I am rebuilding the top end of my blaster. Here are my mods please if I can get some help on a jet size. Currently I run a 250. I have a 66.5mm piston, FMF racing exhaust, no airbox lid with Uni comp filter, but I will prob do an air filter directly on the carb, head mod, I run the quad in NM 5,200 ft elevation with temps over 100 degrees, I don't know if this matters or not and I do pre-mix @ 20:1. Looking for a good jet size, and if i should increase the idle jet size too. any help will be appreciated. thank you
Recommended jet size?
- Thread starter jasindude1
- Start date
You are running lean right now with
250 main
fmf
lid off
I would say you are going to hit 300-320
250 main
fmf
lid off
I would say you are going to hit 300-320
That's pretty high elevation, but I would also say, 300-320. When I ran a full FMF, Wiseco Piston, no airbox lid on a few of my past Blasters at dead sealevel, I ran a 330 main for perfect jetting and they ripped, never fouled a plug and never had any problems.
At 20:1 you would have been running way to lean with your mods.
I mix at 25:1 which means I have to increase the main jet one size from changing from 32:1.
The most common ratio is 32:1 and all jetting advice on the forum is based on that ratio.
Leave the pilot stock 32.5 and plug chop starting with a #320 main jet, if you are sticking to 20:1.
I run an air filter directly on the carb for maximum performance and if you do you need to use a foam filter and increase the main jet one more size.
Bottom of this page is a compression/dome size: yamaha banshee heads
So if OP did a comp test everyone would be crying REBUILD !!
Sealevel jetting might not even run at 5200ft. and 100*
There's a sticky about elevation/jetting effects, don't know if it gives recomendations or just general info.
Plug chopping is the only true answer. Start big, work down.
And yes, you can have to large of jet, it won't run or run properly. You are not to large.
How does it run right now? What's plug look like? Why 20:1?
So if OP did a comp test everyone would be crying REBUILD !!
Sealevel jetting might not even run at 5200ft. and 100*
There's a sticky about elevation/jetting effects, don't know if it gives recomendations or just general info.
Plug chopping is the only true answer. Start big, work down.
And yes, you can have to large of jet, it won't run or run properly. You are not to large.
How does it run right now? What's plug look like? Why 20:1?
It must be understood that more oil in the mix means less fuel to pass through the jets.
20:1 is rich on oil, but the extra amount of oil added to the gas will create a leaner fuel mixture which will cause the motor to run hot.
Most people will tell you to mix at 32:1 but I prefer 25:1 for ultimate protection and power.
The more oil you mix with the fuel must be compensated with a larger main jet and maybe a richer needle setting.
20:1 is rich on oil, but the extra amount of oil added to the gas will create a leaner fuel mixture which will cause the motor to run hot.
Most people will tell you to mix at 32:1 but I prefer 25:1 for ultimate protection and power.
The more oil you mix with the fuel must be compensated with a larger main jet and maybe a richer needle setting.
Answer the questions in RED ^^^ please
Jetting Results
Main Jet
260
Pilot Jet
32.5
Needle
STOCK
Needle Position
3RD
Power Jet
N/A
Air Screw
1.5
Fuel Screw
N/A
Comments
Remove airbox lid snorkel
We have a jetting kit for the selected bike:
FMF POWER UP JET KIT YAMAHA YSF200 BLASTER 88-06
Part #: 011718
$59.99
We know how difficult jetting can be sometimes, that's why when we test our exhausts we also adjust the jetting to see what works best. Sometimes stock jetting works fine, other times a slight adjustment is needed. Here is what we've come up for in our area and is a great starting point for you as well.
We developed these specs with a 32:1 fuel to oil mixing ratio of a 50/50 mix of race fuel and super unleaded, 0 - 1500 ft altitude at 70 degrees outside temperature.
Please note: There are way too many variables in jetting to give you a recommendation that works perfect. Use these specs for a reference to help aid you with your specific bike
Rider Support - Jetting Center - FMF Racing
Kinda did that ^^^ little backwards. From jetting results down is copied from FMF site.
Factor in 5,200ft elevation (leaner jet) 100*temp (leaner) 20:1 (richer) direct air cleaner. He might not be that far off, actually only one size from recomended
For those of you who have never taken a sea level tuned 2s to a higher elevation, if you did you would probably be getting off and wondering WTF is wrong.
Factor in 5,200ft elevation (leaner jet) 100*temp (leaner) 20:1 (richer) direct air cleaner. He might not be that far off, actually only one size from recomended
For those of you who have never taken a sea level tuned 2s to a higher elevation, if you did you would probably be getting off and wondering WTF is wrong.
Oops my bad, I forgot about the elevation factor, start the plug chop with a #280,you may find that a #270 will run fine.
You may need to drop the needle one clip.
So do I need to increase or decrease jet size for my elevation? I know plug chop just want to get a baseline to build off of
You guys like a lot of oil I've been 40 to 1 for 17 years no problem. Do your bikes spit a lot of oil out the silincers?
