Z1 Leak Down Test

rookie wrench here.

The presenting problem is a fouled plug in #1 cylinder (can't find chart right now so I am assuming #1 is the outside left when seated on the bike, #2 is inside left, #3 is inside right and #4 is outside right). Replaced the plug and after riding for 30 miles the plug looks fouled again. I can't tell if it is wet or dry fouled. Not good at reading the plugs. There is no smoke at start up. The bike ran fine for those 30 miles but I know that the longer I go it will begin to misfire as the plug gets more fouled.

I warmed the engine, took spark plugs out and then did a dry compression test. #1: 115 #2: 120 #3: <125 #4: 115

The manual did not say to have the cylinder at Top Dead Center when doing this. Is that necessary?

I did a wet test. Clymer manual said put a table spoon of oil in the cylinder crank it over a couple of times and then get a compression reading. Here's what I got...
#1: 230 #2: 230 #3: 260 #4: 265

I was surprised by those numbers. I thought it would be more in the 160 range. Does that look right?

I'm not sure what this tells me. Can someone please advise. My next thought is to check valve clearances. Would a tight valve cause a plug to foul? If it is adjusted to proper clearances would this likely solve the plug problem? How can I tell if there is a problem with the valve itself?

Any way you can advise me would be appreciated.

Try swapping coils, if the fouled plug moves to another cylinder it the wire or plug boot. You could have a carb issue too.

You should definitely check the valve clearances. Whether or not the low compression is the cause of your plug fouling I can't say. It certainly wouldn't be the cause of wet fouling. An engine that produces high compression requires cooler plugs (to avoid pinging and damage) and an engine that produces low compression needs hotter plugs (to keep them from dry fouling).

So, if after adjusting your valve clearances you still have low compression and want to continue running the engine without doing a ring job (which would be your next step), then try installing one step hotter plugs (lower number) to at least keep them from fouling as easily.

Doing an actual leak down test would help tell you what's up with that engine. What carb service work has been done? It could be a flooding carb.

Has it been sitting? Pics? Do the valve clearances.
Steve

Sorry, I mis-named the thread. I was watching youtube videos on how to do compression tests and watched a couple that showed a leak down test. That was in my mind.

Thanks for replies.

swest wrote: Has it been sitting? Pics? Do the valve clearances.
Steve

It had not been sitting when I first noticed the plug problem. I had been riding it this summer intermittently up until then. It was running really well. Last it ran well was in August. Then after that it started to misfire and i discovered the fouled plug. It has been sitting since then. Started it a couple of times.

What will the valve clearances tell me in relation to the fouled plug? Could adjusting the valves solve this problem? I do know valve adjustment is necessary maintenance and will adjust them while I am fiddling with the plug issue. May start on that tomorrow morning. I want to do things in proper order and solve the problem.

Did the compression tests indicate anything? Is it normal to have the compression be 230 psi after adding a table spoon of oil to the cylinder? My understanding was that if the compression was higher when you add the oil it indicates ring and cylinder wear. But compression in the 115-130 range is good enough to run until you do a top end tear down.

Thanks again!

Didn't you say the seals were replaced? Could be rings but over 200, that seems wrong.
Steve

bugsinmyteeth wrote: ................ Is it normal to have the compression be 230 psi after adding a table spoon of oil to the cylinder? My understanding was that if the compression was higher when you add the oil it.

Adding oil to the cylinders will ALWAYS raise the compression ratio even if the rings and compression are perfect to start with, and a tablespoon is a LOT - nearly 15cc !! This is because oil cannot be compressed, so adding oil to the cylinders reduces the volume dramatically when the piston is at TDC and therefore increases the compression ratio.
Consider the following, and notice how much the compression rises even with a 5cc TEASPOON, so you can imagine the affect of a 15cc tablespoon. Ed

I put zero weight in adding oil to cylinders for compression tests, covers up bad valves and not just rings.

I never had those kinds of results.
Steve

@650ed: Thanks for the diagram and the explanation of why it stands to reason that the compression would increase when adding oil. have you done a dry compression test followed by a wet compression test? If so, how much oil did you use? Clymer manual said 1 table spoon but it seemed like a lot when I was putting it in.

@floivanus: the theory is that if the rings are not tight adding oil will help them seal and so you will get higher compression on the wet test. If you add oil and the wet compression is the same as the dry compression then the valves may be leaking. If rings and valves are good then the compression should increase. But, mine seems so out of whack that I am not concluding anything from the results I got.

@swest, no seals were replaced. The only thing I replaced was one spark plug. I got a new plug for the cylinder that was fouling its plug. After about 30 miles of riding I pulled the new one out and it was black. You asked for a pic. What did you want a picture of?

Gleaning from the collective wisdom thus far...

1. I should check valve clearances first and go from there.

2. I also need to check the coil, wire, and spark plug cap. Come to think of it, I replaced that cap about 15 months ago. It is not the same as the others and perhaps something is corroding or coming apart.

3. Then I need to decide if it needs new rings, depending on compression, etc. after I complete 1 & 2.

Does this seem like the best course of action and in the correct order?