98 CBR600F3 runs rough and loses RPMs

[Qu1ck]

Background: Bought my 1998 Honda CBR600 F3 in October 2005. Had local Honda dealer give it a tune up that 1st month in response to problems starting it. I’m not mechanically inclined so for upkeep I keep it keep it clean and waxed, with proper oil changes and chain lubrication. I put over 4000 problem-free miles on her last year before storing her for the winter with a proper dose of Sta-Bil in her tank.

Problem: Although it runs, shifts, sounds and responds fine during short (less than 6 mi) trips around town -- on longer rides after a while in 5th gear at highway speeds the engine will all of a sudden start to run rough (become noticeably noisier, sputter and hesitate) as engine RPMs and speed drop even while I’m opening up the throttle in an attempt to maintain speed; but to no avail. Then, as I pull over and downshift to 3rd or 2nd gear I’ve sometimes gotten near-normal throttle response and have limped home at 35-45 mph. This happened to me on my first ride this spring, then not at all on the next handful of longer rides. Recently it has happened on each of my last 4 longer rides at highway speeds. Yesterday on a new tank of gas the engine actually stalled on me as I coasted to a stop on the shoulder. I let it sit a minute or 2. Then it didn’t re-start until my 3rd attempt when I gave it full choke. Then the engine continued to ride rough and noisier during my 12 mile trip back home in 3rd or 4th gear although revving in neutral at stop lights seemed nominal from the standpoint of engine noise.

Can’t figure out why the problem always manifests itself when I’ve been at highway speeds for a good while – except for the fact that I do spend more time in 5th gear than any other gear during my usual rural fun rides. I’m stumped and fear major repair costs involved with a lot of trial and error efforts to find the real culprit.

Do any of y’all have any theories that match my observables? The problem seems to be getting worse. Thanx!

[CBRBob]

Could be so many things but here are a few simple ones......
Check the fuel tank vent, make sure the hose is not kinked and clear.
Bad gas.
An over-oiled K&N air filter.
A bad igniter.

[IrocRob]

It's a bit tough to guess through a website, but
it may be time to replace the inline fuel filter.
What you describe sounds to me as if the fuel filter is getting clogged
by crap building up in the filter and that is reducing the fuel flow.

[Qu1ck]

thanx for your suggestions -- will check 'em out soon and let you know what it was -- hopefully.

[High_Revs_17]

Originally Posted by IrocRob

it may be time to replace the inline fuel filter.
What you describe sounds to me as if the fuel filter is getting clogged
by crap building up in the filter and that is reducing the fuel flow.

My first thoughts as well Rob.

Qu1ck, keep in mind there might be more than one fuel filter for that bike so check the repair/service manual and replace and/or clean any/all fuel filter(s) accordingly and start from there.

Also it might be a ingnition issue, it seems you're mehcanically inclined enough to do standard tune-up work on the bike so when you pull the tank to check the fuel filter also inspect the ingnition wires to the plugs and also pull and inspect the spark plugs, if either item is fouled it could cause issues. Regarding the bikes age it wouldn't be a bad idea just to replace them as well, so once that's done you'll have the fuel and spark issues partly cleared of the diagnosis.

FYI: When replacing the plugs be sure to get the same plug recommened from the owner's manual, who knows what plugs are sitting in there now, they might be the wrong one's being hot plugs or miss-gapped, also be sure they're properly gapped when you put the new one's in.

[Cakes206]

Would a regulator/rectifier thats going bad cause this?

[Rev]

Originally Posted by Cakes982

Would a regulator/rectifier thats going bad cause this?

Actually yes...a buddy of ours had the same exact problem sputtering..even shutting off at times and when he would spin his throttle it would not go anywhere but drop speed and you see the rpm's dropping pretty harsh. That was one of the parts he had to change...He also had an f3

[ezpunkx]

If you havent done so yet, replace the plugs and fuel filter. It could definitly be the regulator/rect. I think my F2 was having similar problems untill i replaced it. Maybe find a place that will let you return it. If the bike still has the problem after using a new regulator, send it back, or sell it on EBAY.

[Qu1ck]

Hey, I'm back. My troubleshooting recently resumed after regaining use of my opposable right thumb -- I broke it in 2 places in an ATV mishap in mid-August. Anyhoo, the problem degraded such that I couldn't even ride the CBR600F3 around the block without it starting to sputter and die. I then failed in an attempt ro remove the fuel tank -- but I did manage to raise it up a few inches and peer underneath. In the process I jiggled and straightened out the tank vent tube before bolting the fuel tank back in place. Since then the bike has operated as good as new on every ride, short or long. My guess is that I unwittingly unkinked a kink in that vent tube. [Good call CBRBob.] Life is good again -- yet I still wonder if the Big Guy Upstairs is just setting me up for a big disappointment.
Thanx again for all the suggestions. I'll retain them for future referrence.

[Cakes206]

Sux about the thumb man...glad you figured out the issue