BIG carburation problems after installing 'Hot' cam

[MikaelDK]

If its posseble try original ignition and see what happening In a dyno with a A/F lambda . . Then you Will get answers . .
Iam running a 1000cc Tony Hall Engine In a flat tracker . . I Use a Old Kröber ignition . . My exhaust must be changes (2-1) because i dont get top end performance enough . . So iam into a new exhaust . . My performance last sunday In a dyno was 75 hp and 140 nm on the rear wheel . .

 

[Mannyroad]

eliminate exhaust by bolting on a standard type?
a 2 into 1 with a rephase may cause widely different jetting needs side to side?

Cheers for your comment. Have already bolted on the 79 stock exhausts (but with balance pipe removed and blanked) and just waiting for a dry day to test run it (yeah, yeah, I know, I'm a tart )

 

[Mannyroad]

I can vouch for that; I'm still chasing an intermittent mis-fire on Taffy after two years and three different TCI / Gonzo set ups.
At my witts end with the bike I love!

I know that pain. I love this bike, spent a small fortune on it and its kicking my ass.

 

[Mannyroad]

Is the trigger and magnet(s) working properly? It would explain why two or three different igniters aren't working properly.

(I previously owned a Hinckley Bonneville. Faulty ignition triggers were extremely common. Often only giving a fault after serveral miles and then working normally again for several more miles before going faulty again).

I've no way of checking that. The red LED goes out when it should, comes on when it should and its clearly advancing when revved and strobed. I'm not expert enough to know how to check electronics.

 

[Mannyroad]

If its posseble try original ignition and see what happening In a dyno with a A/F lambda . . Then you Will get answers . .
Iam running a 1000cc Tony Hall Engine In a flat tracker . . I Use a Old Kröber ignition . . My exhaust must be changes (2-1) because i dont get top end performance enough . . So iam into a new exhaust . . My performance last sunday In a dyno was 75 hp and 140 nm on the rear wheel . .

The original ignition system was made by Probe, but it failed totally, so had to source an alternative. I couldn't find one for a true 270 rephase so had Pipes N Stuff make me one, a modified version of their 277 system. The problem is that I now have a new ignition system and a completely different sporty cam and now have a severe misfire from half throttle right through to full, something I didn't have previously. So, it might be the ignition, the cam or maybe these two additions are now showing failings in the exhaust set up. Hard to know which at this point. So I'm putting a standard 2-2 XS exhaust back on to see what effect that has, and go from there.

 

[GLJ]

I've no way of checking that. The red LED goes out when it should, comes on when it should and its clearly advancing when revved and strobed. I'm not expert enough to know how to check electronics.

If your timing stays steady with the light at higher RPMs the ignition is probably ok. If the timing goes bat shit crazy and jumps all over the place it could be the problem.

 

[WideAWAKE]

Another dumb question but we’re sure the cam is set up for 270 and not 277?

And we’re sure the crank is 270 and not 277.

I know… stupid questions but something (I myself included) make assumptions of parts based on what we order and don’t check that what’s delivered is what we actually ordered. - I’ve driven through Taco Bell enough in my life… always check the bag!

 

[Mannyroad]

If its posseble try original ignition and see what happening In a dyno with a A/F lambda . . Then you Will get answers . .
Iam running a 1000cc Tony Hall Engine In a flat tracker . . I Use a Old Kröber ignition . . My exhaust must be changes (2-1) because i dont get top end performance enough . . So iam into a new exhaust . . My performance last sunday In a dyno was 75 hp and 140 nm on the rear wheel . .

I'm assuming you're referring to those direct digital readout guages connected to a lambda sensor which needs a boss welding into both exhaust headers. I understand your thinking but at this point am trying to resolve it without the expense of those units plus the re-chroming of the headers which in total would set me back another £500_600.

 

[Mannyroad]

If your timing stays steady with the light at higher RPMs the ignition is probably ok. If the timing goes bat shit crazy and jumps all over the place it could be the problem.

OK, no, the timing advances smoothly and holds steady once I bring the motor up to around 4000.

 

[Mannyroad]

Another dumb question but we’re sure the cam is set up for 270 and not 277?

And we’re sure the crank is 270 and not 277.

I know… stupid questions but something (I myself included) make assumptions of parts based on what we order and don’t check that what’s delivered is what we actually ordered. - I’ve driven through Taco Bell enough in my life… always check the bag!

The motor was built by the late Daryl Hutcheon of Melbourne. He specialised in building 270 XS650 motors, and to achieve this machined his own special crankpins to ensure a true 270. He also had the cams made specifically for his rephased motors by a well respected cam machining firm in OZ. Strangely though, when I profiled the cam lobes things weren't as they should be in that overlap was huge, so Smedspeed kindly made a new cam for my engine, specifically for 270 degrees. I have checked the profiles for the left cylinder and they look good by my readings, though I haven't checked the rh cylinder.

