budget sv650 cafe racer

gt alex

Active Member
I through myself a curve for a couple of days by not pressing to rear of the manifold all the way home. but I should be back on track now.
 

Brodie

Gold Coast, Queensland
DTT SUPPORTER
Hopefully you get it all sorted. Very unique idea.
How did you fair in the recent wild weather?
 

gt alex

Active Member
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
 

gt alex

Active Member
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.
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
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.
 

Brodie

Gold Coast, Queensland
DTT SUPPORTER
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.
 

gt alex

Active Member
after using sealant on everything and putting a temporary deflector under the carb towards the rear still no go but the rear is lean?
 

gt alex

Active Member
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.
 

gt alex

Active Member
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.
 
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gt alex

Active Member
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.
 

gt alex

Active Member
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.
 

gt alex

Active Member
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.
 

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