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B&S twin 20hp, one cylinder runs hotter

#1

S

slow030

Trying to help my neighbor. John Deere L120A B&S 20hp twin,406777 0139 E1. Has some popping and loss of power. Checked with infra red thermometer and the right side exhaust is about 100 degrees cooler than the left. 1. swapped plugs, no change. 2. checked compression, both around 140. 3. Checked valve lash on both, all set correctly. 4. Checked valve travel, both exhausts were same and both intakes were the same. 5. Will run on each cylinder by itself. 6. Checked diodes in coil ground, both good. 7. Checked flywheel key, good. 8. Checked for intake leak by spraying carb cleaner around all mating surfaces, with no change in running. Not sure what to do next, any help appreciated.


#2

S

slomo

slow030 said:
Has some popping and loss of power.
Click to expand...
Cam timing comes to mind. Maybe a bad camshaft? If the carb and all is 100%, only thing left is opening her up for a CSI investigation.

Possibly set valves on wrong stroke?


#3

S

slomo

Honestly I wouldn't lose sleep over it. On a typical v-8 for example, every cylinder will not have the same air fuel ratio and temp as well. Many a factor causing this. Cylinder head torque and sealing condition. Valves and so on. Could be down to one coil firing hotter or a weak coil for example.


#4

S

slow030

I checked the valves at TDC on compression stroke.


#5

S

slow030

Guess I could swap coils.


#6

S

slomo

slow030 said:
I checked the valves at TDC on compression stroke.
Click to expand...
I hear ya' but just stating the obvious, there are 2 TDC strokes on a 4 smoke engine. Many a folk try it on the wrong stroke and we go to about 15 pages on here LOL.


#7

S

slow030

Swapped coils, seems to run worse, still have temp difference.


#8

B

bertsmobile1

Depending upon which carb is fitted, some have jets of different sizes in the 2 barrel nikki carb
Easy to swap them over which causes one side to run properly & the other to run lean
Another EPA solution to a problem that does not exist
I usually toss the small one and go back to the original large jets


#9

S

slow030

Forgot to mention guy said it was running fine til he ran out of gas. When it started to run bad he replaced fuel filter and fuel pump. Maybe dirty carb?


#10

StarTech

StarTech

Left jet is 1.13mm
Right jet is 1.16mm

O-rings on the jets are bad to shrink allowing the jets to float around causing over rich fuel mixtures.

And yes trash from changing the fuel filter can cause problems too.


#11

S

slow030

Took the carb bowl off and cleaned, sprayed the jets. Still pops. Should I take carb completely apart and clean, replace jets?


#12

B

bertsmobile1

Yes
Gt the rebuild rubber kit and replace both of the O rings around the main jets
Do main jets 1 at a time to avoid mixing them up .
They do have their sizes marked on the sides but you will need a maroscope to read them
I regularly come across them that are reversed .
Outdoorpowerinfo.com will have a detailed photo description of how to do it properly .


#13

D

daman

Take the engine shroud covers off is there clippings and debris plugging the cooling fins on the cylinders?


#14

S

slow030

Just ordered o ring kit. Thanks


#15

S

slow030

Installed the O-ring kit and it runs great. No more popping or sputtering. Thanks for the help.


#16

B

bertsmobile1

Excellent result.
Thanks for coming back
Happy mowing


#17

S

slomo

daman said:
Take the engine shroud covers off is there clippings and debris plugging the cooling fins on the cylinders?
Click to expand...
Of course. But that isn't talked about much. I get oh yes my fins are clean. 8 pages later the OP puts a picture up of the block. Sure enough, fins are slimed over. OP, carb was cleaned too. Picture picture, carb was heavily loaded down with oil and grit on the outside.


#18

flyhalhl@gmail.co.

flyhalhl@gmail.co.

slow030 said:
Trying to help my neighbor. John Deere L120A B&S 20hp twin,406777 0139 E1. Has some popping and loss of power. Checked with infra red thermometer and the right side exhaust is about 100 degrees cooler than the left. 1. swapped plugs, no change. 2. checked compression, both around 140. 3. Checked valve lash on both, all set correctly. 4. Checked valve travel, both exhausts were same and both intakes were the same. 5. Will run on each cylinder by itself. 6. Checked diodes in coil ground, both good. 7. Checked flywheel key, good. 8. Checked for intake leak by spraying carb cleaner around all mating surfaces, with no change in running. Not sure what to do next, any help appreciated.
Click to expand...
Any dirt buildup around cylinder?


#19

flyhalhl@gmail.co.

flyhalhl@gmail.co.

slow030 said:
Took the carb bowl off and cleaned, sprayed the jets. Still pops. Should I take carb completely apart and clean, replace jets?
Click to expand...


#20

flyhalhl@gmail.co.

flyhalhl@gmail.co.

