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Message started by miatamarty on 07/08/23 at 17:57:34

Title: MPG ?
Post by miatamarty on 07/08/23 at 17:57:34

I'm a new owner of a 2003 with a Blue Collar Bobber kit. The previous owner got rid of the air box and did the small battery under the swing arm. There is Harley muffler on there with the bracket that matches with the stock mounting bracket. It's a stock carb with 155 main jet, a 50 pilot jet, idle mixture screw is 2 1/2 turns out. white washer on needle is changed but I can't understand his notes. I think he took it out or changed its position. I have a nice throttle response, no big back fires on trailing throttle, and a nice idle. He set this carb up a basically sea level. Live at 4200ft and cruise up to 7500ft at Crater Lake. I've put about 300 miles on it so far. The gas mileage is right around 46mpg. No town riding just 55 to 65mph cruising. Is this ok or is it possibly running rich because the altitude. 100 mile range is a bit short for me.

Title: Re: MPG ?
Post by DragBikeMike on 07/08/23 at 19:13:45

Your up pretty high, so it doesn't surprise me that you are only getting 46 mpg. You could try adding a washer over the spacer to lower the needle about 0.5mm. The compression is very low, so in stock configuration these engines aren't very fuel efficient.

Title: Re: MPG ?
Post by Dave on 07/09/23 at 04:14:50

Alto that main jet sounds waaaaaay big.

At my elevation of 500-800 msl a 150 main jet works best....with the stock engine and air cleaner. And the needle works best with 3 washer installed instead of the white spacer (steel #5 machine screw washers).

If you don't get burbles or backfires out the exhaust with a trailing throttle I suspect you are running rich.

Title: Re: MPG ?
Post by LANCER on 07/09/23 at 04:30:15

Your main jet (155) is too large for 4-7.5k’ altitude. Drop it to a 150 main jet and see if that doesn’t help your mileage and power in the higher throttle range.
Are there any washers in the carb that replaced the white spacer?. When the previous owner removed the white spacer he hopefully installed 2 or 3 washers in its place.

Title: Re: MPG ?
Post by miatamarty on 07/09/23 at 06:20:03

Thanks for the suggestions. Where to go for main jets? Should I do main jet first see how it goes then possibly try different needle adjustment? I usually only like to make one change nat a time.

Title: Re: MPG ?
Post by miatamarty on 07/09/23 at 06:39:54

Just read the PO notes again. He has 1/2 a white washer for the needle. I'm thinking he means he has washers that are the equivalent . f 2-3 washers Looks like I have a fun Sunday afternoon project.

Title: Re: MPG ?
Post by justin_o_guy2 on 07/09/23 at 13:20:25

Some people ground their washer down.

Title: Re: MPG ?
Post by Tocsik on 07/09/23 at 18:17:46

I average about 52 and live in Denver at 5280 feet. I actually get better mpg on my mountain rides, like today, where I was at about 8500 feet. I get closer to 60 on those days.

Title: Re: MPG ?
Post by miatamarty on 07/19/23 at 14:41:13

Last gas tank was 43mpg. I tried adjusting air fuel mixture. It was 2 1/2 turns out. I screwed it all the way in. The engine did not stall. Shouldn't it? I screwed it out 11/2 turns. The idle was good and steady. At 2 turns out the idle started to stumble. As an experiment I screwed it all the way in then1/2 turn out to eliminate small backfires on trailing throttle from higher rpms. Gas mileage this time was 45mpg. What has the most effect on gas mileage? Needle position, main jet, or pilot jet. I'm at 4200ft elevation. Again main is 155, pilot is 50, and needle has 1/2 of white spacer.

Title: Re: MPG ?
Post by verslagen1 on 07/19/23 at 15:56:09

sounds like your pilot jet is too big.

Title: Re: MPG ?
Post by ohiomoto on 07/19/23 at 17:25:13

It's been pointed out here before but you seem to have ignored the advice.
The main jet is way too big. Try running stock jetting or even leaner at those elevations.

Title: Re: MPG ?
Post by miatamarty on 07/19/23 at 17:40:44

Just PM'd Lance for jet kit. I'm, unfortunately, an instant gratification kinda guy. I was hoping for a miracle by twisting a screw. Not to be.

