johny Posted July 17 Report Share Posted July 17 Looks like item 25 is a waxstat jet and 24 a normal one. As explained above you can convert waxstat to non waxstat without having to buy the expensive conversion. This is by replacing the waxstat capsule (a small cylinder that expands with rising temperature to move the jet and make the mixture weaker) with similar sized coins so there is no longer any movement with temperature change. This mean you still set the mixture as normal but after that there will be no more change to it from the waxstats which can be unreliable... Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 17 Report Share Posted July 17 yes ust look under the carbs the jet is very visible agree with jonny 25 is wax stat 24 is normal jet Doug's picture is of a normal jet this is a waxstat has a larger body on the jet base Link to comment Share on other sites More sharing options...
Carba1984 Posted July 17 Author Report Share Posted July 17 My carburetters are number 24, I have an air intake between the exhaust manifold and the first exhaust section, could that affect the unstable idling? The gasket Is the problem Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 17 Report Share Posted July 17 i dont see the exhaust gasket upsetting the variation in idle use engine oil in the dashpots i would think the mixture is just set too rich the jet sits against the adjusting nut , screw it upwards will weaken the jet setting do 1/2 turn at a time and test Link to comment Share on other sites More sharing options...
Carba1984 Posted July 17 Author Report Share Posted July 17 I am testing every day with a half turn of each nut, I use engine oil in the dashpots, I have disassembled the carburetters and I have seen that by activating the nut they do not go up and down the jet jets perfectly, maybe I do not have them centred? Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 18 Report Share Posted July 18 the awful linkages on SU can bind up jet movement some find the flexi tube is jamming and cur 3mm off its end to ease movement if you pull and return the choke then give the red part of the jet a poke with a finger if it jumps up to the nut then the linkage is the problem, there is nothing in the jet holder its a plain tube . its all down to the awful SU levers and links pete Link to comment Share on other sites More sharing options...
Carba1984 Posted July 18 Author Report Share Posted July 18 I'll check this. Regarding the issue of idling, I find it strange that I have the mixture too rich and I drop the idling when I stop, this seems more mixture too poor although I also doubt it, I will check the colour of spark spints Link to comment Share on other sites More sharing options...
Mjit Posted July 18 Report Share Posted July 18 7 minutes ago, Carba1984 said: Regarding the issue of idling, I find it strange that I have the mixture too rich and I drop the idling when I stop, this seems more mixture too poor... Think about it, if the car's up to temperature and idling fine and you yank out the choke what happens? Generally it will run very badly, then stall. That's an extream example of course but being over-rich doesn't mean "it will run, just not as efficiently as a perfect mixture". 13 hours ago, Carba1984 said: I am testing every day with a half turn of each nut... I take it you mean "half a flat", so 30˚ rather than "half a rotation"/180˚? "half a flat" is normal, "half a rotation" is a huge change Link to comment Share on other sites More sharing options...
Carba1984 Posted July 18 Author Report Share Posted July 18 (edited) Half a flat, but I've tried whit half a rotation, I'll start checking everything when I have time, I've asked if anyone knew exactly what could happen when the revolutions fall suddenly when they stop, Rich? Poor? Both? other problem? Edited July 18 by Carba1984 Link to comment Share on other sites More sharing options...
johny Posted July 18 Report Share Posted July 18 On a hot engine in hot conditions the mixture tends to go rich at idle because the air temperature gets higher (reason for hoses on air box to pull in coolest air possible) so less dense so less oxygen so too much fuel.... This can also cause hot restart problems☹️ Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 18 Report Share Posted July 18 have a look under the body for a piston lifting pin ( later carbs did not have these ) but this is a touchy feely light finger job. you lightly lift the sprung pin to just touch the piston inside. raise it a small 2mm lift if the idle has a small rise its rich if nothing its about right if there is a small falter its weak you are trying for a small change maybe onlly a 50 rpm change , yank the pin up and it will just stall this is a a bit of a faf but it works just dont expect a wild change in running ...small changes only we need to know the jets do return to the nut and there is no sticking going on Pete Link to comment Share on other sites More sharing options...
cliff.b Posted July 20 Report Share Posted July 20 On 14/07/2024 at 12:27, dannyb said: My 1500 spit is set at 17 deg btdc. This was done on a rolling road. With today's petrol 10 deg is not enough. Danny Interesting, as after a bit of experimentation myself I settled on 17 deg BTDC for my 1500 Spit. Seems to run well at that using premium petrol. Link to comment Share on other sites More sharing options...
