budget sv650 cafe racer
- Thread starter gt alex
- Start date
Rear cylinder is still not playing the game. With idle set 2000 rpm It idles 5 seconds then the rear cuts out And runs on the front for 10 seconds at about 1000 rpm and keeps doing this. "Seems" to run ok 2500 and over.
The coil checked ok I put a wire across from the + front coil to the rear to ensure both has the same voltage supply.
new HT wires, plugs, and end caps, also swapped coil from a later model bike just to test(same)
The intermittent nature of the fault makes testing a bit inconclusive.
I put a inductive timing light on the rear and it continues to flash when not running on the rear but as the revs increase back again the light stops twice while revs go up (how weird is that)
I reduces the plug gap to it spark easier to see if that helped it didn't.
I pinched the vacuum pipe going to the fuel pump and the petcock with no change
Any thoughts
I am stuck at the moment
Thanks
The coil checked ok I put a wire across from the + front coil to the rear to ensure both has the same voltage supply.
new HT wires, plugs, and end caps, also swapped coil from a later model bike just to test(same)
The intermittent nature of the fault makes testing a bit inconclusive.
I put a inductive timing light on the rear and it continues to flash when not running on the rear but as the revs increase back again the light stops twice while revs go up (how weird is that)
I reduces the plug gap to it spark easier to see if that helped it didn't.
I pinched the vacuum pipe going to the fuel pump and the petcock with no change
Any thoughts
I am stuck at the moment
Thanks
Just checked valve clearances right on spec min clearance, ideally I would have liked a couple of thou more but I am ruling that out.
I think that just leaves my manifold ether still leaking or design. so first step putting non hardening fuel resistant sealant on all mating surfaces. then if no go, I will put some thing under the carb to stir the income charge in the plenum area as a experiment.
I think that just leaves my manifold ether still leaking or design. so first step putting non hardening fuel resistant sealant on all mating surfaces. then if no go, I will put some thing under the carb to stir the income charge in the plenum area as a experiment.
That is odd. But the manifolds are a bit different front versus rear and I wonder where the spray bar is discharging. Is it favoring the front cylinder at small throttle openings perhaps?
If it's still leaking, try a little ether (Start Ya Bastard) around the outside of that manifold and see if that perks it up.
The continuous sparks on the rear pot suggests that ignition is not the issue, though the stop spark situation is rather odd for sure.
If it's still leaking, try a little ether (Start Ya Bastard) around the outside of that manifold and see if that perks it up.
The continuous sparks on the rear pot suggests that ignition is not the issue, though the stop spark situation is rather odd for sure.
I see a vacuum nipple on the rear cylinders intake.
Have you tried blocking that off while you are doing your tests? Perhaps you are getting additional air coming through that port.
I am assuming you are using a test tank to gravity feed fuel to the carb.
Have you tried blocking that off while you are doing your tests? Perhaps you are getting additional air coming through that port.
I am assuming you are using a test tank to gravity feed fuel to the carb.
It seems the rear cylinder is running lean at low rpm I suspect I its to do with the uneven firing order the air/fuel mix has more time to stagnate and stop flowing as opposed to the front where the flow is still going stared buy the rear. I am thinking of running a 12mm tube from the manifold branch base of the rear cylinder to the front of the manifold.
It won't completely get rid of the air flow pause but it should keep a air/fuel mix in the rear branch while the front is pulling in its mix.
Interested to see what others think.
It won't completely get rid of the air flow pause but it should keep a air/fuel mix in the rear branch while the front is pulling in its mix.
Interested to see what others think.
I just fitted a balance pipe and although not the magic bullet I hoped for it has defiantly changed things for the better.
I can now get a stable steady idle at 1800rpm with just a bit of fluttering from rear cylinder misfire. Any slower and the rear cuts out. no stopping and starting the rear just stops.
So I will make a plate the slip under the front rubber carby mount and hopefully it will run well on the rear.
If it does I could try a larger balance tube but I think moving the balance tube attachment on the rear closer to the bottom of the rear intake would put more mix in the rear leg of the intake. At the moment its is fitted just above the rubber mount which is only 1/2 way down, ideally I would drill into the head about 50mm above the valves, but that is a bit radical not knowing if it will make the difference I want.
I ended up use 3/8 id tube I could upgrade to 1/2 as first planned just to see.
I can now get a stable steady idle at 1800rpm with just a bit of fluttering from rear cylinder misfire. Any slower and the rear cuts out. no stopping and starting the rear just stops.
