Yamaha SR250 Power and Temperature Testing

A couple of notes on the jetting testing with the O2 sensor...

It is quite difficult to get a clear understanding of the settings without some kind of data logger that you can analyse later and compare Lambda readings against engine rpm to identify exactly which areas of the carb are running too rich or lean. With this current set up, I am doing some hard pulls and chopping gears trying to see how the carb responds, then trying to remember what the gauge's readings were and adjust the carb based on that.

Although I got pretty close with some settings, I think further dyno time is necessary. I will book in for some time this November.

What is interesting is how different the O2 readings are based on throttle position, speed and rpm. For example, you can be cruising at 80kph in 4th at say 4000 rpm and be reading in the 14's - which is almost stoich, but a little lean if you want best power. Then you can whack open the throttle, and despite having a CV carb, the O2 readings can jump into the 11's! The way we set the carb up on the dyno last time was through power pulls - from 2500 - 8500 rpm wide open. That gives you the best settings for maximum power rather than maximum efficiency. Although I think what you would find is that under normal cruising conditions, those settings would give readings in the 14's as well.
 
Ah yeah, all testing came to a halt when the O2 sensor packed up. It was giving an error code which when I check in the manual, means its shot and the most likely cause is that it has been run too hot.

So I think the position I put the sensor in is perhaps too close to the exhaust valve. Rather than cutting it out, patching up the hole and relocating the sensor bung, I think I'll get one of the Innovative bung extenders/heat sinks. Most commonly used in turbo and rotary engine applications where EGT's are super high.

I'll wait for the dyno testing this time, but will sort this set up out in time for next season. For now I have just installed a plug into the sensor bung.
 

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I am going to share a couple of mods I have been working on for the stock carb. After reading a tonne of hot rod magazines, 4 stroke tuning and performance books and online build threads/advice, I decided it would be worth while trying the butterfly shaft trim mod. Apparently you can pick up quite a bit of extra cfm/flow by doing this and also reduce turbulence. Through the throat of the carb, increases can be anywhere from 5-12%. This is all theory of coarse, but it makes sense to me - just check out the photo comparison of stock vs modified. I'll dyno test this too to see if this free mod helps at all ;D

I am confident there was plenty of meat left in the one side of the shaft to hold up over time and against the force of the return spring pressure. I could have gone one step further and completely countersunk the screw heads but I didn't feel confident in doing so with my battery drill and countersink bit. There is also, not a lot of thickness in the plate, or threads in the shaft. It would have been borderline. I put some loktite on the screws and filed them smooth with the shaft, then rounded the edges of the chamfered shaft slightly.
 

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And another mod/accessory of my own idea/design. Just to help with carb tunability.

I noticed when doing the jetting testing with the O2 sensor (before it shat itself) there were some cases where I had the bottom end dialled in, as well as WOT, but the mid range was giving me headaches. The biggest issue was when I had a perfect setting for WOT - meaning the main jet was spot on, but the mid range was leaning out. There are a couple options here, either increase the main jet - which actually solves the midrange, but then runs way too rich at WOT. Or you can adjust the slide needle position - by lifting it you get a richer mixture right. The issue I was running into it that it was uneven from say 1/2 throttle to 3/4 - like the slide was lifting too fast and leaning out the mixture no matter what I adjusted.

So my solution was to make a spacer that sits inside the throttle slide - over the jet needle plate and screws. The idea is that the spacer adds a little bit of weight (5g exactly) to the slide to slow it down a little and even stabilise it (dyno footage showed it vibrating and bouncing like mad), but even more importantly, to add a small amount of extra spring tension to the whole moving assembly - slowing down it's lift under vacuum. This way, the spring does not need to be modded, chopped or stretched in anyway to achieve the same thing, and therefor does not introduce any irreversible mods to the spring/carb.

I have no idea if it will work/help, but it adds another option to tune the midrange ;D
 

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I received the final CNC machined engine components this week and they look great! I would make a few small updates to the designs before going into production, but I am hoping to be able to take some pre-orders of these covers if people are interested as well.

I was not 100% happy with the finish, I will need to specify a slightly higher machine finish on the drawings to get them up to standard. Plus the anodising needs to be improved.

