Graham Sewell Posted May 10, 2010 Share Posted May 10, 2010 Hi, my trusty old xflow has been misfiring for some time and I still have not found the cause - but I am not sure that it is the usual suspect. Symptoms - car is fine for upto 10 miles then starts to misfire under heavy acceleration but can quite happily rev to 6000rpm if taken up gently (like where's the fun in that?). I have had the car to the Seven's Workshop - Chris is a seriously top bloke - and all normal settings are fine on the carbs and dizzy and coil (just replaced it just in case). The spark plugs are a nice light grey colour with good gaps and no wear on either electrode. What I did notice last night when I put the bonnet back on is that the air filters are very nearly touching the bottom of the hole in the bonnet. So I am wondering if, as the engine gets warm, the engine mount rubbers or the carb rubber bobbins soften slightly so that under WOT the filters touch the bonnet. This could cause foaming in the float chambers or lift the carbs off the Misab's causing an air leak. Does this sound reasonable? In which case I need to replace the engine mounts (my current prime suspect). How tricky is that without removing the engine? I missed all of last summer with this misfire (not much of a summer anyway) but would really like to enjoy the car this year. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
elie boone Posted May 10, 2010 Share Posted May 10, 2010 It could be that the carburettors got lifted by the airfilter, you also need to look at the engine supports aswel or place a washer in between the engine support and the rubber mount to lift the engine enoug to clear the chassis. Does the engine idle good ? how is the valve clearence and the position of the bolt i.e. do you need to srew the bolds all the way in or is there 7/8 mm left of tread. it could be that the valves are not sealing enough anymore due to the lack of hardened seats. Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 10, 2010 Author Share Posted May 10, 2010 Valve clearance are good and it has an unleaded head from Vulcan. Compression ratios are good and even. So am fairly happy with the internals for the engine. I was wondering about shimming the engine mounts.... So I might be heading in the right direction. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
John Ryan Posted May 10, 2010 Share Posted May 10, 2010 Graham Do you have points in the dizzy? If you drive it more than 10 miles, does the misfire get worse progressively, or stay the same after its started? Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 10, 2010 Author Share Posted May 10, 2010 John, Ignition is currently Aldon Ignitor in an Aldon calibrated ignition curve Lucas dizzy. Once the misfire starts, it is pretty much the same for the next 10 miles (20 mile test drive) and comes in only under heavy acceleration - possible pump jet issue but I would expect that would have started from cold. Battery is fully charged and this is not the sort of misfire that I have had in the past with a broken alternator where the misfire got worse and worse until the car died in about 5 miles. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
Eugene Posted May 10, 2010 Share Posted May 10, 2010 Hi Graham - I've had similar problems with the Alden... Mine was caused by the Rev Counter being old, and causing a back-emf that fried the Alden. I didn't realise this at fists, and changed the Alden only. The second one lasted for only 4 weeks... (The first lasted 4 years before the problem occurred!) Speedy Cables replaced the internals of the Rev counter for me. Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 10, 2010 Author Share Posted May 10, 2010 Eugene, How did you diagnose that issue? The rev counter is 15 years old and the Aldon is at least 7 years old. Cheers, Graham Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
PAC Posted May 10, 2010 Share Posted May 10, 2010 Have you tried a quick blat without the air filters on? P Link to comment Share on other sites More sharing options...
Eugene Posted May 10, 2010 Share Posted May 10, 2010 Yep, I'm betting that's your problem!!! It took me ages to sort this out - if you do a search back a few years (more than a few now) you will find my original thread about this... But, a 15 year old rev counter will not be compatible with an Aldon - definite! Sometimes the Aldons last for years, other time no time at all... Talk to Aldon and Speedy Cables. Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Eugene Posted May 10, 2010 Share Posted May 10, 2010 Here's the old thread: HERE. Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
OliverSedlacek Posted May 10, 2010 Share Posted May 10, 2010 I doubt the air filters have anything to do with it, but at least you can change an engine mount relatively simply. You just need to take the weight off the mount using a jack under the engine and then you can undo the bolts. Link to comment Share on other sites More sharing options...
