I think a container would be a little much,....I think you are on to something with the 3M pad though!!
2.5 HP HF Performance Tips / Tricks
- Thread starter chainmaker
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I tried one briefly. Didn't work well. Well, it was a cheap scrubbie pad thing on an old and not running great engine so might try it again but was to stiff to allow good flow.
http://www.google.com/search?q=bulk...AQ&bav=on.2,or.r_gc.r_pw.&fp=691466ca07669fbe Should have tried this first.
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How about the 4 stroke filter from SBP I put one on HS and it breath's alot better
in combo with Quentons Flex pipe ..I dont have any hard numbers but it feels and sounds better..I pulled the plug A light chocolate color for me just right For now.
But am looking for a 19mm mikuni or equal..There are A lots of new things comming out for these bikes. Some to change the lives of 4 stroke riders forever...........
Stay tuned Flex.............
in combo with Quentons Flex pipe ..I dont have any hard numbers but it feels and sounds better..I pulled the plug A light chocolate color for me just right For now.
But am looking for a 19mm mikuni or equal..There are A lots of new things comming out for these bikes. Some to change the lives of 4 stroke riders forever...........
Stay tuned Flex.............
Sounds good, SBP air filter is a good upgrade.
How did your hot rod bike do at the death race?
Silverbear, if you go somewhere iike ACE hardware you can find foam air cleaner material that is used on lawn mowers and weed whackers I don't think scrub material will make too good of an air cleaner. The mower material and a couple drops of oil make an excellent air cleaner. Drilling main jets is no big deal. But its time consuming. I am now working on making some adapter plates for different carb mounts I have used some insulator blocks off some lawn mower engines. I'm going to try to mount a wabor (sp?) diaphragm carb the ones that have the built in fuel pump and see what kind of results I have. I have an old Sun gas exhaust analyzer I don't know if this will tell me if the engine is running rich or lean, maybe some one knows more about how to read this than I do. I also have one of Firebellies transmissions I need some parts for, whatever happened to this guy? He just evaporated from the forum. I just like tinkering with this engine cause I know its got a lot of possibilities. What a great hobby.
buzzard
buzzard
Got to be A tinkerer to really enjoy this hobbie. Or it's going to cost alot of $ to keep it going...........If you have to take it to a shop everytime something isn't
right............
right............
Going to the hardware store and buying a piece of foam will result in nothing better than what the Chinese have already provided with the HF motor. The foam filter element we sell is made by UNI. If you are not familiar with UNI they are a very big company who supplies high flow air filters for many professional Motorsports. Their air filter element is very high flow and does an excellent job of keeping conaminents out of your engine. If you want a cheaper route you should try to find this high quality filter element at a better price. Or see if K&N sells some of their quality air filter element at a reasonable price. Don't try to substitute a quality air filter with some cheap foam. Your motor already has cheap foam for an air filter.
Quenton did a good job explaining the main jet drilling process. If you still don't understand it send me a PM and I'll try to better explain.
Once you install an air filter that allows more air into your carburetor you will need to drill out the main jet so more fuel can join the additional air. You don't have to use a bigger carburetor. Drilling the main jet in the stock carb will work fine.
Once you have more air and fuel entering your engine the stock exhaust should be addressed. The stock exhaust on these motors is very restrictive. It's amazing these engines even run considering all of the baffles and passages the exhaust gasses have to travel through before exiting the muffler. Replacing the stock exhaust with something high flow really helps these engines breathe.
Chopping off the muffler and using the stock exhaust flange to re-route the exhaust through flex pipe or tubing will help greatly. We recommend replacing the stock exhaust flange because the ID is smaller than the exhaust port, thus choking down the motor. If you use a flange and tubing that matches the size of the exhaust port the exhaust gasses will exit the combustion chamber much easier resulting in more power and higher rpm potential. At the Death Race we turned our 79cc motor 6000 rpm.
Once you install an air filter that allows more air into your carburetor you will need to drill out the main jet so more fuel can join the additional air. You don't have to use a bigger carburetor. Drilling the main jet in the stock carb will work fine.
Once you have more air and fuel entering your engine the stock exhaust should be addressed. The stock exhaust on these motors is very restrictive. It's amazing these engines even run considering all of the baffles and passages the exhaust gasses have to travel through before exiting the muffler. Replacing the stock exhaust with something high flow really helps these engines breathe.
Chopping off the muffler and using the stock exhaust flange to re-route the exhaust through flex pipe or tubing will help greatly. We recommend replacing the stock exhaust flange because the ID is smaller than the exhaust port, thus choking down the motor. If you use a flange and tubing that matches the size of the exhaust port the exhaust gasses will exit the combustion chamber much easier resulting in more power and higher rpm potential. At the Death Race we turned our 79cc motor 6000 rpm.
The 79cc HF engine is excellent in it's stock form. This engine has so much more torque than the 49cc engine. Quenton helped us with gearing on our first 79cc engine. We ended up using a 12.44:1 gear ratio which provided great take off power, amazing hill climb capabilities and a top speed of 32mph at 5500 rpm. We removed the governor from this engine and made a new exhaust.
We built a new 79cc motor for the death race. This motor received governor removal, high flow exhaust, a bigger carb with custom manifold and very mild port work on the cylinder head. This motor performed well and earned us the top finishing 4 stroke at the Death Race.
There is more that can be done with the 79cc motor from a performance standpoint and we're working on a couple more ideas. We came upon a few interesting discoveries when we tore down the 79cc motor. The engine has a flat top piston. The piston was at zero deck height (we cannot deck the block). The valve to piston clearance was less than .020" (we cannot mill the cylinder head for more compression). We already knew the camshaft was plastic. We a little bit of experience re-grinding plastic cams, but this cam had no base circle to reduce. The base circle was all the way down to the shaft of the cam (if that makes any sense).
