Pump gas and Jetting

[Matrix]

How does pump gas affect jetting?

Today was the first day in over a year that I ran 87 in my 84 250r. For the last year I have been running 93 and my 250r has been screaming with joy. Today, it was just... Sad... I didn't think gas affected it that much. It was like my 250r had pneumonia and a sore throat. I couldn't really rip through my yard and wanted to see what it did on the road so I of course putted out to the road and road for about 200 feet and turned around and went straight back to the garage. I also noticed it seemed to run very rich when warm, but when I first started it, it wanted to idle very high and I had to choke it a tad bit to get the RPM's back down like it was lean.

The high RPM's sound like a lean condition and the oil that dripped from where my silencer meets the expansion chamber seem like a rich condition (of course). I am having the same issue with my 200x but I am adjusting things and just ordered a new exhaust gasket so we'll talk about that later.

[Dirtcrasher]

IDK if you have a leak causing an issue or; What is the compression.

What did the plug look like?

[Matrix]

IDK if you have a leak causing an issue or; What is the compression.

What did the plug look like?

I had a post on here where the compression is reading 190 and it should be 165 at most. I could try changing the plug. I didn't think about that. I will go over the fuel system again tomorrow, I just cleaned everything last week or so but I could have missed something. Like I said though, before I put this 87 octane in it, it would scream down the road or trails. But... its just sad now

[MTS]

sounds like you got a batch of 87 full of water, not all that uncommon I would drain the carb into a bottle see what ya got, fresh plug and fuel, assuming every thing else is clean and serviced ect.

[Matrix]

sounds like you got a batch of 87 full of water, not all that uncommon I would drain the carb into a bottle see what ya got, fresh plug and fuel, assuming every thing else is clean and serviced ect.

How would I know if the gas is watered down? It was its normal blue color going in so I didnt think anything of it.

[MTS]

like I said, drain your float bowl or right off the petcock into a clear bottle, if thete is water in it it will settle on the bottom of the bottle if left standing for a few mins. when the tankers at the fuel station fill up the main tanks it stires it sll to hell if they have been sitting low, all that condensation mixes with the fuel...normally not noticed much with new cars n such, but a small carb motor..yea there picky...

[tecat-z]

My first question would be why would you run 87 unleaded? These machines were designed to burn minimum 92oct, which in most cases contained lead untill the late 80's early 90's depending on where you lived. Todays pump gas if full of additives that are designed to reduce emissions in 4 stroke automobile type engines and not effect exhaust scrubbers. Old gas contained MORE GAS! Modern vehicle engine management is designed to work with all of the variables that exist in the world of pump fuels from state to state, county, and season. Modern pump gas is not even close to being up to the task of fulfilling the requirements an old air cooled performance 2stroke. You need access to consistant quality fuel, dial it in, and stick with it.

[MTS]

thanks for posting that mr Ed, takes far to long to explain stuff on my android at my speed, im suprised that r runs good on 93 @ 190 for so long imo

[beets442]

Do the fuel change like the guys suggested.Check your main jet and any air leaks. Did you have to turn your airscrew any?Compression is a a little high.Did you hold the throttle wide open when you checked it?New plug?A little spooge from the pipe, tail pipe clogged/caked?
I mix 2 gal.of VP110 to my 5gal jug and Golden Spectro for trails or Maxima 927 for racing or riding hard.

[falloutboy]

On the fuel, definitely nothing less than premium (92/93 octane), NON-ethanol if you can get it. I suppose a marina would be the most common place to find it. At 190psi I would be running half race gas/half premium. You could probably run full race gas as it is a much higher quality fuel than pump gas but the 50/50 is a good way to stretch a buck.

[nd4speed]

The higher the octane the richer the jetting. So 87 = LEAN = hot fast burn = most power = most heat = fast wave front = possible detonation = loss of power = loss of engine.

High compression to match 115, 110, 100, whatever, well basically compression to match octane rating.

In the summer ethanol corn alcohol is added. Alcohol attracts water and can turn on you. But alcohol requires high compression as it burns slow and rich.

Jetting. Compression. Fuel. Fun.

[nd4speed]

Also humid hot days can affect jetting.