So I will make a plate the slip under the front rubber carby mount and hopefully it will run well on the rear.
If it does I could try a larger balance tube but I think moving the balance tube attachment on the rear closer to the bottom of the rear intake would put more mix in the rear leg of the intake. At the moment its is fitted just above the rubber mount which is only 1/2 way down, ideally I would drill into the head about 50mm above the valves, but that is a bit radical not knowing if it will make the difference I want.
I ended up use 3/8 id tube I could upgrade to 1/2 as first planned just to see.
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I just fitted a 3/8 id balance tube a fraction larger than the first one and I didn't notice a change but the idle still fluttering on the rear can now go down to 1600rpm which is almost a win except spluttering between 1600 and 1800 will equate to a flat spot.
So I will try to fine tune best I can before hitting the dyno. I will try to turn the TB 90 deg so it opens across the knife edge, as it is it does tilt towards the front.
With the throttle plate 1/2 way up the TB I didn't think it would matter but I should fix the obvious, If it does help it may be a redesign for the linkage to fit under the tank.
So I will try to fine tune best I can before hitting the dyno. I will try to turn the TB 90 deg so it opens across the knife edge, as it is it does tilt towards the front.
With the throttle plate 1/2 way up the TB I didn't think it would matter but I should fix the obvious, If it does help it may be a redesign for the linkage to fit under the tank.
I spun the carby 180deg now opening towards the rear cylinder and idling at 1400rpm, pulling the front and rear plug both plugs had similar effect but the idle exhaust sound was not even.
So it looks like it will be worth making an adapter to run the throttle across the plenum.
So it looks like it will be worth making an adapter to run the throttle across the plenum.
I broke down on my test ride last week
I think I found the problem. I lost the vacuum plug I was using on a T piece on the hose to the petcock and in my impatience I used a screw to block it. But it did a bad job.
I found it using a hand vacuum pump,
Unfortunately we are in lock down again so I will test ride it Tuesday if restrictions are lifted.
The pump is pumping well cranking the engine.
I am thinking of fitting a relay and fuse for an electric pump incase it is needed on dyno day.
I need to rebook the dyno after the lock down.
I think I found the problem. I lost the vacuum plug I was using on a T piece on the hose to the petcock and in my impatience I used a screw to block it. But it did a bad job.
I found it using a hand vacuum pump,
Unfortunately we are in lock down again so I will test ride it Tuesday if restrictions are lifted.
The pump is pumping well cranking the engine.
I am thinking of fitting a relay and fuse for an electric pump incase it is needed on dyno day.
I need to rebook the dyno after the lock down.
It has been a good day, I just had my gen 1 sv650 cafe racer with my single throttle body conversion on the dyno for the first time and it looks promising to me.
62hp at 8800 and over 44 ft/lbs torque almost flat 5000-6500
Still needs work idle is way rich
So I will put some effort into the idle and the a gen1/2 cam conversion before another dyno session.
slight edit over 40 ft/lbs from 4700-7500
62hp at 8800 and over 44 ft/lbs torque almost flat 5000-6500
Still needs work idle is way rich
So I will put some effort into the idle and the a gen1/2 cam conversion before another dyno session.
slight edit over 40 ft/lbs from 4700-7500
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Sderbyshire
Into Sailing, classic Triumph cars and motorbikes.
Sounds like great progress!
Dyno day with single TB. Got 62hp 8800 rpm and 44.5 ft/lbs torque 6300 rpm
64.2 hp (47.9 kW) @ 9000 rpm[12]
42.3 lbf⋅ft (57.4 N⋅m) @ 7200 rpm[12] from Wikipedia
So I am both disappointed and pleased
with a single throttle body and a home made manifold I have a better better mid range torque and max power only rolls off 200 rpm early and sacrificing 2hp.
I really think I will stick with this and add cams to see what that does. Also the muffler is nothing flash but I like the look at this time.
I would be very happy with that first run. The intake manifold and exhaust designs are likely to cost HP compared to stock, so overall it's a good place to start. Check the rear wheel HP chart against Air:fuel and see if there's room to fine tune the mid to upper range as well as cleaning up the low end.
Congrats on the experiment. It's always fun to try new ideas and to learn from the experiments.
Congrats on the experiment. It's always fun to try new ideas and to learn from the experiments.
thanks, I already have some thoughts. But since I don't have any good way to check mixture ratios at home I was thinking of taking note of vacuum every 2000 rpm as a bench mark so as I change things, I know if I am making progress
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.
