zenith carb problem (?)

Doug

Doug

Member
Hi all
we have a '74 minibus wigh standard 1725 engine and original zenith carb.
Just recently a fault has developed where when i put my foot down on the accellerator, the engine stalls for just a bit, maybe half a second, then picks up again just fine. It does ghis quite reliably when hot or cold. The only cure seems to be to pull ths choke fully out (even when hot) which of course isnt't good.
it wasnt always like that: he ran really well until about a week ago when this started happening.

I gather the zenith is the type which squirts a bit of fuel as you squidge the accellerator, so guessing it could be to do with that- perhaps its not happening.

I'm not yet familiar with these carbs, so :
* does my diagnosis seem ok?
* commonproblem? is there an easy fix?
Thanks in advance. any advice gratefully received!
 
The 'squirt' is the accelerator pump and may well be at fault.
Worth checking that the ignition timing hasn't slipped or the points may be closing up.
Outside chance of carb icing up but I'd check the timing first.
 
Have a look at the air filter and check it isn't chocked up. Try a run without it to see what happens. If still no good remove the bend off the top of the carb. start the engine and warm it up, rev the engine then put the palm of your hand over the inlet. The suction caused should shift any bits of debris blocking the jets, be prepared though there is a lot of suction when you put your hand over the inlet.
While your there, with the engine off, look down the carb and push the accelerator, you should see a little squirt of fuel from the accelerator pump as you push the pedal.
 
Thanks all, good info. The thing that's making me think it's the carb is that it gets better when I pull the choke out. My logic is:
Presumably if it was dying when accelerating owing to weak spark, the problem is (effectively) flooding the weak spark when the squirt of fuel occurrs.
So I'd have thought when opening the choke, the extra fuel would flood it too.

does that sound right?

Anyways I'll check all this - thanks for your help
 
If you are running with the original fuel tank, untreated, odd things like this happen when a fouled fuel filter restricts the petrol flow.
 
Have you thought about having the carb reconditioned, I had issues with mine and the recondition sorted it out.
 
andrew said:
Have you thought about having the carb reconditioned, I had issues with mine and the recondition sorted it out.
Click to expand...

Well we've only had the van about a month, so I'm still finding my way about. I'm not familiar with these carbs so it's a bit of a learning curve.

I tried Panky's "hand over the inlet" trick and although I was just revving at a standstill, it did seem to improve.
 
Peering down the carb and prodding the accelerator (engine stopped), should I see literally a little squirt of fuel ? I could see that there was 'fuely wetness' appearing on the butterfly valve, so guessing I was more a mist than a squirt.

does that sound right ?
 
Yep sounds right. I actually disconnected it on my first van as an 'economy measure' as suggested in a magazine article. Resulted in slightly lower acceleration but no noticeable improvement in fuel consumption, didn't cause any hesitation though.
As has been suggested though it could be a sign of things to come if you're getting debris through from the tank, if you've got an in line filter installed then change it and check the fuel pump to see if there's any crap in it.
 
yeah there's a filter which, from memory, is after the pump as it rests on the rocker cover. OK I'll check that stuff, thanks again.
I think the van wasn't driven too much for a while before we bought it, so a development of inexplicable debris is in-character.
 
I'd re-position the filter for a couple of reasons - to protect the pump and to stop fuel vapourisation as the heat of the engine will heat the filter up on top of the engine causing a vapour lock
 
Sometimes theres a small filter hidden above the float/needle valve inside the carb, thats worth checking too but means getting into the float chamber.
 
Yeah I've heard about fuel vapourisation in other cars. I'll do that asap.
Which reminds me- one other issue I've noticed is that the pipe to the top of the radiator doesn't get all that hot. It's about like a piping-but-slurpable cup of tea. Is that about right for this engine ?
I'm not sure whether that's just because I was driving in cold weather, or maybe there's some issue with the thermostat. Maybe there isn't a thermostat!
There's plenty of water in the radiator.

The water temp gauge is also very erratic (sometimes reads hot when engine isn't started yet) so I can't rely on that.
niggles .. niggles.. we'll get there though :)
 
The stats are usually set at 88 degrees, yours sounds cooler that that so maybe you are missing a stat. If so I'd get one in as soon as possible as it doesn't do the engine much good without one. The hose does insulate a bit so feel the thermostat housing or radiator inlet to get a better idea - I got one of those infra red laser thermometers to check Bonnie as she seems to run cool but it showed all was good.
 
dodgeram said:
That can happen when the strangler cable bounces over the sender:)
Click to expand...

Cheer dodgeram - where's the sender, though? I was looking right next to the thermostat housing and there's a big flat brass nut/bolthead where I'd expect it to be (given I'm not overly familiar with this engine yet).
I didn't have time to trace the wire.. should it be next to the thermostat housing? between that and the rocker cover ?
also .. strangler cable ? sounds nasty. what's that ?
 
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Should be here. There wasn't one fitted to Bonnie just a blanking plug, yours may be the same and the wire that goes to the gauge might be shorting out somewhere.

2013-04-24 15.55.33.jpg
 
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