Mileage, distance per tank, etc

[Ken Talbot]

Even with recent threads on this, it has only been recently that I finally got a handle on Tsunami's performance.

Background - ever since we got SWMBO's 'H, it has consistently come in pretty close to 50 mpg (Imp) while Tsunami was always under 40, often closer to 35. During this spring's pre-season preparations, I lowered Tsunami's floats by 2mm so they now measure 27mm from the gasket surface. This brought its mileage up considerably, with 8 fill-ups now averaging out at 45 mpg(Imp).

Last night for the first time, I actually managed to run Tsunami right to reserve so I could also verify how much is left in the tank "just in case its needed". I had to switch to reserve at 298.4km (186.5 miles), then took on 18.028 litres (3.97 Imp gal, 4.96 US gal). With my 24 litre tank, I now know I've got 6 litres on reserve, which should be good for another 95km (60 miles).

Bottom line - 'should' be able to run approx 285km (180 miles) before reserve, approx 380km (235 miles) to 'bone dry'.

Ken Talbot

[norm_is_here]

Mileage, distance per tank, etc

Hello,

How do you adjust the floats?

Norm

[Bill]

Re: Mileage & floats: lean or starving?

Ken "Tsunami" Talbot wrote:

I lowered Tsunami's floats by 2mm so they now measure 27mm from the gasket surface. This brought its mileage up considerably, with 8 fill-ups now averaging out at 45 mpg(Imp).

So...you lowered the floats which lowered the fuel level in the float bowls. Enquiring minds want to know:

• How does that affect mileage?
• Does it effectively lean out the fuel delivery?
• Does it cause any high RPM fuel starvation?

XSerendipity starts quickly and runs smoothly at about 37 MPG(US) or 44 MPG(Imp), but since I added the Road King mufflers it's been a little rich. I'm about to go into the carbs to check everything. I was thinking about:

• Lowering the needles or
• Trying smaller jets. (They're currently stock)

Perhaps I should try setting the floats a little lower before making other changes. Thoughts anyone?

Bill

[CA.XSer]

I get around 30 mpg or less to work on my 79sf. I am running a 4 into 2 Jardine with K&N filter and 140 main jets. The floats are set at 25mm. I went for a ride on Fathers Day (about 130 miles) through the mountains and got 37 mpg. Was suprised the mileage got better as I was on and off the throttle quite abit, with some 15 mph turns and 80 mph straights. I am going to try some 142.5 mains and raise the needle one notch. I belive I will look at changing the float level also to see what happens.

[CA.XSer]

__________________________________________________ __
Perhaps I should try setting the floats a little lower before making other changes. Thoughts anyone?

Bill
__________________________________________________ __
Bill
I think I would try the float setting first. It is my understanding that float settings effect the the cruise range. My .02

[Mike Hart]

Bill - floats or mains?

Bill, IMO, adjusting floats is a tweak, and the last thing you do.
Those hd pipes must be more restrictive than stockers, indicating
you should first change the mains.

btw, someone recently reposted Denny's chart of how to change
jets according to various mods, I will mail it to you offline, you
could put it in the carb section.

[Ken Talbot]

Re: Mileage, distance per tank, etc

Originally posted by norm_is_here
Hello,

How do you adjust the floats?

Norm

Carefully!

Really, Norm, you set the carb bank upside-down with the float bowls removed and gently bend the small tang that presses against the end of needle valve. I then use a digital caliper to check the height.

[Ken Talbot]

Re: Re: Mileage & floats: lean or starving?

Originally posted by Bill

So...you lowered the floats which lowered the fuel level in the float bowls. Enquiring minds want to know:

• How does that affect mileage?
• Does it effectively lean out the fuel delivery?
• Does it cause any high RPM fuel starvation?

• For Tsunami, mileage increased by about 20-25 percent
• Yes, fuel delivery was leaned out, which is exactly what I was looking for. Last year, driving at elevation in Colorado, I had quite a bit of trouble with fouled, black plugs. Even hack at home, the plugs were still too dark even with the 120 mains all across.
• No fuel starvation noted, at least not the way I drive. I've probably only pushed to to about 7500 rpm, and it was doing just fine then.

[Bill]

Re: Bill - floats or mains?

Mike Hart wrote:

btw, someone recently reposted Denny's chart of how to change jets according to various mods, I will mail it to you offline, you could put it in the carb section.

Great stuff, for sure! I saved it and started working it into a tech tip. JP thought maybe it needed some pix or review from the original author. However, last I contacted DZ he didn't seem interested in getting involved with the group. Who knows, maybe the forum would be more to his liking?

Bill

[Mike Hart]

Denny's jetting tips

Bill, I notified Denny about the forum. He apparently looked in
as guest, since he told me it was cool and he'd keep an eye on it.

I'm in fairly regular contact with him, you want me to ask him for
permission / review? I doubt he would mind if you emailed him,
but I can do it if you like.

[Yetti]

When I bought my '79XS. It would not idle. A "thorough" cleaning and adjustments to the floats cleared this right up. I also bought a mercury level sync. gauge. I am currently getting about 33/34 miles to the gallon.

Yetti

[Robert Haller]

On a ride in the mountains this weekend I got 43.75 mpg on a tank (usually get 38 mpg for all city riding). All the carb stuff is stock but have a Jardine 4-1 exhaust and K&N stock filter. I thought that I would have to rejet but my headers are just ever so slightly turning gold after 3000 miles. That's a pretty good sign isn't it? I have yet to pull the plugs after killing the engine to check condition.

[kenkrieger]

This is good info,,,,I get just 30 mpg,,,,,,81 SH,,all stock and the carbs might be clean,,,,it was setup using the Yetti's mercury gauges,,,,never set the float height,,,,,,,,looks like I have some work to do. the bike runs great,and quite fast. But some of these mileages are way higher. I was able to get a high of 39 mpg last year at XSEast 2001 riding in the White Mountains,,,,,but never again.

[skids]

Yep, that is good! What carb settings/jetting are you using?What elevation are you running?

Originally posted by Robert Haller
On a ride in the mountains this weekend I got 43.75 mpg on a tank (usually get 38 mpg for all city riding). All the carb stuff is stock but have a Jardine 4-1 exhaust and K&N stock filter. I thought that I would have to rejet but my headers are just ever so slightly turning gold after 3000 miles. That's a pretty good sign isn't it? I have yet to pull the plugs after killing the engine to check condition.

[Robert Haller]

Skids,

All my carb settings/jetting are stock for a 79 Special (I don't have the actual specs with me). The 43.75 mpg was unusually good, normally I get 37 - 41 mpg depending on the mix of city and highway riding I do. My city (Atlanta, GA) elevation is about 1000' and the mountain riding I do in North GA is 2000' - 3000'.
After adding the K&N stock filter and Jardine 4-1 exhaust, I am really hoping to get input to determine if I need to change my carb settings or jetting. I would prefer not to mess with it if I don't have to, but will if I do. My bike seems to run pretty well now, but I don't know how much rejetting may improve.