Rich_s Posted March 2, 2014 Share Posted March 2, 2014 Having had problems with my car recently and in particular the carbs causing problems, i have thought i would try to fix one issue i have always had. The jet bearings in my carbs sit about 2mm lower than the carb body instead of almost flush, because of this (maybe) to get the mixture right the nut is wound out 5 turns on standard needle, it runs ok but i can only just get 39mpg driving slowly, and cruising at 55mph with careful acceleration.the car is standard and just had complete service and carb overhaul. found a picture which shows how the jets should sit, mine is nothing like this, could i have the wrong jet bearings fitted? Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 2, 2014 Share Posted March 2, 2014 Sounds like something is wrong, not sure what though. Are both carbs the same? Any sign of part # on the jet bearing?I'd guess you either have the wrong jet bearing fitted (as you say) OR something is stopping the bearing going fully home into the base of the carb. Quote Link to comment Share on other sites More sharing options...
Pete Lewis Posted March 2, 2014 Share Posted March 2, 2014 check if the needle is proud,not shoulder flush with the air piston if the needle is low then then normal adjustment could give a low 5 turns on the jet , check the jet is centralised and the choke does actually return the jet to touch the adjusting nut,Pete Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 2, 2014 Author Share Posted March 2, 2014 I remember a while back i took it apart and nothing stopping it going in any further, just seemed too short, will take it apart when get a chance and look for a part number.no idea on the needle Pete, which bit should i be checking against, sorry for daft question as never took that bit apart. as far as i know the needle is central and piston moves very freely. both needles sit the same height as well. yes the choke does return in fully as well and mixture is about right.thanksrich Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 2, 2014 Share Posted March 2, 2014 Is the choke fully returning? If the cable is not adjusted the control could go full in, but still have the jet lowered. Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 2, 2014 Author Share Posted March 2, 2014 Nope the jet is def going all the way back up, that was one of the issues recently, the rear carb one kept sticking open slightly giving me running problems.rich Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 2, 2014 Share Posted March 2, 2014 Is the link to the jet from the choke assembly correctly connected?Link correct:Link Wrong:Jet correct:Jet Wrong: Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 2, 2014 Author Share Posted March 2, 2014 Mine has been changed to the fixed jets (what a pain in the arse they are to fit! link rods are not a good design and bend over the float bowl bolt, on mine anyway) and the jet itself can go all the way up but to get it to run it has to be about 5 turns out, my get bearing though is about 2mm lower than in your pics at least, maybe more.thanksrich Quote Link to comment Share on other sites More sharing options...
lancepar Posted March 2, 2014 Share Posted March 2, 2014 How many flats on the jet nut are you lowering from when the jet is flush with the bridge - 12 is approx which is only 2 complete turns. 8) Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 2, 2014 Author Share Posted March 2, 2014 the jet itself doesnt quite go flush, but to get it to run properly and have the correct mixture it is currently at 31 flats or just over 5 turns down. Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 3, 2014 Share Posted March 3, 2014 ok, back to basics.We are talking 1500 1979 Spitfire yes?Do the carbs still have their ID tags? If so, what are the numbers?Have the bowls been changed? Different bowls sit at different heights, wrong bowls would mean the jet needed to be lower.Have the jet bearings been changed? (To your knowledge?) Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 3, 2014 Author Share Posted March 3, 2014 yes, 1979 spit 1500, they do have the tags but not got number to hand, as far as i know everything is completely std on them and the car does run ok, but tickover always been lumpy and seems to lack power compared to what i would expect.as far as i know the jet bearings have not been changed but they certainly dont look right, i'll get a photo of them asap and post on here so you can see what i mean, am just wondering if by swapping them for correct ones it will run better and smoother.thanksrich Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 3, 2014 Author Share Posted March 3, 2014 found a pic of someone elses carbs but looks the same as mine do, although mine may have a deeper recess but you get the idea: Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 3, 2014 Share Posted March 3, 2014 How odd.This is what my bearing looks like removed from the base of the carb: Quote Link to comment Share on other sites More sharing options...
