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

[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....

 

[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.

 

[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.

 

[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

 

[RescueMowerRepair]

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.

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.

 

[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.

 

[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.

 

[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.

 

[RescueMowerRepair]

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.

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

 

[RescueMowerRepair]

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

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.