Intermittent/loss of power issue, CU engine

[Funkychops]

Hi all

Hoping for some words of wisdom

Intermittent loss of power from our '83 CU engined van. First time it did it was going 30mph ISH in 3rd. Noticed a loss of power, van started slowing down but power came back after a few miles. Van was warm and had been running for about an hour before, new fuel a bit before it happened.

Second time it did it was a few days later going up a steep hill. Van was warm, high rpm and started kangaroo hopping up the hill. Very down on power, just about made it to the top with foot flat in 1st gear, crawling along. Pulled over, nothing obvious, carried on and van was down a bit on hills but nothing as bad

Not done it since.

New(ish) fuel filter, rotor, dizzy cap. New fuel pump last year
Have checked connections, plugs, leads, coil (resistance check)
My next avenue is new ignition amp and hall sensor, but I'm stabbing in the dark a bit on those.
Carburettor is another option, been on the to do list for a while as there's an air leak on the idle cut off valve. Debris could be causing it I suppose?

Bit stumped. Any other ideas?

[hotpod]

You haven't mentioned air filter in your list of done things.

[Funkychops]

2L air-cooled

Checked the air filter, looks alright. Changed on last year's service, and I don't reckon there's enough dirt in there to cause a blockage

[Rosie n' Jim]

I had a similar problem when a fuel pipe began to break up. Small flakes of rubber got stuck in the float valve causing occasional blockage.

[hotpod]

I'm going back a long way to remember driving a 2l Aircooled. I had one with a single webber which was very lacklustre but with occasional bursts of epic-ness. I discovered it had air leaks one the various manifold rubber joiners. I fixed the leaks and that became my second favourite engine of all time. It was ace.
I am not sure how that would fit with your symptoms but an easy way to check for leaks is to spray wd40 around the joints with the engine running and the revs will pick up if it gets sucked into any gap.
I was going to suggest easy start instead of wd40 which would do the same thing (probably better) but I use it on motorcycles in the open air and am not sure how I'd feel doing it in an engine bay.

I think I am right in saying that the hall sensor either works or doesn't but I only have one currently on a fuel injected van so it might be different on a carb one. I'm sure the van wont object to you changing it anyway. They do appreciate new stuff.
 

[Funkychops]

Yeah, and I suspect the ignition amplifier is the same - being electronic, it would fail completely or work, not some weird in-between state

Have thoroughly checked for air leaks, but will try the WD40 approach to double check. As I said, there is a known air-leak on the idle cut-off valve, but the assumption I've made (perhaps wrongly) is that would only affect the engine at idle. Perhaps someone can advise otherwise?

Will bring my carb rebuild task forwards I think. Someone once told me; if you're certain its an ignition fault, its probably a fuel fault, and vice versa...

[Funkychops]

Update

Changed the ignition amp for one from GSF car parts and the van didn't start at all, so will be taking that back and sourcing one from somewhere else. I'd made the assumption they are all the same, perhaps not...

Took it out this morning and it was obviously down on power. No obvious misfiring, but gutless and lethargic

[tobydog]

I'd strip the carbs down and give them a good clean out.....

[Funkychops]

I'd strip the carbs down and give them a good clean out.....

Started my much postponed rebuild tonight. I have 2 spare sets of carbs that came with the van, so hoping to salvage something decent from those