Avoneer
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| posted on 9/12/03 at 11:34 PM |
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Carbs fighting back (now tuning probs)
Anyone know why my front carb is now trying to set me on fire by
dribbling petrol out of the ram pipe? It has been running fine for
ages. I was tweaking, screwing the idle mixture screws in and the
front one now seems to be letting too much petrol into the venturi and
it runs out backwards out of the ram pipe. Any ideas anyone? I have
turned the idle screws back to where they were, but the first carb
still dribbles too much.....
Cheers,
Pat...
[Edited on 13/12/03 by Avoneer]
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SteveO
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| posted on 10/12/03 at 09:27 AM |
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I had the same problem plus flames coming out the exhaust. i changed my plugs often also and didn't know why. i post and got good advice in this
section under spark plugs
:http://www.locostbuilders.co.uk/viewthread.php?tid=8741&page=1
it seem to have done it. check it out.
Steve
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Stu16v
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| posted on 10/12/03 at 09:15 PM |
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Seemingly a bad link Steve...try here.
It sounds like the carb is flooding, which could be caused by a wrong float level, a punctured float, a worn needle valve, poo trapped in the needle
valve, fuel pressure too high etc.
HTH Stu.
[Edited on 10/12/03 by Stu16v]
Dont just build it.....make it!
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craig1410
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| posted on 10/12/03 at 11:27 PM |
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I had this problem on my Mini a good few years ago. It was indeed, as Stu suggests, caused by a sticking float mechanism.
I was using an SU carb and the float level was grossly incorrect to the point where it just kept trickling out. The strange thing was that it was fine
when stationary but when moving the vibration was enough to cause the float to bounce just enough to allow the fuel to get past the needle valve.
HTH,
Craig.
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steve m
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| posted on 12/12/03 at 01:40 AM |
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I had the same problem ,
no 1 dripped fuel all over the dizzy
I believe the float level was correct and all of the seals between carb and maniflod were new and ok, no 2 3 and 4 did not drip nor were they wet
underneath !!
any way both carbs are in total bits for a deep clean, and new parts and gaskets ,
so I will see next year if ive got a drip !!!
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Avoneer
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| posted on 13/12/03 at 08:51 PM |
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Hi guys,
Thanks for the info, especially SteveO's link. Very usefull.
Having checked my regulator, it was set at max, so I have turned it down to near nothing and all is well. No leaking.
But that brings me to my second problem - no matter how much I turn the idle mixture screws in or out, I get no variation of engine speed at tickover.
They are jetted right as per Eurocarb.
They are Dellorto 40's, but the Alfa emission type, but that shouldnt't be the problem.
Anyone have any ideas?
Cheers
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Stu16v
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| posted on 13/12/03 at 09:24 PM |
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Eurocarb?? Who/what are they (excuse my ignorance).
My guess is that the throttle butterflies are open a little too far, for whatever reason (I know that might sound silly, but bear with me). In theory
at least, the idle mixture screws are capable of shutting the idle circuit right off when fully screwed in-which *should* stop the engine, so the
carbs have to be supplying juice from elsewhere.
Even if the idle speed of the engine is correct, the throttle butterflies might be in the wrong position, allowing the engine to run on the
progression circuit. If you have a look inside a carb you will see that the butterfly uncovers a series of holes drilled into the top of the body.
Very little angular movement is required to uncover the holes, so if the idle screw is wound out more than ideal to obtain the right tickover, the
carbs will be operating on the wrong holes, IYSWIM.
If this is the problem, there are a couple of thing to try. First, ignition timing. You may find that the timing is too far retarded, especially if
you have junked the vac advance, or you are running aftermarket electronic ignition, or both. Advancing the timing a couple of degrees, will increase
the idle speed, which will then allow you to 'close' the throttle butterfliesslightly, and hopefully bring them back to the idle circuit.
Unfortunately, this *may* over advance the ignition at high rpm, so listen carefully for signs of 'pinking'.
