08:07

Agree it's important to know if it's ever been running for you and what has been done so that it doesn't go now.... just the carb overhaul??

Agree too a squirt of fuel down the carb should make it fire for a couple of seconds if it's a fuel issue... pull the plug and turn over to watch for spark to check if it's strong or weak.

Timing doesn't go out (usually) unless fiddled with.

Does this have electronic ign or points? Electronic is usually reliable but points can fail.... they are rarely checked on an outboard due to the hassle of removing the flywheel.

Mercury · 01 July 2015, 20:52

Quote:

Originally Posted by paintman

If you squirt a small amount of petrol into the carb intake does it attempt to run?
Has it ever run properly in your ownership?

Iv'e not tried the squirt treatment yet, But it was running fine last year, had this from new btw.

phantom 19 · 01 July 2015, 23:51

If the spark is there there is no problem with the ignition system, there are no points and timing can't be out as you cannot adjust it on the 4hp, it has a fixed timing and ignition curve.

99% of the time it is the carb at fault. Go through it again. Check jets, low speed one screws into the side of carb easy to miss if you don't know it is there. Diaphragms definatly the right way round with the little cup washer and spring in position? Spring fits into recess in fuel pump casting and cup washer fits onto spring and presses against diaphragm.

Compression? Without a compression gauge you should be able to get a good feel for it pulling it over. At 30years old the crankseals may be starting to go which does affect starting.

Far better engine than anything four stroke on the market these days.

Mercury · 06 July 2015, 12:08

Quote:

Originally Posted by paintman

If you squirt a small amount of petrol into the carb intake does it attempt to run?
Has it ever run properly in your ownership?

Squirty has done the trick, so it could have been the reed valves throwing the dummy out..