'85 250R Tuning

[Turbeau]

Hi everyone,

I have been building a 1985 250r and I am have some tuning questions. First of all let me inform you of what I have done. The engine is stock with the exception of the head gasket. I am running a CR head gasket. I have an ESR ATC5 pipe, keihin 38mm PWK Air striker carb, V force3 reeds and k&N air filter. I don't run race fuel, but plan to make that switch in the future. Currently running 91 octane 40:1 mix. This is my first 2 stroke and I am going to be racing friends at the dunes later this summer. I have been practicing my take offs and notice that the engine bogs down at take off. I am in second gear at 1/3 to 1/2 throttle when I take off. What am I doing wrong here to cause that bog? Do I need to give it more throttle or am I running at bit too rich? Your thoughts?

Thanks

[barnett468]

OK cool . . Im using a tablet to post at the moment so please excuse typos and incoherent comments lo?

One thing you can try to increase performance is to get an adjustable ignition timing plate and try advancing the timing slightly . . if it starts yo ping then it needs more fuel or less timing.

As far as taking off as if you were in a drag race its a bit hard to explain and takes a lot of practice but if you put a larger rear or smaller front sprocket on it, it will be easier to take off in second.

One thing you can try is sitting way up on the seat so you can get the tires to spin

One throttle technique is to hold it at half then roll it wide open as you slowly let the clutch out . . then hold it wide open and quickly pull the clutch in around 1/2 way as you shift.

Another technique is to open the throttle all the way then let the clutch out slowly.

Shift before the engine reaches max rpm . . this will put you in an area of higher torque.
One thing is certain, the more you practice the better you will get.

[yaegerb]

What are your pilot/main jet sizes and what clip is your needle on?

[Turbeau]

Thank you for the tips. In my carb the jetting is, main 165, pilot 58 and the clip on the needle is at the second from the top position.

[yaegerb]

Try this. 162 main, 48 pilot and leave needle where its at. 165 is a bit large and a 58 pilot is huge for a stock setup and that's the reason your are bogging up to 1/2 throttle. I am surprised you haven't noticed it idling like crap. With a pilot that big, I bet your airscrew is 3 or more turns out. You should be between 1 and 2 turns out on your airscrew.

Even running a CR headgasket with a stock head (assuming the head hasn't been milled), I doubt your UCCR will be higher than 13.6:1 nor will your squish be less than .090". In short, I doubt you will ever need to run race gas with your current setup.

[Turbeau]

Well you are right about the air screw. So I will make those changes to the jetting and let you/everyone know how it turn out. It seems many people ask for help and never report their results. Also what do you mean by UCCR?

[yaegerb]

Well you are right about the air screw. So I will make those changes to the jetting and let you/everyone know how it turn out. It seems many people ask for help and never report their results. Also what do you mean by UCCR?

UCCR = Uncorrected compression ratio. Essentially its a way to calculate your compression ratio and what octane you should be running in your bike.

http://homes.ottcommunications.com/~red/uccr.html

[Turbeau]

Would running race gas hurt anything? I would expect an increase in power. Maybe not a lot, but some.

[yaegerb]

wouldn't hurt anything other than your wallet. IMO, there is no need for you to run it. In a nutshell, race gas is for high compression ratio motors period. "Normal" (87-93) gas will pre-ignite under higher compression loads. Race gas is much harder to combust thus, its a safer/cooler gas for hi-po motors.

[barnett468]

.
Take a compression test with a good gauge . . if it is around 170 or lower, you can likely get away with 91 octane . . if the compression is maybe 175 to 185, you will likely need a 50/50 mix of 91 and 110 race fuel or the VP off road dual . . if it is above 185 I would run 110 or 112 race fuel . . race fuel will make your engine run slightly cooler.

[barnett468]

If you advance the timing you will likely need higher than 91

[Turbeau]

I like riding a lot and don't need it to get more expensive. So I will stick to 91 ethanol free fuel.

[barnett468]

I like riding a lot and don't need it to get more expensive. So I will stick to 91 ethanol free fuel.

Not if your compression is close to 190 or more.