Pit Pony Posted March 3, 2014 Share Posted March 3, 2014 I'm no expert but When I replaced my carbs my car would not run right and it turned out to be the needles. The symptoms were poor idling and.lack of power. New needles did the trick, bought the carbs from Andrew Turner and he sent me some different needles, Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 15, 2014 Author Share Posted March 15, 2014 Finally got time to get the carbs off this weekend so 2moro morning i'll remove one of them and measure the jet bearing to see if that is the problem, thought i would also check what needle i have as well, how does the needle come out, is it just undo the screw and slide out through the top?the carbs are, i think, FZX1327 which looks like the needles do come out through the top but never removed them so not sure...thanksrich Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 15, 2014 Share Posted March 15, 2014 Hi Rich,Unless your carbs are assembled with the wrong parts, the only way I can assemble the carb to give the jet bearing the wrong position is if I don't screw the jet bearing retaining "nut" in all the way - be sure the top nut is screwed all the way up and the you aren't accidentally turning both or the upper one when you adjust the carbs.FZX1327 is the part number for a pair of carbs, each individual carb should have a tag on the float bowl (on one of the 3 retaining bolts) with something like FZX1122 F/R (front or rear) (as seen http://www.canleyclassics.com/?xhtml=xhtml/diagram/spitfire1500carburettorandlinkagetwincarbengine.html&xhtmlcatalogue=xhtml/catalogue/spitfire1500.html&category=fuelandexhaust&xsl=diagram.xsl )Let us know how you get on!Cheers, Sam Quote Link to comment Share on other sites More sharing options...
yorkshire_spam Posted March 15, 2014 Share Posted March 15, 2014 Needle comes out - unscrew 3 retaining bolts on each dashpot, remove damper piston, lift dashpot up vertically. Then removing the dashpot piston should give you the needle. Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 15, 2014 Author Share Posted March 15, 2014 My guess is they are the wrong parts for some reason, will soon find out!As far as can remember the front one is fzx1327f and the rear is fzx1327r, will find out when they come off 2moro morning.thanksrich Quote Link to comment Share on other sites More sharing options...
Pete Lee Posted March 15, 2014 Share Posted March 15, 2014 Hi Rich, just reading this thread as I have been rebuilding my spare carbs for fitting tomorrow. I am not sure you have a problem with the jet bearing. On my older set of carbs the jet bearing is the same as yours, on the newer set the bearing is flush.The newer carbs are original for my 1979 Spitfire, the older set are from a 1977 Spitfire I had as a spares car. One set are FXZ1122 and the other set are FZX1258. I think these had different bearings so shouldn't cause a problem. I also had the non waxstat conversion, but after a layup they had started sticking so I will be trying the waxstat jets but with the wax pellet removed and replaced with washers. Quote Link to comment Share on other sites More sharing options...
WIMPUS Posted March 15, 2014 Share Posted March 15, 2014 Rich, From what year is your spit ? On mine from 1978 i have also FZX series carbs (don't know what number, need to look). Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 16, 2014 Author Share Posted March 16, 2014 The car does run ok but dont seem as powerful as i thought it would and it does seem a bit flat below about 2.5k revs the main issue is mpg, it is averaging about 39mpg being driven as sensibly as i can and cruising about 50/55mph so am in a quest to try and make sure its as good as it can be from a std engine but with electronic iginition. the jet itself is currently at just over 5 turns out just to get it to run although the mixture is about right so just making sure the carbs are all std and bits are correct.Wim, its a 79.rich Quote Link to comment Share on other sites More sharing options...
Pete Lee Posted March 16, 2014 Share Posted March 16, 2014 From my experience 39mpg does not sound that bad. Back in the late 70's and early 80's I used to get 29 to 30 mpg from my MKIV and MKIII, I average 34 to 36 mpg now, that's on a 45mile run to work with overdrive. I think I can remember getting over 40 mpg once, this would have been on one occasion with the MKIV when touring abroad on a long run.If the mixture looks good, the spark plugs are a good colour then the mixture should be correct. Other factors are tyres and type pressure and timing. The height of the jet bearing won't affect the mixture although I am thinking it may affect the turbulence in the carburettor. Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 16, 2014 Author Share Posted March 16, 2014 The mixture seems to be fine, tyre pressures are at 28 all round which seems to give even tyre wear, timing is spot on, plugs and filters brand new, rest is all std stuff. was just hoping to get a bit more mpg out of it if possible, if not then so be it but if a few bits arent right and causing problems then would prefer to change them.my only wonder is why it needs more than twice the amount of turns to get a decent mixture out of it, did think the lower height of bearing is upsetting air flow so petrol isnt being sucked in properly, or someone has put in the wrong needles, important things first though - finish me brew then off outside to get working.thanksrich Quote Link to comment Share on other sites More sharing options...
Rich_s Posted March 16, 2014 Author Share Posted March 16, 2014 Been out and took them apart and got some more pics which show a bit more, first one is how it looks now inside the carb, 2nd is from the outside to show how they are fitted, 3rd one is the jet bearing removed, guessing it shouldnt have those grooves in it heheheheheh, 4th one is a diagram of sizes so looks like its 2.5mm short and final one is another issue i found, the front carb has a bit of plastic sticking out the end of the piston stopping it going all the way to the bottom, what on earth is this as cant see how to remove as it just spins round, any ideas? Quote Link to comment Share on other sites More sharing options...
.thumb.jpeg.b15b81ef10abeea1c3039ae03c4a9f3a.jpeg)
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.