440 hesitation and backfire

ANTON · Post by **ANTON** » Sun Sep 13, 15 10:23 am

Sounds like there is a split in the dizzy van can. Try sucking on it and if it doesn't advance the chances are it's split. Block it off till you replace the vac can.

Hemimad · Post by **Hemimad** » Sun Sep 13, 15 5:20 pm

I've put a vacuum gauge between the carb and dizzy, it's reading 0.8 INS/hg at idle, I took off the gauge and put my finger over the open pipe and there is hardly anything. Checking around the carb base, cannot detect any leaks. Could it still be a problem with the carb, it still seems rich?

Hemimad · Post by **Hemimad** » Sun Sep 13, 15 5:26 pm

Oh and dizzy can is ok, sucking on it showed it was fine.

Blue · Post by **Blue** » Sun Sep 13, 15 7:22 pm

Timing is the first thing that comes to mind, whats the initial & total with the vac disconnected? What does the initial go up to when you reconnect the vac?

morgan · Post by **morgan** » Mon Sep 14, 15 8:16 am

Hemimad wrote:Carb repaired with new needles. Fired up but still with hesitation, pull off the vacuum and it settles down, put it back on and it starts acting up and won't Rev without fluffing and mostly cutting out, similar to the way Morgan describes. It has a new MP electronic ignition fitted only a few hundred miles ago, is it a simple fix, other than blocking the vacuum off?

We put it down to either faulty vac can or faulty 'spring rate' (for want of a better term) on the vac adv part of the dizzy; i.e. it lets the vac advance it far too easily.

I gave up - blocked it off, played with the advance curves, settled on stock curve, no vac, 14-16deg initial. I might go back to it. But I will say mine was a brand new dizzy/ignition system - it had never been used, so was unproven. What you describe is something that was working then started playing up ? Which seems odd.

shovelheadrob · Post by **shovelheadrob** » Mon Sep 14, 15 9:06 am

Where are you taking the vacuum source from? It will make a difference. But as I'm getting old & senile & it's years since I've run with it I honestly can't remember which is best. I'm sure Blue or Dave can explain!

Hemimad · Post by **Hemimad** » Fri Sep 25, 15 6:53 pm

I hope I'm not jinxing myself but I've got to the bottom of the problem and it might be of help to others who have a similar problem. With everyone's help and suggestions, I went through all the checks and also went through the carb again, still with the same results. The car would run with the vac off, put it on and it started spitting, running rough and would die if you were too direct with the throttle. Decided that it must be the dizzy or the vac canister causing the problem, still had my old points dizzy to look at and whilst measuring the vacuum action on both old and new my Dad noticed something odd about the behaviour of the lower terminal, when the vacuum was drawn the wire would move slightly. On closer inspection the solder looked like a claw around the tab with a rubber insulant material holding it in place, when the vacuum was activated the wire started to pull away from the tab causing an intermitant fault. Soldered the wire back on, car runs a treat again vac on or off, might be worth checking as all appeared ok from a visual check, a simple fix of poor quality control....

Thanks to everyone who helped and advised along the way.😀

Charger · Post by **Charger** » Sat Sep 26, 15 11:23 pm

looks like a result

hope it's sorted it

good spot

Dave999 · Post by **Dave999** » Mon Sep 28, 15 9:11 am

missed second page of thread

oops

Dave

Steve · Post by **Steve** » Fri Oct 02, 15 7:17 pm

Well sorted and good to know the symptoms and the cure! Cheers