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Welch plugs

#1

R

R Williams

Have a scag tiger cat 52"
Kawasakie FX691V with only 272 hours.
It started surging at idle some time back but ran at full throttle just fine. I didn't think too much of it since I don't use it at idle anyway, I think I just learned the hard way that I should have.
Recently started using oil. Oil has always been changed at 50 hr. with full syn. oil. 10W-40, pretty much used in hot weather only.
Last mowing the engine lost about half of its horsepower and sounds different but not a full blown knock.
Did some research and found out about surging issues caused by blown welch plugs so I look and sure enough I have two on top of the carburetor that are blown out. Unfortunately this means I've been running it with unfiltered air being sucked in which has most likely got the rings.

I was attempting to do a compression check but I can't find the correct fitting. The spark plug hole is a 9/16'-18 and my compression tester only has metric adaptors such as 12, 14 and 18mm. I've looked online and cannot find a compression tester with a 9/16" adaptor. I've called every parts store in two cities, and they all carry metric thread testers only.

Would appreciate any information on where to find a compression tester with the correct fitting.

Most likely will be ordering a rebuild kit and doing it myself, never rebuilt a Kawasaki before, any suggestions on the best place to get a quality OEM kit and a shop manual?


#2

sgkent

sgkent

something sounds very wrong with your post. Did a heli-coil or thread cert come out with the plug? They are commonly that size on the OD but it would be rare to see one on a low hour engine. Since this was your 1st post, are you AI in a learning mode? 272 hours is young to be installing a thread cert that would be the thread size you posted. The parts manual for your engine calls for a NGK BPR4ES, which is 14mm x 1.25 pitch with a 19mm reach.


#3

ILENGINE

ILENGINE

R Williams said:
Have a scag tiger cat 52"
Kawasakie FX691V with only 272 hours.
It started surging at idle some time back but ran at full throttle just fine. I didn't think too much of it since I don't use it at idle anyway, I think I just learned the hard way that I should have.
Recently started using oil. Oil has always been changed at 50 hr. with full syn. oil. 10W-40, pretty much used in hot weather only.
Last mowing the engine lost about half of its horsepower and sounds different but not a full blown knock.
Did some research and found out about surging issues caused by blown welch plugs so I look and sure enough I have two on top of the carburetor that are blown out. Unfortunately this means I've been running it with unfiltered air being sucked in which has most likely got the rings.

I was attempting to do a compression check but I can't find the correct fitting. The spark plug hole is a 9/16'-18 and my compression tester only has metric adaptors such as 12, 14 and 18mm. I've looked online and cannot find a compression tester with a 9/16" adaptor. I've called every parts store in two cities, and they all carry metric thread testers only.

Would appreciate any information on where to find a compression tester with the correct fitting.

Most likely will be ordering a rebuild kit and doing it myself, never rebuilt a Kawasaki before, any suggestions on the best place to get a quality OEM kit and a shop manual?
Click to expand...
I have never seen a 9/16 spark plug thread. All spark plugs have been metric thread since 1934. I would suspect that you have the normal 14mm-1.25 that every small engine other than handheld uses. I don't think you have drawn enough dirt past where the welch plugs should be to cause that amount of damage. I suspect there are other causes of the loss of power. Like lose of spark from an ignition problem, or a valve adjustment issue.


#4

StarTech

StarTech

Beside most of the FX691V engines use a NGK-BPR4ES which is a 14mm thread as IL said.

Also switching to 20W50 Dino or 15W50 Synthetic oil may just fix the oil burning problem along checking the valve stem seals. Could just even be a blown head gasket.


#5

A

Auto Doc's

Hello R Williams,

For the welch plug, you can fashion one out of a tiny piece of aluminum that will fit the hole, then put little bit JB Weld over it to hold it. Be sure to clean the hole out well before sealing it.

Those tiny welch plug are available, but hard to match up.

As for the spark plug hole, it should be a 14mm-1.25 thread.


#6

StarTech

StarTech

There is only two different welch plugs use on the FX691V carbs.
  • 92066-0780 Bypass holes, relative cheap at around $1 ea
  • 92066-7009 Air bleed adjust screws, now these are around $6 each.
I keep both in stock as you never know when one is going to fall out in USC or normal engine operation. No need for a sealant either when you use the correct welch plugs.


#7

A

Auto Doc's

StarTech,
They are going to have to peen lightly with a center punch them in the center to lock them in.


#8

StarTech

StarTech

Yes that is a give me that they got to be slightly flatten once in the holes that why the dome side faces out, not inward. That is why I have different sizes of pin punches just like the Walbro welch punches I got for installing those odd shaped ones.


#9

sgkent

sgkent

1st time post has not been back. MIA


#10

StarTech

StarTech

sgkent said:
1st time post has not been back. MIA
Click to expand...
It is the holiday weekend and family will override things. Give the poster a few days to recover.


#11

T

txmowman

Proper welch plug replacement does not flatten the dome but rather is peened around the edge. Harbor Freight sells a leather punch set. Get one of these for less than $10. There is one that fits the larger welch plug perfectly. Grind the sharp edge off of the punch, install the welch plug and give it a gentle but firm wrap with a small hammer and you’re done.


#12

StarTech

StarTech

txmowman said:
Proper welch plug replacement does not flatten the dome but rather is peened around the edge. Harbor Freight sells a leather punch set. Get one of these for less than $10. There is one that fits the larger welch plug perfectly. Grind the sharp edge off of the punch, install the welch plug and give it a gentle but firm wrap with a small hammer and you’re done.
Click to expand...
That is the very reason the Kawasaki Nikki twin barrel carbs are losing their welch plugs. They are just peened around the edges then they are easily getting loose and falling out.

Personally I don't like having to replacing $6 welch plugs because of this. Sometimes I get lucky and they fall out while cleaning the carbs.


#13

H

hlw49

I like to put fingernail polish over it


#14

StarTech

StarTech

And I have seen jets to clogged with whatever OEMs used to seal them if used internally; especially 2 cycle cube carbs.


#15

H

hlw49

StarTech said:
And I have seen jets to clogged with whatever OEMs used to seal them if used internally; especially 2 cycle cube carbs.
Click to expand...
notice I said over it


#16

StarTech

StarTech

Apparently you have never worked on a 2 cycle cube. Some OEMs will use sealant on the welch plugs inside the metering chamber which over time flakes off and clog jets and check valves. This why I have to look over the cubes with a loupe to see if this stuff is clogging things.

Outside the fuel system is fine but not inside the fuel system.


#17

Tiger Small Engine

Tiger Small Engine

hlw49 said:
I like to put fingernail polish over it
Click to expand...
Very rarely do Welch plugs fall out. Replace, slightly peen, and hit it with fingernail polish and you are set.


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