HF 2.5HP is a killer engine! New Speed Record!

[Danny3xd]

Hi Everyone, and to Lowracer -

I just ran my engine up to 73 miles on the odometer. It has about 5 hours on it. Been motoring around on common streets, about 5500 feet above sea level. This altitude and the fact the engine is still breaking in leaves me thinking there is power unavailable to me at this time.

How long would you allow for breaking in, on stop and go streets and stock air filter?

My bike is geared for acceptable acceleration at sea level; it is a bit weaker here (allowing 3% power reduction per 1000 feet). I have reached 32 mph for a brief time at 3700 rpm using a jackshaft and Sick Bike Parts MegaRange cassette 3rd gear in back.

Thanks,
MikeJ

I built with the HFs 4 or 5 times. Love em. They have some odd quirks. They hate, and I mean hate the cold. But back to your question. According to their manual, 20 hrs min. for break-in. I say it is closer to between 30/50 hrs. But one of the odd things about em is the are finicky about weather. I have broke them in every way I know how. From "ride it like you stole it" to my last build which was oddly enough, according to the manual, run at half or so power for 3 hrs then easy for the next 17 hrs. This by far worked best for me. She starts easy and sounds happier. Does rev a tad lower then the ones I broke in hard but IMHO, worth the compromise. Vid below is of her with half choke and ambient temp of 37F.
http://s293.photobucket.com/albums/...ew&current=HFwrubbermufflerandeasybreakin.mp4

The muffler is a rubber "blow-bag" It is intended to help plumbers unclog drain pipes and lines. You attach a garden hose then insert in a sewer or clogged drain line. The "bag" inflates and expands and forces a jet of water down stream. I tried it as a joke thinking it would thump a few times and then explode. It didn't and turned out to work great. Kids and animals seem to actually like the sound. (who knew? snork) $20 at Homedepot and $7 at HarborFreight.

Oh, and my top MPH is around 32 @ 4000 RPM. Can run em up to 5K but eats em up.

http://s293.photobucket.com/albums/mm48/dan3xd/?action=view&current=0927001549.jpg

 

[MikeJ]

Hi Dan -

I viewed a few videos; they are good to see. What internal diameter exhaust pipe do you use? And where did you get it? The pipe I am using is 3/4 inch copper hot water heater line (see photo). Some day I might want to replace the current exhaust line either out of necessity or because it may be restricting max power output.

Thanks,
MikeJ

 

[Danny3xd]

Mike, I used EMT electrical conduit. Worked great. Cheap and easy to bend. 3/4. bent on well. Kinda funny, but when it got hot, spit the galvasinasion on the freshly painted tank.

 

[professor]

I maybe mentioned this somewhere, but the these motors are lean- making them requiring a choke to stay on for a long time and hard to start in the cold. I opened the main jet 2 or 3 thousandths and it is all better.

 

[Danny3xd]

Thanks Professor. Gonna try that

 

[samuari86]

i love my HF 2.5 motor,it dose every thing i ask it to

 

[MikeJ]

Hi Guys (especially the recent posters) -

I took my bike out today for a 47 mile spin. I have the "chronic flat tires from thorns" syndrome fixed, now it is time to move on to engine performance enhancements.

My starting altitude is 5500 feet above sea level (asl) and up to 7000 feet asl during my ride on a hilly two-lane road heading east from Albuquerque. The intake filter and carburator are still stock; the exhaust is a 3/4 inch copper pipe and has no muffler. First gear ratio is 14.4:1. I just got done running the engine up to 9.7 hours on the hourmeter. The governor has been removed and I limit rpm on the straightaways to 3700.

Given the above combination of low time hours and high altitude, can you recommend any adjustments to get more hill-climbing power out of this engine? 5500 feet asl is the lowest point of the ride. On a hot day like today, density altitude can easily make the ride seem like 500 feet higher. On some long climbs, the engine simply bogs down to 2500 rpm and the clutch starts slipping; I think it should do better. At sea level on a cool day, I am sure this engine would have plenty of reserve power. Here, I need to make adjustments.

Any comments or recommendations?

Thanks,
MikeJ

 

[ibdennyak]

Hi Guys (especially the recent posters) -

I took my bike out today for a 47 mile spin. I have the "chronic flat tires from thorns" syndrome fixed, now it is time to move on to engine performance enhancements.

I weigh in at 240 lbs. My starting altitude is 5500 feet above sea level (asl) and up to 7000 feet asl during my ride on a hilly two-lane road heading east from Albuquerque. The intake filter and carburator are still stock; the exhaust is a 3/4 inch copper pipe and has no muffler. First gear ratio is 14.4:1. I just got done running the engine up to 9.7 hours on the hourmeter. The governor has been removed and I limit rpm on the straightaways to 3700.

Given the above combination of low time hours and high altitude, can you recommend any adjustments to get more hill-climbing power out of this engine? 5500 feet asl is the lowest point of the ride. On a hot day like today, density altitude can easily make the ride seem like 500 feet higher. On some long climbs, the engine simply bogs down to 2500 rpm and the clutch starts slipping; I think it should do better. At sea level on a cool day, I am sure this engine would have plenty of reserve power. Here, I need to make adjustments.

Any comments or recommendations?

Thanks,
MikeJ

Change the ratio.....or Professors suggestion above sound good.

 

[Danny3xd]

I read back but did not see, what are you using for a clutch Mike?

I've always had a "jerky" start. For my first couple of hundred miles, I had no pedals and was testing my reduction gear hard so always thought it was just that I had beaten the clutch. Although a lot lighter and live in a flat-ish area. is pretty locked in at 2400 RPM. Is a MaxTourq clutch that starts to engage at around 2K. Only one long hill where I ride but will see what the RPM goes down to.

I learned this the annoy me to death way, but would not worry to much about performance a whole lot until she has a lot more hrs. They really smooth out. But that is at sea level with less load/hills.

Just my experiences.
Also forgot to mention, is easy to block air flow with pant leg. In the summer, I remove the cover and replace with chicken wire to hold the foam filter in. Winter, I have a stock cover with a hole the same size and directly over the intake. LOL, kept wondering why I was bogging down. One of them duhhh moments.

 

[MikeJ]

Hi Dan -

I did forget... The clutch is a Max Torque that engages around 2300 rpm or so. It sounds like it is the same model you have. I have a new one on order from Jim at Max Torque. That will have the cartridge bearing. It will engage at 1650 rpm, so shoe slipping at 2400 rpm should not occur. We'll see.

Maybe it is my imagination, but it seemed the motor pulled better an hour into the ride after putting some real stress on it. But it still has a long way to go to compare to a 66cc two-stroke I was using at similar altitudes last year (It also improved with stress). I will give the engine more time.

I may drill a series of 1/4 inch holes in the filter cover; that may help a little. The Professor adjusted the mixture screw on his engine for better performance; I will try that. I remember way back before computer controlled injection that automobile carbs for high altitude driving had to be adjusted for that purpose, versus carbs for low-altitude driving. I'm always open for more ideas.

Thanks,
Mike