Clive doesn't want to do them anymore as they take too long & he's too busy. I've sent mine to Wes @ Waggott Cams in NSW.
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750 big bore carbs
- Thread starter triumph68
- Start date
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- carburetors
Well, I emailed Clivecams and got a response. This is it:
"Because the profile was owned by Daryl, we never did a full check on it and therefore don’t have the full specs. The only spec that I do have is the lift, which is .320” on the inlet and .314” on the exhaust."
I shall still be doing my own map of the cam shortly, so will be able to confirm the above and get the rest of the information needed. Will update soon as I can.
"Because the profile was owned by Daryl, we never did a full check on it and therefore don’t have the full specs. The only spec that I do have is the lift, which is .320” on the inlet and .314” on the exhaust."
I shall still be doing my own map of the cam shortly, so will be able to confirm the above and get the rest of the information needed. Will update soon as I can.
Hi guys,
Hope you've all had a great Christmas and I wish you a happy new year from over the pond.
It's taken a while for my mate to find time to look at my XS in terms of mapping the cam, comp test, leakdown test, valve timing. Anyway, we did it all ove r the Christmas break and the results are:
Compression test: LH cyl: 145psi RH cyl: 145 psi (actual figures read from guage)
Leakdown Test: LH cyl: 6% RH cyl: 6% (actual figures read from guage)
Valve timing was checked and found to be correct, as in the hole in the cam on the RH side was vertical when piston at TDC.
Valve Lift
LH Cyl: Inlet lift: .407" (Lash: 0.006") Ex. Lift: .402" (Lash: 0.012") - see attached file of map.
According to Bob Bertaut's document, detailing 'actual cam lift' for a 1980 stock XS650 motor, the 256 motor has a cam lift of 0.300" and the 447 a lift of 0.314". My motor, being a 1980 XS650 SG, is, I presume a 447 motor, so the stock cam would have had a 0.314" lift OEM. So, allowing for rocker arm ratio (1.27) and my 0.006" inlet valve lash, a stock cam with my lash should produce 0.393" of valve lift i.e (0.314"x1.27)-0.006". As my cam's actual lift is 0.407" this suggests the base circle on my cam has been ground by approx. 0.014", which I guess is a mild grind, as Daryl Hutcheon stated it had. So, now I have a better idea of my cam. Overlap and duration can be determined from my cam map, but I haven't got my head around the implications of these issues and how they might affect my motor's performance.
Since my earlier thread comments I went back to the original carb set up (VM34's), when I acquired the bike, being:
PJ: 32.5
MJ: 190
NJ: 159 P6
JN: 6F9 (@ p3)
Slide: 2.5
On the above settings, when I first got the bike it felt gutless and wouldn't make 75mph, albeit on an 18/38 final drive setup which is a bit undergeared, but had a nice tickover with airscrews at around 1 1/4 turns out. After trying alternative MJ's and PJ's and getting nowhere, I went back to the above settings but now it won't seem to settle down to a nice tickover: annoying. I've currently got an 18/33T final drive set up which I believe approximates to the 650 stock ratio and I still can't get it to roll on past 4500rpm in top gear on a ride, so still runs out of steam at around 75mph.
Given the above, unless I'm misreading everything, and tbh this is all a strange world to me yet, then my poor performance issues may well be down to issues regarding ignition timing, final drive gearing or the aftermarket exhaust. Ignition timing when checked with a strobe a couple of months ago seemed ballpark right (about 3-5 degrees advanced).
So, armed with all this information I'm still not sure where to look to improve things. Everyone, even MikesXS, suggest fitting the big bore kit offers significant performance improvement, but I'm not seeing it, although I didn't start with a stock motor, so have no baseline for comparison. Your thoughts would be much appreciated guys.
Hope you've all had a great Christmas and I wish you a happy new year from over the pond.
It's taken a while for my mate to find time to look at my XS in terms of mapping the cam, comp test, leakdown test, valve timing. Anyway, we did it all ove r the Christmas break and the results are:
Compression test: LH cyl: 145psi RH cyl: 145 psi (actual figures read from guage)
Leakdown Test: LH cyl: 6% RH cyl: 6% (actual figures read from guage)
Valve timing was checked and found to be correct, as in the hole in the cam on the RH side was vertical when piston at TDC.
Valve Lift
LH Cyl: Inlet lift: .407" (Lash: 0.006") Ex. Lift: .402" (Lash: 0.012") - see attached file of map.
According to Bob Bertaut's document, detailing 'actual cam lift' for a 1980 stock XS650 motor, the 256 motor has a cam lift of 0.300" and the 447 a lift of 0.314". My motor, being a 1980 XS650 SG, is, I presume a 447 motor, so the stock cam would have had a 0.314" lift OEM. So, allowing for rocker arm ratio (1.27) and my 0.006" inlet valve lash, a stock cam with my lash should produce 0.393" of valve lift i.e (0.314"x1.27)-0.006". As my cam's actual lift is 0.407" this suggests the base circle on my cam has been ground by approx. 0.014", which I guess is a mild grind, as Daryl Hutcheon stated it had. So, now I have a better idea of my cam. Overlap and duration can be determined from my cam map, but I haven't got my head around the implications of these issues and how they might affect my motor's performance.
