HF 79cc question for new build

chainmaker · Jul 6, 2011

My first throttle set-up used the govenor...I re-mounted the set-up to bypass and I did not notice any increase ( I dont have a tach so I cant be positive) This week the govenor pin fell into the case so I had to crack it open and I am removing the gear as well. I should have it all put together this coming week-end and will take it out for a spin.

WayneC · Jul 6, 2011

Handy tip when removing the gov.
When you knock the gear out of the case, take the gear apart. The shaft is in 2 pieces. The actual shaft and the sleeve that contacts the gov. arm. Bang the pin/shaft back into the case where it came from. It won't interfere with anything as it was there before. That hole is now sealed. The sleeve that was on that pin is a press fit for the gov. arm hole in the top of the case. Bang it in and that hole is sealed! No threading; no gooping/epoxying. Used parts on hand!
Cost: 0!
WC

chainmaker · Jul 7, 2011

Any tips for getting that flywheel off ? I dont have an impact wrench. I tried a socket and grips on the shaft, I might mount the motor to My bench on My day off to get some better leverage on it, but any tips would help.

LS614 · Jul 7, 2011

well, I've never done it to a four stroke, but it's still supposed to work just fine. You take somwhere around 20 or 30 feet of cotton clothes line and cram it into the combustion chamber carefully using a screwdriver. Then, when it is completely stuffed, you can torque on things on the shaft as much as you want and the engine won't turn over. This trick has saved me before, hope it helps

WayneC · Jul 7, 2011

^^^^^^^^^
Yes works fine on 4 strokes too. 20-30Ft!!!!???
Holy smokes! I think I used about 5FT.

LS614 · Jul 7, 2011

oh wow, I normally cram

chainmaker · Jul 7, 2011

Im going to try the rope trick when I get home!!

LS614 · Jul 7, 2011

yeah, I learned that one in an ancient engine repair book I got for like $3 SOOOOO worth it

MarkSumpter · Jul 7, 2011

agk said:
You have a couple options with the govenor. One thing our customers have done successfully is stiffen the govenor spring. This will cause the govenor to kick in at a higher rpm.

You can also bypass the govenor like what is being suggested here.

We go in the motor a pull the govenor out. With the 6.5hp engines, if you bypass the govenor and leave it in the motor, the govenor can come apart inside the motor causing damage. This doesn't always happen, but often enough so we do not leave them in the motor.

The 79cc engine is governed at 3600 rpm. Our 79cc engine turns 6000 rpm now. That little govenor assembly is not designed to spin that fast. When you hold one in your hands you will see why.

One of our 79cc bikes is geared 12.44:1. This bike does a great job climbing hills. It does a much better climbing than our 49cc bike that is geared 17:1. Actually there is no comparison because the 79cc bike has a whole lot more torque.

The 79cc bike I'm talking about went about 25mph at 3600 rpm (going off of memory here...I have some rpm and speed results written in my notes which are not here). We wanted to know how fast it would go if it had the govenor and we kept this gearing.

hahah I have seen the governors fly apart and it isnt pretty...

Where is the link to the AGK Gear reduction for these units? I looked on your page but couldnt find it...

MotorBicycleRacing · Jul 7, 2011

MarkSumpter said:
hahah I have seen the governors fly apart and it isnt pretty...

Where is the link to the AGK Gear reduction for these units? I looked on your page but couldnt find it...

affordablegokarts: 79cc Parts

scotto- · Jul 8, 2011

MarkSumpter said:
hahah I have seen the governors fly apart and it isnt pretty...

Where is the link to the AGK Gear reduction for these units? I looked on your page but couldnt find it...

Did you want the tranny or the gear ratio calculater?

dnut

chainmaker · Jul 8, 2011

Im looking for a calculator with instructions.

WayneC · Jul 10, 2011

Hey guys, what clutch are you folks using. I'm gonna belt drive my project and what I've been able to find out is that the belt pulley clutches engage around 1800RPM. I put a tach on my HF79 yesterday and it idles at 18-1900. Anything lower than that and it shakes and sputters like crazy. Tough to keep running.
Any help?

cannonball2 · Jul 10, 2011

WayneC said:
Hey guys, what clutch are you folks using. I'm gonna belt drive my project and what I've been able to find out is that the belt pulley clutches engage around 1800RPM. I put a tach on my HF79 yesterday and it idles at 18-1900. Anything lower than that and it shakes and sputters like crazy. Tough to keep running.
Any help?

Hey Wayne, Im using a Maxtorque and my HF 79cc Idles nicely well below the engagement speed. Are you sure you tach is right? sounds like maybe its reading higher than actual.

LS614 · Jul 10, 2011

Max torque is the clutch of choice for most of us 4 stroke guys. If you go to their site and call them directly they can help you A LOT. They can do higher rpm springs, belt pulley, whatever you want, and the price is good too

MaxTorque

wayne z · Jul 10, 2011

cannonball2 said:
Hey Wayne, Im using a Maxtorque and my HF 79cc Idles nicely well below the engagement speed. Are you sure you tach is right? sounds like maybe its reading higher than actual.

1800 sounds fast for idle.
These engine's ignitons operate on the lost spark method. One spark per rev. If yer tach is adjustable, you need to set it for that.

WayneC · Jul 10, 2011

Thanks guys. I'm pretty sure the SenDec tach is accurate albeit the lag time of the digital display. BTW, I ran the HF79 up to 5400RPM (no load) yesterday before backing it down. It started running a little rough. when I put the tach on my lawn mower engine it idles @1640. My 52cc 2stroke idles at 2200; clutch engagement springs are supposedly set for 3000 and they start to grab at 3 on the tach. I don't know how else to check accuracy unless buy another and compare the 2. That's an expensive test! As an old flight instructor told me long ago--when in doubt-DON'T and ALWAYS trust your instruments--they're all you got up here!
WC

Elmo · Jul 10, 2011

wayne z said:
1800 sounds fast for idle.
These engine's ignitons operate on the lost spark method. One spark per rev. If yer tach is adjustable, you need to set it for that.

I have three hf 2.5 engines and they all idle around 1700 to 1800 rpm

Elmo · Jul 10, 2011

WayneC said:
Hey guys, what clutch are you folks using. I'm gonna belt drive my project and what I've been able to find out is that the belt pulley clutches engage around 1800RPM. I put a tach on my HF79 yesterday and it idles at 18-1900. Anything lower than that and it shakes and sputters like crazy. Tough to keep running.
Any help?

Same for mine. My maxtorque engagement rpm was 2200 if I remember right. I ordered an 1800 rmp spring and have a little trouble with it trying to engage at idle.

WayneC · Jul 10, 2011

Thanks Elmo. I guess the best thing to do is contact MaxTorque and get their info./ recommendation. 2200 engagement would be fine.

WayneZ, I get what you're saying and halving the 1800RPM would get me an idle of about 900-cool! But if that were true, as far as the tach goes, then my high RPM of 5400 would be cut in half too. Although there is no provision for adjustment of the tach, I've used it on 4 stroke and 2 stroke and it seems accurate.
WC

HF 79cc question for new build

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