[Turbeau]

I was mistaken on the pilot jet size. I am running a 40 currently. Should I get a smaller jet or leave it the way it is and make adjustments to the needle?

[yaegerb]

A 40 and your air screw is out 3 turns? Somerhing doesn't sound right to me. Start the bike, warm it up for a good five minutes and turn your airscrew in all the way. Now unscrew it 1 turn, did you notice the idle get faster? If so, the take it out a another half turn, did the idle get faster? How many turns out until the idle is at its highest point. I am gonna guess less than 1 turn out because a 40 is too small of a pilot to be using in a stock setup. The leanest I have ever seen is a 42 in a 38mm. Leanest I will go is a 45.

Report back your results.

[Turbeau]

The idle reached its highest at 2 and half turns out. I am thinking about buying some pilot jets today. 45 48 50 maybe. What do you think?

[yaegerb]

The idle reached its highest at 2 and half turns out. I am thinking about buying some pilot jets today. 45 48 50 maybe. What do you think?

2.5 turns out? Are you 100% positive that is a Genuine Keihin 40 pilot with the "k" stamped on it? If it is a genuine jet and you are 2.5 turns out then you actually need to drop down some sizes. Never heard of that before. I would get genuine Keihin jets from jetsrus.com. 48,45,42,40,38, 35

Start with the 45 and work your way down from there. Get the engine at its highest idle 1.5 turns out on the airscrew by adjusting your pilot size.

[Turbeau]

I put in the 45 pilot. It starts nice, but it everything remains the same. The air screw is at 2 and half turns out. I pulled out the air filter, cleaned it and recharged it. That seemed to make the throttle a bit more snappy. For now I am going to keep the tune as it is. After my trip to the dunes I will come back and report on my results. Should be a couple weeks. Thanks everyone for your input it was really helpful.

[yaegerb]

Go up one clip on the needle (clip closest to the top). If it still bogs you need a leaner needle. 45 pilot with 2.5 turns out is still indicative of a rich condition in your pilot circuit. Rich is better than lean at the dunes.

[Turbeau]

I will pick up a leaner needle before heading out to the dunes. Thanks.

[Turbeau]

Here is an update from after riding at the dunes. I ran a 45 pilot, moved the clip on the needle up to the top, with a 160 main. It had great power from mid to full throttle. However at a 2nd gear take off it would bog for a second then pick up and go. It just wouldn't stay in the powerband when I let off the clutch.
But the story isn't over, at the end of the day I was riding out on the flats in 5th gear and heard a terrible noise, lost power and that was it. I grabbed the clutch before the engine died but it was too late. The motor seized and I had to be towed back to the staging area. After pulling the head off I noticed there was hardly any coolant in the motor and the piston was broken, the cylinder wall is scored pretty bad. The trike didn't have a degas bottle on it when I bought it. I think that must be the reason I lost my coolant. Going to rebuild the top end and check the engine for any additional damage. I will keep everyone up to date on the rebuild and performance once it is complete.

[yaegerb]

Ok, you are all over the place which tells me you likely have an air leak. From what your air screw was telling me and then you have a seizure from a lean condition usually indicates you are sucking air in somewhere else. Before you tear into the motor, I HIGHLY advise buying or building a case pressure tester and determining where your leak is.

Below is a good how to:
http://www.klemmvintage.com/airleaks.htm

[barnett468]

.
ok, that's a bummer so lets try and figure out why this happened so it will not happen again . . one of the things to try and determine is whether it siezed because it ran out of water or because it was lean etc.

what was the water level in the radiator before you started riding?

what was the level after it blew up before you took it apart?

did you ever hear a faint "pinging" sound from the engine while accelerating?

