Good call on the coil!  That's the next thing I'm trying with the Moke... I've borrowed the Pertronix Epoxy filled coil from my 66, as the Moke looks to have the stock unit from the original 850.  I converted to negative ground to try different fuel pumps and install a tachometer a couple months back, and the coil is about the only thing that hasn't been changed.  Top gear at (relatively) low revs is where a weak coil would indeed show it's hand, so I'll report back after the weekend and I've had a chance to try it....

I have always recommended the German "solid state" pump, but would caution it's use on significantly uprated 1275 or bigger engines based on my experience with my hot-rod Moke. The included sheet does say "up to 70 BHP" and the Moke was flat out "running out of gas" with maximum acceleration demand on it. Changing to the Mr Gasket pump HAS cured that issue, such that the current "fluttering" never results in rolling to a stop, but it sure would be nice to find the cure for what feels like a "governor" kicking in at highway speeds! 

BCE and BDK are richer than BFY,

BCE especially down lower rpm, and BDK at higher rpms (and needle station) altho you never get to all those stations on the thin end of the needle.

I personally tried my 1275 SU 44 with BDK,  really ran way rich, black plugs and soot on the bumper, but if leaning out at higher rpms maybe you need that.

somewhere (maybe still here) this website had a recommendation page for BCE - so I tried the BCE and it is perfect for me : driveability,  and good AF ratio .

look at this needle calculator , just click "all needles" , enter BFY as what you have, the BCE and BDK for comparison - when they get graphed and you can see the difference on the plot. Does not tell you what you need, but either are an improvement if you really are "running out of gas" because of the BDY.

www.mintylamb.co.uk/suneedle/

also, what about the condition (or choice of stiffness options) of the carb spring?

carb oil determines the speed of lift of the carb piston and hence needle station rate of change when you punch the throttle.  The spring helps stabilize fluctuations and helps determine steady state ultimate needle station. (Station means position along the length of the needle and its hence diameter at that point.) 

using my timing light my mark (i use a little white paint) doesn't jump around.

I just looked at my needle and it' a BFY.

I'm going to order a BDK unless someone thinks that's a terrible idea.  I do believe the engine is beyond stock judging by the work that's been done on the rest of the car.

thanks for the input fellas.

+1 to Dimitri's suggestion to check the timing consistency. If your dizzy's bushings are worn, the spark might be "scattering" and not producing combustion at the right time.

+1 to CupCake's damper oil suggestion - too thin an oil would allow the dashpot to lift, allowing too much air past the carb's bridge, resulting in a momentary lean condiion.

A longer shot: What about weak valve springs (or something similar) resulting in valve float and loss of good combustion?

Could be but I've tried two coils with zero change in the problem. 

Sounds more like a coil to me.....just because you have a new one doesn't mean its not an issue .  I've had them test out fine on a professional test bed but just be no good on the road.

Cheers, Ian

Thank you! I'll check my needle this weekend.  If I don't have the bdk I'll get one.   I'll also double check the dashpot.

HIF44 is a pretty good carb way better than HS models IMO. There are 2 issues you have not addressed. ....  damper oil and the needle. Make sure damper reservoir is full of oil and maybe use a thicker grade of oil. You could try running at full rich (adjustment screw all the way in) to see if there's any improvement but to me it seems you have a lean needle so look to see what you have. I high performance 1275 should have a bdk needle. A normal 1275 should have a bdl needle. If your carb came from a MG Metro the bej needle is pretty common which is too lean. 

Or I might dust off an old set of duel spridget su's and try them.

Thanks for the reply Jemal.

I don't know the specifics of the 1275.  It does have headers and I just discovered it has 7.5 inch brakes so someone put some effort into it before i got it.  

I believe that it has a high compression engine due to the second "H" in the ID plate???

I might have an extra fuel pump around i can stick inline and see what it does. 

It does have a bit of sediment in the fuel filter i can see when I shake it up. I've changed filters a few times and they never seem too clogged (but maybe they are and me blowing through them clears it out)

The car powers hard all the way up to 55mph then after just a few seconds of cruising its sputters. I would have to gues approx 3500rpm.

If my spare generic pump does any good I'll probably go with the $119.95 solid state pump.  And also the rubber.

I've been chasing just such a problem with the Moke I built.... I did go to a Mr Gasket fuel pump delivering 4-7 PSI over the "German metal body" SU alternative, which I found out is rated for "up to 70 BHP".   It's just as you describe.... Runs exceptionally well until you blast up to about 55 where it sputters and shudders and seems unable to pull it until you back off a bit and it catches it's breath.  Even then if I ask for power in 4th, it complains and backfires thru the carb as if too lean.  I've tried a BDK and a BBC needle, and just suspect that the HIF44 has a lean spot at very specific loads, and it so happens that the brick-shaped Moke is finding that spot at the RPM range of 55 in 4th.   I even installed a "Gross Jet" needle and seat to handle the extra fuel pressure.... careful because a standard "American" electric fuel pump at 4-7 psi will often overcome the SU needle and seat and dump raw gas into your oil sump, also known as your gearbox.

How is the state of tune of your 1275?  Would you say it is close to stock, or is it a "hot street engine"?  Do you know your final drive ratio, or at least the RPMs at say 55-65MPH?  You are welcome to call me if you want to talk about it!

thanks for the info.  I'm confident of the spark, but will recheck.

also it's a centrifugal dizzy.  and seems to be about right.  I don't have a tach right now. but the timing is about 12 at low rpms and about 30 at high.  Runs very strong until I hit highway speed.

My brain is leaning towards a weak fuel pump.  I have nothing to compare it to, but it's a slow dull sounding tick and it might not have the umph to push thru the fuel filter. although it does seem to push through while just pumping it into a gas can but it might be worth a try.

Just swapping needles is not a good approach. You need colortune or a gas analyzer or an oxygen sensor to get proper tuning of the carb.
You can also use your timing strobe to determine the quality of the spark. If the flashing light is rhythmic and consistent you've got good spark overall.

have you checked for vacuum leaks from the inlet to the dizzy?

Also.  I feel its still the carb that's causing the problem.  I'm just not sure if it's set up right.

The best I can describe it is that when i hit around 55 I lose two cylinders and when I back off they start runnng again.

Hey fellas.

My little mini is still misfiring at high speed.  Every time like clockwork and i'm about at my wits end.

I have rebuilt the carb and double checked the float level. Hif44 with K&N filter.

Replaced points with petronix electronic ignition.

Replaced cap rotor and wires

replaced coil with Flamethrower 40,000 volt coil

set the timing. played with it back and forth. it's a centrifugal advance distributor. 25D4 type.

Replaced the fuel filter.   (clear in front of the carb)

Pump seems to pump fine.

All to no avail. It runs like a bat out of Hell until 55mph then sputter sputter sputter until I let off the gas. Then is smooths out and I can drive at 40-50 as long a I like.  

I actually drove about 120 miles last weekend at 50mph no problems.  

So what next???

Is trying a thinner needle worth a try?

Give me some ideas pretty please! I'm losing it here!!!!

Thanks in advance!!!

btw 1275cc engine.