Couple of loud back fires from the right side on Saturday

[..]

I've checked the header nuts. All snug.

Zipping along back road twisties in 3rd and between 3 and 5,000 rpm.

On a negative throttle down hill coming up to a curve that just needed maintenance throttle. Before opening the throttle slightly the backfire. Loud enough to sound like a shotgun.

Just the one explosion each time not a series of pops.

Petcock diaphragm replaced along with carb intake O rings all fixed up last August. about 6,000 miles ago.

Just replaced the spark plugs. Yes I checked the gaps.

MPG is normal.

[Gavin_Sons]

might consider doing a sync if you have not recently. good intake o rings might have changed it enough to backfire.

[98valk]

u eating pork and beans again?  

some ideas;

idle mixture screws went lean.  reasons, spring/s got weak and/or O-ring failed, esp if u had them apart and installed the washer and o-ring in the wrong order.

battery weak below 10.5 volts and/or alternator going to low on output voltage

loose coil wires and/or plug leads to coils

failing plugs and/or failing resistor in plug cap.

what u describe is some type of spark issue, fuel mixture getting into cylinder and then a strong spark or still spark issue and mixture ignites from hot cylinder parts, etc., then boom.

[Jess from VA]

Paul, after my desmog, over a year later I started getting the same backfires, increasing in frequency and volume over time.  Mainly on freeway (or freeway speeds) and dropping the throttle (to slow).  Big (quick) drops in RPMs resulted in big booms.  (this of course results in big, quick changes in pressure at the intake nipples)

What had happened was the intake runner vacuum caps had torn and/or blown off the nipples on the inside of the intake runners.  The guy who did the job had run out of the good honda vacuum caps, and used run of the mill auto parts vacuum caps.... which are pure crap for this intended purpose (they just will not stand up the heat and pressures exerted on them)  (except for my #6 which still goes to my OE petcock).  I figure each loud explosion was another cap biting the dust.

You need to get a light (and may be a dentist mirror) to look behind the intakes.  Some are easier to see than others.  A couple of mine had blown in two (tip gone, body still on the nipple), and others looked OK, but pushing them sideways (just like a rubber tire valve stem) revealed they were badly torn.

This is what you want (and get extras).  CAP, BOOST 16215-MV4-000


Now if your bike has not been desmogged, then I am betting you have tears (near or on the intake nipples) in your vacuum lines.  As far as I can tell, no other place on the OE vacuum lines is subject to the same amount of pressure and heat.

Long curved needle-nose pliers come in handy.  Another job you do more by feel than sight.  They go on snug, but some nonetheless wrap each one with a small zip tie pulled tight, and others do not.

Tiny zip ties.


After the repairs, no more backfire on either bike.

[98valk]

Paul, after my desmog, over a year later I started getting the same backfires, increasing in frequency and volume over time.  Mainly on freeway (or freeway speeds) and dropping the throttle (to slow).  Big (quick) drops in RPMs resulted in big booms.  (this of course results in big, quick changes in pressure at the intake nipples)

What had happened was the intake runner vacuum caps had torn and/or blown off the nipples on the inside of the intake runners.  The guy who did the job had run out of the good honda vacuum caps, and used run of the mill auto parts vacuum caps.... which are pure crap for this intended purpose (they just will not stand up the heat and pressures exerted on them)  (except for my #6 which still goes to my OE petcock).  I figure each loud explosion was another cap biting the dust.

You need to get a light (and may be a dentist mirror) to look behind the intakes.  Some are easier to see than others.  A couple of mine had blown in two (tip gone, body still on the nipple), and others looked OK, but pushing them sideways (just like a rubber tire valve stem) revealed they were badly torn.

This is what you want (and get extras).  CAP, BOOST 16215-MV4-000


Now if your bike has not been desmogged, then I am betting you have tears (near or on the intake nipples) in your vacuum lines.  As far as I can tell, no other place on the OE vacuum lines is subject to the same amount of pressure and heat.

Long curved needle-nose pliers come in handy.  Another job you do more by feel than sight.  They go on snug, but some nonetheless wrap each one with a small zip tie pulled tight, and others do not.

Tiny zip ties.


After the repairs, no more backfire on either bike.

good point.  I would use BonS's vacuum caps. better longer lasting material.

[Jess from VA]

Do you have a link or other ID to them?

Mine caused me so much trouble, I thought why not just crimp those bastards closed permanently, then was reminded about carb synchs.  Oh yeah, there's that.

I'm 99% this is his problem.  Identical symptoms to mine.

A small header leak will not backfire like a 12 gauge.  I had cars thinking I was shooting at them, taking evasive maneuvers.

BTW, in the meantime, go easy on the throttle.  Running it up to 6K PRM and dropping the throttle will just blow more caps off.

[98valk]

http://thedigisync.com/e-store.html    upper right hand corner

[..]

Paul, after my desmog, over a year later I started getting the same backfires, increasing in frequency and volume over time.  Mainly on freeway (or freeway speeds) and dropping the throttle (to slow).  Big (quick) drops in RPMs resulted in big booms.  (this of course results in big, quick changes in pressure at the intake nipples)

What had happened was the intake runner vacuum caps had torn and/or blown off the nipples on the inside of the intake runners.  The guy who did the job had run out of the good honda vacuum caps, and used run of the mill auto parts vacuum caps.... which are pure crap for this intended purpose (they just will not stand up the heat and pressures exerted on them)  (except for my #6 which still goes to my OE petcock).  I figure each loud explosion was another cap biting the dust.

