Steve J Posted September 16 Share Posted September 16 Hi folks, I have a Moss Malvern kit car using a Herald 13/60 engine with Stromberg 150 carb. There is a problem with the engine running way too rich. The plugs are all sooted up after just a few minutes and not surprisingly the exhaust is pretty smoky too. I've checked the needle valve in the float chamber is shutting off the fuel correctly and the choke mechanism is actuating (at least the external mechanism is moving with the choke control). I've also checked the carb diaphragm is intact and seated correctly. Is there anything else that I should be looking at? This is how the car came to me and I believe it has been standing a while, although the previous owner did somehow get an M.o.T. on it not long ago. Incidentally the plugs are fancy Accuspark jobs and look new. Quote Link to comment Share on other sites More sharing options...
garyf Posted September 16 Share Posted September 16 (edited) Hi Steve You should be able to weaken the mixture of the Stromberg Carburettor by the adjustment screw in the middle of the float chamber underneath if it's a standard CD150 Carb as originally fitted to the Herald. I would screw it inwards (Clockwise when viewed from underneath) say one full turn and then take it for a run for a few miles and see if the plug colours improved to a golden brown colour? Also, it is worth checking the jet needle is correctly centred, with the air filter removed, does the piston raise/drop smoothly after raising with your finger? Gary Edited September 16 by garyf Quote Link to comment Share on other sites More sharing options...
Steve J Posted September 17 Author Share Posted September 17 Hi Gary, thanks very much for your ideas. I think the mixture is set pretty lean but I'll double check it anyway. The piston action feels fine but I'll take a look at the needle itself. I'll report back... Quote Link to comment Share on other sites More sharing options...
glang Posted September 17 Share Posted September 17 yes just to expand on Garys description, the piston should push up with resistance (as long as youve got the damper rod screwed in of course) and then drop smartly with a nice clonk as it hits the bottom bridge👍 Quote Link to comment Share on other sites More sharing options...
Wendy Dawes Posted September 17 Share Posted September 17 Also might be worth checking the dash pot oil level Quote Link to comment Share on other sites More sharing options...
Steve J Posted October 6 Author Share Posted October 6 Back on to this again and I have admit it's got me beat! Weakening the mixture has made no difference to the plugs sooting. After just a couple of minutes running generally two are dry and sooty and two are wet and black. The engine is very difficult to start either with or without choke, often just 'catching' enough to disengage the starter and it also gives the occasional blow-back (with smoke) through the carb. Miraculously I did manage to get it running and idling yesterday for several minutes, but the engine shakes when revved as if it were running on three cylinders and then wouldn't re-start (probably fouled plugs again). The odd thing is that whilst it was running, raising the spring-loaded pin on the carb causes the revs to drop and the engine to begin to stall, which I believe means the mixture is too weak. The dashpot oil is topped up, the carb diaphragm is intact and the needle appears in good fettle. The piston raises smoothly against the damping and drops with a 'clack'. I've had the rocker cover off and there are no stuck valves. I'm getting quite despondent! Quote Link to comment Share on other sites More sharing options...
Dannyb Posted October 6 Share Posted October 6 I think you should check the valve timing. With the engine at tdc and rota pointing to no1. Valves 7&8 should be on the rock. ie equal gap. First adjust 7&8to about 70 thou. Then get engine at tdc and measure 7&8. Doesn't matter what they read but they must be equal. It could be previous owner set the cam wrong or the timing chain has jumped a tooth or two. Danny Quote Link to comment Share on other sites More sharing options...
Steve J Posted October 6 Author Share Posted October 6 Thanks Danny- all good advice. I'll check that! Quote Link to comment Share on other sites More sharing options...
