79cc Sportsman Flyer build

xXNightRiderXx

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Jan 12, 2017
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Wouldn't let me edit my last post, so this is a continuation:

Boise is smack dab in the middle of a bowl shaped valley. Any smoke from fires in the north or south gets funnelled straight to us. There have been some days that visibility was down to a mile, and the air felt heavy. You could even smell the smoke it was so bad. But, that's what it is every year, so we get used to it. Of course, we get our own fires too, but we also get regular weather. In fact, two weeks ago, we had a pretty heavy 3 day rainstorm. Probably put out a fire or two and helped reduce the others. Came in slow, and left slow. Earlier that week, we had a dust storm. Two months without rain left the entire area dry as a bone. Wind kicked up a lot of dust and sand, brought visibility down to half a mile. Worst weather I've seen in this city in years all around.
 

Tom from Rubicon

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Apr 4, 2016
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Nice to be in the shop today for sure.
Rick sent his hot air up here + fugging muggy 93F and no breeze. At least here at Rancho Pedro.
Pines and brush almost a 360 perimeter = no breeze.
Inside the shop, 75F and a dehumidifier running. All chains are on. Added a little slack to the primary.
On the hot rod rebuild, I got the primary too tight as in not wanting to run freely. Fixed.
If you watch some of the Son's of Speed youtubes their chains are flip flopping alot. So will mine.
Lines are fine, Likely the lack of stress will ease sprocket wear.

One last thing I wanted to do. Pat removes the rubber feet from the NYC Tour Double kickstands and extends the legs with machine bolts. The rubber feet do not stay on. Minor design flaw.

And the only beer I brought in the shop is still half full, I got time to give it a go,
It appears the aluminum tube legs were swaged into a taper. I didn't even center punch the leg ends, the drill went center.

Started with a 3/32" drill but as soon as I realized the drill would not wander off center, I fitted the cordless hand drill with a 1/4" drill to tap 5/16-18.
The American Standard and Unified Standard letter F .257 and taps are designed to cut threads in steel that size bore to achieve the 75% engagement between screw and fastener or threaded object.
The kickstand legs being aluminum I went with a slighter fit. 5/16-18 button head screws with a lock washer underneath the head will add at least 1/4" length to the kickstand legs.

Proving the port, polish, and compression increase of a Harbor Freight engine, has been a long time coming. the fruits of my lazy beer imbibing labors. Stay tuned for my further adventures. Like a break in the rain.

Tom
 

xXNightRiderXx

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Jan 12, 2017
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Will you also be adding a cam, or keeping the stock cam?

I'm wanting to modify my valve timing a couple degrees, make it as efficient as possible. Have the exhaust open a couple degrees later and the intake a couple of degrees earlier, and have them both close a couple degrees later. In essence, increasing intake duration while maintaining exhaust duration, while at the same time increasing the amount of time the intake charge has to both enter the cylinder and push out the remaining exhaust. This should increase thermal efficiency since there would be a minimum of remaining exhaust gasses hindering combustion, and the maximum intake charge. Lift will not be changed. This along with a port and polish should make the most out of the fuel being consumed, rather than having some be wasted. I'm thinking an 80 grit bit would be enough to maintain or even increase atomization. If I'm wrong about this, don't hesitate to say so.
 

indian22

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Dec 31, 2014
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Tom I also replace the aluminum bolt in my drive off stands with steel and weld a 1.5" round support plate on it. No dig in tip overs with the resulting setup on a variety of soft surfaces. Comes in handy parking just off roadways.

I also modify the stand to lock securely while up on stand to prevent accidental stand folding...really great security for a variety of situations during.maintenence work or in public situations. Also slows down a thief having to figure out the stand mech.

Rick C.
 

Tom from Rubicon

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Apr 4, 2016
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Will you also be adding a cam, or keeping the stock cam?

