Stock size being 70, what elevation range was that intended for? I'm at 6000ft approx. Anyone else that is, what jet are you using on a stock straight head motor?
Jet size in relation to elevation
- Thread starter mogollonmonster
- Start date
You didn't trell us what engine or carburetor you have but we'll assume it is a Chinese 2 stroke with either the standard NT carb or the equivalent. It's always best to tell what you have so the advice given is at least for that engine.
Jet size, or those numbers used, mean little to a lot of us. We've found too much inconsistancy between vendors and manufacturers. The only way to know exactly what size (orifice size) you have is to measure it with wire gage drill bits, either metric or SAE.
As for your question regarding elevation, I used to be of the opinion that you had to go leaner as your elevation went higher. I'm also at 6000' and tune my carburetors leaner that many do. However, this past summer I took a bike to central Illinois. The local elevation where we rode was less than 1000' and my bike ran great. It showed no evidence of being too lean for that lower elevation. I typically use a .024 to a .026 jet size in the NT carb on a basically stock engine. No major modifications.
One would think that a 5000' difference would be enough to adversely impact how these little engines perform. Nevertheless, seat-of-the-pants, my speedometer and how the engine sounded all told me that my small jet size worked equally well at both altitudes.
Tom
Jet size, or those numbers used, mean little to a lot of us. We've found too much inconsistancy between vendors and manufacturers. The only way to know exactly what size (orifice size) you have is to measure it with wire gage drill bits, either metric or SAE.
As for your question regarding elevation, I used to be of the opinion that you had to go leaner as your elevation went higher. I'm also at 6000' and tune my carburetors leaner that many do. However, this past summer I took a bike to central Illinois. The local elevation where we rode was less than 1000' and my bike ran great. It showed no evidence of being too lean for that lower elevation. I typically use a .024 to a .026 jet size in the NT carb on a basically stock engine. No major modifications.
One would think that a 5000' difference would be enough to adversely impact how these little engines perform. Nevertheless, seat-of-the-pants, my speedometer and how the engine sounded all told me that my small jet size worked equally well at both altitudes.
Tom
Sorry folks
Sorry Tom, and everyone else. I have the SD Stinger 2-stroke with the NT carb.
The bike will only really run smooth under load, like uphill. When I reach ANY rpm, and let off the throttle a bit to maintain that speed, and the idle should smooth out, it starts four-stroking. I think. My frame of reference being a rather large number of chainsaws and trimmers, mostly STHIL. I've rebuilt whole saws on my tailgate before, carburetor too, and much more complicated than the little China Doll and it's little NT carb. I don't believe I've ever experienced four- stroking before. Not from any of my saws, or my friend's.
And I concurr Tom, I live in Arizona, and I set my saws up in Overgaard (~6500') and they run fine in Pheonix, or Flagstaff, or on the sides of Sunrise Mountain, one of our two skiing/boarding spots.(13,000' and change at the summit) To be fair, I can't even recall having to adjust anything, ever. I just dial them in at my ACE Hardware, and generally just maintain them until it's time to rebuild, which ain't often with my STIHLs. You can tell I love my saws because I use all capital letters, just like the big kids, hehehe.
As for resizing the jet my self, it's likely going to be my only option, as I'm having no luck at all sorceing them locally, and I don't have plastic for online shopping. Any recommendation as to solder type? I have lots of the lead free stuff for plumbing, if I'm not mistaken it's pre-fluxed. I don't use it much and I'm not at the house and won't be for a few days, but I have cash and a well supplied ACE Hardware, other than grade 8 hardware, what should I grab?
By the way I've got about 100 miles on the kit, and I'm 50 from home, and it looks like the bike May be my only way home. I've got myself in a bit of a pickle, I'm sure. The possibility of walking is after all why I brought the bike along to begin with.
A prompt reply would be appreciated, but I believe the bike will get me home, once I replace my hardware. I wouldn't have brought the bike really but I live in Snowflake now, and the ACE there sucks. The ACE in Overgaard is easily the best in about a hundred miles, their overall selection is only edged out by the two big box stores, Lowe's, and Home Depot, both 40mi away and across the street from each other. I'm still scratching my head there...My hardware has to come from somewhere and I believe in customer loyalty. Besides after ten years I know EVERYONE at the store, and who knows what, who doesn't know, and who thinks they know. That's a huge advantage on any project, especially ones that involve, what's the "PC" term now? Afro-American Engineering. I'm working on my master's in that subject by the way. Thanks everyone, for any info and reading my rather long post.
Sorry Tom, and everyone else. I have the SD Stinger 2-stroke with the NT carb.
The bike will only really run smooth under load, like uphill. When I reach ANY rpm, and let off the throttle a bit to maintain that speed, and the idle should smooth out, it starts four-stroking. I think. My frame of reference being a rather large number of chainsaws and trimmers, mostly STHIL. I've rebuilt whole saws on my tailgate before, carburetor too, and much more complicated than the little China Doll and it's little NT carb. I don't believe I've ever experienced four- stroking before. Not from any of my saws, or my friend's.
