Compression, cam timing, and poor starting/running

1981XS

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I have an '81 XS650, bought new, with about 24k mi. on the engine. I was a Honda auto mechanic from 1981-'87, so not a novice, but I haven't personally seen this before. About 9 years ago I began a cafe racer conversion on this bike. Did a complete engine rebuild (no bore out, no crank changes, just new guides, lapped valves, rings, bearings, seals, gaskets, w/ported and polished heads). I removed of lots of weight incl. starter and battery, added a 2-into-1 header, new pipe and muffler, and 34mm Mikuni flat slides. I've got the fuel system covered and ruled out. I replaced ignition & charging with an HHB system, and triple-checked everything. If I'm able to start the engine (rarely and only cold), It's breaking up above 2.5kRPM, with no power, and minor backfiring. I thought it was ignition, and still think it may be a bad ignition module, but I can't test that. I want to avoid ordering ignition parts as costs will add up and funds are scarce.

The other primary suspect in my mind is that the cam timing isn't correct. I did hundreds of Honda head gaskets, timing belts, and top end overhauls, so I know how to index a cam. But mistakes can happen. Perhaps a brain fart? '81's don't have points or any external index marks on the cam (that I've seen), so I'll have to pull the engine to see the cam index mark in order to check it perfectly. I DON"T want to have to pull the engine. I could use a degree tool to figure out if the valves are opening at the correct times, but IMO I could still be off by a tooth and not know it. To test the current compression I used a drill, turning the crankshaft at a couple of hundred RPM, with the throttle wide open, and the engine stone cold (since it won't start). I got 90PSI and 84PSI compression readings, which didn't seem great but high enough that incorrect cam indexing may be a longshot. My question is would I be able to get compression readings that high if the cam is off one tooth?

Appreciate any feedback. Thanks.
 
If your camshaft timing is one tooth out it's pretty obvious if you do a simple check. I validated the timing was correct on my bike a couple of weeks ago. You need a DTI, alternator cover open and one inlet valve cover removed. There's a thread about it, but this is the most relevant post. Doing this check is detailed in the Yamaha shop manual. One tooth wrong is 10 degrees of timing error. I found mine to be good. - https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-838935
 
If your camshaft timing is one tooth out it's pretty obvious if you do a simple check. I validated the timing was correct on my bike a couple of weeks ago. You need a DTI, alternator cover open and one inlet valve cover removed. There's a thread about it, but this is the most relevant post. Doing this check is detailed in the Yamaha shop manual. One tooth wrong is 10 degrees of timing error. I found mine to be good. - https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-838935
Thanks for this. I'll check the link and see what I come up. Not sure if I'll be happier to find out it's right (now what?) or wrong (got my work cut out for me...).
 
Was running good before the rebuild and cafe conversion?
Did you put on pods or still have stock airbox?
Timing is advancing when you throttle up with using a timing light?
 
Was running good before the rebuild and cafe conversion?
Did you put on pods or still have stock airbox?
Timing is advancing when you throttle up with using a timing light?
It was running fine before the rebuild, but not at full potential. Using K&N's on the Mikunis. I had to use a drill to crank the engine to check timing (without spark plugs in), and it appears that the CDI advance unit may be the culprit. Trying to eliminate the easy, mechanical issues, like cam timing, from the equation.
 
If your camshaft timing is one tooth out it's pretty obvious if you do a simple check. I validated the timing was correct on my bike a couple of weeks ago. You need a DTI, alternator cover open and one inlet valve cover removed. There's a thread about it, but this is the most relevant post. Doing this check is detailed in the Yamaha shop manual. One tooth wrong is 10 degrees of timing error. I found mine to be good. - https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-838935
Thanks for this - it worked like a charm once I changed the default rotation direction to counterclockwise. I found my cam timing to be good as well, which saves me the trouble of pulling the engine.

At this point I have compression and fuel covered. Spark is next. I have spark, but it seems weak and there's no guarantee that it's hitting at the right time. I've exhausted everything I can diagnose, and have checked spec on all pieces. The CDI controller is the last piece, and the only way to check that is to replace it. My choices are to buy more product from HHB (they haven't answered any of my e-mail questions - hope that's because they're customer service is atrocious, and not because someone is seriously ill), or scrap the HHB and go with a Vape system. The money's huge for the Vape, but after 9 years of taking my time with this project it's time to get it on the road before I'm too old to ride, and I want something that is fairly bulletproof, which the Vape seems to be. I have a question in to a Vape reseller, and we'll see how their customer service response is.
 
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