Post Number: 27
|Posted on Sunday, 17 August, 2008 - 20:49: |
I have an irregular idle on my Cloud I, and I recently did a compression test to see if that would throw any light on the problem. I unfortunately didn't have the throttles fully open (re-reading the instructions before doing the test would have been better than after!! So the readings are probably all lower than they should be because of this). Anyhow, the results were (from front cylinder backwards):
1 90 psi
2 112 psi
3 108 psi
4 112 psi
5 108 psi
6 106 psi
I then squirted some oil in the 1st cylinder, and the compression increased to 99 psi on this cylinder.
My queries are- do these reading sound okay, and is the lower compression on the first cylinder different enough from the others to indicate a problem? From what I've found out so far, it seems a variation of more than 10% from the average would indicate a concern- this difference is 18%, so not good??
I guess the next stage would be to do a leak-back test, to see if the problem is the rings, or the inlet or exhaust valves?
Any thoughts would be appreciated.
Post Number: 84
|Posted on Wednesday, 20 August, 2008 - 20:16: |
As nobody else has come back to you, I will have a go at long distance diagnosis.
If the problem is a miss, then, assuming you have been right through your ignition system, I would rule out rings, and look towards valves. Have you checked your valve clearances?
Post Number: 28
|Posted on Wednesday, 20 August, 2008 - 21:05: |
Thanks for your reply.
I have pretty much overhauled the ignition, and also just about done the carbs. One thing left to do on the carbs is replacing the jets and needles (waiting for them to arrive from the UK). I used a Gunson Colourtune for adjusting the mixture, but could only get a yellow (rich) combustion. Leaning the mixture out resulted in missing and I couldn't get a blue (correct) combustion, so I think the jets/needles are worn. Hopefully the new ones will help with the idle, I guess it's just a process of elimination.
I thought I'd check the compression in the meantime, but wasn't really sure what is "normal".
I've adjusted the inlet valves, but haven't tackled the exhaust valves yet. Sounds like this might be the next thing on the list? By the look of it in the service manual, it looks a bit trickier than the inlet valves, so I think I've probably been avoiding it!! Do you think a leak-back test would be the way to go to check which valves it is first?
Thanks for you advice.
Post Number: 9
|Posted on Wednesday, 20 August, 2008 - 21:54: |
SWA82 was an English delivery- does it have the UK aircleaner still? That means it should have the TA needles. 6.6 compression (if the head has not been shaved) wouldn't give you much over 110 anyway if my calcs are right. I am still inclined to number one cylinder rings.
Keep us posted
Post Number: 29
|Posted on Thursday, 21 August, 2008 - 06:23: |
Yes, SWA82 came to New Zealand in the early 70's from England. It still has the UK air filter, so I've ordered the TA needles.
I'll see if I can hire a compressor to do a leakdown test this weekend- will let you know how it goes...