newbie with a 3.5 briggs

[frazzled]

first - i'm very new to any of this, so i apologize up front.

i'm trying to put together a kart for my kids and have a 3.5 briggs off of a used tiller i bought for $50 - i think it is a 1991. i was told the motor was a replacement for the tiller and the way the throttle/choke linkages were converted work for the tiller, but not a kart (attached). out of confusion, i drilled a hole in the butterfly, added a bike cable for the linkage and a return spring on the carb to get the butterfly back to idle (i can provide a pic if needed). it seems to work, but my concern is that it negates the governor spring and i want to be sure doing that won't cause some major issue or hurt the kids if he spring is not attached/able to function - any ideas?

also, the kart has i guess a jackshaft with a pulley at the engine end. the motor has a pulley still attached from the tiller. i understand that i should get a clutch, otherwise it takes off as soon as the engine starts - unless someone knows how to do it otherwise. i found a pulley clutch at northern tool for about the same money as converting to chain and somehow converting the jackshaft to a gear - any ideas on this clutch or is it not worth it? is there any benefit to going chain vs. belt? safety issues with either?

thanks for your help.

 

[landuse]

Have a look at the pic at the end of this thread. Maybe it will give you some ides.

http://www.diygokarts.com/vb/showthread.php?t=11973&page=2

 

[karl]

Can we get pics of your throttle connection, Jackshaft, and motor pulley?

 

[frazzled]

thanks for the link to that post, that last pic might be just what i need. here are some other pics. of the motor, throttle connection and jackshaft. appreciate your thoughts and insight.

 

[frazzled]

clutch barely engaging?

i installed a hilliard cent. clutch to the 3.5 briggs and finally have it ready to go. now there seems to be a problem with the clutch engaging? with it lifted, there is obvious engagement, but on the ground the kart barely wants to move. i know the motor isn't loads of power, but it barely moves the kart alone and not at all with any weight. the clutch started to give off a small amount of smoke at full throttle - it seems like it isn't engaging - but i'm not sure what i didn't do correctly - any ideas? i can take a picture of the assembly if needed. thanks for your help.

 

[DaiSan76]

Do you know your gear ratio? my clutch struggled quite a bit till I geared it was down.

 

[landuse]

Do you know your gear ratio? my clutch struggled quite a bit till I geared it was down.

I agree. If your gearing is not right your kart is not even going to move. Post some pics of your drive system and provide us with all the tooth counts on your sprockets. Oh....also give us the diameter of your rear tyres.

I don't think its your clutch giving problems, its your gearing imho

 

[frazzled]

thanks for replying. on the engine side, the clutch is a 10 tooth and a 10 tooth sprocket on the jackshaft. on the wheel side, the jackshaft sprocket is 12 tooth and the drive sprocket is 54 tooth. if i understand calculating ratios correctly, that gives me a 5.5:1 which i thought was good since top end speed is not what i wanted, just wanted it to be quick and enable my kids to have some fun bouncing around. did i think about this incorrectly? maybe i should have gone with 12 tooth all around?

as for the tires, i think they are 15x6. i'll confirm and post pictures at lunch. thanks for your help.

 

[landuse]

thanks for replying. on the engine side, the clutch is a 10 tooth and a 10 tooth sprocket on the jackshaft. on the wheel side, the jackshaft sprocket is 12 tooth and the drive sprocket is 54 tooth. if i understand calculating ratios correctly, that gives me a 5.5:1 which i thought was good since top end speed is not what i wanted, just wanted it to be quick and enable my kids to have some fun bouncing around. did i think about this incorrectly? maybe i should have gone with 12 tooth all around?

as for the tires, i think they are 15x6. i'll confirm and post pictures at lunch. thanks for your help.

We will wait for the pics before we comment. I calculate your gearing at 4.5:1. You might want to go a bit lower than that.

 

[Doc Sprocket]

Your final ratio is 4.5:1. With 15" tires, that's not low enough. If you replace the 10T jackshaft input sprocket with a 14T, that would bring you down to 6:3:1, which would probably be a more clutch-friendly ratio. That still gives you a projected top speed of 25MPH@3600RPM.

 

[frazzled]

obviously i didn't understand the theory behind gear ratios as i just got the 10 tooth sprocket for the jackshaft. tires are confirmed as 15x6. toystory you mention going to a 14t on the jackshaft and i want to be sure i understand this more before ordering another sprocket, since it appears impossible to purchase locally - if the desired result is to not be as worried about top end speed, but more focus on torque and off the line speed, is a 14t going to do that or should i look at something with even more teeth like a 18? should i change both sprockets on the jackshaft to 14? the kart is for my kids that are 5 and 8. also attached are a few pictures of the setup. thanks to all for your input - this forum is a huge help!

 

[Doc Sprocket]

You really only need to change the one sprocket. Given the ages of your kids, you might consider gearing lower still. Even 25MPH is mighty fast for kids that age. That said, we can examine a lower ratio by replacing the 14T I suggested with something larger. As the kids age, you can regear it for more speed.

 

[frazzled]

so 18t or more than that?

 

[Doc Sprocket]

Depends on your desired performance. Although projected top speed is subject to several factors, the result it usually pretty close.

If, for example, you decide that a 16MPH top speed is something your kids can handle, then put in a 22T, for a reduction ratio of 9.9:1.

What sort of area/terrain will they be riding around?

 

[frazzled]

10-15 mph for now would be fine for them - they are just going to be playing in parking lots and a few open grassy fields - no major hills.

 

[Doc Sprocket]

Gotcha- I geared my kids kart for 13MPH. It still thrilled them, bombing around the yard at that speed. I'll regear 'em later. So in your case, you oughta get 15MPH by gearing at 10:8:1- which you will achieve by changing out the above mentioned sprocket to 24T. This is assuming your engine is still factory-governed to 3600RPM.

 

[frazzled]

i'm sorry, i just found the thread on gear ratios and a calculator - thanks for all the help guys.

 

[frazzled]

toystory you've been a huge help! i found a large array of sprockets here: www.surpluscenter.com, in case someone else needs it and go with the 24 you recommended. this kart doesn't have roll bars, but i was thinking of adding a seat belt - any thoughts on that?

 

[Doc Sprocket]

For the help, you're perfectly welcome.

The safety rule of thumb is as follows- If there's a roll bar or cage, install a restraint. If there is not a bar or cage, do NOT install a restraint.

 

[landuse]

Sorry frazzled, but I got in too late to help you some more. Toystory did a brilliant job of that though. I hope you get your desired result.