Yes indeed! There are several references to disconnecting the governor. And not anything, that I saw in my re-read, that said special flywheel.
I know for certain that you know what you are doing with small minibike engines and I have never got too deep into them. Other than increasing the compression ratio and changing the rocker ratio [on an Intec], and re-grinding cams I don't have much experience. The cam thing was only done when the engine was to operate above the governed RPM.
I am wondering if you will agree with the following: If the question is "How do I get the most bang for my buck in a single hop-up mod?" I say, no question, it would be to greatly increase the compression ratio. Simple for a flathead. No big thing, really, for a overhead valve engine. LEAVE the damned governor alone.
I think, due to the relatively low gas speeds encountered, when the engine is left with it's governor intact, there is little reason to spend a lot of time and money on porting and larger carb....the gain for such things is only realized, in large measure, at RPMs above the regulated 3600.
The engines that I have bumped the compression ratio on were mostly Briggs flatheads and you can't easily get a whole lot of extra squeeze. But boy how it wakes up the little motor. Added performance from idle all the way up! Then there is absolutely no need for a high-zoot flywheel and piston and rod. Reliability of the little motor is not seriously effected and that is a big plus.
Where am I wrong?
I know for certain that you know what you are doing with small minibike engines and I have never got too deep into them. Other than increasing the compression ratio and changing the rocker ratio [on an Intec], and re-grinding cams I don't have much experience. The cam thing was only done when the engine was to operate above the governed RPM.
I am wondering if you will agree with the following: If the question is "How do I get the most bang for my buck in a single hop-up mod?" I say, no question, it would be to greatly increase the compression ratio. Simple for a flathead. No big thing, really, for a overhead valve engine. LEAVE the damned governor alone.
I think, due to the relatively low gas speeds encountered, when the engine is left with it's governor intact, there is little reason to spend a lot of time and money on porting and larger carb....the gain for such things is only realized, in large measure, at RPMs above the regulated 3600.
The engines that I have bumped the compression ratio on were mostly Briggs flatheads and you can't easily get a whole lot of extra squeeze. But boy how it wakes up the little motor. Added performance from idle all the way up! Then there is absolutely no need for a high-zoot flywheel and piston and rod. Reliability of the little motor is not seriously effected and that is a big plus.
Where am I wrong?
Thanks for the response.
I do appreciate the wealth of experience and knowledge shared on this forum.
I agree with the higher compression thing totally Oldsalt.
According to the "Modding 5hp Briggs' thread and this dyno summary, it was the 2nd most substatial gain...behind porting and losing the stock exhaust.
http://www.oldminibikes.com/forum/b...some-guide-modding-briggs-5-hp-flatheads.html
http://www.aviator.cc/briggs.txt
I just thought if I could bring a broader range of power by inceasing flow and installing a cam and springs it would be a good idea.The rod is, from my understanding, is a weak link if these briggs motors go above recommended rpm and if I remember correctly the minibike I have seemed to have valve float at this range and just didnt seem to be what it could be.
I found Jeep2003's insight pretty interesting about valve timing.
Well just trying to get as much info as possible before diving in with a dremel for a port and cutting eyebrows.
Right now as it stands I've got the milled head and will be searching for this so called 94ss cheater cam or any other advice to try pull a few more horses out of my stock 5.
Thanks in advance
I do appreciate the wealth of experience and knowledge shared on this forum.
I agree with the higher compression thing totally Oldsalt.
According to the "Modding 5hp Briggs' thread and this dyno summary, it was the 2nd most substatial gain...behind porting and losing the stock exhaust.
http://www.oldminibikes.com/forum/b...some-guide-modding-briggs-5-hp-flatheads.html
http://www.aviator.cc/briggs.txt
I just thought if I could bring a broader range of power by inceasing flow and installing a cam and springs it would be a good idea.The rod is, from my understanding, is a weak link if these briggs motors go above recommended rpm and if I remember correctly the minibike I have seemed to have valve float at this range and just didnt seem to be what it could be.
I found Jeep2003's insight pretty interesting about valve timing.
Well just trying to get as much info as possible before diving in with a dremel for a port and cutting eyebrows.
Right now as it stands I've got the milled head and will be searching for this so called 94ss cheater cam or any other advice to try pull a few more horses out of my stock 5.
Thanks in advance
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I was led to believe that its not always just about compression. Adding flow via some eyebrow shaving would be a good for some gains, then maybe offset the compression lost by the eyebrow shaving by using a thinner head gasket? Otherwise I think you would need some machine work done to the head and block to get more compression.
