Bill McMahon

I've got a cbr 900rr with a 98 motor. Just recently my beautifully running motorcycle began to backfire out of the exhaust when clutching up a wheelie. It will pull the front tire up an inch or so and then BANG, the motor begins to backfire out the exhaust and it sets back down. It doesn't do it everytime, and it doesn't do it under acceleration, just clutching it up. If it doesn't do it when I clutch up, then as I'm setting it down it backfires, and will backfire for certain if I try to pull it up immediately there after. The plugs look good ( doesn't seem to be running rich). Has anyone else ever run into this on a 900? If any one has some insight it would be appreciated.

Schwartz

Sidestand saftey switch??

Bill McMahon

I'll disable it and see

cedz

wow, u might have some major problems on your hand. the bike is carbureted, right? if your carburetor is runnin' rich, and your cam-timing is advanced, which is common for high performance sportbikes, this sudden hot spot in your cylinder could cause a backfire under rapid engine revs...or in other words, when u clutch it up. turn your fuel mix screw in (or your air mix screw out) to lean it out a lil' and see if that works.

Schwartz

WHAT!?!??!

fab5fiddy

HurricaneF2

does it do it on deceleration? check your header for leaks. usually cause its lean

zrex

sounds like its going LEAN on ya. all the wheelies/landings can change the float level a little. might be worth your time to pull the carbs and check your float height and make sure you dont have any rubbed thru wires that may be grounding out as you clutch it up.

Six Eight Nate

Well I don't know a whole lot about your setup so I'll just shoot some ideas at you but I really wouldn't start getting all freaked out. You mention a "98 motor" but you don't mention the bike it is in so I'm going to take a wild guess and assume that you have done some type of engine swap to update an older model. Whatever the case, your most likely dealing with a carb issues...it is common when these carbs need a rebuild for them to really start to show that they need work during wheelies and specifically during clutching up. 900rr's are such good bikes that alot of people forget to do maintenence because it is actually outside the norm for them to go out. We have at least 5 900rr's in our flock and 3 of them have over 50,000 miles on them and it was only last year that they began to show some signs of needing carb work, HOWEVER the first in the flock to really NEED carb work had only 26,000 miles on them...so it is always hit and miss with carbs. If you did a motor swap and used your old carbs, i think they might be jetted a little on the leaner side than the 98-99's in the first place, but in either case, it might be time for a good rebuild. Alot of people would recomend cleaning first, but to be honest, the level of work involved in just doing a good cleaning and doing an actual rebuild is identical...i always recomend saving up the extra cash and doing a rebuild in the first place for that simple reason. There are some known issues for weak spark, as well, but you should be showing signs of a weak battery or poor charging too so if you are not showing weak charge on the battery or signals lights going out intermittantly, then I would start with the carbs and just do a rebuild. A proper shop can richen up the mixture even if you are running stock everything and squeeze a couple extra ponies out of those bad boys too...or you can space your stock needles with NUMBER 5 NYLON WASHERS available from any local hardware store to richen up the mixture yourself a little bit, but if the carbs are starting to go, no amount of quick fixes will stop it...they will eventually become a serious problem when riding whoolies as they will drop out of sync right smack dab in the middle of the rev range and the bike will fall on it's face when you're expecting that mid-range grunt.

a couple hundred bucks is a small price to pay for a smooth running 919 series motor...with a fresh set of carbs, I can barely tell the difference between my 929, 954 or the old 919 motors...well at least for the fun factor because a smooth set of carbs are a sweet sweet thing!

Bill McMahon

I'm pretty certain it's an electrical issue at this point. Last night I took the tank off, read the plugs, made sure all of the wiring underneath looked right and it ran great, as it did today until it backfired during a long backroad balance point wheelie in first gear. At that point the front end came to the ground, the engine was dead, and I was stranded. It's has no spark, so now I have to find out why. If I can find my manual (Honda's are so reliable a shop manual is an easy thing to misplace as it's so seldom used) I'll try to check out the coils with an ohm meter and go from there. If any one knows the specs in the mean time it would be appreciated.

Ford

try jetting it richer. i'd put new plug in too, even if they look good

Ford

stator? plug wires grounding to block?

Schwartz

I had a wire come loose on my ignition switch (Key Switch) might want to check that. Sounds like your going to right direction with electrical problem. Jetting problems usually come on more gradual. Let us know what you find.

GSE Nick

hey bro check the wires where the fuses are ive had to bypass three already from harness they seemed to just come lose from the harness. also theres a little black box hooked to the back side of your gauges. its looks like a relay box but its not if it gets hit to hard it kills the bike. its there in case the bike gets wrecked it kills all motor and every thing. i just unpuged mine. the box prob isnt the prob but take it off anyway. id say its gotta be eletical

Schwartz

You don't know!
LOL

GSE Nick

hahaha sometimes i just like to hear myself

Six Eight Nate

Ignition coil Primary Peak voltage test:
MINIMUM peak voltage reading of 100 volts...all readings that vary AND exceed at LEAST 100 volts are acceptable

Ignition pulse generator Peak Voltage Test:
MINIMUM peak voltage reading of .07 volts

Now here's a couple classic known wiring issues for these models that will short your bike out:
(1)Three wires running from your generator/stator to your voltage regulator are known to melt together during hard use meaning these bikes like to be moving and during stunts they do not circulate enough are, these wires are known to melt together which will create a drain on your ignition and cause intermittent (sp) poor running and actual spark failure...check these wires and if they are melting together, replace them entirely with heavy guage well insulated wires...We ussually run them seperately from eachother now zip tying them off and allowing them to breath better and not jump or arc to eachother...
(2)At the ignition switch itself (as brother schwartz mentioned)...these wires can come loose and/or melt together...check and repair as necessary
(3) Known melting issues at the various plugs located in your right inner faring between the upper and the inner...remove the upper/frame cover that indicates fuse box and check at and around all connections...typically these last two issues also will cause intermittant headlight function and blinker issues....all of these wiring issues can be quick fixed with some zip ties and electrical tape, but they will come up again later...for a more permanent fix, replace wiring sections with heavy guage wire and use heat shrink and solder to repair...i also ussually re-route and zip zip to safe points, any wires and or relays that are being over-stressed with heat

don't worry...we'll get through this

Bill McMahon

Thanks for all the help gentlemen, it turned out to be one of the connectors had worked it's way back out of the harness on the plug for the ignition. I pushed it back up there, taped the wire liberally with electrical tape, and all is good.

GSE Nick

see i told ya u gotta keep an eye on those harnesses there goofy on the nines for some reason.


i guess schwartz was prob the closest with the help though