I have been running the Mikuni VM16 with good results. Plug color showed a bit on the rich side for the 79cc, but pretty close to correct. I set the clutch to pull in just above the choke-on idle rpm so I can comfortably start the engine without the bike pulling. This is usually around 2800-3000 rpm for the start of clutch engagement. I usually cruise along comfortably at 35-38 mph, so 5200-5600 rpm. These are real numbers as I do it all the time.
Sportsman 80 Build
- Thread starter sportscarpat
- Start date
By the way Rick, I have not been porting the heads or even pulling them to install the valve springs. I rotate down to bottom dead, fill the cylinder with rope, rotate up to hold the valves, then just by hand compress the spring to remove the retainer and swap out the springs. Remove rope, readjust lash and it's done. It's not a race bike, just a solid daily driver with "real world" performance and durability.
That's a good trick!!
I've never used a 79cc HF, (only 99cc & 212cc), so I don't have any personal experience between the 79 & 99, but I've heard from many guys that there's a notiable difference of power (not top speed) between the 79 & 99.
Using heavier valve springs is a must for any of the HF engines... I've also heard that there isn't very much difference in using a big cam. :/
I'm somewhat addicted to motor forums & your the first one I've run across to describe the "rope trick". First time I saw the rope employed in such fashion was by a local mechanic in about 1957. Since then I've had ocassion to use it from time to time. I use a small, .25" or so, diameter hemp rope, well oiled to lessen the amount of fiber contamination in the cylinder. Nylon won't shed as bad but my simple theory is that any oily hemp fibers left behind will burn better than the nylon. Probably it's just because that's what we had back then & also that's how the 2nd. guy I saw use the rope trick did it...fellow by the name of Alf Francis (the former head mechanic for World champion Sterling Moss of Formula one racing fame) while he was working as shop foreman for the Ferrari distributor Breen Kerr in Oklahoma City back in the early 1970's. The memory made me smile as I read your informative post! Rick C.
Geez, Rick, those are some important people there. I am a huge vintage racing fan. I go to the Monterey Historics every year and they are only a couple weeks away. Can't wait!
I can't believe nobody ever mentions the rope trick. It's the second best way to change valve stem seals. I prefer using an old spark plug (hollowed out) that's been welded to an air fitting. Thread it in and hook up air, and it holds the valves open no problem. Unless you have massive leakage, then there's no point in changing the seals. Plus it leaves no stringies, which really do no harm anyway. It's just faster this way, which means everything to an auto mechanic.
I have used compressed air to hold valves in place to replace valve stem seals. The hose fitting popped off and I dropped both valves. Fortunately that cylinder (it was a V8) was close to top dead so we rotated the engine and it was enough to raise vales back into their seats and reapply air. Didn't have to pull the head. So air works good, too, but ALWAYS be at top dead first.
Think some of the photos you've posted were from that great event, just a guess as I've never been. It must be terrific.
I'll keep this brief, reducing the temptation to ramble about Alf (never met Sterling Francis) thereby jacking your build thread.
My wife worked for Breen Kerr son of the late U.S. Senator from Oklahoma. In 1971 I traded my 1970 911S Porsche at his dealership for a new 1971 Ferrari Dino 246 Spyder & became acquainted with Mr. Francis during my 2 year love affair with the little mid engine sex machine. During my visits to the dealership he kindly regaled me with stories of the great team & driver. His stories mean more to me now than the sweet red auto! Rick C.
Here is the Sportsman three piece sprocket adapter being installed on my Worksman rear wheel.
Sprocket Adapter by Pat Dolan, on Flickr
Due to the sprocket offset I need running the four stroke with my reduction drive system I need to modify the coaster brake arm. This is not necessary on two stroke builds, but with the four stroke I need all the offset I can get.
Brake Arm by Pat Dolan, on Flickr
And here it is with adapter mounted. By the way, I now only use the aluminum Worksman rims and not the steel ones. The aluminum rims have better manufacturing so the quality is superior to the steel rims. They also come standard with stainless spokes.
Worksman Wheel by Pat Dolan, on Flickr
Sprocket Adapter by Pat Dolan, on FlickrDue to the sprocket offset I need running the four stroke with my reduction drive system I need to modify the coaster brake arm. This is not necessary on two stroke builds, but with the four stroke I need all the offset I can get.
Brake Arm by Pat Dolan, on FlickrAnd here it is with adapter mounted. By the way, I now only use the aluminum Worksman rims and not the steel ones. The aluminum rims have better manufacturing so the quality is superior to the steel rims. They also come standard with stainless spokes.
Worksman Wheel by Pat Dolan, on Flickr
Aluminum wheels & the Sportsman hub adapter work just fine on these large 4-stroke bikes!
I used 50mm aluminum Felt wheels & a Sportsman Flyer hub adapter (with a 56T sprocket) on my 212cc Ruff Cycles build & it hasn't slipped or had a single problem.
Here's a link... http://motorbicycling.com/showthread.php?t=52906
I used 50mm aluminum Felt wheels & a Sportsman Flyer hub adapter (with a 56T sprocket) on my 212cc Ruff Cycles build & it hasn't slipped or had a single problem.
Here's a link... http://motorbicycling.com/showthread.php?t=52906
My adapter design is pretty well documented, but one of the nicest features is it easily installs through the fat Worksman spokes without bending spokes or grinding on the adapter. As far as offsets once I modify the coaster brake arm it is no longer the limiting factor. I can then run the sprocket all the way away from frame centerline until it contacts the frame, then I just move in just enough to not rub the frame.
Not only do I trust it, it's all I use. The tooling used by the aluminum rim supplier is far superior so the quality of the rolled rim comes out nice and round with a good blend through the seam area. The steel rims are a pain to properly true and always have a rough seam.
What is the Worksman part number for the Alu. rim? All I can find is #329 and it's a steel wheel.