And I concurr Tom, I live in Arizona, and I set my saws up in Overgaard (~6500') and they run fine in Pheonix, or Flagstaff, or on the sides of Sunrise Mountain, one of our two skiing/boarding spots.(13,000' and change at the summit) To be fair, I can't even recall having to adjust anything, ever. I just dial them in at my ACE Hardware, and generally just maintain them until it's time to rebuild, which ain't often with my STIHLs. You can tell I love my saws because I use all capital letters, just like the big kids, hehehe.
As for resizing the jet my self, it's likely going to be my only option, as I'm having no luck at all sorceing them locally, and I don't have plastic for online shopping. Any recommendation as to solder type? I have lots of the lead free stuff for plumbing, if I'm not mistaken it's pre-fluxed. I don't use it much and I'm not at the house and won't be for a few days, but I have cash and a well supplied ACE Hardware, other than grade 8 hardware, what should I grab?
By the way I've got about 100 miles on the kit, and I'm 50 from home, and it looks like the bike May be my only way home. I've got myself in a bit of a pickle, I'm sure. The possibility of walking is after all why I brought the bike along to begin with.
A prompt reply would be appreciated, but I believe the bike will get me home, once I replace my hardware. I wouldn't have brought the bike really but I live in Snowflake now, and the ACE there sucks. The ACE in Overgaard is easily the best in about a hundred miles, their overall selection is only edged out by the two big box stores, Lowe's, and Home Depot, both 40mi away and across the street from each other. I'm still scratching my head there...My hardware has to come from somewhere and I believe in customer loyalty. Besides after ten years I know EVERYONE at the store, and who knows what, who doesn't know, and who thinks they know. That's a huge advantage on any project, especially ones that involve, what's the "PC" term now? Afro-American Engineering. I'm working on my master's in that subject by the way. Thanks everyone, for any info and reading my rather long post.
I did a video tutorial on soldering and drilling carb jets. It might help explain the details. It isn't professional quality by any means just something to illustrate how it can be done.
Maybe it will answer some questions for you. Good luck.
Check here > https://www.youtube.com/watch?v=GcYd97t-6ns
Tom
Maybe it will answer some questions for you. Good luck.
Check here > https://www.youtube.com/watch?v=GcYd97t-6ns
Tom
You rock Tom, you Rock. Thank you sir, I only wish I could return you the help, but I'm a plumber and we only need to know three things; which end of the shovel to use, lefty loosey, and $#¡% don't run uphill.
Pretty much unless you're racing where 1/1000 of a second can make a difference, you'll never feel the difference between riding at sea level or at 5000 feet... especially when we're talking about engines that put out under 3hp to move a 50+ lb bike and a 200+lb rider... now if we were talking about a 150 or so hp crotch rocket that only needs to move about 600lb you might notice a difference, but when we're talking about 80 to 100 pounds per horsepower the difference won't be noticed at the seat of the pants....
For the jetting, I definitely agree that soldering and drilling is the way to go but if you can aquire different sized jets in small increments you can still get it right but don't trust the numbers stamped on the side of these cheap Chinese jets since you can have 5 different jets stamped 65 and each one will perform differently... but there's always the risk in buying a set from 65 to 70 and none of them will dial in your carb perfectly...
For the jetting, I definitely agree that soldering and drilling is the way to go but if you can aquire different sized jets in small increments you can still get it right but don't trust the numbers stamped on the side of these cheap Chinese jets since you can have 5 different jets stamped 65 and each one will perform differently... but there's always the risk in buying a set from 65 to 70 and none of them will dial in your carb perfectly...
When I had the CNS carb on my bike, I had a **** of a time getting it started at 8800' and it ran like poop. My home elevation is about 1200'.
I've now got the NT Speed carb with one of the smallest jets. I'll see how it does in the mountains next week ---- maybe.
I've now got the NT Speed carb with one of the smallest jets. I'll see how it does in the mountains next week ---- maybe.
My bike was running lean at low rpm, and 4 stroking at WOT, and moving the carb needle clip up or down made both conditions worse. Turns out there was a tiny bit of crud stuck in my main jet, all i had to do was blast it out with some acetone and i was able to properly tune the carb and get everything working right.
Yeah I had a cns carb on mine for a while... a true pain to tune but it did good once tuned... I ended up swapping it out for a standard nt carb tho since I got tired of always fixing air leaks with the cns installed. I was able to get excellent performance and speed out of the nt carb once it was tuned proper.
My newest build is getting a mikuni vm18 but I also got the right size intake for it and I'm going to run it with the #70 jet initially then tune it after the engine breaks in. I've read these carbs do best with a #65 main jet but I like to run a little rich for the first hour or so of run time before trying to lean it out until it runs best.
