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Post by tommydp on Nov 20, 2011 11:53:26 GMT
Thanks, Dave! I'll look into the fuel pressure first, I believe this is the main issue now. I don't really understand though why the high pressure would give rough idle and variable mixture, as long as the float needle manages to keep closed and float level remains correct. Perhaps I'm missing something again:-) The only thing I can think of is that the higher pressure plays up as the float needle opens to let more fuel in.
The coil thing is really strange, but I'm not sure if this matters, after all the car starts right away in all conditions and behaves well above idle, the spark is healthy and there's no backfiring etc. I have received an electronic kit for the distributor, but would really like to make it run well on points before introducing further variables:-)
Tommy
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Post by dave1800 on Nov 20, 2011 12:30:09 GMT
If the fuel pressure is too high then it forces fuel through the float needle valve as it cannot close properly, raising the level (and hence the pressure) in the float chamber. The result is too much fuel goes past the carb piston needle leading to a rich mixture. The pump should go into "idle mode" once the corrrect pressure is reached and the needle valve is closed, similar to the SU electrical pump. If the pump diaphragm and / or its valve is sticking then this could prevent the pump going into idle mode and would lead to inconsistencies in the fuel delivery especially noticeable at tickover as you are seeing. Have a look at the w/s manual; you could always do a quick swop with your Marina fuel pump to see whether you have a defective 1800 pump you may be able to take apart and sort out, or a copy that's out of spec and will need a remedy along the lines of my earlier suggestion. We can ask Chris to check whether the ignition unit you have bought varies the dwell with RPM or not. If it does it should make the coil run much cooler, but I take your point about trying to get it to run properly first! However the electronic ignition may overcome plug fouling from the oil leaking past the valve guides, so it may provide a solution if not a cure. regards David I don't really understand though why the high pressure would give rough idle and variable mixture, as long as the float needle manages to keep closed and float level remains correct. The coil thing is really strange, but I'm not sure if this matters, after all the car starts right away in all conditions and behaves well above idle, the spark is healthy and there's no backfiring etc. I have received an electronic kit for the distributor, but would really like to make it run well on points before introducing further variables:-) Tommy |
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Post by tommydp on Nov 20, 2011 15:31:33 GMT
Tried out another pump and managed to get a pressure below 4 PSI, but the symptoms remain and it's impossible to get a stable mixture. I'm not exactly surprised...
I have no idea what to try now, really:-( Not sure about changing the cylinder head either, as I had the exact same problem on the other head. Only clue to the electrics is the ever heating coil and the fact that idle rises and car runs smoother when I disconnect the alternator output wire.. If that matters.
Still lost, I'm afraid:-)
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Post by Penguin45 on Nov 20, 2011 21:20:00 GMT
We can ask Chris to check whether the ignition unit you have bought varies the dwell with RPM or not. I have a Powerspark unit from SIMONBBC. Reading through the blurb, it says that the advance is programmed into the unit. Mine was one for the MGB, as they hadn't done a specific unit for the 'Crab when I bought it. It works very well, so I leave it strictly alone. Chris. |
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Post by tommydp on Nov 20, 2011 22:13:32 GMT
Yes, I've got a cool coil- after 2 years:-) Not there yet, but closer!
I couldn't resist, so installed the Powerspark kit this evening. It took 4 minutes, and so far it seems the best spent £28 ever!
It started right away, and it was a relief to feel the coil now stayed absolutely cool, after ages of idling and a long run. The improvement on the road was beyond belief, I'll never run points again! Very smooth and responsive with loads of torque. All in all, marvellous!
After a time of idle, the stalling is still present though, but now it has to be down to fuel. After a while rpm goes down and it starts stumbling. Lifting pin indicates rich mixture, earlier it was correct. I decided to let it stumble on and finally it flooded. A relief really, as I can't imagine anything else than this confirms a fuel issue now. During all this idling, I must say I was happy to feel the coil kept cool anyway:-)
I think I'll rule out ignition now and get into the fuel system once again. The timing marks are rock steady when using the strobe. I set it to 12 degrees BTDC. Just out of curiosity, I hooked the strobe to number four cylinder. It shows 10 degrees at the same setting. I would expect it to be the same, but perhaps it's not critical.
