2 stroke questions

BIF

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#1
I just recently bought a used 2001 250exc. The bike was in very good condition and appeared to be well maintained. The previous owner said that he estimated the bike had about 1200 miles on it. This is my first 2 stroke so I don't have history to determine whether the following "issues" are normal. I have rebuilt and worked on many different types of 4 stroke motors but have never touched a 2 stroke motor.

The bike smokes considerably when accelerated and it spooges a fair amount. I am using Motorex "Low smoke" oil, pre-mixed at 50:1. It also has a knock in deceleration, which I noticed has been discussed in another topic on this forum.

In addition, I notice something very peculiar about it after it warms up. The power falls off, BUT unlike a 4 stroke where you would shift down to a lower gear, you must shift up and the power comes back on. Is this normal, and why after it gets warmer?

Thanks for any input for a 2 smoke ignoramus.
 
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#2
I currently own an 2000 250 EXC that I bought new. I had some of the same issues you are asking about. I removed the stock silencer and installed an FMF PC II and the spooge was gone. Got that tip from another local KTM rider. I also had the knock issue. Kinda sounds like someone hitting the engine case with a hammer. I began running a 50/50 race gas mixture and the knock was gone. I run it 40:1 (silkolene) Hope this helps.
 

DougRoost

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#3
Spooge is most affected by jetting, not premix oil type or ratio. Too much spooge means you're probably jetted too rich. You first need to determine what pilot, needle, and main jet you're running then get some brass (Sudco or Carb Parts Warehouse) and work with it. It is a bit of a PITA but there is no better bang/$$ on any 2 stroke than $30 worth of jets and needles. You can change the bike's characteristics from rippy to linear and 4 stroke-like with just jets.

Some pre-mix oils will reduce octane since they have kerosene in them. Mobil MX2T comes to mind as it has 25% kerosene (read it's MSDS if you don't believe me). When I hear someone say they run race gas in a stock bike because they were getting detonation it's usually due to this type of pre-mix oil. FWIW, I've tried a few and am very happy with Amsoil 2000.
 

Rich Rohrich

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#4
Originally posted by DougRoost
Some pre-mix oils will reduce octane since they have kerosene in them. Mobil MX2T comes to mind as it has 25% kerosene (read it's MSDS if you don't believe me).
That sounds like something Amsoil would put on their website. Did you get that direct from them? LOL :laugh:

The MSDS for MX2T clearly states HYDROTREATED LIGHT DISTILLATE (CAS REG. # 64742-47-8) 15-25% (by weight NOT volume)

This is a light fuel oil used as a dilutant (all two-stroke oils have something similar that works as a dilutant even Amsoil ;) )

The CAS REG. # for Kerosene is 8008-20-6 which doesn't appear on the MSDS sheet . It's unclear from the MSDS sheet what percentage of neat kerosene exists (if any) in MX2T.

FWIW, I never found MX2T to cause a major change in octane requirement in CLEAN fuel even when mixed at 9 oz per gallon (aka 14:1). Pump fuel has a number of unpredictable heavy components in it that may give different results.
 

DougRoost

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#5
Sorry if I passed along less than accurate info.  Got it from a pretty knowledgable guy on another forum and he does note below the 15-25% by weight spec you pointed out.  Here was the bulk of that post in case I interpreted it wrong:

In comparing the MSDS of both the Mobil 1 and Amsoil TCR 2000, there are some differences.

Here is the Amsoil:
TYPICAL TECHNICAL PROPERTIES
SERIES 2000 SYNTHETIC 2-CYCLE OIL (TCR)
Kinematic Viscosity @ 100°C, cSt (ASTM D445) 8.3
Kinematic Viscosity @ 40°C, cSt (ASTM D-445) 51.02
Viscosity Index (ASTM D2270) 139
Pour Point, °C (°F) (ASTM D97) -42(-44)
Flash Point, °C (°F) (ASTM D92) 110(230)
Color Red
SAE Miscability/Fluidity Grade 4

And the Mobil:
Viscosity @ 100°C, cSt 13.7
Viscosity @ 40°C, cSt 91.4
Pour Point, °C (°F) -42(-44) (same)
Flash Point, °C (°F) (ASTM D93) 76(169)
Color Amber
Kerosene 15-25% by wt.

