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Briggs L head runs rich no matter what I throw at it.

#1

R

RescueMowerRepair

Working on a 6hp 128h02 0515 E1. mounted to a DR style trimmer. came in not running and had a trashed carburetor. I replaced the carb, and did a filter oil and plug and new primer bulb at the same time. It fired on the first pull but ran just rich enough to bog but not blow black smoke, and is spitting fuel out of the carb throat.
The following is everything I've checked and thrown at it so far with zero improvement (in no particular order):
-installed 2 other new carburetors
-checked for vacuum leaks (even though it's not a lean condition)
-pulled the plug to read it and it was black, but not terrible.
-checked compression
-over gapped the plug hoping for some more heat
-changed plug again
-adjusted the coil gap
-pulled the muffler to verify not clogged also ran it with no muffler
-checked flywheel key
-verified proper oil level
-checked for spark strength visually

What did I miss? I can't think of anything....


#2

StarTech

StarTech

Definitely need to verify engine model and type number as the one posted is coming back as a 13hp and not 6 hp one.


#3

R

Rivets

More questions than answers. As Star said, double check the model numbers. 6hp engine will normally not have an oil filter? 13hp engine will normally not have a carb with a primer bulb? What was the part number for the new carbs and were they OEM? You say it is running rich, but not blowing black smoke? What tells you it’s running rich, plug color? Could you have 2-cycle mix instead of raw fuel? Have you blocked off the fuel supply to see if it runs better when the level of fuel drops in the float bowl? Gravity feed or fuel pump? Some where we are not getting the full story on this one, too many questions.


#4

R

RescueMowerRepair

Sorry guys. I was looking at the wrong work order on the model and wasn't paying attention good enough to recognize. I updated the original post. 128H02 0515 E1


#5

R

RescueMowerRepair

Rivets said:
More questions than answers. As Star said, double check the model numbers. 6hp engine will normally not have an oil filter? 13hp engine will normally not have a carb with a primer bulb? What was the part number for the new carbs and were they OEM? You say it is running rich, but not blowing black smoke? What tells you it’s running rich, plug color? Could you have 2-cycle mix instead of raw fuel? Have you blocked off the fuel supply to see if it runs better when the level of fuel drops in the float bowl? Gravity feed or fuel pump? Some where we are not getting the full story on this one, too many questions.
Click to expand...
You got the full story aside from the typo on the model number. The carburetors are aftermarket units that I've never had any issues with. Plus the fact that I tried 3 different ones...

I have run it with just the fuel in the bowl and when I say its running rich, it acts like it has the choke closed, though this one has no choke plate. Plus its spitting fuel out of the carb, and dribbling carb cleaner in it while running chokes it out even more than it already is.


#6

R

RescueMowerRepair

Just made another verification on the rich condition. It runs tad better with no air filter at all. And even better when you force feed it some additional air.


#7

StarTech

StarTech

This engine runs with the main jet from the 5hp version. PN 498978 which is a 71 C marked Briggs jet. I didn't have my micro bits so I didn't gage actually jet opening. BTW not all 71 marked jet are the same either as I had one marked 71 M which was for a 3.5 hp engine.

Also just because you have never problems in the past with AM carburetors doesn't mean you continue to not have problems. Find the old carburetor and try its jet

IF spitting fuel out of he carburetor you might have valves that are out of adjustment. IE intake with nearly zero clearance.


#8

R

Rivets

Have you checked to see if the float level is correct? High float level may be your problem, especially on a non OEM carb.


#9

R

RescueMowerRepair

StarTech said:
This engine runs with the main jet from the 5hp version. PN 498978 which is a 71 C marked Briggs jet. I didn't have my micro bits so I didn't gage actually jet opening. BTW not all 71 marked jet are the same either as I had one marked 71 M which was for a 3.5 hp engine.

Also just because you have never problems in the past with AM carburetors doesn't mean you continue to not have problems. Find the old carburetor and try its jet

IF spitting fuel out of he carburetor you might have valves that are out of adjustment. IE intake with nearly zero clearance.
Click to expand...
Good idea on the main jet swap. I tried that first thing but unfortunately, no change. Then I checked the valve clearance. Zero lash on both valves. Good call again. I've been doing this for 12 years and have never seen an L-head that bad. I'm really surprised it doesn't backfire as well. I'm also surprised the customer gave me the go ahead to fix it.

Thanks again
Chad


#10

R

RescueMowerRepair

Rivets said:
Have you checked to see if the float level is correct? High float level may be your problem, especially on a non OEM carb.
Click to expand...
I did not check the float level persey, but I did check it in a way I have done in the past by cutting fuel supply to see if it improves as it uses the fuel in the bowl.


#11

S

slomo

RescueMowerRepair said:
Good idea on the main jet swap. I tried that first thing but unfortunately, no change. Then I checked the valve clearance. Zero lash on both valves. Good call again. I've been doing this for 12 years and have never seen an L-head that bad. I'm really surprised it doesn't backfire as well. I'm also surprised the customer gave me the go ahead to fix it.

Thanks again
Chad
Click to expand...
All non hydraulic valve engines require valve clearance adjustments. L head, scratch your head, OHV or OHC love it. And being an L-head Briggs, most people NEVER think of this for some reason. I just did one of mine, 1989 era Briggs with 0 lash.

slomo


#12

S

slomo

New doesn't mean new at times. Chinese carbs are a gamble. Some are okay and some are like yours. Get the OEM carb for it.