Well, there is some progress then! At least it goes like a rocket and the coil is cool. I can hardly believe it:-)
Tommy:-)
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Post by dave1800 on Nov 21, 2011 0:45:40 GMT
It sounds as though the timing wheel magnets are slightly out of alignment by 2 degrees (1+4). I understand Simon BBC are good at sorting out problems under warranty. Try checking cylinders 2,3 using your timing wheels. 2 degrees shouldn't make too much difference on this engine, but it would be better if they were all even. ( I assume you don't have any play in the distributor shaft bearing that could affect the triggering?) Yes, I've got a cool coil- after 2 years:-) The timing marks are rock steady when using the strobe. I set it to 12 degrees BTDC. Just out of curiosity, I hooked the strobe to number four cylinder. It shows 10 degrees at the same setting. I would expect it to be the same, but perhaps it's not critical. Tommy:-) |
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Post by Penguin45 on Nov 21, 2011 0:49:23 GMT
That's a result, Tommy.
It is interesting how we have come to this position from two completely opposite directions. I have never managed to do timing properly on any of the cars I have owned over the years. I fully understand the process and what is involved - I just can't do it and get it right! The electronic route meant that I could do the job once and forget about it.
So, set up the carb and she'll be done.
Chris.
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Post by dave1800 on Nov 21, 2011 6:55:16 GMT
I've found further info that suggests that the fuel pressure for the SU carb is best set at no more than 2.5psi and a pressure regulator is a good investment. I have only ever once run one many years ago on a Frog-eye Sprite and didn't really notice any difference but I did use an electric fuel pump (ex Morris 1000) so it was probably superfluous.. Try packing the fuel pump with additional gasket(s) behind the insulating block to bring the pressure down to 2.5psi you may then need to adjust the mixture (richen) to compensate. It has to be too much pressure, needle valve stuck, air vent blocked on the fuel side if the carb is flooding. Just to be clear is the fuel overflowing from the float chamber or do you mean the mixture is getting too rich? If just the latter is there any crankcase ventilation blockage, I can't see how but!!! Tried out another pump and managed to get a pressure below 4 PSI, but the symptoms remain and it's impossible to get a stable mixture. I'm not exactly surprised... Still lost, I'm afraid:-) |
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Post by tommydp on Nov 21, 2011 11:13:54 GMT
Thanks all! I noticed the magnetic trigger was a bit loose on the distributor shaft when I installed it. Suppose the lobes are worn. Did you experience this Chris, or was the trigger a firm fit on your distributor? Ill check this out later.
Will try to get the fuel pressure down by adding gaskets. It floods from the ventilation hole on the float lid, Dave. I agree on lowering the pressure further as you mention. The data sheet of BL Norway, which I keep coming back to, states 0.18-0.21 bar for the 1800 mk 2. This is 2,6 - 3 PSI.
Tommy
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Post by dave1800 on Nov 22, 2011 0:41:13 GMT
It is important that the trigger wheel is a firm fit on the shaft to ensure consistent timing. I know some other similar triggers are tack bonded to the rotor arm. Not sure whether you could do this or maybe just a bit of teflon tape to pack it out. regards David Thanks all! I noticed the magnetic trigger was a bit loose on the distributor shaft when I installed it. Suppose the lobes are worn. Did you experience this Chris, or was the trigger a firm fit on your distributor? Ill check this out later. Tommy |
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Post by threelitre on Nov 22, 2011 9:41:51 GMT
The trigger in the 22D6 and 25D4 where I fitted such units to has been a snug fit. I did not check timing across different cylinders - wouldn't be too easy with just a standard stroboscopic flash. The timing needed to be reset by a good chunk in both cases, but I was tired of fiddling a re-fiddling the points, which seemed to wear quite quick (both at the contacts and the follower!). So far the impressions are quite good. I measured dwell on these units and it seems to be a constant charge time, as the dwell angle raises with raising revs.
