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Old 09-18-2015, 04:51 AM   #1
Canuck12345
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Default G16 low end power, limit top speed

Hello folk's, I believe I have a rather unique need to modify a G16 for use exclusively in rough/ hilly terrain while carrying an approx 150lb load at as slow as possible speeds.

I am hoping to get some advice on the best way to limit the top speed to as low as 4-5 mph (even less would be better), while having generous power to carry loads up a steep hill.
I know I am in for some clutching modifications, just not sure where to get the best outcome.

Here is where I am at now and hoping for advise on the most effective change that I can make.

The terrain is very rough and to gain ground clearance I am adding a 6" lift kit and 22" offset tires. Adding the larger tires will increase the speed and the load on the engine at engagement. This is not desired, but understandably a necessary evil.

I also have on order an 85+ Clutch Kit Sheave & Power Spring to modify the clutching and to bring up the rpm slightly in the lower speed power band.

If I could have everything (I think), I need I would like to have the clutches engage with the belt, stay engaged, but not continue to increase the final drive ratio by working its way up and down the drive/driven clutches.

I have a new belt on the cart, but it is not at the top edge of the driven clutch. Can this be changed to go to the outside rim of the driven? If so would a wider belt do it without dragging on the driven clutch at idle?

If I have been able to explain my need, has anyone got suggestions on the best way to go about doing this?

cheers
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Old 09-18-2015, 06:44 AM   #2
slonomo
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Default Re: G16 low end power, limit top speed

Without changing your gear ratio in your transaxle, you will be limited to clutching mods and belt change. A heavier spring in the driven clutch will help to prevent upshift, keeping you in "low gear" for longer. The beauty of the CVT system is that it is "load sensing". So it will constantly shift the clutches to maintain the engine in the "power band" so to speak. Your throttle position will have a lot to do with the ground speed of the cart, but the CVT has the ultimate say so in where the gearing needs to be. Yes a wider belt will give you a little bit lower take off gear ratio, but it will likely drag on the drive clutch and want to surge forward while starting. It can be done, but I don't know if you need to go that far.

Here's what I would do:

1. Install new clutch kit
2. Install new belt, proper size for the clutches
3. Tune the engine up so you are sure you are getting max power
4. Give it some good test runs.

I had a stock Yamaha G1 with the little 215cc 2 stroke engine. I had the engine running perfect, and installed the "Plowman's Performance Clutch Kit" as well as the "Plowman's Hot Setup" for more power. I can tell you that I was able to crawl up some of the steepest hills in Southern Ohio with that setup. With a load (a 200 lb passenger) it would slow down up the hills, but it would still go. I would say my ground speed was in the 8-10 mph range. Rpm was probably in the 3000 rpm range.

Your ground speed up those hills under load will be determined by the gear ratios of the clutches, the clutch spring, the powerband of the engine, and the position of the throttle plate on the carb. With so many variables you'll need to get some data first. Make some test runs with your tachometer and gps and record rpm and speed up the hill. Report back and we'll see where you're at.

Andy
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Old 09-18-2015, 07:30 AM   #3
bigstik40
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Default Re: G16 low end power, limit top speed

I agree with slonomo. I had a similar requirement for my G16 as I had 2 very steep hills to climb to get to my cottage from the lake. I overhauled and lubed my primary clutch (had flat rollers), put on a new belt, and installed the heavier white spring from CPP in the secondary. This worked like a charm for me.. I have carried as many as 5 people up the hills with no problem (just keeps chugging along !!). Also, I have seen recommendations here to use the secondary spring for a concierge cart (which is heavier) as a lower cost solution. Good luck - Ray

Last edited by bigstik40; 09-18-2015 at 07:32 AM.. Reason: added info.
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Old 09-18-2015, 08:43 AM   #4
Canuck12345
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Default Re: G16 low end power, limit top speed

Thanks for the tips gent's.

I am familiar with the CV clutching on snowmobiles, but no experience with carts. Ironically we are usually trying to achieve higher speeds vs lower.

I'm still going to try and find a way to limit the speed and have a couple more questions that may be crazy, but here goes.

Has anyone ever modified the dive or driven clutch's to mechanically prevent them from closing/opening any further than they need to after engagement? I'd think the driven would be the one to modify.
I might try this and hope to learn from others trial and errors.

I wasn't aware we could reduce the transaxle gear ratio?? I have only seen where the ratio is increased for higher speeds. I'll need to look into this.

What can be done with the position of the throttle plate on the carb? I assume this may be related to the governed rpm?

A much heavier secondary spring from another cart/model also sounds like it will help.

Thanks again gent's
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Old 09-18-2015, 09:00 AM   #5
raydhd
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Default Re: G16 low end power, limit top speed

I see they sell a high torque gear set 15:1 ratio for the G16.
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Old 09-18-2015, 09:12 AM   #6
Dave in VA
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Default Re: G16 low end power, limit top speed

I don't understand why you want to limit top speed to 5mph. With the gov nut turned all the way out it wouldn't be much more than that.
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Old 09-18-2015, 05:12 PM   #7
sho305
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Default Re: G16 low end power, limit top speed

The low speed gears might be the best option. Otherwise I would tell you to service the primary clutch on the engine, ensure its working properly. Then get a HD kevlar belt from CPP, get a cut secondary sheave someone has them new CPP or cartpartsplus maybe others but be wary of the cheap china ones that are too thin. Also make sure the engine is not moving under torque, check the tension cable if it has one it holds the engine away from the trans, tighten it up if it has one. You can tighten them until the belt is starting to drag. Also get a umax spring for the secondary that will keep rpm up. The governor will limit speed for you but not sure what the point of that is. The low speed gears will do a lot for that use but they are not given away or the labor to install them. i would say the cut sheave would help you the most it gives a lower gear, the belt works great and will also help lower the low gear a little, neither of those will affect much other than initial take off and power at the lowest 'gear'. The umax spring will hold rpm higher until you get to high speeds when the rpm is higher anyway, and its a yamaha part. It you preload it more it will hold rpm quite high all the time. If you put the low gears in you may not have to do that stuff other than making sure the clutches work right and I'd recommend a new belt or the HD belt would be nicer.
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Old 09-19-2015, 05:29 AM   #8
Canuck12345
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Default Re: G16 low end power, limit top speed

Thanks for all the tips and what a great site! Gladly going to donate to the cause.

