engine misfiring at motorway speeds intermittently

[ben50]

Hi, we're on the way to the ferry to France. The engine has started to misfiring. It started with just a bit of a blip, but as we travelled further it has increased in frequency. And lost power and the revs have dropped right off but I managed to rev through it.

Rather worried as we're catching the ferry in an hour. Any ideas?

Thanks in advance,
Ben

[CovKid]

Clogged fuel filter?

[ben50]

Thanks for the reply. Shouldn't be the fuel filters as they've both been replaced recently.
It's also recently had a new power spark distributor and coil, new rotor arm, dizzy cap, plugs and leads, a new electronic fuel pump, and relay, refurbished twin dellorto 40's and a new stainless exhaust.

I though that little lot would have prevented misfire! But such is life I guess :'(

We're In the queue for the ferry now, so I'll have to have a proper look tomorrow when we get off in France.

Properly stressed about two an a half weeks in France now though

[what2do]

I'm no scientist BUT how many vans have started playing up in France these past couple if weeks? Could they be xenophobic?

[California Dreamin]

Whilst this could be one of several things, my initial guess would be that the ignition leads are breaking down at the plug caps. quick and permanent fix is to cut off the metal shrouds on each of the four plug caps. This can be done without any detriment and can be left like this indefinitely....worth a try.


Martin

[ben50]

Thanks Martin, not quite sure what you mean though.
Is the plug shroud part of the ht lead? Or part of the spark plug? I removed the little screw tops from the spark plugs as the leads wouldn't fit with them on, could that be related? Although it's run with them removed on the previous sets of spark plugs, so probably not.

Cheers,
Ben

[California Dreamin]

Hi Ben.....no mate.....the spark plug caps (that push onto the spark plugs) have what looks like a tin shield around them, this needs cutting off....easier said than done as you will need some good side cutting plies to get them off.

The metal outter shields need cutting off......like these.




Martin

[toomanytoys]

If its got the correct leads on it, they don't have the metal covers..
Is all the tinware and all seals installed?? this is especially important when running higher performance carb and exhaust setup

What distributor are you using?? I suspect.. and 009, these have the wrong ignition curve for the type 4 and no 3 cyl is retarded also.. and what ignition timing setting was used?? Static at 7 degrees??

I presume the carbs etc were all set up on a rolling road after everything was installed????

[ben50]

Martin that sounds a bit drastic! I'm not sure it has the metal outers like that. I've now driven about 150 miles into France and so far I've only had three repeats of the misfire.

The distributor is a power spark svdc (iirc) it was rolling roaded after the carbs were fitted, then the same guy rest the timing and duel pressure after the exhaust and distributor and fuel pump were fitted.

The tin wear and seals are all ok, only there is a hole left that used to feed the air box from under the tinwear.

Only another 200 miles to go!

[California Dreamin]

I didn't see that you had a 2.0l CU so hasn't got these kinds of cap......lol.

Martin

[ben50]

Well, we managed to get to our destination. The engine kept up the intermittent misfire all the way. Once all set up at the campsite I swapped out the dizzy cap and roror arm with the spares I had on board and wound electrical tape around any suspect looking vacuum inlet pipes. On the day trips round and about the misfire hasn't reappeared. But the most we've driven has been under an hour just under the time the issue started to show on the way down.
Whilst looking around the engine bay I noticed that the hot air inlet is left open (it used to feed into the original airbox) does anyone know id I should block it off now I have the dellorto's fitted?



Thanks in advance

[CovKid]

At motorway speeds your carbs and pump are going through petrol like nobody's business. If they're not quite keeping pace it can cause issues like this. I suspect its more likely to be that - if its running fine at moderate speeds rather than ignition lead probs that can happen at almost any speed. How old is the pump?

And whats that canister with the rubber hose on? If its a fuel filter (and looks like it) - no way should it be in a hot engine bay. You only need one, just where pipe exits fuel tank underneath.

[ben50]

Thanks for the reply. Yeah thats a fuel filter there, tgechap that fitted the carbs added that. I did think at the time it was an odd place to fit a filter. Ill remove it when im back home I think. The fuel pumpis an electric one and only a couple of months old, there's also a fuel king pressure regulator which the carb guy set up too.
So ill leave the hot air feed as it is and drive back on rhe minor roads. Thanks again