Partial valve shim swap - not good results

[Guest]

Hey Fellas,

Checking valve clearances and got ambitious when I saw that I had a few of the shims I THOUGHT I needed.

Basically, the smallest feeler gauge I have is .038mm, so those that really seemed to grip the gauge at that thickness, I slotted to go down one size.

By swapping shims around I managed to get 4 of the 6 shims to the size I'd calculated.

Afterwards, two of those measured at .10mm, and I'm getting really low idle and no power. I haven't had a chance to troubleshoot yet, but I'm just pinging the forum to see if the incomplete swapping or 2 x .04mm clearances could do that.

Current (mm): (in order from left to right)

Ex 0.08 0.10 0.03 0.04
In 0.03 0.03 0.08 0.10

Thanks for any ideas!

[Griffin]

If you have any clearance at all, the valve will seat all the way and you won't adversely affect performance. The more clearance you have, the louder the "ticking" sound you'll get from the head when running, but the longer you'll go before you have to adjust the clearances again.

I'd rather be at .10mm than .03mm, only because it means I'll maintain clearances longer. I normally set all my clearances from .06-.10mm, just so I know that everything will be kosher for the next 4,000 miles.

[Nessism]

.03 mm is minimum, and I'm not comfortable running the valves that tight because heat expansion may be an issue. .10 on the other hand is no issue.

[Roostabunny]

Odd, so would increasing clearance on only some of the valves possibly make it run worse, or might it have been something else?

True confession - I also swapped out two plugs. I think I still had the PO's plugs in there, and found that I had 2 x B8ES's (which is spec) and 2 x BP7ES's (which I think runs a little hotter - definitely has the electrode a little more exposed than the stock plugs. I had three new B8ES's in my toolbox, so I checked the gaps and swapped those in for the two 7's and the oldest-looking of the 8's.

I know which ones went where - Maybe I should put the plugs back where they were and see if that makes a difference. Could it actually throw off the combustion process?

[Flyboy]

You could try swapping the plugs back again, but I seriously doubt it will make a difference, especially if you are running all stock B8ES as per spec, I would put it down to something totaly unrelated, that by chance just happened to raise its head now, or induced when swing spanners during the shim work.
If you were turning the motor over with a spanner on the bolt at the ignition pick ups, maybe check that the timing plate was not slightly loose, and could have moved a bit, throwing out your ignition timing?
Or if the trigger that is held on by the bolt has not moved.
I know it sounds improbable but worth a check, stranger things have happened.
I would bet it is something small, just go through everything methodically trouble shooting one thing at a time.
PIA, I know.

[Rein]

Well, did you sync afterwards? swapping out the shims changes vacuum a bit, especially if you were on the tight side.

[Roostabunny]

OK, after first round of checks, here's what I found...

First off, I feel dumb, but I realized I had not reconnected the crankcase breather hose to the airbox. I figured that would impact vacuum, and it probably was. It helped smooth things out a bit - but when I got back on the bike there was still no power.

Swapping spark plugs - no effect, left the new 8's in there.

Ignition plate - still tight and about where I remember leaving it.


I noticed that the carbs seemed to be moving - pulsing forward & back slightly mostly on the left side. While idling, I pulled the plug wire on 1, put it back, then pulled the #2 wire, and there was no effect. Then I pulled the wire on #4 and the thing died immediately. A few minutes later I checked the headers and noticed that 1&2 were warm, but not nearly as warm as 3&4.

At that point my battery gave up from all the starting and I'm charging it now. Once it's charged I'll check to see if and where I have spark.

[Rein]

I believe the pulsing is normal. There's a LOT of vacuum in those boots.

[Roostabunny]

OK cool - figured that might be the case on my pulsing carbs, just never paid attention before.

Looks like I have spark on all 4 cylinders.

I did not sync yet - was planning on doing that in a week or two, thinking that changing shims would not have this dramatic an effect.

Any other opinions about whether swapping out 4 of the 6 shims that needed replaced could have this effect, or if my .10mm clearances could be causing the issue? It just bugs me that they're out of spec, but I don't know what the impact would be... too much clearance, valves not open long enough?

[Griffin]

You've received all the advice you need at this point. Follow it, then report your results. I will reiterate.




.10MM CLEARANCE IS NOT AN ISSUE.



SYNCHRONIZE YOUR CARBS AFTER EVERY VALVE ADJUSTMENT.

[850 Combat]

Any possibility that you swapped the plug leads on one and two?

[1948man]

Maybe there's a reason the PO had hotter plugs on 2 cylinders. Were the hotter plugs in cylinders 1 and 2?

[Roostabunny]

You've received all the advice you need at this point. Follow it, then report your results.

Easier said than done, my friend. I won't bore you with my logistical challenges, but I have good reasons for my question.

So, I can sync now, order shims, then finish the valve adjustment and sync again in a week when my remaining shims arrive OR I can put the shims back where they were, ride till the shims arrive, and then do the job right (as opposed to this harebrained way I went about it this time).

Either way, if you're saying that any valve adjustment (complete or not) will impact your sync, you've given me the answer I was looking for.

Seems like 2/3 of the challenge for me is asking the right question.

[Roostabunny]

Given that I forgot to e reattach the breather hose, anything's possible.

Double checked the wires - they're all set.

Any possibility that you swapped the plug leads on one and two?

[Roostabunny]

Maybe there's a reason the PO had hotter plugs on 2 cylinders. Were the hotter plugs in cylinders 1 and 2?

Actually, they were.

But, since swapping them back and forth didn't seem to have an impact, I'm going to table the plugs till I work on the sync.