So what does it mean? Even though the Mobil is thicker in viscosity it's flash point is much lower than the Amsoil due to the kerosene content. While the Mobil 1 is burning away, the Amsoil will still be oil vapor. The kerosene is also lowering the pour point as mentioned above, but unless you are at the winter X-Games with an oil injected bike, low pour points are unimportant. Pour points become irrelevant when the oil is mixed with the gasoline. As far as the comment goes about kerosene being a mixing agent, that is true. But if you need a mix agent because the oil will not dissolve in the gas, you need another oil. In addition, I'll take Toluol over kero as a blend agent any day, and get an octane boost along with it. Both Mobil 1 and AMSoil are hydrocarbon derivatives here (I'm leaving bean oils out in this discussion). Some are "designer genes", (truly man made molecules) but many synthetics are simply highly refined petroleum basestocks (PAO's in the group IV catagory reference below for a spec sheet and tech data ), with an additive package. It is the additive package that truly makes an oil. The oils ability to lubricate under heat and pressure is a basestock function, while the additive package keeps the engine clean, and helps the oil flow when cold. Given these two choices, I would pick Amsoil for mixing with race gas in a racing effort, and run the Mobil if I was using pump and pleasure riding, to help clean up the trash left behind from the pump fuel. As I originally stated, Mobil 1 isn't horrible it's just that there are some better oils. Also, do not fall prey to the "less oil is better" attitude. Too much data has been collected about 40:1, 50:1, and higher having less power, and more engine wear. The guys running as high as 100:1 with their mix will have issues down the road. Lets say for the sake of discussion that the bike is designed to run on a 32:1 mix. The jets will be sized approximately for this mix. If you began to mix at double that, say 64:1 (one half the amount of oil) , you will wind up rejetting leaner for the increase in gasoline introduced into the engine. When you jet leaner to compensate for that, you will again be DECREASING the amount of oil also. Of course you will get rid of spooge somewhere along the way, but you will be running hotter, and shortening the life of pistons, rings, cylinders, etc. and probably be getting less performance also. For the AMSoil, I would stay with the recommended ratio from them. With the Mobil, info is available and validated that it performs better at lower ratios in the area of 25:1, again because of its dilution with kerosene. In either event, it is not wise to cut back on oil. A.Graham Bell, in the book "Two Stroke Performance Tuning validates this , and he is one of the leading experts on 2 strokes.
In reply to the comment of getting whatever looked good at the shop, I had a 1976 Yamaha DT 175 that I ran 2 stroke boat oil in, both on and off road, for 6000 plus miles. I sold it with the original top end in it too. I agree that you can abuse a lot of things in life and get away with it. But with as much money as is invested in a bike as you or I have, why skimp on oil? Plus, my peace of mind when riding is worth every penny I spend on race fuel and oil to protect the engine, just as it is on equipment to protect me.
One last thought. Mobil 1 comes in 16 oz. bottles, so, 8 of those make 1 gallon of oil. At 3.50 for 16 oz., times 8 is 28.00. Now 28.00 a gallon for oil isn't bad, but at 25% kero, you just paid a whopping 7.00 for a quart of kerosene.
Think it over....
 

DougRoost

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#6
BTW, this guy's favorite premix oils are neiter of the above but rather Xamax and Shell X2.
 

Rich Rohrich

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#7
Xamax is my oil of choice as well in a serious engine, but at $15.00/LITER and limited availability it's hard to justify for the average guy riding on the weekend.

I'm not sure where you are getting the info that says MX2T has that level of kerosene. The MSDS from Mobil has the info that I posted earlier , and it makes no reference to neat kerosene, either by name or CAS number.

My original post wasn't intended to sound like a sales pitch for MX2T, I just don't like to see a product get smeared due to less than accurate information. It's a basic character flaw I can't seem to shake. ;)

One last thing as long as you brought it up, FLASH point is not the same as the distillation point. The difference is pretty important.
 

DougRoost

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#8
Rich, I'm not sure where he got it either since I went to Mobil's site (http://emmsds.ihspsl.com/msds/frames.htm) and saw what you posted.  One of his other MSDS's came from a distributor's site (http://www.advantage-on-line.com/index2.html) so maybe he got it the Mobil one from a disty, or perhaps it was dated (that post goes back to 3/03).  In fact, the MSDS on the Mobil site had slightly different numbers everywhere so perhaps he had an older MSDS.