Post a photo of your spark plug . . it may or may not tell us if it was extremely lean or not.


here's a couple of errors that were made.

you installed a smaller main jet even though there was no indication that your previous one was too large . . this is why i did not suggest you install a smaller main.

you lowered the needle.

you went from a 58 pilot to a 45 pilot . . this leaned out the top end also slightly so it was like you installed a 157.5 main instead of a 160.

you did not do a compression test first as i suggested to determine what octane gas you should run.

you ran your bike wot in 5rh gear with 40:1 gas and oil mix . . you need 20:1 of you are going to do this . . the higher the engine rpm is, the more oil the engine needs.

it sounds like you increased the compression without INCREASING the main jet size . . the main jet size often needs to be increased when compression is increased . . one reason this is, is because, increasing compression increases cylinder, piston, and cylinder head temps, and the gas acts as a cooling agent . . more gas equals more cooling up to a certain point after which increasing the amount of fuel will not increase cooling and will cause perf problems like burbling/stuttering when the fuel drowns the spark plug.


based on your description thus far, i would suggest the following, but there certainly are other approaches . . also, in general, the bigger the bore, the MORE fuel it needs, therefore, after you bore it out, it will need MORE fuel than it previously did.

put the top end back on and do the leak down test yeagerb suggested . . there is no point in rebuilding the top end and doing this test after you rebuild the top end because it will have to come off anyway . . this being said, if it did not have a high idle or smoke excessively, i doubt it has an air leak, or at least not a very big one . . replace the crank seals if they are bad.

install a coolant overflow bottle if you don't have one.

install a higher pressure rad cap to prevent the coolant from flowing out.

do not run waterless coolant.

50 pilot jet

raise the needle to its previous position.

32:1 for normal abuse and 20:1 for wot 5th gear runs lasting more than 5 seconds.

172.5 main jet . . this is because you raised the compression plus now you will be increasing the displacement slightly which will also raise the compression slightly but the richer you mix the oil, the leaner your jetting becomes because you have more oil and less gas per unit of premix.

install a new plug of the proper heat range . . you can estimate the jetting by looking at the plug . . i compiled the following as a guide.

If it stutters/burbles even the tiniest bit when you accelerate, it is rich somewhere . . If it simply hesitates as if it is out of gas, it is lean.

you will not seize from running too rich, therefore, imo, it is best for a person whom is inexperienced at jetting, to start off with a setting that is too rich.

Post a photo of the plug . . The plug on the right is shiny which means it is wet which means its oily . . It is possibly rich too but its hard to tell because of black deposits from the oil . . This engine should be repaired . . The middle plug is perfect . . The left plug is lean.

..............http://i.imgur.com/eCSbd.jpg

...............http://www.4secondsflat.com/Plug-2.jpg


This plug is bone dry so the black means it is rich . . If both the threads and the porcelain is black, i would start by reducing the main jet size first . . In the case of a plug that has extremely heavy deposits like this, I would go down 3 sizes on the main because just one will not be nearly enough and two will likely no be enough . . Four would be too much.

http://www.dansmc.com/spcarbon.jpg
.

[barnett468]

.
exactly what oil are you using with the gas?

[Turbeau]

I think you have some information mixed up. I didn't install a smaller pilot. I went from a 38 to a 45. I did a plug check halfway through the day and the plug was brown and slightly wet. I then adjusted the needle to check performance. I was informed by a racing company that I know and trust to keep running 40:1 because I only installed the CR head gasket not a high compression piston.

There is a possibility that there is a problem with the water pump (just speculation). The plan right now is to break down the motor and inspect for additional damage. Replacing the crank seals is a must, the idle wouldn't return towards the end of the day. I am not going to go big bore. The spark plug was a light brown and blasted with small chunks of piston. So I know it was too lean. I plan to raise the needle with a larger pilot maybe a 50 once I get everything back together.

I do appreciate all the comments and help.

[barnett468]

.
Post 4

…the jetting is, main 165, pilot 58…


Post 14

I was mistaken on the pilot jet size. I am running a 40 currently.


Post 18

I put in the 45 pilot.




I think you have some information mixed up. I didn't install a smaller pilot. I went from a 38 to a 45.

First you said the pilot was a 58, then you said it was a 40 which I apologize for missing but I didn’t see where you said it was a 38.



I I did a plug check halfway through the day and the plug was brown and slightly wet.

