Messages

1

Vintage Two Strokes / Re: Name 3 of your favourite old school riders..

« on: February 28, 2010, 07:21:02 PM »

Pomeroy
Hannah
Shoot, this is tough.  How far back are we going?  I suppose if Chandler qualifies you gotta admire a 3rd string unqualified guy arriving on the scene and owning everyone like he did at the des nations.

2

Technical / Re: yz250 vin number

« on: February 28, 2010, 04:03:30 PM »

If it is the 17 digit vin then:

The 10th digit in a 17 digit V.I.N. or frame
number represents the year of your machine.

A - 1980 H - 1987 R - 1994 1 - 2001
B - 1981 J - 1988 S - 1995 2 - 2002
C - 1982 K - 1989 T - 1996 3 - 2003
D - 1983 L - 1990 V - 1997 4 - 2004
E - 1984 M - 1991 W - 1998 5 - 2005
F - 1985 N - 1992 X - 1999
G - 1986 P - 1993 Y - 2000

The series repeats with a 2010 being an "A" again.  The older vins are harder to find but I found it via google once before for a friend with a 70s YZ400 so it is out there.

3

Technical / Re: nikasil or sleeve? which ones better?

« on: February 28, 2010, 09:52:31 AM »

I'm not an expert on all the nuances here but I was under the understanding that:

Oil builds up between the silicon carbide surface on a nikasil bore naturally.  A sleeved bore must have a rather complex plateau honing process utilized to have similar properties.  Benefit nikasil
The piston heat gets drawn through the rings to the bore at the bottom of the stroke and nikasil is better than a sleeved cylinder for this.  Benefit nakasil
Modern rings aren't chrome they are some type of nitrided steel.  While the nickel surrounding the silicon carbine helps alleviate some of the wear characteristics we're still talking about silicon carbide aka an abrasive.  The rings are hardened because they would wear too fast otherwise.  I've also read the argument that a 4-stroke has better lubrication on the rings than a 2-stroke.  Whatever the cause nakasil allows you to run a very hard ring against a very hard bore.

I've never done any testing to validate any of this, it is just what I've read or heard.

My practical experience has been that you have to ignore a lot of signs and have a very catastrophic failure to destroy a nikasil bore.  The benefit of having a top end you can replace with nothing other than some simple tools and a 6 pack of beer far outweigh the very infrequent need to send you cylinder in for repairs.

4

Technical / Re: 86 yz 250 carb

« on: February 25, 2010, 09:05:53 AM »

Lever down is choke on for the VM.  Bog without cleanout is lean, bogging and then cleaning out is rich.  I would look for air leaks too, some bikes from the 80s needed to be jet several sizes leaner than stock.

5

General Two Stroke Talk / Re: What to Say?

« on: February 25, 2010, 08:32:44 AM »

I don't have any first hand experience with the four bangers but everyone I race with tells me the problem with the 250F is the valve train.  Something goes awry and you end up getting new valve train and a head.  The number I keep hearing is $1500 per fix and to plan on it at least once a year.  In general I hear the 450f is much more reliable HOWEVER out of the two 450F riders I ride with the most one had to have the head done twice and the other even had to replace his cases.

In contrast I get a lot of hours on my ringading and chain/sprockets, air filters, piston/rings (once a year), brake pads and tires are about all I ever have to replace.  I started using Seal Savers to drastically cut down on fork seal replacment.  This will be my 5th year on my current bike so I've got some history with it.  Sad that I just can't find an suitable replacement for it, regardless of what the mags say those 05-07 CR250s are just a killer machine.

In any event, for your purposes I would get an estimate on what it would cost to replace the head, valves, camshaft, timing chain, getting the cylinder replated, and put in a new piston.  That would be the cost of a catastrophic failure in the valve train at high RPM.

6

Technical / Re: What brand Air filter and air filter oil do you like best

« on: February 22, 2010, 12:51:14 PM »

No-Toil can ruin filters, I think Uni or Twin even warned about that.

I used it for over a year and I really liked the concept of it being water soluable but eventually I just couldn't deny any longer that I had more dirt getting through the filters and in to the airbox boot.

7

Technical / Re: 2009 yz250 break in.

« on: February 22, 2010, 12:43:02 PM »

The shape of a piston at room temp will not be the shape of it when hot, that is a given.  Manufacturers compensate some with the shape but can't completely.

