RG500 MPG

Simon wrote:

Hi Al
My bike is running LG filters and 220 main jets, I reckon on around 100 miles before it goes onto reserve. To be honest that seems very similar to what it was like on std jetting. (more difficult to start though) Certainly the figure of 25mpg is according to the press considered around average for an RG, frugal they are not! When you add in the cost of goodish two stroke oil (say £8 a litre for around 500miles (?)) you reach a running cost best > not calculated.......Lets face it the thing is a GP rep though so what should we expect!?

I had an interesting experience just recently with my RG. After running the same std. bore cyls for over 50,000 kms (with several sets of pistons), I decided to build a new motor with the same performance work and fresh 0.5mm overbore. I started with another set of cases and went from there, not using anything from the previous motor but the carbs. When I installed the new motor I also repainted my TC pipes and fixed a lot of small stuff that had been neglected (brake light, throttle cable, etc.). After a tank of gas for break-in, I felt that the throttle response was a little lethargic. FIrst thing I did was a complete carb sync.

Next I tried some different carb settings and here's what I found out: Several years ago I installed some 27.5 pilots (for use with carbs which I bored to 31mm) or so I thought. I was out of the 27's at the time so I drilled some 22.5's to the first size drill bit that wouldn't pass through the Mikuni 27.5 pilot. This turned out to be slightly richer than a std. 27.5. I now have the correct 27.5 pilot jets.

Next I set the float height to 17mm from the gasket (18mm from the gasket surface) While I had the bowls off, I decided to try 230 mains in place of the 240's that I had run in California.

Then I turned to the needle setting. I had slightly raised the needle to compensate for the 31mm offset carb bore. I now reversed this back to the stock (#2 clip with nylon washer underneath) position, thereby lowering the needle 1/3 of a clip. With these changes (and a good carb sync and filter cleaning) I then rode the bike on 6 occasions and for 3 tanks of gas. What a difference! Whereas before my bike had always been slow to warm up and would not allow driving off too soon without fouling a plug, it now starts easily and can be driven away in less than a minute. I had marveled before how Rocky's RG (using the same 31mm bored carbs and filter kit) could be so user friendly and drive off several minutes before mine without ever fouling a plug. Now mine behaves the same way. Amazing! But the best was yet to come.

For many years and many kms my bike had consistently averaged 180 kms before going on reserve (110 miles) while in this state of tune. Now the mileage is MUCH better! My 3 tanks of fuel went onto reserve at 249, 246 and 230 kms! Plenty of spirited sport riding was done on all 3 tanks with a little more rowdy behavior on the last one. On tank 2 my total mileage was 310kms at which time it took 5.5 U.S. gallons to refill. I suspect that a little of this improvement can be attributed to having a fresh motor but the majority is from the improved carb tuning for my particular motor.

Throttle response is crisp and instantaneous with no hesitation, particularly in the mid-range. I think that my plug fouling days are behind me as well. The point of all this is to emphasize the importance of proper carb setup, regardless of whether you have stock or modified machines. It's been a real eye-opener for me and I can't wait to ride my bike again!
- Rick