tim hunt Posted August 8, 2018 Report Share Posted August 8, 2018 John, I just came across this thread which I have read with mounting interest. Each idea I had has been suggested and subsequently discounted by you. I thought at first that Alan's idea of a loose insert could be on the money since I had just this problem a few years ago but of course if this were the case the engine would be on three cylinders immediately on starting. Your having now removed the head and found nothing amiss simply deepens the mystery. This is truly one for Sherlock Holmes and I will not be the only one to be fascinated to learn the cause when it is finally tracked down. Tim Quote Link to post Share on other sites
Peter Cobbold Posted August 8, 2018 Report Share Posted August 8, 2018 Perforated manifold heater pipe allowing water fouling of #2 plug after water jacket heating up and pressurised ? Peter Quote Link to post Share on other sites
oldtuckunder Posted August 8, 2018 Report Share Posted August 8, 2018 I had been pondering a reply on this, as its just possible that a valve seat could be in place whilst cold, but loosen when it gets warm/hot which might explain why it would run for a couple of mins before #2 dropped out. Still a long shot, but given what hasn't been found, we are in strange territory. The other long shot I pondered was a valve sticking open when the engine gets warm, might not be obvious to spot with engine running, and I suspect only 0.050 might be enough to kill any usable compression. Alan Quote Link to post Share on other sites
tim hunt Posted August 8, 2018 Report Share Posted August 8, 2018 Alan, my insert dropped out when the engine cooled after parking and lassoed the valve stem. I don't see how an insert could drop out when the engine was running, since even on tick over each valve is opening and closing about six times a second. Tim Quote Link to post Share on other sites
oldtuckunder Posted August 8, 2018 Report Share Posted August 8, 2018 There is a difference between dropping and jambing out, and dropping out and being pulled back in to place. I'm fairly certain that Mick Richards posted on having such an issue in one of his race V8's in the past, recently. Just looking for oddities, as when cold, #2 was still apparently giving good compression. Alan Quote Link to post Share on other sites
PYU940F Posted August 8, 2018 Report Share Posted August 8, 2018 Are you 100% sure that the problem is with No.2 cylinder? Maybe your dizzy drive is wrongly installed and someone has changed firing order to compensate?? Simon Quote Link to post Share on other sites
AGR 441 B Posted August 8, 2018 Author Report Share Posted August 8, 2018 Thanks for all ideas, they`re all appreciated. I`ve had dizzy out and in several times to put in new parts from Dizzy Doctor and swap rotors points and condensers in the early days of the issue while looking for this. The 1,3,4,2 sequence is well and truly implanted in my head and the N0. 1 TDC spark and pully marks definitely in correct synchronisation. As is the 4 deg BTDC. No mistake in connecting to the crank and cam. Manifold water pipe to heater is a stainless relatively new one and doesn't appear to have any cracks. Quite a few in our Group are pondering over this in moral support which I appreciate but as yet nothing revealed. No marks in the sooty head to suggest valve seat slippage, and we`ve watched the valves and rockers operating for sequence, distance moved and sticking with no result. Everything down in the block looks normal so I`m going to try a spare head on it and build it up again to see if the misfire is still there. John Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2018 Report Share Posted August 9, 2018 Pinhole in liner ? Quote Link to post Share on other sites
stillp Posted August 9, 2018 Report Share Posted August 9, 2018 I know you said you'd blown through the fuel pipes, but have you done the same with the fuel duct in the carb? Pete Quote Link to post Share on other sites
AGR 441 B Posted August 9, 2018 Author Report Share Posted August 9, 2018 Pete, done that on both carbs, but that would put two cylinders off and it was consistently only N0. 2. Put a different head on this morning. I`ll put all the ancillaries back over the next couple of days and see if its the same. John Quote Link to post Share on other sites
stillp Posted August 9, 2018 Report Share Posted August 9, 2018 Pete, done that on both carbs, but that would put two cylinders off and it was consistently only N0. 2. I would have thought so as well, until I had a similar problem! Pete Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2018 Report Share Posted August 9, 2018 I would have thought so as well, until I had a similar problem! Pete Firing order is 2134. So #2 is supposed to fire after a period of slow air flow across the jet, when rear carb was flowing air to 3 and 4.. #I gets more fuel as the inertia of fuel in the jet has been overcome during #2 operation. If fuel feed is resrircted, and fuel level falls in jet, that may well starve #2 and not #1. Peter Quote Link to post Share on other sites
stillp Posted August 9, 2018 Report Share Posted August 9, 2018 I had a feeling you'd be able to explain it Peter C! Pete Quote Link to post Share on other sites
oldtuckunder Posted August 9, 2018 Report Share Posted August 9, 2018 well just goes to show what you can learn, as I only work on 6's which are perfectly balanced front to back, i'd never thought about the firing order on 4's. Never realised it was 1342 no wonder twin carbs on them can be behave strangely and 4's break cranks. Alan Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2018 Report Share Posted August 9, 2018 I had a feeling you'd be able to explain it Peter C! Pete Pete, Just guessing ! Peter Quote Link to post Share on other sites