This is most likely a sign of a bad crank seal on the clutch side because gas would have dried off instantly and you do not have enough pil mixed with the gas for it to leave an oily residue.



I then adjusted the needle to check performance.

Did changing it have any obvious affect?



I I was informed by a racing company that I know and trust to keep running 40:1 because I only installed the CR head gasket not a high compression piston.

Compression has very little to do with how much oil you mix with the gas . . The ratio is primarily determined by engine rpm, because the higher the rpm, the faster the oil migrates thru the engine . . The faster it migrates thru, the more you need to maintain the proper amount that is actually in the engine at any one time.

All, I will say about your oil ratio for now is that I was a professional Motocross racer, and 3 Wheeler racer and 4 Wheeler racer, and ran the R and D department for Kawasaki motors for several years, and neither I nor the Kawi factory race bikes ever used 40:1, and it is certainly not the ratio I, or they, would use at wot in 5th gear across a dry lake because it can cause a bike to seize due to insufficient oil.



I am not going to go big bore.
You don’t need to go to a big bore for it to require a bigger jet.



I do appreciate all the comments and help.

No prob, just hope it doesn’t happen again.

[Red Rider]

All, I will say about your oil ratio for now is that I was a professional Motocross racer, and 3 Wheeler racer and 4 Wheeler racer, and ran the R and D department for Kawasaki motors for several years, and neither I nor the Kawi factory race bikes ever used 40:1, and it is certainly not the ratio I, or they, would use at wot in 5th gear across a dry lake because it can cause a bike to seize due to insufficient oil.Just because neither you, nor Team Kawasaki, uses that ratio doesn't mean it can't safely be done. I've been running a synthetic oil mixture ratio as lean as 100:1 for over 20 years with no issues. And yes, my 250R gets plenty of wide open throttle abuse at the dunes doing hill shooting & top-end sprints across the flats. My friend also used the same oils & ratio (HPS & Redline) on his '87 Tecate with no issues. Well, no lubrication related issues, he still had plenty of stator issues LOL.

[barnett468]

.
Turbeau, the following is just a little more info on 2 stroke oil I thought to add . . There are excerpts from Harry Klemm and Bob Verret . . Just the engines that Harry built for Kawasaki alone have won more than 20 National Championships and over 100 National races . . Harry did the top end on my Tecate race bike as well as the ones on Donnie Luce's and Chris Whites . . He also did one on Mike Coe's factory Honda race bike . . I have known him for many years and know that he too has never run 40:1 on a bike that would see high rpm's . . Bob Verret is a noted oil expert.

Using ratios leaner than 32:1 are simply abnormal, and I have never seen anyone here run the mix that lean . . Just because it “can” be done under certain conditions with the right oil, does not mean it “should” be done, or that it is better to do . . An engine will NEVER seize from excessive lubrication, however, every engine will seize from insufficient lubrication, therefore, there is no reason/benefit to run one on the edge of being too lean on oil other than a benefit to a shop that will make money off of boring your cylinder.

The fact is, your engine seized, and it did not seize because it had too much oil . . The other fact is, you do not know the exact cause of the seizure, and there may have been more than one contributing factor, however, if you run a richer oil mix, you GREATLY reduce the chance that it will seize from having too little oil.

This being said, not all oils provide the same protection when mixed at the same ratio, therefore, some oils CAN be mixed leaner than others to some degree, however, determining exactly which brand these are is difficult and risky, since the proof will be in the experimentation.


Here’s another oil article from Bob Verret which he wrote just 2 months ago.

http://www.sea-doo.net/the-late-great-oil-debate/2015/04/


http://www.klemmvintage.com/oils.htm

"About Premix Ratios and “Oil Migration Time” - Oil Premix ratios are another subject that some folks tend to get emotional about … and like oil brand choice, our choices are about science and results…not emotion.

The objective of the premix ratio is to maintain a certain level of “oil-presence” in the engine interior during it’s average “operating-use” cycle. But how does one measure or assess the “oil-presence” … The most effective way has been with a radioactive additive. We explain below.

