Gas Mileage Question

[Chaharly]

Hey yall. My venture has been getting about 35-37 mpg consistently, but I KNOW I can do much better. I also know that I have holes in all of my diaphragms. I know with the vacuum leaks I really can't accurately set the carb tuning, so my question is. If I replace the carb diaphragms will I see a significant increase in mileage?

[Flyinfool]

My 88 with good diaphragms gets 38-40 mpg with my style of driving.

Changing the diaphragms will make the bike run better and get better throttle response which the fun factor will reduce mileage but then the engine running better will get you better mileage. How these two mix is kind of up to you.

 

I would change the diaphragms before doing any kind of tuning or adjustments. Just a few tiny pin holes does make a big difference.

[Chaharly]

My 88 with good diaphragms gets 38-40 mpg with my style of driving.

Changing the diaphragms will make the bike run better and get better throttle response which the fun factor will reduce mileage but then the engine running better will get you better mileage. How these two mix is kind of up to you.

 

I would change the diaphragms before doing any kind of tuning or adjustments. Just a few tiny pin holes does make a big difference.

 

Have you been fortunate enough to have to change your diaphragms?

[Flyinfool]

Yes I have, bout 3 or 4 years ago.

[utadventure]

You might consider changing the washers on the needles. I did it on my '86 and helped with the mileage. I may have been done already but easy to do.

 

dave

[Chaharly]

I read up on that too. I should pull the plugs after a few hundred miles with new diaphragms and see how they look. Usually you shim it to make it run what? Richer?

[Flyinfool]

Depends on if you move the needle in or out. You can adjust either way.

[cowpuc]

Hey Cha, here is some info on adjusting the Metering Rods.. Take a few minutes and read thru it in its entirety and you will be amazed at what folks came up with for mileage.. I dropped the needles on Tweeks back in 2014 before we headed out for a couple months. Went down to Ace Hardware and bought nylon shims to do so. Took a pair of Verniers with me and checked em for size right at the store, was SHOCKED at how exact the washers measured. I know that Skydoc (was one of the responders in the link) does sell a "kit" for doing exactly what I did, I had already completed the job with the washers so I didnt end up with his kit but I can say, he was spot on with his suggestions..

Thinking I ended up dropping mine 60 thou with NO issues of spark nock and NO problems running cheap fuel (even lots of 85 octane). This was all over the west - mountains, prairies, salt flats, two tracks and even a number of high speed - long distances across places like Montana..

Do your diaphrams and sync her down first - your peeing in the wind trying to tune with bad diaphrams. Then crispen it up/fine tune it with the meter rods IMHO..

http://www.venturerider.org/forum/showthread.php?86325-Carb-metering-rod-question&highlight=tweeks+metering+rods

[MiCarl]

When I replaced my holey diaphragms my mileage dropped, which makes sense. Those holes let in extra air and cause the fuel metering rods to open less - leaning it out a bit.

 

I put in a Skydoc kit and my mileage went to 40. Low range response was a bit lacking until it was well warmed up and it ran a little hotter than I was used to. I added a 0.020" washer to lift each metering rod. That improved throttle response, reduced the temperature and didn't hurt the mileage.

[LukeMacPU]

Just getting my '83 up and road-worthy. Finally got all slides moving well (diaphragms had separated from slides) and my MPG 50/50 city/highway was 40 mpg last tank. I was going to ask a similar question about where I should expect to be, but it sounds like I'm close to normal. Night/day difference in performance when slides work vs. when they don't. Got 40 MPG with 3 slides not moving at all, but the bike was a dog and didn't run smoothly.

[bongobobny]

I would say normal MPG for 1st gen's is around 40 mpg, slightly more or less depending on your driving style...

[Venturous Randy]

I used to get around 36 to 40 and years ago I replaced the diaphragms and that did help the running and gas mileage and it also helped the idle gas smell, but it was still there. I then did the washer thing by using different thicknesses where I even got to the point that I was getting some hesitation. When I got it to where the hesitation was gone, I also noticed most of my idle fuel smell was gone.

From this, running around the mountains and two lane back roads, I have routinely gotten from the mid to upper 40's and have even gotten 50mpg. Now, I have never really ridden for gas mileage and tend to ride a bit aggressive, so I don't poke around. And, I do see a drop in gas mileage when doing the interstate thing and running 70mph and up.

To get your best gas mileage, don't lug the bike in any gear. If you are running at a set speed and drop a gear WITHOUT changing the throttle position and the bike speeds up, you are not running at the optimum throttle/gear setting. How much the throttle is open has more to do with gas mileage than RPM's.

Randy

[mralex714]

You might consider changing the washers on the needles. I did it on my '86 and helped with the mileage. I may have been done already but easy to do.

 

dave

 

Do I need thicker or thinner washers to improve gas mileage?

[MiCarl]

Do I need thicker or thinner washers to improve gas mileage?

 

The nylon spacer under the needle clip needs to be thinner. Skydoc sells a kit.

[videoarizona]

CJ, Puc said it all in one sentence: "Do your diaphrams and sync her down first - your peeing in the wind trying to tune with bad diaphrams"

 

Then go from there. And yes, normal mpg's should be around 40 for average driving. Above 70mph and/or 2 up/trailers/heavy winds....mpg's go down.

I average 38 to 44 with 75 mph indicated depending upon winds.