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

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
So.... Given a Craftsman 6.5 HP mower that was left sitting for at least a couple years. I don't know the model year, I'm guessing it's at least 10 years old. The gas had dried in the tank and carb leaving a varnished mess. Here's what I did:

1. Unpluggd Fuel hose and sprayed carb cleaner in the tank until is started draining, didn't see anything really nasty come out of the tank. Refilled with clean fuel, standard gas station 87 octane with Ethanol. Bad idea?
2. Did a carb rebuild with new float needle and seal, gaskets, and thorough cleaning, fresh gas, new air filter, new plug. Engine started second pull and ran great for about 1 hour, then wouldn't restart. Primer bulb doesn't work.
3. Looking into carb, I see primer isnt pumping gas up through the emulsion tube.
4. Tried replacing carb gasket to air cleaner housing, check primer bulb, still won't prime. Air cleaner housing looks a little warped due to overtightening bolts. Remove carb, clean again, repeat, NFG.
5. Tired of screwing around, I replace carb with Amazon special Chinesium carb, replace air cleaner housing with OEM B&S part with integral primer. Replaced cracked fuel hose. All new gaskets throughout. I used (2) carb/air cleaner gaskets thinking I might have an air leak.
6. Engine starts second pull, runs great for 5 mins, then starts surging, spitting, missing, then dies.
7. Let it cool off a while, same issue, starts, runs, then surges and eventually dies, like it's fuel starved.
8. Gas cap is missing the metal "cone" inside I see on B&S gas caps in videos, I can see the plastic pin that broke off at some point, rubber seal is still there, but no aluminum piece. NFG, engine starts right up, but starts surging after about 5 mins.

From everything I've seen online, this sounds like a fuel blockage or vapor lock, but since it's a brand new carb, brand new fuel line, etc, hard to believe its that. I did double check the bowl nut jet, some reports of metal debris on these carbs, none visible here, Confirmed that float is parallel to carb body, moves freely, gas flows when float drops.

The tank shows no sign of leakage, and I didnt see any debris in it via flashlight, but is there a filter in these plastic tanks that might have gotten clogged?
Advice appreciated, I am stumped!
 

Rivets

Lawn Royalty
Joined
Mar 11, 2012
Threads
55
Messages
14,681
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Try something simple the next time it starts surging. Loosen the gas cap, the vent may not be working. If surging stops replace the cap.
 

Scrubcadet10

Moderator
Staff member
Joined
Sep 24, 2017
Threads
248
Messages
6,431
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
2nd the gas cap.
Also, if you have the engine i think you have i would check the plastic intake pipe or manifold, for small cracks, surging means not enough fuel or too much air.
 

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
I did replace the gas cap, NFG. Also tried running it with the gas cap entirely off, it surges with or without the cap. I've read there is a filter inside the gas tank itself, any way to clean that? Is there a way to testy the tank for air tightness? My next idea was to remove the tank and try appying compressed air to the outlet with cap on an see if I have leaks anyplace?
 

Scrubcadet10

Moderator
Staff member
Joined
Sep 24, 2017
Threads
248
Messages
6,431
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Get some WD-40 in a trigger sprayer, no aresol can.
With the engine running, spray it around the carburetor area where it meets the intake pipe, if there is a change in RPM, or the mower blows white smoke, you have an air leak at the carb.
If you have good constant flow of fuel out of the tank the tank should be OK.
 

slomo

Lawn Addict
Joined
Jul 14, 2019
Threads
76
Messages
4,677
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Did you try loosening the gas cap? Sorry but I had to pile on LOL.

Get an inline spark tester. Run the engine on flat ground as long as you can. See if the spark dies on you.


slomo
 

Hammermechanicman

Lawn Addict
Joined
Jan 10, 2020
Threads
49
Messages
3,485
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Have you pulled the fuel line off the carb and checked the fuel flow. I have seen crapped up tanks have very small fuel flow and what happens is the unit sets for a few minutes and the carb fills up and engine starts and runs till float bowl runs out of gas then when it sets for a few mi s it will start again. You can't use air to clean the tank. If it sat and dried and varnished that crap will keep coming loose.
 

slomo

Lawn Addict
Joined
Jul 14, 2019
Threads
76
Messages
4,677
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Take an air compressor blow gun and blow the fuel line each way. Remove the fuel tank and fill with 8 ounces of ammonia. That should remove any old varnish slash residue in the tank. Wash the tank out with Dawn soap and water. If the tank is really bad add some BB's for agitation. Drain all the water out and spray down with WD-40. Reinstall the tank and test. Tank should be like brand new.

Get an inline spark tester.

Sounds like you got the carb issue resolved. Tried every carb trick there was including the new fuel cap trick. You need air, fuel, spark and compression. You should have air and fuel. How about the last 2?

slomo
 

Gilmourisgod

Member
Joined
Jun 27, 2020
Threads
1
Messages
10
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
I did take the bowl off the new carb with (new) fuel line connected, seemed to get good fuel flow when I lifted the float, so I think it's getting fuel. The tank is the one thing I haven't thoroughly cleaned or replaced, so that's worth doing anyway. I'll try the WD-40 air leak suggestion as well, since I see no obviuos fule issues, I figure it's air or spark, and since it seems to run great for the first 5 minutes after startup, the spark seems unlikely. I have read that one symptom of a bad coil is missing when it heats up.
 

slomo

Lawn Addict
Joined
Jul 14, 2019
Threads
76
Messages
4,677
  • / Craftsman 6.5 HP B&S Motor Surges, Have I Tried Everything?
Unlikely or not, your mower runs like crap. Fuel is covered and air. Get a cheap inline spark tester. Here you go a whopping 5 bucks.


slomo
 
Top