Ok well heres how i do it on briggs flatheads. You should get a valve spring compessor if you dont have one. makes it alot easier to get the keepers in.
First pull off the shroud and head and carb so you can get into the valve spring comparment.
Good time to clean the carbon out of the head and piston too.
So now you can check the valves. turn over the flywheel so you can get a feel for the firing cycle. Intake combustion exhaust.
Now take your two fingertips and twist a valve while turning it over slowly. Youll find it doesnt close tight on the compression stroke. Usually the piston will only have an inch or less worth of full compression until its at top dead center.
So to remedy this patheticly handicaped engine you need to shave the back of the valve stem to get the valve to stay seated a bit longer. You dont want to take so much off that the valves are closing at the bottom of the compression stroke. Just half way or maby a touch less. This is what is known as valve overlap. When the intake and exhaust are open in the compression cycle.
So you need to pull out a valve . grind a little off the stem and replace it and check again. this is where the valve spring compressor comes in handy. because youll usually need to pull it out and replace it 2 or 4 times till your satisfied. Youll end up taking off quite a bit of the taper on the valve stem. Try to grind it as flat and even as possible. A sander or file works ok too if your afraid youll take too much with a grinder. Usually the exhaust will take alot more than the intake.
Again you dont want to take too much off. Take it slow because there is no going back unless youve got extra valves laying around. Again youll want to leave atleast 1/4 -1/2 the stroke of overlap.
Throw that baby back together. and ride
Youll find the pull start quite a bit harder to pull . thats the first sign of good compression :thumbsup:
Iv also found many engines to be much easier to start after this. Probrobly helps alot on the pulse carbs .
I havnt noticed any ill effects from going a bit beyond the manufacturers recommended valve lash. But Id recommend doing it on an engine that you dont much care about the first time around. Just incase :laugh:
First pull off the shroud and head and carb so you can get into the valve spring comparment.
Good time to clean the carbon out of the head and piston too.
So now you can check the valves. turn over the flywheel so you can get a feel for the firing cycle. Intake combustion exhaust.
Now take your two fingertips and twist a valve while turning it over slowly. Youll find it doesnt close tight on the compression stroke. Usually the piston will only have an inch or less worth of full compression until its at top dead center.
So to remedy this patheticly handicaped engine you need to shave the back of the valve stem to get the valve to stay seated a bit longer. You dont want to take so much off that the valves are closing at the bottom of the compression stroke. Just half way or maby a touch less. This is what is known as valve overlap. When the intake and exhaust are open in the compression cycle.
So you need to pull out a valve . grind a little off the stem and replace it and check again. this is where the valve spring compressor comes in handy. because youll usually need to pull it out and replace it 2 or 4 times till your satisfied. Youll end up taking off quite a bit of the taper on the valve stem. Try to grind it as flat and even as possible. A sander or file works ok too if your afraid youll take too much with a grinder. Usually the exhaust will take alot more than the intake.
Again you dont want to take too much off. Take it slow because there is no going back unless youve got extra valves laying around. Again youll want to leave atleast 1/4 -1/2 the stroke of overlap.
Throw that baby back together. and ride
Youll find the pull start quite a bit harder to pull . thats the first sign of good compression :thumbsup:
Iv also found many engines to be much easier to start after this. Probrobly helps alot on the pulse carbs .
I havnt noticed any ill effects from going a bit beyond the manufacturers recommended valve lash. But Id recommend doing it on an engine that you dont much care about the first time around. Just incase :laugh:
jeep
valve overlap occurs at the top of the exhaust and intake strokes to force out exhaust gases and draw in fresh air/fuel mix. not during the compression cycle as you stated. the intake should remain open slightly into the compression stroke as the velocity of air fuel mix allows positive air flow to continue as the piston starts to rise in the compression stroke increasing dynamic compression. exhaust should open at the bottom of the power stroke(how far into the power stroke i don't know) to maintain more piston velocity through the exhaust stroke.
It sounds like you have the right idea, this is just the theory behind what i understand you to be explaining.
valve overlap occurs at the top of the exhaust and intake strokes to force out exhaust gases and draw in fresh air/fuel mix. not during the compression cycle as you stated. the intake should remain open slightly into the compression stroke as the velocity of air fuel mix allows positive air flow to continue as the piston starts to rise in the compression stroke increasing dynamic compression. exhaust should open at the bottom of the power stroke(how far into the power stroke i don't know) to maintain more piston velocity through the exhaust stroke.
It sounds like you have the right idea, this is just the theory behind what i understand you to be explaining.