Misfire help please

[montypsx]

Hi guys just got a misfire and a splutter that I can't get to the bottom of and I need help please. It's a 1641 twin port with twin 34icts and a 009 distributor and a cheap electronic ingnistion.. I thought it could be electrical as when I checked the spark I had a very week spark(at the cap) on cylinders 1 &3 when I pulled the leads 2 & 4 had a bright blue spark that cracked as the spark jumped back to the the cap and when pull the lead away the engine tried to stall but when I pulled 1 &3 the sparked was week,orange and made no noise at all and the tick over stayed the same. I've checked voltage to coil changed the cap and rotor arm, new leads and spark plug gone back to points and condenser, changed the coil and checked the tappits and now I've just changed the distributor but still no difference any ideas please! Answers on a post card and post to .......only joking. But please any ideas cheers Phil

 

[jonboylaw]

Did you try changing the dizzy cap ?


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[montypsx]

Yes pal I have

 

[gvee]

Checked the spark plug gaps?

 

[Zcat7]

When does the splutter/misfire occur?

One thing with the 34ICTs is that being single choke 1&3 suffer from "robbed vacuum" at tickover because of the firing order. Hence when you pull the plug lead off for those pistons you will notice hardly any difference in tickover as its only really firing on 2&4. I went through all this with my twin Solex 40s. The vacuum sorts itself out when you throttle up.

I wonder if this somehow affects the conductivity of the spark too. Maybe the lack of a decent air/fuel mix in the cylinder (which is what the robbed vacuum causes) means that the spark doesn't jump so well hence appears weak? No science behind my theory, just looking to explain the coincidence!
You could try revving the engine to see if the spark intensity improves...

 

[montypsx]

Thanks for the reply yes I've tried reving it the misfire improves masively but it's still there and the sparks no brighter. When it's on tick over it sounds lumpy if that makes any sense.