Yamaha 2HP 2 stroke problems

G

glitchy

New Member
Joined
11 Sep 2018
Messages
5
Visit site
Got 2 motors had in shed for a long time.
Wondering if someone can possibly shed some light on the problems.


Yamaha 2A, bought as sold as seen with no information decided to take a look at it now. condition is great, had electric drill on flywheel and pumps water but doesn't fire up.
Cleaned carb, cant see spark with plug unplugged, do i need to touch it with metal? any other things should look for? Can these be fitted with the 2B recoil pullcord?

Also got a Yamaha 2B, was a great runner but been very problematic since sheer pin snapped and engine over revved.
Runs fine in a barrel and put it on back of dinghy and it dies refusing to start after 2 minutes.
Stripped her, impeller changed (wasnt too bad), gearbox oil had no water residue and seal is okay.
Power head seals are knackared (never had her apart before), not sure how to get to cylinder to check that. not sure if water leaked into it.
Worth buying new seals? or check something else first?
 
You need to earth the thread/hexagon part of the spark plug against the block or cylinder head before you will see a spark. However, unless you are in dull conditions, the spark can be very difficult to see. I use a spark tester which fits between the HT lead and the plug which shows up the spark very brightly, even in sunlight.

The failsafe method, which I have used when desperate, is to bridge the spark plug gap with my finger ..... but you can get quite a jolt so take care. :ambivalence:

Richard
 
No spark on the 2A then, had finger on spun it with drill didnt feel a thing. also tried with all lights off in garage (pitch black) nothing.

I'll check power switch and earth tonight.

As for the 2B, thought if i'm going to buy gaskets so may as well do them all
I removed the head and here is what it looks like - could this of been the problem? It's filthy, does that mean head gaskets failed and water was getting in? as stated, the power head gasket had failed and was mostly made up of sealant rather than genuine gasket.

Any further damage caused? Do i need to dig deeper into the engine?
Don't want to spend 30gbp on gaskets if i'll end up selling for spares.

https://imgur.com/a/1inr57A
 

Attachments

  • photo_2018-09-12_10-10-10.jpg
    photo_2018-09-12_10-10-10.jpg
    121.1 KB · Views: 9
  • photo_2018-09-12_10-58-49.jpg
    photo_2018-09-12_10-58-49.jpg
    124.8 KB · Views: 3
  • photo_2018-09-12_10-58-50.jpg
    photo_2018-09-12_10-58-50.jpg
    145.7 KB · Views: 5
Bore and cylinder look about right, difficult to tell from pics. Pore some petrol into the bores (piston above the inlet and exhaust ports) it should not run away quickly if the rings are ok, you should of done a comp test before taking the head off really.
Check for side to side play in flyuwheel and crankcase seals( can only get to top one) if you got an air leak from this it will run erratic (drawing air in will effect fuel/air mix)
I think you may have jumped ahead a bit with taking the head off,
 
Last edited:
Would of pressure tested but no idea how. Had a look at the tools to do it and theres too many options!

So does it look like head gasket hasn't failed then?

I'll pour some petrol in as suggested thanks.

When she was in one piece she ran smooth but after few minutes use died and refused to start until a week or so later

thanks for help
 
Generally before tearing things apart

Check for a good spark(s) . With cdi ignition you should be able to get a spark best part of a centimetre from the plug lead . Not quite so much from a coil and points system. Just testing the spark across the plug gap is not an adequate test. An air gap tester, such as Ricahard uses, is the best way of testing.

Always worth trying a new plug if the spark is good.

If the spark is non existent or poor inspect the coil for overall condition and continuity of windings. In the case of a points system check, clean and reset, or replace, the points also suspect the condenser if the rest is OK

Always check the stop button/ kill switch circuit.

Check the compression using an ordinary car type compression tester. You'll not likely find specified figures for a 2 stroke but under 60 psi is too low. It ought to run if 80 or above . Run well if over 100.( If over 120 then the gauge is wrong. :) )

If you have a good spark and the compression is good then look at fuel flow and carb.. Try a spray of fuel direct into the carb throat. If it fires and runs briefly It confirms everything else is good.
 
One little bit to add. Mine wouldn't spark, until I found the lead into the plug cap had seperated and the wire was to far from bit that holds the top of the plug to connect. Cut a bit off and screwed the spiked fitting back into the wire. Worked fine. I was assuming coil etc was duff and was about to toss it.
 
You must log in or register to reply here.

Share this page

Top