40:1 is inadequate for any motor around 200cc, the smaller the cc and the higher the revs the more oil is required.
A 400/500cc two stroke will perform well at a ratio of 40/50:1, due to their large intake of pre mix and their slower revving.
Owing to the smaller intake and higher revving of a Blaster motor the oil at 40:1 just does not have enough time to come out of suspension and accumulate in the crankcase, this can cause oil starvation.
I have always run a heavy oil concentration, not only for increased power but to reduce the amount of time between rebuilds.
My silencer never has, and never will spit oil as I jet according to my oil ratio.
I have at times run a ratio of 16:1 to adjust for extreme temperature changes, to save having to change a jet in the dirty conditions of a MX pit..
I may add that in 60 years of 2 stroking I have yet to foul a plug, even when we were using just plain old engine oil as a lubricant (well before the onset of self mixing 2 stroke preparations).
That's what I run in 2 banshees and 1 blaster and for 17 years and counting. Oh and 100 percent duning with paddles.
Not my writings but explains the theory.
Pre-mix 101
OK, looks like it's time for a little pre-mix 101. I don't usually get into ratio discussions, because mix ratios are like religions to most people, and they tend to be closed-minded on the subject, but I'll put in my $.02 here anyway.
There is a prevailing myth that less oil is better, and that the oil in the fuel is what lubricates the engine. Both are wrong.
*less oil is better* People think that if they have a plug fouling problem or a lot of spooge, they need to run less oil. Wrong! Both problems are caused by rich jetting, and have nothing to do with the mix ratio.
*the oil in the fuel is what lubricates the engine* The engine is lubricated by the residual oil that builds up in the crankcase. All the oil in the fuel does is replenish this oil.
The best way to determine if you are running enough oil is to check the level of the residual oil in the crankcase. If the ratio you run leaves enough residual oil in the crankcase to cover about 1/8" of the bottom of the crank wheels, then you are fine. If you don't have that much residual oil in your crankcase when you pull the top-end off, you aren't running enough oil for your riding style and conditions.
With that said, to have that amount of residual oil in the crankcase at 50:1 (a ratio made popular by magazines and oil bottles), you can't be riding very hard, or your bike is jetted richer than necessary simply to deliver enough oil. I arrived at 26:1 for my bike with my riding style because that is the amount that gives me the proper amount of residual build-up. Small-bore engines require greater oil concentrations than larger engines to achieve the proper amount of residual build-up, because they rev higher and have higher intake velocities. Along the same lines, someone that pushes the engine harder, and keeps the revs higher, also needs to use higher oil concentrations to achieve the proper residual build-up.
To understand why the residual oil is so important, you have to understand what happens to the oil in your fuel when it goes into the engine. While the oil is still suspended in the liquid gasoline, it can not lubricate anything. It has about as much lubricity at that point as straight gasoline. When the gasoline enters the engine, it evaporates, dropping the oil out of suspension. Now that the oil is free, it can lubricate the engine, but it must get to the parts to lubricate them. The way it gets to the bearings and onto the cylinder is by being thrown around as a mist by the spinning crankshaft, and the droplets are distributed by the air currents moving through the engine. Ever wonder why there are two small holes in the transfer port area of the crankcase, right over the main bearings? These are to allow some of the oil droplets being flung around inside the engine to drip down into the main bearing area.
Some of the oil eventually makes it into the combustion chamber, where it is either burned, or passes out the exhaust. If the combustion chamber temps are too low, such as in an engine that is jetted too rich, the oil doesn't burn completely. Instead, some of it hardens into deposits in the combustion chamber, on the piston, and on the power valve assembly. The rest becomes the dreaded "spooge". The key to all of this working in harmony is to jet the bike lean enough to achieve a high enough combustion chamber temperature to burn the oil, but also still be able to supply enough oil to protect the engine. If you use enough oil, you can jet the bike at it's optimum without starving the engine of oil, and have excellent power, with minimal deposits and spooge. At 50:1, you simply can't jet very lean without risking a seized engine due to oil starvation, unless you're just putt-putting around on trails without putting the engine under much load.
With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained.
One small point. No one ever broke an engine by using too much oil.
__________________________________________________ _______________________________________________
Pre-mix ratios and power production
I have run Dyno tests on this subject. We used a Dynojet dynamometer, and used a fresh, broken in top-end for each test. We used specially calibrated jets to ensure the fuel flow was identical with each different ratio, and warmed the engine at 3000 rpm for 3 minutes before each run. Our tests were performed in the rpm range of 2500 to 9000 rpm, with the power peak of our test bike (a modifed '86 YZ 250, mine) occuring at 8750 rpm. We tested at 76 degrees F, at 65% relative humidity. We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1. Any more oil than that, and the engine ran poorly, because we didn't have any jets rich enough to compensate for that much oil in the fuel, and the burn-characteristics of the fuel with that much oil tended to be poor. The power loss from 18:1 to 32:1 was approximately 2 percent. The loss from 18:1 to 50:1 was nearly 9 percent. On a modern 250, that can be as much as 4 horsepower. The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
Now, I realize that 18:1 is impractical unless you ride your engine all-out, keeping it pinned at all times. But running reasonable ratios no less than 32:1 will produce more power, and give your engine better protection, thus making it perform better for longer.
