Hey MM, I was thinking of you and this thread when I fueled up the other day. I had gone 120 miles and it took 2.14 gallons giving me basically 56mpg. The Honda 1100 generally give me around 45mpg. Maybe someday I'll a get a newer fuel injected bike.

MM:

The Pilot Jet (small one) has very little affect on fuel mileage - it mostly controls the mixture at idle.  Once you start to open the throttle the needle and needle jet are adding fuel as the slide rises.  By the time you have 1/4 throttle the pilot jet no longer has any affect.

The Main Jet controls the mixture once you start to get over 3/4 throttle and is in complete control of the fuel mixture at full throttle.  There are times I go on a ride and never use the main jet the entire day - as the local twisty roads limit the speed to about 50 mph and that is 1/2 throttle on my bike.

Unless you ride at full throttle a lot - the majority of the fuel mixture and mpg is controlled by the position of the needle.  The needle has control of the mixture from 1/4 to 3/4 throttle - which is likely where you spend most of your time riding.

To choose a Pilot Jet (small one) - adjust the idle speed down below the normal 1,100 rpm to around 800 rpm.......you do this so he slide drops and it is not adding extra fuel through the needle jet.  Then adjust the fuel/air screw to achieve the smoothest idle - if you can turn the fuel screw all the way in and the engine still runs, the jet is too big.  If you have to turn the screw more than 2.5 turns out, the jet is too small. (The taper in the screw stops adding fuel when it is 3 turns out - so you should not open it more than 3 full turns).  Once you have a jet that provides a smooth idle at between 1.5 - 2.5 turns out - you have the correct size pilot jet......the range of jets that works in a properly set up carb are between #47.5 - #52.5.  When you have the proper jet size chosen - turn up your idle speed to 1,100 rpm and rejoice in having that job done.....as you won't have to fuss with it again.  Changing air filters or mufflers have very little affect on the Pilot Circuit and you likely will never need to change the Pilot Jet again....however you may have to clean it someday as the holes are very small and get clogged up easily).

The next step is to choose a main jet.  This is done by finding a nice long straight section of road......a steep uphill helps to limit your speed while still getting a good indication of how the bike runs at full throttle.  I start with a #150 jet and go from there.  Choosing a proper main jet is the hardest part for me - as it includes "listening" and you really need to pay attention to how the bike responds.  I ride with the #150 and see how the bike runs at full throttle - the engine should be pulling strongly and the exhaust note should be "crisp"......not with a "burble"  (See....I told you this wasn't easy).  Once the engine is pulling hard and you are going pretty fast.....start to roll off the throttle a tiny amount....and listen/feel what the bike does - if you hear the exhaust note become more crisp and you feel like the bike begins to accelerate a little bit - that is an indication the fuel mixture is too rich at full throttle.  Then you need to repeat the procedure with a different size jet and see if the performance improves or declines.  DragBikeMike has a tachometer and uses time runs between 2 or 3 thousand rpm to see if the performance improves.  You could do the same between 40 and 70 mph on the same section of road.  I normally put in other jets and find the place where I know it is too rich by the obvious blubbering sound the engine makes.....and the place where I know it is too lean by the surging and uneven acceleration that occurs when the engine is too lean - then I know for sure the range somewhere in between where the proper jet is.  This Main jet can be affected by air cleaner and muffler choices - however I thing a reasonable range is between #147.5 to #152.5......a #155 is likely too rich unless you have made some wild changes in the intake/exhaust.

The needle is pretty easy to select - even though it is a bit of a pain to get to and make changes.  For a needle without the multiple positions for the clip - I remove the white plastic spacer and use 3 machine screw washers (I believe they are #4 size -but don't get brass ones as the OD is too big to fit in the slide).  If you have a needle with multiple positions for the clip, you start with the middle position and work up/down depending on how the bike runs.  When the mixture is correct you can get smooth acceleration at low throttle once the engine is fully warmed up.........you likely have the proper fuel mixture if you can feel the bike surge a little bit under light throttle settings while the engine is cold.  When my engine was stock the bike would not accelerate smoothy with 3 washers.....changing the Main jet did nothing - to correct the surging at low throttle I remove 1 washer and it ran great with 2 washers - however most of the carbs I have adjusted ran fine with 3 washers.  If the bike runs smoothly while cold with 3 washers.....then add another and try 4 - you should feel a slight surge on a cold engine if the mixture is proper (if the engine runs smooth while cold the mixture is likely too rich for the best fuel mileage).

