Top speed and rpm loss?

[DJEEPER]

maybe you need to get an IR thermometer to check the temp that it is running at....

What octane fuel are you running? If the engine is running hot and you cant help it, put some 93 in there....


Maybe you should get a tuned pipe?

Drop your carb in an ultrasonic parts cleaner. Maybe you have a partially clogged jet?

Rebuild the motor?

 

[arceeguy]

My thought is that he is too rich, and the warmer weather combined with the high altitude are making things worse. If it is humid, it'll make things worse as water vapor (not combustible) displaces oxygen in the air. So hot and humid at 5700 ft. = cr@ppy running engine!

If you are too lean, you will have more power at part throttle than at full throttle, is this true?

Have you performed a "plug chop"? This will be an excellent indicator of which way you need to go.

 

[danlandberg]

DJ; I don't think it's running to hot (looking at the chrome header) hardly any discoloration, you know how chrome turns blue. And I do plan on getting a tuned pipe & a carb made for the 66/80cc engines. I'm going to pull the tank and clean fuel valve. I do have a new jet & tube, probably change that too. The rebuilding part will come after I get another engine (GRUBEE 66/80cc)!!!

 

[MikeJ]

A question for you high-altitude guys. I have an engine with right at 200 miles now on it. The first 175 miles was at a 24:1 ratio; the last 25 at 28:1. I'm running at altitudes ranging from 6,000 to 7,000 feet above sea level. The factory default carburetor setting is in place.

Reading the opinions about leaning tends to support my observation. At WOT and 24:1, my max speed was about 29 mph. (24:1 is less burning gasoline per unit volume of air; a leaner condition. I am assuming the oil does not provide power.)

At WOT and 28:1, my max speed was about 26 mph. (28:1 is more burning gasoline per unit volume of air; a richer condition).

I may keep the 24:1 mixture to provide the greater quatity of oil and the little-better speed. I prefer not to tinker with the carb. I'm not especially interested in max speed at WOT.

And another observation: My bike's rear tire seems more unstable on rough-surface roads ("chip and seal" it is called around here) at max speed. It is more stable on more costly smooth-surface roads. Anyone else sense this? Maybe it is time to check air pressure again.

Any comments?

Thanks.

 

[danlandberg]

Well I was a little confused about gas to oil mixtures lean & rich. But I'm learning from these threads! I'm at 5500 feet, and I had to drop my needle 1 notch to get it to go faster than 12 mph. I have hit 42 mph at a 20:1 mixture. I had a loss of top speed with this last gallon of prem. fuel (25:1) I am going back to reg.fuel and 20:1. But toward the end of the gallon I started to get speed back, I "think" that evaporation caused a drop in mixture ratio. As far as the unstable rear wheel, Check your spokes for tightness. I ride on dirt roads all the time and have to check mine every week. I ride an older heavy Royce Union mountain bike with 14ga. spokes (wish they were 12ga.)What are you riding, MB, Beach Cruiser, ect.? I run 45/50 psi, max is 65 psi.

 

[MikeJ]

Hi Dan -

When you moved the tiny clip, did you move it toward the blunt end of the needle? Or toward the pointy end of the needle? Was the change significant enough to justify digging into the carb? So it sounds like: a change in needle clip setting, regular gas, and more oil per unit of gas is your best performance combination. Is that right? If so, I may copy your recipe.

Are you running a 44-tooth sprocket? 26 inch wheels? At 42 mph? According to my calculation, you were winding that engine out to almost 9800 rpm! Is that sane? I can't get any more than 5800 rpm out of mine with SBP jackshaft drive. I am under the impression that about 7200 rpm is redline. Maybe some other reader can provide a better number.

Not to get off of engine settings, but: Thanks for recommending spoke tightness. And I will check for max tire pressure for a 26 x 1.95 mountain bike tire. I have a Haro V3; a fairly hefty frame for my fairy hefty frame. With a wide seat, I am ready to tackle a 150-mile ride.

Mike

 

[danlandberg]

Toward the blunt end (needle is lower) allowing more air than fuel. It made the difference between night and day!!! I am thinking at this alt & temp. (weather conditions), Was the ticket for me, anyway. Yes I am running a 44 tooth Sprocket, Going to go to a 36T.( I HAVE A NEED FOR SPEED )!!!! And yes it did sound like disaster in the air!!! I don't know what rpm I was pushing, but it sounded like it was up there! I do run 26" rims and 210 tires. Just look on the sidewall of the tire for max psi. I like to run about 5/10 psi from max for traction and ride comfort. If your going to do (not try) a 150 ride, take care, your hands will get numb, I know it happened to me, I went down at 32mph. Had to look down to "SEE" how much brake or how little brake I was using (Could not feel my hands or fingers) Vibration at 30+ is a killer! Even after 10 or 12 mi. I weigh in at 140 + a 20lb back pack & a 30+ bike (gravel on a dirt road don't mix well)!! Lost my job over the accident, But oh well it gives me more time to build more of these things!!! LOL

 

[danlandberg]

I did the 20:1 mix this time, And I can tell the differance! I hit 30mph in windy conditions. I'm getting close to my 50mph goal!! And still mostly stock set up! I hope everyone is safe on these things! They can be to MUCH FUN !!!!!Check this out!!! http://www.maniacworld.com/Record-New-Years-Eve-Jump.html Don't try this at home, unless you can peddle really fast!:batman::78: The guy is nuts, or has one missing!

 

[danlandberg]

I tried to edit, But there is something wrong Try www.maniacworld.com Check out the new years eve jump

 

[MikeJ]

Hi Dan -

I'm thinking, "Whew! This guy has too much horsepower or the gumption to try something that only Evil Knievel would try!" Be sure get a helmet and witnesses who knows first aid to support your story and that you lived to tell about it.

Back to engines: If your combination gives you that much difference in performance, I will try it as well and let you know. Aug 16 is my planned date, weather permitting. If you see me on the highway, I will be in a white motorcycle helmet, bright yellow jacket, leather work gloves, and long jeans. At 30mph max at any time!

MikeJ