hif44 misfire at 55mph cruising

[Steeeeeve]

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 with in front of the carb)

I'll probably try another fuel pump next, but seems to be running fine.

All to no avail. It runs like a bat out of Hell until 55mph then sputter sputter sputter until I let of 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???


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

Thanks in advance!!!

btw 1275cc engine.

[greyghost]

sound similar to an issue i had, turnout to be the fuel pump, for me anyway.
car was fine until you held a constant high speed, then it would get a miss. the pump was fine just couldn't deliver enough fuel for that constant speed.
not saying it is but i ended up doing what you have chasing my tail looking for the issue, until i changed that pump.

[wantafaster1]

Can you floor the throttle and rev it right out? What is the rest of your engine spec?

[Steeeeeve]

sound similar to an issue i had, turnout to be the fuel pump, for me anyway.
car was fine until you held a constant high speed, then it would get a miss. the pump was fine just couldn't deliver enough fuel for that constant speed.
not saying it is but i ended up doing what you have chasing my tail looking for the issue, until i changed that pump.

Greyghost. That's exactly what it's feeling like so I believe I'll try a new pump.
do you use a different type of pump or just replace a worn out with fresh?

also, Not sure of the specs exactly. I just bought the car. It's a 1275 with a header, and seems to have quite a few hop ups.
I also discovered I am running a BFY needle and am going to try a BDK. Along with a new pump.

Thanks for the input fellas!

[Steeeeeve]

Can you floor the throttle and rev it right out? What is the rest of your engine spec?

Yes it revs well. And pulls hard all the way up the gears until it seems to run out of gas after A few seconds of cruising at high Rpms.

[greyghost]

no i parked the SU pump on the shelf and used a new solid-state pump

[Steeeeeve]

Finally sorted it out.
It turns out i needed to advance my timing just a little more.
Instantly cured the problem.
Thought i'd post this in case anyone else is chasing the same problem.