Wow Dave  

Right away I see that the needle on the DR200 needs to be raised a notch !   Thanks for the diagram !  

Yea , it has a dead spot (when 1/2 warm or cold) about time its moving into the "Needle" range .   The higher speeds are just fine.
............

Getting back to the LS650 ,    that restricts noise....and flow!  I don't think so , the DB killer's most restrictive area is a "1-inch" pipe about "<1-inche" long before the first exit hole and its at the end of the muffler where the gasses have cooled off/shrank and quit pulsing as much as they are going too.  I'm not sure that is a problem being the inside header pipe is only 1.4-ish to begin with up on the hot/pulsing end of things ..
 
I could move the obstruction to the middle of the pipe (or anywhere back up stream) ... but the gasses are still hot and expanded back toward the head pipe.
The pipe has plenty of room inside (1.75) and 3" dia outside.  

So the exaust is going from the head pipe (Pulsating - high pressure zone) to the muffler (Steadying - low pressure expansion zone a foot and a half long)  , then to a (Smooth/Steady - medium pressure zone) at the exit.
I don't see any restriction in the set up at all .  

Moving the solid divider to the middle of the pipe is where I was 10 muffler designs ago.  I've learned better but , it does have more of a quieting effect on the system , but I'm going lower pressure after the head pipe now.    I think you missed the part where hot gasses need more room than Cooler gasses , then there is the pulsing vs smooth flow thing too.

You recon a lack of back pressure hurts MPG do ya ?   That might be the low mpg problem I'm having more so than anything else we have come up with ! ...   Seem like I saw a U-tube to that effect one time ?
I'm not having lack of power problems at all !  

Why is exhaust velocity so important?  

https://www.gomog.com/allmorgan/exhaustbackpressure.html

I've got good scavenging in the 4 to 5K rpm now , I normally ride below that area or right at the bottom of it.  



I was surprised to see the 5 rings and the lack of taper on the needle ?

Some times I can't help but wonder if a narrower windshield  might be the ticket to better MPG .  

MM, bike is looking good. Had not seen your hard bags. Nice.

Dave is the expert on all that technical stuff and I would probably follow his advise. I will admit though as you well know, I have never had a windshield or saddle bags on the S-40. Just my fat self!

I shamed him into eating the spaghetti I made.
He ate a bit and quit. I wasn't having that. I asked him if I stopped by,needing an overnight place in a journey if he would resent me in his house and eating the food he fixed for me.
No..

Okay, then enjoy!

Maybe my spaghetti sauce got him.
????????

JOG, that spaghetti was pretty darn good and I was hungry. Thanks.

I guess fat is a relative term. Being the extremely tall man that I am (5'7") and only pushing around 195 lbs., yeah, maybe I should consider myself thin.

Can't stop laughing. Seriously, I would like to get back below 185 lbs and preferably below 180. I just love to eat!!!

You are a good role model there Lancer. That is what I am hoping to do. I have not been in the 170's since my early forties. I'm doing much better during the day. It's the night time at home where I just can't seem to resist snacking. Even if it is a healthy snack it is still additional calories. Working on it though!

Guzzi sure made some UGLY Bikes back in 1997 !  

I believe the 1100cc motor was a gas hog !!   Besides being ugly those are "Way too HEAVY for me" at this time in life .  Really , I never have liked those "HEAVY" bikes , they just don't seem like "BIKES" !   Heck , I had a 1200 Sportster durning my prime ridding years and couldn't make it keep up with the little Suzuki Savages !  

So , I've got a 250 pounder , a 380 pounder , and a 420 pounder and like them all .  

Dave you need another bike one with nice firm stand-up cylinder heads .

Hay Dave , This little DR200 is "FUN"  ,  and its got 3.4 gallons !
I'm thinking on replacing the 18 year old tires on it.  They aren't wore out  (2Kmiles on them" .    
I'm looking at these :Shinko 705's
https://www.ebay.com/itm/373420257817?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p...

You get the DR650 and I'll trade with ya if ya don't like it.