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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!

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.

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.

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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.

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.

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

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

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!

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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.

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.

OEM will give you the best performance

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

I guess it all depends on what you want this tractor for? We have tractor pulls around where I live and can get around 50 HP out of some of these small engines. Its all about on how much money you want to spend? The Kohler K model is a very popular engine to modify for this.

reynoldston said:

I guess it all depends on what you want this tractor for? We have tractor pulls around where I live and can get around 50 HP out of some of these small engines. Its all about on how much money you want to spend? The Kohler K model is a very popular engine to modify for this.

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Well, I wouldn't mind being able to use it for as much as possible! Of course, making it as quiet as possible is one goal, but more important than that is making it as strong as possible. Even with its 12.5hp it seems a little weak from time to time, and if I could pump its muscles up enough to have it double as a snowplough during the winters, that would be an extra plus (albeit not necessary).

Indeed, silence and power are generally contradictory goals, I do realise that.

ricebridge said:

Well, I wouldn't mind being able to use it for as much as possible! Of course, making it as quiet as possible is one goal, but more important than that is making it as strong as possible. Even with its 12.5hp it seems a little weak from time to time, and if I could pump its muscles up enough to have it double as a snowplough during the winters, that would be an extra plus (albeit not necessary).

Indeed, silence and power are generally contradictory goals, I do realise that.

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Living in upper NY state I know all about snow removal. I am using a 12 HP Wheelhorse garden tractor with a snowblower and find other then wet heavy snow it has all the power it needs. You will find that using a snowplow it traction that is lacking other then power.

reynoldston said:

Living in upper NY state I know all about snow removal. I am using a 12 HP Wheelhorse garden tractor with a snowblower and find other then wet heavy snow it has all the power it needs. You will find that using a snowplow it traction that is lacking other then power.

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Yes, it's snow chains that you need, right?

ricebridge said:

Yes, it's snow chains that you need, right?

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Yes chains and weight. I don't know your snow conditions in Sweden but don't expect to move large amounts of heavy snow in one bite. It sure will be a lot better then a shovel. If you do have a lot of snow to move you will like a snowblower much better.