You need to get a light (and may be a dentist mirror) to look behind the intakes.  Some are easier to see than others.  A couple of mine had blown in two (tip gone, body still on the nipple), and others looked OK, but pushing them sideways (just like a rubber tire valve stem) revealed they were badly torn.

This is what you want (and get extras).  CAP, BOOST 16215-MV4-000


Now if your bike has not been desmogged, then I am betting you have tears (near or on the intake nipples) in your vacuum lines.  As far as I can tell, no other place on the OE vacuum lines is subject to the same amount of pressure and heat.

Long curved needle-nose pliers come in handy.  Another job you do more by feel than sight.  They go on snug, but some nonetheless wrap each one with a small zip tie pulled tight, and others do not.

Tiny zip ties.


After the repairs, no more backfire on either bike.

It has been desmogged.

Now I need to find someone with smaller hands. Mine are 3/4XL and even without trying I know I'm going to be using a few choice words to switch these little caps out.

[..]

http://thedigisync.com/e-store.html    upper right hand corner

Thanks. Ordered 2 sets cause I know a couple will get FUBARED 

[Michvalk]

Use forceps, or angled needle nose pliers to change the caps

[jim@98valkyrie.com]

Now I need to find someone with smaller hands. Mine are 3/4XL and even without trying I know I'm going to be using a few choice words to switch these little caps out.

I have jumbo size hands as well and have had a lot of issues getting into some of those tight places...until, I saw BonS use a pair of these very long reach needle nose pliers last year at IZ. I bought the set and never been happier. It is the best $30.00 I think I have ever spent on tools.

http://www.crescenttool.com/pliers/x2tm-pliers-2/crescent-psx204c-2-pc-x2tm-long-reach-plier-set.html

[Gabriel]

http://www.harborfreight.com/16-inch-long-reach-pliers-set-38598.html

[da prez]

  Tho I prefer name brands , Harbor Freight has these for about $15.00 , and use a 20% coupon , and get a free gift of something you may or may not need. (mention my name so I get my commission)

                                        da prez


           Gabriel ,  you beat me by a few seconds.

[Ricky-D]

I've checked the header nuts. All snug.

Zipping along back road twisties in 3rd and between 3 and 5,000 rpm.

On a negative throttle down hill coming up to a curve that just needed maintenance throttle. Before opening the throttle slightly the backfire. Loud enough to sound like a shotgun.

Just the one explosion each time not a series of pops.

Petcock diaphragm replaced along with carb intake O rings all fixed up last August. about 6,000 miles ago.

Just replaced the spark plugs. Yes I checked the gaps.

MPG is normal.

 

If this was just an unusual event and not happening on a regular basis I suggest to not bother to do anything about it. Now, on the other hand, if it is happening on a regular basis, then it should be looked into.

***

[Gabriel]

 Tho I prefer name brands , Harbor Freight has these for about $15.00 , and use a 20% coupon , and get a free gift of something you may or may not need. (mention my name so I get my commission)

                                        da prez


           Gabriel ,  you beat me by a few seconds.

I have two pair and they are both Snan-on, but for something like this HF is all we probably need.
I looked at a few tools the last time I was in HF and was actually impressed for the price...

[..]

Zip ties?
We done need no steenkin zip ties!

Big BF did this back in August to five new caps. Does this remove the caps as a possible problem???

[Jess from VA]

Maybe, if you carefully check each one for rips or tears.  Those look like run of the mill auto parts vacuum caps (though I would not change them if they are holding up OK).  

Just because the clamps are in place, does not mean a cap is not leaking (maybe on the side away from your visual inspection).  My bad ones all had small zip ties on them (job done by Big Bill too).  

Based on your backfire being identical to mine (hard decell, loud bang), I was pretty sure this was the culprit.

I was thinking there might be another way to check.  Wearing a led headband light, get a good cigar going, start the bike, and blow a little smoke down on each nipple (but you'll need to rev the bike some too), to see if the smoke is just wafting, or being blown around by something like a leak (maybe bending the caps to and fro a bit too - burned fingers).

I suppose it could be the #6 going to the petcock too (if you still have that).

If this is not the problem, I punt.

  

[Gavin_Sons]

let it idle and hold a propane torch (not lit, but gas on) up to each one and see if the rpms go up. that will tell you if one is leaking.

[..]

  Wearing a led headband light, get a good cigar going, start the bike, and blow a little smoke down on each nipple (but you'll need to rev the bike some too), to see if the smoke is just wafting, or being blown around by something like a leak (maybe bending the caps to and fro a bit too - burned fingers).
  

If only you had suggested this yesterday. 

Think about it.

[Jess from VA]

  Wearing a led headband light, get a good cigar going, start the bike, and blow a little smoke down on each nipple (but you'll need to rev the bike some too), to see if the smoke is just wafting, or being blown around by something like a leak (maybe bending the caps to and fro a bit too - burned fingers).
  

If only you had suggested this yesterday. 

Think about it.

Those are not the nipples I was talking about.  But good for you.