This is the first finned cam cover prototype in aluminium and it is probably the part I am most happy with. It came out great. Also looking forward to testing the harmonic intake ;D
 

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A few posts back I mentioned the updated oil filter cover cooler design. First I will explain the function of the original and the discovered flaws...

I first thought that the best solution to a bolt on cooler (without needing to plumb in an external one) would be to have straight bolt on solution - by that I mean, leave the oil filter in its stock position and use the standard mounting hardware etc. The design increased surface area by 400% and oil capacity by exactly 100ml - one thing to do to increase oil cooling ability is to increase capacity. So in theory this should work.

With the limited testing I did do, I found that this design only reduced oil temperatures by 2-3 degrees like the valve covers. I was looking for a more drastic effect than that. Hopefully more like 5-6 degrees would be ideal (don't want to remove too much heat either!). Something I found was that the entire right side crank case cover acts like a giant heatsink, losing around 10 degrees of oil temp from its journey from the sump to the oil filter. This is pretty cool and something that I gained concrete data of - with my two oil temp sensors in the sump plug and just after the oil filter I could compare exactly. This meant that with the oil cooler in place, temps should drop by more like 15 degrees, when they were only dropping by 12-13.

After scratching my head for a while and looking at the design, I realised something. Sure, this design exposes the oil to much more surface area and provides cooling potential, but how much of that oil actually flows through the cover and interacts with the cool aluminium surface? And how much just stagnates and sits there? I concluded that, due to oil temperature differential, the hot/warmer oil flows faster, easier, better than the cool oil, therefore bypasses the extra surface area and just flows straight into the filter and up to the head instead! Its about the viscosity of the oil.

So I decided to update the design and intentionally re-route the oil, forcing it to pass though the finned cover. More in next post...
 

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On to the updated version... I still wanted to use the stock oil filter and not specify another one (to reduce space required), risking affecting the flow capabilities of the filter compared to stock. But I also wanted the oil to pass through the entire finned cover.

The solution was to put the filter back into the cover, instead of in the engine, this way, forcing the oil out and around the cover before it can go through the filter and up to the head. This required a special spacer tube. One issue with this, is that whatever heat the oil lost, now needs to be pumped back through a bath of hot oil before it actually travels to the head. The solution here was to use a material with low heat transfer properties - stainless steel, grade 304. So the oil looses its heat passing over the cool aluminium surface of the cover, then does not pick it back up again through the special spacer that runs through the hot oil. That is the idea anyway! I think that no matter what, this will work better than the original design, but testing will prove just how much better.

The other drawback with this design is that it is slightly trickier to install - now that the filter sits out of the engine cover and in the cover. It's not too bad, just requires lining up. I have designed in guides in the cover that help with alignment as well. The special spacer tube was designed to be sealed in the engine by using the rubber washer from the old filter - so you just pull that off and use it when you change the oil and filter in a service :D

If anyone has any questions, feedback or input, I'd be super happy to discuss! The great thing with this cover is, if it works, it fits the SR400's, SR500's and SRX600's too!
 

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Neat oh! Suggest tho that the thickness of the tube part inserted into the motor will block a good percentage of the oil port, maybe consider a notch cut to allow full flow?
 
Tune-A-Fish© said:
Neat oh! Suggest tho that the thickness of the tube part inserted into the motor will block a good percentage of the oil port, maybe consider a notch cut to allow full flow?

Good point, I'll double check that. I could either add a notch or pull back it's length a couple mm. Cheers!
 
One last mod I want to test is advancing the stock cam timing. I have read up a lot on this and figure it is worth a shot to see what affects it has on the engines characteristics and power delivery.

It is common knowledge that you retard cam timing for high end power - with sacrifices down low, and advance cam timing for low end and midrange power - losing out a bit on top. Over time and use, the cam timing is only ever going to head in the direction of retard - due to slippage, wear and cam chain stretch. So I have decided it will not be worth testing retarding the timing of the SR - which already has quite a high revving engine. It might be interesting to see if advancing the cam brings on the power a little earlier.