Steve J Posted October 9 Author Share Posted October 9 (edited) In a moment of (possible) inspiration, I'm wondering about the aftermarket Accuspark plugs which were fitted by a previous owner... If they are of a type that possibly have a higher internal resistance than standard plugs, I would guess that could account for a weak spark and resultant poor combustion, causing them to foul up and give a similar appearance to rich running, despite the carb being set to run lean. Accuspark make electronic ignition conversion kits (which my car doesn't have) and I wonder if the plugs are designed to work with that set-up rather than an old-fashioned coil and points. I've ordered a set of standard N9YC plugs to see how that changes things. I may be completely wrong but it's worth a try! Edited October 9 by Steve J 1 Quote Link to comment Share on other sites More sharing options...
Jonny-Jimbo Posted October 11 Share Posted October 11 I had a vehicle that used to do this (not a Herald, but the same sort of age and technology type). The issue was a few things; ignition timing was out, wrong plugs fitted, engine was leaking a bit of oil into the cylinders. Not a lot, but a bit that was gradually burning and coking the plugs up. Also, the coil was on the way out. I'm not saying this is your problem specifically, but a few pointers that sooting plugs isn't always mixture related if other things are preventing a good ignition cycle. Quote Link to comment Share on other sites More sharing options...
glang Posted Saturday at 06:55 Share Posted Saturday at 06:55 I think a compression test is definitely needed! Low readings would explain the symptoms you have.... Also check the carb float level as if too high you'll struggle to stop a rich mixture. Quote Link to comment Share on other sites More sharing options...
Steve J Posted Saturday at 14:50 Author Share Posted Saturday at 14:50 (edited) Right then, a compression test reads a consistent 120 across all four cylinders, so at least they are even. More importantly, I discovered this afternoon that the ignition coil was connected the wrong way round. Now that certainly won't help matters! I also found that there's a lot of nasty white corrosion in the king-lead socket on the coil. I'm surprised I was getting any spark at all. New coil on order and we'll see how things go from there. Edited Saturday at 14:51 by Steve J Quote Link to comment Share on other sites More sharing options...
glang Posted Saturday at 15:27 Share Posted Saturday at 15:27 Sorry could you do the compression again but wet ie. with a cap full of oil down the bores to see if the readings are improved by better sealing of the rings? Also it would be interesting to see what the tester shows on another vehicle if youve got one to hand... And yes all these issues do add up👍 Quote Link to comment Share on other sites More sharing options...
Steve J Posted 6 hours ago Author Share Posted 6 hours ago (edited) Well, I'm very relieved to report that having renewed the coil (ensuring it's connected the right way round!) and fitting a new set of standard spark plugs the engine miraculously now starts and idles pretty well. I've also treated it to new HT leads, distributor cap, points and condenser. The fuel mixture seems to be about right as pushing the pin on the Stromberg carb causes the revs to rise and then settle back. No doubt it will need some fine tuning, but it seems to rev cleanly from idle with no hesitation. I had it running for about 15 minutes today and was able to engage gears and move the car backwards and forwards on the drive. The exhaust is still rather smoky (grey) but I'm hoping a bit of use might improve matters as the car hasn't been on the road for some years and probably needs the cobwebs blowing out. Next step is to get it taxed and insured and take it for a cautious test drive... Edited 6 hours ago by Steve J 1 Quote Link to comment Share on other sites More sharing options...
65redspit Posted 6 hours ago Share Posted 6 hours ago 10 minutes ago, Steve J said: Well, I'm very relieved to report that having renewed the coil (ensuring it's connected the right way round!) and fitting a new set of standard spark plugs the engine miraculously now starts and idles pretty well. I've also treated it to new HT leads, distributor cap, points and condenser. The fuel mixture seems to be about right as pushing the pin on the Stromberg carb causes the revs to rise and then settle back. No doubt it will need some fine tuning, but it seems to rev cleanly from idle with no hesitation. I had it running for about 15 minutes today and was able to engage gears and move the car backwards and forwards on the drive. The exhaust is still rather smoky (grey) but I'm hoping a bit of use might improve matters as the car hasn't been on the road for some years and probably needs the cobwebs blowing out. Next step is to get it taxed and insured and take it for a cautious test drive... Brill - well done you !!! 💪💪 Quote Link to comment Share on other sites More sharing options...
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