The "At witt's End Backfire Cure"

Written by Ken "the Mucker" Sexton

Friday, 11 June 2004

Reprinted by permission from Mr Tidy's tech tips

I report this as a last ditch effort for those who may experience extreme situations where their bikes are persistently backfiring through the intake OR exhaust, AND conventional efforts to fix the problem prove fruitless.

It is not a panacea for problems that might be fixed through normal jetting and adjustments. I do want to stress that this is not the best way to fix MOST backfiring problems. Usually the correct fix is performed with alterations to jetting and insurance that the intake and exhaust systems are sealed.

My own Road Star has been plagued with vicious intake backfiring since it was new. The backfiring has frequently been so forceful that stalling the engine was common and at least twice it reversed the engine's rotation.

The Yamaha factory rep couldn't do a thing with it, while it was under warranty and it has largely resisted my efforts as well. I had managed to reduce the intake backfiring a lot by reducing the accelerator pump volume and adjusting the pilot fuel system. That also reduced the stalling by 90% and eliminated the potential for engine reversal.

But the backfiring refused to be fully exorcised. Recently I filled the pilot air correction with solder and then drilled it to .031" (from an original approximate size of .040").

Because the jets are brass, I find it easier to clean them up good and solder them closed. Then drilling the solder to the desired hole diameter is easy with a #1~#80 drill index and a Dremel tool. Some people might be tempted to epoxy the jet closed and then drill, but epoxy is less secure, harder to fill such a small hole and may chip out when the drill is put to it.

It has not popped up the intake even once in the last 200 miles. Again, end of problem.

While they do make alternate air correction jets (as I recall ours is a #100), I've never known a shop that stocks them and, in fact, few would know who to order them from. Sudco (http://www.sudco.com/) would probably be the best source, but I don't think they do retail.

Questions should be asked in our forum (Use discuss link below). The forum is very active and you stand a good chance of getting your questions answered there. If you would like to leave feedback for the author, or have additional information you think will benefit others, please use the comment section at the bottom of this page.

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DISCLAIMER: This information and procedure is provided as a courtesy and is for informational purposes only. Neither the publishers nor the authors accept any responsibility for the accuracy, applicability, or suitability of this procedure. You assume all risks associated with the use of this information. NEITHER THE PUBLISHERs NOR THE AUTHORs SHALL IN ANY EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, PUNITIVE, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, OF ANY NATURE ARISING OUT OF OR IN ANY WAY CONNECTED WITH THE USE OR MISUSE OF THIS INFORMATION OR LACK OF INFORMATION. Any type of modification or service work on your motorcycle should always be performed by a professional mechanic. If performed incorrectly, this procedure may endanger the safety of you and others on your motorcycle and possibly invalidate your manufacturer’s warranty.

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Comments (10)

Opps, heres my address
Written by old_mikee, on 06-03-2015 19:43
My email address is mplesh@propmakers.com

hsr
Written by blkhwn, on 04-30-2015 11:12
how can you be contacted?

This Solution solved my 11 year carb cou
Written by old_mikee, on 01-13-2015 18:05
Thank You Ken Sexton…… I should have done this 11 years ago, but of course I had to wait until I was at wits end, which happened today.
I own a 1700cc, 2004 R/S with 63K miles. I bought it new and kept it stock except for the air box and a set of V&H Longshots. It has popped back through the carb, regardless of what I did to the rest of it.

This absolutely worked for me…... and if you are having popping through the carb problems, I would suggest you take your air cleaner off, and place your little finger over the Air Jet Ken refers to, and see if that stops the coughing and/or hesitation….. if it does, simply follow Kens advice, solder it up and drill it out to .031 or thereabouts. (For those of you that do not own drills this small, you can send your jet to me in an envelope along with return postage, and I will solder it up and drill it out for you)

thanks for writing the fix

mike

just bought a 04 roadstar that wont idle
Written by skidmark, on 10-28-2013 20:46
i just purchased the 04..it has hard krome longshots and a k&n air filter...I don,t know if the carb was jetted as the previous owner lied about a few things so...i really don,t know what he has done..she will idle high with the choke out..popps out the carb at low rpm...and when slowing down she back fires to beat the band..could it be the jetting or the carb gunked up...20 k miles in almost 10 years..where to begin....p.s. she goes down the road real well after getting out of the hole..thanks guys.skidmark

Going pumpless cured mine
Written by HoseDog, on 08-16-2013 17:12
My '06 has SpeedStar pipes & air, and used to pop and backfire regularly while blipping the throttle on downshifts. It's only happened maybe twice in the last 2 years since being pumpless. Don't know why, but NOT complaining!

backfire/carb popping
Written by kites, on 08-14-2012 21:33
Cured the backfiring(100%)by simply installing a new fuel filter on my 02 1600 midnight RS.Who would have thunk?Bike still pops through the carb.Could this be vacumm related?This happens mostly when taking off from a stopped position and when downshifting.Any sugestions.

Written by 72XS2, on 05-23-2012 22:24
My bike has this backfiring problem too. So, if I understand well what you said, you change change the pilot jet for a 0,031 and it'll be ok. My bike is a 2001 and the stock pilot jet is 0,035, not 0.040. Thanks for your help !

0.031 PILOT JET -Backfire out the Carb-
Written by brianmac, on 12-02-2010 07:30
tks for the advice, worked like a charm. yamaha dealer, "roadstars are known for that", but offered no solution.
BTW, boats.net will ship any yamaha part from fiche, and little stuff like the 0.031 jet was $7.70 including shipping to your front door. try it! others want $10 for shipping.
WERE ALL TRYING TO FIGURE WHY-PROBABLY ETHANOL/VISCOSITY/OCTANE/ATOMIZATION ISSUE.

Written by redhotrider, on 06-17-2010 19:32
my o6 road* (2000 miles-stock air box) does the occasional pop in carb also at acceleration from stop or just blipping of the throttle on down shifts. was jetted at dealer when Vance and Hines longshots were installed I just got new twin veocity air intake from Kuryakin.they recommend upsizing? the pilotair to a 1.3 that comes in their jet kit(FTC USA)never heard of them. any thoughts on this???

42mm carb
Written by lunchboxx, on 11-20-2008 19:12
I just installed a new 42mm carb and it is popping on deceleration and idling like crap.help !!!!!!!!!!!!!

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