Reader Question: GL650 Jetting?

Here’s the latest reader question, along with my reply!

Leonard asks: I watched your videos and read your article on up-jetting your GL650. I’m getting ready to overhaul my carbs and was wondering how your’s has been working. Are you still happy with the modification and have there been any ill-effects from the up-jetting? Has the fuel mileage suffered any?

My reply: I’m very happy with the re-jetting – richer – which was was necessary because the fuel generally available today is leaner than the fuel this bike’s engine was designed for.

Which fuel was 100 percent gasoline.

The fuel generally available today is 90 percent gasoline – and 10 percent ethanol. This leans out the A/F ratio, which has to be mechanically compensated for by replacing the factory jets with larger ones. (Modern fuel-injected/computer-controlled vehicles automatically adjust the A/F ratio.)

Re-jetting to  correct for a lean condition is particularly important if the engine is air-cooled (our GLs are of course water-cooled) because the engine will run hotter if the mixture is lean.

The bike – or car – will also run better. Mine starts more easily and throttle response/power is noticeably better.

I did notice a slight mileage dip – but that’s to be expected because the 90 percent “gas” contains less energy than 100 percent gas, so you have to burn more to go a given distance.

My main concern, though – and probably yours as well – is tuning the bike so it’s running optimally, which will increase its longevity.

I plan to keep my GL650 as long as I can; it’s one of the best bikes I have ever owned and the one I pick to ride the most often.

The upjetting is a simple job on this bike; you don’t even have to pull the carbs. Just drop the fuel bowls. Both carbs are easily accessible. And the jets are readily available at your local Honda store – another great thing about Honda bikes. You can almost always get parts, even for a bike pushing 40 years old!

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