I have a Phatmoto 79cc 4 stroke can I put a bigger carburetor on that engine say a carburetor that’s for a 125cc? Or even a 270cc?? Reason I ask is I got two new carburetors at Mardens for pennies on the dollar and I’m curious if I can upgrade my carburetor to one of those if it’ll give me one a higher speed or more miles per hour or more power or if it would hurt the engine
Can I increase carburetor size on a Phatmoto 79cc 4 stroke to higher cc?
- Thread starter Doodles
- Start date
Tony01
Well-Known Member
The function of a carburetor is to provide the correct air/fuel mixture at all throttle positions. Engine power is derived from the parts and fits within the engine itself. A carburetor for a much larger engine will at best need only rejetting, but more likely will not work properly due to reduced intake velocity.
If it ain’t broke, don’t fix it. You could get a little more torque by fabricating a longer intake, better exhaust, shaving the head, advancing timing, pretty much doing all “free” mods. A bigger carb usually isn’t one of them unless the specific engine build calls for it (headwork, high rpm billet internals, etc).
Tony01
Well-Known Member
Did you mean, eliminating the Governor? I’m not familiar with that specific engine on the PM79, but usually weak stock valve springs will limit engines before they blow internal parts.
By a long intake I mean increasing the distance between the carb and the engine. Your carb is probably right on the engine. Fab up an intake or find one like my old Briggs build with the s-shaped intake. I think about 3-4” is the best.
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I need help. I remove the governor arm. I removed the plastic sprocket inside the engine. I left the clip in the little rod where I attached to, and when I first took the side plate off the metal sprocket on the right ended up coming out with the plate, which I didn’t know to hold back all my pins fell, which I ended up gathering I figured out how to put them back together. I made sure the timing was correct with the dot do lined up on each on the left and right sprocket and first time I didn’t know that I had to like gap the valve lash or whatever that is so I bought I tightened it down way too much and friggin thing wouldn’t even I couldn’t pull the rope at all, but I went and bought a tool I needed. I gapped them correctly and now I got it to fire a couple times and I noticed I looked down cause I had my clutch cover thing off. I took the plastic guard off, and I noticed that the clutch is spinning like crazy. It’s just like fullbore spinning, but the bike’s not moving like the sprocket behind the clutch isn’t moving. It’s not moving the chain just the thing itself is friggin flying and I shut it off. I try to get it. Turned back on a couple times now. I can’t get it to turn on and it’s like flooding my air filter with gas. What what did I do?
I need help. I remove the governor arm. I removed the plastic sprocket inside the engine. I left the clip in the little rod where I attached to, and when I first took the side plate off the metal sprocket on the right ended up coming out with the plate, which I didn’t know to hold back all my pins fell, which I ended up gathering I figured out how to put them back together. I made sure the timing was correct with the dot do lined up on each on the left and right sprocket and first time I didn’t know that I had to like gap the valve lash or whatever that is so I bought I tightened it down way too much and friggin thing wouldn’t even I couldn’t pull the rope at all, but I went and bought a tool I needed. I gapped them correctly and now I got it to fire a couple times and I noticed I looked down cause I had my clutch cover thing off. I took the plastic guard off, and I noticed that the clutch is spinning like crazy. It’s just like fullbore spinning, but the bike’s not moving like the sprocket behind the clutch isn’t moving. It’s not moving the chain just the thing itself is friggin flying and I shut it off. I try to get it. Turned back on a couple times now. I can’t get it to turn on and it’s like flooding my air filter with gas. What what did I do?
Tony01
Well-Known Member
I don’t know what happened there, I didn’t really understand much of that response. Maybe break it up and edit for accuracy, you may be using voice to text and I’m confused… use the proper terms like crankshaft, cam, lifters, valves, rockers etc.. I don’t know a thing about that engine maybe provide a link to one… is it a flathead? Ohv?
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MEASURE TWICE
Well-Known Member
For a Briggs 3.5hp 80202 engine, I know I have seen mechanical timing off for intake valve.
If the intake valve stays open too long into the compression stroke, the venturi effect does just as well, but in the opposite direction. The gas gasoline mist instead of going into the cylinder, instead goes and soaks my paper air
filter with gasoline.
From that point on, the engine will be starved for air, flooded, yep.
I have a no adjustable mechanical timing on the old Briggs. I will need to get back to grinding valve stem tips, a crude way to compensate for reduced valve lash, caused by valve seat compression.
The new engine your using you will use the feeler gauge to adjust, but needs to be where in the cycle with relation the piston being to top dead center. A manual for the engine should have the specs and procedure so it is right.
MT
If the intake valve stays open too long into the compression stroke, the venturi effect does just as well, but in the opposite direction. The gas gasoline mist instead of going into the cylinder, instead goes and soaks my paper air
filter with gasoline.
From that point on, the engine will be starved for air, flooded, yep.
I have a no adjustable mechanical timing on the old Briggs. I will need to get back to grinding valve stem tips, a crude way to compensate for reduced valve lash, caused by valve seat compression.
The new engine your using you will use the feeler gauge to adjust, but needs to be where in the cycle with relation the piston being to top dead center. A manual for the engine should have the specs and procedure so it is right.
MT
Venice Motor Bikes
Custom Builder / Dealer/Los Angeles
There was a member on here many years ago who's name was Bike Guy Joe...
His signature was 'If it isn't broken & you mess with it enough, it will be'
Words of deep wisdom
In fact... I'm going to make that my new signature!!!
His signature was 'If it isn't broken & you mess with it enough, it will be'
Words of deep wisdom
In fact... I'm going to make that my new signature!!!
Wevil Kenevil
Well-Known Member
Wevil Kenevil
Well-Known Member
I had my ol lady tattoo that on the inside of her pudding cup.... ( Her mouth... get your minds out the gutter... Smh
Gordy
Active Member
Hey Tony01, I've got tons of old Briggs flatheads. I collect them. I've been wanting to build a bike with one for a while. How did you mount yours??