Decarb Question

[da_ardvark]

Ok, I did a compression test on my 1985 70 HP Johnson.
Top Cylinder was 105 psi
Middle Cylinder was 105 psi
Bottom Cylinder was just shy of 105 psi

All the plugs looked good. Tan in color and oily around the edges. No oily residue on either sides of the electrodes.

I read the Decarb FAQ and I want to know a coupla things. Can I just use my extra fuel tank to mix up the 3/4 gal to 1 pint of seafoam?

Should I run seafoam thru before I spray seafoam into the carbs and cylinders?

What kind of compression increase can I expect under best case scenerio?

I'm going out next week with family and I want to make sure (as much as possible) that the engine is going to perform well.

A little background. I just bought the boat and engine, and have had it out twice. Each time at WOT the engine cut out (didn't stall but I had to reduce throttle and only happened 3 times the first time out and twice the second) I cleaned out the tanks and the fuel fliter (There is no fuel filter in the VRO pump right??)

Anyway I'm trying to be careful during this process so as not to make matters worse.

On last question. Should I buy ready made plug wires, or can I use auto high performance wires that I cut and make myself.

Thanks

Denny

 

[reload]

Re: Decarb Question

Compression numbers look good. I don't know any history of this motor but decarb might not increase compression at all. Plug wires should be solid copper wire. Sounds like it is starving for fuel, I would check carbs. Pull apart and rebuild. When it gives you trouble, do you think it is a cylinder dropping out. Is it a dead miss or does it sputter.

 

[tashasdaddy]

Re: Decarb Question

your number aren't the worst, but i like to see higher, but guages are different also. decarb is not a guarantee to bring compression up, it cleans the engine and allows the guts to operate easier. your problem sounds like a coil heating up and failing, causing you to drop a cylinder. if you make your own, and use the type that the pin sticks thru the insulation as a fastener, strip the wire back, and wrap around the spring contact. i prefer premade.

 

[da_ardvark]

Re: Decarb Question

I thought I read where others are getting compression numbers of 130 psi and upwards of 150 psi?? What should I expect from a fresh rebuild? I looked in my manual and there were no ideal compression numbers givens. That aside, when it dies out it's as if I pulled back the throttle quickly. I'm not sure if this engine has the S.L.O.W. system. I'm fairly confident that the impeller is good, but if this continues, I guess that's what will be next. I really want to get this done before Tuesday. I suppose a rebuild of all three carbs is probably in order. I will learn this engine!!!! It shall not defeat me..............unless it costs too much


Thanks

Denny

 

[iwombat]

Re: Decarb Question

Don't use automotive carbon-core wires. Only solid-core marine type wires are acceptable.

 

[da_ardvark]

Re: Decarb Question

tashasdaddy,you said "your problem sounds like a coil heating up and failing, causing you to drop a cylinder."

My question is, if this is the problem, will this damage the engine?

As always, I assume all responsibility of anything I will do.

There are just too many scary places out there when you are a newb

 

[reload]

Re: Decarb Question

I don't see many 2 strokes with numbers above 110.

 

[da_ardvark]

Re: Decarb Question

Bump

tashasdaddy is the overheating coil going to damage my engine?

Thanks

Denny

 

[GlasV162]

Re: Decarb Question

If you even suspect a fuel restriction, check that first. My motor had similar symptoms of missing at wot; turns out it was a clogged jet. My mech. checked everything else first, then the carburetors last. As a result my motor locked-up on me. No fuel = no oil. I'd also highly recommend installing an additional fuel filter or even a fuel/water separator; it should help trap any crud in the high quality fuel we're all buying these days.

 

[wbeaton]

Re: Decarb Question

A misfiring coil won't damage your engine, but it will cause it to run poorly. If a coil is failing you need to replace it.

I have lots of motors with more than 110 psi compression. Also lots with less. I wouldn't be concerned unless the numbers were under 100 psi.

 

[tashasdaddy]

Re: Decarb Question

a failing coil means the cylinder is not getting spark to create the combustion. thus the other cylinders are dragging that cylinder, and your motor is not performing at the optimum. it won't damage the engine, unless you continuallly run it, it put more stress on the other cylinders. you really need to get an OEM manual specific for your motor, and do some troubleshooting. outboardbooks.com

also there are a lot of qualified people on the forum. please don't call out for one person.

 

[da_ardvark]

Re: Decarb Question

I have a manual that came with it. It's for a 1980 vintage 70 and mine (as i later found out is a 1985) I'll test the coils for proper resistance tonight and then see where I am from there.

I also think I'm going to go ahead and replace the impeller. I don't know how well the engine was maintained before I got it, so I think it would be a wise thing.

Thanks for all the replies.

Denny