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Post by tommydp on Jul 29, 2011 7:38:07 GMT
Dave, you are involved in this and I truly appreciate it:-) Your help is fantastic!
I'm sure there's something obvious too, and we will solve it sooner or later! I'm quite sure it can be narrowed down to fuel or ignition problems or a vacuum issue, but I've scratced my head more on these possible things on this very car, than I've totally done on problems on the other 30ish cars I've owned...
Well, I'm quite sure the jetis perfectly centred. I checked the "clunk" at all jet positions, and it's identical. The piston runs smoothlyinside the chamber. I'm also certain the spring is correct. I have loads of carbs, or rather bits and pieces of them but I'm sure I'm running the yellow one, though no one have got the colour identification. I may compare it to the untouched MArina's spring- which sould be yellow too.
Blowing down the breather pipe, which now runs to the carb is identical to the Marina and other 1800. With oil cap on, theres a blow out of the cap and a slight blowback when I remove the hose from my mouth. Cap off, there's unrestricted airflow from the oil filler hole. Exactly the same on all the engines.
Regards, Tommy:-)
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Post by kelsham on Jul 29, 2011 10:14:45 GMT
Hi, I know this question may seem to be unrelated, but what thermostat is fitted? I had problems with my car which eventually proved to be a faulty stat. I mistakenly replaced it with a MG 77 centigrade type. I believe it should be 82 centigrade.
Regards Kels.
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Post by tommydp on Jul 29, 2011 10:41:53 GMT
Hi! it has the standard 82 degrees thermostat. Keeps normal temperature.
Thanks for reply:-)
Regards, Tommy
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Post by tommydp on Jul 29, 2011 22:59:15 GMT
Sports coil arrived today, so will try it out tomorrow.
I had a look at the plugs today, which I installed yesterday. After driving a lot today there's no sign of debris on them, almost like when I installed them.. I would have expected some tan coloured debris.. Not sure if it matters. Still needs a lean mixture to idle smoothly. I must admit it idles smoother after I re- centered the jet yesterday, but the miss and hesitating when driving is still present, especially as it gets warmed up.
Checking out the new coil tomorrow and have a look at the ignition again, perhaps I'll try to advance it now the idle is better. At least there has been no sign of pinking since I changed the cylinder head last week. It's almost strange how quickly it fires and starts both cold and hot. That could perhaps indicate a rather late timing, though the timing is about 12 degrees at slow idle according to the timing marks.
Regards, Tommy:-)
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Post by dave1800 on Jul 30, 2011 0:27:06 GMT
Tommy
Just a couple of quick and obvious questions so apologies up front for asking.
1. Have you changed the oil filler cap to a non vented type now you are not using the PCV but the carb inlet for crankcase breathing?
2. Have you ever (or suspect someone else may have mixed the carburrretor suction (bell) chambers) and pistons - they are carefully matched.
3. If you suspect late timing, really check the TDC and pulley marks (again) very carefully.
regards
David
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Post by tommydp on Jul 30, 2011 10:05:56 GMT
Tommy Just a couple of quick and obvious questions so apologies up front for asking. 1. Have you changed the oil filler cap to a non vented type now you are not using the PCV but the carb inlet for crankcase breathing? 2. Have you ever (or suspect someone else may have mixed the carburrretor suction (bell) chambers) and pistons - they are carefully matched. 3. If you suspect late timing, really check the TDC and pulley marks (again) very carefully. regards David 1. I have the vented cap in place.. I thought they were all supposed to have the vented one, regardless of breather arrangement. 2. The piston and chamber may very well have been mis- matched. I believe I still have some complete HS 6 carbs, so could try swapping a hopefully matched pair from one of these. I take it pistons are interchangeable regardless of using a spring loaded needle or not? 3. I will try to determine the TDC once again, carefully. Perhaps the mark is a bit out. I take it the marks should line up the instant moment the piston reaches TDC on its way up. I suppose the piston stays at TDC a little while before going down again. Thanks again:-) Regards, Tommy:-) |
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Post by tommydp on Jul 30, 2011 14:52:46 GMT
Installed the sports coil today, and it seems to stay cooler at long periods of idle. It does not get abnormally hot, just "lukewarm".
Another thing crossed my mind. As the engine is over- bore, would the original air filter and box, which I'm using, restrict air flow into the engine at high vacuum, playing up the mixture and making it impossible to run at nothing but a weakish mix? After all the mixture changes a lot when removing the filter. Filter is clean by the way. Also, there's no intake "roar" at all when driving. If I block the filter box intake on the Marina, it wil stall- not the 1800. The Marina has a "healthy" intake roar too when revving, not the 1800, at least not when filter attached. Perhaps due to the design of the box though..
Perhaps I'll try to adjust it without the filter, and try it for a spin..
Regards, Tommy
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Post by tommydp on Jul 30, 2011 17:58:59 GMT
Took it for a ride with the new coil, and it made no difference.. Looks great though, the golden thing:-) Have not tried without the air filter etc.
