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Carb or Timing?
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Rootes75



Joined: 30 Apr 2013
Posts: 3785
Location: The Somerset Levels

PostPosted: Mon Mar 22, 2021 4:41 pm    Post subject: Carb or Timing? Reply with quote

So, got our Commer starting lovely now although even when warm she needs a quarter pull on the choke, it can be pushed in as soon as she fires and then she idles very nicely.

The main issue then is that give her any throttle and she pops and bangs a bit and the engine simply dies.

So, is this likely to be an issue with the fuel supply or the timing?

If it were timing would we not notice this when she idles, she doesn't miss a beat on tick over?
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peter scott



Joined: 18 Dec 2007
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PostPosted: Mon Mar 22, 2021 4:54 pm    Post subject: Reply with quote

I think I would look for blocked carb jets first.

Peter
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alastairq



Joined: 14 Oct 2016
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PostPosted: Mon Mar 22, 2021 5:11 pm    Post subject: Reply with quote

Does the distributor have a vacuum advance module?

Does the carburettor have an accelerator pump device?
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Rick
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PostPosted: Mon Mar 22, 2021 5:13 pm    Post subject: Reply with quote

Does the carb have an accelerator pump in it? Although I'd expect a problem with that to make itself more known under load rather than at idle. As Peter says perhaps a blocked jet somewhere? If the points have closed right up then that too could cause problems.

RJ
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Penman



Joined: 23 Nov 2007
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PostPosted: Mon Mar 22, 2021 7:02 pm    Post subject: Reply with quote

Hi
Rick wrote:
Does the carb have an accelerator pump in it? Although I'd expect a problem with that to make itself more known under load rather than at idle.
RJ


If it was a Ford the accelerator pump was the first place to look when the car won't start, or should I say strictly speaking it was the drivers right foot that was to blame. Laughing Laughing
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alastairq



Joined: 14 Oct 2016
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PostPosted: Mon Mar 22, 2021 9:13 pm    Post subject: Reply with quote

Possible air leak creating weak mixture off idle?
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ukdave2002



Joined: 23 Nov 2007
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PostPosted: Tue Mar 23, 2021 7:50 am    Post subject: Reply with quote

Do you have a Vacuum gauge that can be attached? simple and quick tests that can take loads of guesswork out of diagnosing these problems.

Dave
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Rootes75



Joined: 30 Apr 2013
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PostPosted: Tue Mar 23, 2021 1:22 pm    Post subject: Reply with quote

The carb is a Solex 40 FAIE, it has no air cleaner so is left open at the top aside from a lid that stops debris falling into it.

It does have the air retard pipe back to the distributor, it also has an air pipe attached that drops down into the engine next to the manifold.

I will take some photos at the weekend when I am next down the yard.
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Rootes75



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PostPosted: Tue Mar 23, 2021 1:24 pm    Post subject: Reply with quote

Actually, if you follow the link to the video you can see the carb quite clearly.

https://www.flickr.com/photos/52197579@N07/50921326988/in/dateposted-public/
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peter scott



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PostPosted: Tue Mar 23, 2021 11:26 pm    Post subject: Reply with quote

You might be able to tell whether a blocked jet was the problem by pouring petrol into the top of the carb as you open the throttle. If it revs rather than stalling then you've found your culprit.

Peter.
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Keith D



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PostPosted: Wed Mar 24, 2021 6:32 am    Post subject: Reply with quote

If you pour petrol into the top of the carby with the engine idling, then rev the engine, be aware that if she "pops and bangs a bit' both you and the truck are going to get a nasty fright and maybe a burn or two.

Keith
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Rootes75



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PostPosted: Wed Mar 24, 2021 8:03 am    Post subject: Reply with quote

We have a replacement carb but the casing is slightly different from the original.

On the top the original has two threaded holes that the cover is fitted to, the replacement has no holes in the top of the casing so is obviously a little later and suitable for use with an air cleaner.
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Rootes75



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PostPosted: Sun Mar 28, 2021 6:52 pm    Post subject: Reply with quote

We try again.

Again, she will only start with choke even when she is warm. As soon as you put your foot down she backfires a couple times then dies completely.

We checked the advance/retard on the ditributor and that is working. It still sounds to us like a carb issue, the backfires burning off the excess fuel etc.
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Rick
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PostPosted: Sun Mar 28, 2021 6:58 pm    Post subject: Reply with quote

alastairq wrote:
Possible air leak creating weak mixture off idle?


This sounds like a possibility, my 2.5 Spitfire had a problem with terrible running, in the end I found that it was sucking in loads of air out of sight, underneath the carbs where they bolted to the inlet manifold. Someone had bodged the carb-manifold joint. If there are any vacuum take-offs from the inlet manifold, maybe try removing them and plugging the hole(s) to see if there's a problem there (Fords with the vacuum wiper motors can have issues if the pipe to the motor has a leak in it).

If with it running try spraying EasyStart or similar around the manifold and see if the idle picks up, suggesting an air leak.

RJ
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ukdave2002



Joined: 23 Nov 2007
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PostPosted: Sun Mar 28, 2021 7:41 pm    Post subject: Reply with quote

Rick wrote:
alastairq wrote:
Possible air leak creating weak mixture off idle?


This sounds like a possibility, my 2.5 Spitfire had a problem with terrible running, in the end I found that it was sucking in loads of air out of sight, underneath the carbs where they bolted to the inlet manifold. Someone had bodged the carb-manifold joint. If there are any vacuum take-offs from the inlet manifold, maybe try removing them and plugging the hole(s) to see if there's a problem there (Fords with the vacuum wiper motors can have issues if the pipe to the motor has a leak in it).

If with it running try spraying EasyStart or similar around the manifold and see if the idle picks up, suggesting an air leak.

RJ


As I mentioned previously, a simple old fashioned vacuum test will take a load of guesswork out.
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