50 2strk running rough

[almetelo]

Hi guys need some help please!

I'm trying to help a friend with a 50DEO/50ELR PID 6H5 2 strk, 3 cylinder, electric start, oil injected, no T&T that is running rough and stalls untill it dies... (motor running on muffs)

We replaced a defective fuel pump by a new one, the compression is good, cylinder #1 118psi, #2 116psi, #3 108psi, new set of spark plugs, timing 5º ATDC at idle as recomended by SM, spark gap of 7 1/6 or 11mm good on all 3 cylinders, carbs cleaned 3 times, float height (15mm) and pilot screws (1-5/8) as recomended by SM, throttle linkage properly tuned by SM, my MT2700 reads #1 spark plug/coil around 7KV, #2 11KV, #3 6KV ( I consider these values when "conventional" light stops blinking and stay lighted.

Cylinder/coil #3 have good spark (gap) but no signs of combustion on the spark plug, if I disconnect #3 spark cap while running and reconnect it nothing happen, however the spark is wet so fuel is getting there... spark plug cap 4.5 ohm resistence on all 3.


I suspect that may be a electrical problem... (or not)

What else can I test without a DVA adapter? (already bought a CDI 511-9773 in US but I'm waiting that friend in the end of the month go to VA in a business trip to bring me the DVA because I want to stay away from costumes)

The lack of combustion on #3 cylinder may have to do with fuel enrichment valve? (that is attached on #3 carb)

I don´t know if to be a little older model but SM is not very educational (at least as SM of my own outboards)

What else should I test? Which way should I go now?

Help please!

[rodbolt17]

your compression numbers on cyl 3 are about at the limit.
I would do a leakdown test .

once its verified that the engine can mechanically seal then I would index the flywheel, verify proper timing an each cyl the continue chasing fuel issues.

[almetelo]

Hi Rod!

Thanks for reply.

This afternoon retested compression and got almost same previous values (110psi on 3# cyl " not a big improvement" )
After the compression test did a leakdown test and the motor is sealing really good, have no leaks... so I must head other possible causes.

How do I test timming on each cyl???
May be a defective pulsar coil??? How do I test it?

What else do you recomend?

Thanks!

[99yam40]

Not sure on your 50 but should be like my 40. It has the fuel pump pulse port on #3 crankcase , so if it leaks it enriches the mix into the cylinder to the point that it does not burn properly. If it has a vacuum leak at the gasket it could mean it is too lean of a mix into the cylinder maybe
You could also have a lower seal leaking maybe and causing # 3 to run too lean to burn properly

Have not seen it but think it could happen.
Just read you replaced the pump already, hope it was with a new gasket

[TownsendsFJR1300]

spark gap of 7 1/6 or 11mm good on all 3 cylinders,


Help please!

11mm gap on the spark plugs??? That is a typo, correct?

[rodbolt17]

what were the leakdown % numbers?
its rare to have electrical issues with that motor but it can happen.
its simple to index the flywheel and verify spark timing on all 3 cyl.

[almetelo]

Hi guys!

Thanks for reply!

99yam40 This is 50 PID 6H5 if your 40 is PID 6H4 is the same stuff.
In fact we placed a completely new fuel pump but we keeped the gasket, so We'll change the gasket that at least looked to be good.

FJR1300 yes, 11mm spark gap not 11mm spark plug gap (spark plug gap 1mm) all 3 (coils) tested at the same time on my home made "stevens" spark tester untill I'll get the original next month that I already bought there in US

Rod I´m sure that is easy index the flywheel and verify spark timing on all 3 cyl (for you of course) I don´t know how to do it, can you teach me please.

I'm placing a foto so you can have a look on #3 cyl leakdown test at TDC3

[99yam40]

Some flywheels have the 3 pistons TDC already marked on them.
If not , just pull plugs and turn motor by hand until each piston comes to Top dead center (usually using a dial indicator in the plug hole) and mark the flywheel at the timing pointer.
That way you can move timing light to the different plug wires and see where the spark is hitting on each.

If you mark the TDC you can measure how far the proper timing is from TDC on #1 and mark the others where it should be with white paint to make it easier to see with the light

[almetelo]

99yam40 is that simple??? loool

I hope I got it right... yes, flywheel have TDC #1,2 and 3 marked on the top so I just have to switch the inductive clamp of timing light to the proper cyl to check timing, right?

Correct me if I'm wrong...