The other option is to drill very small hole in the actual butterflies, it is a bit trial and error, but around 1.0mm is a good starting point. This
will allow air to bleed through, again allowing you to close the butterflies for the same idle speed. If it doesnt work, no problem, just solder the
holes up again.
Finally, you *may* find there is separate adjustment for 'air bleed'. Later Webers have this facility, but I am not sure about
Dellorto's.
Of course, it may also be that the carb fuel levels are too high within the float chambers, this will play havoc with low speed running adjustments.
Caused by the potential problems listed in the above posts. Until you are sure that the carbs are 100% OK in this area, dont try any of the above, you
will be wasting your time.
HTH Stu.
Edited to correct the size of hole required to be drilled. And as a further explanation, the bigger the hole, the further closed the butterflies will
be foe the same idle speed.
[Edited on 16/12/03 by Stu16v]
Dont just build it.....make it!
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givemethebighammer
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| posted on 13/12/03 at 10:36 PM |
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Euro carb = carb specialists, never used them but here is the link
http://www.dellorto.co.uk/
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Avoneer
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| posted on 13/12/03 at 10:54 PM |
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Jesus Stu16v, wasn't expecting a reply so soon that actually sounds bloody useful! (that's not a dig at other replies though).
Will have a good look tommorow with a torch etc, to check the butterflys are fully closed etc. and check both float levels.
I take it that the butterflies should be fully closed on idle - this makes sense with the idle cricuit / progression circuit thing?
Cheers,
Pat...
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Avoneer
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| posted on 13/12/03 at 11:18 PM |
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Hi,
Just noticed that when looking through the progression holes on top of the carbs (screw cover removed), there are 5 on my emmission carbs. 4 the same
size and one small one at the front. This small front one is on the engine side of the butterflies (when the butterflies are shut) and the rest are on
the air filter side of the butterflies. Should they all be on the air filter side of the butterflies?
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Stu16v
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| posted on 13/12/03 at 11:27 PM |
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Yup, none of the holes should be 'uncovered' with the butterflies at idle-i.e. they *should* be on the air filter side. As soon as the
butterflies start moving, the holes should start 'opening'. That is the ideal position. Too far closed however, and you will end up with a
flat spot, where the butterflies are letting in more air, but the progression holes are not being uncovered, causing the mixtur to go weak.
P.s. how did you go about the ignition timing?
HTH Stu.
HTH Stu.
[Edited on 13/12/03 by Stu16v]
Dont just build it.....make it!
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Avoneer
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| posted on 13/12/03 at 11:47 PM |
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Hi m8,
Going to check the timing in the morning. Think it was set at 8-10 degrees. Will check that first, then take of the carbs and refit the butterflies
and then check the float level.
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Stu16v
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| posted on 14/12/03 at 02:53 AM |
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Hoping that you read this first. before venturing into the garage...
Order of priority:
1. Check the carbs are in perfect health (float needles for wear, punctured/maladjusted floats, etc)
2. Fiddle with the engine timing (with the engine at normal operating temp). Try advancing the timing, try it down the road listen for pinking. If
that doesnt work-
3. Whip carbs off again and drill a small hole in each butterfly.
Good luck, Stu.
Dont just build it.....make it!
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SteveO
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 posted on 14/12/03 at 08:33 PM |
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Stu16v,
Your knowledge on carbs is never-ending.
cheers matey.
Steveo
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Avoneer
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| posted on 14/12/03 at 09:16 PM |
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Hi,
Have taken one carb off to check and have noticed that I have idle circuit bypass screws. They are filled with a coating (probably to stop them
moving). After a good scrape, there is a screw under each one (one per choke). Apparantly they have no effect when fully screwed in, which they appear
to be. Shall I leave them well alone?
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Stu16v
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| posted on 14/12/03 at 09:25 PM |
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They are worth playing with mate, as they will be doing the same function as drilling small holes in the butterflies. Winding them out (1/4 turn at a
time, equally on all carbs) should raise the idle speed, which can be shut back down by the idle adjustment screw, which will in turn hopefully bring
the butterflies to the correct position in relation to the progression drillings (keep checking the position by removing the screw cap and checking
with a torch). Once they are right, adjust mixture. You may find that if the mixture is way out, you will have to fine tune the above again, but the
hassle will be more than worth it.
