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Hot!Briggs flathead 8hp horiz - instant start at first then dies, backfires

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Iseefromhere New Member Total Posts : 1 Scores: 0 Reward points: 0 Joined: 2024/04/22 17:58:15 Status: offline 2024/04/22 18:12:46 (permalink) 0 Briggs flathead 8hp horiz - instant start at first then dies, backfires Briggs 8hp flathead horizontal shaft. New carb, New plug, good spark visible, flywheel key good & properly positioned. Gas in float bowl. No change in symptoms: - "starts" instantly from cold with recoil starter on choke & runs for 3-5sec then dies. - Subsequent starting attempts ineffective; backfiring through muffler - motor ran for several hours of use in the fall and then began exhibiting these symptoms. I've changed the carb since then with no different result. Is my exhaust valve sticking open? Haven’t pulled the head yet; prefer not to if avoidable... Other possibilities? If it is stuck/not sealing valve: next steps? Incidentally the new carb has a brass nipple under the choke - nothing to attach to it. Is this where a primer bulb would go? Should I seal it or? Doesn't need bulb as tank is above the carb. Quote #1 1 Reply Related Threads
SRTsFZ6 Super Member Total Posts : 2063 Scores: 74 Reward points: 0 Joined: 2018/11/18 07:20:58 Status: offline Re: Briggs flathead 8hp horiz - instant start at first then dies, backfires 2024/04/23 08:22:13 (permalink) 0 Sounds like your exhaust valve is staying slightly open. If you don't want to pull the head, do a "Leak Down" test. That will / can confirm any and all cylinder leakage (including open valves). **You can also check valve clearance after removing the intake manifold. There's a rectangular breather (about 1" x 3") under there which needs removal. Once off you can measure valve clearance between the bottom of the valve stem and the lifter. . Scott Quote #2

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Iseefromhere

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Total Posts : 1
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Joined: 2024/04/22 17:58:15
Status: offline

2024/04/22 18:12:46 (permalink)

Briggs flathead 8hp horiz - instant start at first then dies, backfires

Briggs 8hp flathead horizontal shaft. New carb, New plug, good spark visible, flywheel key good & properly positioned. Gas in float bowl. No change in symptoms:

- "starts" instantly from cold with recoil starter on choke & runs for 3-5sec then dies.

- Subsequent starting attempts ineffective; backfiring through muffler

- motor ran for several hours of use in the fall and then began exhibiting these symptoms. I've changed the carb since then with no different result.

Is my exhaust valve sticking open? Haven’t pulled the head yet; prefer not to if avoidable... Other possibilities?

If it is stuck/not sealing valve: next steps?

Incidentally the new carb has a brass nipple under the choke - nothing to attach to it. Is this where a primer bulb would go? Should I seal it or? Doesn't need bulb as tank is above the carb.

Quote #1

1 Reply Related Threads

SRTsFZ6

Super Member

Total Posts : 2063
Scores: 74
Reward points: 0
Joined: 2018/11/18 07:20:58
Status: offline

Re: Briggs flathead 8hp horiz - instant start at first then dies, backfires 2024/04/23 08:22:13 (permalink)

Sounds like your exhaust valve is staying slightly open.

If you don't want to pull the head, do a "Leak Down" test. That will / can confirm any and all
cylinder leakage (including open valves).

**You can also check valve clearance after removing the intake manifold.
There's a rectangular breather (about 1" x 3") under there which needs removal.
Once off you can measure valve clearance between the bottom of the valve stem and the lifter.

.

Scott

Quote #2

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