Pete Lewis Posted June 16, 2022 Report Share Posted June 16, 2022 I watched someone drop one very quickly will that do ha! pete Link to comment Share on other sites More sharing options...
Chris A Posted June 16, 2022 Report Share Posted June 16, 2022 3 minutes ago, Pete Lewis said: I watched someone drop one very quickly will that do ha! pete Hummm .... Link to comment Share on other sites More sharing options...
PeteH Posted June 16, 2022 Report Share Posted June 16, 2022 Ok, Daft one here, BUT back in the 60`s, I, with the help of some very good friends in the Aircraft Industry (`nuff said) ported and devised a "Racing" conversion for a Norton 99 Twin. One of the issues we found was the fact one plug tended to foul, eventually with a lot of head scratching, re machined the "new" manifold to bias the carburator slightly was the answer, we surmised one cylinder was getting a richer charge than the other?. Later I had more success with a twin carb conversion, another story. (which Norton Copied?,😁Not true). Pete Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 16, 2022 Author Report Share Posted June 16, 2022 The best thing I’ve done today is to put my tools away and make a cup of tea. Colourtune in No 4 was a nice blue, as expected. No 1 was yellow and blue. No 2 (sooty) was mostly yellow and, subjectively, didn’t look to be firing as frequently/regularly as the other two. Screwing the jet nut appeared to have absolutely no affect upon combustion. I believe that the front carb choke mechanism has a (not exclusive) effect upon the issue. Often, but not always, I can push the jet a fraction upwards until it’s hard against the screw. I’ve played with the linkages and now it’s slightly better but I don’t think it’s right. Also, every few times that I twist the connecting rod (actuate the choke), the jet will stick open. I then reset the jet to exactly the same dimension as the rear carb and took it for a ride. It was approaching commuting hour so some slow moving traffic. Engine idle now sounds as rough as a badgers backside. The exhaust note sounds like a spitting V8. At 40 mph, light road load, it will misfire as though it is momentarily starved of fuel. If, however, I put my foot down it will go like a scalded cat, very brisk acceleration. I did my customary spark plug removal at the end of the 3-4 mile drive. No 4 looks as though it’s starting to clean after my tinkering but No 1 and No 2 both look as though they have done a shift down the coal mine. Is there anyone, commercial or willing privateer, within a reasonable distance of south Manchester with an intimate knowledge of SU carbs? Link to comment Share on other sites More sharing options...
Josef Posted June 16, 2022 Report Share Posted June 16, 2022 Is your jet Centred? Can you slacken the choke mechanism on number one to stop it influencing the carbs at all (after you start the car) and then re-test? You do sound like you’re getting somewhere with having found both cylinder 1 and 2 over rich. Link to comment Share on other sites More sharing options...
Wagger Posted June 16, 2022 Report Share Posted June 16, 2022 Do as Josef suggests. If no joy you google a tutorial on tuning SU's. You may discover that the front carb piston is sticking up. Clean the inside of the pot carefully. Before setting off next time, open the bonnet and shove the jets up to normal position. That is a similar suggestion to Josef. Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 16, 2022 Author Report Share Posted June 16, 2022 Thank you Joseph and Wagger. Yes, the jets are centred. I went through that pain a few years ago. Likewise, I don’t think that the piston is sticking but I’ll check and clean it. Don’t know if it’s relevant but just looked at the WSM IPL and noticed that there should be a ferrel/bush between the small screw and the choke bracket as it attaches to the jet. Both of my brackets waft around in the breeze. A bush may help to apply more upward force to keep jet hard against the nut. I’ll have another attempt to set the mixture on the front carb tomorrow. More and more thinking that the linkages between the two carbs is having an effect, too. I need to read the manual another hundred times before I understand what it’s saying. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 16, 2022 Report Share Posted June 16, 2022 some ideas on choke sticking its a Normal SU problem and can be solved with some manipulation some cut a few mm off the jet tube as they seem a bit too long makes sure (if you have one) the screw into the red jet base is not fully tightened it needs a bit of slack bend the levers and arms to align the way they travel so many get bent over the years and can need quite drastic bending and realigning they are a simple bit of kit and following a few guide lines dont need any dark art specialist we can spell out a lot on here but there are many clues in WSM or on Burlen website etc youve got this far abit of twiddling should not put you off colour tune yellow flashes suggests you have a control ring problem Link to comment Share on other sites More sharing options...
