budget sv650 cafe racer

gt alex

Been Around the Block
dyno results My base line for further changes
 

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Brent

Been Around the Block
A decent WERA legal superstock first gen SV should be getting 72-75 rwhp. That is a totally stock motor with a valve job and very careful assembly with timed stock cams, thinner head gasket, stock airbox and rejetted stock carbs and an M4 exhaust. My last stock motored racebike made slightly less than that as I had not slotted the cam sprockets and was running a Micron exhaust.
The first engine I ever rebuilt was from a snowmobile I had back in the '70's. An older neighbour, who was a mechanic, said I could use his shop and he would give me a hand. I was a kid and wanted it fixed in 20 minutes and started rushing at it. He grabbed my hand, gave me a "Whoa There" and said, "The first lesson here is that there is 10% more horsepower in a properly assembled engine and it's the cheapest power gain you can get, slow down, do it right".
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
Looking at that dyno chart and ignoring any differences between dynos ( they can be significant), let's focus on Air:fuel ratio.

Was the throttle 100% wide open by 4,000 RPM? If not we have a transient and part throttle issues. If it was wide open, we can focus on that.

At 4,000 it's the same as from 7,000 up to the red line and that's a bit rich all the way. His chart has a dotted target line at 13:1 which is close enough for government work. In theory 12.5: 1 is ideal but the curve is pretty flat around there, so go a touch leaner to 13:1 and it will be close enough to spot on. The GS is quite a bit rich all the way up the rev range, so I would lean out the whole thing slightly before tweaking the 4-7 region. Watch the torque curve and it should rise across the whole curve. When that's right, start looking at that lower rev range.

Not too shabby for a first dyno trip.
 

ex119x

Been Around the Block
I think that is a pretty good first run. The SV is very sensitive to its intake and exhaust. Teazer has given some good ideas that will get you closer to 70. I suspect that some cam timing adjustments and some exhaust work will gain even a few more hp. But, if you get close to 70 with good drivability it will be a great street ride. Keep it up, the SV is a great bike. I guess I better find the missing spark on mine before Spring.
 

gt alex

Been Around the Block
Looking at that dyno chart and ignoring any differences between dynos ( they can be significant), let's focus on Air:fuel ratio.

Was the throttle 100% wide open by 4,000 RPM? If not we have a transient and part throttle issues. If it was wide open, we can focus on that.

At 4,000 it's the same as from 7,000 up to the red line and that's a bit rich all the way. His chart has a dotted target line at 13:1 which is close enough for government work. In theory 12.5: 1 is ideal but the curve is pretty flat around there, so go a touch leaner to 13:1 and it will be close enough to spot on. The GS is quite a bit rich all the way up the rev range, so I would lean out the whole thing slightly before tweaking the 4-7 region. Watch the torque curve and it should rise across the whole curve. When that's right, start looking at that lower rev range.

Not too shabby for a first dyno trip.
Kept in mind this is an experiment using a single vintage throttle body similar to ones used on some early nascar
Unlike a carburettor you set up the max fuel flow and the metering shuts that flow off down to idle, mid range is adjusted by moving the throttle plate so the air supply matches the set fuel,
Because this is a custom application it wasn't designed for motorcycle applications and the throttle plate ended up set way in the rich direction to get enough fuel mid range after restricting the top end adjustment so much to suit the small engine, but the metering can only move so far.
End result rich idle and at full throttle the plate was sitting about 5 deg off full open. That is how it was for this test.
So I hope drilling the fuel spray bar for more fuel will let me open the throttle plate in relation to the spray bar/throttle shaft a little, fixing all issues
Fingers crossed
 
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gt alex

Been Around the Block
My torque curve compared to later efi model with k&n filter and slipon.
Today I drilled the spray bay and as luck would have it, it's much better low down and at WOT the throttle plate is now opening right up.
It will still need tweaking and an other dyno run.
IMG_20210211_141724.jpg
 

gt alex

Been Around the Block
I have drilled the spray bar for a bit more fuel which indirectly allows the throttle to open more.
So I am ready keen the run another test.
But I will ride it around a bit first.
 
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gt alex

Been Around the Block
Ok, Idle is still an issue but not cylinders cutting out or manifold imbalance.
Although I knew it I hoped I wouldn't have to address it. The throttle plate can spin around in the bore of the throttle body.

So it is a fraction, small even in the closed flat position to much air get past and when the mixture is correct it idles too fast.
I can get the idle speed correct by running rich but I want it correct.

So my mission I have chosen to accept, is get the throttle plate sealing at an appropriate angle,

The throttle plate is not just a flat plate so I need to work with what I have.
I am thinking of running lead/tin solder around the edge fitting it on the shaft and tapping it closed, filing where needed and hoping the soft solder will also conform a bit.

Any other ideas are welcome feel free the throw ideas at me, Thanks
 

gt alex

Been Around the Block
Isn't the butterfly aluminum? If so, you should source a new one that seals off completely.
No it looks like brass, unfortunately Getting another one is not an option, I have been collecting these throttle bodies for 20 years and never seen one this size before. Thanks for your thoughts
 

pidjones

Over 1,000 Posts
IF it really is brass, solder should stick fine. If anodized aluminum, you will have to make a new one. You could try JB Weld build-up, but I wouldn't trust it on the intake.
 

gt alex

Been Around the Block
IF it really is brass, solder should stick fine. If anodized aluminum, you will have to make a new one. You could try JB Weld build-up, but I wouldn't trust it on the intake.
Thanks, I feel the same, the net has info about putting JB weld in the bore but I just don't trust the idea. Making one is beyond me it's not just a plate.
I could section what I have and make it a touch bigger but that would be over kill I think.
 

gt alex

Been Around the Block
IF it really is brass, solder should stick fine. If anodized aluminum, you will have to make a new one. You could try JB Weld build-up, but I wouldn't trust it on the intake.
Today I soldered around the throttle plate and filed it to shape it now snaps closed to about a 3 deg angle. No sticking and although I can see light around most of it when held up to the sun I am happy with the fit.
Bolted it on throttle "closed" and it idle steady 800 rpm. (win)
I have noticed the idle air by-pass doesn't shut all the way off when screwed in, but like the throttle plate I will wait and see if that is a problem or not. No mixture checks have been done yet
My new Chinese Reg/rec has died but good news is the stator still tests ok. Maybe the dyno killed it.
The Li battery runs out of puff scary quick with no charge going in and the head light always on.
I am thinking of getting a Honda cbr unit
 

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