What Should I Run For A Main Jet, And With What Octane Fuel???

[masterblaster97]

Here is a list of my mods. I need to know what size jet I will need to use in my aftermarket Keihin(28mm) carb, and what octane fuel I should run. If I put a 3mm stroker crank in, will that effect the octane fuel that I will need to run? I don't want to run any higher octane fuel that I can get at a gas station. In other words, no race fuel. It's just a trail bike. Here's the list.

Keihin 28mm carb
Boyesen RAD valves
K&N air filter
Port and Polish
FMF Gold Series Fatty w/ a PowerCore 2 silencer
.030 over Wiseco piston
Vito's 3mm stroker crank (I hope)

Any suggestions would be extremely helpful. When I bought this quad a year ago, it was a pile. I decided to put all new parts into it, and I only want to run 93 or 94 octane fuel in it topps. Whatever they sell at a gas pump. The jetting help would help too. Thanks

 

[mutany15]

Try a 148 main jet to start, it might be a bit rich but i have alot of similar upgrades and thats what i run in my 28mm carb. Run 93 octane, if recall correctly however Vitos 3mm stroker kits come with a spacer plate so you dont have to worry about chaning the compression ratio.

 

[Valhalla]

run 87 octane. you have no mods listed that bump up your compression so you are safe at the lower level. you should always run the lowest octane you can get by with if you are looking for the most performance and power from your motor. octane is nothing more than the fuel's ability to not detonate under pressure. the higher the octane, the higher the compression it can handle before it explodes. a stock compression will run just fine off of 87 octane without detonation.

here are a couple of octane facts for your entertainment...

1. higher octane fuel does NOT create more power
2. race gas is not the same as aviation gas (avgas)
3. avgas is leaded, race gas comes either way.
4. leaded fuel will destroy valve seats if used in newer 4-stroke engines over time and leaves a nasty buildup in your motor.
race gas comes in all octane levels and does not necessarily need to be more than 100 octane. you can even get it in 87 if you want.
5. 80% of modified engines will run just fine on 87 octane. only when you get over about 10:1 compression will you really need to go any higher and sometimes depending on your timing, you can still run lower octane and be safe.
6. high octane fuel does not burn faster, cleaner, or make your motor more fuel effiecnt (unless it is a high perofrmance motor that requires high octane fuel.)
7. gas pumps have only 2 types of fuel underground. they have 81 octane and 91/93. the middle gas is a 60/40 blend of the two that is done inside the gas pump.
8. if you have a half tank of 87 and add a half tank of 93, you just paid alot more money for 89 octane gas.



read more here.....

HowStuffWorks "What does octane mean?"

 

[samolia]

if i remember right correct me if im wrong but im pretty sure running really high octane gas will acually give you lower performance because the higher octane gas requires more compression to take advantage of the octane level so if your running race gas in a stock motor it cant burn all the gas in the chamber so you have more raw gas in the exhaust which means a waste of money.

 

[mutany15]

I don't know if its safe to say it will lower peformance, Remember the Yamaha Blaster owners manual recomends running premium unleaded fuel. They say to use 93 for a reason, I don't know what the engineers reasons were but I KNOW that engineers don't just make up numbers.

With all this talk about octane ratings though I will say that If running 87 gives better perfomance then will running 93 improve reliability? Valhalla says that anything with a compression ratio under 10:1 can run on 87. Maybe they specify 93 in the manual to improve reliabilty for possible warranty reasons? I'm also curious to know if running higher octane gas will help the engine run at cooler temperatures?

 

[89custom]

I don't know if its safe to say it will lower peformance, Remember the Yamaha Blaster owners manual recomends running premium unleaded fuel. They say to use 93 for a reason, I don't know what the engineers reasons were but I KNOW that engineers don't just make up numbers.

With all this talk about octane ratings though I will say that If running 87 gives better perfomance then will running 93 improve reliability? Valhalla says that anything with a compression ratio under 10:1 can run on 87. Maybe they specify 93 in the manual to improve reliabilty for possible warranty reasons? I'm also curious to know if running higher octane gas will help the engine run at cooler temperatures?

i dont know bought trusting them engeers lol. they did make a stock pipe that was totaly garbage and put it in a coma.

 

[blasterboy91]

naaa a high octane gas doesnt burn as hot so it makes ur engine cooler wen it burns...and they say run 91-93 cuz its better then 87 or anything else under 91

 

[Valhalla]

premium fuel is rated at anything above 91 octane. the 93 is actually getting harder to come by due to added cost with minimal diffrences so it is beign phased out in the USA.

highter octane DOES NOT burn cooler, cleaner, or provide more power. it is simply the rating at which the fuel resists detonation. the higher the octane rating, the more pressure it can resist before going bang. nothing more, nothing less. your engine remains the same temperature as long as you dont have detonation before the spark fires. if you do, you will hear a noticable knock in your engine and that will cause engine temp to rise slightly. on a 2-stroke, engine knock is easy to get and even easier to get rid of if you have it.

personally, im on my 4th blaster and they have all ran 87 octane with no problems at all. i haven't seen one yet with a stock head/piston that needed premium octane to run right. big bore kits dont require it either unless you are running a high compression gasket kit or shaved head.

 

[mutany15]

i dont know bought trusting them engeers lol. they did make a stock pipe that was totaly garbage and put it in a coma.

LOL, good call.

Well, its not often you can get away with going cheap and actually getting an advantage out of it, i guess I can start running the same gas as the mower in my blaster... makes life easier.