Topic: Could a backfire do this?!

[JZEROE]

So I adjusted my valves last weekend because I was hearing some ticking, and now the bike runs like total #$%*. First it developed an exhaust leak (still have yet to find it), and then it sounded like it was detonating like crazy. I adjusted the timing, set the points, and it seemed to get a little better, but there were still the pinging sounds. I was so nervous about the harm I could be doing to the engine, that I just parked it at work and drove a car all week.

Tonight, though, I figured I would take her home since it was the weekend and I'm planning on tackling the problem tomorrow. Then, in the lot, I noticed this:



It's a totally shredded foam pod filter. And there was melted something-black all over my kick start lever and side cover. And my right pant leg has been smelling like gas lately.

Could I have been misinterpreting the popping noise as detonation, when in fact it was a backfire? The noise gets is worst around 6k rpm, and, up until that point, increases with revs. Thing is, it was running fine before; could I have caused it to backfire by adjusting the valves and setting the points?

And oh yeah, the ticking is still there, and I'm 100-percent sure about the valve clearances: Engine was cold, triple-checked everything.

[754]

Did you clean the points ??

[mattcb350f]

I had a snowmobile do that  

It was two stroke of course and two strokes tend so spray back a bit of fuel when running (two stroke thing) and the filters had a bunch of fuel sitting in them. When she back fired, the filter caught fire and melted like yours.

Because the bike's a four stroke, I doubt that's what happened but maybe there is something going on with that carb which soaked the filter in fuel and either the foam didn't like it, or a backfire lit it up.

BTW, Backfires through the intake are pretty distinct. Hard to confuse with pinging IMO.

 Matt.

[754]

I had it happen with UNI socks....melted all over my gloves.. 

Go for cloth filters..


 The answer to your Q.. yes it can & did happen to you..

[JZEROE]

BTW, Backfires through the intake are pretty distinct. Hard to confuse with pinging IMO.

Let me just state, for the record, that I am an idiot. It is entirely possible that I am mistaking the two.

[mattcb350f]

BTW, Backfires through the intake are pretty distinct. Hard to confuse with pinging IMO.

Let me just state, for the record, that I am an idiot. It is entirely possible that I am mistaking the two.

  No way! you're here asking the right questions not an idiot at all.

If it's a backfire through the intake, and therefore back out the carbs you'll hear a more "poofy" sound and pretty much feel the pressure pulse if you're right in close to whiteness this. Pinging is more metallic sounding like theres some lose nuts rattling around in the cylinders (this is from my experience with non-bike engines, some folks on here might be better at telling bike pinging  )

Also, I know that some foam doesn't like gas. Sort of silly for carb filters but I've seen it.

 Matt.

[JZEROE]

So, uh, proving once again that I am an idiot, what causes a backfire through the intake?

[mystic_1]

If the intake valve tappet clearance is too tight, the intake valve might not be fully closed when things go boom.

mystic_1

[cafe750]

If the intake valve tappet clearance is too tight, the intake valve might not be fully closed when things go boom.

mystic_1

+1 Remember that some noise is natural with anything with mechanical valve gear (no hydraulic lifters). When things are perfectly silent, thats bad...

[SHORTROUND]

it looks like oil/gas disolved the adhesive that holds the filter together

[scondon]

it looks like oil/gas disolved the adhesive that holds the filter together

+1    Looks like your carbs overflowed a bit while sitting and made a runny mess of your foam. If your float heights aren't set proper and you have too high/too low fuel levels in one or more carb then your bike will run badly.


   Oh yeah, never be 100 percent sure about any work especially if the bike ran fine before you did it

[kayaker43]

That filter was melted, one of the backfires lit it off, and it only takes a second. 4 stroke dirt bikes put a metal screen under the foam filters to prevent this. Ethanol in gas can disolve glued seams but that one is melted.

Tight intake valves or incorrect timing could both cause backfires, and since that's what you did,.. better check them both. Crank position is crucial when setting valves. Did you have to adjust any of them by a large amount, that would be a clue the crank wasn't positioned right for that cyl. Did your timing marks move as you revved it and did they stop between the two marks?

[hapsh]

I also think it was caused by backfire through the carb.  Gas shouldn't melt pod filter foam, they are made out of gas/oil resistant foam.  Backfires out of the carbs are due to way to far advanced ignition timing or intake valves too tight and not closing fully.  Did you check your cam chain tension before your valve clearance?  Both valve adjustments and timing are suspect so I would go back over them very carefully.

[andy750]

All good answers so far and you obviously have to check your valve clearances again - do it twice just to be sure  You also mentioned an exhaust leak and this can also cause a ticking sound when running. I had the same issue last year and thought my engine was about to blow up when really it was just the exhaust studs needed tightening. Or could also be due to exhaust gasket.

The other type of "pinging" Ive heard is when travelling at speed and my rear wheel spokes were snapping off one by one over the course of a few hundred miles riding 2-up on the highway....I would stop, check the engine sounds - find nothing and carry on not knowing what it was......needless to say I found out when the rear wheel finally collapsed at a stop light 

Good luck with it!
cheers
Andy

[UnCrash]

The other type of "pinging" Ive heard is when travelling at speed and my rear wheel spokes were snapping off one by one over the course of a few hundred miles riding 2-up on the highway....I would stop, check the engine sounds - find nothing and carry on not knowing what it was......needless to say I found out when the rear wheel finally collapsed at a stop light   

Wow! That's a good one!  ~  I could easily do that!

Hey JZEROE,

These engines do make a bit of noise.  It took a while for me to get used to.  My 750F sounded like it had loose marbles inside it when I got it.  After setting the tappet height, adjusting the points and timing, cam chain, carb synchronization, and tightening the exhaust it quieted down about 50%.  But she still makes a bit of noise.  At least now she sounds like a well oiled printing press....

Go over the tuning procedures again, and check those floats.  I truly sympathize with your pain.  It's part of the bonding process you're doing with your bike.   

[lazyguy400F]

     My old 160 had big cheap foam filters, which caught on fire big time when I had it warming up once- good thing I wasn't on it, as the wiring harness and the seat were history. I did get it hosed down before the tank could blow, but those nice knee rubbers were melted...

     

[JZEROE]

This is all great information, and I'm super-appreciative of it all.

I got sick last weekend so didn't have a chance to get elbow-deep. This weekend is my time to dive in. Hopefully I'll have her running like a 30 year-old bike in no time.

[JZEROE]

Oy f#ck.

So I had basically parked the 550 for a couple weeks because I was pretty bogged down at work. Finally took a deep peek today, and HOLY S#IT. Turns out the valve adjustment screw on the #4 cyl, the one that toasted my pod, had somehow come OFF. Operator error, I'm sure. The screw was just sitting there on top of the valve... I hate to think what the inside of that cylinder looks like now, but thank god for bulletproof hondas: re-adjusted the valves, tweaked the timing, and synced the carbs, and the bike runs beautifully now.

I will, however, be doing some headwork this winter, possibly a full rebuild.