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Old 10-06-2016, 08:59 AM
Bbqjoe Bbqjoe is offline
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Default What did I run out of?

We have some really steep roads out here. I would say a few of them have a grade close to, if not at 12%.
I was pulling one yesterday and doing alright, but wanted to see what would happen @ WOT.

The bike sped up to a point, but after that, bogged down, and there was still some throttle left.
I had to back off the throttle to get back to the original speed before I opened it up.

So what did I run out of?

HP?
Gearing? (I have a TC)

I know I wasn't going fast enough to be floating the valves.

Thanks.
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Old 10-06-2016, 09:21 AM
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Is this all happening on the incline?
I'd say not enough torque.
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Old 10-06-2016, 09:27 AM
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If FR was here he'd tell you it's not what you ran out but what you had too much of and go on a diet.

Seriously, though...IIRC.. You're running a pretty small axle sprocket...refresh my memory on size. But you're most likely geared a touch too steep.
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Old 10-06-2016, 09:45 AM
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The rear sprocket is the standard issue 50T.
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Old 10-06-2016, 10:04 AM
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What is the jackshaft tooth count and tire height again?
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Old 10-06-2016, 10:09 AM
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Quote:
Originally Posted by Poboy kartman View Post
What is the jackshaft tooth count and tire height again?
10t. 19"
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Old 10-06-2016, 10:20 AM
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Originally Posted by Bbqjoe View Post
10t. 19"
Yeah...5:1 with 19" tires is a bit much....even for a minibike. A 60 tooth would be more belt friendly and still probably fast enough for you...but make climbing hills easier.
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Old 10-06-2016, 10:46 AM
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Remember when I said to fix the gearing before you get a camshaft?
We ran the numbers to find out 6000 RPM is like 75 mph with 5:1 gearing, 19" Tires and the 0.9:1 overdrive from the TC.

I suggested 60 on the rear and 8T on the TC

---------- Post added at 10:46 AM ---------- Previous post was at 10:42 AM ----------

Letting off the throttle maybe helped the TC shift back into lower gear?

I rock a 54T and an 8T with 13.5" Tires (6.75" radius)
Since your tires are 19" (9.5" Radius).....

9.5/6.75 = 1.41

1.41 * 6.75 = 9.5
9.5 :1 with 19's is same as 6.75:1 with 13.5" Tires.

So the 60T with the 8T gives 7.5:1

7.5:1 gives 50% more torque than you have now.
Still won't be geared as low as mine, but will be a vast improvement.

I can do 50mph at 7000 RPM.
I can do wheelies from a stop.
I can climb hills without slowing down.
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Old 10-06-2016, 10:53 AM
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yepp definetely torque..

what felt like bogging down could have been a mix of two things happening..
first and most important: the engine torque dropping at higher rms (i.e. above max torque rpm which is likely close to 2600 rpm soo quite some throttle left)
then as a consequence of a lack of engine torque the TC 'shifted' down to try and compensate (which then slows down the mini bike... drastically at times)

if it doesn't stall and the belt didin't slip you'd still have had the torque required just not at speed.

As Doug already said... a lower ratio would'Ve made this inclination easier for your bike to climb.
especially since your wheels are not exactly mini at all

'sid

PS maybe 55T will do already, but to be safe I'd also say 60T here.
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Old 10-06-2016, 10:58 AM
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Quote:
Originally Posted by Bbqjoe View Post

So what did I run out of?
Faith, Trust, Belief ????
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Old 10-06-2016, 11:22 AM
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Quote:
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Faith, Trust, Belief ????
Money.

---------- Post added at 09:22 AM ---------- Previous post was at 09:19 AM ----------

Also, How much more chain would I need for a 60t?
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Old 10-06-2016, 11:25 AM
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roughly 6 links I'd say (well ~12 more rollers)

actually a good question.... hmmm I'll do some math

'sid

[EDIT]
Odd... assuming the two sprockets being a foot apart and half inch pitch ..
it's 40 links for a 50T rear sprocket and only 43 links for a 60T half of what I was assuming it to be,
(39.8" chainlength vs 42.7"...)
so only six more rollers then...
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Old 10-09-2016, 10:27 PM
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Okay, gonna listen to you guys. Just ordered a 60T sprocket from GPS.
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Old 10-11-2016, 09:29 PM
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An 8 tooth front sprocket on the tav would have been a cheaper and easier fix but you can still add that with your 60 tooth. I run a 8 tooth and stock 50 on the back for a ratio of 6.25:1 which is a little lower that the 6.0 you will get with 10t front and 60 back.
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Old 10-11-2016, 09:46 PM
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Quote:
Originally Posted by minibiker View Post
An 8 tooth front sprocket on the tav would have been a cheaper and easier fix but you can still add that with your 60 tooth. I run a 8 tooth and stock 50 on the back for a ratio of 6.25:1 which is a little lower that the 6.0 you will get with 10t front and 60 back.
Thanks
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Old 10-12-2016, 12:01 PM
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Sounds lean to me. Have you read the plug right after a wot pull?
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Old 10-12-2016, 09:23 PM
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I don't think it's torque I'm running out of.
I was coming down a pretty good sized hill today, and decided to go WOT.
Cracking it 3/4 plus, it bogs down with a boooooooooooaaaaaaaaaaaaaaaaaHHHHHHHHHHHHHh, and I'm sure if I held it open, it would die.

Signed, still confused.


ETA: Maybe I need a bigger main jet?
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Old 10-12-2016, 09:35 PM
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oh.. well.. that's indeed odd...

You did a plug reading after that? maybe flyinghillbilly is correct about your fuel/air ratio.

Is there any chance you could tach the engine?...
maybe you hit the valve flutter already *shrugs*

in case you have an android phone maybe this can give you at least a clue:
https://play.google.com/store/apps/d...viery.rpmgauge

Just to be clear...
Quote:
Originally Posted by Bbqjoe View Post
I don't think it's torque I'm running out of.
...............
ETA: Maybe I need a bigger main jet?
Whenever the engine is unable to accelerate any further its ALWAYS a lack of torque
but in your case it might be due to an insufficient fuel mix indeed..
so yeah maybe a bigger jet.. read the plug (after such WOT run) and see what it's telling you about the fuel mix.

'sid
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Old 10-12-2016, 09:50 PM
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Quote:
Originally Posted by itsid View Post
oh.. well.. that's indeed odd...

You did a plug reading after that? maybe flyinghillbilly is correct about your fuel/air ratio.

Is there any chance you could tach the engine?...
maybe you hit the valve flutter already *shrugs*

in case you have an android phone maybe this can give you at least a clue:
https://play.google.com/store/apps/d...viery.rpmgauge

Just to be clear...

Whenever the engine is unable to accelerate any further its ALWAYS a lack of torque
but in your case it might be due to an insufficient fuel mix indeed..
so yeah maybe a bigger jet.. read the plug (after such WOT run) and see what it's telling you about the fuel mix.

'sid
Thanks.
I don't think a whole lot of torque is needed when descending a 12% hill. It's almost as if the engine is being turned off, then has a bit of a time regaining itself when the throttle is backed off.

I seriously don't believe I've reached the end of the powerband, nor am experiencing valve float.

I vaguely remember reading that rejetting might be needed with the new cam. :facepalm:
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Old 10-13-2016, 01:42 AM
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It'll be fine for an old guy putting around in the desert.
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