Strange Vacuum Reading

I got a single vacuum gauge today in hopes of syncing my carbs the cheap route one by one. When I hooked it to the first carb, the gauge needle jumped around like crazy! It was jumping from vacuum reading to psi alternately. I assume this means that I have an intake valve hanging open? I know some of my clearances are super tight inside, but I didn't think they were that tight. It has been running pretty well, save for a very erratic idle. Cleaned the pilots, mains and thought that solved the problem. It didn't, which lead me to trying to sync the carbs.
Does this sound right? I wonder if someone could suggest what to do. Simply re-shim the valves or take the head off and check for damage? Had the head off recently to replace head gasket, and it all looked good inside.

If the vacuum reading fluctuates within the normal range-the gauge needle bounces around a lot-uneven compression (broken rings or leaking valves or head gasket in one or two cylinders) is a likely culprit. An uneven air/fuel mix, erratic ignition timing, a misfire, misadjusted valves or a manifold leak near one or two cylinders also are possible causes.

If vacuum drops intermittently at idle, one or more valves may be sticking open or dragging. Higher-than-- normal vacuum at idle is a common clue to overly advanced ignition timing, while low vacuum can indicate retarded timing.

findarticles.com/p/articles/mi_qa3828/is...08/ai_n8978956/pg_2/

Stop-stop-stop for a moment, do not do anything with your valves, yet....

"I got a single vacuum gauge today in hopes of syncing my carbs the cheap route one by one. "

THIS IS IMPOSSIBLE TO DO!!!!
THERE IS NO POSSIBLE WAY YOU CAN ACCURATELY ACCOMPLISH!!!

Even with my brand new CR specials, one carb tweak effects the others... You will be chasing this all over the place trying to dial in the syncing of your carbs...

You think you have erratic idle now, wait till you see what happens after trying to do this with one vacuum gauge... Seriously, all you will do is totally hose your carbs up!

Jeff @ Z1 or JPCycles offers a set of 4 analog gauges for ~ $60-$80.... Do yourself a HUGE favor, buy a set of 4...

With that said, if your valve clearances are not within spec then yes, get this right first... Shims!

But for KZ Gods sake, buy a set of 4....

OMR

BTW, Did I mention buy a set of 4 gauges...

www.z1enterprises.com/detail.aspx?ID=2727

www.jpcycles.com/Search/ProductDetail?sk...e&Ns=&results=10&No=

OMR is correct that it will be difficult if not impossible with one gauge. but you probably do not have a valve problem. the motorcycle specific gauges will have a damper or orific built into them to slow down the effect of the intake pulses. that air is starting and stopping close to 9 times a second at idle.

Better yet, spend a little more ($40) and get the Morgan unit....

You won't get the job done with a singe gauge, but the jumping you describe may be because the gauge has no damper. When you get a set of 4 gauges, make sure they include dampers or you will see 4 needles bouncing all over the place. Ed

Sooo, lemme get this striaight: buy a correct set of gauges? OK, I hear ya. I appreciate the responses. One more quick question: Since some of my valve clearances are incredibly tight, how do I get the appropriately sized shims? 3 sizes down then remeasure, reorder shims?

P.S. I promise to buy a 4 gauge vacuum meter. It was not all waste though, I can use the Harbor Freight Special on my 67 T-Bird

OMBG! Edit is back!!!!!!! Thank you, thank you, THANK YOU

"how do I get the appropriately sized shims? "

I don't have the 650 Manual so maybe yours does...

In the manuals you should find something similar to what's in my KZ900 shop manual...

Basically you measure where your at now, find it in the column and scroll down to what size is recommended to get you within specs....

I appreciate the response, but the problem is that my shims have no clearance to measure! That said, tables and charts will not help me. I wonder if I can take out the shims, install the buckets and cams, then measure the distance subtracting proper cam clearance?

So none of your valves have any clearance, you can not get the smallest feeler blade in there?

When everything is installed and properly timed for clearance checking, can you at least rotate the bucket? If you can rotate it but not get a feeler in there, then consider it to be zero clearance. If the bucket won't rotate then you have to buy the 2.00 mm shim and install it. Check the clearance again, etc.

Proceed to check all the valves, then pull the shims out and use a mike or vernier caliper to measure the thickness (convert to millimeter); then apply the shim size and valve clearance to get proper shim from the chart.

Some shims may be marked with the thickness but trust me not all marks are correct. I have shims that are one size off from the mark so MEASURE them.

You may find that you can swap some shims between valves. If you're lucky a Kaw service tech may swap shims with you and it won't cost anything.

Why don't you pull all your shims and check their sizes. It should be marked on the shim. So if you had a 2.85 that gave no clearance you want a smaller shim like a 2.80 or a 2.75. once you have some clearance you can measure and do the math to find the correct size that you need.

I highly recommend you get a set of metric feeler gauges. That way you're not converting inches into mm all the time.

I have found engines with the correct shims but in the wrong buckets before.