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General Category >> Rubber Side Down! >> backfiring...not what you'd think.
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Message started by BurnPgh on 10/08/10 at 22:33:28

Title: backfiring...not what you'd think.
Post by BurnPgh on 10/08/10 at 22:33:28

Last few days I'll get a nice solid pop when I start it up. My shutdown backfiring is essentially cured excepting extreme changes in temp from day to night (open air filter). Any ideas? Idles just like always. Run's just fine. No loss of power, no stuttering, no smells or smoke etc etc. Everythings normal except for the start up.

I DID just clean and re-oil my KN filter. Maybe went overboard with the oil?

Title: Re: backfiring...not what you'd think.
Post by cornfuzed on 10/09/10 at 07:41:03

when i was playing with jetting and the air curcit, i would get that issue when my idle was off either high / low... could it be the petcoc ?

Title: Re: backfiring...not what you'd think.
Post by Routy on 10/09/10 at 07:49:55

Pop on startup ??
Seems like thats a new one..... to me anyway.

Title: Re: backfiring...not what you'd think.
Post by Serowbot on 10/09/10 at 08:45:06

I think you might have over-oiled...
wash it out and try again...

Title: Re: backfiring...not what you'd think.
Post by verslagen1 on 10/09/10 at 09:07:27

I get a pop on startup every so often.
stock filter, stock 88 carb
won't start if I touch the throttle.

on the '96 if it didn't start on the second rev I could open the throttle a little and it would start.

Title: Re: backfiring...not what you'd think.
Post by B1-66er on 10/09/10 at 15:06:18

How did you cure the shut-off backfiring? I have that problem, but only after it's bee b ridden, not after only idling.

Title: Re: backfiring...not what you'd think.
Post by verslagen1 on 10/09/10 at 15:24:34

097A667D7D2E394B0 wrote:

How did you cure the shut-off backfiring? I have that problem, but only after it's bee b ridden, not after only idling.

You got your idle mixture a little bit lean.
turn the screw about an 1/8 turn CCW or till it poofs on shut off.

Title: Re: backfiring...not what you'd think.
Post by B1-66er on 10/09/10 at 15:31:25

It smells like it's running rich. However, I have zero motorcycle experience, just cars. Do bikes naturally smell richer than cars?

Title: Re: backfiring...not what you'd think.
Post by verslagen1 on 10/09/10 at 16:26:12

In order to "afterfire", there has to be fuel (rich smell), some oxygen (fresh air) and an ignition source (hot pipe).

The last two are easy to come by even after a short ride. Fuel has to go thru a gantlet to accumulate in the muf. A lean adjustment makes this easy as when the engine misfires due to insufficient fuel mixture it passes thru and collects in the muf.

naturally an overly rich idle mixture will do the same thing.

Title: Re: backfiring...not what you'd think.
Post by Boofer on 10/09/10 at 17:02:11

I may be WAAAY wrong, but this is my second Fall with the Savage. Been through one winter. Our humidity is low and temps are 50 morning 82 daily. I have noticed a start up pop ocassionally. I also have a little more trouble with the petcock in winter riding. (40 Degrees) I just ignore most symptoms unless they seem life threatening to my engine. I am also showing signs of wear and get the grumble pops on waking up in the morning. Some of these "problems" described may be weather or temp related. We have to tune our engines for optimal riding in all weather. When weather changes our bikes are slightly out of tune.???

Title: Re: backfiring...not what you'd think.
Post by cornfuzed on 10/09/10 at 22:29:34

1C3131383B2C5E0 wrote:

Heeyyy i get the grumble pops when i wake up too! im probably running a little rich these days or maybe my air circuit is running a foul... lest thats what the misses tellls me ....

Title: Re: backfiring...not what you'd think.
Post by cursal on 10/10/10 at 08:17:33

mmmmmmmmmmm....I head for Grumble Pops when i wake up

Sounds like commercial for a bikers breakfast cereal :)

Title: Re: backfiring...not what you'd think.
Post by verslagen1 on 10/10/10 at 10:06:27

mmmmmmmmmmmmm... Grumble pops! :P
Looks like red corn pops... ;D
taste like Klotz with a racy smell... ::)
pops like an old harley... 8-)
guaranteed to keep you running. :-?

Title: Re: backfiring...not what you'd think.
Post by prechermike on 10/10/10 at 12:09:57

Back to BurnPgh's original thougth.

I have noticed mine doing the same thing a few times when I started it first thing. I have not done anything to the bike lately, my thoughts were it had to do with the changes in humidity, temp and so forth. i was relly hoping someone would have come up with something.

