BIG carburation problems after installing 'Hot' cam

[Kevin Werner]

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.

I am afraid to go that fast... My BBK pulls really hard (really really HARD) 4000-5500rpm. I almost never go beyond that. Also, I have little clocks that are not calibrated what so ever so my speed (and probably revs) are a close indication.

 

[Jan_P]

Again talking about things that can be Wrong
But with a Modified cam . There can be overlap in opening and closing intake and exhaust
( feel free to correct )
And with a 2 into one system When the exhaust stroke on one cylinder
It has a gas connection to the other cylinder.
I would guess ejector function the exiting gas pulls out fluid from the other side or create
pressure changes.( drop )
And can be different between sides since the headers can be of different Length right and left
Getting that right via design of pipes can be difficult or impossible
We have one answer ..2 into 2 was better.
(with balance tube removed and plugged)

 

[Kevin Werner]

Curiously enough, I didn't notice a "pics request" in this thread. How about some pics of the project. Also, if you zero in on jetting it will all go to hell when you fit 1.5" or 1.75" headpipes in exchange for the 1.25' stock pipes. Congrats on the progress. Good luck.

 

[Mannyroad]

Again talking about things that can be Wrong
But with a Modified cam . There can be overlap in opening and closing intake and exhaust
( feel free to correct )
And with a 2 into one system When the exhaust stroke on one cylinder
It has a gas connection to the other cylinder.
I would guess ejector function the exiting gas pulls out fluid from the other side or create
pressure changes.( drop )
And can be different between sides since the headers can be of different Length right and left
Getting that right via design of pipes can be difficult or impossible
We have one answer ..2 into 2 was better.
(with balance tube removed and plugged)

Yes, I understand, no-one said it would be easy, or achievable, but worth exploring maybe

 

[Mannyroad]

Curiously enough, I didn't notice a "pics request" in this thread. How about some pics of the project. Also, if you zero in on jetting it will all go to hell when you fit 1.5" or 1.75" headpipes in exchange for the 1.25' stock pipes. Congrats on the progress. Good luck.

Yes, I realise that any new zorst, be it 2-2 or 2-1 with different bore will require re-jetting.
And, pics of what project? You mean if I try to knock up a variation of the collector?

 

[Kevin Werner]

Yes, I realise that any new zorst, be it 2-2 or 2-1 with different bore will require re-jetting.
And, pics of what project? You mean if I try to knock up a variation of the collector?

We like "all" XS650 based bikes. There are collectors, resto mods, cafes, bobbers, choppers and even LSR bikes on this forum and lots of projects. When you mentioned that you wanted that 2 into 1 to fit your "scrambler" idea I naturally wanted to see where you were going.

 

[Dunc]

Any chance of having a look at a pic of the 2-1 collector? A mate of mine has a 2-1 on an XS powered Wasp sidecar & it sounds great. I've been investigating designs/theory & am going to have a crack at building one myself but will get it running with 2 pipes first.

 

[gggGary]

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.

Plenty fast for an XS650?
I quit doing serious top end runs at least 15 years ago.
I'd be surprised if it was much past 110, 115 MPH on a street chassis.

 

[Kevin Werner]

Plenty fast for an XS650?
I quit doing serious top end runs at least 15 years ago.
I'd be surprised if it was much past 110, 115 MPH on a street chassis.

On my first Ozarks rally I saw 85mph on my speedometer catching up to the group. Then I asked myself "what would Carmella think?". Last time I ever pushed it to catch up.

 

[WideAWAKE]

Gary for the win!!!!!!!

As for top speed - I never went full redline try to blow it up mode on mine but I know I put it in the 90s a couple times. I was also on knobby tires.

A lot may depend on gearing.

 

[Kevin Werner]

An essentially stock 78 will push 100 mph on the speedo. I forget what the tach was saying. It was a long tumble and slide to zero.

 

[jay760]

I don't have top speed recorded, only speed at 1/8 and 1/4, mine is obviously c94

 

[Mannyroad]

We like "all" XS650 based bikes. There are collectors, resto mods, cafes, bobbers, choppers and even LSR bikes on this forum and lots of projects. When you mentioned that you wanted that 2 into 1 to fit your "scrambler" idea I naturally wanted to see where you were going.

Ah, right, gotcha. The scrambler is already built and had a 2-1 that suits it nicely, hence my great disappointment if I have to lose that feature. See pic of bike

 

[Adamc]

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.

No Kenny rode one more like mine....

Pi$$er is mine is behaving just like @Mannyroad bike; mine is standard 650 motor however!

 

[Adamc]

Ah, right, gotcha. The scrambler is already built and had a 2-1 that suits it nicely, hence my great disappointment if I have to lose that feature. See pic of bike

Those 'K&N style pod' filters ain't helping the bike to breathe either. UNI Pods straight foam filters work well.

 

[Signal]

Although the 2 into 1 exhaust may be a problem I doubt it is. Your bike is a 270 rephase same firing as a Ducati Pantah which run well with 2 into 1 exhausts.
At the throttle position you encounter problems the needle and main jet are starting to dominate.
On VM34 and VM36 we generally use 6F9 needles and either uni filters which are a bit restrictive or genuine K&N filters that are like a cylinder. That set up works good enough on just about every ignition, cam, exhaust combo for XS powered rigs to get them running. Fine tuning from there but often the tweaks makes little difference.
Nice bike by the way.

 

[Its been a long time]

Ah, right, gotcha. The scrambler is already built and had a 2-1 that suits it nicely, hence my great disappointment if I have to lose that feature. See pic of bike

Is that the Delkevic 2 into 1 system?

Clearly the system isn't working on a rephased motor. I am struggling to understand why the symptoms are showing as very lean conditions on the spark plugs. I would generally have expected to see sooty black plugs. I would have more expected an unsuitable exhaust system to display reversion symptoms which to my knowledge always causes a overly rich mixture in the reversion rpm region. Very odd sounding, but obviously a problem.

 

[Signal]

Ha shows what I know, reading back it looks like the exhaust was the problem. Good you got your bike running, please keep us updated on your testing.

 

[GLJ]

Ah, right, gotcha. The scrambler is already built and had a 2-1 that suits it nicely, hence my great disappointment if I have to lose that feature. See pic of bike

You could go with a 2into2. Similar look.

 

[Kevin Werner]

I have seen pictures of these fitted to XS650s