The Kat's not well

[dangerous]

well I have been working on the new Kat over the weekend and something just isn't right... seems to take a while to warm up and has a mag drop at a certain rev, ya cant feel a miss but it does not sound right.

Checked the tappit clearances out and all seems ok, cams are good apart from exhaust lobe 2, which dosent look as shiny as the others.

Now check out the state of the plugs in the attached pic... #2 not looking good aye? why is that? heres the compression results

rounded up to the nearest 5psi
165
145
160
165
actual reading
165
148
162
168

My 1st thought is burnt valve as the exhaust sound is the same as I have heard before when this has been the case.
However it has been pointed out that if a valve was burnt out then the compression reading would be 0psi.

What do you guys reckon? I havent had a chance to strip the carbs yet...

[Colapop]

Not knowing enough but at a guess (going through the options)
Cacked head?
Rings?
Stripped plug thread?
Burnt valve?

Burnt valve is apparently out, so process of elimination....

(Not much help eh?)

[TonyB]

Erm, rounded to the nearest 5 psi should be
165
150
160
170

[Joni]

You have been told how to diagnose if its rings or valves... why dont you start there?

[Bonez]

Doesn't look like the plug has been firing. Try a new/replacement one. Could be duff HD lead connection or cap. Where all 4 headers getting hot? Could explain the strange exhaust note if one cylinder wasn't firing.

This happened with Gerty. Turned out one contact on the coil had erroded away and not supplying ergs to the sparktplug.

[paturoa]

Redo your comp test with a teaspoon of oil into each the plug hole. If the compression goes up then rings if stays roughtly the same then valves. As a rule the highest comp pot will have the least rise and use this as a base. So if pot 4 goes up by say 5psi and pot 2 goes up by 20 then pretty safe to assume rings. If pot 2 also goes up by about 5psi then rings.

A burnt exhaust valve will still have compression in the early stages.

For the the sooty plug, is it wet and oily soot, particularly in right deep in the plug (rings), or a dry fluffy soot (carb)?

Have you run your finger nail on the cam lobe?

Still it could be both at the same time!

A good site for help is http://www.thegsresources.com/ Search the forum posts. Lots of good stuff about carbs etc.

[dangerous]

You have been told how to diagnose if its rings or valves... why dont you start there?

Yes JO... thanks for that... BUT as I said to W I will do the old oil down the plug hole when I get the chance... W knows that I was going to post this thread because it doesn't hurt to to get other opinions, I am NOT doubting his

[boomer]

I'd put the poor bugga down if i were you.. sounds I'll and your home style vetinary skills sound ill'er

[_Gina_]

if a valve was burnt out then the compression reading would be 0psi.

may not be zero, blown head gasket would drop comp readings thou

[FROSTY:Me]

Mate I've had a few of them thar bikes.They still seem to keep on keeping on even with burnt valves. Pull the head off and Ill betcha one of the zorst valves has a bit burnt off of it.
I'd pull all the valves out and give em a lap in

[dangerous]

For the the sooty plug, is it wet and oily soot, particularly in right deep in the plug (rings), or a dry fluffy soot (carb)?

dry n fluffy
cheers P

Doesn't look like the plug has been firing. Try a new/replacement one. Could be duff HD lead connection or cap. Where all 4 headers getting hot? Could explain the strange exhaust note if one cylinder wasn't firing.

This happened with Gerty. Turned out one contact on the coil had erroded away and not supplying ergs to the spaktplug.

Well, I would know if it was not firing on all 4, but theres something in the exhaust not that isn't right.... it is, just not producing all the power.

I'd put the poor bugga down if i were you.. sounds I'll and your home style vetinary skills sound ill'er

have you been drinking more than me???

ill?
veterinary?
more ill?
sorry I find you no help at all

[paturoa]

may not be zero, blown head gasket would drop comp readings thou

never seen a GS head gasket blown, spose it must happen some times??

[boomer]

have you been drinking more than me???

ill?
veterinary?
sorry I find you no help at all

I now know why your nick name here is Dangerous.

and don't apologise buddy..it's a sign of weakness

[T.W.R]

From a wee magic book

Compression range is : 9 - 12 kg/cm2 which is 128 - 170psi

and heres a plug diagnosis chart for you so you know what your looking at

[Bonez]

Well, I would know if it was not firing on all 4,

Prey tell how? The slow to warm up description you made sounded very similar to what happened with Gerty. Once warmed up she'd fire on all 4 but not on every firing stroke. Replacing the coil sorted it out.

That chart indicates it could be weak voltage also.