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Old 28 Aug 2012, 21:02 (Ref:3126558)   #1
Mk1Tom
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Uneven fueling on Weber 45 dcoe

Hi folks, I've recently completed the build of a classic mini with the intention of hill climbing it.

The engine is proving difficult to set up however as first I had an issue with the megajolt mapable ignition and now after trying to road test it, it is running like an absolute dog.

It runs rough and at some points lets out almighty backfires, when accelerating at some points it is almost like someone has turned everything off and power just drops as though I have taken my foot off the pedal.

We whipped the plugs out and 3/4 are running very rich and 1/2 are running ok.

Does anyone know of any reason my weber would be fueling unevenly? Its just been jetted etc by a man who knows what he is doing so I think there may be a problem with the carb somehow.

Is there anything I can do to clean it all out?

I'm getting fed up of this bloody car

Many thanks
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Old 28 Aug 2012, 22:38 (Ref:3126606)   #2
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........ Its just been jetted etc by a man who knows what he is doing .......
hmmm I'd look here first....
one reads far too many threads about supposed experts and their expensive ministrations... one presumes he set it up on a rolling road, why not take it back and ask him to sort it out properly this time please, and no charge is expected.
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Old 28 Aug 2012, 22:57 (Ref:3126613)   #3
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What sort of inlet manifold are you using, who ported the head, what sort of cam, exhaust manifold, etc.
Get yourself a copy of Vizards Tuning the A Series 1st, read it through, then as MG David says find someone who really knows about A Series and rolling roads.
Which part of the country are you in.
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Old 28 Aug 2012, 23:16 (Ref:3126616)   #4
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Seems very strange to me as the fault would appear to be on the right hand choke (assuming 3 and 4 are on the clutch side) make sure that all the jets etc are the same in both sides and screwed in tight O rings correctly fitted and 2 1/2 psi fuel pressure.
The Weber ain't rocket science and is very easy to work on, however it may not be a carburetor fault and I'm afraid it's a waste of time asking on a forum as we can't be hands on.
Has it got a scatter cam ?
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Old 29 Aug 2012, 00:39 (Ref:3126633)   #5
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Dirt? Until you have cleaned out every orifice, gallery and tube and jet you are wasting your time looking at anything else, even when you think its clean, dirt is probably still blocking something and causing problems.
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Old 29 Aug 2012, 07:58 (Ref:3126734)   #6
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Thanks for the replies folks. The guy who set up the carb saw nearly 100bhp at the wheels earlier in the week so I am confident that it hasn't been set up incorrectly.

I think it may be dirt as it was run low on fuel. I have a filter king fuel pressure regulator and also a filter in the pump but maybe I should fit a pre-filter as well?

I will investigate the carb jets etc and see if there is any dirt stuck in them.
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Old 29 Aug 2012, 11:48 (Ref:3126849)   #7
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Have you also checked that you dont have an air leak, maybe via one of the misab plates. Try spraying carb cleaner when running and see if revs change, if they do then you have an air leak.

Where are you based?

Cheers

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Old 29 Aug 2012, 11:52 (Ref:3126851)   #8
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Do you have the plug leads on the correct way round and have you checked the timing is correct and ignition working properly.
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Old 29 Aug 2012, 11:57 (Ref:3126857)   #9
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Do you have the plug leads on the correct way round and have you checked the timing is correct and ignition working properly.
Plug leads are correct and part of the reason I need it running is to road test the ignition system as it is fully mapable. It may be a combo of blocked carb and poor timing causing the back fire.

The car runs a crank sensor and trigger wheel
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Old 29 Aug 2012, 12:03 (Ref:3126863)   #10
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Errr.... if the problem is dirt blocking the various jets on one side of a 45DCOE, then isn't it most likely that the cylinders served by that side would show as running weak, yet the OP reports that 3&4 are running rich, whilst 1&2 seem to be OK?

