budget sv650 cafe racer
- Thread starter gt alex
- Start date
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".
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.
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.
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.
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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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
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
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
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.
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
Next stage. on my sv650 cafe racer all mixtures seem ok (will dyno again before cam swap.)
Fitted a GSXR 600 reg seems good and battery hold charge better now so the other one must kave been faulty all along.
Getting really frustrated by intermittent fuel cutting out. when I have previously checked the vac fuel pump and petcock and it has looked ok but today it did it again and the pump was not working.
I believe a new vac pump should work reliably on my custom intake system but, I have an electric pump so despite wanting to retain the standard pump that's the job at hand.
So the pump I have fits well, I have made a cross shaped bracket which mounts where the stock pump bolted to the frame using the stock rubbers and bolts.
The pump runs inside the right frame in the standard place.
Next the bit I dreaded finding 12v to run the pump.
After sliding back the rubber boot on the harness I found an unused 2 wire connector one wire black/white -earth and orange/yellow + 12v ign switched
Looks like its for carby heating not used here, Perfect
So tomorrow it should be done and I will post how it goes.
Fitted a GSXR 600 reg seems good and battery hold charge better now so the other one must kave been faulty all along.
Getting really frustrated by intermittent fuel cutting out. when I have previously checked the vac fuel pump and petcock and it has looked ok but today it did it again and the pump was not working.
I believe a new vac pump should work reliably on my custom intake system but, I have an electric pump so despite wanting to retain the standard pump that's the job at hand.
So the pump I have fits well, I have made a cross shaped bracket which mounts where the stock pump bolted to the frame using the stock rubbers and bolts.
The pump runs inside the right frame in the standard place.
Next the bit I dreaded finding 12v to run the pump.
After sliding back the rubber boot on the harness I found an unused 2 wire connector one wire black/white -earth and orange/yellow + 12v ign switched
Looks like its for carby heating not used here, Perfect
So tomorrow it should be done and I will post how it goes.
pidjones
Over 1,000 Posts
I like electric fuel pumps, dislike vacuum or "pulse" pumps. Electric pumps need care in wiring to stop them in event of crash. Probably using oil pressure with bypass to start circuit should work. More complex includes bank angle sensors. For a cafe, at minimum take care that key off kills power.
The cct only comes on with ignition and I was going to keep the vacuum petcock which will stop fuel flow if the engine cuts out with ignition on. In a accident it might cook the pump running dry, but if I have had an accident I don't think I will care.
Cold air intake?
I was thinking of fitting a baffle to separate hot air from the radiator but if I go to that much effort I feel I may as well make a cold air intake.
So, I don't have the standard air cleaner but if I use the original air box shape around the seam as a starting point.
Once I have a neat fit to the inside shape of the tank some foam will seal it off.
Now to get air in, race cold air intakes twist down to the small gap between the radiator an the frame.
After scratching my head a while I decided a scoop on the top of the tank didn't do it for me. But standing back and looking, it appears the natural place is to make the handlebar dents into scoops. I think they are already in some positive air flow and won't be obvious. The dents will go through to the air cleaner.
So as usual I am interested in what ideas others have before starting.
Thanks
I was thinking of fitting a baffle to separate hot air from the radiator but if I go to that much effort I feel I may as well make a cold air intake.
So, I don't have the standard air cleaner but if I use the original air box shape around the seam as a starting point.
Once I have a neat fit to the inside shape of the tank some foam will seal it off.
Now to get air in, race cold air intakes twist down to the small gap between the radiator an the frame.
After scratching my head a while I decided a scoop on the top of the tank didn't do it for me. But standing back and looking, it appears the natural place is to make the handlebar dents into scoops. I think they are already in some positive air flow and won't be obvious. The dents will go through to the air cleaner.
So as usual I am interested in what ideas others have before starting.
Thanks
