750/850 weight comparison

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worntorn

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The common belief is that the 750 is considerably lighter than an 850, enough to feel "more nimble". I would guess that for an average rider to notice any difference in handling we would need to see 25 lbs or more between the bikes?

We are doing a weigh in this am.
The 750 is a 71 with Interstate tank.
The 850 is a 73 with Interstate tank. Both are stock bikes, kickstarter only. I weighed the 850 yesterday on the digital hanging scale.


We are also doing a roll on comparison but giving a big handicap to the 750.
The 750 owner says his 750 accelerates much quicker than his 850. I've heard this many times before, there must be something to it.

For the roll on I'll ride my 850 MK3 porkster.
That gives the 750 a good advantage. In addition I outweigh the 750 rider by about 40 lbs.
With that much extra weight on the already heavy MK3 and it's lazy 850 engine, it should be no contest, winner 750.

Glen
 
Well, I've seen 1/4 mile tests from back in the day that showed a best of 12.6 for a 750 and a 12.8 for an 850. No idea if they had the same sprocket/rider weight, etc.

So, assuming both bikes are stock (including carbs/timing, etc) you should do a couple of roll-on tests and trade bikes so that the difference in rider weight doesn't MAKE the difference. Also, the ignition used may matter, depending on the advance curve. For example, an OEM points/AAU will out-accelerate an analog Boyer in a roll-on through the midrange because the OEM has a much quicker advance curve.
 
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FWIW my own '73 850 weighed in at 460 lbs. with about 1/2 a tank of fuel.
 
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This 850 weighed 447 with the Interstate tank filled to 3" from the top of filler.
We'll be using the same scale.
Different scales give very different results, much like dyno tests!

I'll also weigh the MK3 again to verify the weight difference between that bike and a kickstart 850.
Another friend has a 73 850 with Alton fitted that could be weighed, but it is very pretty, fresh resto, wouldn't want to put a scratch on it!

Glen
 
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The 750 weighs 442 with the same fuel amount.
That is 5 pounds less than the 850. This makes sense, both bikes have virtually the same parts except the 850 cases, crank and frame all have a small amount of metal added for added strength. 5 lbs of metal as it turns out!


Glen
 
Acceleration test
I stopped at the top of 2nd as it was no contest.
That's with the 750 rider at 198 in gear and me at 240 in gear. We weighed that too!
So the MK3 is carrying about 80 lbs more than the 750 here.
Both bikes have EI. Both have 20 tooth cs.
Go figure.

 
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Were there two "races?" It looked like you initially ran away from him but then when you slowed/he went by it appeared that he continued to pull away when you got back on it. Or did it just appear that way? Where you on the 850 or the 750?
 
Just one race really. Yes I am on the MK3 850 with the camera.
I shut the 850 off at 6500 in second after going by, as it wasn't even remotely close, I could seem him in the mirrors, way back there and falling further behind.
He kept the 750 on full bore and eventually caught up and went by as I was idling along.
It should be much closer than that.
I have two more 750 riders that want to give it a try. One is has a modified head ( done by Jim Comstock) is supposed to be very quick.

Glen
 
No, I purposely let him go first!

When he was rolling and full bore (and in front) I finally rolled it on.
The two bikes just aren't very close in power output.

Side by side won't help, he'll just disappear behind instantly.

Glen
 
Might like to give my 850 a go at this.
Its running very well these days.
 
The other 750 rider says he will smite me & the MK3 next week. This is the hotrodded 750, but it does have an Estart and the rider is about my weight.
Should be fun.

Glen
 
worntorn said:
Acceleration test
I stopped at the top of 2nd as it was no contest.
That's with the 750 rider at 198 in gear and me at 240 in gear. We weighed that too!
So the MK3 is carrying about 80 lbs more than the 750 here.
Both bikes have EI. Both have 20 tooth cs.
Go figure.

Click to expand...

I'm not sure what I'm looking at here
The 750 rider pulled away so slowly and I can't tell from the sound but it just doesn't look like he was giving it the beans to me?
 
I asked him afterward and he said he rolled it to full bore as soon as he got straight on the pavement.
I rolled it on about a half second later.
His bike has a quiet exhaust which might account for the power difference. When his bike zips by at the end it is still full bore. You can hardly hear the engine. I think he has an overly restrictive exhaust, but he's happy with it.

We wont do drag starts, no need and it's hard on the bike.
Get the clutch out with a few revs then wack the throttle open, simple.


Glen
 
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Can I borrow your Go Pro? Kidding

I like to pretend like my 750 is quick for Norton 750. However, when I give it the beans it's still an old 750 twin. I was going to go out and do a run up the freeway to 90mph to test my modified exhaust, but the air quality around Seattle is like sitting 1 foot from a campfire on the windward side. Too many fires burning in the Pacific North West

Thanks for the test info. Your 9xx would make them both look sad I think.
 
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