50 2strk running rough

[TownsendsFJR1300]

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

With that said, I recently had to repair my 2 stroke weedeater. It wouldn't idle and was very irratic running. Its an older Ryobi but the issue turned out to be the cylinder to base bolts, LOOSENED UP. That allowed air to enter (bypass the carb) in between the two gasket surfaces. The fix was some RED loctite, some different bolts with lock washers..

In ref to the above OB issue, if its sucking air thru a crankshaft seal(leaky reed, etc), that'll screw up the mixture.


How does #3 spark plug look compared to 1 & 2?

Does the op have access to a lazer temp gun and compare cylinder head temps?

[almetelo]

Ended not working on this motor because spent the few time left installing the water wressure and water temperature gauges and sensors on my F100 for the weekend...

Left to right,
#1, 2 and 3 cyl spark plugs

[TownsendsFJR1300]

Ended not working on this motor because spent the few time left installing the water wressure and water temperature gauges and sensors on my F100 for the weekend...

Left to right,
#1, 2 and 3 cyl spark plugs

No doubt #3 isn't working. I just re-read your first post.

You mentioned the gap was correct on the plugs and #3 was firing and was wet with fuel. Even if compression sucked, it should have some color to it..

I'm not sure how you came to that conclusion that you have spark.

Can you, one at a time, install a spark plug into the plug cap, NOT INSTALLED IN THE head, ground it and have someone crank the engine over (visually) checking for spark at #3. Please report back.

[almetelo]

The quality of pic is bad because is already night here.



Test made with home made 4 way spark gap tester (spark gap 7/16 or 11mm)

Thats way I'm saying that I have spark...

[TownsendsFJR1300]

Please try it using the actual spark plug, connected to #3 wire, grounded out to the head, just to rule that out...

If there's an internal short at the end of the wire itself (your meter won't catch that in the cap).

Some Yamaha spark plug caps (in the motorcycle industry), the screw in wire end comes loose, over time from the wire and definitly affects performance. Any black arcing at the end of that wire to the cap is a sign of it as well...

[almetelo]

Already tested the spark plug caps... all 3 with 4.5ohm resistence (yamaha require 4 to 6 ohm resistence)

will test that any way.

Thanks

[TownsendsFJR1300]

Please do, it could be as simply as the end of that wire not having a good connection to the cap..

Especially if the plug is wet with fuel, it HAS TO FIRE (if there is spark making it to the combustion chamber)

[almetelo]

Hi!

Just tomorrow morning I'll have the time to test all you sugested but have one more question...
As last option I'll have a look on cranckshaft seals and o-rings



#15, 16 and 17 on the pic.

To access to this seals and o-rings I just need to remove/lift the entire block or open it? I think I just need to lift it.

Any other ideas of possible causes are wellcome.

Thanks

[TownsendsFJR1300]

Looks like they reside inside part #14 which is bolted to the bottom of the engine.

My guess would be yes, the powerhead would have to come off to access it..

[almetelo]

Hi!

Today did the tests that you suggested

FJR1300 spark is good tested by the way you suggested

99yam40 Sprayed premix fuel to #3 carb throatle at several rpm range and got no improvements

But found this on #3 carb fuel valve diaphragm



Can this be the cause of motor fault?

Removed power head and crankshaft seals and looked to be good but we'll replace it anyway.

Did other leakdown test with the power head removed, without crankshaft seals and not warmed of course and confirmed good sealing on cyl #1 and 2 (almost in the end of green scale) not so good on #3 ( but guess is good (not sure), had 110psi compression on last test)
The leakdown test showed same values with power head on place and with crankshaft seals/o-rings

[TownsendsFJR1300]

The top pic / diaphram doesn't even look like the corect gasket, 1/3 of the holes are misaligned??

Is that goo carbon or watery sludge or ? on there?

[almetelo]

yes, seems to be the right part, looks like misaligned on pic because 1 corner is raised

[99yam40]

Hi!

Today did the tests that you suggested

FJR1300 spark is good tested by the way you suggested

99yam40 Sprayed premix fuel to #3 carb throatle at several rpm range and got no improvements

But found this on #3 carb fuel valve diaphragm



Can this be the cause of motor fault?

seems like diaphragm is coming apart and maybe leaking too much fuel into the pulse port causing over rich problem maybe

[almetelo]

Hi!

Replaced cranck shaft seals (not necessary in my opinion but my friend wanted them replaced anyway) and o-ring (necessary)

Also replaced Solenoide diaphragm valve on #3 carburetor.

Now already have combustion on #3 cylinder but motor still failing.

When it starts at idle RPM's goes to almost 2000 then suddently down to 800 rpmīs and motor fails untill it dies...

Have look on video and give you opinion.

https://www.youtube.com/watch?v=QX0t...ature=youtu.be

[TownsendsFJR1300]

Sounds like a fuel issue to me.

Once it stalls out, is the #3 plug wet (actually, whats all the plugs look like((firing))?

Can you get it to run at 800 RPM's with the throtle stop screw?

Were all the jets in the carbs REMOVED and visually inspected (you can see light thru them) and cleaned? Clogged idle jets would keep it from idling down..

A vacuum leak would cause irratic idle/stalling as its not pulling air/fuel thru the carb too.