Overall, we really like this motor in a bike, stock or modified. I can't wait to try one with the q-Matic.
We built a new 79cc motor for the death race. This motor received governor removal, high flow exhaust, a bigger carb with custom manifold and very mild port work on the cylinder head. This motor performed well and earned us the top finishing 4 stroke at the Death Race.
There is more that can be done with the 79cc motor from a performance standpoint and we're working on a couple more ideas. We came upon a few interesting discoveries when we tore down the 79cc motor. The engine has a flat top piston. The piston was at zero deck height (we cannot deck the block). The valve to piston clearance was less than .020" (we cannot mill the cylinder head for more compression). We already knew the camshaft was plastic. We a little bit of experience re-grinding plastic cams, but this cam had no base circle to reduce. The base circle was all the way down to the shaft of the cam (if that makes any sense).
Overall, we really like this motor in a bike, stock or modified. I can't wait to try one with the q-Matic.
There is one important safety factor I would like to bring up for those modifying a 79cc HF engine. The govenor keeps these engines at 3600 rpm. When you remove the govenor the engine will easily exceed 3600 rpm. Your top rpm will depend on other modifications you have performed. If you are still running the stock exhaust this will choke the motor down and limit rpm at some point. Our HF motor turned 6000 rpm with the modifications we performed on it.
The point I want to make is these engines were not designed to spin over 3600 rpm. One concern is the stock connecting rod. This rod has it's limits. We haven't played with this engine enough to know what that limit is. The more important concern is the stock flywheel. The factory uses epoxy and a screw to secure the magnet to the flywheel. This design is fine for a motor that turns 3600 rpm, but becomes a concern for motors spinning higher. Again, we don't know what the limit of the stock flywheel is. When we arrived at the Death Race my 79cc motor had 13 minutes of run time on it. We hope to have billet flywheels available before anyone discovers the limit if the stock flywheel. Those magnets are extremely destructive when they come off at high rpm.
Just a heads up.
The point I want to make is these engines were not designed to spin over 3600 rpm. One concern is the stock connecting rod. This rod has it's limits. We haven't played with this engine enough to know what that limit is. The more important concern is the stock flywheel. The factory uses epoxy and a screw to secure the magnet to the flywheel. This design is fine for a motor that turns 3600 rpm, but becomes a concern for motors spinning higher. Again, we don't know what the limit of the stock flywheel is. When we arrived at the Death Race my 79cc motor had 13 minutes of run time on it. We hope to have billet flywheels available before anyone discovers the limit if the stock flywheel. Those magnets are extremely destructive when they come off at high rpm.
Just a heads up.
I have 1800 miles on mine. I have an exhaust with a flange that I matched to the port with 39 inch straight pipe and a free flow air filter. I do not have a tach but using the gear calc and a speedometer that is true the valves float at 6200 rpm. when it was geared at 12 to 1 it would top out at 38.5 mph now I have it geared 13.65 to one because I pull a trailer sometimes. It will pull to just a little over 35 before the valves float. I would like to find some heavier springs for it but no luck so far. the carb is bone stock. Like Dan said they are pretty much maxed out stock except for the air cleaner and exhaust.
We have stiffer valve springs. We didn't try the stiffer springs because they will likely flatten the plastic camshaft. Turning this engine 6000 rpm already makes me worry about the magnet separating from the flywheel. You would really be taking your chances turning this engine up higher with stiffer valve springs especially considering the engine is between your legs.
The next area of concern will be the stock connecting rod. The stock rod will only take so much. We've already taken a 3600 rpm motor to 6000 rpm. I don't imagine the stock rod will handle too much more than that. It certainly would be fun to put in stiffer valve springs just to see what she could handle.
The next area of concern will be the stock connecting rod. The stock rod will only take so much. We've already taken a 3600 rpm motor to 6000 rpm. I don't imagine the stock rod will handle too much more than that. It certainly would be fun to put in stiffer valve springs just to see what she could handle.
I took my Greyhound for a run last evening after having modified the stock filter. I removed the plastic cover and made up a rectangular (almost square) cover for it out of electroplate tin. Using an awl I punched a whole lot of holes in the cover, punched mounting holes for screws along the sides where it is bent over. Then I drilled out the small holes in the face of the cover to increase the air flow more. I put the original foam back inside, closed it up and took it for a ride. This engine already had the flex exhaust. I don't know if it's my imagination, but the engine sounds better now... more gutsy. What I am not imagining is the increase in power, which I would call dramatic. I'm able to pull hills now that I could not before this single no cost modification. I'm a believer. It makes me wonder if changing the foam element to something more free flowing will make more difference. Guess I'll find out and will take a plug reading to see what's going on inside the engine.
SB
SB
Here's the cover for the stock air box. First I measured what it would need to be and cut a piece of 1" pine to that dimension to use as a form for the cover. I cut out the cover from electroplate tin leftover from making a gas tank. I snipped the corners at 90 degrees so that it could be folded over to form sides. Where I wanted to make the bends I sandwiched the tin between two pieces of wood and bent the tin by hand. Then I put the cover over the block of wood and used an awl as a punch to make a bazillion holes. Later on I drilled out those holes to a larger diameter to allow for more air to come in. That's it.
SB
SB
Attachments
You're welcome. I don't know that it looks great, but it works. I don't see why you couldn't just drill a bunch of holes in the plastic cover and get the same effect.
SB
SB
