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Briggs Intex 18HP constant backfire

#1

B

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


#2

EngineMan

EngineMan

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


#3

Fish

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.


#4

T

truckinguy

brehas said:
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
Click to expand...

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.


#5

B

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


#6

Fish

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.


#7

Fish

Fish

Can I have your old carb?


#8

B

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.


#9

B

brehas

Fish said:
Can I have your old carb?
Click to expand...

Sorry I don't have it anymore.


#10

Fish

Fish

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

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


#11

Fish

Fish

You sound like you have a bad cam lobe, now that we have some info. I guess we can trust this info. You will need to pull the
engine and go into it. It is not too big of a deal....


#12

Fish

Fish

But either way, you will need to buy some feeler gauges, to confirm things.

Really, this stuff is not all that complicated, it is just a matter of folks giving accurate details usually.


#13

B

brehas

Fish said:
What do you mean, "Anyone else"????

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

I seem to have offended you, I'm not sure how, but I apologize and I appreciate your help. FWIW, what I actually said was " If anyone has any other ideas, please let me know. thanks. " Again, sorry if I said something wrong, but I'm not sure how else to say what I said.


#14

Fish

Fish

Well if your valves are adjusted properly, when you rotate the engine, the valves should open equally the same distance, if one barely moves, that indicates a wiped out cam lobe.


#15

Fish

Fish

Here is a pic of a cam with a wiped out lobe, and is why the compression reading doesn't really help much.

cam lobe.jpg


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