Seems like a misfire at mid range

Hi Guys, I have a 1800 twin carb type I engine. It has Perttronix electronic ignition. The car ticks over fine, is great under acceleration but seems to be retarded ignition at 30 - 40 miles an hour (around 1500 - 2000 revs) any ideas? Has a few backfires occasionally during slowdown in gear.

What are you doing driving around at 1500 to 2000 RPM? Going downhill coasting I hope!

I have the same issue in 3rd gear in town crusing at about 40 MPH...seems like a lean issue, a little bit like when you run out of gas... doesn't do it when you have the power on. Also pops a little if your down shifting and engine breaking.

Jay

Stephen,,
I too have the pertronix svda, and when my car developed a lower rpm's miss last year,, I found it was the rotor and distributor cap. So check them out and replace if it is time. For me, it was a quick fix.
cheers, Alan

What carbs are you running? Weber 40s and 44s will bog, sputter and backfire on deceleration if one of the so called idle jets is clogged. The idle jets actually are working through the mid range. If you are running dual throat Webers, and know the carbs, pull the idle jets and give them a cleaning, and pull the needles and blow out the circuits. Good luck.

Thanks guys, I did change the rotar arm and cap. It seemed to get better. I'd already cleaned the rotar arm and cap which led me to change them out as there was a little improvement. It's not gone completely though. I suspect the carbs as I left it for a month or so and I've always had problems with carbs. They're webber clones (don't know the make though) 1500-2000 revs is all you get driving in London, unless you just want the engine to race at 30-40mph.

Mine has the 1915cc w/dual carbs that came with the car from VS. I don't know who makes the carbs...will have to call Kirk and ask. It has the standard .009 distributer that came with it.
I now have 5000 miles on the car.
Had some noise from exhaust leaks...got that all tightend up.

The problem in 3rd at 40MPH is almost inperceptible...almost. and it pops a little when down shifting.

Figured it was a lean situation? and need to get info on tearing down the carbs.

Jay

Giday, Stephen. I had the exact symptoms near the end of the big trip earlier this year. Jack Crosby noticed my distributor clamp bolt was loose and thereby providing an intermittent ground. A quick fix by tightening the nut on the bolt. My distributor is a very tight fit in the block so the timing stayed put.

Thanks for the input guys. David, I'm going to look at that tomorrow. It sounds like it might be possible (easy fix if it is - wishful thinking !!)

Guess I committed a faux pas by trying to piggy back off of a simular question.

Thanks anyway

Got my answer from Kirk
Jay

Hi Guys, just to complete the loop. I took it to an aircooled engine guy and he found the idle jets were too small (50's in the carbs, should have been minimum 55's but 60's were better) Anyway, it's running so much better now.

Thats good news, Stephen!