Most if these carbs have single throat carbs, thus common jet for both cylinders. May be intake leak on gaskets causing that cyl to run lean.


#21

StarTech

StarTech

flyhalhl@gmail.co. said:
Most if these carbs have single throat carbs, thus common jet for both cylinders. May be intake leak on gaskets causing that cyl to run lean.
Click to expand...
You should take the time to look up the engine's IPL before posting. A post like yours is unrelated to the OP problem.
1684771537793.png


#22

flyhalhl@gmail.co.

flyhalhl@gmail.co.

slow030 said:
Trying to help my neighbor. John Deere L120A B&S 20hp twin,406777 0139 E1. Has some popping and loss of power. Checked with infra red thermometer and the right side exhaust is about 100 degrees cooler than the left. 1. swapped plugs, no change. 2. checked compression, both around 140. 3. Checked valve lash on both, all set correctly. 4. Checked valve travel, both exhausts were same and both intakes were the same. 5. Will run on each cylinder by itself. 6. Checked diodes in coil ground, both good. 7. Checked flywheel key, good. 8. Checked for intake leak by spraying carb cleaner around all mating surfaces, with no change in running. Not sure what to do next, any help appreciated.
Click to expand...
Cracked/broken cylinder ring. But need good check on intake to that cylinder.
slomo said:
Honestly I wouldn't lose sleep over it. On a typical v-8 for example, every cylinder will not have the same air fuel ratio and temp as well. Many a factor causing this. Cylinder head torque and sealing condition. Valves and so on. Could be down to one coil firing hotter or a weak coil for example.
Click to expand...
Backfire and popping sounds like lean running. You might run engine with some choke and see what happens. Bad cyl temp increase while good cyl decreases?
Also check head temps both cylinders after warmed up.
Checked spark plug color when first removing spark plugs. Lean plug would be white. Normal is slightly tan? This is your first indicator on engine problem.
.......Have you replaced carburator base gasket?
What is exhaust temp? Should be like 1200°F measured 3" from cylinder but normally with thermocouple in small hole in tubing. So tube on outside just slightly lower. Cylinder head under 400° F.
Does your carb have mixture jets as well as idle mixture? Parts diagram shows 2 ports - each for cylinder


#23

flyhalhl@gmail.co.

flyhalhl@gmail.co.

slow030 said:
Trying to help my neighbor. John Deere L120A B&S 20hp twin,406777 0139 E1. Has some popping and loss of power. Checked with infra red thermometer and the right side exhaust is about 100 degrees cooler than the left. 1. swapped plugs, no change. 2. checked compression, both around 140. 3. Checked valve lash on both, all set correctly. 4. Checked valve travel, both exhausts were same and both intakes were the same. 5. Will run on each cylinder by itself. 6. Checked diodes in coil ground, both good. 7. Checked flywheel key, good. 8. Checked for intake leak by spraying carb cleaner around all mating surfaces, with no change in running. Not sure what to do next, any help appreciated.
Click to expand...
Where are you measuring exhaust temp? Normally measured near cylinder. Normal would be small hole about 3" from cylinder with thermalcouple probe about near 1200°F. But if on outside tubing little less. Heads less than 400° F (200 maybe idle). What adjustments on carburetor, maybe only 1 idle mixture and fixed high speed jets? Carb dies have a port for each cylinder. Replace carb base gasket?
We are assuming hot engine running lean. Does popping only occur at high rpm? If so, may be lack if fuel. I have seen plastic gas tank with output nipple whole shrunk causing problems at high rpm, but OK on morning startup but then problems after 5 minutes mowing. Last 3 Cub Cadets; one 5yrs old with 24hp, I fixed had this problem. Easy check by removing hose at fuel pump and a hose below tank level should run small stream, gravity flow - as long as gas in tank, or a few minutes; not slow to dribble. Should easily insert 1/8" drill bit in tank. I fixed by cutting off nipple, enlarge hole and threading with 1/8" pipe tap. Then get 1/8" pipe to hose adapter fitting. Do not overtighten fitting in plastic tank.
(Also, hose can develop low flow.)

Lot of weird issues. Internal engine problems are tough.


#24

B

bertsmobile1

And to add to Stars comment back in post # 16 Slow030 replied that he fitted the rebuild kit and his mower is running like new
It is good that you took the time to respond but please read the entire thread.
I will guess that you are using a phone not a computer so it is hard to go back to the start .


#25

flyhalhl@gmail.co.

flyhalhl@gmail.co.

slow030 said:
Forgot to mention guy said it was running fine til he ran out of gas. When it started to run bad he replaced fuel filter and fuel pump. Maybe dirty carb?
Click to expand...


#26

flyhalhl@gmail.co.

flyhalhl@gmail.co.

Check gas flow.from tank


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