Popping/back firing

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Popping/back firing

Postby Tom Rybak » Thu May 30, 2019 7:48 pm

Looking for suggestions. 1998 Honda Helix with approximately 2000 miles. Just broke it out for summer after long winter. After spending some time getting it up and running I do notice significant popping when I come off throttle while on ride? Happens when coming down from 50 mph as well as lower speeds. Almost like it is farting. Things I have done to scoot so far and still popping.
1. Drained fuel and did new inline fuel filter
2. Air filter clean
3. Plug is nice tan color
Any suggestions appreciated. Thanks again.
Tom :roll:
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Re: Popping/back firing

Postby zozman » Thu May 30, 2019 11:58 pm

Backfiring on deceleration is a direct result of too much air (lean condition) of the carburetor. Replace the air valve on the carburetor.


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Re: Popping/back firing

Postby GrahamH » Fri May 31, 2019 1:17 am

I have had similar exhaust farts which were cured following the advice of Zozman to change the carb' jets. Apparently the first Helix form 1986 had main jet of 115 and slow jet of 38 but this was changed to 110/38, possibly to cut emissions? The 115 jet cured the problem. However it is also important to seal the exhaust, there is a flat sealing washer in the exhaust recess of the cylinder head and also a tubular packing where the muffler pipe fits into the exhaust flange. Change both of these with genuine Honda parts plus a little exhaust paste to get a good seal.....and it can't hurt to look at the air valve in the carb as zoz has suggested.
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Re: Popping/back firing

Postby Tom Rybak » Fri May 31, 2019 8:52 am

Thanks for help. Just to be clear, are you talking about the air cut off valve that sits on back of carb and vacuum tube hooks up to it? Kind of looks like flying saucer? Not sure how to post pics on forum.
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Re: Popping/back firing

Postby zozman » Fri May 31, 2019 12:39 pm

Tom Rybak wrote:... are you talking about the air cut off valve that sits on back of carb and vacuum tube hooks up to it? Kind of looks like flying saucer? ...


A: Yes. The purpose of the air cut valve is to cut off excess air from entering the combustion chamber on deceleration. When the air cut valve is malfunctioning, it allows air to bypass it because it has a hole in it or is dried out or is weak and on decel, you get baby farts or explosions from your scooter.

While changing the jets to 115/38 or 115/40 will help with performance, it has little effect on decel.

The air cut valve is expensive. Why? Because there are no after market replacements.

From Honda:

VALVE ASSY., AIR CUT
16510-KS4-753
$75.93

The good news: All you need to do to replace it on your carburetor-assuming all is well with it-is the air cut diaphragm and the tiny o-ring. Remove the top of your air cut valve, then replace the diaphragm and o-ring, tighten it back up.

ZOZ Rule #1 The air cut valve is 32.6% cost of a new carburetor. If you do a test on your automatic choke (autobystarter) and find that you may need to replace it mainly due to hard cold starts, now you are at 58.7% cost of a new carburetor. See where I'm going here?

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Re: Popping/back firing

Postby Tom Rybak » Fri May 31, 2019 12:52 pm

Thanks so much for helping explanations. Always learning. Will keep you updated. Enjoy weekend.
Tom
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Re: Popping/back firing

Postby Tom Rybak » Mon Jun 03, 2019 12:22 pm

Just ordered online oem unit so time will tell. $78.95 for little sucker.
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Re: Popping/back firing

Postby zozman » Tue Jun 04, 2019 9:01 am

Hi Tom.

Yes, that little air valve is precious.

Using a vacuum gauge on your current air valve. A good valve diaphragm will hold 28-30 Hg. A bad one will have vacuum seep past it to zero.

When you remove your old diaphragm, it may look OK. Hold it in front of a flashlight and you may see tiny pin holes or cracks.

Those racing fellows who don't care about popping on deceleration and use the CV carburetor (which is an excellent racing carburetor) disable the air valve.

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Re: Popping/back firing

Postby Tom Rybak » Sun Jun 09, 2019 8:32 pm

Replaced air cut off valve today with OEM equipment. Scoot runs like a dream. No more popping and or backfiring. No longer sounds like Harley on de-acceleration. Thanks you zoz. Much appreciated. By the way, are you a tech? Anyways, thanks again.
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Re: Popping/back firing

Postby zozman » Mon Jun 10, 2019 1:43 am

Thank you for the update. File this one in the archives it may help others too.


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