1998 8hp E8RECR Fouling and runs poorly.

[cprodave]

Compression last checked in March 2021 was 90psi Upper Cylinder, 95 Lower Cylinder. Was running OK but had a Slow Speed Cough which I eliminated in September by backing out the Slow Speed Screw by 1 1/2 turns (seemed like a lot at the time but made engine run better in water tank). In November engine ran poorly--Upper spark plug seemed fine, lower plug appeared fouled. I replaced both plugs using L77JC4 (best guess these plugs were at least 3-4 years old although probably had less than 1 hours on them). Past week ran engine again, it still runs poorly. Seems to have a lot of unburnt fuel dripping out of exhaust after 30-40 minutes runtime on new plugs. Top plug is definitely fouled, lower plug looks nice Tan color. Using adjustable Spark tester each Cylinder is getting blue spark greater than 3/8 inch. Both pistons are moving ( I haven't borrowed a Compression Gage yet) i.e. no Broken Rod, etc.
Another engine runs fine using this same Fuel Tank, Bulb and Fuel Line. Pumping the bulb while engine was running rough did not make any difference.
So what should I look for as I further investigate? I have never cleaned/rebuilt the Carb on this motor (which I acquired about 5 years ago). I am thinking that is needed or (as a minimum) turn the Slow Speed Screw back in at least 1/2 turn, then on-the-water test.

 

[cprodave]

Added photos. Photo dated today top plug is upper cylinder, bottom in photo is lower cylinder.
View attachment VID_20220110_121841.mp4

 

[racerone]

Remove cowling.----Run with timing light hooked up and observe flashing light to see how spark behaves.-----Test both cylinders.---Clarify.----First you say lower plug is fouled and top plug fine.----Then with new plugs the top is fouled ?----Checked the thermostat?----Perhaps replace fuel pump diaphragm.

 

[cprodave]

Racerone, thanks for the prompt reply as I am in a hurry to fix this engine (to be used as a backup engine) before our duck season ends on 1/31. The ducks may be happier if I don't get this fixed. I will try to borrow a Timing Light although I am unsure how to use it.
Unfortunately when I found the fouled plug in November the photo I took did not indicate upper vs. lower spark plugs. I laid the plugs side-by-side on the Flywheel and have to rely on notes I took re: which plug was in which position. It is possible my recollection of November plug position is wrong. But I am certain most recent fouling was on Upper Plug.
I replaced the Thermostat (full kit) in February 2020. There was a Water Leak between the Thermostat Cover and Cylinder Head that eroded away both the Cover and the Head. I installed a "new design" Cover and had to grind flat the Head by a couple thousandths where the erosion had occurred. Inspecting the Thermostat area just now I discovered the Top Left (Port side) Bolt for the Cover was slightly loose--although I see no signs of water leakage could this cause the engine to run poorly?
I too was thinking Fuel Pump Diaphram could be the problem but I pumped the Bulb when engine was running poorly and it made no difference. Or am I missing something there?
Thanks again.

 

[racerone]

I took a 95 model 6 HP apart a while ago.-----Bottom crankshaft seal was kaput.----If there is one , then there might be more motors with the issue.----Sorry I can not see , feel your motor.

 

[tblshur]

ii would at least take carb apart and clean maybe spray little premix fuel in carb while running to see if it makes any difference adjust mixture screw back where it was good luck

 

[billnorth1946]

2 stroke or 4 stroke? Probably not a fuel problem if both cylinders are running on the same carb. If a 2 stroke, sounds like bad reeds on one cylinder or a head gasket problem. If 4 stroke, could be the head gasket.

 

[racerone]

The model # clearly indicates a 2 stroke motor !!

