Honda Hobbit PA50 low end power and gearing

Hi, fairly new to moped ownership and new to this forum, I'm hoping you can help me.

We have a Honda PA50 II which we use for off-road charity moped races. We bought it already converted for off-road use with knobbly tyres and with the lights removed.

The bike runs well and is well maintained, top end speed is not a problem but we struggle with the hills. What we need is more low-end power and lower gearing. Does anyone have any advice that can help us with this?

Is there an exhaust which aims for torque rather than high revs power?

Is there a way of making '1st' gear lower or the overall gearing lower? Maybe by swapping the pulley(s) or by changing the gearing in the rear hub?

Most tuning seems to be aimed at higher gears and top-end power which works on the road but not off road.

Re: Honda Hobbit PA50 low end power and gearing

Alan Wattam /

Thought you might want to see a photo of the bike.

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Re: Honda Hobbit PA50 low end power and gearing

You have a ton of options. Are you required to stay at 50cc? If not a 70cc kit would help alot with low end. I believe that you can get different transmission ratios for the rear hub as well.

what you really need is to tune your variator for a higher stall speed. Keeping your bike in the power range whilst on the low end gear of the cvt. That would help alot with the hills.

Wouldn't recommend it for street use, but you are in a unique situation.

Re: Honda Hobbit PA50 low end power and gearing

DrGeorgeTompson (Alan) /

Yeah i would lighten the weights in the front pulley by drilling them open a little more. That's a pretty straightforward and effectively free way to keep it in the power earlier.

The proma circuit is going to be your best bet for lower rpm power. It's a very solid all around pipe. You'll probably need to re-engineer that bash guard though.

Heck, it might be worth it to try a pipe before messing with the variator tuning. The stock suitcase exhaust doesn't really provide much.

also, that bike is so cool (edited)

Re: Honda Hobbit PA50 low end power and gearing

Normally i'd say a circuit pipe cuz theyre easy and great, but clearance is poorer, which in your specific case would matter.

but also variator tuning. for a quick one, your camino variator should have 6 rollers, try taking 3 out and see what the difference feels like.

Re: Honda Hobbit PA50 low end power and gearing

Playing with the Tig welder the other day I made a more ripping stock like muff box for our hobbit dirtped. Although the circuit pipes do hit low(er) than other style tuned pipes, a stock ISH muffler is still best for low low rpm grunt. And hard to destroy/dent. (edited)

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IMG_20191115_165131.jpg

Re: Honda Hobbit PA50 low end power and gearing

Alan Wattam /

Thanks for the replies.

We have to stay 50cc to meet the rules unfortunately.

We've already removed 3 of the weights, would drilling them to be lighter make a difference, or is it just a better engineered version of the same?

We have tried a pipe, the bike came with what seems to be a Turbo Kit S1 pipe from Moped division. It seemed to make it run badly, and caught on the stand so we went to a standard box.

Nick, did you find an improvement with your custom box? We'd be up for making one if it helps, is it just empty inside?

Re: Honda Hobbit PA50 low end power and gearing

Definitely an improvement over a stock muffler in both sound and performance. Very throaty and low pitch. Perfect for 35mph stock-like builds. I actually did add some baffles and packing in this one, but I may build a few more and play around with a few different baffle orientations.

Work on getting the belt as low as possible in front Vario, and as high as possible in the rear. so that you are starting in the lowest gear ratio possible. Every mm makes a noticeable difference in acceleration.

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Re: Honda Hobbit PA50 low end power and gearing

> Nick / Ratbone Wrote:

> -------------------------------------------------------

> Definitely an improvement over a stock muffler in both sound and

> performance. Very throaty and low pitch. Perfect for 35mph stock-like

> builds. I actually did add some baffles and packing in this one, but I

> may build a few more and play around with a few different baffle

> orientations.

>

> Work on getting the belt as low as possible in front Vario, and as high

> as possible in the rear. so that you are starting in the lowest gear

> ratio possible. Every mm makes a noticeable difference in acceleration.

Dude that looks like catalytic converter.

Dude buy a 50cc kit , big carb and pipe.

If your worried about clearance you can obviously use a welder lol

Re: Honda Hobbit PA50 low end power and gearing

DrGeorgeTompson (Alan) /

> Rocco Taco Wrote:

> -------------------------------------------------------

> > Nick / Ratbone Wrote:

>

> > -------------------------------------------------------

>

> Dude that looks like catalytic converter.

>

> Dude buy a 50cc kit , big carb and pipe.

>

> If your worried about clearance you can obviously use a welder lol

Dude that's not OP

Re: Honda Hobbit PA50 low end power and gearing

Alan Wattam /

That exhaust looks great, nice work. I'd be interested how you get on with changing it and the difference it makes. Definitely looks like a fun project. I wonder what a straight pipe (no box) with a silencer would do? That's what 2 stroke trials bikes do for low end torque and smooth power.

I'm be tempted to make an expansion chamber pipe, but with numbers aimed at low end power rather than top end like most. I've got Graham Bell's 2 stroke tuning book and it goes through how to calculate exhaust dimensions if you know the revs you want to tune for and the exhaust port duration.

If you're tuning for low RPM it looks like the exhaust would be crazy long, like 3 metres, but I'd like to work it out properly and see.

Does anyone know the exhaust duration for this engine?

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