Badwolf Posted June 16, 2022 Report Share Posted June 16, 2022 I'm not sure if I understand why a single carb, working into two cylinders would give a sooty deposit on only one plug. When I had my problems it was both plugs, hence my enquiry about the ignition side. Surely the only other cylinder independent control are the valves. Link to comment Share on other sites More sharing options...
Wagger Posted June 16, 2022 Report Share Posted June 16, 2022 3 hours ago, PeteH said: Ok, Daft one here, BUT back in the 60`s, I, with the help of some very good friends in the Aircraft Industry (`nuff said) ported and devised a "Racing" conversion for a Norton 99 Twin. One of the issues we found was the fact one plug tended to foul, eventually with a lot of head scratching, re machined the "new" manifold to bias the carburator slightly was the answer, we surmised one cylinder was getting a richer charge than the other?. Later I had more success with a twin carb conversion, another story. (which Norton Copied?,😁Not true). Pete On the Triumph twins there was a thick 'Tufnol' block between manifold and carb. It was tapered to correct 'Bias' for the same purpose as PeteH's post. It also served to insulate the carb from the engine and prevent fuel evaporating. In the Winter I had to remove it or the throttle froze open in cold damp weather. I fitted twin carbs with a T100 GP manifold with no balance pipe treating each cylinder as a separate entity. That sorted mixture issues. Always fiddling with it though. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 16, 2022 Report Share Posted June 16, 2022 3 hours ago, 1969Mk3Spitfire said: Engine idle now sounds as rough as a badgers backside. The exhaust note sounds like a spitting V8. At 40 mph, light road load, it will misfire as though it is momentarily starved of fuel. If, however, I put my foot down it will go like a scalded cat, very brisk acceleration. How's the timing? I'm wondering if the timing is off, so as to give poor idling or low speeds, but on acceleration the advance kicks in and the spark improves. Just a thought. All this talk of modern vs original plugs has made me dig out an old set of pink Lodge plugs... Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 16, 2022 Author Report Share Posted June 16, 2022 18 minutes ago, Colin Lindsay said: How's the timing? I'm wondering if the timing is off, so as to give poor idling or low speeds, but on acceleration the advance kicks in and the spark improves. Just a thought. All this talk of modern vs original plugs has made me dig out an old set of pink Lodge plugs... The timing is one of the few things that I haven’t touched. I’m confident that it’s idling as rough as a badgers backside because I’ve now completely cocked-up the mixture on the front carb. Hopefully, I’ll be able to address this tomorrow to at least restore a decent idle. Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 16, 2022 Author Report Share Posted June 16, 2022 1 hour ago, Badwolf said: I'm not sure if I understand why a single carb, working into two cylinders would give a sooty deposit on only one plug. When I had my problems it was both plugs, hence my enquiry about the ignition side. Surely the only other cylinder independent control are the valves. That’s the nub of the problem. I’m not as yet understanding the relationship between valves, rings and incomplete combustion. Specifically, how to test without tearing down the engine. I’d hate it to be a wild goose chase. Pete L, you have me worried suggesting that yellow flashes signifying control ring issues. Can you please explain more…….is it possible to investigate to confirm? Link to comment Share on other sites More sharing options...
PeteH Posted June 16, 2022 Report Share Posted June 16, 2022 No 2 (sooty) was mostly yellow and, subjectively, didn’t look to be firing as frequently/regularly as the other two. Are you absolutely sure?. Because to me that would suggest ignition issue not fuel. Very many years ago I had a defective plug lead a new one it took weeks to track down because being new I ignored it. It might pay to compare the resistance of each lead and see if there is any issue?. Pete Link to comment Share on other sites More sharing options...
Badwolf Posted June 16, 2022 Report Share Posted June 16, 2022 Easier just two swop two leads over of suitable length. If that doesn't work swop two plugs over and see what, if anything happens. Don't assume that just because you have renewed something that you haven't got a duff replacement. Speaking of which just check out my leaf spring experience on my restoration thread if you really want paranoid!!! Link to comment Share on other sites More sharing options...