 

[cprodave]

Thanks to All for the inputs. I will do simplest things first:
1) Reinstall Thermostat, make sure all 3 Cover bolts are tight. (Could a Cover be loose enough to prevent the Thermostat from opening properly, yet not be so loose as to leak water visible outside the Powerhead? I wouldn't think so.)
2) Set Slow Speed/Mixture Screw back by turning inward/Clockwise 1 1/2 (or at least 1) Turn. Then perform on-the-water test (PITA for me, boat ramp is at least an hour away and my available time to do that is limited). Recall that engine ran OK in water tank so on-the-water test is necessary to check the Thermostat and Mixture items.
3) Recheck Compression (PITA-- I have to borrow a gauge--time to break down and buy one I guess. Have to take wife out to dinner to offset purchase lol. Buy once cry once.) Will determine if there is a Head Gasket problem that has developed since March 2021. No on-the-water test needed for this.
4) Fully disassemble and clean Carburetor. Repeat on-the-water test.
5) Consider replacing the Fuel Pump membrane even though pumping the Bulb didn't seem to temporarily offset the problem. I am guessing this membrane is original to the motor, i.e. 23-24 years old. Repeat on-the-water test.
6) Keep my fingers crossed this engine doesn't have a Crankshaft Seal problem.

Thanks again All.

 

[racerone]

Once again I say that good trouble shooting needs to be done.----So which plug is fouling ?----A black plug indicates that conditions in that cylinder are colder than the other cylinder.----Colder conditions due to a number of reasons.-----Too much fuel , low crankcase compression, low cylinder compression , no thermostat.----Up to you to figure it out.

 

[flyingscott]

Does your motor have the manual Primer? If it does is it leaking by?

 

[cprodave]

Racer, thanks for clarifying that colder cylinder is what's going on...now I need to pinpoint the root cause.
Flyingscott, this engine does not have the manual primer . (I am familiar with that--i have an older "parts engine" with the manual primer.) But if this engine did have that manual primer what would you suggest I look at?

 

[racerone]

Parts book shows conventional choke flapper on this model.

 

[raczekp1]

if thermostat area is discoloured so its time to pull of the head, flatten the head surface and instal new gasket.
simple job

 

[tplo]

Don't overlook or forget to check the continuity of your spark plug wires, could be that simple.
Bend and move the wires while checking them

 

[cprodave]

I doubt if there is a problem with spark--per my original posting I tested with an adjustable gap spark tester and found a blue spark greater than 3/8 inch.

Meanwhile I found some better notes/photo from the November timeframe which clearly showed the Upper Spark Plug was fouling. So this is consistently an Upper Cylinder problem. Local weather is not conducive to doing a Compression Test--my Water Tank is outside, needs ice broken refill tank dragging garden house out of storage, etc. Also I hurt my arm (the one I use to pull start) and it is just now starting to heal. So today I removed the Cylinder Head and found a possible Root Cause for reduced compression in the Upper Cylinder. There is a very small dent in the metal part of the Head Gasket Upper Cylinder portion. So I will resurface the Cylinder Head (very slight grinding using fine grit Silicon Carbide paper on sheet of Glass) then install a new Head Gasket along with new Thermostat Cover Gasket.
Is there any value in using Permetex non-hardening Aviation Form-a-Gasket when I install the new Head Gasket?

 

[cprodave]

Forgot to mention I did inspect the Fuel Pump Diaphragm, no punctures and diaphragm seems flexible. Some photos attached, dental pick is pointing to dent in gasket in one photo.

 

[cprodave]

Update: my new Head Gasket, Thermostat Cover Seal and Fuel Pump Diaphragm arrived yesterday. A couple questions for proper reAssembly: 1) when I last replaced the Thermostat in Feb 2020 there was a problem whereby the #22 Thermostat Cover Seal 336947 popped out of the groove/channel where it belongs in the #14 Thermostat Cover 336181. As a result the Seal got pinched/deformed (photo to follow although I am unsure whether it leaked. The new Seal keeps popping out of the Groove and will likely pinch/deform unless I do something different to keep the Seal in a stretched position. Any tips/tricks to hold the Seal in place during Reassembly (perhaps Silicone lubricant, Silicone Sealant clamped and let it dry, a couple dabs of Crazy Glue clamped and let it dry)?
2) Vernatherm 434671 has a small brass pin/rod that slides in and out of the larger body. The pin/rod is flat on one end, slightly rounded on the other end. Does the rounded end face outward or inward?
Thanks for any input, I am looking forward to reassembling and testing compression in outdoors water tank (to not damage Impeller) next few days while we have a break in subfreezing weather.

 

[cprodave]

Photos added showing deformed/pinched old Thermostat Cover Deal, new Seal popping out of Cover and small Pin/Rod part of Vernatherm.