My newest build is getting a mikuni vm18 but I also got the right size intake for it and I'm going to run it with the #70 jet initially then tune it after the engine breaks in. I've read these carbs do best with a #65 main jet but I like to run a little rich for the first hour or so of run time before trying to lean it out until it runs best.
Well I would say the motor is broken in, significant gain in power, but still my carb problems continue. I did as instructed, soldering and redrilling, still to rich I think. All the plugs I've pulled say so. Smallest bit I have mike's out at .024 and that was considerably smaller than "stock", but she's still not smoothing out till I hit a grade or s really stiff headwind, and even then I have to milk the throttle a bit.
Unfamiliar with "four-stroking" as I am, it's running rough, and seems like it's drowning. The plugs and it's behaviour on hills prove this out, and with time spent riding I can say with certainty it's not fireing when it should, more like every other stroke...
Nothing like firsthand knowlage! I can't seem to chase down a decent set of machinists drills, and according to the wife, I have to by jets.
She says when I buy tools I end up buying things to work on, bit when I buy parts we can afford toilet paper.
Unfamiliar with "four-stroking" as I am, it's running rough, and seems like it's drowning. The plugs and it's behaviour on hills prove this out, and with time spent riding I can say with certainty it's not fireing when it should, more like every other stroke...
Nothing like firsthand knowlage! I can't seem to chase down a decent set of machinists drills, and according to the wife, I have to by jets.
She says when I buy tools I end up buying things to work on, bit when I buy parts we can afford toilet paper.
Sounds like your wife has completed the Masters level of Men's Studies....... Sometimes, it's a scary thing when they know us better than we know ourselves!
Oh, and glad you've got the toilet paper!!
.024 = .61mm = 61 jet which is a lot smaller than stock (.70mm). Seems like a lot of people are calling and emailing about their engines "4 stroking, bogging, etc" and generally not responding to throttle twisting.
For sure reading the plug is key, a great starting point. If you are down to a 61 jet and the plug is still carbon wet rich, then I question the technique for shut down before reading, or the oil mix.
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Pablo, not arguing with you, just curious.
Could you define what you mean by "stock"? I've never encountered an NT carburetor that came with a jet as small as a .024. That's a pretty small orifice. It is however what I've found to work for most applications. It's the size jet that was in the bike I mentioned above that ran well in Illinois as well as here at home @ 6000'.
Tom
I'm using 6.4oz of STHILL HP ULTRA to one gallon of 87 octane. What would be the recommended method of shut-down?
Just found out my intake ANF exhaust gaskets were leaking, and that may be contributing to the problems I'll test run it in a few and reply.
Just found out my intake ANF exhaust gaskets were leaking, and that may be contributing to the problems I'll test run it in a few and reply.
20:1 with HP Ultra = extra oily and will be pulling air:fuel even leaner and with you running a 61 jet, I would say you are too lean. What you are seeing on the plug is oil unless you have some other issue.
Method for shutdown is full throttle, hot engine for a slightly extended period, then throttle closed, cut power via kill switch immediately, then glide to stop and allow engine to cool.
Fix gasket leaks.
Method for shutdown is full throttle, hot engine for a slightly extended period, then throttle closed, cut power via kill switch immediately, then glide to stop and allow engine to cool.
Fix gasket leaks.
Thanks. You had me second guessing myself because I respect your knowledge.
I probably should add that I run Opti-2 @ 100:1. That certainly impacts my mix and what jet works for me. Less oil = more fuel to air, hence probably why I get away with such a small hole.
Thanks for explaining the proper 'plug chop' to the OP.
Tom
Thanks Pablo, I agree I'm to lean regardless what the plug says as it just ran worse on my test run than ever! Like I said all my experience is with chainsaws, and so far it counts for just about poop!
Chainsaws are not pulling 200lbs up a 6% grade.
Coincidentally, that's my shut down method for everything all the time, I may drive like Methuselah, but I AM 25 after all...I just don't much like to go fast. I've received 6 tickets for impeading traffic, in various full sized trucks.
So apparently I moved the wrong way resizing, and the oil hid it? The extra oil shouldn't hurt anything, right? It being a 2-stroke, it should just gunk up the exhaust, maybe the carb. I don't think the extra lubrication hurts when it's typically running 50 miles at a stretch. With plenty of little breaks, mind you, my butt can only take so much of these lovely Arizona roads at a time.
Chainsaws are not pulling 200lbs up a 6% grade.
Coincidentally, that's my shut down method for everything all the time, I may drive like Methuselah, but I AM 25 after all...I just don't much like to go fast. I've received 6 tickets for impeading traffic, in various full sized trucks.
So apparently I moved the wrong way resizing, and the oil hid it? The extra oil shouldn't hurt anything, right? It being a 2-stroke, it should just gunk up the exhaust, maybe the carb. I don't think the extra lubrication hurts when it's typically running 50 miles at a stretch. With plenty of little breaks, mind you, my butt can only take so much of these lovely Arizona roads at a time.