Thanks!

[99yam40]

2 & 3 do not have the other timing marks around the TDC mark so just need to measure how far #1 marks are that you are looking for and transfer to the others.
might check to make sure those marks are at TDC
At least that is how I believe this should work.

I do not under stand timing getting off on just some cylinders and not others, but maybe it is possible. I did have the idle timing retard to far on my C40 , had to replace CDI to get it straightened out. But all were off the same when I checked them

Just thought of something that may come into play,
at cold start the Idle timing is advanced some on motors with prime start
once motor warms up the timing will retards back to what the specs call for at idle

[almetelo]

Hi!

Today replaced the gasket of fuel pump and had no improvements
Checked timing again and at idle (800rpm) have 8º ATDC and not 5ºATDC anymore.
The degrees (distance) of TDC is the same on all 3 cyl (8ºATDC) today.
When the motor stalls the timing oscillates but that is suposed to be normal, right?
At 1500rpm timing is 3º BTDC.

What else guys?

[99yam40]

If there is good compression, good spark, and correct timing then you are left with a fuel to air ratio not being what it should be in the cylinder.

Carb problem, reeds, or seal leak

Not sure how to see if #3 is running too rich to fire properly, but read you can pinch the fuel in closed to the bottom carb with a needle nose plirs or something else to see if it starts firing when it stars to run out of fuel.
to check for too lean, you can take some premix in a spray bottle and spray into the bottom carb throat and see if cylinder hits.

If lower crank seal is leaking it probably will not be sucking through the carb properly to get the correct fuel into the crankcase and cylinder

If the fuel pump leaked too much straight gas into crankcase and cylinder for too long it could have washed off too much of the oil and hurt rings, piston, cylinder walls, bearings, or crank.

Does this motor have oil injection or is it premix?
Choke or prime start?
If reed has a problem it would be blowing back through the carb instead of sucking fuel and air

[almetelo]

Hi!

Motor have a Solenoide Valve and is oil injected



Yesterday when have been on my local Yamaha dealer to buy the fuel pump gasket and talked with the owner of the dealership (not the mechanic) when I refered to little low compression on bottom cyl compared with top and mid cyl he sugested that could be a bad oil seal or o-ring on crank shaft but #3 cyl is sealing good so I thought that not would be the problem...

But when you refer this:

If the fuel pump leaked too much straight gas into crankcase and cylinder for too long it could have washed off too much of the oil and hurt rings, piston, cylinder walls, bearings, or crank.

That makes me reconsider.

I remember that when my friend bought the boat he had to navigate 3 or 4 miles to the ramp whid a defective fuel pump leaking lot of fuel and the motor unable to plane the boat.

Today will test what you sugested and will leave cranck shaft for last option because #3 cyl have a good sealing despite the little low but acceptable compression.

Should I check the diaphragm of solenoide valve?

When timing is OK on #1cyl shoudn´t be the same on all others (same distance of TDC)?

If you remember a few more things to test please let me know.

[rodbolt17]

I am not sure how briggs and Stratton marked there tester nor their acceptable limits.
typically on a 4 stroke the limit is 20%.
typically a 2 stroke is 15%.
I wont accept anything over 10% on a 2 stroke.
leaking crank seals can cause poor idle but wont affect secondary compression nor cyl ring sealing.
it can affect primary compression.
timing spec on that motor should be 7*ATDC at idle but double check your manual as this spec is for a US market 50.

[99yam40]

I am not sure how briggs and Stratton marked there tester nor their acceptable limits.
typically on a 4 stroke the limit is 20%.
typically a 2 stroke is 15%.
I wont accept anything over 10% on a 2 stroke.
leaking crank seals can cause poor idle but wont affect secondary compression nor cyl ring sealing.
it can affect primary compression.
timing spec on that motor should be 7*ATDC at idle but double check your manual as this spec is for a US market 50.

Rodbolt,
I was just thinking of reasons # 3 cylinder is not firing properly if cylinder compression and spark are good.
it has to be the wrong fuel to air ratio in only that #3 cylinder.

I have found chainsaws with the pulse hose from crankcase to the auto chain oiler coming apart and that leaked enough vacuum out of crankcase to keep the carb from sucking enough fuel to even start. If I shot some premix into the carb throat it would fire off and run at higher RPM but not idle. Of course that was just a single cylinder but this motor with three seems to be hitting on 1&2 but not #3