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Post by dave1800 on Apr 1, 2012 1:53:07 GMT
Tommy I think we are all as baffled as you are! My latest thoughts are: I have read of an oil separator apparently working as tested by blowing through it, but in fact it was full of a very thick black sludge that would occasionally break off and allow oil into the manifold. Solution - clean out thoroughly with a solvent. As the problem appears worse at high manifold vacuum going down hill you need to ascertain whether the puff of smoke is blue oil or black - excess fuel. If it is blue it points to valve guides / seals and would expect a similar effect after idling for a while and blipping the throttle. If it is black it could be a sticking float valve or dirt in the fuel. Going down hill on trailing throttle can show up ignition system weaknesses. A weak mixture as is seen in this situation is harder to ignite. Another thing to check (again) is if the vacuum advance is sticking, it should be zero under trailing throttle. I know you've checked these many times! Regards David I now use the early type oil separator and PCV valve. I've also tried the other design, without mixing the two. I don't think this makes a difference to the engine. The PCV valve seems to work fine, diaphragm is good and the idle speed rises a bit when I open the oil filler cap and has a lumpier idle, as supposed to. Also, the problem seems more pronounced at high vacuum, as at idle and going downhill in gear. When it's good it will roll happily downhill in gear, keeping steady speed while on bad days it will hesitate and slow down going down the same hill at same speed, meaning I have to keep the throttle a bit open to keep up speed. When it's good there's no puff of smoke after downhill driving in gear, while there is some on a bad day. I am quite sure this smoke is from unburnt fuel rather than oil. Regards, T |
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Post by tommydp on Apr 9, 2012 20:06:41 GMT
Took the crab to my cousin's garage today and he will do further investigation on the car's running issues. I really hope we get to the bottom of it soon!
I've not touched a thing on it since he had a look at it earlier, using a scope and adjusting carb and ignition very accurately. As you may recall it then behaved brilliantly for a week before it started messing up again, for no obvious reason.
The plan now is to accurately check the cam/ valve timing and check the operation of each valve. He suspects the carb, but I don't..
I've actually got hold of a NOS correct, genuine carb so I guess we'll try that in the end. It would be interesting to see if this would make adjustments easier, strange how it always boils down to the carb being very sensitive to adjustments. It's not supposed to be this way! I also find it strange I never achieve correct behaviour from the lifting pin test. I suspect something messing up the combustion of the engine, making it hard to tune correctly. I wonder if the crankcase pressure gets too high for some reason, oil still finds its way up into the PCV valve and I suppose too much pressure here could mess up the combustion.
Well, time will show, hopefully! I'll leave it to my cousin now and see what he figures out. What's really annoying about this problem is how the car can perform well for days, only to misbehave suddenly without any obvious reason. "Luckily" it had one of its bad days when I drove it to the garage today, so perhaps that can make diagnoses easier.
One day....
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Post by tommydp on Apr 27, 2012 21:20:40 GMT
Hi all!
Had the crab back from my cousin today. He says the cam is correctly installed, so I guess I can finally rule that out. He checked the carb settings and the ignition again, and the settings are exactly as last time.
So, he has no further ideas to what's playing up from time to time when it's not performing as supposed to. His suggestion is that a valve is playing up now and then. As I've tried different heads, cam followers, rocker assemblies etc I can only imagine there is a fault at the cam itself.
All in all, I'm not really any wiser. Perhaps I'll end up firing up the engines of the crab and Princesses I'm thinking of buying here, and if one of them runs to my expectations, just move the whole, damn lump over into the long troubled crab. My cousin is absolutely sure there is nothing wrong on the car itself, as electrics or fuel supply etc. The fault has to be engine mechanical, he claims. I'm still not sure but hope he's right.
Tommy
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Post by dave1800 on Apr 29, 2012 2:20:02 GMT
Hi Tommy I can't see how there is an intermittent fault with the camshaft. It is just a lump of metal that cannot morph! The most likely mechanical fault is with the head; have you received the reconditioned head from Peter Burgess yet at least that should rule it out positively. The symptoms, if it's not a head valve issue still seem like a fuelling problem maybe a sticking float valve but I know you've changed everything. At least the weather is more conducive to working on the crab now! Regards David Hi all! Had the crab back from my cousin today. He says the cam is correctly installed, so I guess I can finally rule that out. He checked the carb settings and the ignition again, and the settings are exactly as last time. So, he has no further ideas to what's playing up from time to time when it's not performing as supposed to. His suggestion is that a valve is playing up now and then. As I've tried different heads, cam followers, rocker assemblies etc I can only imagine there is a fault at the cam itself. All in all, I'm not really any wiser. Perhaps I'll end up firing up the engines of the crab and Princesses I'm thinking of buying here, and if one of them runs to my expectations, just move the whole, damn lump over into the long troubled crab. My cousin is absolutely sure there is nothing wrong on the car itself, as electrics or fuel supply etc. The fault has to be engine mechanical, he claims. I'm still not sure but hope he's right. Tommy |
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Post by tommydp on Apr 29, 2012 19:39:00 GMT
Thank you, Dave! I couldn't resist fitting the genuine NOS carb I've just got hold of. It made a difference for sure, although I'm not claiming it's solved!! It looks very promising however!
The carb is the AUD 524, stated for 1971/2 mk2 1800. I believe the only difference to the AUD 280, which goes from 68 to 70, is this one has a pipe for the later type crankcase breather. Needle and jet etc are the same. As I'm now running the original oil separator and PCV valve I blinded this pipe.
I went back to the original, progressive(?) throttle arrangement rather than the Princess type I've had for a while. I also re installed the throttle damper. Unfortunately this does not allow room for the Princess type heat shield so now running withouht this. Not too concerned about that. I will however arrange some kind of float chamber shield later, first of all in order to guide fuel away from the exhaust manifold if there should be a leak from the flat chamber or jet tube.
Anyway, I managed to adjust the carb by ear and the lifting pin during a longer run and it ran very well in deed. Using the original throttle arrangement makes driving far smoother than the more direct acting Princess type, and I suppose it's good for the engine mountings and drive couplings.
At least on this test drive, the car performed very well without any hesitation and signs of the problems I've had with it. Plug readings after the run were spot on. Lovely biscuit brown. So I believe the mixture is about correct.
Fingers crossed, again!
Regards, Tommy
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