Now, I think I've tried just about everything but theories still come up. They don't always make sense though:-) I must admit I'm getting somewhat desperate, it's driving me mad.. We're not exactly talking spaceship technology here..
Now, if I've put the distributor drive in one tooth out, would that cause trouble? It wouldn't matter would it, as long as I manage to turn the distributor to the correct setting? I'm totally sure the timing gears are correctly set, after all the work on the cam, timing the new cam etc. But I may have put the distributor drive one tooth out.
Checked the mixture again when I took it for a drive. Seems to be somewhat correct using the lifting pin. Not steady though. Correct one minute, the next to rich. It misses occasionally still at idle. Opening the oil filler cap it runs a bit smoother. Using the lifting pin then, with oil filler cap off, it stalls completely, as from weak setting. Putting the filler cap on while running, it will stumble, almost stall until I revv it once.
Regards, Tommy
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Post by threelitre on Jul 31, 2011 0:05:48 GMT
Have you ever tried using a colortune plug to get the mixture right? These things are worth a lot if you think you have fuelling trouble. A wideband O2-sensor will be a step further - expensive in comparison and not really needed for an engine close to standard. It may well be that the standard needle does not match the engine anymore.
Stick a straw in the dashpot of the carb and leave the damper out. Will the piston lift all the way when the engine accelerates? (or look into the back of the carb with the airfilter off. If the airfilter restricts the engine, then it will be at high load and high rpm - when the engine needs most air. I tend to set up my cars with the air filter off and never found a significant change when I put it back on.
Regards,
Alexander
Regards,
Alexander
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Post by dave1800 on Jul 31, 2011 1:29:05 GMT
Hi Tommy I'll try and answer your questions as best I can, but would appreciate comments from others as I am floundering here too! Carburretor; possible mixed vacuum chambers and pistons. Your best solution IMO is to now determe whether this is the cause. I suggest the easiest way for you is to use the vacuum chamber AND piston AND needle AND spring assembly from your Marina altogether as a set. If it cures the problem you are half way there. Alexander suggested using a straw in the top of the vacuum chamber after removing the damper to determine the piston lift. A good idea. Just remember to accelerate the engine slowly or it will splutter without the damper. You can then see if the piston is working properly; ie it will fully and smoothly open and fall back, but only reach full opening at high engine revs. If it fully opens too soon it means the spring is weak and will result in a weak mixture at higher rpm and it will no longer be acting as a SU variable venturi carb at higher speeds. If it doesn't fully open either the spring is too strong (unlikely) or the vacuum chamber and piston clearance is too great and the vacuum is leaking - if you've mixed them up this is a possibility. Alexander also suggested a Colourtune which was always part of my essential kit as it show what is actually happening in the cylinder. Distributor 1 tooth out. Turn the engine until the contact breakers just open - check with a meter. Now see if the rotor arm is pointing to a plug lead terminal in the distributor cap. Turn the engine 40-50 degrees backwards and see if the rotor arm is still pointing to the (same) plug lead terminal. This will ensure the spark can readily jump the gap across the gap over the whole of the advance curve. Rebore effect. I've never noticed any issues having gone as far as +60 other than a bit of tweaking of the mixture. Air filter - I agree with Alexander that unless it is blocked it makes very little differrence to setting up the tuning on these crude and tolerant (you won't agree with this word!) engines so wouldn't worry about it. It is often easier to adjust the mixture with it off - I used to allow about half a flat compensation for setting up with it off. Oil filler cap - I have double checked and it appears the UK spec MGBs and therefore very likely UK (and Norwegian?) 1800s all had vented oil filler caps irrespective of crankcase breathers although he USA cars changed to non vented. There is some more helpful info on the engine and breathing on this site www.mgb-stuff.org.uk/enginetext.htmFinding TDC - not quite so easy now you have the head back on, but there are a number of ways. Possibly the most accurate is as shown in this video but it's a bit messy I think a better way if you have a compression gauge with a detachable hose is shown here: A quick and simple way is to put and indicator on top of the No1 piston. However, as you are aware the piston moves very little between +/- 10 degrees either side of TDC so if you put an indicator on top of the piston then you will need to mark the point at which the piston just reaches the top and the point it just starts to move down again and take the mid-point. If anything is peculiar then maybe something more sophisticated as per the videos is needed. Hope I've answered your questions good luck again regards David |
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Post by tommydp on Jul 31, 2011 10:20:20 GMT
Well, I tried the complete assembly from the Marina, and the symptoms remain.. Hesitating at the same speed and rough idle when warm, like hunting. Advanced until a slight pink at load, but not better.
I've got no idea what to look for or do now. The rotor arm points directly to the cap segments when at TDC, on all cylinders. As far as I can tell, the mark for TDC is spot on.