As a side note, I no longer run 26:1, I now run 32:1. I'm not a young man any more, and I just can't push as hard as I used to, so I don't need as much oil now. 32:1 is enough oil to do what is needed for me now, since I'm getting slow...
Pre-mix 101
OK, looks like it's time for a little pre-mix 101. I don't usually get into ratio discussions, because mix ratios are like religions to most people, and they tend to be closed-minded on the subject, but I'll put in my $.02 here anyway.
There is a prevailing myth that less oil is better, and that the oil in the fuel is what lubricates the engine. Both are wrong.
*less oil is better* People think that if they have a plug fouling problem or a lot of spooge, they need to run less oil. Wrong! Both problems are caused by rich jetting, and have nothing to do with the mix ratio.
*the oil in the fuel is what lubricates the engine* The engine is lubricated by the residual oil that builds up in the crankcase. All the oil in the fuel does is replenish this oil.
The best way to determine if you are running enough oil is to check the level of the residual oil in the crankcase. If the ratio you run leaves enough residual oil in the crankcase to cover about 1/8" of the bottom of the crank wheels, then you are fine. If you don't have that much residual oil in your crankcase when you pull the top-end off, you aren't running enough oil for your riding style and conditions.
With that said, to have that amount of residual oil in the crankcase at 50:1 (a ratio made popular by magazines and oil bottles), you can't be riding very hard, or your bike is jetted richer than necessary simply to deliver enough oil. I arrived at 26:1 for my bike with my riding style because that is the amount that gives me the proper amount of residual build-up. Small-bore engines require greater oil concentrations than larger engines to achieve the proper amount of residual build-up, because they rev higher and have higher intake velocities. Along the same lines, someone that pushes the engine harder, and keeps the revs higher, also needs to use higher oil concentrations to achieve the proper residual build-up.
To understand why the residual oil is so important, you have to understand what happens to the oil in your fuel when it goes into the engine. While the oil is still suspended in the liquid gasoline, it can not lubricate anything. It has about as much lubricity at that point as straight gasoline. When the gasoline enters the engine, it evaporates, dropping the oil out of suspension. Now that the oil is free, it can lubricate the engine, but it must get to the parts to lubricate them. The way it gets to the bearings and onto the cylinder is by being thrown around as a mist by the spinning crankshaft, and the droplets are distributed by the air currents moving through the engine. Ever wonder why there are two small holes in the transfer port area of the crankcase, right over the main bearings? These are to allow some of the oil droplets being flung around inside the engine to drip down into the main bearing area.
Some of the oil eventually makes it into the combustion chamber, where it is either burned, or passes out the exhaust. If the combustion chamber temps are too low, such as in an engine that is jetted too rich, the oil doesn't burn completely. Instead, some of it hardens into deposits in the combustion chamber, on the piston, and on the power valve assembly. The rest becomes the dreaded "spooge". The key to all of this working in harmony is to jet the bike lean enough to achieve a high enough combustion chamber temperature to burn the oil, but also still be able to supply enough oil to protect the engine. If you use enough oil, you can jet the bike at it's optimum without starving the engine of oil, and have excellent power, with minimal deposits and spooge. At 50:1, you simply can't jet very lean without risking a seized engine due to oil starvation, unless you're just putt-putting around on trails without putting the engine under much load.
With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained.
One small point. No one ever broke an engine by using too much oil.
__________________________________________________ _______________________________________________
Pre-mix ratios and power production
I have run Dyno tests on this subject. We used a Dynojet dynamometer, and used a fresh, broken in top-end for each test. We used specially calibrated jets to ensure the fuel flow was identical with each different ratio, and warmed the engine at 3000 rpm for 3 minutes before each run. Our tests were performed in the rpm range of 2500 to 9000 rpm, with the power peak of our test bike (a modifed '86 YZ 250, mine) occuring at 8750 rpm. We tested at 76 degrees F, at 65% relative humidity. We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1. Any more oil than that, and the engine ran poorly, because we didn't have any jets rich enough to compensate for that much oil in the fuel, and the burn-characteristics of the fuel with that much oil tended to be poor. The power loss from 18:1 to 32:1 was approximately 2 percent. The loss from 18:1 to 50:1 was nearly 9 percent. On a modern 250, that can be as much as 4 horsepower. The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.
Now, I realize that 18:1 is impractical unless you ride your engine all-out, keeping it pinned at all times. But running reasonable ratios no less than 32:1 will produce more power, and give your engine better protection, thus making it perform better for longer.
As a side note, I no longer run 26:1, I now run 32:1. I'm not a young man any more, and I just can't push as hard as I used to, so I don't need as much oil now. 32:1 is enough oil to do what is needed for me now, since I'm getting slow...
so lets say i go with 25:1. I like the idea of performance with protection, so if I make that adjustment what size should I start with?
