Classic van running problems

[bricol]

Was the carb rebuild kit new or new old stock? Are fuel lines, filters etc new? Ie New modern, not new as in bought 40 yrs ago and sat on a shelf. Modern petrol with ethanol plays havoc with rubber fuel lines - swells them and rots them. Might have o-rings or seals in carb that haven't taken kindly to it.

Quite a lot of the fuel pipe you can still buy now isn't rated for fuel containing ethanol - as I found out with my integrale . . .

 

[Gareth J]

I once put a carb float in upside down. May not be possible in your particular carb and doesn't really tie in with symptoms making no difference when you swap carbs (unless it's wrong on both carbs)

 

[the snooper]

It has to be over fueling, carb related especially as the mixture screw does very little, I once repaired a mini for someone that failed on emmisions no matter what I did I couldn't lower the emmisions, a used carb cured it straight away

 

[frank horton]

a lot of the time if it's been stood it's the rubbish fuel these days..........I tend to recomend an Ultra sonic carb clean, I understand it's running rich but when clean uhave a good place to start.........
if it's an early model it'll have a Zenith carb, pretty good but the later models had some rubbish (can't remember now) of the Victor ??, cheap and horrible, always in trouble....especially running rich thru over fueling.....
seem to remember forever changing needle ans seats.........ALSO if the carb is completely original u must check that the float is not pourus, the old 1's don't like modern fuel........
all my old vehicles run on 98 Octane fuel, less of the VEGGY fuel in it.........
hope it works out........Keep the old'un running I say........I have a 1928 Citroen pick-up and a 1934 Commer bread van........
oil on ur shoes bee's in ya hair..........hahaha.......

 

[colnerov]

Hi, Modern fuels attack the hoses and the brass and solder of the floats and the needle valves, check the needle valve, you need a Viton tipped one. You need R9 rated fuel hose try ajlelectronics of this parish for the correct stuff, not all R9 hose on ebay is of the right quality.

http://ajlelectronics.co.uk/

Colin

 

[Wallace]

Have you tried a new condensor?

 

[CompoSimmonite]

Spray WD40 around carb to manifold and manifold to head faces. If it sucks the WD40 in then you know there is an air leak which the carb has been adjusted rich to compensate.

 

[ms08]

Brass or plastic float...any holes and fuel leaking in causing it to sit low?

 

[keithski122]

Thanks for all the suggestions.
Carb was rebuilt in the last couple of weeks with a kit bought direct from zenith so should be new, not nos.Fuel was replaced in the last month.So fuel should not have attacked any rubber yet.Got a cracking spark.Checked for air leaks but none found, surely would cause a running weak scenario.If its not overpressurising with fuel I will take the carb apart myself next time, dad tries but sometimes bodges a bit.

 

[CompoSimmonite]

Air leak would cause running weak but people often adjust carb without knowing so compensate hence why worth double checking if things have been disturbed.
BTW love the van / camper

 

[Cobbler]

I learnt to drive on one of those, not a Dormo, but a Utilibrake I think it was, also by Martin Walter. The Bedford recommendation for adjusting the tappets was to do them with the engine running, sounds crazy, but it works & is quite easy. I've seen the fuel pump diaphragm puncture & fill the sump with petrol, this causes running problems & petrol smells..

 

[Wendelspanswick]

You must have some pictures of your van @OllyO .

 

[OllyO]

I can't find a pic of ours, I'm sure I must have one somewhere. Zeniths are not great. They get wear quite badly on the throttle spindle and that causes rough running. A lot of people swap out for a Webber. We rebuild carb and diaphragm pump as well and that helped. Also accuspark to electric point in a neat little kit for cheap which is handy

 

[Nomad]

@RichardM has already listed my first thoughts - fuel level in the carb (punctured float / wrong level set / fuel inlet valve not closing 100% ?) and / or dirty air filter.

Most of the other suggestions (air leaks, fuel pump etc) give weak mixture not rich running (from my experience).

Can you beg or borrow an old school Gunsons colortune kit (a glass sparkplug - lets you see the colour of the burning mixture at tickover)? I've found this gives the smoothest running on my 60s/70s Hunter motor.

 

[colnerov]

@RichardM has already listed my first thoughts - fuel level in the carb (punctured float / wrong level set / fuel inlet valve not closing 100% ?) and / or dirty air filter.

Most of the other suggestions (air leaks, fuel pump etc) give weak mixture not rich running (from my experience).

Can you beg or borrow an old school Gunsons colortune kit (a glass sparkplug - lets you see the colour of the burning mixture at tickover)? I've found this gives the smoothest running on my 60s/70s Hunter motor.

Hi, I agree with nearly all you say, except that colourtune can't be relied on 100% nowadays because the use of modern fuels which are lead free and their use of additives can give false readings.

Colin

 

[Nomad]

@colnerov - thanks for the info !
I've got a colortune kit sitting on the bench, was planning to use it sometime this week.
Expect it will still get used but I'll keep your advice in mind.

 

[jenki]

+1 for fuel float level did your Dad replace all the washers under the fuel inlet valve?

 

[keithski122]

I use a gunson gastester for co readings.Dads been told on a forum that someone else had the same problems and cured it with an electric pump so he's gone ahead and ordered one, so we'll get that fitted and try again.I'm not totaly sure myself as I tested my fuel pressure guage with an airline and got movement so I'm thinking more towards carb now rather than pump.Apparently he checked the float level height, I always like to check things myself though.

 

[colnerov]

Hi, How is he checking the float level height? Is he checking it by the normal method of by holding the top of the carb vertical and measuring the gap between the carb face and the float, that's OK unless the float is semi submerged and the fuel level needs to be higher than normal to shut the needle valve. You need to check that the float actually floats. Also that the needle valve actually stops the fuel coming through.

So, in short you just need to put the egg in your mouth and suck.

Colin

 

[RichardM]

Do you have a drain plug at the bottom of the float bowl. If so make an adapter up to have a piece of clear hose connected to it which will allow fuel to flow through it. Take the clear hose up the side of the carb, turn fuel on and it will fill with fuel. It should come to a level at the design fuel height - this is not the height you set the float at, but is a more accurate, if fiddly, way to set the fuel height.
If it doesn't stop filling with fuel then you have an issue with valve or float.