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]

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

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]

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.

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 !!!

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

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]

Euro carb = carb specialists, never used them but here is the link

http://www.dellorto.co.uk/

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...

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?

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]

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.

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.

Stu16v,

Your knowledge on carbs is never-ending.
cheers matey.

Steveo

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?

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.

Any ideas how to turn the seized screws now? I don't want to tell you how I eventually removed the seized idle srews.

Perhaps the application of a hammer on the end of the (old) screwdriver wil do the trick....

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...

What was your budget Pat?

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.....

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...

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]

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!

quote:

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Maybe I should try and borrow an analyser and see what is happening?
Maybe things will be ok after all?

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Hi Stu,
Just read this in Des Hammils book:
"If the engine being tuned does not have sufficient idle speed advance, it will be impossible to get good clean performance below 2700 to 3500rpm without resorting to very large idle jets and lots of turns out on the idle screws."
I set my timing to 8 degrees BTDC as per the Haynes manual for a 2ltr Pinto with single carb.
Doh!
Maybe my twin carbs and fast cam have changed that somewhat - maybe I should set it more in the region of 12 degrees (estimate). Will have a go tommorow!
Looking promising for a change (and money saving).
Pat...

As per the 'timing' thread, using a timing light is a waste of time for setting up. What Des is saying is spot on, I dont know if he explains the various reasons why. If he doesnt, here goes....

When you bolt a pair of twin carbs onto your engine, the first thing that is usually affected is the vacuum advance-that is, it is usually left disconnected. Idle/low rpm is exactly where the vacuum advance is applied the most, so already your engine is now running quite a bit more retarded when compared to the orignal spec. Ive no idea exactly how much the Sierra vac can advance the timing, but it could possibly be in the region of 8 to 10 deg!
Trouble is, you cant just advance the dizzy the same amount to compensate, because at higher revs, when the vac advance mechanism stops working, the timing would then be 8 to 10 deg too far advanced, and holed pistons would result
Compounding the problem even more is the issue of 'lumpier' cams. At low rpm, when the engine is 'off cam' the gases flowing through the engine are not as as efficient as a standard cam, and what tends to happen is exhaust gases mix with the fresh inlet charge in the cylinder. This diluted mix burns slower, and needs more advance from the ignition timing. But at high rpm, the situation is reversed, so the cylinder fills better, and needs less advance than a standard engine!
To summerize, a standard dizzy in an engine with twin carbs and a 'fast' cam is far from ideal, in fact the complete opposite to what the engine probably requires. Thats why a timing light is good for diagnosing misfires, and nothing else on a modded engine.
If there was some way of reconnecting the vac advance, that would go a long way to helping.......

Pat, you might want to have a word with Col, he has his Vacuum advance connected

Cheers Stu.
Got my vacuum advance connected from the dizzy to one of the carbs. Will have a go at using the timing light tommorow to set it nearer 12 and see what happens!
Pat...

Pat don't you need it connecting to atleast two of the cabs to stop pulsing. And you really need to use one of those anti pulse thingys. The pulsing is also made worse by a lumpy cam

Hi guys,

I've just passed my MOT pre SVA and as you know i had sme problems. with the webers i had to get an amazing 72year old guy who was amazing with my 40s and he talked and i listened. first like you, one set was running too rich because unknowingly the metal piece on the 2nd carb by the side was not allowing full closure on that carb when the 1st carb is fully closed, so we took it off totally as it wasn't going to link a third carb anyway.
Then screw down all 4 idle screws, get the two spring mounted screws for the rev(don't know the name) just touching the horizontal plates, if the engine stalls turn the idle screw half a turn. Then to balance and tune remove the plug leads from 4,3 and then 1,2 listen and compare the sound; adjust rev screws until they sound the same. do the same with plug leads 1,3 and 2,4 but here adjust the idle screws, do the same with 1,2 and 3,4. It takes a long time but when we put it on the analyzer this guy got it spot on Lamda under 1%, HC <800 and CO2 was way under. (I used the Dave Andrews jetting for 7500 power band, road rally kent cam with vac advance on one of the inlets.)

hope this is useful.

steve

quote:

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Pat don't you need it connecting to atleast two of the cabs to stop pulsing. And you really need to use one of those anti pulse thingys. The pulsing is also made worse by a lumpy cam

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I was going to connect to all four

Wow, I knew something

I'm only connected to one of the carb outlets, the other three are plugged and I can idle smoothly so there!
Re-set my timing to between 12 and 14 and gues bloody what - I have some tweakability with the idle mixture screws!
Whoopee!
Borrowing a gas analyser soon as well - what should I be looking at?
Cheers everyone so far.....
Pat...

I would personally still try and get the others connected too. Easy way to check if it advancing fully is to let engine idle with vac connected and note where timing is with timing light. Then pull off pipe,block hole at carb end and suck the pipe yourself until you are blue in the face. If you can get more advance by sucking, you probably want the other three connecting...

CO% and especially Hydrocarbons can give you good indications of what is going on with the engine. CO% is the mixture strength, and with the engine in a good state of tune it should run sweetly at around 2-2.5% at idle.
The Hydrocarbon reading is an indication of unburnt fuel. High readings can be caused by a number of things. Excessively high readings are usually caused by misfires, very weak mixtures, very rich mixtures (flooding carbs), low compression, incorrect ignition/cam timing and to a certain extent high lift cams. This reading needs to be as low as possible. A standard engine in good health/state of tune shouldnt exceed much more than 300ppm, however your mileage will vary.



[Edited on 16/1/04 by Stu16v]

Hi,
Managed to get myself another pair of plain and simple 40's, not emission type like my current ones, and they are already jetted and set up for a 2ltr.
Hopefully, will make things even easier!
Pat...

quote:

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Originally posted by Dave Ashurst
Stu16v,

Sorry to be thick, but how does that work?

I'd like to fit a vacuum advance dizzy but I'm having trouble with the logic of connecting vacuum advance to MORE THAN ONE side draught tube manifold - so that it works properly.


Also what's an "anti pulse thingy"?
do you make it or buy it (and where from) ?


thanks and regards
Dave

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