Regards,
Alexander
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Post by threelitre on Nov 22, 2011 9:43:21 GMT
Tommy,
I did not read through all your previous posts again - are you sure the needle valve is spot on? I've once had one that did not close properly - leading to a stalled engine and a puddle of fuel on the road.
Regards,
Alexander
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Post by tommydp on Nov 23, 2011 18:09:24 GMT
Right, I managed to fit the magnetic trigger firmly by putting some tape on the distributor shaft. The timing is now identical on cylinder one and four and the timing marks are stable when using the strobe.
Fuel pressure is now 3 and I've fitted a new seat and needle and the float height is correct. I even double checked the piston and metering needle and it's centred and does not stick.
And the stalling and cutting out at idle? Oh yes, it's still there! Not better at all:-( At least the float chamber doesn't overflow. And as always it's very sensitive to adjustment of the mixture.
I really need to get a colortune, to see what's happening inside each cylinder. Don't have a clue at all what's going on with this car.
Regards, Tommy
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Post by tommydp on Nov 25, 2011 21:36:37 GMT
Ok, I think I've narrowed down further. I'm really looking forward to solving the odd idle miss and think I'm getting closer. Everything is accurately set and at least double checked on this engine no. In addition to this the electronic ignition is brilliant, so I suppose the engine will be in perfect tune soon, or at least before spring:-) We're now awaiting a hurricane, so the crab is resting in the barn anyway:-) The vacuum gauge is a marvellous instrument, thanks again Dave:-) It seems it can tell everything about engine trouble. I'm now 100 % sure the irregular miss, catching up, and miss again at idle shows up on the gauge as well as matching the occasional tapping sound of cylinder three inlet valve. This sound is more a hammering sound than the usual tick. No doubt, as this hammering sound appears the vacuum drops. When idling smoothly, the vacuum is 20. The needle drop is around 3 as the miss appears. At higher idle speed the needle is steady at 20. I understand this points to a valve/ guide issue as suspected. As mentioned before the valve guides seem to be seriously worn. Can the valve be sticking if this is the case? The followers don't stick. They rotate freely in the block. I believe the guides could be so worn the valve will not seat properly all the time. At least, now that I guess everything else is ruled out, I'll send a cylinder head to Burgess for reconditioning. I had a look at this, which I think confirms my vacuum readings as valve related. tidentenn.com/pdf/the-vacuum-guage.pdfTommy |
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Post by dave1800 on Nov 26, 2011 2:32:38 GMT
I am still uncertain as to the cause of the stalling and uneven idling. Your earlier description of being able to rock (one of?) the valves does suggest a lot of wear and so there is likely to be oil fouling the plug(s). There should only be 0.0015-0.0025" clearance (inlet) or 0.002-0.003" (exhaust) between the valves and guides. Sticking is more likely with overtight guides and noticed at higher RPM. Perhaps a valve is a little warped, have you tried a compression test with the engine hot to see if it consistent? I think another change of plugs may be worthwhile. I have read reports of a lot of failures recently. (DON'T check by removing plug leads now you have the electronic ignition, you will damage it!!) The oversensitive response to the carb adjustment MAY be a result of the valve guide problem(s) but still suggests to me a fuelling issue or air being sucked in assuming the ignition timing is correct. Perhaps the easiest thing to try first is varying the ignition timing say +/- 8 degrees to see if you can remove this oversensitivity (block and disconnect the distributor vacuum pipe). If not the ignition, put it back to where you are now. Now see if there is too much or inconsistent air venting from the the crankcase system - if using the PCV block the pipe from the manifold and let the crankcase pipe vent to the air- if using the later type leave the pipe from the crankcase open and block the carb. You will probably need to adjust the carb to compensate. If the over sensitivity of the adjustment has decreased then this points to the next area to investigate further. Guess a Colourtune is on the list from Santa? regards David And the stalling and cutting out at idle? Oh yes, it's still there! Not better at all:-( At least the float chamber doesn't overflow. And as always it's very sensitive to adjustment of the mixture. I really need to get a colortune, to see what's happening inside each cylinder. Don't have a clue at all what's going on with this car. Regards, Tommy |
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