The fuel filter between the pump and carb, which is new, seems to get absolutely full when the car has run and the problems occur. There's no pulsing on the hose from pump to carb then. When it's cold, and sometimes when running to, it's about half full, and you can se a rythmic flow as well as feel the pulsing on the hose. There's never any vacuum when opening the petrol flap. I find it hard to believe it's related to petrol delivery though, but who knows..
The strangest thing is there is still no debris on the plugs, after a lot of driving. The insulators are white. Number one is a bit wet after problems occur, from petrol I believe, there's no smoke, number three is absolutely clean, number four a bit like number one, some sooth on that not wet. Number two is like number three. Find this a bit strange, and it matches the firing order. All piston tops are somewhat wet, after driving to, strange the plugs are not affected by this..
Well, what can I say? I've got no ideas.. Thanks for your great help, again:-) I wish you were closer, so you could have a look:-)
Regards, Tommy.
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Post by tommydp on Jul 31, 2011 11:05:56 GMT
Had a look at the distributor drive now. Removed it, and installed it again, as per manual. When installed correctly, it's more 1-7 o' clock than 2-8, meaning a 45 d will have to be positioned with advance pipe straight up to fire cylinder one on tdc, and match up with the cap's segment. The advance pipe usually points at the heater outlet from the cylinder head in my opinion, at least the Marina does, and I haven't touched that.
So perhaps the cam is still one tooth out, then? I don't believe it, if so... I did it most accurately. After all, would it run reasonably well with the cam one tooth out, I mean there's a regular nice blow from the exhaust, though it misses sometimes.. I believe a cam out would have caused even more trouble..?
Regards, Tommy
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Post by dave1800 on Jul 31, 2011 11:08:23 GMT
Look on the bright side. As you have parts from the Marina that are working you are able to work towards the solution through substitution. So now you know the top of the carb and needle are not an issue, the only real clues seem to be the apparent weak running and the wet pistons. You need to check what is causing the wet pistons, fuel or oil, hopefully not water, strange it isn't on the plugs. You would expect cylinders 2,3 and 1,4 to be similar because of the siamesed inlet ports and the way they rob the fuel from the outer cylinders. From your description it seems as though the engine is running with too weak a mixture - or the engine running too hot. That means insufficient fuel or too much air. If you over richen the mixture and adjust the idle to compensate what does this do? Does it still run weak at higher revs. If so the fuel just isn't being delivered fast enough. Is the jet and feed pipe OK? Not sure why you sometimes get the fuel pulsing in the filter, other times not, maybe a clue there? Is there a problem with the float chamber vent, just a wild guess. The alternative, which I keep coming back to is that there may still be an air leak. I've never seen a problem with an inlet manfold but could be worth checking as you have looked at everything else many times. Does your servo hold the vacuum for at least ten minutes after the engine is turned off? Do you have anyone there who can have a quick look at the engine for you? Sometimes a new pair of eyes can work wonders. If you want to buy me a return ticket I'll gladly have a look!  regards David |
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Post by tommydp on Jul 31, 2011 11:22:11 GMT
Thanks again! I've borrowed the complete float lid from the Marina, so should be ok. There's no smoke from the engine when hot, so I really don't get the wet cylinders. No appearant loss of oil or water.
I'll double check the valve timing again, as I found the distributor drive setting a bit suspicious..
Well, perhaps a flight ticket is the only solution:-) I've presented the problem to others, but they scratch their heads too. All of them find it to run sweetly, but I don't, it's really not what it should be.. I'll check the servo's pressure holding later, but I assume it's fine.
Regards, Tommy
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Post by tommydp on Jul 31, 2011 13:47:06 GMT
Well, it's back to camshaft research again.. As mentioned earlier, i find the rotor position too far advanced when distributor drive is installed correctly, meaning the distributor will have to be in a rather retarded position for correct timing, not as in advance pipe pointing against the area of sparkplug 3. Ok, so could this mean the cam timing is still incorrect, ie the cam is advanced compared to the crankshaft?
Well, I have checked the valve timing now, and it could be out even though I believe I was quite accurate when installing. I opened valve clearance on cylinder one inlet valve to 0.020 and as far as I can see it's "about to open" as manual says at 10 degrees btdc, not 5 as it should be on this standard cam. I believe "about to open" means the moment there's no clearance between valve and rocker.. I'm afraid I've asked abaout this on the other cam issue, but can't remember. If I'm correct, at 5 degrees it has definetely opened, the valve spring compressing.
Well, how accurate are my readings, and is this enough proof, to get into the timing chain once again? I'm unsure. My 0.020 setting is at least not too tight, so I don't think a tight setting would cause a too early reading on the timing marks. Perhaps the cam is 5 degrees ahead of the crank then, after all? Could it at all have started and run reasonably well if this is the case? Well, the other cam ran 10 degrees out as far as I remember, and the car ran. Perhaps the "advanced camshaft" is why it fires the moment I turn the key?
OMG, I feel I've been down this road before, on the other "hot cam" issue..
So, into the timing gears again? I'm really not sure, so suggestions are welcome.. It would be worth it if this is the problem:-)
Regards, Tommy..
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