Another top end/header noise..but very different 94 650l

12 replies to this topic
  • scotttco62

Posted February 06, 2008 - 03:48 AM


Ive been reading of alot of topend noise making partyfavors called honda...our hondas to be exact! This one ,however .is not a cute, lil song bird....Its a bass beritone of belching(detonating ?)BRP power . Ans only happens on deceleration .or after bliping the throttle./ ..It sounds to me like detonation at the top of the header..but by the time you hear it thru the supertrapped rear exhaust , its like a bongo players been shoved up the pipe...and that mother can hit those skins....and loud! scares the neighbors...(hell it scares me!)
The bike has been desmogged ( all smog stuff long gone)sealed up,,de snorkeled,drilled ,shimmed)dave mods) Shes mostly a street fighter type SF mahem maker.daily ride...and runs strong.
I put in shop over two months ago for repair of said noise and the shop has (allow me to list...and youll hear the cash register ring in background...ready?
new timing chain, new tensioner,new subrocker pins ,new springs on decomppression ..of yeah new valves and nec headwork. ...the mechanics are stumped and stumped ,frustrated ...and going broke from theyre "guessing" at problem,s
Please...any info appreciated\

scottco62 (the belhing bongoed breathed BIG RED(WHITE)PIG

  • Motosprtman

Posted February 06, 2008 - 10:45 AM



"its like a bongo players been shoved up the pipe...and that mother can hit those skins"

This makes me think of a lean condition. I know you said you have done the mods, but the poppity pop of bongo's sounds like it is lean. What Main jet and pilot jet are you running? check the plug and if the center electrode is white, it's lean. Is your Fuel Air Screw out the 2 1/4 to 2 1/2 turns ? are you running 92 octane? Had the top end ever been apart before the dealer worked on it? leaking head gasket? nawwwww...... man I dunno - just thinking out loud with ya.

  • martinfan30

Posted February 06, 2008 - 01:09 PM


This start after the mods? I would carefully recheck your carb work.

  • scotttco62

Posted February 06, 2008 - 02:26 PM


thanks for your response.bought bike used over two years ago,not sure if head had been removed before,however the shop(not a dealer)has taken it off to rework/replace valves .This noise is very different from anything ive ever heard,and is deffinately a detonation in the header right out of the head,just as engine winds down from a throttle blib or as backpressure /engine braking or deceleration...I did the mods more than 1000 miles previous to this happening. Ill check the jetting cant recal right now (it was a constant change and try when i did it..but have records at home.ill check plug,and confirm 92 gas. The bike is at the shop.awaiting next thing to try. To note i removed all smog ,drilled 5/32 whole in slide ,shimed the speced amount.. The bongo thing is verysharp withreverberationing thru the pipe......thanks for your help, and i hope this updated info helps .....

  • martinfan30

Posted February 06, 2008 - 02:55 PM


Poss. a partially plugged pilot circuit.

  • Motosprtman

Posted February 07, 2008 - 07:19 AM


still sounds as though it is lean, check the main jet and the pilot, if Kehien jets should be a 55 pilot and 158 main.

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  • scotttco62

Posted February 07, 2008 - 07:28 AM


thanks guys im going to get back to the shop thisafternoon and get all the other info on the old as well as new instalations so i can answer all of your earlier questions. Ill also head them down the carbueration avenue,seems like they should have thought of that allready......but theydidnt.....thats abit troublesome to think huh? thanks again,ill be back. scotttco62
srry no time to spellcheck on this

  • scotttco62

Posted February 09, 2008 - 11:41 AM


First off..thanks for everyones help,sorry iwas not able to get you more info to work with .However the culprit was discovered,if not by mistake,then shear luck. Mind you this has been going on for nearly two months(not continuous,due to holidays,but still....) Ill cut to the chase (cause im tired of typing and want to go get my bike back) I went to shop to relay some suggestions to the shop about possibilities i found here on TT. Upon arrival the shop owner informed me they had completely broke down and cleaned carb,they were now cleaning the head and checking all the valves and their train of rockers and seats. The shop owner (the second most frustrated person in this ordeal) was pressure/steam cleaning the actual head and brought it to the bench where we were i was already discussing the mysterious attributes of valve seats that a fellow flat track racer has had in past. When the owner started blasting the head with air ,to dry the now very hot head(due to steam blasting) ,just as the stream swept across the exhaust valve seat, it started rattling like a quarter in a boxcar.......valve seat loose as hell! just lifted right out while the head was hot.
Thanks again, and i know there will be future contact.........scotttco62

  • cleonard

Posted February 09, 2008 - 02:21 PM


The valve seat is not an OEM replaceable item. The Honda way is to replace the entire head. Competent shops can make a valve seat and install it in the head. That's what did when I had a similar problem. My local shop couldn't do this kind of work. Mine was fixed a few years ago by XR's only.

  • martinfan30

Posted February 09, 2008 - 04:52 PM


That will do it, glad you found the problem!

  • resurrection

Posted February 10, 2008 - 04:19 AM


Off the point alittle but I once found ,on an ascot 500 the inner pipe broken off inside the outer pipe .
thats a srange sound ,rattle on the off throttle if I recall .:applause:
20 yrs ago now ,I may be getting old.

  • scalejockey

Posted February 10, 2008 - 07:40 AM


Off the point alittle but I once found ,on an ascot 500 the inner pipe broken off inside the outer pipe .
thats a srange sound ,rattle on the off throttle if I recall .:applause:
20 yrs ago now ,I may be getting old.

Lesson #2 wow that's cool to know! Thanks guys I learned something today.

Remember your not old until you look in the mirror.:)

  • resurrection

Posted February 10, 2008 - 01:37 PM


Old is cool when we have something to share .I'm training an aprentice tool maker at work this will be my 4th two have completed the program one dropped out .(it's 10,000 hrs of pitfalls and going to school threw the TMA classes) it's tuff ya know,@ 19yrs old to learn, your future in this trade means you will be swallowing your pride and maybe have to learn something .

It's a challenge to convey the differance between taking your time for safety,or tight tolerances,and when you can let loose alittle and fly.,but I sure injoy watching a young fella progress.

Sorry I'm old ? not one bit!

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