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+--- Thread: Constant misfire ?????? (/showthread.php?tid=9472)
RE: Constant misfire ?????? - Steve Jones - 16-08-2024
After all sorts of different needles, Trials Chummy ended up with an EB needle (my Father's initials
)The only way to properly set up an SU and get the correct needle is via a rolling road session because all engines are slightly different. However, for a 1 1/8" SU, M (rich), EB (mid way), GG (weak) works well. Oil in the damper should be thin - SU do a specific damper oil but 3 in 1 works fine. Set the float height such that if you remove the dashpot and piston and then blow across the bridge, fuel should bubble up out of the jet (from JG, Malc. He knew his way around SUs as well as anybody I've ever known). However, unless you have some sort of air leak that forms once the engine heats up I still feel your issue is more likely electrical be it a condenser, coil or earthing problem.
Steve
RE: Constant misfire ?????? - Bluebird7 - 16-08-2024
Busy w/end, off to 750MC at Silverstone,
but will pop the SU off and check needle/jets/etc early next week.
RE: Constant misfire ?????? - Bluebird7 - 20-08-2024
Just had a thought !!!! Since I've virtually eliminated the issue being ignition ???
would/could running the car on E5 97 octane be the problem ?????
RE: Constant misfire ?????? - Reckless Rat - 20-08-2024
E5 is actually 98 octane, but to be honest a properly set up A7 engine will run on anything, chip fat, diesel, TVO, paraffin, melted wokerati (bit of an exaggeration but there's nothing wrong with a bit of diesel or paraffin in the petrol, it will run fine). Mine runs on E10 95 and has for years without any problems
RE: Constant misfire ?????? - Ivor Hawkins - 20-08-2024
Thumbs up from me on that Bruce, I’ve run mine in everything over the years…still trying to find the melted down wokerati though!
RE: Constant misfire ?????? - David Stepney - 21-08-2024
(20-08-2024, 09:56 PM)Ivor Hawkins Wrote: Thumbs up from me on that Bruce, I’ve run mine in everything over the years…still trying to find the melted down wokerati though!
Try your nearest local government office. Oh dear! They are all working (Woking?) from home.
RE: Constant misfire ?????? - Bluebird7 - 26-08-2024
Right Chaps, here's an update on my woes. Drained tank and fuel very clean for a 89 year old f/tank, no rust or water.
Stripped SU 1 1/8" carb and the best I can make out on the SU Needle is GC ????? which in the Burlen book is Morgan !!!!
So what needle would you chaps suggest and best place to buy ???
RE: Constant misfire ?????? - Alan - 26-08-2024
GC strikes me as way too rich. As an approximation try an AN, or what I’d really recommend is an hour on a rolling road with someone who understands SUs. But are you sure about GC. Could it not be GG which should be ok.
RE: Constant misfire ?????? - Bluebird7 - 26-08-2024
(26-08-2024, 04:27 PM)Alan Wrote: GC strikes me as way too rich. As an approximation try an AN, or what I’d really recommend is an hour on a rolling road with someone who understands SUs. But are you sure about GC. Could it not be GG which should be ok.
The plugs at present are sooty so yes I agree I'm too rich. EB has been mentioned and AK, but I'll try your suggestion too.
RE: Constant misfire ?????? - Ruairidh Dunford - 26-08-2024
Here are the three needles (mentioned above) compared on the Minty Lamb site: http://www.mintylamb.co.uk/suneedle/
Screenshot 2024-08-26 at 17.14.32.png (Size: 134.73 KB / Downloads: 83)