Misfire after "Spirited" driving

[lusciousthelock]

My Humber Sceptre has been running really well of late which has caused me to push her a little bit more for fun. Can't really beat RWD action on a moist morning haha!  This however, has highlighted a problem. If I take a roundabout at speed I seem to suddenly experience a misfire and power loss which is quite scary on a duel carriageway roundabout, outside lane (inside of the roundabout) then having to limp over to the slow lane at 15mph. The same happened today, turning left rather quickly due to a change of lights and making the rear end slide a little bit (Yay! Sweeney style!). Everything fine, then 30yds after the junction I had to rumble on with what felt like 3 cylinders for about a mile and then it cleared itself.

Obviously the answer is to stop driving like a tit, but more seriously, how do I cure the problem? All leads seen tight and secure. I can't see it being a fuel problem, since I have twin carbs, so must have plenty of fuel in its bowl's to be able take a bend every now and again? the car drives fine with plenty of torque under normal circumstances. A friend suggested it may be the distributor throwing a wobbly as it does seem a little noisy, but surely it doesn't have anything that could move out of whack on a bend does it?

[shin2chin]

Could be some crud at the bottom of your tank getting disturbed when you're getting body roll? Might be worth giving it a flush and giving your fuel lines a blow out.

[composimmonite]

Are the oil pots on the carbs topped up ?

[lusciousthelock]

Yep, both carb's topped up. My fuel pump has the glass top so I can see there is plenty of fuel getting to the engine and it looks fairly clean, although I am going to look into the float bowls to check for debris. Reading something else on the interweb, my car is currently running an auto transmission but hopefully not for long. Could this cause the loss of power / misfire as I read somewhere that harsh driving can confuse the poor things? And if so what does it feel like, symptoms etc?

[ChasR]

I'd be tempt to look at the carbs and possibly the floats in them.

However, on the offchance I would look at any loose ignition items (are the leads loose, worn, touching other parts when cornering for example.

[composimmonite]

I assume the carbs are original strombergs and haven't been changed for SU's. They have a rubber diaphragm inside that can split.

[lusciousthelock]

What are the symptoms of split diaphragms? I haven't looked at those- buggers are bound to fall apart if I open the cover to look at them even if they are in good shape haha.

I suspected loose ignition, but everything seems tight although well played with. I'm thinking of buying one of those electric ignition kits with a new dizzy I spotted on ebay since the weird looking unit currently fitted has blinking lights, a hundred wires and no manual to tell me what's going on! I'll have a fiddle and a wiggle in the morning.

[composimmonite]

If in doubt change both of the diaphragms - new are around £5 the pair so not worth messing around with old items.

[taurus]

Anything with blinking lights is bound to go wrong. Seriously, back in the day when aftermarket elecky ignition kits came on the market the more blinking lights they had the more they broke down.

I used one of the Accuspark kits on my Viva, keep the original dizzy and just use one of their kits to replace the points. Cheap and very effective.

Split diaphragms usually cause lack of throttle response - I limped home a few times with an old crisp packet in there. I can't remember one every going so that it only showed on cornering, but then there's lots of things from those days I don't remember any more.

[baggabones]

sounds fuel related to me if it's only doing it in the bends? fuel starvation somehow? ...as said I'd check and clean/rebuild carbs, flush the tank and replace the lines

[elmotheewokking]

How much fuel is in the tank?
Take a right hand bend in the Dolly too fast with under a 1/4 tank of fuel in it and it starves the engine for a few seconds.

[ChasR]

My Escort does as well if it gets towards a 1/4 of a tank!

[lusciousthelock]

Tank was full to the top so its not that, but doesn't seem to make any difference how full the tank is. I checked the diaphragms, no spilts or tares but do seem a little aged so will replace soon as a precaution. I do need to top op the oil in the dashpot's again though. Strange as I only did it like 200 miles ago, where does the oil go?

[djefk]

To me it seems your carbs could use a rebuild with all-new gaskets, the oil should not disappear after only 200 miles. It's so cheap and easy to do if your follow the instructions / Haynes manual it will give you piece of mind at the very least.

The misfire is almost certainly connected to this in some way, imo.

[lusciousthelock]

Well, I had a wiggle of everything that may have came loose and only found one dodgy wire. It was the wire from the positive side of the battery to the starter solenoid. So being ready, armed with a 10mm spanner I tightened the nut. Flash!!! Ooo, better disconnect the battery first... Tightened the nut and thought I better go for a drive after topping up the dashpots again. Key in the ignition and... Nothing!

Checked all the fuses (all 3 of them) and now I can only assume I've blown the solenoid as everything else works.

[lusciousthelock]

So yeah, after a wiggle of everything, cant see too many problems so when I order a new solenoid I'll get a carb rebuild kit also.

[composimmonite]

In an emergency you can short out the solenoid connections (battery to solenoid and starter to solenoid) with an old screwdriver.
Some solenoids have a red button between the connections to allow "manual" operation - just press (hard) -


This type doesn't have a button -


I always prefer the red button type as useful for when working on the engine.

[kevralpina]

I would suggest if you drive the car like its meant to be driven upgrade to an electric pump manual pumps after a while cant keep up and with twin carbs will take a while to fill back up

[nomad]

I had fuel starvation probs for ages on mine finally traced the prob to a crud blockage where the hardline enters the tank (remove gland nut & pull out pipe - check no crud has snagged on the olive)
The pickup in tank is unfiltered, advise you fit a gauze strainer from a new car (and send me one as I need to do mine )

Twin carbs - as said, maybe stock pump is struggling to feed them.

Electric ignition is always good news.