Billyboy Posted May 10, 2010 Share Posted May 10, 2010 Run it in as black as a place as possible with bonnet off - see if there is any ignition tracking - from any of the ignition system - even slight leakage will cause an issue under full load Link to comment Share on other sites More sharing options...
jonboylaw Posted May 10, 2010 Share Posted May 10, 2010 Mechanical or electric fuel pump? Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 11, 2010 Author Share Posted May 11, 2010 Mechanical pump. All ignition leads were changed < 300 miles ago. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
virden Posted May 11, 2010 Share Posted May 11, 2010 I had very similar symptoms. Car ran well for ten minutes, then started misfiring, progressively lost the ability to rev and finally died. 40 mins later started on the button and repeated the cycle. The problem was traced to the brand new coil I had fitted. I changed back to the old one and all is fine. 1996 Super Sprint, live axle with clams Link to comment Share on other sites More sharing options...
Area Representative dikko Posted May 11, 2010 Area Representative Share Posted May 11, 2010 Same as Eugene, Aldon worked for years then started to argue with the rest of the car. Went the way of Bestek system (based on Jag V12 coil, dizzy and black box = bombproof). He sells by ebay. Link to comment Share on other sites More sharing options...
Eugene Posted May 11, 2010 Share Posted May 11, 2010 Indeed Dikko, and who was it suggested your fault a the time 😬 Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
andy couchman Posted May 12, 2010 Share Posted May 12, 2010 Condensor? Andy Link to comment Share on other sites More sharing options...
PETER HERTS Posted May 12, 2010 Share Posted May 12, 2010 I had what I thought was a misfire last year through France. Changed the usual things, leads, plugs, dizzy cap but then found the real problem was the adjustable fuel restrictor. Took it off and everything was fine. When I dismantled it I found a bit of grit in it. Worth a try if you've got one fitted. Link to comment Share on other sites More sharing options...
jonboylaw Posted May 12, 2010 Share Posted May 12, 2010 Have you checked the accelerator pump diaphragms in the carbs? they may be split causing a leaning or even fuel starvation during hard acceleration. Jonathan My Flickr ----------------------------------- The rebuild has started :) 92 Supersprint, Ford LSD LA, RK AX Crossflow. Link to comment Share on other sites More sharing options...
Eugene Posted May 16, 2010 Share Posted May 16, 2010 Hey Graham, what news? Got a fix yet??? Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Bob_Rich Posted May 16, 2010 Share Posted May 16, 2010 Hi One of the posts suggested the old style tacho (assume it is a smiths type triggered by inductive pick up in series with the coil) could break the ignitor module. I find this hard to believe. Certainly the ignitor may result in the tacho not responding correctly -- but that is usually easy to modify. the Aldon ignitor , I believe, replaces the points in the distributor, and works on a similar principle to the points ( spark generated by current interruption in the coil) except that a transistor is turned off to get the spark and the trigger is by a magnetic pick up. The energy stored in the tacho pick up is small compared to that in the ignition coil so it is hard to see how the tacho could break the Aldon. Not sure this helps much! just suspicious that the tacho was/is not the real source of the problem best of luck Bob Link to comment Share on other sites More sharing options...
Eugene Posted May 17, 2010 Share Posted May 17, 2010 Hi Bob, It is indeed true that the old tacho gauge can kill the Alden, and I had it confirmed by Alden and Speedy Cables... Speedy Cables replaced the tacho internals for me. The problem is a back emf when the revs drop... Small Boy - with Loud Toy! Co-founder of the BOG Club See Eugene here and see what I do here Link to comment Share on other sites More sharing options...
Graham Sewell Posted May 17, 2010 Author Share Posted May 17, 2010 We are heading to Chris Wheeler on Friday for a set of mechanical adjustments/checks first - engine height (clearance of the filter hole), pump jets, float levels - anything that could cause fuel starvation. Pray that this solves the issue - otherwise, I am looking at the Weber Alpha ignition management becuase if I am spending a coulpe of hundred on a new Ignitor and new/repaired tacho, knowing that my dizzy has a small amount of slack already, I may as well go 3d mapped for a couple of hundred more. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
jonboylaw Posted May 17, 2010 Share Posted May 17, 2010 Megajolt ? a cheaper option than the Weber and works really well. Lots on here have done it and some maps available. Website here Jonathan My Flickr ----------------------------------- The rebuild has started :) 92 Supersprint, Ford LSD LA, RK AX Crossflow. Link to comment Share on other sites More sharing options...
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