Missing at high revs?

[Taipan]

Hi All,

My 03 twin spark Rockster has a problem, which I wrongly thought was TB balance.

The bike seems to have a lot of initial go, but then it sort of fades if you snap the throttle wide open?

At just past 5k there is a definite problem, its almost a misfire. It then tries to clear between 5.5 - 6k , but then dips again? You can really hear the bike struggling at these revs and feel the power delivery jumping about? Best way I can think of describing it is, its like when I put too larger main jet in my KTM. It would run but wouldn't pull high revs properly. if you've re-jetted a carb'ed bike before and run too bigger MJ you may know what I mean by this?

Bike is fitted with a Y piece and Remus (removable baffle in). Apart from that its standard. Removing the baffle doesn't help. Any ideas or has anyone come across this before?

Many thanks.

[darthrider]

How many miles?
How many miles on the plugs?
Air cleaner clean?
Possibly have water in the gas?

[Taipan]

How many miles?
How many miles on the plugs?
Air cleaner clean?
Possibly have water in the gas?

Hi,

The bike was serviced 600 miles ago by a dealer with a good reputation. So I assume the plugs and air cleaner are ok. It did have fuel lines replaced under waranty at the same service. Fresh gas every other day?

[darthrider]

Taipan -
I was just wondering if the bike was high total mileage or what. Some of these things can be age/miles related...like old plugs & air filter condition.
It still sounds like plugs...maybe they put the wrong type or heat range in when they did the service.
I'd check the quick-easy-cheap stuff first. It's easy to see if the plugs are the recommended type & heat range.
The air filter might take a bit longer but Cyclerob posted a tip for a quick mod to make that a lot easier.
Put a half-bottle of a good brand fuel injector cleaner in the next fill-up from a reputable brand of station with a lot of traffic (& therefore no old gas).
If nothing turns up with those things I'd take it back to the dealer and tell them what it's doing and that it started shortly after their service.
They probably won't be able to take it out for a speed-run trying to duplcate the symptoms (insurance, libaility, shop policy, etc. I never let my Techs or Svc. Mgr. take a customer bike out for a fast ride for a long list of reasons), so be prepared with a real good description. Can the symptoms be duplicated in a "speed limit" run?
What was wrong with the fuel lines that they had to replace them?

[dallara]

One thing you might check...

Make sure that they put the friggin' spark plug caps on all the way. Pull the little plug cap covers and pull the spark plug caps off, make sure there's no moisture inside, spray 'em out with contact cleaner and then push them back on and make sure they go on all the way.

Past that, check to make sure the caps are not cracked and are solidly on the spark plug leads.

I once chased a "miss" like you are talking about in the upper rev range and finaly figured out I had a cracked spark plug cap on one cylinder of a Honda four. Drove me nuts!

Good luck!

Dallara

[socalrob]

Dalara & Darth - Thanks for the tips, my twinspark 9,200 miles has been doing the exact same thing for the past couple of weeks. Hit around 5.3K RPM's under hard acceleration (in maybe 3rd or 4th) & there is actually enough of a pause in the power band to be very noticable, then power picks back up around 6.0K. Reminds me of the 2 stroke street bikes I used to ride with twitchy power bands. I've been debating to take it in or wait it out at the next service, which I'll do at about 10K miles (instead of 12K) as I do a whole lot of short trips.

[fnfalman]

Definitely sounds like a spark plug problem. My Rockster is near 9000-miles w/ the Remus Y and can. It runs just fine without a hitch. But at the 6000-miles service, the dealership found the bottom spark plugs about to crack and replaced them under warranty.

[Guest999]

You also mentioned the fuel lines being replaced - If this involved removing the tank (as it should), then they may have pinched/squeezed one of the fuel lines. Will show as similar syptoms under high rpm or high load. Reason is simple - Bike runs fine at low fuel requirements as enough gets through pinched lines, but leans off under high fuel needs. This is a regular screw-up on tank removals.

[pbenoit]

Taipan,

My 2004 Roadster just started doing the same thing and I wondered if you figured out what was causing the problem. It is very noticeable in 3rd and 4th gear under hard acceleration. My bike has 18,000 miles on the clock and I have not changed my spark plugs yet. Additionally, I accidently put 89 octane gas containing 10% ethanol during the last fill up.

[CycleRob]

Gee, So many bikes with a hesitation problem. It's like a conspiracy.

From the symptoms you describe, I'd suspect either fuel quality or fouled plug(s). About the fuel - - - If a station recently switched to Ethanol, the Alcohol will enable the gasoline to mix with any water in the underground tanks and then they sell that gas/water/alcohol mixture to you. It will not run great. Wintertime fuel formula c0cktails may also have some water pickup and combining attributes. This is the time of year when those Winter formulas come out and I wonder if gasoline has some sort of freshness standards so they can't sell you last winter's leftover fuel. The unnatural way gasoline smells today, I don't recognize it anymore. One time I noticed it smelled just like kerosene, but the bike ran OK. Have you taken a wiff of gasoline lately? It's nasty. Since many bikes everywhere are having a similar problem, I say fuel anomalies.

About the sparkplugs, they can be ruined by the conductive black sooty carbon deposits on the porcelin caused by many short trips. A frequent cold engine ride will cause the Motronic to accurately feed the engine a richer but correct mixture, greatly shortening sparkplug lifespan.

[Sinan]

Taipan,
Have you been able to solve the hesitation problem on your 03 Rockster.
I have the very same problem on my 04 R1150R and do not know what to do.
Thanks
Sinan

[iowabeakster]

hello Sinan,

this thread was started over a year ago (some of the members in the above thread left or were booted out). i see that this is your first post. so first of all welcome! feel free to start a "new topic." list your symptoms, ask your questions. people around here will be glad to give whatever advice they can.

the advice given over a year ago is still valid. Fuel quality, spark plugs, air filter are probably the best (cheapest) place to start looking.

[Sinan]

Thnaks
Sinan

[single650]

The main spark coils (The plug caps) on twin sparks can fail leaving just the secondary spark working.

Check by pulling the secondary cap off one side and see if it misses on that side, repeat. a quick and easy check

[CycleRob]

If you do any "spark tests", it should go without saying that you should NEVER-EVER open fire ANY ignition system. Open firing is when the primary, the thin wires from the bike's harness to the coil -or- the secondary (fat plugwire) is held away from it's intended connection. That means do NOT unplug the primary wire from the coil where the primary voltage isn't connected to the coil, and run the engine. To test this type system, plug a spare sparkplug into the connected coil/cap and securely mount it to a grounded surface like a bolt head. I should emphasize securely connected, as the engine's vibration will jar it loose and you'll then be open firing the system. The R1150R cylinder fins are not a good ground as they're painted. You also must not ground the disconnected thin primary wire either or the ground's zero resistance path can damage the electronic's power transistors.

Do NOT unplug the hi-volt sparkplug cap and let it hang free where it's spark energy cannot go to ground. Doing so creates an inductive kick back into the primary circuit and/or force the spark energy to try and jump the coil tower to ground or internally thru the coil's imperfect insulation to the internal primary circuit. 40,000 volts to the primary (computer) circuit is a bad thing. Use the same hard-grounded spare sparkplug routine like above.

Testers may have gotten away with open firing their ignition system, but knowing what's happening, I would not ask for expensive trouble like that.

That was a lot of DO NOT's, but unless you want to buy expensive new parts, you should learn and understand the only correct way to perform these shadetree mechanic's tests -OR- you DO NOT do the tests.

Test away!