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Phillip H
Phillip H, ASE Certified Technician
Category: Motorcycle
Satisfied Customers: 514
Experience:  Vehicle Technician at Richmond Motor Services
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Honda. CBR 900RR 1998.Starts fine,after approximately 5mins

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Honda. CBR 900RR 1998.Starts fine,after approximately 5mins under load it starts misfiring? Please any ideas
JA: How many miles are on the car? Is it a steady misfire? Or random?
Customer: It’s a motorcycle,70000mls,steady misfire.
JA: What is the model of your '98 Honda?
Customer: Cbr900rr Fireblade
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: Yes myself.Charging system checked.Regulator/Rectifire checked.All cylinders firing on start up and idle.
JA: Anything else you want the Mechanic to know before I connect you?
Customer: Air and oil filter changed in the last 100mls.

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Customer: replied 1 year ago.
Disappointed with first question!!!


With your misfire it suggests that something is breaking down as it gets hot.

As items warm up in electrical circuits the resistance changes and this is what I suspect is happening.

I would start by checking the Spark Plugs and the High Tension Leads or Coil Packs whichever your engine has fitted!

When you remove a plug you might notice some short black lines down the side of the plug. This is an indication that the HT Lead / Coil Pack is tracking down the side of the plug which will cause a misfire. You would have to renew these if this is the problem or try some dielectric grease down the lead!

If there is no fault with the Igniiton System it could be misfireing due to a faulty fuel injector if the engine iis an injected version. Again the only option would be a relacment injector.



Customer: replied 1 year ago.
Thanks,I recently changed the air filter and had to remove the petrol tank and air box etc.Would a split or damaged vacuum hose cause such an issue?.The bike is a inline 4cyl,carburettor fed system.
Customer: replied 1 year ago.
The engine runs fine up to normal operation temperature.Its when you begin to ride/load the engine it begins to misfire/bog down


A split vacuum hose would certainly give you running problems. It wouldn't necessarily be a misfire. You would more likely get poor running, maybe a lack of acceleration escpecially on an engibe with a vacuum advance system for the ignition.

Again if you had a blocked jet on the carburettor it will cause poor running under load/acceleration.



Phillip H, ASE Certified Technician
Category: Motorcycle
Satisfied Customers: 514
Experience: Vehicle Technician at Richmond Motor Services
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