I modelled up the cam gear in CAD and calculated just how much offset in terms of mm would be needed to achieve a setting of 4 degrees advance (at the crankshaft - double the camshaft degrees) and then a setting of 8 degrees advance. It is quite surprising to see just how little it is and how much difference it 'could' make - you can see the transparent overlay in one of the images. When people advance and retard timing, it is usually to within 10 degrees either side of the stock spec, no more, so I thought 4 and 8 would be interesting to test.

Then I filed off that amount from the correlating side of the keyhole on the cam gear and I when testing I will pack out the slack with two different thickness shims - trimmed from a spare feeler gauge set I had. These cam gears are not hardened so there shouldn't be any excessive pressure or wear on the newly ground face - the cam gear bolt will take up all the load when correctly torqued up.

I also checked to make sure there was going to be enough valve-piston clearance by shifting the cam chain a whole cam sprocket tooth - an 11 degree cam rotation, 22 degree crankshaft rotation (which is extreme!) and there seemed to be plenty, so 8 degrees will be fine :D
 

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Badass. As an engineer, I totally dig the thought process and mechanics of your testing procedures. It will be very cool to analyze the results once you've had a chance to put your theories to test!
 
The exhaust thread in the head of the Jadus Test Mule 1.0 finally gave out :( Swapping headers around and bolting down the clamp flange a few times did it. If you look closely at the hole you can see the old bolt is actually still there - in the middle of where the new thread should have gone. But sadly, the muppet that did this repair job failed to extract it and then just decided that a new M6 tapped hole, 3mm to the right at a 15 degree wrong angle was good enough. Same person that bolted in a wood screw remember! Gah.

I took it as a sign. I am going to do a full rebuild of this engine eventually and make a separate build thread of it. I'll get that exhaust thread repaired properly with the head off - hopefully even welded up and re-tapped in the correct position. I have lots of ideas for the build... Cam, high comp piston etc. It's gonna be a killer.

In the mean time, plans go ahead to complete the testing on the Jadus Test Mule 2.0 ;D
 

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Tune-A-Fish© said:
If you made a drill jig to bolt to the other hole and went slow you could get a timesert in that head.

That was my original thought too, but unfortunately, the new threaded hole is so far off centred and crooked that it has removed a lot of meat where the timesert would nead to go :-\ So I think I will extract the bolt that is there and try have it welded up - def a job for a pro. The jig is an awesome idea for the new hole though.

Btw, pros and cons for Timesert vs Helicoil? I have used both and didn't quite evaluate if one was better than the other :eek:
 
Helicoil is like a thread spring, sub par but will work. Timesert is a solid part and installed with a roll form tap that sets the od threads in the tapped hole with a shoulder to both stop it and provide a perfect opening for alignment.

I got a set that provides a four step process... drill, shoulder cut, tap and driver/thread roller.

Really better than new if installed in aluminum.

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Sent from my iPhone using DO THE TON
 
Ah sweet, that definitely looks like the way to go! Have just read a bit more and it looks like these are the ticket for cylinder blocks and things too - perfect :)
 
One of my favourite shows on Youtube (after MCM and Roadkill ;D) Engine Masters have done some pretty awesome tests with exhaust systems - both collectors, inch size and mufflers. Although slightly different, a lot of this stuff is applicable to bikes too. I have been inspired by their methods and love their enthusiasm!

https://www.youtube.com/watch?v=bXQ-cXeri1Y
 
Incase anyone missed it, here are what the cooling engine covers look like on the other Jadus bike...

I will continue to conduct testing on them as summer (e-ven-tu-al-ly) rolls around here in Sweden. But the testing will be carried out on the orange Jadus test mule. I will swap over the sump oil temp set up and the head temp set up, but probably won't bother with the oil galley set up. Even though if I wanted to, I could just swap the whole engine case over ;)
 

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Here was the jetting options I accumulated leading up to the last dyno session, which happened around 4 weeks ago now. I am going to add some pretty lengthy posts here summing it all up :)

I also decided to become a reseller for Keyster carb kits too, because they are amazing! I ordered a couple sample kits and had the chance to test out the jets on the dyno day as well. They are spot on. The kit includes all the things that usually wear out or break on the SR250 carb. But I think my favourite things included are the different jet needles. What we found during both dyno sessions is that moving the needle clip position up and down does not very often put the mixture where you want it. But with these different needle diameters, it really does wonders to evening out the air-fuel ratios :)
 

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