Jim S Posted June 9, 2016 Share Posted June 9, 2016 Hello all. Helping a friend with his newly restored MW but can't get the engine to run properly. It has been rebuilt, new rings, big ends etc. but won't run properly. It spits back through the carb and backfires if it is revved up slightly. Doesn't really run all that smooth on tickover either. We are running out of ideas. Checked the following: valve clearances, static timing, points gap, plug gaps. Changed the following: plugs, new copper plug leads, new coil, new rotor arm, new dissy cap, new condenser, nos carburettor. Tested: 12v to the coil with ign ON. There are no suppressor components in the plug leads. Noticed that using a Sealy timing light that it does not flash consistently, if at all, on all plug leads pointing to weak spark. (Timing light works perfectly O/K on my 6v system TE20 grey fergy using a 12v supply for the light).. Any guidance please.... Regarda Jim. Quote Link to comment Share on other sites More sharing options...
GeePig Posted June 9, 2016 Share Posted June 9, 2016 Here are some things that come to mind. Are you absolutely sure that the cam timing is right? I see you have replaced many of the components (haven't we all been there...), but are you sure that the ignition is receiving a consistent supply? Which plug leads do not produce a consistent flash on your timing light? Some? All? Have you pulled the plug leads off and tested to see you can get a consistent spark to jump to a head stud? These things are darn frustrating, because you cannot see the fault... trev Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted June 9, 2016 Share Posted June 9, 2016 Have you got all the HT leads in correct order? Sounds like two may be transposed. Quote Link to comment Share on other sites More sharing options...
thedawnpatrol Posted June 9, 2016 Share Posted June 9, 2016 I had a similar problem on my PU last weekend, not firing and fuel dumped out of air intake on carb, turned out that as I was running off an Autovac I needed a larger needle in the carb, it's fine now. Are you running an Autovac ? Check your carb jet Jules Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted June 9, 2016 Share Posted June 9, 2016 Another thought as the engine has been rebuilt, the Bedford 28 hp needs care when fitting the manifolds, to ensure both are aligned and there are no air leaks (leaks will mean weak mixture which could be one of the causes of your symptoms). Quote Link to comment Share on other sites More sharing options...
Starfire Posted June 10, 2016 Share Posted June 10, 2016 Air leaks and cam timing will both cause the issue that you're describing, but the poor operation of the timing light is quite an alarm bell for me. Try another light, but if it works fine on other engines, I would suggest that you have a significant problem with your ignition system (I believe that the coil is about the only thing that you haven't changed). Also check the shaft of your distributor for excessive play; worn bearings can do some weird stuff. Cheers, Terry Quote Link to comment Share on other sites More sharing options...
paulbrook Posted June 10, 2016 Share Posted June 10, 2016 All new HT stuff eh? Try putting the old bits back one at a time - starting with the rotor arm. Back in the 70s I can never ever remember having to change a rotor arm. Now its the first place I look. Quote Link to comment Share on other sites More sharing options...
matchlesswdg3 Posted June 11, 2016 Share Posted June 11, 2016 Converting to electronic ignition comes highly recommended......whether or not your problem lies in fuel delivery or ignition. Quote Link to comment Share on other sites More sharing options...
Jim S Posted June 14, 2016 Author Share Posted June 14, 2016 Thank you all for your comments. Found out that these timing light pickup sensors are directional! There is an arrow moulded into the plastic that should point to the plug. That improved its operation. The six plug leads are connected to the right plugs and the coil was changed. There is 12v at the coil. Have since replaced the distributor condenser and it was better. Then stripped the carb, replaced the diaphragm, refitted and it was better still! Still spits back a bit if the throttle is opened a lot but it made our local steam rally last weekend and back, a distance of about 15 miles each way, plus round the ring twice - it looked smart! Beginning to think that this engine is a bit touchy and needs a lot of fine tweeking to get the best. Thanks all, Jim. Quote Link to comment Share on other sites More sharing options...
matchlesswdg3 Posted June 15, 2016 Share Posted June 15, 2016 Jim, Richard Farrant worked over my MW engine for me and once he had sorted the head, valves, manifolds, etc (!!), that left a rather worn Zenith civvy carb (supposedly a better performer than the military lump) which he managed to get functioning reasonably. I sold on my MW, but I think the chap who bought it was intending to install electronic ignition and I am told this transforms the running, which tends to be a bit lumpy due to all the rather worn ignition bits that have to whiz round and make contact (sorry if I am getting too technical). Richard does no quite approve as he likes the "beat" of the Bedford motor, which is evened out to a steady purr when you put in an electronic box.......but once installed, it does remove a potential source of unreliability. Spitting back still indicates you are getting a weak mixture......air leak at carb/manifold.......fuel pump not up to scratch? Good luck with it.....I parted with my MW with some regret, but that truck made my military L/R Defender feel like a 4WD Rolls Royce! Quote Link to comment Share on other sites More sharing options...
Richard Farrant Posted June 15, 2016 Share Posted June 15, 2016 Jim, Richard Farrant worked over my MW engine for me and once he had sorted the head, valves, manifolds, etc (!!), that left a rather worn Zenith civvy carb (supposedly a better performer than the military lump) which he managed to get functioning reasonably. I sold on my MW, but I think the chap who bought it was intending to install electronic ignition and I am told this transforms the running, which tends to be a bit lumpy due to all the rather worn ignition bits that have to whiz round and make contact (sorry if I am getting too technical). Richard does no quite approve as he likes the "beat" of the Bedford motor, which is evened out to a steady purr when you put in an electronic box.......but once installed, it does remove a potential source of unreliability. Spitting back still indicates you are getting a weak mixture......air leak at carb/manifold.......fuel pump not up to scratch? Good luck with it.....I parted with my MW with some regret, but that truck made my military L/R Defender feel like a 4WD Rolls Royce! Hi Ferg, Only reason I was cautious regarding converting to electronic ignition was due to having had some failures with them. I did an Austin K2 ambulance and it went superbly and was impressed with the performance, but consumed rotor arms due to the increased HT voltage. There was another problem on a Bedford, which I cannot recall details, think it was the cap that got destroyed that time, by burning. There is a solution with rotor arms now, where new ones have been made to combat the problem of shorting out. regards, Richard Quote Link to comment Share on other sites More sharing options...
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