Yamaha 55hp AE 663

[bmb779]

Hi,having a mare with this engine,won't run on no1 cylinder until about 3500 rpm and then it still drops in and out,strong sparks both cylinders compression tested at 120psi on each cylinder,new cOils fitted tried swapping coils but no difference,ran engine with air box off and sprayed fuel into carb no difference anybody any ideas please.......?

[Davie]

Take out the reed block and have a look at the piston skirt.

[bmb779]

Hi Davie, what exactly am I looking for?

[Davie]

The bottom of the piston. I had a problem with one which had that exact problem. Why it burst into life now and again remains a mystery.

[bmb779]

How did you repair it,does the lower skirt break off ? Secondly is it a viable repair cost wise.

[bmb779]

Checked piston skirt tonight all ok,,at a total loss now,I'm wondering if the spark it is producing is too weak and the plug is oiling up,or sparking at the wrong time.

[RIB-Teccie]

These are the worlds easiest engines PM me.

[RIB-Teccie]

Yes, your small jet on the top carb will be blocked. Jet is housed under the small brass screw. Do not attempt to remove this jet unless you absolutely have to, they can chew up and write the carb off.

Simply blast through with air or even coke.

The small jet Is the slow running one.

Another thing to look for is the wires that enter the stator plate below the flywheel, at that age they go hard and crack, so when you close the throttle they touch and when you open it they don't and the spark fails.

[RIB-Teccie]

This is the jet.

[bmb779]

Hi Teccie, top jet cleaned all clean as a whistle,waiting on a CDI unit and stator ring.i changed a ignition coil but the replacement coil was from a 3 cyl 60hp which seemingly works at a different voltage.

[RIB-Teccie]

If you have strong sparks, it is usually a fuel problem, fuel pump problem or a leaky seal. Can't see it being electrical, but stranger things have happened.

[bmb779]

See pm

[RIB-Teccie]

See PM

[bmb779]

We'll after some head scratching and an amazing amount of help from Rib Teccie another Yamaha 55 Two Cylinder is running like a Swiss watch,the problem turned out to be a blocked carb,replaced with a good 50hp carb using 55hp jets and all is well.This man is a credit to the forum without his help I would have had an expensive anchor but now looking forward to Loch Lomond tomorrow.Thanks again.

[RIB-Teccie]

It's true, the amount of simple faults that can cause engines to be written off before their time is incredible. Without parts and knowledge, the process of repair can be horribly frustrating or expensive. Just try not to blow yourself and the garage up next time!!! Enjoy Loch Lomond, boat engine & water, were designed for each other.

[spartacus]

Well done RIB-Teccie.

[bmb779]

Out on Loch Lomond today,engine runs like a dream,pulls cleanly up to red line and still wants to go.Then disaster struck,control box fell apart and had no throttle or gear selection managed to get back to slip manually working throttle with hood off,back to the workshop!