Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?

Rivets

Lawn Royalty
Joined
Mar 11, 2012
Threads
45
Messages
10,600
The OEM carb number Is 799868, same as what you ordered, but it should use a solid float needle with a replaceable viton seat. If yours has a solid seat you have a chinese knockoff.
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
Needle and seat test

Take the "car-bu-trator" off. Remove the fuel bowl. Turn carb upside down. Blow into the main fuel inlet hose barb. Needle and seat should hold back your lung power. Then raise and lower the plastic float. Should hear your air go in and out of the "carb-bu-trator". This is a must if you are cleaning a dirty carb. Verify the needle and seat is working proper. Sucks to reinstall a cleaned carb and find fuel on your mower deck.

Confirm that the carb float is LEVEL with the carb body, where the carb bowl seal is. And that the needle and seat stops the fuel flow when the float is parallel to the carb body.

Make sure you put that thin paper carb gasket on the correct way. Those are easy to install upside down or back'ards.

How was the 15 minute spark test?

If you buy an OEM Briggs carb, buy DIRECTLY from Briggs. Don't get it off Ebay or Amazon. Go directly to the manufacturer. That way you KNOW that carb is proper and will run another 30 years. I say this as there are a ton of Briggs parts being copied from China and other countries.

Running like crap and popping after 5 minutes, that tells me you are pretty lean while running on the main jet. Something in the MJ is starving the engine for fuel. Or like others said, you have a vacuum leak some place. Vacuum leaks allow more air into the cylinder causing a lean running condition.

Page 1 says you ran/run E10 fuel. Get real 100% gasonline if you can. These engines "tolerate" E10 but are really made for 100% unleaded. Run fuel stabilizer year round. E10 is a bad idea.

slomo
 
Last edited:

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
It's definitely a Chinese Knocoff, can't imagine it's anything else for $10.99. The 13mm bolt nut/jet indicates its not OEM. Is that the likely source of my surging problem, just a crappy Chinese carb? If so, I'll return the damn thing and cough up the extra cash for an OEM B&S carb. I know they have theirs made in China too, but maybe the QC is better?
 

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
The latest update in this little fiasco:
Tried the carb needle test, its definitely working to seal fuel in or out. If its the Chinese carb, its something more hidden, like an improperly drilled air passage. I've cleaned it, wheedled all the passages with a twist tie wire, float nice and level with the carb body, damned if I can see anything wrong with it. To recap, this is what I've done so far:

1. Cleaned gas Tank with Ammonia, let sit overnight. This did liberate a small amount of varnish like gunk, but nothing chunky. Let it dry for 48 hours and then hosed it out with WD-40, which seems to have pushed out the last bit of water that didn't evaporate. If it's an internal filter clog, I can't get to it. I tried blowing through the gas fill opening and didn't get air out of it anywhere but the outlet tube.
2. Aftemarket Carb Replacement
3. New gas cap
4. New Air cleraner housing with new primer
5. All new gaskets, carb to air cleaner, carb to intake manifold.
6. New fuel hose
7. Resistance test (apparently a wast of time) and cleaning of the coil, tested within spec, set magneto gap to .010". Kill switch wire looks good, obviously working.
8. Inspected and removed intake manifold, no cracks or obvious problems with the manifold gasket to cylinder head, looks likes it's never been removed. Having removed the intake manifold (gasket stayed on the head like it's glued on), I should probably replace it.
9. New Spark plug
10. WD-40 test for air leaks around carb while running negative, but I did NOT try spraying around the cylinder head to intake manifold gasket, which requires removing engine shroud while running. I think I'd rather just replace the gasket.

I have a useable mower here, I can get through the whole lawn without it stalling, but it usually requires 2-3 pulls to start, and begins surging after 5 mins. +/-.

From the suggestions posted, all I have left to try is a spark test (which I'll do as soon as I can get over to Harbor Freight to pick one up) and replacing the carb with OEM. I'm returning the Chinese Cheapo.

One question on the gas cap: Neither the OEM B&S cap or the aftermarket replacement has any kind of hole in it anyplace I can see. How does air get sucked into the tank through the cap if it has no openings?

BTW, does anybody know if the E-Replacement part carb is OEM, its around $38 vs. $50+ on the Briggs website. I realize thats the safest bet, but hate paying $20 more for literally the same carb just becuase B+S is cranking up the price.
 
Last edited:

Rivets

Lawn Royalty
Joined
Mar 11, 2012
Threads
45
Messages
10,600
Briggs caps are now vented through the threads, no more holes, so I doubt that is the problem.
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
I trust you on pricing but Briggs normally has competitive parts pricing? Shouldn't be too far off other reputable places.

slomo
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
I'd bet that Chrinese carb is not a 1:1 parts wise carb to a real Briggs. It might work just fine. Is there a pilot screw to adjust on the Chrinese carb?

slomo
 

Scrubcadet10

Lawn Addict
Joined
Sep 24, 2017
Threads
141
Messages
3,512
$49
 

slomo

Well-Known Member
Joined
Jul 14, 2019
Threads
25
Messages
914
This ebay page has a couple cheaper OEM Briggs carbs. Are these labeled OEM Briggs Ebay carbs legit or what? Those Sten carbs should be okay, I've never used one myself. The other real experts here might have.


slomo
 

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
It Runs!
I replaced the intake manifold gasket and put in an OEM B&S carb ($38) and it ran for a full hour without any real surging. I did notice a tiny bit of surge when I tilt the front wheels off the ground to turn it, but otherwise runs smoothly. The existing intake manifold gasket seemed pretty tight and fully intact, but it came off in bits, so maybe it had hardened or shrunk. Since I replaced both carb and gasket simultaneously, I can't say for sure which solved it, but I'm guessing it was the carb. Lesson learned, don't bother with the cheap aftermarket carbs, a real crapshoot quality-wise.

Thanks for advice, All.
 
Top