A clue, methinks!
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Old 29 Aug 2012, 12:04 (Ref:3126864)   #11
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I'd try an ordinary dizzy and see if it works and go from there. It could be any one of a dozen or more causes. Things I'd check if you're convinced it's the carb are float level and or if it's flooding. Blocked jets. Blocked filters in carb. Sticking accelerator pump, have you played with the idle mixture? Air leaks inlet or exhaust manifolds. Does it have an air filter?
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Old 29 Aug 2012, 12:06 (Ref:3126866)   #12
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Hi, I'm going to take the jets out and see if there are any issue on the weaker side. I can't tell whether one side is weaker than it should be, or just running leaner than the other side.
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Old 29 Aug 2012, 12:09 (Ref:3126867)   #13
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I'd try an ordinary dizzy and see if it works and go from there. It could be any one of a dozen or more causes. Things I'd check if you're convinced it's the carb are float level and or if it's flooding. Blocked jets. Blocked filters in carb. Sticking accelerator pump, have you played with the idle mixture? Air leaks inlet or exhaust manifolds. Does it have an air filter?
The car was delivered back to me with the carb fully set up, only the timing needed fine tuning on the computer.

Since then the running has got worse.

The car is running no air filter and I don't want to start messing with mixture etc. as I don't know enough about what I am doing.
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Old 29 Aug 2012, 12:15 (Ref:3126872)   #14
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If you only played with the timing then I'd bet this is where the trouble lies. Webers have a filter where the feed pipe connects so that may be blocked. Check it' not flooding, pump on engine not running.
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Old 29 Aug 2012, 12:24 (Ref:3126876)   #15
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If you only played with the timing then I'd bet this is where the trouble lies. Webers have a filter where the feed pipe connects so that may be blocked. Check it' not flooding, pump on engine not running.
Cheers, I shall try this when I next have patience.
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Old 29 Aug 2012, 13:05 (Ref:3126896)   #16
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Have you tried phoning the man who knows what he's doing? He's probably the best person to advise in the first instance.
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Old 29 Aug 2012, 13:26 (Ref:3126905)   #17
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Have you tried phoning the man who knows what he's doing? He's probably the best person to advise in the first instance.
I'm not exactly that keen on the bloke after the way he treated me, lets just say he was very rude and made me out to be a liar. He is well known in engine building circles and well respected but it seems his 'people' skills aren't great
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Old 29 Aug 2012, 17:46 (Ref:3127016)   #18
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The mixture screws won't make an awful lot of difference on higher revs.
Jetting makes the big difference , make sure the air corrector jet on the right hand side is not blocked.
As I said basically its not a complex carb and is designed to be worked on track side easily as all the jets/emulsion tubes can be changed from the top.
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Old 29 Aug 2012, 17:54 (Ref:3127025)   #19
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The car runs a crank sensor and trigger wheel
Maybe these are at fault, does it have a throttle potentiometer?
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Old 29 Aug 2012, 20:35 (Ref:3127090)   #20
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Maybe these are at fault, does it have a throttle potentiometer?
Its got a genuine weber TPS on the car but this shows on the laptop as working correctly.

Tonight I have started at the back and taken the fuel pump apart to check the filter in the fuel pump. There were no signs of dirt in the fuel pump.

I am also running a filter king pressure regulator as well.
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Old 30 Aug 2012, 05:51 (Ref:3127206)   #21
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Have you got petrol in it? I once spent an hour or two head scratching over exactly the same symptoms and found that having enough fuel in the tank worked wonders
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Old 30 Aug 2012, 06:59 (Ref:3127221)   #22
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Have you got petrol in it? I once spent an hour or two head scratching over exactly the same symptoms and found that having enough fuel in the tank worked wonders
I would expect that of you Tim !
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Old 30 Aug 2012, 08:09 (Ref:3127250)   #23
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Have you got petrol in it? I once spent an hour or two head scratching over exactly the same symptoms and found that having enough fuel in the tank worked wonders
Ha ha, yes there is £30 worth of fuel in it because I was paranoid it was running too low!

I found this to be loose this morning...?

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Old 30 Aug 2012, 08:15 (Ref:3127256)   #24
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That's the emulsion tube holder so depending how loose it won't help matters.
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Old 30 Aug 2012, 08:25 (Ref:3127258)   #25
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That's the emulsion tube holder so depending how loose it won't help matters.
Basically it was 100% loose! AND that is the side that is running very rich. I've tightened it up but I took the fuel pump off last night to check for dirt and the fuel pump showed absolutely no signs of dirt.

Here is the car in question which seems reluctant to be on the road


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