Peter Cobbold Posted August 9, 2018 Report Share Posted August 9, 2018 There' a trick for clearing crud out of SU transfer duct/hose. Remove air fliter, rev up and clamp a palm over the air intake, Peter Quote Link to post Share on other sites
stillp Posted August 9, 2018 Report Share Posted August 9, 2018 John, are you on SUs or Strombergs? Pete Quote Link to post Share on other sites
RdeJ Posted August 9, 2018 Report Share Posted August 9, 2018 John, is there a possibility that you have an issue with the petrol. Did the issue started after filling gas. Make sure you have a rotor-arm with an arrow pointing to the left when observing from the top. At TDC the rotor is pointing left upwards ~ Another considderation while troubleshooting is to bypass the electrical harness and put a straight connection beween the plus of the battery and plus of the coil. (would remove the the existing lead). Robert Quote Link to post Share on other sites
AGR 441 B Posted August 10, 2018 Author Report Share Posted August 10, 2018 still on SU carbs but have checked fuel flow several times. Priming with the lever, and just turning ignition key. Fuel gushing out at feed pipe to front carb. 1lb. jam half full in seconds. Trouble did start immediately after a fill up. Straight away I drained 75% out and topped up from another station to dilute the remainder. Since then I`ve done 400 miles in bits and pieces while it was intermittent, and topped up again, but when it went to No. 2 permanently out I`m stuck in the garage. Got a different head back yesterday, torqueing it down in stages, still got the plumbing etc to put back. John Quote Link to post Share on other sites
stillp Posted August 10, 2018 Report Share Posted August 10, 2018 Fuel gushing out at feed pipe to front carb. 1lb. jam half full in seconds. Right, so the pump and the pipes are OK. Try dropping the float chamber off the front carb and removing the float valve. Is the flow the same? Pete Quote Link to post Share on other sites
stillp Posted August 10, 2018 Report Share Posted August 10, 2018 Another thought - is the front float valve sticking? Try swapping it with the one on the other carb. Pete Quote Link to post Share on other sites
tonythecat Posted August 18, 2018 Report Share Posted August 18, 2018 still on SU carbs but have checked fuel flow several times. Priming with the lever, and just turning ignition key. Fuel gushing out at feed pipe to front carb. 1lb. jam half full in seconds. Trouble did start immediately after a fill up. Straight away I drained 75% out and topped up from another station to dilute the remainder. Since then I`ve done 400 miles in bits and pieces while it was intermittent, and topped up again, but when it went to No. 2 permanently out I`m stuck in the garage. Got a different head back yesterday, torqueing it down in stages, still got the plumbing etc to put back. John Any news John?? Tony Quote Link to post Share on other sites
tim hunt Posted August 19, 2018 Report Share Posted August 19, 2018 Yes John, haven't heard from you for over week now and I am sure there are many of us keen for an update/answer. Tim Quote Link to post Share on other sites
Tony_C Posted August 19, 2018 Report Share Posted August 19, 2018 Yep, I’ve got similar issue with same engine.. Thanks Tony Quote Link to post Share on other sites
AGR 441 B Posted August 20, 2018 Author Report Share Posted August 20, 2018 Evening all, sorry about delay but you can guess I`ve been busy working on it and I`ve got the good news tonight. With a different head back on it was still the same so just started working through the routine items again from the start. However my brother in law, a retired trained mechanic joined in on Saturday and detected that although No. 2 was not pushing at all, No. 1 was very weak. Making it more logical that the front carb, serving them both was the culprit. Off with the feed from the pump and a strong jet of fuel was ejected as the residual pressure in the line from the pump was released. Taking the top off the front float chamber it was empty obviously because the needle valve was stuck shut trapping the fuel in the feed pipe. The needle valves have been replaced twice over the past few weeks, first with a set I have carried in my spares for a while, (red teflon tipped), and then with a new set, (grey Teflon tipped), bought a couple of weeks ago to restock the spares pool. The plastic floats have been checked time and time again and have no leaks or defects. Why it should repeatedly stick is still a mystery, however I have changed the valve unit again and swapped the floats front to back in case it was the plastic float to blame. Its running fine on four now and went round my local test route with a 1 in 5 hill, junctions and traffic lights without hesitation. Just got to get it tuned back to normal again now. So why on previous occasions did the float chamber have fuel in? We have a possible theory. When the float chamber floods its usually due to the valve sticking open and traditionally a bit of tapping on the top was a common fix to disturb it when it returned to normal. Over the past few weeks when I started applying tools to release the feed then unscrew the top, this may have been sufficient to simulate the old tapping dodge, especially with the fuel under pressure trying to open it. Then by the time I got the top off it had been filled when I was working releasing the feed pipe. Very thin theory I know but I can`t think of anything else. Similarly I can`t understand how you can replace the needle valve twice with new and not fix the problem. Does this new petrol make Teflon sticky? Maybe I should hone the old brass ones in to face the seats and put them back? Anyway, saga is over. Thanks for all your support, A happy John now. Quote Link to post Share on other sites
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