Engine lurching problem

[Smcknighty]

Or you have a dodgy fuel gauge?

[CovKid]

Whatever the cause, it does sound like you're running out of petrol then. Perhaps fuel line and pump deliver enough for it to tick over (just) but float chamber rapidly drops once you put your foot down until it runs out altogether. You should see a healthy squirt of fuel if turning the engine over with pump outlet hose put in an empty jam jar. Usual culprits are too short a pushrod, ineffective pump (new or not), insecure fuel line, tank virtually empty, clogged filter, blocked jet. Must admit I went electric as I had no end of problems like that but as you've fitted a new pump, check what its actually delivering.

Its not unusual for fuel to run back to tank overnight but I'm wondering if when you start and set off, its running wholly on what was left in float chamber and once that runs out, it dies because the pump isn't (for whatever reason) able to fill it up again or at least fast enough. 500 metres (or less) would sound about right for a carb that has run dry.

[Santa79]

So.
I got it running really well on idle after a lot of parts changed.... Took it out, and ran out of fuel! Turns out that my fuel gauge reads half full when there's nothing in it!
Anyway, I got it back, put 20 litres in there and got it running again A quick 5 mile test run last night and it was all good!

So we went out in it tonight, just to make sure (and fill up with petrol)... And it cuts out again when moving! It idles fine though. It seems to just lose power when the engine is under very little load (ie. constant speed at low ish revs. 50mph in 5th, for example). Once it starts going again, with my foot still on the accelerator pedal and clutch in, the engine almost surges. It revs up and down for a few seconds then it's ok. The really weird thing is that for a few minutes, it will be fine, then it happens again!

Did I buy a duff fuel pump??! Or could it just be crud from the tank getting in the carb from running out of fuel?

Also, when it sits at about 2000 revs when warm, there is an occasional (very slight) blowback from the exhaust...
I REALLY need this to be fixed this week, or I shall lose our Big Bang tickets!


Any advice here would be greatly appreciated!

[CovKid]

Whatever the cause, it does sound like you're running out of petrol then.

A failing ignition lead can cause that hesitation or random power loss. Had it in the past where I've struggled to find cause and it was simply the ignition leads breaking down.

Try cleaning the hidden cone filter inside the carb fuel inlet - that can crud up and starve the engine of fuel at certain throttle openings - as can muck in the float bowl.

Make sure dizzy vacuum works.

[Santa79]

The ignition lead gave the RAC man a belt when he checked it last week... So I think that is ok.
I checked the cone filter too. That was fine.

How do I check the float bowl? I can't find that in my "trusty" Haynes manual!
And how do I check the dizzy vacuum? I assume I remove the vac pipe from carb to the dizzy at the carb end, give it a good suck and blow, and make sure therer are no air leaks?

[Santa79]

Well the dizzy vac is fine. I couldn't such anything through the hose.

All the ignition leads are pretty new (as is the dizzy and the cap by the looks of things). So I am officially at a loss now. I can't think of anything else apart from me messing something up from running it dry. It's just really weird how it is fine, then this, then fine again.

[CovKid]

There may be muck in the float bowl (you have to remove top of carb to check) but intermittent probs are certainly difficult to crack. You'll need to remove distributor cap when checking vac. The plate inside should move noticeably when you suck on the pipe.

I'm tempted to say thoroughly clean and fit a new carb kit but time is not on your side here. Whats your fuel filter like?

Perhaps a good run will help things.

[Santa79]

I just went out to look at the fuel filter before I read your post haha! It is new (I fitted it 2 weeks ago) and is still very clean. I was half hoping to find it clogged up, at least I would know what the problem is then!

I gave it a blast with carb cleaner yesterday before I took it out and it was great for about 5 miles. Then today it was "pooh" again. Although, while running at higher revs (4th instead of 5th gear at 50mph), it was ok. So I am definitely thinking I take it out for a good hour tomorrow with loads of redex in the half tank of petrol and a good spray of carb cleaner first....

[Santa79]

Just did the vac test properly (with the dizzy cap off) and the little black part inside moves and it stays where it is when I block the pipe with my tongue....

So I guess it must just be a problem from running out of fuel.

[tobydog]

Strip the carb down and clean all the jets. If it runs while on choke and cuts out when warmed up it sounds like fuel and not usual electrical problems. I've had an ignition amplifier start to fail after warming up, once that happens it's terminal.

2p worth.

[Santa79]

Blimey... Another 20 quid to replace!

[what2do]

This is something that I read elsewhere, thus I can't vouch for the validity of it; your symptoms are similar to another van, they too replaced loads of bits including fuel line and filter. It turned out that there was a blockage in the pipe upstream if the filter next to the tank. Pity you've just filled it up otherwise you could poke some wire up in the direction of the tank and see if you feel any resistance.

Hope your plans for the week end won't be spoiled by this. Good luck.

[NicBeeee]

How do I check the float bowl? I can't find that in my "trusty" Haynes manual!

As Covkid said I would be looking at dirt in the float chamber, I had almost identical issues a couple of years back and after a quick blast with compressed air in the float chamber all was fine, the float chamber is below the domed mesh at the top left (as you look at the carb from the rear) of the top of the carb. Give it a blast if you can but be careful with the spraying fuel so hold a rag over the carb when doing it. When I came around to stripping and cleaning the carb I found some crystals in the float chamber that must have been swilling around and occasionally they must have blocked the fuel outlet. Hope its that simple for you

[CovKid]

Its also not unknown when running dry to end up with water in the bottom of the float chamber and grit, despite the filter on the line. Its like crumbs in a bed.

[Santa79]

Thanks for that gents...
I shall have a look at that after work tonight. Here's hoping, eh?!