Trying to keep it simple…here is how it works. A test lab sets up an engine on a dyno stand, and begins feeding the engine a premix of an oil that has a specific level of mixed-in radioactive additive. As the engine is run, a Geiger counter at the exhaust exit measures the amount of radioactive material being eliminated. In this way, it is possible to factor the amount of radioactive material being put into the engine, verses the amount being sent out the exhaust. The net result is the amount of “oil-presence” inside the engine. In short, these tests showed that the oil-presence in the engine is a function of the operating rpm. That is, the “oil-presence" inside a two stroke drops significantly as the operating rpms increase. What this means is that an engine being run at 4000 rpm can maintain a very healthy and happy level of oil-presence with a 40:1 premix. However that exact same engine being run at 8000rpm needs to have a 20:1 premix to maintain the exact same level of oil-presence inside. This is why our 350 Bighorn road racers ran happily on the public roads on 40:1, but needed 20:1 for our sustained high rpm racing use. It bears noting that in both the 40:1 street and 20:1 racing situations, our Bighorns made no visible exhaust smoke at all, except when they were held at idle speeds for a long time.

A further example of this is shown in the carbureted two-stroke 951cc SeaDoo watercrafts of the early 2000s. In an effort to reduce the smoking during initial take-offs, SeaDoo engineers setup the oil injection systems to deliver no oil at all at idle speeds (and we mean zero oil). The logic was that at idle speeds there is virtually no oil migration at all. The high oil presence from the previous high speed runs was enough to allow the engine to run happily at idle for 10+ minutes with no oil at all being added…. And it worked great.

The lesson here is that your premix ratio should be a function of the average operating rpm that your vintage two stroke runs at. If you are at peak rpm all the time, 20:1 is a good idea. However for recreational level riders that don’t “scream” their engines constantly, leaner premixes will yield excellent long term wear.

About 100:1 Premix Oils - Since the 70’s there have been repeated advertising claims made by various oil brands claiming that their oils can offer suitable lubrication for competition two-stokes on a 100:1 or 80:1 premix. In many cases, these claims are “supported” by testimonials from various users. Despite the oil makers claims, and the sincerity of the testimonials … it’s not so. Running a 100:1 premix would be much like running only 2 quarts of oil in your truck, expecting that the quality of the oil can make up for the quantity …. It cannot….. no matter how good the film strength is “claimed” to be. The truth is, many two-stroke engines can “operate” on a 100:1 pre-mix so long as rpms are kept very low (as might be the case on a novice class open bike). But the first time that 100:1 engine makes an extended higher rpm run … it will lose the mathematics of oil migration, and score a piston. There is just no way around the math."
.
.

[Turbeau]

Thank you for the articles. I will read them. I do know why the motor seized, I over heated the engine. The coolant level was too low. I could change the fuel ratio or richen the air/fuel mixture. But as for now I am still in tear down mode. I am having the cylinder bored and sized for the new piston. I want to stay as close to stock displacement as possible. I plan on replacing the crank seals while the motor is apart and check on the water pump. Once the engine is back together and running I will take it back to the dunes for tuning only. I plan to do some plug chops to get an accurate tune. Again thanks for the help.

[barnett468]

.


Thank you for the articles. I will read them.
No prob, you’re welcome . . I hope you find them interesting at the least . . The latest “Super Oil” is mPAO which was invented/created by Chevron and is what Joe Gibbs Racing now uses in their race cars and regular engine oils.

What oil are you using exactly?



I do know why the motor seized, I over heated the engine. The coolant level was too low.
Ok, xlnt, knowing the primary cause is a big help . . Ok, I would definitely look at trying a stronger rad cap as I previously mentioned then . . Who knows if yours has weakened over the years or if it is just inherently a little weak . . Rocky Mountain ATV sells them.



I could change the fuel ratio or richen the air/fuel mixture.
Since the bike is new to you and you didn’t mention that it was burbling/sputtering with the 165 main jet AND the fact that the bore will be slightly bigger AND that it will be a new top end, I would definitely go up to the 167.5 I suggested earlier for starters at least because it certainly won’t be excessively rich based on all your previous comments, also, as I mentioned, it will run leaner if you increase the oil ratio to 32:1 which I would definitely do.



