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Hey folks, can someone tell me the size difference between a 3hp and 5hp flathead? I'm looking to get more power out of my bike but am not sure the 5hp will fit since a predator did not. thanks!

Well to answer my own question, I took a peek in my carb throat and saw that the butterfly was not able to open up all the way do to the lever my throttle cable attaches to butting up against the carb. I went ahead and bend it up rather than grind my carb and now the buttery can open all the...

Held up a ruler for a rough double check. Seems pretty close to my measurements

I’m reviving this ancient thread to ask, did folks ever come to a consensus on wether or not to remove the spiral from a pulsa jet carb on a fairly stock motor?

I ended up measuring the intake and buying this foam filter for pretty cheap: https://www.ebay.com/itm/Red-Bent-Foam-Air-Filter-32MM-For-50cc-110cc-125cc-ATV-Quad-Dirt-Bike-H-P/164228946839?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 Its about a mm bigger than the intake so...

Hey y'all, while doing research about the usual posts covering trying to get a little more power out of 3hp briggs flathead I saw someone mention grinding a bit off the top of your carb that stops the throttle plate from continuing to rotate. By throttle plate I mean the one that your idle...

That’s awesome! Worth a shot. My bike runs way better with the filter off so I’m looking for a less restrictive air filter. Any cheap suggestions?

I think I imagines maybe a more high flow air filter and and a more flowing exhaust could help the engine get some minor gains easily. Know of any simple mods worth doing to the stock muffler?

Thanks y'all these are some interesting points. I might just try and see how loud it is since the hardware store is nearby and pipe is cheap.

I see a lot of folks running straight pipes on their bikes rather than the stock muffler. Will this help give your engine more power or is it mostly an aesthetic choice? I'm wondering if running a straight pipe with my stock muffler attached to the end of it would make any performance difference.

thanks for the tips its a pretty silly looking thing, I plan on cutting the frame stretching it and welding something that hopefully looks a lil more like a tradition mini bike. def gonna ditch the plastic and lil tank and all that. I'm mostly just stoked about the fork, swingarm and wheels

this thing looks awesome, love that frame

Not sure where the 2hp is coming from? Its a 3hp briggs but thanks for the tips, sounds like jackshaft is definitely going to be the way to go. Also I know from the pic it looks like a big ol dirtbike, here is a shot from online of one or scale:

Oooops amidst my confusion I ended up ordering an 11 t clutch and a 72 rear sprocket last night. Wasn't really sure what to do an wanted to get the project started. Gonna see if I can change that 11 to a ten, thanks for the help!

hmmm good to know. I had a feeling the ratio calculators I've been looking at might be a little bit ambitious. The calculators are helpful but it is definitely tricky for someone building their first bike to speculate about what the low end might be like.

I'm leaning towards a 10t max torque clutch in the front and a 60t sprocket in the back. Anyone know a cheap source for a sprocket? They are surprisingly expensive online

Hey y'all, I'm working on planing out a diy build from an Old Briggs 80202 3hp I got running thanks to this forum. I have a pretty odd italjet bambino mini dirtbike frame I plan on cutting up to build a more traditional looking minibike. Probably just going to reuse the swing arm and fork. I...

thanks for the help folks, got it running! turned out to be the valves, gonna start a new thread specific to the ratio

Hey thanks for the tip n the coil gap! Sounds like a good thing to check. I ended up getting the engine to run! The problem was my intake valve. The gap was non existent to the point where it never closed. I ended up filing the valve by hand until the valve lash was right and it fired up...

It is a magnetron so no points and the flywheel keep looked fine when I opened it up to check. My understanding is that the timing is fixed with that system so it’s good as long as the key isn’t sheared?