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Engine backfire #5395344 04/06/20 10:12 AM
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dawgn86 Offline OP
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Hi all

I have a pressure washer from Northern Tool..Honda GX 160 engine 5.5 HP / Comet pump that is about 3 years old. Bought new / used several hours per season and always well maintained.
Always runs fresh fuel / 90 octane...run carb empty when done, etc. New plug every season.

It starts great, runs strong but has an annoying backfire when you let off the pressure wand. Doesn't do it everytime. I adjusted the valves last year and it seemed to help, but it still backfires some.

Any suggestions on what to look for?

Last edited by dawgn86; 04/06/20 10:19 AM. Reason: update

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Re: Engine backfire [Re: dawgn86] #5395354 04/06/20 10:25 AM
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Rand Offline
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Does it seem to be when the engine is on light load or a heavy one.

sticking unloader?


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Re: Engine backfire [Re: dawgn86] #5395357 04/06/20 10:28 AM
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dawgn86 Offline OP
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Engine doesn't surge and pressure can be adjusted easily, although I guess you can't rule that out.
I usually use heavy pressure to clean driveways, etc, but it's not all the way up.


2019 Acura MDX
2019 Ford F150
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Re: Engine backfire [Re: dawgn86] #5395361 04/06/20 10:32 AM
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CT8 Offline
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Mine doe the same thing [ it is 20 years old] I would guess it is running lean for emissions.


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Re: Engine backfire [Re: dawgn86] #5395371 04/06/20 10:48 AM
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JohnG Offline
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One rule of thumb to follow for ANY engine: If it backfires from the carburetor, the mixture is LEAN, If it "backfires" out of the EXHAUST, the mixture is RICH.

Re: Engine backfire [Re: dawgn86] #5395383 04/06/20 11:10 AM
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ironman_gq Offline
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Is it really a backfire (snorts through the carb) or is it an afterfire (bangs out the exhaust), if it's popping out of the carb it's too lean or timing/valves need attention. If it's popping out the muffler it's too rich or timing/valves need attention.

It could be that the throttle slamming shut is causing a rich condition, might be able to play with the governor to fix that.

Re: Engine backfire [Re: dawgn86] #5395425 04/06/20 12:03 PM
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Also, if it has a catalytic muffler, it could simply be igniting a bunch of raw fuel once O2 levels are sufficient.


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Re: Engine backfire [Re: dawgn86] #5395462 04/06/20 12:50 PM
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Check the compression with the throttle & choke open. You want to see 85+ psi. If less, suspect rings or valves. I would double check valve clearance. .004"-.006" intake,exhaust. If it checks out, then I would move to fuel delivery. I would think about pulling the carb and cleaning it really well. These things are on the ragged edge of too lean from the factory and the slightest obstruction can cause problems. Or if you want to gamble a little, a new chinesium carb is $10 online.

Re: Engine backfire [Re: dawgn86] #5395503 04/06/20 01:37 PM
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dawgn86 Offline OP
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Think I will check valve clearance again...clean the carb really well. Not really sure if it is popping through the carb or exhaust; usually does it after I release the trigger on the wand.


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2019 Ford F150
2007 Acura MDX
2016 Volvo XC90
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Re: Engine backfire [Re: dawgn86] #5396580 04/07/20 03:44 PM
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A backfire through the carb will generally be a very dull sound, sometimes with a quick dull whistle as air goes backwards through a carb, whereas an after fire in the exhaust has a sharp pop or pow to it.


People who count on their fingers should maintain a discreet silence.
Re: Engine backfire [Re: dawgn86] #5396619 04/07/20 04:22 PM
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This is a sharp pow.

Re: Engine backfire [Re: dawgn86] #5396923 04/07/20 10:27 PM
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I have the same thing happening to the same size of Honda on an air compressor. Just cleaned the carb as it it was oozing. Still didn’t help. Forgot to check the float and needle to make sure they are sealing. Gonna do valves tomorrow. It is popping out the exhaust then dying when it goes from full speed to idle or when running at full speed for a few minutes. It will idle forever.


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Re: Engine backfire [Re: dawgn86] #5397033 04/08/20 06:10 AM
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Running rich or valve issues come to mind.


The "thinking" man's friend.
Re: Engine backfire [Re: jhellwig] #5397112 04/08/20 08:17 AM
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bigdawglanecreek Offline
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Originally Posted by jhellwig
I have the same thing happening to the same size of Honda on an air compressor. Just cleaned the carb as it it was oozing. Still didn’t help. Forgot to check the float and needle to make sure they are sealing. Gonna do valves tomorrow. It is popping out the exhaust then dying when it goes from full speed to idle or when running at full speed for a few minutes. It will idle forever.


Sounds basically what mine does. Runs strong. Let off the pressure wand it returns to a smooth idle but backfires once.

Re: Engine backfire [Re: bigdawglanecreek] #5397307 04/08/20 11:12 AM
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jeepman3071 Offline
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Originally Posted by bigdawglanecreek
Originally Posted by jhellwig
I have the same thing happening to the same size of Honda on an air compressor. Just cleaned the carb as it it was oozing. Still didn’t help. Forgot to check the float and needle to make sure they are sealing. Gonna do valves tomorrow. It is popping out the exhaust then dying when it goes from full speed to idle or when running at full speed for a few minutes. It will idle forever.


Sounds basically what mine does. Runs strong. Let off the pressure wand it returns to a smooth idle but backfires once.


+1

I have a Honda GX200 that's a year old on a tiller I re-powered. It does the same thing at the end of a row. It goes from working very hard to almost over-revving on the governor when I stop to turn around, it can sometimes pop a little when this happens. Valves are in clearance, timing is good, carburetor is clean. I attribute this issue to the emissions jetting, these things are run pretty lean for emissions requirements, and the governor tries to compensate with the changing load. I have an older GCV190 on a pressure washer that doesn't do this when the load is taken off of it, but I can tell by the exhaust smell it is running a bit richer than the tiller engine.

For the record the GX200 is probably a bit under powered for the tiller and what I till, and the GCV190 is plenty powerful for the size of pressure washer I have.


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