I have a heavier secondary spring on order and will look into the cut sheath.
My new belt is approx 1/4" from the top of the secondary sheath, which is no doubt effecting some available low end torque.

I have read that the existing sheath can be ground down by a machine shop,
would anyone know how much the sheath is suppose to be ground?

Would adding spacers behind the secondary spring be the way to increase the pre-load further?
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Old 09-19-2015, 10:40 AM   #9
sho305
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Default Re: G16 low end power, limit top speed

The preload is two things, static and torsional. Static is spring pressure the spring has. Torsional is traditionally what is preload and the springs have a tang on the ends that lock into holes. Many aftermarket springs are for something else and do not have them so you can't preload them. If you get a umax they have them. Then you rotate (wind up) the sheave to the next ramp when you install it. The different holes will change the degrees you turn it to get to the ramp thus changing the pressure. The pressure is against the ramps causing them to shift down more with more pressure, this raises rpm. Static is spring pressure against the belt straight from the spring based on its size and the helix ramps have nothing to do with it. A G1 runs backwards in reverse and has ramps both ways for example, so you can't preload it, it runs more spring pressure with no preload. Most all 4 cycle carts run one way and can preload with the stock spring, in case of yamaha the HD umax spring also, aftermarket you are on your own. The umax was for carts with boxes factory or utility use to haul things etc. its longer and thicker wire.

With a ton of preload the stock spring can keep rpm very high, like WOT rpm all the time, though its not very nice to drive and there is not reason you need to go that far to get max power.

You can spacer a non tang spring but be careful of too much pressure on the sheave and you can lose top speed because the spring binds up.

Remember the static pressure on the spring is technically used for belt pressure so it does not slip, too much pressure wastes energy. The preload makes it not shift down to lower rpm so the rpm stay up with more preload but pressure is not changed a lot. The engine torque on the ramps is what increases belt pressure (clamping pressure) when under more power so it does not slip then. Aftermarket springs are a bandaid and that is why they are quite difficult to install and can in some cases even break cheap thin aftermarket sheaves, some of them are huge (some off ebay). That is why I recommend the umax and twist it up to what you need with preload.

You can turn your sheave down you ideally need a lathe, you cut the inside hub flat so they go closer together is all. The cut face is about 1/2" wide when complete. You can put the other sheave on it and fit a belt to see where you are at. Using a 1 1/4 wide belt on a yamaha can also do this somewhat but can drag more on the primary, but works, and is really nice on worn clutches. I have both wider belt (hd kevlar) and cut sheave. I think the sheave cut will help you the most as its the only thing that actually lowers gearing, then run the belt tight as you can get away with, it makes a big difference at <5mph speeds.

My HD wider belt and cut sheave the belt would stick out the top at rest about 3/16". As the belt wears it goes down some. Stock new belt sticks out less. The one sheave is metal and rounded edge so it can't stick out too much.
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Old 03-28-2017, 02:08 AM   #10
Canuck12345
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Default Re: G16 low end power, limit top speed

Hello folk's, I am dragging out an old post to show the objective I am tring to achieve and the great advise I have been given by the more experienced cart wrencher's so far.

My objective to is limit the speed of the cart to run as slow as possible. It will only ever be used to crawl up a steep rocky path to a cottage and then back down. Having the belt engaged between the clutches provides good engine braking going down hill and stops the cart from running away at high speeds by coasting (when the clutches are disengaged). At this point to keep the clutches engaged going downhill we hold the brake and throttle at the same time to engage the driven clutch. Of course this doesn't work well as the secondary will start to open and the cart will pick up more speed than desired. I'm thinking if the secondary won't open, a bit of throttle is all that will be needed to keep the clutches engaged and better limit the speed.

So far I have added a heavier secondary spring and clutch kit to provide more resistance to the opening of the driven clutch. It has helped, but given the clutch opens at all causes the cart to have reduced power and higher speeds than we desire.

The cost of gearing the cart down is big bucks and beyond the budget.

My latest idea (maybe a crazy one), is to mechanically prevent the driven clutch from opening at all by locking the sheaves together with a dyi bracket drilled and tapped into the center hubs of the clutch.

Here is my question. If I am able to make up a bracket that locks the hub/sheaves from opening at all, will the forces of the drive clutch closing on the belt cause other issues?
Will the forces break the driven clutch, or any fab'd brackets made up to lock it closed?

I know the cart will rev to the governor limit setting and this is a good thing providing the the rest of the drive can handle the stress of the driven trying to open against the locked secondary.

I have a few G16's that will have this same requirement so I'm wiling to make an investment in parts/machining costs for this experiment as required.

Hope this explanation make sense so I can get some experienced opinions on the feasibility of the concept.

Appreciate any opinions on how to achieve this.
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