jc5515

Hi Paul, Thanks for that. I hadn't noticed that before. I have some new screws as the two fast idle screws were somewhat 'forced' in my the previous owner and are a bit bent. That being said, although the picture does not really show it the fast idle screws are backed off enough to clear the cam. As such they shouldn't be the cause of my sticking butterfly issue. Thanks, James

Thanks for the picture. I see now that your carb setup is different to mine. My understanding is that there are two types of HS4 throttle shaft setup. Yours, and then mine has large 'arm' which acts as a pivot to shut the butterfly using the spring on the cable bracket. I have added a picture to try and demonstrate what my setup is like. Since this issue only comes into play when the engine is hot and I cannot replicate it unless the engine is running and air is being drawn through the venturi I reckon it must be throttle bush wear. Even if it isn't enough for me to noticably measure it must be causing some friction when things expand.

Hi Rob, Interesting. Do you mind expanding on what spring you had put in the wrong position? Regardless, I will be sure to check mine. The only thing I have noticed is that I only have the two throttle return springs - the ones that run parallel to each other and attach to the funny U-shaped bracket that also holds the throttle cable. However, in some diagrams I have also seen a third spring added that attaches to the exhaust. My setup has never had this spring. 

Hi Rob, Thanks for the response. I did re-centre the butterflies when installing. I hold up the body to a light and check that there is a uniform slither of light around the butterfly. I then exercise the throttle shaft  to check it is seated properly once I have tightened down the split screws. I would agree with you regarding the throttle shafts. This was my first assumption. However, these are new-ish shafts (less than 200 miles) and I have also tried using some throttle shafts with o-rings in them. I found that the ones with o-rings added too much friction to the whole setup.  I understand that the bushings can wear in the throttle body too. However, I have done the standard tests of spraying something at the throttle linkage whilst it is running to check for an air leak etc. I have even tried to check for play and movement with more 'scientific' means (using a dial gauge indicator) but cannot detect anything that has raised alarm bells so far. Maybe, as you suggest, there is some roughness somewhere that I cannot detect but is adding some friction to they shafts. Is there any 'at-home' solution to this? Or do I need to send these carbs off for a re-bushing? Anyone have a good contact for who can do this in the UK? In the past I have been reluctant to send the SUs off for a complete restoration due to the cost (and I like doing these things myself). Thanks again for the thoughts. I will continue my investigations today! 

Good Evening All, I have finally got my Spitfire 1500 back on the road (perhaps the only good thing to come out of lockdown for me!) However, the SU HS4s are causing me a minor headache. When I press on the accelerator the rear carb's butterfly does not seem to close properly. I either have to blip the throttle or I have to manually push it closed. The amount it is open is small, but it raises the idle speed to about 2000 - 2200 revs unless closed. I have been experimenting over the last week to try and pinpoint the exact source of the issue and have identified the following: - The butterfly will only remain open if the engine has warmed up to temp. At first I thought that this was the linkage binding, but I have checked this and verified that it is free to move with enough of a gap in all directions not to expand and cause any issues. - I then thought the butterfly itself was at fault as in the past I have changed the butterflies to solid plates (opposed to the poppet type). I even went so far to remove the poppets from the previous plates, solder up the holes and re-install the old butterflies incase the new butterflies were not made correctly. I also checked, double checked and triple checked the butterflies were the right way around. - I checked that the throttle cable, choke cable and linkage were all functioning correctly and not holding the throttle open slightly. What I have now identified is that this phenomenon ONLY occurs when the engine is actually running. When it is off and hot I can exercise the rear carbs butterfly shaft freely and it always closes fully. It is almost as if the amount of airflow pouring into the carb creates just enough resistance to overpower the spring and not allow it to gently close. However, when you 'blip' the throttle it creates a more aggressive closing force that sometimes will shut the butterfly fully. The springs are new and I don't think they are the issue... I think the 'easy' option would be to just install stiffer springs. Maybe this issue will disappear if I re-install the air filters? I have had them off for my several experiments. I am not entirely sure which avenue to pursue now so any tips would be greatly appreciated!  Other than this small issue the carbs and engine run great!   

And another picture:

Good Evening All. I have been scratching my head about a couple of items recently and whilst I have done my best to research some results I thought I should ask the collective knowledge pool. I recently pulled the head from my Spitfire 1500 Engine which is actually a Dolomite engine but (as far as I know) is internally identical. The valves felt a little too wobbly in their guides so I have recently had new guides pressed in. Question 1 - On the inlet/exhaust face of the head there is a significant ridge which I can easily catch my fingernail on. It seems oddly large and straight as if it is a machining error or something? Is this something that I should try to eliminate but sanding it all down flat? Or even getting a shop to machine it smooth? I attach some pictures - although you can't really see the groove you can certainly see the line where it stands out (pointed via the pencil). I have another head kicking about (for a second engine I am rebuilding) and this doesn't appear on that head. Question 2 - the old valves in the new guides are still a little wobbly. Not a huge wobble, but definitely something I can feel what I pull the valve out slightly and wobble from the valve head. Is this something to be overly concerned about? I don't want to just throw money at a whole set of new valves just to find it is exactly the same. I have invested in micrometer and will be doing some checks on the sizes of the valves but just wanted to see peoples opinion on this. Any wisdom is always appreciated!

