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Top Speed? Given a flat road, no wind,
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Mannanan
Leigh On Sea, Essex. Uk.
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October 19, 2018 - 8:06 am
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Now getting some miles on the rebuilt standard B175 and so far, so good. I see from the blurb that max speed is listed as 65mph. That seems rather optimistic to me at the moment. Given a flat road, no wind and a 70kg rider sitting upright, what realistic top speed should I see indicated on the speedometer? I should add that I don’t intend to keep it at top speed for any length of time but just curious to know if it’s running as sweetly as it should do. Thanks.

Ed.

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swalsh58
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October 19, 2018 - 9:34 am
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There are so many variables to predict an accurate answer. In my younger days my mate who had an FS1e swore blind he had 70mph out of it. I had another guy who told me he had 50 out of a Puch Maxi.

In truth, no one rides a Bantam for the speed. You can tell if it’s running well without thrashing the ***** off it. My D5 was happy pootling along at 45, 50 at a push, but clearly didn’t want to go much beyond that.

Remember you have to stop the damn thing too, and with Bantam brakes being as ‘good’ as they are, you should be careful doing anything beyond 50mph!

Current bikes......1958 D5, a 77 Suzuki GT250 and a 77 Honda CB125S. I have a 74 Kawasaki S3 400 and a B175 waiting for restoration. A 1980 Honda CB400N waiting for MOT.  Everyday ride is a 2011 Harley Davidson Sportster. 

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chris
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October 19, 2018 - 10:38 am
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A good standard B175 will do a genuine 65mph but it will feel like its going to vibrate itself to pieces. Mine was only comfortable in sustained cruise at around 50 - once over 55 it felt too much like it was getting too stressed.

1970 B175, '49 D1, '66 Spitfire MkII, '57 Venom, '76 Cb750K6, some of which are actually complete & working...

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cocorico
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October 19, 2018 - 12:06 pm
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You'll probably find that as you get more miles on the clock, you will get a 'feel' for the bike's sweet-spot. All my bikes have had one, all at different revs (but usually above 3000rpm) and different speeds. My D3 has shown an indicated 50 mph, but feels better at about 40 - 45. I also have a 100cc step-through 2 stroke scooter. That will do about 55, but again feels happier at 40 - 45.

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Wilky
Newton Aycliffe, County Durham
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October 19, 2018 - 12:51 pm
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I recently had 54mph on my D14/4 - I'm 6'1" tall and weigh 19st.

Since then I'm lucky to see 45mph as it won't take full throttle, awaiting a dose of looks regarding jets etc soon.

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nickjaxe
Runcorn Cheshire UK
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October 19, 2018 - 2:46 pm
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I weigh a bit more that you prob around 95kg...I would imagin on a windless day flat road I could hit 60m with a bit of a run up.

My bike is nice at 40...vibrates at 45...smooths out again at 50...to be honest I feel I'm pushing it at 50...I will do it to keep up if I need to.

At your 70kg it should do well.

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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b175er
saltfleetby
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October 19, 2018 - 3:01 pm
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I'm with Nick on this one - though he's a bit bigger than me. I'm about your weight and I tend to cruise between 37 and 44 mph and my top speed (on my Cateye computer; which is accurate according to the lamp post mounted speedos I've passed) is usually just over sixty. That feels pretty quick to me and I wouldn't want to do it for very long ! Motorbike speedos are notoriously inaccurate. Ken.

two B175s and a CB360

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nickjaxe
Runcorn Cheshire UK
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October 19, 2018 - 3:19 pm
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 "though he's a bit bigger than me"  Thats very polite of you Ken...some would say fat ########

My Bantam video              https://www.you.....jpOFmzRZRI

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b175er
saltfleetby
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October 19, 2018 - 3:30 pm
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I'd never be that rude Nick !

two B175s and a CB360

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Mannanan
Leigh On Sea, Essex. Uk.
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October 20, 2018 - 8:53 am
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Ok, thanks for the replies. Think I will be happy if the needle nudged 60mph momentarily. I am having fun around the 45mph mark at the moment and it seems unstressed at that. Not intending to do any motorway cruising so I agree top speed is all a bit irrelevant really. The front brake is certainly a sobering issue when thinking about 60mph. I think I have now mastered the foibles of the gearbox that tries to be difficult going up from 2nd to 3rd. That technique of dabbing down lightly before going up works well and now only the occasional false neutral. It’s taken a while but I am slowly falling in love with my Bantam.