daverclasper Posted July 20 Report Share Posted July 20 On 18/07/2024 at 10:47, johny said: On a hot engine in hot conditions the mixture tends to go rich at idle because the air temperature gets higher (reason for hoses on air box to pull in coolest air possible) so less dense so less oxygen so too much fuel.... This can also cause hot restart problems☹️ That's what I have always assumed can make it run rough/harder to start, though I did read that any fuel vaporisation, will/can?, introduce air that makes the mixture weak? Link to comment Share on other sites More sharing options...
johny Posted July 20 Report Share Posted July 20 Fuel vaporisation is possible but it has to get pretty warm and once fuel is flowing much less likely especially on the discharge side of the pump as thats under pressure. As soon as the pump starts any vaporised fuel pockets (including carb float chambers) will be pushed through by fresh cool fuel and out of the carb vents. I suppose if theres a lot you might then get starting problems because of the fuel vapour collecting in the air filter box being sucked into the engine... Link to comment Share on other sites More sharing options...
Peter Truman Posted July 20 Report Share Posted July 20 If your talking vaporization here's one from left field, I had an unusual case which took me several weeks to analyze on the daughters Mk2 Spit with SU carbs, the float chamber on the rear carb had come loose and had swung round near the exhaust manifold causing the fuel vaporisation, the cause was the plastic bush which keeps the float chamber vertical and is located in the main carb body (with the one bolt thro it into the chamber) had failed allowing the float chamber to rotate. The front carb plastic bush was also starting to fail, both only a 10min fix. Link to comment Share on other sites More sharing options...
Carba1984 Posted July 20 Author Report Share Posted July 20 I like to learn with you guys, let's see if I'm able to find the unstable idling failure, tomorrow I'm going to lower two faces to the nut (poor), let's see what happens Link to comment Share on other sites More sharing options...
johny Posted July 21 Report Share Posted July 21 And some people call this fun😁 Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 21 Report Share Posted July 21 think you need to screw the nut up upwards to weaken unscrew will richen and the unstable idle sounds more on the rich side than the weak side but turn it to see what it does , set it to give the fastest idle Pete Link to comment Share on other sites More sharing options...
Carba1984 Posted July 21 Author Report Share Posted July 21 Today I have ¿impoverished? I don’t know the word in English 😂 the two-sided nut mixture, I have a firecracker when I stop accelerating (pops in the exhaust pipe) do you know if that is caused by rich mixture or poor mixture? I have also noticed that when the car heats up with many kms it no longer turns off when I stop but I still have an unstable idle, I really don't know if I need to impoverish or enrich to fix the unstable idling. Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 21 Report Share Posted July 21 have you found the piston lifters (small sprung pin) just under the main body ??? Pete Link to comment Share on other sites More sharing options...
johny Posted July 21 Report Share Posted July 21 1 hour ago, Carba1984 said: Today I have ¿impoverished? I don’t know the word in English 😂 the two-sided nut mixture, I have a firecracker when I stop accelerating (pops in the exhaust pipe) do you know if that is caused by rich mixture or poor mixture? I have also noticed that when the car heats up with many kms it no longer turns off when I stop but I still have an unstable idle, I really don't know if I need to impoverish or enrich to fix the unstable idling. You mean 'weakened' the mixture and it sounds like its now too weak which will cause backfiring and engine run on... 1 Link to comment Share on other sites More sharing options...
Carba1984 Posted July 21 Author Report Share Posted July 21 Yes, I have already tried them, the car does not make variation when I lift a few millimetres Link to comment Share on other sites More sharing options...
Carba1984 Posted July 21 Author Report Share Posted July 21 4 minutes ago, johny said: You mean 'weakened' the mixture and it sounds like its now too weak which will cause backfiring and engine run on... Maybe the guide does not go up and down correctly when I activate the nut of the mixture, maybe I have to centre it so that it goes up and down correctly Link to comment Share on other sites More sharing options...
johny Posted July 21 Report Share Posted July 21 well it seems that the adjustment you made has certainly worked so I think the mechanisms must be working quite well.... Link to comment Share on other sites More sharing options...
Carba1984 Posted July 21 Author Report Share Posted July 21 7 minutes ago, johny said: well it seems that the adjustment you made has certainly worked so I think the mechanisms must be working quite well.... If I keep raising the piston up, there is a carburetter that wants to drown before the other, but by putting them up a lot Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now