 

[GLJ]

OK, no, the timing advances smoothly and holds steady once I bring the motor up to around 4000.

That sounds like the ignition itself is ok. Should check both sides to make sure they are both ok. Also make sure the ignition is set up for 270. I would bet the coils, wires and plugs are fairly new but new does not always mean good. Then as has been suggested make sure the cam is set up for 270.

 

[Mannyroad]

That sounds like the ignition itself is ok. Should check both sides to make sure they are both ok. Also make sure the ignition is set up for 270. I would bet the coils, wires and plugs are fairly new but new does not always mean good. Then as has been suggested make sure the cam is set up for 270.

OK, fair points for sure, though the coils, leads and plugs are less than 2000 miles old and I had no issues with misfiring etc before I installed the new cam and ignition, so it's probably fair to assume at this point that they're OK. So, current plan is road test bike tomorrow with 2-2 std xs exhausts and see if that changes anything. If not then I agree its time to check the ignition unit and cam.
My friend, a bit of a Triumph guru, who's spent a lifetime building, modifying, racing and tuning Triumph twins, checked the voltage while running. I can't recall the value he got but he assured me it was good, so I'm doubting it's that.

 

[GLJ]

so it's probably fair to assume at this point that they're OK.

With the problem you are having don't assume anything. You have a lot of quality parts that are not playing nice together.

 

[Bruno_c]

Do you know if both cylinders are misfiring or one only?

 

[Kevin Werner]

At !/2 throttle you are transitioning to the main jets but your pilot is still very much in play. I had a similar issue and went down on the pilots to solve my missing/barking issue. As someone pointed out 2 into 1 on a 277 motor might be bad idea. Kenny never rode one like that.

 

[Jan_P]

Not read through and this can be stupid --But putting it here
As I understand it an Ignition Brand --- Probe was on there.But stopped working
And the company is no longer active
I would try to contact Auto electric firms or Home Electronics repair firms
Here on this forum, is also Boys that know how to repair the Boxes for XS 650
Sleddog83 is One.
If the Ignition box can be opened I assume that it is mostly some transistor or so at the output and close ..
there
If it can be opened it can most likely be repaired

 

[Mannyroad]

Not read through and this can be stupid --But putting it here
As I understand it an Ignition Brand --- Probe was on there.But stopped working
And the company is no longer active
I would try to contact Auto electric firms or Home Electronics repair firms
Here on this forum, is also Boys that know how to repair the Boxes for XS 650
Sleddog83 is One.
If the Ignition box can be opened I assume that it is mostly some transistor or so at the output and close ..
there
If it can be opened it can most likely be repaired

Thanks for your comments. The Probe system had all the electronics set within resin inside an extruded aluminium 'tube'. Great for ensuring durability and water exclusion but makes trying to get to the electronic components impossible, hence no longer have it.

 

[Mannyroad]

OK, well, some news.
After not achieving any improvements to the misfiring problem, either with Mikuni VM34s or MK1 Amal Concentrics, and after trying a wide range of jets and needle positions, we concluded that the problem could not be a carb issue. So we fitted a pair of stock 79 XS650 Special headers/exhausts (with balance tube removed and plugged) from my chop build donor bike and voila, misfiring all but gone, with Amals fitted. However, the throttle response felt a little sedate. So I replaced them with the VM34s, re-jetted to:
MJ: 180
PJ: 22.5
NJ: 159-P8
JN: 6F9

Got the motor warmed up and took it for a run up the mile long straight outside the workshop. Result: throttle was crisp, pulled well through whole range of throttle and apart from just the slightest of cough on full throttle it was misfire free. Totally transformed. So I think it goes without saying that the 2-1 exhaust was the problem (most likely the collector). Obviously this is a major success, though I shall run it for a few days under varying loading conditions just to be sure, and check out the plugs to see how they're looking, but after just a couple of hard, fast runs along the mile straight today they'd gone from being quite white to quite a nice biscuit brown on the bridge. Early days. I should be happy you're saying. Well, yes and no. Yes, it's great to have a bike that is responding how I would expect, but, I've lost the 2-1 exhaust that was a big part of the street scrambler look that I wanted on the bike. So I either settle for new headers and two reverse mega's (not perfect) or start looking at further experimentation by way of re-fabricating a new collector, this being the likely cause of the problem. So it's, dig out the exhaust design books, churn the calculations and test a few options. At least I've now got a backstop position if I can't get a good 2-1 set up fabricated.
Just like to say thanks to everyone who input into this post. All very helpful comments. Will let you know how I get on with the 2-1 testing.

 

[GLJ]

The joys of a modified engine. The lows when it doesn't work as planned and the highs when you find the problem.

 

[Mannyroad]

Oh, yes, something I am curious about. You guys out there running a 750 big bore set up, what sort of top end speeds are you getting. I'm not looking to squeeze every mph out of the motor, just curious is all.