Good Evening everyone, Recently I have attempted to purge my cooling system of 20 years of crud and debris from my newly acquired Triumph Spitfire. All was kind of going to plan (well - for someone who has never done it before) and I really learnt a lot from the whole experience. However, as my temp gauge died one journey, I decided to inspect the sender and opened up the Thermostat Housing and to my surprise there wasn't a thermostat. I bought the mid-range one from Moss Motors and have just installed it and a new gasket as the old one was crumbling away. Just started her up to recirculate all the fluids and now the is a huge amount of leaks (pressurised spurts) from the housing. Now, I am just curious as to whether this would be an issue with the thermostat being installed OR is it my plumbing? I also don't really seem to be getting any hot air through the vents from the heating unit, despite having flushed and back flushed the heater matrix at great length and cleaning out literally every part of the system. I know that may seem daft, but I was hoping to do some cruising with the top down when we have a sunny autumnal day! In addition to this, there is an increasing amount of white smoke coming from the exhaust, which to my knowledge probably indicate water getting into the head. Or is this a completely different issue? Just for the record, the car is currently in Herts (near Welwyn Garden City) if anyone is local! Thanks guys!

As per usual, fantastic responses from everyone. Thank you so much for the information. I have a fair pit of work to do on the Spit, so I will follow the suggestions given and report back. Along with upgrading to Canleys trunnion-less conversion and SimonBBC electronic ignition... I think I have a fair bit to do! Thanks once again guys!

Guys, Thank you SO much for a quick reply - it has already put my mind at ease. esxefi - is there any particular method or feature to get rid of fuel vapour locking in the future? And is there a hard and fast way to get the rust in the pipes... or just... pull 'em apart and inspect? Thanks once again guys.

Good evening all, Yet again, after only a month and a bit of ownership - my 1500 has broken down for a third time. We were out on the roads and then she started to cut out - I determined it was probably a fuel problem since the fuel gauge seemed to be higher then than it was when I set off. So, and walking to a petrol station to get a jerry can, I topped her up with some super unleaded fuel and off we went. HOWEVER -  there is a brand new sound to the mix. A hideous rattle that seems to be stemming from the inside of the engine. Higher up (opposed to down in the bowels). I don't know much about the engine other than I am the first frequent user in about 20 odd years, it isn't converted to unleaded and it seems to leak oil here and there (but not at a scary rate). She seemed to struggle to idle and will rattle a bit and eventually cut out so I had planned to tidy up the carbs over this weekend, but now it doesn't seem so bad? Also... maybe totally unrelated, but normally, even before this, when I turned it off she would seem to shake violently to a stop. Sorry if these are all simple questions. I must admit... normally I would love this sort of thing. It would give me a project and a challenge to work on. But today... it got a little dangerous as I was in the middle of a cross road on a ring road in town. Luckily, it was quite busy and I was pushed to safety... but... it has... rattled me a little. To the extent where I just really wanted just to get to A to B (a 5 minute drive) without wasting my entire evening. Sorry... like I said... I am a bit rattled. I fear this will be an expensive fix, and if it is... I'm not sure how much of the road she is going to see this year.   Anyway... if anyone has any ideas as to where to start (I am a bit of a newbie at this) please please please let me know. Thanks in advance!

Hi guys, Thanks for all your responses. I went and checked the Amps between the positive terminal and lead and it wasn't drawing anything, so I changed the battery - which in the end seemed to be leaking? So after a large acid spillage (I don't recommend that) and installing another battery - it starts on the button! Now I am just swapping out the old style battery leads - the round ones with a screw hole in the top - to more modern clamp one and whilst I am at it I will clean up all the connections. Thanks again guys!

I posted this on a previous thread, and thought I would start a new one as I am eager to resolve this now the weather is getting nice! Last week I drove the Spitfire from A - B. When I came back to the car half an hour later she wouldn't start. Due to my work I had to call a local garage chap out as I didn't have the time to rustle around myself (and it was in a public car park) and he said it was an easy fix of tightening up a ground connection. Anyway, all was well until just now when I went to hop in (still very exciting for me) and exactly the same thing has happened. I turn the key and just a click, small bit of engine movement but then nothing! My little knowledge shows me that this is a battery issue, so I checked the voltage and it's just below 12V which I have heard is not ideal. Now I have the time to try and remedy this for myself I am eager to resolve it on my own. But where to start? I was going to disconnect the battery, clean all the points from it to the starter and go from there. Is this a wise or poor move? If so, any tips on how to clean the contacts adequately? Or any other suggestions as to how to resolve this problem? And sorry if this sounds daft and simple - I'm just a beginner so be gentle! Thanks in advance!