Mack

Apologies about the scale of the video 😑 engine test.mp4

Update. The adapters bolted to the manifold with some countersunk allen headed bolts and the carbs then bolted to them. I have made up new gaskets for all four connections. I have added some pics to vaguely show the manifold adaptions already present. Unfortunely I didn't take one of the adapter plate! Also shown is the stub stack fitted. I think getting the manifold altered properly is the way forward in the future and they definitely need balancing and the cabling sorting out. Having got the carbs back on it seems to have sorted out the low power issue. It will idle off the choke pretty quickly, however when going to rev it, it will then stall. This seemed to clear itself quite quickly though. After a quick test drive it seemed mostly back to ''normal''. However there seems to be a distinct whistling sound coming from somewhere still. I presumed this to be the vacuum leak but now I am not sure, unless there is another one somewhere! I will try and post two videos to try and demonstrate it. It might just be my inexperience shining through and that might be normal?? At least it will be driveable to it's new garage and I can get properly stuck in!

Thanks for that Ian(and Iain) Looks to be a well engineered solution. The PO already fitted stubstacks so that's one job done already. I will definitely look into modifying the manifold further over winter, the current set up needs changing. The gasket material arrived so hopefully a new gasket will solve the problem temporarily. I will report back! Matt

Thanks Ian, further details would be appreciated. That is a very neat set up you have there. I have seen the isolators mentioned elsewhere, is their function to isolate the carb from heat from the manifold? The manifold on mine has indeed been modified so I am keen to stick with the SU's, especially as the car was running well previously. I plan on getting it on a rolling road at some point when this is all sorted to get a better idea of how they can be improved. The heat shield seems like a great idea! Matt

The aluminium section is the adapter plate. I feel it could be improved with some studs to give the correct number of mounting bolts for the SU's but for now I just plan on making sure it is sealing correctly.

Found a couple of pics on my phone. Filters removed here. I think the culprit is the adapter plate to manifold gasket. I plan to sort out a better throttle return spring setup and feel like the adapters could be improved.

Pete the filters are some quite tired K&N pancake filters. I gave them a good blow out with compressed air at work but they will need replacing. My first port of call is tracing the air leak. I have ordered some gasket material to make some new gaskets for the carb to inlet manifold junction as there is an adapter plate so twice the gaskets to go wrong! When I sprayed carb cleaner in this junction the revs changed so I am hoping this is the culprit. If not then I will go back to basics as advised by Iain. I haven't spoken with the PO since sorting the starting issue, he was as helpful as he could be on the phone when we were in on the way to Goodwood and advised about the initial float chamber problem. I will get back in touch if stopping the air leak doesn't sort it. Mark I also have a 6-3-1 manifold. I am going to start at the beginning with the carbs when the car is back in the garage. ( a couple of weeks from now when we move) so will check the balancing. I will take some pics on the weekend. Thanks all, Matt

A good thought Johny but I actually just put the originals on there. Matt

Evening all, Replaced the air filters this evening and started her up. Took a good five minutes to idle without the choke, where on previous times I have hardly had to use the choke at all. Took her for a brief drive up the road and again had no power, however when I pulled the choke out it drove almost normally. I assume this confirms the lean condition? I am hoping that it is simply the air leak that I found before but I have yet had a chance to check the timing. Matt

Thanks for the replies and advice. I changed the fuel filter, checked both float needles, which seemed fine. Removed air filters so I could see the barrels, both of which fell nicely when I lifted them but I topped up the dashpot oil regardless. Some of the hoses were not as snug as they could be so I tightened those up. Some of those will need replacing soon I imagine, which I will do at the same time as the fuel lines. The car started but wouldn't idol without the choke and would falter when trying to rev it. Let it idle for a bit on the choke and then it seemed a bit happier, sprayed some carb cleaner around the carb to manifold junction, where there is an adapter plate. The revs picked up! Hopefully found my air leak. Tightened up the mounting bolts as best I could. I will have find some replacement gaskets and fit them. Now seems to idle and rev quite happily but I haven't had the chance to take it for a test drive yet as I need to fiddle with the air filters. A bit annoying to have a problem so soon after buying the car but I have learnt a lot already! Cheers, Matt

Thank you both for your replies. I don't believe the cam is different to stock but I will have a good look through the history file and see what I can find. There is an inline filter before the pump, which I will change on Saturday as well. The hose from the pump to the first carb is rubber and then braided from there. I believe the carbs have been on there since the rebuild and the PO did multiple 10Countries runs and LeMans Classic runs since then so I imagine they are the correct needles. I will learn more when I rebuild the carbs over winter I guess! I will have a good look at adapter plates for the carbs and try and order some new seals. Cheers, Matt

Thanks Iain, I will check the wiring and connections. Maybe time for some new carb gaskets as well. I had planned to do a thorough service over winter but I am without a garage for another two weeks! I believe the engine is mostly standard, but the head and inlet manifold have been gas flowed. From the paperwork I have I believe the ignition is Pertronix Ignitor unit with a Flame thrower coil. Matt

Hello all, This is my first post so please bear with me. Apologies for the wall of text backstory but I thought I would put as much info as possible in case any of it was pertinent. 3 weeks ago I bought myself an early 40th present, a beautiful mk3 GT6 that had been well cared for but also well used. The engine was rebuilt in 2014. Converted to unleaded and is running on SU Hs6 1.75 carbs with electronic ignition on Lucas distributor and a Huco electric fuel pump. A bit of background to my problem. Picked up the car from the PO and drove it from Essex/Suffolk border home to Tunbridge Wells. No problems for about a week and then it refused to turn over in a supermarket car park. Walked home to pick up jump leads and my other car, only for it to start on it's own when I got back to it. Charged the battery. A couple days later drove it down to Goodwood Revival, started first time but after an hour or so it started to idle at 2000 rpm. Then after stopping for lunch, refused to start again. Had to push start it, now thinking there was an issue with the starter motor/ starter solenoid. Tried various things over the weekend to test if it was the starter or the solenoid but ended up having to push start it a few times to get us to and from Goodwood. During this time I also noticed that the carb float bowl on the carb closest to the pump was overflowing after I shut the engine off. Took the bowl cover off and jostled the float needle and it seemed to sort it. The car had the occasional hesitate and backfire out of the front carb when warming up but that would mostly stop on the short drive to Goodwood. The car then ran well on the hour and half drive back home. The next weekend I changed the battery for a new one having tested the starter out of the car. The car now starts ok but is idling quite roughly, with the carb backfire still present and what I can only describe as a hollow whistling coming from the engine. I opened the other float chamber and cleaned out gunk that was in the bottom. Warmed up the car, which was still idling roughly and tried to take it for a test drive. The car had no power and would try and cut out with the choke. Only just made it around the block. So, bearing in mind that I am pretty unexperienced and not done any of this before, this my current plan for Saturday: Take off and check both float needles and floats. Replace gaskets as one is damaged. Remove air filters and check the carb cylinders move freely, check Dash pot oil and top up if needed. Check for vacuum leaks(?) It seems the way to do this is with a small unlit propane torch waved around the hoses and carb/inlet junctions, is that correct? Check fuel flow from pump by taking the hose going to the carb off and directing it into an empty petrol can. (Petrol gauge currently reads 1/2 full) Check timing with timing light and I have an inline spark tester to check for spark to the plugs. Check the plugs. What else should I try? I will try and take a video if nothing I do helps initially. Also the PO said he usually ran it on E10 but I filled it up with 97 Ron E5, would this cause an issue with the timing? Any help would be greatly appreciated! Matt