Nonetheless power comes from compression.  Getting the best ring seal is the primary goal of a break in.  Still I must confess, I've never been able feel any seat of the pants distinction from a slow easy break in or a fire it up and drop the gate approach.  Same with longevity, without keeping a detailed log I don't know that you could determine any particular approach that makes an engine last longer.  I'm basing this all on experience with 2-stroke single cylinder bikes.  Planes, trains, and automobiles may vary.

8

General Two Stroke Talk / Re: Two versus Four

« on: February 22, 2010, 12:33:38 PM »

I read MXA more than any other magazine but I still have issues with them.  I think they have an agenda at all times which is for the most part massaging their ego.  I think it clouds their bike reviews.  The other issue is they get so much free stuff they don't seem to have any ability to comprehend what $100 purchase has any real benefit to a person that only has $100 to spend.

9

Technical / Re: Oil and ratios

« on: February 19, 2010, 04:17:26 PM »

I for the most part agree with all of this.  Spooge can be hard to avoid when you have large temperature swings unless you are willing to constantly reject and with the aluminum framed bikes that can be a real PITA.

I've noticed that spark arrestors will spooge more than silencers.  While it is possible that is just a jetting issue I suspect that the arrestor lowers the exit temp of the exhaust gas and causes the spooge to drop out of suspension.

My experience has been that lower rod end bearings fail first from a lack of 2T oil.

Hello everyone. I'm new here, and just thought I would start with a bang! This is my personal take on mix ratios.

Pre-Mix 101

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 and hard-headed on the subject, but I'll put in my $.02 here anyway.

Anyone that believes that spooge and plug fouling are caused by too much oil in the mix is flat out wrong. If you know how to jet, you can run any amount of oil you choose, and have absolutely zero spooge.

There is a prevailing myth that less oil is better. This simply isn't the case. While there isn't a magic "one-size-fits-all" mix ratio, and it is possible to use too much oil for your conditions, generally speaking, more oil is better, within certain limitations.

When an engine is jetted too rich, the excess fuel leeches heat from the combustion process, causing the combustion chamber temperatures to be too low to effectively burn the oil, or even completely burn all of the fuel. The result is spooge and deposits. The spooge is nothing more than unburned fuel and oil passing out the exhaust.

If you have a spooge problem, you have a jetting problem. You don't get rid of the spooge by reducing the oil, you get rid of it by fixing the jetting. Correct jetting will produce an air/fuel ratio of about 14:1, which will produce combustion temperatures in the 6000F range and exhaust temperatures in the 1200F range. This will provide sufficient heat to consume the premix oil.

The same goes for plug fouling. Rich jetting does two things. First, it promotes incomplete combustion of the fuel and the oil due to reduced combustion temperatures. The incomplete combustion of the fuel and oil promotes deposit formation inside the engine. Second, rich jetting reduces the combustion temperatures, which in turn reduces the engines ability to burn off deposits. Combine increased deposit formation with reduced ability to burn off those deposits, and what do you get? Spooge and plug fouling.

You don't choose a mix ratio based on "spooge" or plug fouling, you choose the ratio based on the amount of oil your engine needs to provide sufficient protection and adequate ring seal. The common misconception is that mix ratios are "one-size-fits-all", when in fact nothing could be farther from the truth.The amount of oil that is correct for one rider on his bike may not be enough oil for another rider/bike, or it may be too much oil. It all depends on engine displacement, riding style, and how hard you push the engine. A trail rider on a 500 that never reams the bike out is probably fine on a diet of 50:1, where a super-fast up-and-coming young future pro that screams an 85 'till the dogs howl the entire time he's on the track might not get a full day of racing out of an engine on less than 30:1. Your engine's oil needs are determined by displacement, rev range, and the loads you put on your engine.

When you shut your engine down and let it sit, much of the oil drains down into the crankcase and forms a puddle in the bottom. The depth of this puddle is your indicator of whether you are running the correct amount of oil for your engine's needs. Ideally, you want this puddle to be between 1/8 and 1/4 inch. If it's less, you need more oil in your mix. If it's more, you are running more oil than you need for your 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 32:1 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.

When I was much younger and a lot faster, 32:1 wasn't enough oil for my conditions. I needed 26:1 to have enough oil. And I have run as much as 18:1 with no spooge or plug fouling issues.

To understand why the mix ratio 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. The oil mist is distributed throughout the engine by the spinning crankshaft and the moving air currents to coat all the internal surfaces.

