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For those of you that don't know, I originally had a 78 motor in my XJ when I purchased it. Shortly after that, I bent the valves checking shim clearances that included removal of the cams to do this. The only other heads I have had have belonged to other XJ motors with the bigger valves than the 78-79 heads. I have been running the 78 cams since then in all the heads. I have run many motors through this bike with many different motor/head combinations, yet I always used the 78 cams. I have always heard of better performance from them so I have always stuck with them.
Recently, I rebuilt a motor with the 1179 big bore kit, had the head done (3 angle grind on the valves, quite a bit of porting done to the intake and roughed back up just a bit to help with atomizing of the fuel, a wider valve seat to sit more to the edges of the valves instead of in the center of the face to allow more air and changed the angle a bit of air flow so it didn't have to turn 90 degrees so sharply to enter the intake... nothing done to the exhaust) Anyway... after re-assembly, I couldn't get the bike to run very well. I went to John and Kat's after that and we tried to synch the carbs, but there wasn't enough vacuum being drawn on the carbs to do it well... only 2-3 MBs when the same gauge got 14-15 on his bike. It also had little puffs of air geting blown back into the carbs. I had set the shim clearances when I installed the motor, but Prometheus told me later that within the first 500 miles of a new motor, these would change. I had @ 5 thousand already.
This weekend, we tore into the top end of my bike a bit at John and Kat's Meeting of the Minds in Texas. We checked compression and it was only about 105 PSI... not very impressive for a big bore. We could also see that the cam timing was retarded a bit... but not so much that it was off a tooth. The valve clearances were off a bit also. We removed the 2H7 cams ('78) and installed the 3H5 cams ('80-'82) that the motor originally had. We measured clearances of the shims, removed the cams again and fixed those, then re-installed the cams again. We noticed an immediate improvement in compression to a little over 150 psi (Which I was delighted to see after so many tries to use a shim tool and cams in and out) and the bike has idled for the first time in a LONG time... probably 3 motors back or so. Also, the cams' timing marks matched exactly when they didn't with the early cams?? The motor has always been a little bit "Lopey" and would only idle a short time before slowly dying if left alone. Not ant more.
So after properly synching the carbs again, the unofficial results of the 78 and 82 cams difference by way of seat of the pants dyno.... The motor now has more low end torque than it's EVER had. I haven't run it much to top end, but it hasn't changed that enough to ever go back to the early cams. I'm talking MAYBE a mile or two an hour if that in the top end and I don't ride there very often (And shouldn't at all) I have the 750 final drive and you would never guess it. You can let the clutch out at almost idle and take off normally.
Before, I would be going 15 or 20 mph, goose it a bit and pop the clutch to get a good wheelie going. I tried the same thing afterwards riding with Kat, and it just about went over backwards on me. I could actually let off to get the wheel down a bit and get back on the power to keep the wheelie going now.
So with 99% of my riding done below 8k RPM, this is a no brainer for me to keep the original cams in with these bigger valves. Even with me being probably 100 pounds heavier.... it will sure beat some skinny guy on a couple different XS1100s that knows how to ride... (Sorta sorry Hobbyman) lol. He may or may not still beat me in the top end.... but he'll have to stop sometime!
I can't honestly sit here and say for a fact that the 3H5 cams are better than the 2H7's on these heads. There were too many other variables including carbs, shim clearance, cam timing, and the fact that Prometheus was there throwing monkey wrenches into everybody's stuff and smiling smuggly to himself. I never had one set setup right, then set the other set up right to know for sure. But knowing this bike pretty well over all these different motors, I can honestly say that in the 1k-8k rpm range, it has never run stronger.
Prometheus, thank you for all your help... even when I didn't like the answers. The bike is running better than it ever has. Sorry about the book everyone.
Tod
Recently, I rebuilt a motor with the 1179 big bore kit, had the head done (3 angle grind on the valves, quite a bit of porting done to the intake and roughed back up just a bit to help with atomizing of the fuel, a wider valve seat to sit more to the edges of the valves instead of in the center of the face to allow more air and changed the angle a bit of air flow so it didn't have to turn 90 degrees so sharply to enter the intake... nothing done to the exhaust) Anyway... after re-assembly, I couldn't get the bike to run very well. I went to John and Kat's after that and we tried to synch the carbs, but there wasn't enough vacuum being drawn on the carbs to do it well... only 2-3 MBs when the same gauge got 14-15 on his bike. It also had little puffs of air geting blown back into the carbs. I had set the shim clearances when I installed the motor, but Prometheus told me later that within the first 500 miles of a new motor, these would change. I had @ 5 thousand already.
This weekend, we tore into the top end of my bike a bit at John and Kat's Meeting of the Minds in Texas. We checked compression and it was only about 105 PSI... not very impressive for a big bore. We could also see that the cam timing was retarded a bit... but not so much that it was off a tooth. The valve clearances were off a bit also. We removed the 2H7 cams ('78) and installed the 3H5 cams ('80-'82) that the motor originally had. We measured clearances of the shims, removed the cams again and fixed those, then re-installed the cams again. We noticed an immediate improvement in compression to a little over 150 psi (Which I was delighted to see after so many tries to use a shim tool and cams in and out) and the bike has idled for the first time in a LONG time... probably 3 motors back or so. Also, the cams' timing marks matched exactly when they didn't with the early cams?? The motor has always been a little bit "Lopey" and would only idle a short time before slowly dying if left alone. Not ant more.
So after properly synching the carbs again, the unofficial results of the 78 and 82 cams difference by way of seat of the pants dyno.... The motor now has more low end torque than it's EVER had. I haven't run it much to top end, but it hasn't changed that enough to ever go back to the early cams. I'm talking MAYBE a mile or two an hour if that in the top end and I don't ride there very often (And shouldn't at all) I have the 750 final drive and you would never guess it. You can let the clutch out at almost idle and take off normally.
Before, I would be going 15 or 20 mph, goose it a bit and pop the clutch to get a good wheelie going. I tried the same thing afterwards riding with Kat, and it just about went over backwards on me. I could actually let off to get the wheel down a bit and get back on the power to keep the wheelie going now.
So with 99% of my riding done below 8k RPM, this is a no brainer for me to keep the original cams in with these bigger valves. Even with me being probably 100 pounds heavier.... it will sure beat some skinny guy on a couple different XS1100s that knows how to ride... (Sorta sorry Hobbyman) lol. He may or may not still beat me in the top end.... but he'll have to stop sometime!
I can't honestly sit here and say for a fact that the 3H5 cams are better than the 2H7's on these heads. There were too many other variables including carbs, shim clearance, cam timing, and the fact that Prometheus was there throwing monkey wrenches into everybody's stuff and smiling smuggly to himself. I never had one set setup right, then set the other set up right to know for sure. But knowing this bike pretty well over all these different motors, I can honestly say that in the 1k-8k rpm range, it has never run stronger.
Prometheus, thank you for all your help... even when I didn't like the answers. The bike is running better than it ever has. Sorry about the book everyone.
Tod
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