81, super hard to kick after new valve and valve adjustment on compression stroke

PunkRockJosh

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Hey guys,

I have been digging through a million posts and I am pretty stuck at this point. Im hoping one of you brilliant MFers can help me out.

I bent an intake valve after swapping new plugs and not checking clearances.. yea.. learned that lesson.

Anyway, I swapped that valve with a new one, lapped it, replaced it. This was my first time doing this so I took photos and videos for reference but I didn't happen to get one with my piston and TDC and show where my cam was in the same video so I lost my reference point to the original set up.

I have tried both .003/.006 and .006/.012 intake/exhaust valve lash. I adjusted each on compression stroke for that cylinder, when both rockers are loose. I have my pistons at TDC and my cam has the lil circle hole at head level at 6:00 and the notch is pointed straight up at 12:00.

Chain tensioner is in place.

Before this I could kick this baby over no problem. I have kicked it in flip flops and slides dozens of times without issue. She was a bit torquey at low RPMs and I don't know if that's just how they are geared or if maybe the torqeuy at the bottom end alludes to it being tuned slightly different than stock.

Its not rephased so both cylinders are at TDC or BDC at the same time.

What am I missing? I can feel a good increase in compression now to the point I don't know if I wanna try kicking it in anything other than my boots.

I referenced the details in https://www.xs650.com/threads/camsh...ed-one-crankshaft-tooth-out.66347/post-838929

One final detail, I have the PMA swap so I don't have any reference marks. I marked TDC with a sharpie for now.

It sticks in two points, each time when the cylinder is on compression. There is a lil overlap so I can feel some suction on the exhaust side and some pressure on the intake side. I feel like this isn't quite right but the post above made it seem like that's correct

Please, XS650 Gods, what am I missing?
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'There is a lil overlap so I can feel some suction on the exhaust side and some pressure on the intake side.'

Reads like you are testing without carbs attached.
If so, you are effectively running wide open throttle and compression pressure will be higher, resulting in heavy kicking.

I would suggest to mount the carbs and try again.
 
That is a great point! And you are 100% right, my carbs have been off while I was testing. Let me slap it back on and see what happens. Its late here and I have no light but ill give it a shot in the morning.
 
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With compression flip flops trying to start can hurt
It needs some force as can be seen in JetM s video
I use center stand and right leg standing on the right side
Jump up and on the down movement kick it.
Usually with 2 or 3 priming " Soft " kicks before
 
Hey guys,

I thought I would give you an update. First, I did have the carb off, which was allowing more air, but after putting it back on, I quickly realized this wasn't the issue.

TLDR; It was valve lash..

I have never done any of this before and I have a PMA with no TDC markings. Add those together and you end up with me, someone making changes without understanding the impact.

I DID have my timing set right the first time.
I DID set my valve lash with the right cylinders on the right stroke.
I DID NOT have my valve lash gaps set properly.

I misinterpreted the conversions and ended up with more lash than I needed. This was causing my valves to close a little early. When set properly, the valves nearly close but will hover just above the seat for a bit which allows pressure to escape. With the extra gap I gave it, they were closing fully and allowing that pressure to build.

Set them to 0.0024 on Intake and 0.006 on Exhaust and bam. Significant difference.

I can kick barefoot again. She starts right up, usually first kick without any choke or priming, just straight kickin it, they way I liked it. Need to doublecheck I've got everything bolted back and that my tolerances are checked and whatever.. Its 1am so I'm gonna pass out.

I will note, this will cause me to lose a little compression. If I give it a bit more lash like .004/.009 then I would get more compression and potentially a better running bike. Trade off is how hard I want to kick. SO, someone will probably correct me but that's what I have learned so far.

Thank you all!
Im not gonna spellcheck this either. Its bed time. Later guys!
 
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