There was one reference to Kerosene in the current MX2T MSDS:

14. TRANSPORT INFORMATION
SHIPPING NAME:             Kerosene Solution

So now I don't know what to think.  I was going to try MX2T but never did after hearing lots of good things from guy in our club on Amsoil.  I did run a few quarts of Bel-Ray H1R and must say my bike runs so much better (crisper, less smoke, etc) with the Amsoil 2000 that I'm just sticking with it and perfecting jetting.
 

Rich Rohrich

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#9
If Amsoil is working for you it makes no sense to change IMO.

I'm unclear on what specifically is in the dilutant when it's listed under the CAS # on the Mobil MSDS. Unfortunately I think that's the type of info that tends to be proprietary. Generic CAS numbers seem to cover a fairly wide range in some cases. Just look at a VP MSDS and you'll see what I mean. :)

Kerosene solution seems to be a generic term used for fuel oil based solutions for transportation. The listing for transport purposes seem extremely generic.

I have a friend who might be able to shed some additional light on this. I'll see what I can find out.
 

MWEISSEN

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#10
Originally posted by BIF

The bike smokes considerably when accelerated and it spooges a fair amount. I am using Motorex "Low smoke" oil, pre-mixed at 50:1.

In addition, I notice something very peculiar about it after it warms up. The power falls off, BUT unlike a 4 stroke where you would shift down to a lower gear, you must shift up and the power comes back on. Is this normal, and why after it gets warmer?
Back to our friend's original questions....

It sounds to me like the bike is just too rich. Smoking is the first indicator. The second indicator is the power falling off after warming up.

I'd try 40:1 gas:oil. That alone will lean out your motor a little. However, jetting is most likely mandatory. I'm not real 2 stroke expert either, since my last one was back in the eighties, and I've been on 4 strokes for awhile. I still have learned a lot the past couple years, and find between the '03 Honda CR250 and the '02 KTM 250, the KTM is quite finicky in terms of jetting.

My best jetting combo at 70 degrees and 5-800 ft above sea level has been an NOZG needle on #2, a 172 main and a 45 pilot. I use James Dean's jetting spreadsheet to compensate for altitude and temp changes and use this setting as a baseline for adjustment.

Hope this helps!
 

BIF

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#11
Ah ha....the jetting being too rich seems to make sense about the power and the spooge. I wonder if thats the source of the knock too? The description of the knock above is dead on. It has an FMF silencer on it, so that doesn't seem to affect spooge level. I just recently purchased half a case of Amsoil 2000, so I'm going to check that out. Amsoil's recommended mix ratio is 50:1. Let me get this straight, if you use a lower ratio, then the mix is leaner because there is more oil and therefore less gas?
 

DougRoost

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#12
Correct. This can be confusing. The air/fuel ratio is leaner since you have less gas. Some people like to describe the oil/fuel ratio, which would be richer, but that's not what affects combustion.

I hear you can run the Amsoil 2000 at 50:1 just fine, but I run 40:1 since a little more oil is better than a little to little (longevity, ring sealing, etc.).
 

MWEISSEN

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#13
Exactly, the higher the oil ratio the richer the bike is.

I would suggest not running 50:1, even though it says you can. 40:1 would be better.

Are you sure it's pinging you're hearing when letting off of the gas? That seems inconsistent with your other statements.

Also, you may want to check out the condition of the reeds. When worn or frayed, they can do funny things to jetting and performance.
 

BIF

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#14
I really wouldn't describe it as a ping, at least not what I have called pings. Its really a knock. It literally sounds and feels like someone is pounding a hammer on the cases. You can feel it.

I do need to check out the reeds too, haven't yet. I think the previous owner put in a V-force reed, or something like that, the name escapes me.
 
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#15
IMO - "Kerosine Solution" for transportation purposes - generic - in its behavior (i.e. flamability, viscosity, vapor pressure, reactivity, toxicity) when spilled in the event of an accident (like a tank car) so that the responders react accordingly.

IMO - I am not sure how the chemical abstract service defines kerosene but I think it would be whatever aliphatic/paraffinic hydrocarbons are cracked off in that distillation range. Kerosine is a mixture.