Since my earlier thread comments I went back to the original carb set up (VM34's), when I acquired the bike, being:
PJ: 32.5
MJ: 190
NJ: 159 P6
JN: 6F9 (@ p3)
Slide: 2.5
On the above settings, when I first got the bike it felt gutless and wouldn't make 75mph, albeit on an 18/38 final drive setup which is a bit undergeared, but had a nice tickover with airscrews at around 1 1/4 turns out. After trying alternative MJ's and PJ's and getting nowhere, I went back to the above settings but now it won't seem to settle down to a nice tickover: annoying. I've currently got an 18/33T final drive set up which I believe approximates to the 650 stock ratio and I still can't get it to roll on past 4500rpm in top gear on a ride, so still runs out of steam at around 75mph.
Given the above, unless I'm misreading everything, and tbh this is all a strange world to me yet, then my poor performance issues may well be down to issues regarding ignition timing, final drive gearing or the aftermarket exhaust. Ignition timing when checked with a strobe a couple of months ago seemed ballpark right (about 3-5 degrees advanced).
So, armed with all this information I'm still not sure where to look to improve things. Everyone, even MikesXS, suggest fitting the big bore kit offers significant performance improvement, but I'm not seeing it, although I didn't start with a stock motor, so have no baseline for comparison. Your thoughts would be much appreciated guys.
Attachments
Exhaust reversion? I recall a forum member having a similar problem.... an engine built to go like hell and wouldn't go past 75mph. Maybe @arcticXS remembers who?
It's pretty easy to check for. Pull the air filters off and rev the bike. If the inlets of the carbs form white clouds (fuel vapor) at around 4-5k rpm, it's a reversion problem.
Found it. Forum member @Bjorn
https://www.xs650.com/threads/not-reaching-top-speed.54109/
I didn't reread the thread, but if memory serves it was restrictors in the header pipes that fixed it.
https://www.xs650.com/threads/not-reaching-top-speed.54109/
I didn't reread the thread, but if memory serves it was restrictors in the header pipes that fixed it.
Not to discount the possibility of reversion, but I'm having difficulty getting my head around the valve timing represented by the attached chart. I'm expecting an intake opening 30ish BTDC, closing 60ish ABDC (depends on OEM lash spec .012" or Megacycle lift .040") - not what I'm interpreting there.
Yeah... sounds a bit too much duration. I may be out to lunch, but aren't both valves set to .012" for degree-ing?Not to discount the possibility of reversion, but I'm having difficulty getting my head around the valve timing represented by the attached chart. I'm expecting an intake opening 30ish BTDC, closing 60ish ABDC (depends on OEM lash spec .012" or Megacycle lift .040") - not what I'm interpreting there.
It depends on the supplier; Yamaha does spec lash @ .012", intake and exhaust for the purposes of cam timing (guessing consistency as that was the original spec for clearance too). Others often spec a certain lift off the valve seat (Megacycle .040). Stock cam: intake begins to open @ 38* BTDC........
Megacycle specs:
The opening and closing points were somewhat of a surprise to my mate, who's very much into the techy talk surrounding overlap, duration, exhaust gas pulse waves etc., so we double checked the set up and did the map twice. Got same results both times, I plan sending this info over to Smedspeed here in the UK for their take on it.
Will have a look at the exhaust reversion thread Jim and check it out on the bike if it's a simple matter. Out of interest, what is the stock final drive gearing for a 650 SG? I understood OEM was 17\33T.
Will have a look at the exhaust reversion thread Jim and check it out on the bike if it's a simple matter. Out of interest, what is the stock final drive gearing for a 650 SG? I understood OEM was 17\33T.
Bjorn
XS650 Addict
Stock is generally considered to be 17/34. A 750cc kitted, cam'ed, tuned XS should easily pull 18/33. I run a 277 stock bore, lightly modified and it easily pulls 17/32
Get onto mikuni Oz. There in Brisbane l think, great advice and price for what you need.
From a Megacycle timing card for an XS 650 cam. "Timing at 40'' lift at valve. timing checked with zero clearance.
That's the equivalent of drawing a line through the 40 thou mark on my graph then reading down to bottom scale for duration etc.
I may be "all wet" -so don't take this as fact - I've approximated stock cam timing (not actual curve) opening/closing in purple & orange. If then, your blue line is your intake lobe, it indicates you're approximately 180 degrees early on the cam timing (also assuming left Cyl.)
It'll be interesting to see what Spedspeed says. Did Clive have lift or opening specs?
It'll be interesting to see what Spedspeed says. Did Clive have lift or opening specs?
17/34 US spec. Europe 17/33. Please note also the 18 tooth countershaft sprocket requires some attention to the shift shaft.
Just a note. Old Brown with 750 kit 38 cv 's and stock cam would pull redline with 18/32. "Front straight TWS lap after lap"
What rear wheel/ tyre combo on that bike? Any port work? And what exhaust? And which track is TWS?
Lots of questions, sorry.....
TWS. Sorry meant to spell it out. Texas World Speedway. https://en.wikipedia.org/wiki/Texas_World_Speedway
4.25 18 Dunlop tt100. Dead stock TXA engine , BS38 with 750 kit and two into exhaust.
The red curve is the inlet valve, blue exhaust. And Clive only gave me the cam lifts, being 0.320 inlet, 0.314 exhaust. With the 6 & 12 thou respective lash, the inlet & exhaust valve lift should be 0.400 & 0.386, but I'm getting 0.401 & 0.407. Note: the zero lift points on my curves are the locations where lash has just been removed and the valve is at the start of opening.
I have an 18t fitted and that seems fine for the shift shaft but the chain links are awfully close to the clutch actuator rod, but not touching and no evidence of touching under normal running conditions. May go 1 tooth less to see if that helps push the motor over the torque hump to get me past 4500rpm
