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I consistantly get around 50mpg on my 72 TR-6R. It diminishes greatly if your tires are not properly inflated. I go for around 28 front and 30 rear. Set your idle around 1,000-1,200 rpms.

td
 

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Does it remotely make sense to you?
Erroneous posts have been removed. (And I'm awaiting delivery of my '72 TR6R this coming week, sheesh.) But it would seem to me that a single carb (Tiger) feeding two cylinders is less efficient than twin carbs, each one dedicated to feeding a single cylinder (Bonneville). And I'm here to learn rather than speculate.
 

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Erroneous posts have been removed. But it would seem to me that a single carb (Tiger) feeding two cylinders is less efficient than twin carbs, each feeding one single cylinder (Bonneville).
40% more efficient? I think not. I would think the opposite, that 2 carbs feeding the same motor would use more fuel, same as fitting a larger carb.
 

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40% more efficient? I think not. ..........
I stated that a single carb would be less efficient..... What have I missed here and I'm here to learn from all of your experience????

(EDIT) Multiple carbs drink more fuel and a single carb less.! I got it. AAaaaahhhhh.
 

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I stated that a single carb would be less efficient..... What have I missed here and I'm here to learn from all of your experience????
Bigger or multiple carbs feed more gas for more power, thus it would be less efficient than a single carb. While there may be slight differences in efficiency depending on how much throttle input you give it, I doubt you would see a 40% difference.
 

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Depends on if you're talking about power efficiency or fuel economy.

Hmmmm interesting point that I've never thought of before now. And I hope that the OP doesn't feel that his thread has been hijacked. In the future I hope to contribute more solid experience from owning a real Triumph.
 

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40ish mpg likely. Set the idle around 1000-1100 rpm. Some folks try to set it lower and then complain about stalling at lights and poor pickup. It doesn't need to idle like a one cylinder John Deere.
 

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my 72 T120 got 42mpg on concentrics. i put on 32mm mikunis and at 55mph it would get 50mpg with a 19/47.

i put on a morgo with headwork and it went down to 42 again.

now i have 34mm mikunis and 21/47, and i have no idea what the mpg is anymore. but it goes 117mph so i dont care.
 

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my 72 T120 got 42mpg on concentrics. i put on 32mm mikunis and at 55mph it would get 50mpg with a 19/47.

i put on a morgo with headwork and it went down to 42 again.

now i have 34mm mikunis and 21/47, and i have no idea what the mpg is anymore. but it goes 117mph so i dont care.
Yup, MPG isn't everything. I have a CRX that got 42mpg with the 78hp motor it had in it, I swapped in a B16 Vtec motor that made 100hp more. Lost 10mpg, but with the extra 100hp it was a decent sacrifice.
 

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I get 50mph on my '72 Bonnie on trips where I'm going about 60mph for long periods at a steady speed..........
 

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Hi Shiftless, Interesting about MPG. I ride with lots of guys. Last weekend I rode 97 miles with a friend that has 64 Bonnie with monoblock carbs. I often ride with friend has 69 Bonnie concentric carbs. Often I do 100 mile rides with the club. Lots of Bonnies & several 650 Tigers. I have the only 750 Tiger. Most interesting all the bikes are very close on MPG about 50 on average with country road riding & seldom over 55mph. On freeway at 60-65 still about 50. With head wind drop 5 mpg. At 70 down to 40. We all keep tire pressure up & bikes are well maintained. This is in California with 91 octane, 10% ethanol gas. 10% supposedly drops mileage about 5% over normal. However running aviation fuel or leaded race gas consumption is the same. Those stop pinging though.

On the spec sheet Bonnies should out run Tigers, but on the road, they are about the same. Bonnies might pull harder at 6k+ RPM, but only a little. I think most the Triumphs start very easy, but over all I think Tigers start & idle better. Often Tigers run a little better at part load also, say 25-45 mph. A perfectly tuned Bonnie runs well also, but it must be well tuned.

Regarding the idle Htown is right on point. It can depend on your fuel, but overall a low idle will allow motor to die a long stoplights on hot days. If you very slowly rev motor in neutral you'll find a speed where motor will vibrate/shake bad. Often the shake is about 1300 or so. You want to be just a little below that with motor hot after riding a good 20 miles.

You want to adjust your idle mixture when hot after 20 miles also. I go to smoothest ilde then in a 1/16 to 1/32nd turn or so. Then trim idle RPM, then re trim mixture. Over a several hour ride you'll find the sweet spot if you keep fiddling with it.

After 20 miles of freeway at bottom of off ramp idle will be a little higher. When motor cools slightly idle will go back to where it was. If you adjust for the highness at bottom of off ramp it will be too slow later.

Cold it probably won't idle reliably for the 10-15 minutes depending on how cold it is. No cure for that since carb has no cold high idle system like a car does. Just hold some throttle on.

Johntioc mentions needle jet wear. He is most correct. If you have wear there, motor will be rich. Once you reach a certain point more fuel doesn't give more power, just wastes gas. Lean is interesting. Under light load lean can save gas. However under even modest loads you end up opening throttle more so no savings.

For an experiment put some tape on bar & throttle & mark it so you know how much throttle is open for the load & speed you are riding. Then print the carb tuning guide Johnitoc wrote. Go for an all day ride. Study the guide & compare throttle opening. That will teach you a lot.

After I finally did that I was shocked at how little throttle it takes to ride. I change the needle, needle jet, needle clip position, main jet. What a difference! Very time consuming, but if you want best running you need to go over the tuning guide. You may be best way now or not....

On a side note the 64 Bonnie has TriSpark igniton with idle stabilization. It adjusts the idle by advance/retard timing slightly at idle & has extra retard durning cranking for easy starting. I did not ride bike but observed it started 1st kick every time & idle was rock solid & even at all times, even after long freeway ride or after several stop lights in town. I specifically paid attention to this as I was curious how well it work. Looked like it worked quite well. Also all electronics are inside points cover so no separate module to mount & visually bike looks stock.
Don
 

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.........................Johntioc mentions needle jet wear. He is most correct..................Then print the carb tuning guide Johnitoc wrote. ........................
Can you PLEASE provide a link to Johntioc's carb tuning guide as I'd really like to get a copy of it. THANKS!
 

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& has extra retard durning cranking for easy starting.
Thanks for the kind recommendation. It actually advances the timing for starting., then retards for idling. Idle stabilization was first adopted for our motorcycles with the Boyer Micro-Power systems some years before Pazon started using it.
John
 
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