weird... I just think electrical because I've had the same sort of thing, but if you've ruled it out then it's ruled out...



you should be able to confirm this by pulling the choke out a little while it's doing the misfire thing



yep, if the valve is stuck open a bit then the compression pushes back into the head...

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Ok, well tomorrow morning diagnostic drive to some flat and smooth roads. choke in and out.

I am sorry its not the coil.

Is your engine standard in all respects

Will the engine miss fire if you gently rev it and hold it at 3k or only when driving

the engine is a standard 1098. stamped 1015, which is from a leyland mini/leyland van.

don't be sorry mate, ill figure it out. i've basically traced the entire ignition system, i'm sure i can rule it out now. that just leaves two more systems:
fuel and mechanical.

problem only happens under load - seems electrical but a lean out could do the same.

my engine is pretty old now, worn. But I have a different needle i'm going to put in tomorrow morning and i'll take it for a swing. Ill give feedback tomorrow.

Stay posted.

Tried the other needle, but was nowhere near rich enough. I had to wind the jet down 42 flats before I even got close enough for a proper mixture, has any one experienced that before? My worn ADF needle wants to work at around 12-16 flats, but that ACB wants 42+. any thing above, and my plugs are white.

The ADF needle also has a slight bend in it. Could that alter the mixture that much?

Bought an ABP which I have researched is the standard needle for 1098 with single 1.5 SU, also ABJ looks ok, but has a richer top end.

I also consulted Vizard's book and he recommends an M1 needle, which is very close to an ABP needle through WinSU's database.

Going to put in the ABP and see what it has to say.

weird... http://www.morrismini.com/SUNeedlesV2.a ... &size=.090

edit: well... ABJ would be better if you do have a leaning out problem when cruising, because it's a bit richer than the others, then leans off at the top end

ACB is a bit leaner at idle and cruise, but not much

I'm just about to go and put my new needle in the drill and make it a bit richer in the cruise stations

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To check if it is a lean out just pull the choke out slightly when it does it see if it clears the problem.

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Why don't you try pulling the choke out Sorry couldn't resist

There is to much choke here will be flooding soon

was thinking about this one, did you check that the piston was free to move up and down after you installed it? sometimes the dashpot cover goes on a bit skew and jams the piston down... 42 flats is a looong way

also, any of the 1 or 2 letter (plus a number) needles are fixed needle type, the 3 letter needles are swinging. They aren't interchangeable without mods to the piston, not difficult mods, but still not a direct swap

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Hey yes i have tried to pull the choke out, I have a feeling at certain amount of choke, the problem does go away, I say that hesitantly because I'm never sure because of the bumpy roads. I also havent had a lot of time to take it onto smooth roads and try the choke trick.

Thanks for the info on carb needles, I am familiar with swing/fixed setups. I have only ever dealt with the swing type, A** needles. Had a 1.75" HS6 and it needed a BDL type for the larger jet.

I did a bit of research on standard needles for 1098cc engines, got a lot on ABP needle - which seems to be the standard (even according to SU book itself), ABJ is also common. so I bought one of the ABP.

Just about to put it in and do an initial tune, take it onto some smooth roads etc. will let you know how it goes! Fingers crossed!

Anybody near you got a portable air/fuel ratio meter? Makes it easy to see what's what under load.
Or, put it on a dyno, with their A/F meter hooked up.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi everyone, I'm pretty sure my problem is a leaning out, I'm running the car a bit richer and it seems to have gone away. I beleive my needle is slightly bent, causing it to be hard to pin down the problem. a bit of trial and error.

Thanks!

If the needle is bent then you should also change the jet. Given the fine tolerances it's hard to repair
This will most likely be your issue