HTH Stu.
Dont just build it.....make it!
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Avoneer
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| posted on 14/12/03 at 11:14 PM |
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Any ideas how to turn the seized screws now? I don't want to tell you how I eventually removed the seized idle srews.
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Stu16v
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| posted on 15/12/03 at 09:09 PM |
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Perhaps the application of a hammer on the end of the (old) screwdriver wil do the trick....
Dont just build it.....make it!
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Avoneer
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| posted on 10/1/04 at 03:30 PM |
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Hi,
OK, carbs removed, stripped and cleaned and float levels set (15mm in Dellorto). Idle by pass screws freed. Everything bolted back together. Still
idles smoothly, but no matter how much I turn the idle mixture screws, the engine speed doesn't change. I turned the idle by pass screws out 1/2
turn which increased idle speed (trimmed down with idle screw) but still no variation in engine speed no matter how far in or out I turn the idle
mixture screws. The butterflies are fully closed. So the engine is definately running on the idle circuit only. Any further ideas, or is it time to
scrap them and buy some new ones?
Cheers,
Pat...
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Northy
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| posted on 11/1/04 at 06:44 AM |
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What was your budget Pat? 
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing! 
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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Stu16v
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| posted on 11/1/04 at 11:27 PM |
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Errrm, you have got me stumped! I certainly wouldnt think of scrapping them (yet! ). With the idle mixture screws full in the engine *should* stop, or
run as rough as a bears arse now, so there sounds like there is still fuel entering the carbs from further upstream, for whatever reason. Other than
that, not much help I'm afraid, other than perhaps trying to get the car to somewhere with an emissions tester, to see if the screws are
actually doing something. The engine rev thing is a *ballpark* thing after all.....
Dont just build it.....make it!
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Avoneer
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| posted on 11/1/04 at 11:48 PM |
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Hi Stu,
Thanks. By scrapping, I meant putting on a shelf to gather dust...for now!
Going to try one more time tommorow before making a decision. If I screw the idle mixture screws all the way in and the engine stalls - I guess that
is good and shows that fuel is only entering the engine via the idle circuit - and if this is the case, but still doesn't make any difference
how far out they are turned - could it be that the emission type carbs like mine have fixed idle and the idle mixture screws will only adjust the co2
mixture?
Sorry for all the questions - just trying to figure out what to do!
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Stu16v
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| posted on 12/1/04 at 10:01 PM |
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The idle mixture screws *only* adjust the fuel (and hence co2) anyway, the idle speed reference is only made as a DIY way to get the mixture
'somewhere near'. When checked on an analyser more often than not you will find that when (or in your case 'if' you adjust
the screws to obtain max rpm, the mixture is likely to be too rich anyway. I used this method to adjust my Webers. When I finally got it to an
emissions tester, the reading was 6%! As a matter of interest, what size idle jets have you got fitted, and how does this compare to the Dave Andrews
guide?
[Edited on 12/1/04 by Stu16v]
Dont just build it.....make it!
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Avoneer
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| posted on 12/1/04 at 11:52 PM |
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Hi Stu,
Thanks for you reply (once again)!
Can't remember the size, but they are as per Dave A and Eurocarb. I have about three different sizes now!
Maybe I should try and borrow an analyser and see what is happening?
Maybe things will be ok after all? Might have to wait until just before SVA, have it towed to a garage for MOT and get them to have a go - if not, buy
some new carbs ready to roll (painfull on the wallet though!).
Cheers,
Pat...
At least she runs and idles. Managed to get her up into 2nd gear on my cul-de-sac, span the wheels like anything after the gear change and went
sideways as well as forwards, but it was good - my motivational booster!
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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Stu16v
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| posted on 14/1/04 at 06:56 PM |
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quote:
Maybe I should try and borrow an analyser and see what is happening?
Maybe things will be ok after all?
Thats what I would personally do mate. The analyser will tell you sooo much....
Good luck, Stu.
Dont just build it.....make it!
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