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Louie, Technician
Category: Motorcycle
Satisfied Customers: 11442
Experience:  25+ yrs. experience
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I have a 2002 Honda cbr f4i and I changed spark plugs.

Customer Question

I have a 2002 Honda cbr f4i and I changed spark plugs. Because I was getting horrible gas mileage. Now my catalytic converter is glowing red hot. What is going on?
Submitted: 30 days ago.
Category: Motorcycle
Expert:  Louie replied 29 days ago.

Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, please click HERE. Using the diagram, please post back which particular part is "...glowing red hot..."

Additionally, post back with the burn colors of the old sparkplugs.

Customer: replied 29 days ago.
Little circular area Right after 02 sensor
Customer: replied 29 days ago.
Could it be fuel pressure regulator
Expert:  Louie replied 29 days ago.

For any part of the exhaust to glow red would almost always point to an incorrect fuel mix.

With the engine off, is that portion turning gold or blue ?

Customer: replied 29 days ago.
gold a blueish
Customer: replied 29 days ago.
Vacuum line 1 is not closed off
Expert:  Louie replied 29 days ago.

It should be closed as it would offset the air/fuel mix of cylinder 1 and would affect also the others particularly when idling.

Normally, rurning Gold would point to a slightly rich fuel mix while blue would be lean.

Customer: replied 29 days ago.
It was not glowing before I changed plugs but gas mileage was horrible
Expert:  Louie replied 29 days ago.

A likely possibility is that #1 sparkplug was not firing (cleanly) before hence the vacuum leak has no (heating) effect but of course would cause very poor fuel consumption since running (efficiently) on only 3 cylinders.

Customer: replied 29 days ago.
closing off the 1 vacuum and getting fpr should correct it
Expert:  Louie replied 29 days ago.

Yes on the closing of the vacuum (leak).

And it would help to determine the burn color of the sparkplug tips as it would point to whether the mix is rich, lean or correct.

Sorry, but "...getting fpr..." ?

Customer: replied 29 days ago.
Fuel pressure regulator. I changed spark plugs because bad gas mileage and forgot to close 1 vacuum line off.
Expert:  Louie replied 29 days ago.

Hold the fuel pressure regulator but yes on closing the vacuum leak.

Observe the F4i for a couple of days and then check the burn color of the spark plug tip. If:

  • brownish, then just about right and mileage may have already improved;
  • very light brown to whitish, then lean and/or possibly an air leak;
  • black, then rich.
Customer: replied 29 days ago.
OK thanks slot it's a project bike but only has 9000 miles. You have been a big help. On last question do these bikes have catalytic converters like cars. If so can it get clogged
Expert:  Louie replied 29 days ago.

To my knowledge no; well not exactly catalytic converters on 2002 models but rather a closed loop since it has an O2 sensor.