NonMember Posted June 16, 2022 Report Share Posted June 16, 2022 3 hours ago, Badwolf said: I'm not sure if I understand why a single carb, working into two cylinders would give a sooty deposit on only one plug. It can happen. The firing intervals for a twin-carb four cylinder mean that the two cylinders are not equally spaced. The one that sucks in first will get what's sat in the manifold, and the second gets what it pulls through the carb. This means the first cylinder tends to run richer than the second. Because the firing order on the Triumph engine is 1-3-4-2, the inner cylinders are the ones that get a richer mixture. The twin-port-injection on the last of the classic Minis needed some very careful setting up to minimise that effect and meet emissions limits. Link to comment Share on other sites More sharing options...
Badwolf Posted June 16, 2022 Report Share Posted June 16, 2022 N/M - Ahhh... And there's me thinking that I just put fuel in one end, turn the key and away you go!!! Sorry!! Thanks for the info. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 16, 2022 Report Share Posted June 16, 2022 G4074_Chart.pdf (gunson.co.uk) most of the clues here are like reading any fault charts all a bit vague so Yellow is rich sorry thats not how i remember the results but aged brain fog or whatever to me yellow was oil burning but its not given in the listing Pete Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 17, 2022 Author Report Share Posted June 17, 2022 9 hours ago, PeteH said: No 2 (sooty) was mostly yellow and, subjectively, didn’t look to be firing as frequently/regularly as the other two. Are you absolutely sure?. Because to me that would suggest ignition issue not fuel. Pete I have a 27 second iPhone video but no idea how to post it, if anyone can help? Link to comment Share on other sites More sharing options...
Josef Posted June 17, 2022 Report Share Posted June 17, 2022 35 minutes ago, 1969Mk3Spitfire said: I have a 27 second iPhone video but no idea how to post it, if anyone can help? Should just be a case of starting a new post while logged in to the forum on your phone and using the Add Files button at the bottom of the new post box. Though video has been hit and miss on here before now with it just not appearing for certain other people! Link to comment Share on other sites More sharing options...
PeteH Posted June 17, 2022 Report Share Posted June 17, 2022 42 minutes ago, 1969Mk3Spitfire said: I have a 27 second iPhone video but no idea how to post it, if anyone can help? Hi I posted one when I got the PAS working. I seem to remember it being just a case of treating it like a photo;, sent it from my phone to an E-Mail address (mine), save to file, on laptop, and literally just copy the clip and paste?. Drag and drop. just done, shortest one I could find:- Pete IMG_2238.MOV Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 17, 2022 Author Report Share Posted June 17, 2022 Try this……. Colourtune in cylinder No 2. IMG_2064.MOV Link to comment Share on other sites More sharing options...
Badwolf Posted June 17, 2022 Report Share Posted June 17, 2022 Vid works fine for me. Yes, it's very yellow in there. 1 Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 17, 2022 Author Report Share Posted June 17, 2022 17 hours ago, NonMember said: It can happen. The firing intervals for a twin-carb four cylinder mean that the two cylinders are not equally spaced. The one that sucks in first will get what's sat in the manifold, and the second gets what it pulls through the carb. This means the first cylinder tends to run richer than the second. Because the firing order on the Triumph engine is 1-3-4-2, the inner cylinders are the ones that get a richer mixture. The twin-port-injection on the last of the classic Minis needed some very careful setting up to minimise that effect and meet emissions limits. This was very motivating to read, thanks for the explanation! Link to comment Share on other sites More sharing options...
1969Mk3Spitfire Posted June 17, 2022 Author Report Share Posted June 17, 2022 Breaking news! I no longer have a sooty plug, thanks to you all for your perseverance with me. Started this morning by checking front carb float chamber and continued to strip and clean all carb components. The only anomaly was the choke mechanism. The lever was not exerting upward pressure to hold the jet tight against the nut, gravity was lowering the jet and richening the mixture. Very fiddly but I managed to remove the lever and change the bends to shorten it by 5mm. The IPL shows a small grommet/bush between the screw and the lever and these were missing so I made a couple using plastic servo control lines for model aeroplanes. The jet is now held in place by spring force. It’s not all good news. I took the car for a test drive along my usual 10 mile route. A couple of miles from home it started to misfire again. The miss was very slightly more prolonged, not instant recovery. It also developed a kangaroo in the tank but accelerating seemed to clear it. It felt more like fuel than electrical. Approaching home the misfire was quite bad and I was ready to throw in the towel. However, at home I pulled the plugs and was absolutely delighted with the colour of No1 and 2. There are a few threads about Pete’s slithers. Could this be a case? What’s the best way to clean/purge the fuel lines? Anything else to investigate? Nearly there! 2 Link to comment Share on other sites More sharing options...
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