I'm wanting to modify my valve timing a couple degrees, make it as efficient as possible. Have the exhaust open a couple degrees later and the intake a couple of degrees earlier, and have them both close a couple degrees later. In essence, increasing intake duration while maintaining exhaust duration, while at the same time increasing the amount of time the intake charge has to both enter the cylinder and push out the remaining exhaust. This should increase thermal efficiency since there would be a minimum of remaining exhaust gasses hindering combustion, and the maximum intake charge. Lift will not be changed. This along with a port and polish should make the most out of the fuel being consumed, rather than having some be wasted. I'm thinking an 80 grit bit would be enough to maintain or even increase atomization. If I'm wrong about this, don't hesitate to say so.
My engine mods. were made per Pat Dolan, port. polish, .050" head deck, and 18# valve springs. Pat advised against a modified cam. He said the performance was negligible.
Combustion chamber and valve pockets were finished 320 grit and the intake and exhaust bores were flex honed 220.
The only other mods. were the AGK flywheel and Sportsman Flyer intake manifold and 19mm Mikuni carb..
Tom
 

indian22

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Dec 31, 2014
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Tom these mods are sensible hp mods and Pat makes his living selling bikes which are all around performers. Same with parts. I've not heard a single customer ***** about bikes or components from Pat. His advice is golden. I'm thinking you will see a 2hp + gain on power and this will be power that you will feel during everyday riding with enough torque on the low end to feel smooth. 4 or 5 hp from small displacement motor will get it down the road in a hurry and without fuss.

I've one bike in my stable that I seldom ride because of poor low speed manners. It's just not happy around town unless in first gear and getting with it. I went wild with the power mods and lost tractibility at lower rpms. The same engine in my Simplex has very few motor mods and is a dream at slow speeds. Chasing big deal power in an everyday rider is a mistake in my opinion.

I think you'll like riding your bike Tom.

Rick C.
 

Tom from Rubicon

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Apr 4, 2016
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I think all that's left to do is fill the crankcase with 1/2 qt of racing oil (high zinc additive) and open the petcock and see if it fires.
Taking Rick's advice about kickstand feet to mind.
I went with 5/16-18 button head cap screws, shimmed with 1/16" thick lock washers which added to the stand legs length will easily keep the rear tire from contacting pavement. If parking on soil where there not a tree to lean on.
I would made feet as Rick describes if I thought I had a need.

I have never found any empirical data pertaining to the proper amount of oil required in a 79cc Predator engine with a vertically oriented cylinder. Static fill I think should be 2mm short of the crank shaft seals.
Misfit has been off the radar for a while. As I recall he had put a sight glass in to his side cover.
My last engine oil fill in 2020 using 1/2 qt. did not pump oil into the catch can, and the engine did not seize.
Input please.

Tom
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Just chiming in here about the oil fill level... When I did one of my 212cc upright engines, I measured how far down from the crank shaft the normal oil fill level was; then when it was turned upright I measured down & drilled & tapped a hole (with a plug) in the side cover so I could see the correct oil fill height.

I'll look for the post & link it later.


Also...as far as modding the 79cc engine?, I say 'go for it'!! Those little engines are gutless & they need all the help they can get!
If you need any advice please let me know. :)
 

Tom from Rubicon

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Apr 4, 2016
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Thanks for replying Norm, I like the brass plugged port. Classic old school. Like me.

Port, polish, and head deck were completed before Easter of this year. After that. Inertia strikes deep. Lack of a real job.
For most people, walking away at 70 is a want to do. Structured work I miss.
I am leaving the carb needle clip in the center slot and see who it goes.
Tom
 

Tom from Rubicon

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Apr 4, 2016
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Pulled the brass filler pug and poured in 16oz. of the high zinc 10-30 oil.
Let her down onto her feet, and all is as intended. And then I choked. Took to tidying up the work bench. Beer and a half. There are places on the bench with Deer Mouse turds. I hate mouse turds. While sucking on a beer, i started try to find a new home for all the wrench tools. All four sets. That doesn't include screw drivers and 3/8 drive Allen sets.
When I die, I wished I could be at the auction.
Tom
 

Tom from Rubicon

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Apr 4, 2016
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Rolled the Flyer out and after I figured out which position the ignition switch is fire. It light right up, nice steady idle. (^)
Hopped on and barely needed a pedal stoke to accelerate and on the level or down grade it really wants to go but it has no steam on any up grade. The stock engine was reluctant climbing. Even on 5% WOT today and it bogs down. If I back off on the throttle it gains a bit of power. Am I running too lean? The exhaust blued up fast I have not pulled the spark plug yet.
As I said, on the flat of down slope this engine wants to go.
Carb needle clip is in the middle notch of the $19 Mikuni clone.
As an aside.
The MTB brake lever is way better drawing up the Sturmey Archer drum front brake using it cautiously to avoid an endo.