People believe that the oil just rushes right through a two-stroke along with the fuel, but that just isn't so. It can take 90 minutes or more for the oil migration through a two-stroke to result in a complete oil exchange on a slow trail ride, and even as much as 5 minutes for a full-throttle 20 minute moto.

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 in a small-bore engine, you simply can't jet very lean without risking a seized engine due to oil starvation.

One small point. No one ever broke an engine by using too much oil.

Now we come to the issue of ring seal. Simply put, the rings alone can not effectively seal the cylinder. They also need oil to provide a complete seal against the bore surface. And up to a point, more oil will provide a better seal.

I have run Dyno tests on this subject, as a school project in Tech School. 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 (an '86 YZ 250) 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. 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.

The bottom line? Choose a mix ratio that is adequate for your needs, and jet accordingly. You don't fix plug fouling and spooge by adjusting your mix ratio.[/color

This is an interesting read that also supports my "more oil is better" claim.

http://www.bridgestonemotorcycle.com...oilpremix6.pdf

And this is a good article as well:

http://www.maximausa.com/technical/l...summer2001.pdf

10

Technical / Re: 2009 yz250 break in.

« on: February 19, 2010, 03:59:49 PM »

Run it like you stole it, nikasil bores don't have much of a cross hatch to them and you need to fully seat the rings as soon as possible.  Somewhere on the net I once found a guys dyno results where he concluded you need to run the piss out of them initially.  That doesn't mean you should run it for a lengthy first ride, just a hard first ride to build up pressure and force those rings against the cylinder walls.

11

Technical / Re: What two stroke pre mix is best?

« on: February 19, 2010, 03:53:19 PM »

Power valves seem to like oils like Motul 800, Mobil 1 MX2T, and Castrol TTS.  I think these are classified as group V esters.  All of the ones mentioned are very good but the Castrol is widely available and now that they sell it in a quart bottle it is more affordable than the others.

Read the fine print, small engines need more oil than large ones.  I wouldn't run a 65 cc bike with less than 32:1, the lower rod end bearing has a tendancy to go out.  I say that but my youngest sons 65 cc bike recommends 60:1 but only because they did a crappy power valve design and it gums up and breaks.

12

Technical / Re: What Gearbox Oil For KX 250?

« on: February 19, 2010, 03:35:41 PM »

For years I ran a motor oil and changed it often.  Then I had a bike that had smoother clutch engagement and shifted better with Maxima MTL.  Since then I just always use MTL.

Clearly a motor oil can work for a gearbox or you wouldn't have a zillion bikes out there that share the tranny, clutch, and gearbox oil.  That said some of the characteristics of a gearbox oil (i.e. high contact pressure) will differ from something like a motor oil that might favor anti-foaming additives.  Is the minimal gain achieved by using a gearbox oil worth the cost?  Likely not but I'd rather my kids and I didn't have a DNF either.

13

General Two Stroke Talk / Re: This is a rant, and it's LONG, LONG, LONG....

« on: February 17, 2010, 08:28:20 PM »

We all want something different.  What I want is an updated 2-stroke with the latest suspension and frame geometry for today's tracks.  I want R&D money poured in to my bike, not BNG.  Yesteryears motocross bikes become obsolete.  If I must accept a new technology that complicates things then I must, that doesn't mean I prefer it only that it is the lesser of the two evils (complexity or obsolescence).

Hello Everyone,

I can only speak for myself here, but I don't want a direct injection 2 stroke UNLESS it's going to make something available to us that we don't already have.

If it means NEW RD350's, RZ350's, S2's, S3's, H1's, H2's, Suzuki GT's instead of GS's and things like that, then I'm probably into it, until I have the opportunity to buy one of the originals. If all we'd be getting out of it is more homogenized versions of what we have already, then forget it. I've heard that D.I. makes a 2 stroke run a little more like a 4 stoke... That's all I have to hear to say "I'll Pass.." for the time being.

Because I love the way all my current bikes run right now, just the way they are... What more could D.I. bring to a YZ250 that it doesn't already have?

Would it produce better throttle response? Not likely, as the throttle response is already just short of telepathic.

Would it make the bike easier to start? Puh-Leeeeze.....

Would it be any easier to maintain? I don't guess so...

Would it make the bike lighter? I don't know, is one of those systems really lighter than the carb that's already on there, you think?

One of the most enjoyable aspects of riding a motorcycle is the act of metering the fuel mixture flow into the engine. A carburetor is a fairly simple device that makes this a very immediate, in your face experience. The rider has un moderated control of his machine. He can make a mess of everything or that thing can sing motown down, it's all up to the guy pulling on the throttle cable.

