20 HP Briggs V-Twin Intek Issues

[MurkyAsparagus]

Engine is a 20HP Briggs V-Twin Intek. Model #407677.

I brought my mower into service a few weeks ago. Changed the oil, oil filter, and air filters. Mowed my yard, ran a little rough. I checked the plugs, one looked perfect, the other one was black as can be. Swapped out the plugs, right cylinder fouled within 10 minutes, plug was not wet, just soot, running very rich. I expected the push rods on the right cylinder to be dropped based off the reputation of the engine. Took off the valve covers, both sides looked good. I then took off each head to check the head gaskets, also both good. Put it all back together, did a valve adjustment, ran well until this week. Got done mowing, looked over and saw the left cylinder had oil pouring out of the vacuum line for the fuel pump, still not having full power. Any ideas on what it can be?

 

[Elkins45]

Oil in the fuel pump line is something I haven't seen. Maybe try asking here: https://www.lawnmowerforum.com/forums/briggs-stratton/

 

[ripcord]

Most likely a blown head gasket. Verify that the oil isn't way overfull and loaded with gasoline, though.

Blown head gaskets are often due to overheating when critters build nests under the cooling tins which blocks the airflow.

 

[Lubener]

You put new head gaskets on hopefully. I would do a compression check of both cylinders. A leakdown check is better if you can. Possibilities include excessively high oil level, blowby (low compression) due to a ring issue or a problem with a damaged breather. I am currently working on a much older Briggs which had both breathers damaged. Oil was forced out with great pressure out the breather tubes. Compression was good.

 

[blkwtr]

First of all: How did the engine run before you serviced it?

 

[oldcodger]

My vote is a head gasket problem. I know you said they looked good but the oil getting in only one cylinder points to head gasket leaking. Check that the head gasket surface is flat. My mower developed the same problem and it was a head gasket leak. You really had to look close to see the small area that had failed.

 

[Fordiesel69]

Head gasket is blown in a way that compression is entering the push rod gallery area. If you take the valve covers off and start it up, you will no doubt have an oil bath but you may be able to visualize the breach and see the compression leakage.

The will cuase your exact issue. And it will push so much crankcase vacuum into the fuel pump that it will blow thru the brass vent hole of the pump.

 

[MurkyAsparagus]

Most likely a blown head gasket. Verify that the oil isn't way overfull and loaded with gasoline, though.

Blown head gaskets are often due to overheating when critters build nests under the cooling tins which blocks the airflow.

I’ve been thinking this. Motor was swapped on two summers ago, only 5 hours on motor, cooling good.

 

[MurkyAsparagus]

Looks like I will be replacing both head gaskets along with rebuilding the carb and replacing the fuel pump. Carb has one cylinder running very rich, an unfortunate result of a bad double barrel Nikki carb design.

 

[Lubener]

Looks like I will be replacing both head gaskets along with rebuilding the carb and replacing the fuel pump. Carb has one cylinder running very rich, an unfortunate result of a bad double barrel Nikki carb design.

You said you removed the heads and the gaskets looked good. Did you reuse the old gaskets when you put it all back together and mowed with it ???? I would hope not.

 

[The_Eric]

Looks like I will be replacing both head gaskets along with rebuilding the carb and replacing the fuel pump. Carb has one cylinder running very rich, an unfortunate result of a bad double barrel Nikki carb design.

I'd be surprised that the design has one running really rich. I have a similar engine and carb on one of my mowers and the plugs are showing pretty lean. You may benefit from a carb freshen, but sounds like you have some other factors at play here. Also if you didn't already know, many of those carbs are stagger jetted, so pay attention to which main jet came from where.

 

[MurkyAsparagus]

You said you removed the heads and the gaskets looked good. Did you reuse the old gaskets when you put it all back together and mowed with it ???? I would hope not.

Aslong as the head gaskets come off clean with no tearing or anything like that, they can be reused.

 

[MurkyAsparagus]

I'd be surprised that the design has one running really rich. I have a similar engine and carb on one of my mowers and the plugs are showing pretty lean. You may benefit from a carb freshen, but sounds like you have some other factors at play here. Also if you didn't already know, many of those carbs are stagger jetted, so pay attention to which main jet came from where.

From what I’ve read and seen, there’s a small gasket that allows the gas to split off into each cylinder. Over time, it swells or becomes clogs and then the flow gets diverted to mainly one cylinder.

 

[Lockasiam]

those carbs are pretty junk, while you have it apart next time pull the piston and check the ring gap, if good hose them off with some brake/carb cleaner incase there's junk in the oil ring

 

[MurkyAsparagus]

those carbs are pretty junk, while you have it apart next time pull the piston and check the ring gap, if good hose them off with some brake/carb cleaner incase there's junk in the oil ring

That's about what I've read about these Nikki carbs. I thought about replacing w/ aftermarket chinesium, but I would rather just rebuild with a decent quality kit. I hopefully won't have it that far apart, but will run some Valvoline R&P if I notice any oil burning after its all said.

 

[Lockasiam]

the only good thing tecumseh did in regards to carburetors was have a seperate carb per cylinder on some of their vtwins. B&S should've just done that since these stupid 1 Nikki 2 Cylinder setups ruin the vtwin briggs reputation and cause way more problems than it's even worth. i hate them so much

 

[MurkyAsparagus]

the only good thing tecumseh did in regards to carburetors was have a seperate carb per cylinder on some of their vtwins. B&S should've just done that since these stupid 1 Nikki 2 Cylinder setups ruin the vtwin briggs reputation and cause way more problems than it's even worth. i hate them so much

I'd agree with that sentiment. I need to go back to just running every machine I have dry at the end of the season rather than using fuel stabilizer, it never works in carbed engines IMO, only EFI. This engine gets treated like a queen with a really early maintenance schedule in a mild climate, so I hope to not have the bent push rods caused by overheating or worn cam lobes.

 

[Lockasiam]

I'd agree with that sentiment. I need to go back to just running every machine I have dry at the end of the season rather than using fuel stabilizer, it never works in carbed engines IMO, only EFI. This engine gets treated like a queen with a really early maintenance schedule in a mild climate, so I hope to not have the bent push rods caused by overheating or worn cam lobes.

if your'e dedicated and want an experiment, try this out https://ecotrons.com/small_engine_fuel_injection_kit/400cc_to_800cc_engine_fuel_injection_kit/
robot cantina did this on a predator engine (single) and had success running it. not sure how your finances and dedication would work out but it would be an interesting youtube video series

 

[The_Eric]

From what I’ve read and seen, there’s a small gasket that allows the gas to split off into each cylinder. Over time, it swells or becomes clogs and then the flow gets diverted to mainly one cylinder.

I see what you're saying now - I misunderstood. I think you're referring to the jet tube (or whatever it's name is) and the o-ring that seals it up. It's a really easy fix at least.

 

[MurkyAsparagus]

I see what you're saying now - I misunderstood. I think you're referring to the jet tube (or whatever it's name is) and the o-ring that seals it up. It's a really easy fix at least.

Yeah, it's kind of a crappy design, but o well, rebuild time.