Newbie looking for advice

Dirtdad

Dirtdad

Member
#1
#1
Picked up this 3 1/2 motor for 20.00. Basically the guy just wanted it gone, was ready to throw it in the trash. I want to use it on my minibike project. I started a thread on that under projects. The motor seems clean, has spark, gas in the tank is old and varnish smelling. The oil level is good, just looks a little used. Compression seems ok with the very crude check of just holding a finger in the spark plug hole. The thing is, there was no spark plug on the motor, it had been removed, and who knows when. Do I just clean the tank, and carb, and try to start it, or should I order a head gasket and remove that and take a look. I have also thought I could buy one of those cheap inspection cameras that use your smart phone, and just check nothing has fallen in there. Everything feels ok when I pull the rope with the plug removed, even get a little gas smell, like its sucking fumes from the carb. I have not played with one of these motors since I was 12, 59 years ago, and figured some of you have been in this situation before. What would you do?
Also, if anyone has converted one of these motors for mini bike use, what did you do to adapt the controls to a twist throttle? I think I want to retain the governor, not sure how that works. Is this motor a flathead? Points, or electronic ignition? How do you turn it off once converted to minibike use? It currently has a pulley for a belt, that Ill need to remove.
Really appreciate any and all help, and thanks in advance. 3.5 hp Briggs and stratton.jpg
 
cl350rr

cl350rr

Well-Known Member
#2
#2
Put some gas in it and start it. It is a flathead with electronic ignition. You have already pulled it through and found that it turns freely without a plug installed, that would pretty much eliminate anything which could have fallen into the plug hole, there is not much room in the combustion chamber for foreign objects. If it still worry's you, pulling the head is fairly easy, the head gasket can likely be reused.

please post a pic of the other side of the engine showing the output shaft.
 
Last edited:
cl350rr

cl350rr

Well-Known Member
#4
#4
Looks to be a short 5/8" output shaft, if you are going to run a centrifugal clutch you will need to drill and tap the center of the shaft for a retainer bolt.
 
Havasu Dave

Havasu Dave

Moderator
#5
#5
In addition to the good advice from cl350rr, you'll want a minibike throttle set up. It makes it all easier, though you lose the air vane governor. Not that big of a deal, if you don't hold it wide open. Also, those pulsajet carburetors will gum up if left in fuel for long. That is the long tube from the bottom of the carb to the tank. It's job is to pump fuel from the tank to the smaller "tank within the tank" where the shorter tube picks up fuel. That gets clogged, and the pump itself gets worn- accessed by the four tiny screws on the side of the carb. A rebuild kit for the carb has all the parts you need, and is a simple thing.
 
Dirtdad

Dirtdad

Member
#6
#6
so, what size and pitch bolt should the shaft be drilled and tapped for? Where do you get the minibike throttle set up, do you have a link?
How would you set up turning off the motor for a minibike, cut off power to the ignition module, or? I seem to remember on my home built on a Frijole frame, when I was a kid, it had a kind of lever you flipped against the spark plug, and it just grounded the ignition?
Thanks for the info, guys.
 
Dirtdad

Dirtdad

Member
#7
#7
Just looked at my thread on "Projects", and Jim Donovan mentioned 5/16, fine thread (24) for the tap size. Ill work on that after I get the motor running.
 
Havasu Dave

Havasu Dave

Moderator
#8
#8
Dirtdad said:
Just looked at my thread on "Projects", and Jim Donovan mentioned 5/16, fine thread (24) for the tap size. Ill work on that after I get the motor running.
Click to expand...
That's the one. It's easy (soft) steel and not difficult at all. I don't know if our host Hent sells throttles, but these guys do, as well as ebay. For a kill switch, run a wire from the magnetron coil to a handlebar mounted bush button switch. It's the wire that is "not" the ground, but that wire is going to be found on your stop switch on your current control panel- which you will not be using. I note that Hent.com sells the parts for your carburetor. I would definitely pull that all apart and clean it and inspect it, and check for varnish obstruction as cited above. (And cool to hear you had a Frijoe when you were a kid!) :)
 
sparkwizard

sparkwizard

#9
#9
If you remove the air filter housing...the bottom also...take a look at how that throttle lever is connected. Some of those multipurpose engines had a little groove with a screw and a clamp to attach a remote cable. You will also see the kill switch wire clipped onto the control assembly. You can un plug that wire and wire it to a kill switch grounded to the engine or frame remotely.
 
Minimichael

Minimichael

Well-Known Member
#13
#13
Now that's pure gold. Thanks, Dave. Hey it even looks like Google's AI is just plagiarizing your work, lol. Interesting option, too, when you explain the cable can install on a lower throttle arm – and effectively opposite the (otherwise functioning) governor. Even seems preferable over rigging your cable directly to the butterfly assembly.
 
Havasu Dave

Havasu Dave

Moderator
#14
#14
Minimichael said:
Now that's pure gold. Thanks, Dave. Hey it even looks like Google's AI is just plagiarizing your work, lol. Interesting option, too, when you explain the cable can install on a lower throttle arm – and effectively opposite the (otherwise functioning) governor. Even seems preferable over rigging your cable directly to the butterfly assembly.
Click to expand...
Thanks Pard! LOL, being plagiarized by a Superior Intellect is the epitome of my existance as a human! :)
 
massacre

massacre

#15
#15
I prefer a rocker style switch over a push button, just for safety. You gotta keep that button pressed until the engine stops turning, otherwise it can start back up. In a "oh crap" situation the switch shuts the ignition off and it won't start back up.
It happened to me once with a button and almost ended really badly.
just imho
 
sparkwizard

sparkwizard

#16
#16
massacre said:
I prefer a rocker style switch over a push button, just for safety. You gotta keep that button pressed until the engine stops turning, otherwise it can start back up. In a "oh crap" situation the switch shuts the ignition off and it won't start back up.
It happened to me once with a button and almost ended really badly.
just imho
Click to expand...
You still need to be sure it is securely and cleanly grounded.
 
Dirtdad

Dirtdad

Member
#18
#18
Hadnt thought about having to hold down the button, but youre right, I dont need that in an "o'shit' situation, not that I need any of those. I do like the look of those better, but looks arent everything. Mostly.
 
Havasu Dave

Havasu Dave

Moderator
#19
#19
Dirtdad said:
Hadnt thought about having to hold down the button, but youre right, I dont need that in an "o'shit' situation, not that I need any of those. I do like the look of those better, but looks arent everything. Mostly.
Click to expand...
I use kill buttons on all of my dirt bikes as well. The reason is, if I need to shut down with a stuck throttle, I have the button right there at the bars where I can maintain control of the bike. If I have to reach down and flip a switch, I am taking my eyes off the road, and riding one handed. I also like the slim look, and using the one wire, though there are toggles that are externally grounded.
 
You must log in or register to reply here.
Top