I just don't want to see another step in the direction of BORING, that's all. 2 strokes are the most exciting motorcycles to experience, by far, no doubt about it. Wallowing WAY behind that excitement is the rather bland and predictable experience of riding 4 stroke motorcycles. Yes, you still get down the track/trail/road on your mount, but they're not going to start rewriting the menu at Spark's any time soon, just because you can survive on baby food. Electric motorcycles aren't quite worth a mention in my opinion except maybe to demonstrate just exactly HOW boring and emasculated the experience of motorcycling can be made, for people who go to hell....    

When a significant addition to the complexity of a machine is made, the gains should be relative in value. If not they're not worth the added complexity in my opinion. I believe that in the case of the 4 stroke bikes, EFI was worth checking out because there were frustrating problems to be overcome with regard to the way the bikes ran. But even in that case, there have been losses to go along with the gains. They have engines with neater manners, but riders keep saying they lack the raw power of the carbureted bikes. When the hype settles, I'm not sure EFI is really exciting news unless you're a service department, or a guy who rides in Florida at the beginning of every week, then Pike's Peak at the end of every week. The systems are dependable but should there be a failure, are you going to fix it yourself? How were bikes of your machine's type working before EFI? Not very well? Then it's only right to go for it! If your bike was working EXTREMELY well with a carb, then there's a chance you'll end up as a fist prize sucker if you let someone replace a slide, needle, and a small assortment of ingeniously arranged orifices with a fuel injection system.  

My point is that if I was bummed out because 1/2 the time when I went to throttle my bike above idle, it flamed out like a carbureted 4 stroke does sometimes, or if it liked to occasionally stall in a corner and feel like it just dropped anchor as the rear wheel locked and dragged, maybe I'd be looking for an alternative fueling system... But, since I can't even remember the last time the fueling system on ANY 2 stroke has ever let me down, I'm just not looking. No thanks, I'll just keep my Mentos box of 70 cent brass jets and I'm fine.

REGARDING THE ENVIRONMENTAL EFFECTS...
I don't feel obligated to fret over the exhaust emissions of relatively tiny little dirt bikes, or any other bikes for that matter. Never have, never will. At displacements between 1/8 and 1/2 liter, I really don't think our bikes would be Mother Nature's biggest worry even if we each triple jumped a set of beached whales and landed on a rainforest telethon while carrying a sack of seal clubs, pipelines, and drilling rigs up north for hunting season. I've heard the chorus line of Kashi Gobblers, and Transworld KoolAid Kross California types singing about "Dirty", or "Smokey" 2 stroke engines, but I think we 2 stroke riders already do a lot to help our bikes run relatively clean.

Since our bikes use tuned exhaust and power valves (Except on those old Maicos and TS's) in conjunction with the intake to charge the cylinder from both upstream and downstream, some of the power band is quite efficient and unburned fuel loss is minimal. That's the part of the power band every rider seeks out and spends most of their time with, the sweet spot where the bike is most responsive. The inefficient part of the power band is the part that feels less responsive to the rider because the cylinder charge is less than ideal and riders can feel the lost potential, so we don't spend much time there.

Emissions tests can be run with all different types of test parameters, with a vast spectrum of results possible from the same engine. All engines have rpm ranges of peak efficiency for both power output and fuel usage/emissions. There are very large differences in efficiency, regarding both power output and fuel usage/emissions as a 2 stroke engine goes through it's rpm range, but that's a big part of why we love them. This also means you can test one and get either a very bad emissions sample, or a very good one, and all you have to do is change the rpm, engine load, or throttle position to get almost whatever result you're looking for.

I tune rich on purpose to keep engine temps down, my engines last for ever, and the smoke is just fine with me.

Thanks,

Jim

14

General Two Stroke Talk / Re: What should i buy 2 stroke or 4 stroke.

« on: February 17, 2010, 08:07:50 PM »

With that year RM you need to change 3rd gear about as often as you clean your air filter.  I think that got sorted out around 2004.

Early Honda 450F handles horribly and stalls easily.

I don't remember what the 2001 Honda CR250 power is like.  02-04 CR250 Aren't a beginner bike.  Irregardless of what MXA says the 05-07 have fantastic power although some come from the factory with the power valve cable adjusted wrong.  Not really a beginner power band though.  I'd research the YZ250, a reliable brand and I know the later models had a smooth mellow power delivery better suited for novice riders.