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nickjaxe
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October 20, 2018 - 11:31 am
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I had that prob with my box...req...a tiny bit of work with a file in my case.

My Bantam video              https://www.you.....jpOFmzRZRI

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johnsullivan
east sussex
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October 21, 2018 - 1:05 pm
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If you go to the members area there is a road test by Bob Currie.Comprehensive performance details and a good read .

67 D10. and a D7    2007 Honda Hornet FA. Suzuki 89  DR 250S, Sinnis SC 125. 78 Honda 90  75 Montesa Cota 247 an electric scooter of famous make.

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SpacedMarine
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October 21, 2018 - 2:13 pm
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Seem to remember the d14 doing an indicated 65 years ago 😂

What's 7/16 in mm again?

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Doug Brown
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October 21, 2018 - 6:03 pm
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I think it definitely needs the bigger main jet. Its o.k. in the mid range but later on after another speed test, It started to feel a bit tight . I have filmed the other run but its more of a little run and a 15 min vlog  (  video blog ), might put it up just to see what people think.

Triumph Thunderbird 900 Yamaha rxs 100 and too many bantams !

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nickjaxe
Runcorn Cheshire UK
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October 21, 2018 - 6:58 pm
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You sure your speedo is accurate Doug...very hard to tell in a video but that didn't look that fast....as I say hard to tell in a vid.

I do the opposite when coming off the throttle zap it closed to avoid a weak burn situation.

I have cross checked my speedo with a GPS....I was amazed just how accurate it was.

My Bantam video              https://www.you.....jpOFmzRZRI

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SpacedMarine
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October 22, 2018 - 12:04 am
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You'd hope it was accurate as Smith's made aviation stuff didn't they?

What's 7/16 in mm again?

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GlenAnderson
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October 22, 2018 - 2:06 am
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My D1, when it had a D7 engine fitted, would sit at 50 indicated, all day long, and would happily sail past the 55 and beyond to an estimated 60 ish if conditions were right. A good D14/4 should manage 60 without a struggle, and only drop below that up a steep incline. Downhill, with a following wind you should see north of 70. I might weigh more now than I did thirty (+) years ago, but I don’t load the bike up like I used to back then either, so they cancel each other out. laugh

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Doug Brown
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October 22, 2018 - 11:46 am
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Aha  what you have to watch out for is the jaunty angle my speedo is at! Its rotated round and I can't be bothered to disconnect the cable etc. to fix it. Its rotated clockwise and is an essential  mod for speed 😂.

Interesting idea about snapping the throttle shut . Do you think it gets more fuel and lube that way?  Its just that Sara did a high speed like that and when she got to her turn off she says she shut the throttle and it seized.  I'm starting to question that though . Did she just trail the throttle?🤔.

Triumph Thunderbird 900 Yamaha rxs 100 and too many bantams !

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GlenAnderson
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October 22, 2018 - 1:22 pm
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I have always taken great care to keep a trailing throttle on any premix two strokes I ride. Shutting it completely at speed, particularly on a D1/D3 with no idle circuit, is a quick way to a new piston. 

On a more modern bike with autolube it’s less of an issue, although it can lead to plug oiling as your oil keeps getting injected without the additional fuel needed to burn it off. That said, I used to love shutting the throttle off on my full-power TZR 125 at 70 or so, letting it drift down to 50, then dropping two or three gears and giving it the beans. You could lose sight of everything behind you in a cloud of 2t smoke. laugh 

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_Paul_
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October 22, 2018 - 1:39 pm
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My old D13 would show over 70 on the clock, current D14 goes straight up to an indicated 65 but vibrates harshly around 45-50 when accelerating hard in top, once it reaches top whack it is significantly less harsh, if I roll off the throttle it will sit at 50+ all day long and it's fairly smooth at that speed?

Paul

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