Saving a 1980 750 twin.

nice work sir.


leon

I remeasured the cylinder head volume. The new titanium valves have no dish and intakes are bigger so the volume is smaller than previous. cyl 1 is 46.4cc and cyl 2 is 47cc
maintaining my desired squish (0.035") this should leave me at about 10.25 -10.35/1 static compression.

I downloaded the C5 ignition software and started playing around with it. its very simple to use. I decided to compare it to the stock curves and WOW what a difference! talk about turning the wick up

'76-'80 Stock ignition curve with points. idle = 5 degrees full advance 30 degrees @ 3750 RPM
'81+ stock electronic ignition. idle= 10 degrees full advance = 35 degrees @ 3750 RPM
C5 ignition curve. idle = 23 degrees full advance = 38 degrees @ 3000 RPM

What are you up to? Some searching turned up powerarc.com and c5ignitions.com.

I see an optical trigger with programmable timing maps. The only thing that jumps out at me that's unusual is the multi-spark operation.

So two questions:

One, why do the factory timing curves have an upper and lower bound. Is that the acceptable error in timing? Some sort of hysteresis?

Second, how are you determining the new timing curves and limits for the programmable system? Is the Power Arc software suggesting those values based on engine parameters?

Oh, one more. Does that Power Arc/C5 gizmo have the ability to read a throttle position sensor, so you can do a full load/rpm 3D timing map? Something similar to the K-TRIC system Kawasaki used?

So two questions:

One, why do the factory timing curves have an upper and lower bound. Is that the acceptable error in timing? Some sort of hysteresis?
I believe that is the case. acceptable error in timing., I personally found that TDC was off almost 2 degrees from the marks on the advancer plate.

Second, how are you determining the new timing curves and limits for the programmable system? Is the Power Arc software suggesting those values based on engine parameters?
This ignition curve came programmed from C5. they sold it specifically for the KZ twins. I ran this ignition, with this curve, on both the stock engine and my mild hop up, it worked well. With this new engine package I want to be able to modify the timing to get the most out of it without making it go boom.

Oh, one more. Does that Power Arc/C5 gizmo have the ability to read a throttle position sensor, so you can do a full load/rpm 3D timing map? Something similar to the K-TRIC system Kawasaki used?

I don't think it gets quite that complicated, but you can add in any sensor. It can only store 4 different maps. On the C5 site he uses a a MAP sensor to get vacuum readings to switch to 4 different curves depending on load. I haven't planned on messing with this but i probably will at some point.

www.c5ignitions.com/classroom--timing-maps.html

I talked with a guy in Canada who has been racing and developing this platform. He has given me tons of good info including this tip to run the clutch from the belt drive engine. This clutch is different because it has an aluminum clutch basket, and the clutch is actuated from the right side of the bike. This not only allows a much larger countershaft sprocket by removing the clutch push rod, but also removes over a pound from the flywheel!

This project is pivoting. I have decided to build a track/race version with the big bore engine. I've started a build thread HERE if you are interested.

As for this bike I will be building a nice, fairly stock engine.

I had 3 spare engines lined up and I chose the best one from the bunch. Other than being stored with an exhaust valve open this may be the cleanest engine internally I have every seen. It must have had low miles because everything is barely worn, evident by the cross-hatching in the bores, and the small end of the connecting rods looks mint. Because of that I'm just going to clean it up and rebuild the top end.

I started by tearing the cylinder head down, polished all the fins back how I like them, sand blasted, re-polished the fins, and painted with Gun Kote Satin Black. After the paint is dry I wipe the fins clean with acetone before baking the paint. I then do one last polish with 320 so the fins are super bright. I find this process gives me really well defined fins and reduces the risk of damaging the paint during fin polishing significantly

I also took the time to polish the intake and exhaust runners and to blend in the valve seats. This is a common issue on these heads; the ports and valve seats are not aligned very well and leave a sharp internal edge. I'm no porting expert but I know that this is bad for flow. Other than that I mostly just removed the large casting flash present in the runners and tried not to remove much material as these ports are already too bg for stock displacement. I also took te time to port match the carb boots, and polish the combustion chambers.

Now its time for a thorough cleaning in the parts washer before going out for a 3 angle valve job and getting the head decked. I will be using NOS valve springs (the big ones, cant find the small ones) along with high quality teflon valve seals. 

BEFORE/ AFTER


 

Gonna be sharp!  

Progress.... One of the shocks was leaking so I had them rebuilt, I guess this version of Works shocks used some type of proprietary tool to fill nitrogen so they had to be machined to accept a nitrogen valve. Before tear down I had this weird pulsing/chatter at low speed with the new EBC disk despite having less than .005" of run out. I had the disk ground by Tru-disk to eliminate the surface as a potential source of the problem since that was all that changed from the stock disk, if this doesn't work I will look at some different pads. Also installed the lightweight custom front axle while i was at it. Hope to get the top end back from machining next week.

 

Parts back from machinist. Assembly continues.

I went with these 1mm over pistons from Scheuerlein in Germany over NOS pistons/rings because they use a 3 piece oil ring design where stock is a single. The pistons are coated which allows for a very tight piston/cylinder fit. The quality is high, they are faithful copies of the OEM pistons.

I usually bench shim the valves if the head is off so i don't have to mess with it on the bike. it looks like i have alot of shims but they are all in the same sizes from bikes i have parted out, luckily I had exactly what i needed from the last head rebuild.

Anytime you have the head or cylinder block decked you need to check and make there the oil passage is de-burred and has a chamfer, otherwise you can cut the o-rings as you press in the oil restrictors.

 

Annnnndddd its a runner. seems to be pretty close on jetting, runs great. put about 10 miles on it. The new rotor surface totally removed the chatter from braking. The only thing that seems to need to be addressed is it needs a new starter clutch, bad. The stock engine is reminding me why i hot rodded it. I leaves me wanting more power. Its a fun rider though.