AFR at steady cruise?

[guest]

Mike, I have a carbed flht with 95inch flat tops and tw21 cams. It is running very good but I feel I should be getting a little better gas milage. The afr is pretty much flat line 13.2 at wot with only a bobble from2200-2400 where it goes to 14. I am running 48 slow jet and 190 main with a woods kt1 needle. My question is will a 185 main help milage and/or will it have much effect on messing up my near perfect wot afr? My dyno operator said you really can not do a steady cruise afr on a carb. elevation is about 3200 feet. Iwill try and attach a copy of the dyno graph. thanks guest

[Mike]

If the dyno is equiped with load control and an afr meter, you can do steady state simulations on carb bikes. You cannot, however, graph a steady state test. But you can use the info to tune for fuel milage. Changing the main will not affect milage and will affect WOT (only thing shown on dyno graphs). To do a steady state, apply approx a 25% load to the load control cell and run the bike at mph's you would normally cruise in, holding the throttle steady. While doing so, simply observe the AFR readings and decide if a leaner needle setting can be used. You can run as lean as 14.7 under these conditions. You can also vary the load to test different throttle openings for the same mph's as when climbing hills. The higher the load, the steeper the simulated hill. This allows you to make sure changes to one area do not adversly affect another. Ideally, as the load and throttle opening increases, the AFR would decrease progressively to 13.2. Remember, what you are trying to do is simulate and duplicate what is actually happening while riding. This includes load, throttle opening and mph. The needle will have the largest effect on milage, with the low speed jet next and then the accelerator pump. The main can have an effect but you want it to be best for WOT, so this dictates it's size.
Thanks, Mike

[guest]

Mike, thank you for sharing your knowledge. What would you consider normal mpg at steady 65mph for an ElectraGlide with the above numbers. My bike runs really well and has smooth throttle transions whether on or off the throttle and at any speed. Maybe I should leave well enough alone. Does the graph look like what you would expect on a dyno250i? thanks for your opinion.

[Mike]

The AFR line at WOT is actually really good for a carb bike. The numbers are pretty much what I would tell a customer to expect. We use STD corrections which will give slightly higher numbers. The reasons for this are explained in our dyno library notes. The correction for your SAE is pretty high at 1.12 (we typ see .98-1.02) so I assume conditions and air density altitude were poor. Also, I assume you are aware that 250i dyno's read lower than the older 250 models since you noted that your chart is from a 250i, so numbers between them should not be compared (but the shape of the curves can be compared). Your torque curve is very good and should feel so from the saddle. We tell our customers to expect 40-44 mpg under ideal cruise conditions (see our notes about fuel milage on this web site). With EFI bikes, we are able to get slightly better milage in some cases.
Thanks, Mike