Briggs Intex 18HP constant backfire

[brehas]

Hi all,

I just picked up a mower with a 18HP Intek 1 cyl. I bought it not running, and I'm trying to fix that. The carb was bad so I replaced that today. The mower will fire up and keep running, but it consistently backfires through the carb. Not just every now and then, but it seems to be every other fire of the motor. It seems like (may not actually be the case) the exhaust alternates between the exhaust pipe and the carb. I replaced the spark plug and verified the gap on it. The engine obviously has very little power in this condition. Does anyone have any ideas? Is it possible for the ignition to only fire every other time? Thanks in advance.

Brent

 

[EngineMan]

Do a compression test, or check the valves (inlet valve)

 

[Fish]

Don't run it like that anymore!!!

Remove the valve cover and look at the valves, while rotating the flywheel, you will likely see the intake valve sticking, or a loose valve seat letting the valve to come back out all of the way. Either way, you could easily destroy the engine if you keep running it.

 

[truckinguy]

Hi all,

I just picked up a mower with a 18HP Intek 1 cyl. I bought it not running, and I'm trying to fix that. The carb was bad so I replaced that today. The mower will fire up and keep running, but it consistently backfires through the carb. Not just every now and then, but it seems to be every other fire of the motor. It seems like (may not actually be the case) the exhaust alternates between the exhaust pipe and the carb. I replaced the spark plug and verified the gap on it. The engine obviously has very little power in this condition. Does anyone have any ideas? Is it possible for the ignition to only fire every other time? Thanks in advance.

Brent

If it has a plastic manifold check for warpage. My V Twin had backfireing and it was a warped plastic manifold. Check for open gaps were the manifold seals.

 

[brehas]

Thanks for the info, I'm going to do a compression test tonight. I've not been using the mower in this condition; I replaced the carb, fired it up, and noticed that it was running as described.
thanks
brent

 

[Fish]

The ignition fires every time, but it is a 4 stroke engine!!!!

Just pull off the valve cover and look at the valve action and see if it is sticking or the seat is loose. If it is backfiring through the intake/carb, well....Then we should expect the problem at the intake valve then.



Take a pic of the valve tops for the edification of the gang here.

 

[Fish]

Can I have your old carb?

 

[brehas]

Took the valve cover off and the valves are closing fine. I'm getting just over 100 psi on a compression test which seems OK for a mower. The top valve (don't know if that's intake or exhaust) doesn't move much. The pushrod only moves a tiny bit causing the rocker to just move the valve just a tiny bit. The bottom valve seems to be moving fine. I didn't have a feeler gauge with me so I didn't actually adjust anything. Not sure there's much point since the pushrod isn't moving much. I'm going to take a few days off from messing with it since I have family coming into town for the 4th. If anyone has any other ideas, please let me know. thanks.

 

[brehas]

Can I have your old carb?

Sorry I don't have it anymore.

 

[Fish]

What do you mean, "Anyone else"????

You just laid it out plain by finally responding to a question or two.