Lost gas mileage

[Oldgold]

While searching for causes for mileage being down from ~ 45-46 to 40-42

I noticed gas weakly spraying from the bottom port of #3 Vacuum piston at idle, the diaphragm has no visible tears and the float level is correct, the only ports that appear to go to the cover side of the diaphragm seem to be the purge jets. Any ideas what's happening here? Carbs are synched

and compression is within 5# on all cyl. Thanks

[Yammer Dan]

More Sea-Foam

[CrazyHorse]

Mileage looks fine to me I might get 40 on day I ride 45 mph the whole time. Mostly 38 mpg. Colder weather mileage goes down.

[Oldgold]

I know there's quite a variation in gas mileage on some of these bikes, but I've had this for years and it's always been more in mid to high 40's. The gas is spraying from the diaphragm piston side into the carb throat as if the diaphragm cover side was getting gas into the chamber and mildly pressurized.

[Guest Popeye]

Mine has gotten 32 mpg, mostly 2 up, since I've had it.

Had carbs redone, diaphragms, plugs, etc., this summer.

Took it to Eureka Springs, AR this summer & was still 32 mpg.

 

Throttle cable broke & lost LF cylinder. LF cylinder died in shop, they messed something up or this is a HUGE coincidence, since i never noticed it, until I picked it up.

 

However, no one can explain poor mileage, only 38k miles on engine with excellent maint.

Its really frustrating.

 

Tech told me today he will tear it down until he finds problem.

I'll post results & cause(s).

[Gearhead]

I agree, that's excellent mileage, both your old and new mileage! I'm very lucky to get 40, average maybe 36. All the same, it's no fun to lose mileage.

 

I have an idea. Did you just replace the front tire? That makes the diameter a little bigger, making the ODO read lower, meaning your indicated "miles" got bigger, so you cover less of them.

 

As for the fuel spraying as you say, I can't think how fuel would possibly get up there. Plus, I would think that such a phenomenon would cause your mileage to be much worse. Fuel is supposed to come up from the needle jet just below the slide piston.

 

Jeremy

[Gearhead]

It just occurred to me to ask - did you check float / fuel level in all carbs?

 

Jeremy

[Oldgold]

Thanks to all for suggestions. Yes, I did check float levels. Front tire is actually down to the last few thousand miles. I'm looking at the pistons at idle,filter removed, all pistons will dance, when I first noticed this I thought the fuel was coming out of the main jet but it's definitely coming out of the bottom of that piston. The old YICS is still hooked up, if it stops raining I'll try unhooking it and see if that has any impact, the only other

thing that comes to mind is leaky intake valve, if that allowed some compression to leak back into intake passage at idle, pressurizing ports under throttle plate?? Just rambling on here, if I find anything I'll post.

On another note, I just replaced a rear Dunlop E2 with an E3, seems to handle and ride a bit better. The E2 rear gave me the best mileage I've ever had out of a rear tire, but never really felt as planted as some of the other tires I've had on the bike.

[oldandcrotchety]

my '83 consistently gets 46-48mpg. (i think it is kind of lean since the pipes are always chalk-white.) i check milage all the time just out of curiosity. so a couple of months ago i checked and it showed i had dropped to 41mpg. i was thinking i would look into that soon, but with the very next tank of gas i was back to about 47mpg. have been ever since. maybe a tank of poor gas......

[CrazyHorse]

my '83 consistently gets 46-48mpg. (i think it is kind of lean since the pipes are always chalk-white.) i check milage all the time just out of curiosity. so a couple of months ago i checked and it showed i had dropped to 41mpg. i was thinking i would look into that soon, but with the very next tank of gas i was back to about 47mpg. have been ever since. maybe a tank of poor gas......

 

You must be driving 20 mph to get 48 or your spedometers way off. ( Of course Im just jealous.)

[rewindgy]

Depending on mileage - check the tubes where your needles slide in and out. If you can imagine the needles ( diaphrams) move in and out in a sawing motion constantly and it is the last place anybody looks for wear! I have seen alot of backyard mechaincs drop the needles thinking this is the best fix when changing out the tubes will make the thing run like a top! Of all of the 3 First gen's I've had at around 100,000 km's ish they were starting to get oval and then the mileage would start to go bad. Then when you pulled the cover off the diaphrams you would notice un burnt fuel hanging around. Just a thought!

[Gearhead]

Very interesting. I wonder what they gouge you for new needle jets, or if they're even available.

 

Jeremy

[Squeeze]

for the '83 and '84 it should be ...

26H-14941-06-00

NOZZLE, MAIN

 

for all others including Vmaxxes

 

26H-14941-90-00

NOZZLE, MAIN

 

Price ???

 

 

ooops ... '83 -'84 is $55.44 and for the others is $37.72 each at Powersportspro.com

[cbmel]

Can't help you on the fuel spraying issue, but I thought I'd chime in on the mpg situation. I've had the 86 for a couple of months and mileage has been pretty consistent around 45-47. Solo or 2-up, doesn't seem to make a difference. If I was only getting in the low 30's I'd be tearing into it - I get THAT kind of mileage with my car!