High altitude tuning question

GoldenMotor.com

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
I live at 7000 ft, and I am having a hard time getting my engine to pull me any faster than 25-28 mph. I have port matched my manifolds and my needle is maxed out to the leanest setting. I am running the stock muffler, and Opti-2. My spark plug is a gray color, (alittle on the light side, but acceptable). I ordered my 66cc silver flying horse kit from bike berry and the ports on the intake and exaust looked clean out of the box. I have changed spark plugs to a NGS H7BS, because the engine was running hotter than what I have read here. My engine runs strong up to about 18-20 mph and then the exaust sound changes dramatically to a splatty sound and then the last bit of speed take for ever to max out. If I go down a hill with WOT it will get up to some scary speed, and then is seems to run a little better on the flat afterwords for about a mile. I am planning on ordering an expansion chamber in the very near future, but I was wondering if anyone has any tips first. Also, the performance seams to be speed based and not throttle possition. I say this because it will run fine WOT untill it reaches a sertain speed (rpm) and then it changes. Also, it will ramp to a really nice high rpm without the clutch engaged, but with it engaged I can only get to this rpm going down hill. The compression on this engine is high (I can't turn the engine over with one foot while holding the rear tire in the air with one hand as I have read some people can), and it has only went through one tank and a half. I am only looking for more speed so that there will be less cars passing me and less chance of being hit.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,266
1,797
113
Los Angeles, CA.
That spark plug is too cold! A colder plug won't make your engine run cooler, it'll just foul & not burn off the gas & oil from itself. Use a NGK B5HS.

High altitude means less air, so you also need to have less fuel going into the mix.
That 'splatty' sound that it's making is from being too rich. Change the plug & raise the c clip on the carb needle to the top notch (farthest from the point) & tell us how it's doing.
 

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
Thanks for the reply.

The engine performed the same before I changed plugs, and I know the engine will not run cooler with a lower temp spark plug, but the engine performance in a temperature range is related to the spark plug temp, ie hot runing engine requires a colder temp spark plug.

The c-clip is already in the top slot or "the leanest setting" and my spark plug is a nice grey color which I thought meant it was not running rich. Any other suggestions?
 

freewheeling frank

New Member
Mar 10, 2009
440
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73
ridgway colorado
hello where in big wonderful wide opening are you at? i grew up in lander! ok so i also live at 7k and ride over 9 quite often, here is what i did first i broke the engine in very well 24-1 for 4 tanks then i went to hobby lobby and bought a set of hobiest drill bits soldered up the jet and used the smallest bit in the kit to drill er out cant remember the bit size but it is tiny the made both of my 2 smokers run great as i had the same prob as you describe,you prob dont have a hobby lobby but if you can find someone that works with gas appliances like the gas company or propaner guys they can prob hook you up. hope this helps frank
 

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
I am in Laramie, right on the Co border. I guess that I will try that. How light of a grey can your spark plug be before it is to lean.
 

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
I have tried richer settings on the needle and the performance suffers, but the plug looks the same. I ordered the tuned exaust last night, so I am waiting for that. This town is horable for finding things in. I went to several stores and asked for wire gauge bits or a jet boring tool and they just looked at me like I was crazy! I do think that I am still running alittle rich on the top end, but I think that I will wait to make any mods to the jet untill after I get the pipe, that way I don't have to redo the jet work. It runs really well up untill it hits the rpm zone where it starts to splat even with WOT, so maybe it needs some more miles too. Thanks again and I will let you know what I find soon.
 

RonInColorado

New Member
May 4, 2010
27
0
0
Colorado
I've found Ace Hardware to be an excellent place to get wire gauge and a host of other things like a good assortment of quality nuts, bolts and washers that can be bought in the quantity you actually want or need rather than blister packs of ten times what you need.
 

SnowyRangeDesign

New Member
Apr 1, 2011
3
0
0
wyoming
This thread is probably long since dead, but I am in need of some help. I have just installed a Grubee 48cc on my son's bike and it doesn't run unless the choke is partially engaged. This makes no sense to me since we live a 7000 ft. Oddly enough, my weedwacker runs the same way. I tried new gas since the original tank was from a can of last year's supply. It seems that the engine should be running rich at this altitude, but I am not familiar with two stroke carbuerators.

Thanks for any suggestions.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
This thread is probably long since dead, but I am in need of some help. I have just installed a Grubee 48cc on my son's bike and it doesn't run unless the choke is partially engaged. This makes no sense to me since we live a 7000 ft. Oddly enough, my weedwacker runs the same way. I tried new gas since the original tank was from a can of last year's supply. It seems that the engine should be running rich at this altitude, but I am not familiar with two stroke carbuerators.

Thanks for any suggestions.
If you have to close the choke to get it to run that is a good indication that you have an air leak somewhere. Start simple and take a close look at where the carburetor attaches to the intake manifold. Don't rely on a metal to metal seal at that point. Use a gasoline resistant sealer and make sure you seal up the ends of the slots in the carburetor throat where it slides onto the intake manifold. Some of them are cut too deep and will allow air to enter. Look also at the intake to cylinder gasket. The kit supplied gaskets are notorious for leaking. Replace it with a good quality automotive gasket material.
There are other places to look for air leaks, crankshaft seals, etc. But start at the carb and go from there. Let us know what you find.
Tom
 

SnowyRangeDesign

New Member
Apr 1, 2011
3
0
0
wyoming
Thanks Tom. I have reattached the carb and redone the manifold to cylinder gasket with some Coppercote. The engine idles nicely now which would indicate to me that the leak is gone. However, when the throttle gets past 1/3 open the engine just dies. It is pretty lively in that limited throttle range. Our altitude here would indicate that a smaller jet is needed, but I seem to get more throttle range if I engage the choke a little. I am going to try soldering the jet and sizing it down a bit.

Mark
 

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
Make sure he is wearing a helmet! I just finished a month and a half stent in the rehab hostpital, along with six months of outpacient rehab, due to someone flipp'n a ***** in front of me. I guess that at least it was right in front of my house so that my wife found out about it right away! Otherwise, who knows how long it would have taken due to them thinking I was a John Doe. I wasn't even going that fast because I just made the turn on to my street and these little bikes don't excellerate that fast. Just to point out the falacy of our laws, he got a $65 ticket and I racked up a $225,000 hospital bill. Oh and make sure that he wears long pants, two skin grafts later I realize that the engine and exhaust will melt flesh to the bone! Now if I only could remember that month and a half following the accident and the accident its self I could tell you more details!
 

JesseN

New Member
Jul 2, 2010
15
0
0
Wyoming
By the way the expansion chamber exhaust that I had installed did make the bike run richer, and I had the needle moved all the way to the inside most noch. I had to dremile out the carrier and add a washer to the back and that seemed to make the engine run pretty good. I was just about to try to soldier the carb shut and then redrill, but it then became property of the police department and they can keep what is left of it.