Paudman Posted April 24, 2011 Share Posted April 24, 2011 I've been trying to eliminate the poor running of the Gt6 following the winter layup - it starts, idles well, but any kind of acceleration or load on the engine gives a rattling noise like an air-cooled engine, and I've a top speed of about 70. I would think it was down a cylinder except for the good idle and lower range revs, but if I rev the engine over about 3500 revs this rough running comes in and remains until the engine revs drop down again, whereupon it either stalls at idle or almost dies, then picks up and runs again. A restart has it running normally until the next rev.Compression test gives all the cylinders the same compression. I've changed both carb diaphragms and refilled the dashpots before setting the carbs from scratch. There's no sign of fuel starvation, if anything they were running rich but as there's been a lot of idling it has sooted up the plugsI've cleaned out the petrol filter and added fresh petrol. I've changed the SimonBBc ignition module for an Aldon ignitor unit, replaced the distributor cap, rotor arm is a new red version and I've changed the sparkplugs.The leads are new silicon version from a major Triumph supplier and I've been told they can break down under load, although they ran perfectly all Summer last year. I was going to revert back to the original Delco dizzy with points but until I verify the leads or get another set it'll probably run the same.Any thoughts on the leads, or on the poor running? Link to comment Share on other sites More sharing options...
Nick Jones Posted April 24, 2011 Share Posted April 24, 2011 This sounds alot like an issue I was having with the PI a couple of weeks back. It turned out to be due to seriously (like 30º :o) over advanced ignition, cause by the damper ring having moved on the pulley, putting the timing marks well out and the PO to have set the timing very advanced as a result.It idled well and would drive ok if you were very light with the throttle and kept the revs down, but hoof it and it would just misfire and make odd, rattly, rumbly noises. Only after I'd backed it off a good 15º did it start to pink. Another 15º off and it was going really well.You should also to check to see whether either the vacuum advance or centrifugal advance have stuck. Vacuum advance stuck in the advanced position would be more likely to cause your symptoms. Stuck mechanical advance would make it pink at low rpm.Other possibilty is that the relationship between points/EI module and rotor arm is not quite correct causing the rotor arm to be out of line with the pins in the cap and giving cross-firing (rotor arm points the spark to the wrong plug) when the ignition advances as the revs increase.CheersNick Link to comment Share on other sites More sharing options...
piman Posted April 24, 2011 Share Posted April 24, 2011 Hello Paudman, does it misfire when you rev up the engine with no load, if so get it in a dark place and look for sparks.I you have you opened up the spark plug gaps, try reverting to standard gap as this will reduce the H.T. voltage and may cure it, which would point to an insulation break down.Have a look at the mechanical advance to ensure it's free and functioning.Alec Link to comment Share on other sites More sharing options...
Paudman Posted April 25, 2011 Author Share Posted April 25, 2011 it's even worse!I've changed the Lucas distributor with Aldon ignition for a Delco model with points; idles well but no power at all - I got 100 yards from home and travelled back at a top speed of 10 mph. I can rev right up the range with no missing or backfiring at high idle, but any attempt at driving at all meets with disaster. It's driving me up the walls, and nowhere else! Link to comment Share on other sites More sharing options...
Nick Jones Posted April 25, 2011 Share Posted April 25, 2011 Are both carbs getting fuel? Saw this quite recently where one SU carb had its jet pipe blocked completely. The car actually idled quite well, but as soon as revved it was obviously a few cylinders down and struggled to spin itself up, never mind drag a car.Other than that, general lack of fuel flow? Or newish NGK plugs that have been wetted with fuel and rendered useless...?Nick Link to comment Share on other sites More sharing options...
Raider Posted April 25, 2011 Share Posted April 25, 2011 I'm a technical numpty but if changing the distibutor makes it worse that sounds like a timing issue or something similar.Whenever I get anything like this I think "it's always on the oignition side" and it usually is :-/ Link to comment Share on other sites More sharing options...
Paudman Posted April 25, 2011 Author Share Posted April 25, 2011 Nick_Jones wrote:This sounds alot like an issue I was having with the PI a couple of weeks back. It turned out to be due to seriously (like 30º :o) over advanced ignition, cause by the damper ring having moved on the pulley, putting the timing marks well out and the PO to have set the timing very advanced as a result.It idled well and would drive ok if you were very light with the throttle and kept the revs down, but hoof it and it would just misfire and make odd, rattly, rumbly noises. Only after I'd backed it off a good 15º did it start to pink. Another 15º off and it was going really well.NickThis is very interesting - I've just warmed it up and checked the timing (again); it's about 10 degrees BTDC. I backed it off to about 20 degrees and the idle speed immediately picked up; another ten degrees back and it's revving very well with no hesitation at all. I'll try a drive tomorrow evening, but it appears the timing is wayyyyy off going by the pulley marks.I'll update again tomorrow evening. Link to comment Share on other sites More sharing options...
Nick Jones Posted April 25, 2011 Share Posted April 25, 2011 Ok, bit of caution needed though as some of the above info is duff.Today I have been checking timing marks properly by measuring TDC exactly using DTI in preparation to fitting a trigger wheel. In fact the marks are correct within a degree. This caused me to investigate the distributor (which I should have done before) and this revealed that the mechanical advance is partially seized leading, in effect, to random timing settings.You can check the mechanical advance by removing the distributor cap and carefully twisting the centre shaft back and forth. It should turn a few degrees in one direction against spring pressure and return by itsef to a positive stop. It should return all the way to the stop by itself, every time.Nick Link to comment Share on other sites More sharing options...
CRAJ Posted April 26, 2011 Share Posted April 26, 2011 Just a suggestion, your timing light hasn't got advance settings on it has it? I have caused myself problems by not zeroing this before use and ended up with similar symptoms!Colin Link to comment Share on other sites More sharing options...
don cook1 Posted April 28, 2011 Share Posted April 28, 2011 After I fitted Aldon ignition and a Flame Thrower coil I got through quite a few HT leads. I ended up investing in Magnacor leads. One way to test the leads while the engine is running is to wave your hand around the leads...if it hurts then it could be the leads. Link to comment Share on other sites More sharing options...
willcolumbine Posted April 28, 2011 Share Posted April 28, 2011 Or you could just look at the plug leads in low light conditions - sometimes you can see the electrikery arcing to the engine block. It hurts less than the above method! Link to comment Share on other sites More sharing options...
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