Title: Re: MPG ?
Post by Dave on 07/20/23 at 03:40:02

66626A7F6A666A797F720B0 wrote:

I tried adjusting air fuel mixture. It was 2 1/2 turns out. I screwed it all the way in. The engine did not stall. Shouldn't it?

If you left your idle speed up around 1,100 rpm - the idle fuel screw will not have enough effect on the engine to cause it to stall. At a fast idle there is enough vacuum to raise the slide a bit - and that will allow some fuel/air to flow out of the needle jet. To properly adjust the idle mixture you need to have the engine fully warmed up, and then lower the idle speed down to around 800rpm. Then when you are finished adjust the idle speed back to 1,100-1,200 rpm.

Title: Re: MPG ?
Post by Dave on 07/20/23 at 03:59:33

6A6E6673666A6675737E070 wrote:

As an experiment I screwed it all the way in then1/2 turn out to eliminate small backfires on trailing throttle from higher rpms. Gas mileage this time was 45mpg. What has the most effect on gas mileage? Needle position, main jet, or pilot jet. I'm at 4200ft elevation. Again main is 155, pilot is 50, and needle has 1/2 of white spacer.

The pilot jet has little or no affect on mileage. Nobody rides slow enough to be using the pilot jet as the main source of fuel/air while riding.

The fuel mileage while you ride is dependent a lot on how you ride. If you ride at 70mph and are using 3/4 throttle or more all the time, then the main jet is likely controlling the majority of the fuel flow. If you ride 1/3-1/2 throttle the majority of the time the needle position is likely contributing to your mpg and performance.

Jetting for how your engine runs with the throttle open is more important than jetting to eliminate backfires when you close the throttle. Closing the throttle while slowing down or while shifting gears causes the slide to drop and the needle to close most of the fuel flow from the needle jet....and this causes the mixture to do lean as the majority of the fuel is provided by the idle circuit. If you make your idle circuit richer to reduce or eliminate the exhaust popping - your engine will be running rich when you are idling or opening the throttle. If you learn to roll the throttle slightly open when the noise begins you can ride quietly while still having the engine jetted correctly Roll the throttle open only enough to reduce the noise - not enough to cause the bike to accelerate.

A 155 main js just tooooo big for the elevation where you ride, and you may even require a #47.5 pilot jet. An engine that is too rich can run smoothly and seem just fine - but when you get it running at a proper mixture you will be surprised how much crisper and more responsive the engine is. When jetted properly you should feel the bike idle a little slower and feel a bit of a lean surge for a few minutes as the engine warms up.....if the bike runs smoothly when cold it is likely jetted too rich.

Title: Re: MPG ?
Post by Gary_in_NJ on 07/20/23 at 10:54:23

Jetting is adjusted for best throttle response, not fuel mileage. How's the throttle response? Of course, leaning the jetting could improve throttle response - jetting is always an iterative process settling on the best compromise.

Title: Re: MPG ?
Post by miatamarty on 07/28/23 at 12:06:24

I changed out the main jet to 145 and the pilot to 47.5. Gas mileage was 47mpg. A little better. Was cruising at 65mph for 74 miles on mostly flat roads. I'm thinking I will have to change the needle position next. Presently has half of the white spacer. Will pick up some #4 washers. I'm thinking 3 washers to lean it out. Throttle response is ok with hardly any back fires.

Title: Re: MPG ?
Post by ohiomoto on 07/28/23 at 14:05:27

33373F2A3F333F2C2A275E0 wrote:

-----------------

Given your elevation, I would try a full spacer and you maybe try jetting even leaner. Or just leave it if you feel like the bike performs well enough (it's not like these bikes are fast anyway).

I think I'm running the same jetting. I may have gone up to a 147 on the main. My riding is between 500 and 1100 ft. I get around the same MPG, high-40s to low-50s. My bike runs pretty well from the low-40s to the low-80s. When it gets really hot and humid, it starts to run rich, especially on top.

It had a 55/155 combo when I got the bike it was a turd. It struggled to go much past 70 mph when it was warm out. I hardly ever ride over 65 mph, t pulls pretty strong to 85 mph now. Not bad considering my 6'3", 265 lb size.

Title: Re: MPG ?
Post by miatamarty on 08/01/23 at 14:20:48

Hallelujah! Latest gas tank was 57mpg. I put 2 washers on top of 1/2 of a white washer. Throttle response is great. I guess I was cruising mostly on the needle even at 60-65mph. That was a huge improvement.