I am having the cylinder bored and sized for the new piston. I want to stay as close to stock displacement as possible.

You can still buy new Honda pistons and rings from the link below if you want . . Otherwise the other common ones are Wiesco and Wossner.

http://www.cmsnl.com/honda-atc250r-1985-usa_model68/partslist/E++07.html#results


The Wossner pistons are forged and have a friction reducing graphite coating but go up two sizes at a time.

http://www.wossnerpistons.com/products/mode/filter/search/Honda?fitment-category-id=81BADF2E-0BEE-E011-963B-000C29296656&fitment-category-name=2+Stroke


Wiesco increases one step at a time but does not have the coating.

http://www.wiseco.com/ProductSearch.aspx



I plan on replacing the crank seals while the motor is apart and check on the water pump.
If the impeller looks good, see if the bearing spins smoothly and I would buy a new seal for it.



Once the engine is back together and running I will take it back to the dunes for tuning only. I plan to do some plug chops to get an accurate tune. Again thanks for the help.

The dunes can be brutal for new engines . . I would try to break it in on a hard surface and run it for at least 1 hour before doing any high speed plug chops, especially since it sounds to me like the 165 main was pretty close before you changed it . . It’s not like it is so rich that it won’t rev past 3,000 rpm, or so lean that it has a massive flat spot and your plug was stark white.

[Turbeau]

Just a question. What would low octane levels do to a engine?

[barnett468]

Just a question. What would low octane levels do to a engine?

In short, it can damage a piston, but if the octane level is definitely too low for the amount of compression, the engine will make a pinging or rattling sound upon acceleration, however, it can take a trained ear to hear this, plus, if your bike is loud, the exhaust can be louder than the pinging so you might not hear it anyway, therefore, one can use a basic guide such as the following that I just made which is a conservative estimate.

COMPRESSION VS OCTANE

. .0 - 134 psi - Repair engine
135 - 135 psi - 87 octane
136 - 155 psi - 89 octane
156 - 170 psi - 91 octane
171 - 180 psi - 93 octane or E85 or 104 race gas or half 91 octane and half 110 - 112 race gas
181 - 200 psi - E85 or 112 race gas

[Red Rider]

What would low octane levels do to a engine?As the air/fuel mixture is compressed by the rising piston, it heats up. If the compressed mixture gets hot enough, it will ignite prior to the desired ignition time (Pre-ignition). This is bad because the piston is still traveling upwards as the mixture ignites & expands, hammering the upward moving piston back down. As barnett said, this can damage the piston, which is taking the brunt of the impact, but it can also damage the rod & crank as well. The lower the octane of the fuel, the more suceptible it is to pre-ignition. Also, using a high octane fuel, beyond what your compression requires, will not give you more power, but it will waste more of your money.

[Turbeau]

Here is an update: The motor is being rebuilt. The crank was bad,(replaced with a Hot Rods crank and rod assembly) as well as the main bearings, found a bent center shift fork, and the cylinder was bored .80 over and the piston was replaced with a weisco. I will be running race fuel and will be running a brand new 38 mm airstriker carb.(may not be needed but I had new one laying around) I am having a squish test done before I pick it up from the shop and will be running a richer fuel mixture. I took the time to tear down the trike completely. I sent the frame and swing arm out to be powder coated. The frame is back to a beautiful honda red and the swing arm has been returned to gold. I wanted the stock colors because I wanted my R to look like a 1987 model. Only need the white rear plastics to complete the build. Later I will install a 310 or 330 kit from ESR with a +8 swing arm. Again I will update everyone on the progress of the break in and tuning so people have some results.

[Mattematt]

85 ATC 250r
I'm having trouble with jetting i think.
It's breaking up on acceleration.
This is what i have...
Bored 50 over
Main jet 142
Pilot jet 52
Needle 3rd notch
Fuel/Air 2 turns
Gold series exhaust
NEW items
Stator
Cdi box
Voltage reg.
Coil

Compression test 182 psi
I don't know whats next?