I don't think it is hurting anything, at least not that I can notice.

Title: Re: backfiring...not what you'd think.
Post by bill67 on 10/10/10 at 12:41:50

You can get moisture in your tank from the change of weather,Sea Foam gets that out.

Title: Re: backfiring...Suppositions-Questions
Post by J2 on 10/11/10 at 08:38:41

I get the occasional backfire when disengaging the clutch and coasting up to a stoplight. This is most often a single bang, not a gumble pop, pop, pop. This occurs mostly afterI have downshifted or run a gear up toward the shift point and let off the throttle or clutch (maneuvering in traffic).

A friend, who works on engines, has told me that this can damage my engine. Supposition: the exhaust valve may be slightly open and burn because of the excess fuel ignition in the hot pipe. True or false or maybe?

From what I have read on this forum, CCW makes the engine richer. True or false ?... no maybe. Note: limited carb experience. Supposition: the screw being turned MAY meter an air passage. If so, backing it out would permit more air and thus a leaner burn. Second Supposition: the screw being backed out is a fuel flow needle valve, thus backing it out would permit more fuel and a richer burn. Which is it?

If I am enjoying two or three backfires in a 20-minute commute to work, should I rush straightaway to get help resetting the carb, or should I consider resetting it when I get a roundtuit?

Title: Re: backfiring...not what you'd think.
Post by Oldfeller on 10/11/10 at 08:46:06

;)

We just call it the air screw ....

It actually meters a small fuel passage, CCW or out means more fuel going into the low range mix.

If you have go to 3 turns or more to get your bike to run right, then change out your pilot jet to the next bigger jet size -- keep on turning it out past 3 turns and it will likely vibrate free and fall out on the street and leave you with an open hole.

(no retaining spring pressure out that far to keep it from moving on out you)

============

Seafoam Bill,

Didja know that the addition of 10% ethyl alcohol in regular fuel means any air born H2O type moisture gets chemically assimilated into the fuel (happens automatically and requires no expensive additives such as sea~~fool~~ .... oops, I meant Seafoam).

And all commercial fuel contains chemicals to make sure moisture does no harm to the fuel should it actually get in there in any appreciable amount (lawsuits cost too much NOT to do this no matter how cheap the gas).

Title: Re: backfiring...not what you'd think.
Post by J2 on 10/11/10 at 08:54:57

Roger that. Turn out ... richer mixture. From my limited experience, I would probably find manufacturer specs ... turn in all the way ... turn out to manufacturer specs and then maybe a quarter turn out from there. Right?

Now, regarding the urgency of all this. I much prefer riding the bike than screwing with it (pun intended). I am getting more backfiring now that I use 87 fuel ... maybe two or three in a 20 minute ride. Should I restrict my riding until I get this at least mitigated (thumper will always clear her throat), or is this one of those round tuit things?

Title: Re: backfiring...not what you'd think.
Post by verslagen1 on 10/11/10 at 09:01:55

false
true
fuel
check your header bolts, and muff clamp
increase your idle speed and readjust idle mixture.

Title: Re: backfiring...not what you'd think.
Post by Oldfeller on 10/11/10 at 09:07:38

'round to it type thang, I suspect.

As far as "burning your valves" because of backfiring --

let's see, mmmm Let's think about it a bit.

Exhaust gas is naturally glowing burning hot already and exhaust valves normally glow dull red in normal use.

A common EPA trick from the '80 and so on is to dump fresh air into the exhaust manifold just down from the valves to help combust the excessively high hydrocarbon content of unmodified exhaust gases.

If something was gonna "burn a valve" that would do her, don't 'cha think? It doesn't ....

Backfiring and popping

A pulse of hot hydrocarbon rich stuff winds down the header pipe and hits the muffler chambers, finds some free O2 hanging around down there and has a party. What does that have to do with the situation way upstream at the valves?

If you want to burn a valve, let your exhaust valve clearance get way too tight so the exhaust valves don't close all the way -- that'll do her !!

Title: Re: backfiring...not what you'd think.
Post by J2 on 10/11/10 at 09:20:11

OK. Stupid question #7: If the backfiring is being caused by excess fuel firing in the pipe .... why would I want to make the low speed mixture richer, thus adding more fuel to the fire?

I get the head bolt response and the muff clamp, which could be adding that air portion of that explosion.

The guy with whom I had the conversation about backfiring indicated that he once actually holed his piston, due to backfiring. Must have been a hell of a bang. Of course, this guy put a two-stroke outboard engine on a Schwinn bicycle and proceeded to do 70 mph with it.

Ooops ... didn't mean head bolts ... Exhaust header is assumed.