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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Re: Popping/back firing

Postby kenyrider » Wed Aug 07, 2019 8:45 am

Man, mine does this popping stuff, and then doesn't. I have now rebuilt the carburetor (jets, floats, etc), auto bystarter, ignition coil, fuel pump, spark, carb insulator boot (was cracked and made it stall instantly), checked the fuel filter, gas tank, etc., the bike STILL has issues. When I did the carb rebuild kit last weekend, I did examine the "air cuttoff diaphram," but not with a flashlight. Maybe I'll try that. it looked good though...

I was all happy as it ran smoother after the rebuild, then blammo, same old sh!t This bike will be mid throttle and obviously struggling, sounding farty, poppy on decel (when slowing down), but mid throttle, holding it totally still, SUDDENLY "fix" itself and take off like it did the day I got it. That'll last a while sometimes, or I go over a freakin bump and its right back to it. I filled the tank this last sunday and its gone on wed... obviously burning through fuel.. I womder sometimes with that arb being right under the seat if im bumping into it? I've definitely had times where it will hardly drive and "OH!"' the spark plug wire is off and just bouncing on the plug, or one of the little hoses to the big air hose, before the air filter, is off!!


It had been doing this stuff less this week (more stable kinda after the rebuild) than it WAS, but still not right. I can seriously feel the bike hesitating like someones stomping the brake real fast intermittently on me, and wont go over 50-ish up a hill.. I used to wonder if i was sensing it doing this stuff going over BUMPS, but now i KNOW it is. I can totally tell.

Again, like I said, it will suddenly fix itself in the middle of a ride and be able to do 70-72 like it should. sometimes when i stop the bike its bad when i turn it back on.. sometimes the opposite. I swear sometimes in the morning in colorado, I go down a big hill where the temp is colder at bottom and I'll feel this crap happen, get back to top of hill and its fine again????

HELP!!!

Is this possibly a collapsing vacuum hose or something? I don't want to take this bike to honda OR a harley shop because nobody seems to know these things and I've read all the stories here, that they'll take a bunch of money for messing with the "stupid little scooter" and never really fix it.

I've never seen such an intermittent thing in my life! With the carb rebuild I did, when its not doing this, it runs like mad! Smooth and fast. I've spent all this time and money and its probably something so stupid. My next gambit is to replace the hoses on the carb. I notice when its heated up, the little hose supplying the coolant to the carb gets looser, and even was bubbling when i pulled it back a bit, but that wouldn't affect the air mixture, which is what I seem to think this is.. Ive been dialing up and dialing back the mix ratio under the float bowl all week, but it aint the problem obviously, cuz yesterday it drove great for a half hour, then this morning back to suck.
again, the farty muffler stuff all goes away completely when its running right.

I AM LITERALLY THE GUY spending more than a new carb wouldve!!!!

What do I do next?
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Re: Popping/back firing

Postby zozman » Wed Aug 07, 2019 12:30 pm

I'll try to be kind here.

If you did not check the air valve with a vacuum gauge, you haven't determined if it is operating correctly. A bad air valve resuts in a backfiring issue on deceleration.

If you did not check the autobystarter with ammeter for excessive resistance, it may be bad which contributes to an over rich running condition. If you replaced it with a cheap chinese knock-off, you wasted your money.

I don't know if you rebuilt your carburetor correctly so that may well be a continuing drivability issue. By the time I rebuild your carburetor, you're way over the limit on expenses and then sometimes even with a rebuild, I fail.

Stop the bleeding: There is no sense throwing good money into already bad results with your carburetor. Get the OEM Honda carburetor and replace yours.

If any drivability issues remain afterwards, let us know and we'll take it from there.

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