Exhausted?!

ricebridge · May 18, 2017

Hi all! How sensitive is a Briggs 12.5 hp engine to having the right exhaust system? I, er, tried replacing it with, er, one of my own design, with less resistance but a longer throw, and suddenly the garden tractor won't start.
Could be a myriad of other problems of course, but I'd like to rule this one out.
Thanks!

cpurvis · May 18, 2017

It should still start. I've never seen a gas engine that wouldn't start with no exhaust system at all. Diesels will run with no intake system or exhaust.

ricebridge · May 19, 2017

cpurvis said:
It should still start. I've never seen a gas engine that wouldn't start with no exhaust system at all. Diesels will run with no intake system or exhaust.

Thanks, that's what I thought. The only thing that bothers me, however, is whether such small engines are sensitive to changes in counter pressure from the exhaust system.

reynoldston · May 19, 2017

ricebridge said:
Thanks, that's what I thought. The only thing that bothers me, however, is whether such small engines are sensitive to changes in counter pressure from the exhaust system.

They will still run but not as efficient. Two Cycle engines more so then 4 cycle.

Pumper54 · May 19, 2017

Unless you went with something totally whacked out the engine should run. Go to youtube and look at the exhaust systems people have put on mowers, everything from vertical stacks with flappers to zoomies to straight pipes and they all run, some better then others.

Tom

bertsmobile1 · May 21, 2017

ricebridge said:
Hi all! How sensitive is a Briggs 12.5 hp engine to having the right exhaust system? I, er, tried replacing it with, er, one of my own design, with less resistance but a longer throw, and suddenly the garden tractor won't start.
Could be a myriad of other problems of course, but I'd like to rule this one out.
Thanks!

Wont start covers a myriad of sins.
Won't crank
Cranks but wont fire
Fires but won't stay running ?
As others have told you, no muffler is no problems over a long time it will burn exhaust valves and that is it.

ricebridge · May 22, 2017

Thanks all! Turns out the fault was – of course –*in a completely different place (faulty safety switch under the seat), so now it runs. But I'm still a little intrigued by just how much changed counter pressure affects the engine. "Burnt exhaust valves", could you pls elaborate? How could I optimise it for best performance? etc.

reynoldston · May 22, 2017

OEM will give you the best performance

bertsmobile1 · May 22, 2017

With no header pipe you get air around the exhaust valve which runs red hot so it oxidizes ( burns ) then that gets knocked off and it does it again and again eventually leaving a V in it's head.
These are very low tech engines so tuning an exhaust on a standard engine is something of a joke.
Exhaust systems are optimised for a specific volume of gas moving at a specific speed.
Changing the exhaust usually requires changing the carb as well or you will get little to no benefit unless the system was choked in the first place to make it quieter

ricebridge · May 23, 2017

Exhausted?!

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