Tom
 

xXNightRiderXx

Active Member
Jan 12, 2017
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Boise
Rolled the Flyer out and after I figured out which position the ignition switch is fire. It light right up, nice steady idle. (^)
Hopped on and barely needed a pedal stoke to accelerate and on the level or down grade it really wants to go but it has no steam on any up grade. The stock engine was reluctant climbing. Even on 5% WOT today and it bogs down. If I back off on the throttle it gains a bit of power. Am I running too lean? The exhaust blued up fast I have not pulled the spark plug yet.
As I said, on the flat of down slope this engine wants to go.
Carb needle clip is in the middle notch of the $19 Mikuni clone.
As an aside.
The MTB brake lever is way better drawing up the Sturmey Archer drum front brake using it cautiously to avoid an endo.

Tom
Yeah, you're too lean. With a 4 stroke engine, it's easy to tell. If you gain power with less air, your jet is either too small, or your needle too low. I'd say lower the clip a notch and retest. If it's still lean, lower the clip another notch. If it's still lean, then jet up one size and try again from the middle. I'd like to see your intake style. I really want to ditch this stock carb for a pbhg 19, and from what I remember, the mikuni uses a collar to attach the carb, much like the pbhg. The pbhg has an idle circuit adjustment that I would like to have, so I can idle lean but run a little rich under load.

Your exhaust shouldn't be blueing up at all. This engine likes to be run at no load and low RPM for a while before putting a load on it. Most likely, your rings haven't seated, so your rings are letting oil pass into the combustion chamber. It's good that you're using a high zinc oil, but are you using full synth or a synth blend? I used royal purple break in oil, which is a high zinc synth blend, and have no blue in my exhaust at all.
 

Tom from Rubicon

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Apr 4, 2016
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Before I got up this mourning I was rethinking yesterdays engine performance or lack of it. And I am thinking this engine is too lean. I never looked at the plug when I swapped engines.
Then I saw NightRider's post this AM. Bingo!
AGK recommended starting with the C clip in the middle slot and that is where it was. Which explains why the stock 79cc engine struggled too though not as bad. Had a different spark plug, non stock
Out to the shop and pulled the carb slide and got the needle out of the slide.
Popped the C clip and set in the bottom groove and before I could grab a needle nose to snap it into the slot. It vanished!
And I ain't no magician. Cleaned a section of the work bench. Lots of mouse $hit no clip. Serious scan of the floor and waved around the Tank Lifter super magnet. Mildly reprogrammed my Pacemaker steel chips but no clip.
As a rule, nothing gets me agitated. This did. :mad: Went to town and got a 12 pack of Leine's.
Got home and on the inernet and ordered PZ19 carb, be here Monday.

Pop a top and and head to the shop. Carefully searching amongst the mouse $hit. Then a thought, an inspiration.
Eurythmics, Annie Lennox, Dave Stewart - Missionary Man (Official Video) - YouTube
There was a woman in the jungle
And a monkey on a tree.
The missionary man he was followin' me.
He said "Stop what you're doing."
"Get down upon your knees." Thank-you Annie Lennox

So I did, and there it was right before me. Snapped that tricky clip into the bottom slot of the needle and reassembled the slide and fitted it into the carburetor.
Gas on, stitch on, starter cord wound on the spool, no choke, slight throttle advance, and briskly pull. We have ignition!
Took off with barely a pedal stroke. I mean this thing has steam, but while not as doggy on up grades. It will not accelerate up slope. WOT under load, the bog is there. I am not a carburetor guy. Genetically inherited. My people were long on four legged horse power.
Jetting info needed, or drill size to mod the existing jet.
Speed is not the goal as much a grunt.
By comparison, My Huffy 49cc Huasheng and 31T rear sprocket performs about the same. May a bit better.
Tom