If I were a mower repair shop guy, I wouldn't even entertain getting Ebay or Amazon "Gambler Series" mower parts. Wouldn't be worth it to me at all.

Back to your issue. Over rich is carb needle hanging open, dirty air filter or overly large main jet in that order.

Back off topic, clean the combustion chamber free of carbon, set valves to proper specs and clean cylinder cooling fins all the way around the bore. Then fire is up and check for rich burn.

slomo


#13

S

slomo

Spitting fuel out of the carb is carb needle sticking open. Pull the dipstick and smell for fuel in the oil.

Like Rivets said, look at the float level. Carb upside down should hold 7PSI of air pressure. Test yours with a hand pump and gauge. Make sure the float is LEVEL to the carb bowl flange. Several youtube videos about it.


slomo


#14

S

slomo


slomo


#15

Richie F

Richie F

If it spits out the intake the exhaust valve is not opening enough.
Being that the exhaust is not set correctly the engine is getting choked do to lack of air flow.
You have tried more than one carb with the same results so the carb/float level doesn't come into play.


#16

M

mwshaw

I don't know the model but if it's a model with the carb mounted to the gas tank, they will suck gas through the missing air cleaner screw hole. Must replace screw to even begin to adjust the carb. Looks like you have tried everything but that. So I though I would throw that in.


#17

S

slomo

Richie F said:
If it spits out the intake the exhaust valve is not opening enough.
Being that the exhaust is not set correctly the engine is getting choked do to lack of air flow.
You have tried more than one carb with the same results so the carb/float level doesn't come into play.
Click to expand...
Yup, I mentioned to set the valves a few posts ago. Give the ol' girl a fighting chance.

slomo


#18

S

slomo

mwshaw said:
I don't know the model but if it's a model with the carb mounted to the gas tank, they will suck gas through the missing air cleaner screw hole. Must replace screw to even begin to adjust the carb. Looks like you have tried everything but that. So I though I would throw that in.
Click to expand...
Different carb you are talking about. Good to know, just doesn't apply here. Thanks for sharing anyway. Might help someone else.

slomo


#19

T

Tommy Mckeown

RescueMowerRepair said:
Working on a 6hp 128h02 0515 E1. mounted to a DR style trimmer. came in not running and had a trashed carburetor. I replaced the carb, and did a filter oil and plug and new primer bulb at the same time. It fired on the first pull but ran just rich enough to bog but not blow black smoke, and is spitting fuel out of the carb throat.
The following is everything I've checked and thrown at it so far with zero improvement (in no particular order):
-installed 2 other new carburetors
-checked for vacuum leaks (even though it's not a lean condition)
-pulled the plug to read it and it was black, but not terrible.
-checked compression
-over gapped the plug hoping for some more heat
-changed plug again
-adjusted the coil gap
-pulled the muffler to verify not clogged also ran it with no muffler
-checked flywheel key
-verified proper oil level
-checked for spark strength visually

What did I miss? I can't think of anything....
Click to expand...
The only way fuel is coming out of the throat is if the float is bad or the needle and seat is not sealing. Before putting the bowl back on verify that it is in fact sealing when you lift the float.


#20

S

slomo

Tommy Mckeown said:
The only way fuel is coming out of the throat is if the float is bad or the needle and seat is not sealing. Before putting the bowl back on verify that it is in fact sealing when you lift the float.
Click to expand...
Which takes us to the videos I put up on post 13 and 14. Great tip, check the needle and seat prior to starting the engine. But the carb was new???? LOL :) (y)

slomo


#21

B

bertsmobile1

IF the fuel is dripping back out of the carb then it would normally be a float problem but as this is a tank mounted carb with an overflow bowl that can't happen.
So something is causing blow back through the carb
Two sources of blow back at cranking speeds
1) breather
2) valves out of adjustment / time

On side valves it would normally be something preventing the inlet closing or the exhaust opening
Exhaust opening includes furry things dead in the muffler blocking it off .

On OHV engines it is generally excessive exhaust valve lash causing excessive valve overlap .


#22

K

ken2

Seems to me dad had a similar problem with two brand new Briggs 12.5hp when he was a Snapper dealer. He ordered high altitude jets and that solved the problem.


#23

F

fixit1ddh

Probably has plastic cam in it that has slipped a few degrees. Reason why You are getting the spitting fuel from carb. And sounds like its running rich.


#24

Fish

Fish

Drain the fuel out except for what is in the carb, then run the engine until the system is dry, and note the engine performance as the last of the fuel is burned up.


#25

R

RescueMowerRepair

Thanks for all the replies. I've been out of town a few days so that's why the delay on my response. Sorry I'm not quoting everyone who's posted here.
As far as the float level-
This is not a tank mounted carb.
I already verified the needle being stuck open is not the issue. it holds pressure, and cutting off the fuel inlet and letting it burn the fuel in the bowl does not improve the rich condition of the spitting fuel.
I also-
checked the valves and found zero lash. Which tells me the valves have worn deep into their seats, or ?? But this would be possibly causing both valves to be hung slightly open no? Would that cause a rich condition?
I also verified that if you pull the (new) air filter it ever so slightly improves, and furthermore, I can lean it out if I force feed it a dribble of air, improving it even more.

It's back on the bench to get the valves done tomorrow. I'll report back my findings.


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