Webers spitting back on start up is this normal?.

[Firemang]

Having changed the jets and tuned the carbs on my 1600 vx after a Blydenstein conversion I am now getting spit back through the carbs on run up from cold for the first couple of minutes while the engine is cold.

 

After the engine has had a chance to warm slighly its fine.The car drives and runs fine when there is a bit of warmth in the engine. Is this normal and would this spit back cause damage? I know it makes passers by stare!

 

I didnt have this problem before although it was running very rich on the previous pump and idle jets the idle mixture is set with a color tune plug with it just on blue just off yellow rich.

 

Ian

 

 

[stevefoster]

Spitting means too lean.

To get it right warm / cold would mean a compromise between perfect warm mixture and richer needed for cold running.

Enter EFI and coolant / air temp compensation maps...

 

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

[Normans_Ghost]

Ian, Most weber carbed cars "spit back" when cold. It's not the engine that needs to be warm but the manifold. The longer the manifold the longer it takes to reach operating temprature. (Obviously the engine must get warm to warm the manifold)

 

Most cars (with carbs) have a choke. Webers have a choke system but this is rarely used (even when there is a choke cable). The normal cold start procedure is 3 pumps and start.

 

If the mixture is Ok when properly warm then I would leave well alone. However the only proper way to sort it is on a rolling road with a wide selection of jets to get the mixture right throughout the range.

 

One tip is that to check the mixtures go for a long (10 mile) run and check the mixtures several times on the road. Do not leave the engine ticking over too long when adjusting as the head gets too hot and upsets the mixture. The other thing to bear in mind is altitude. I live 600ft above sea level and if I leave the peak district and come down much lower, I adjust the mixtures. Will normally change about 1/8 turn.

 

Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here

[Firemang]

Thanks Norman,Steve

 

I am tempted to leave alone. I have richend the mixture and it appears to make little difference even with a overly rich mixture.

 

The set up I have seems to run well when warm. A rolling road may help but i presume the engine will be at operating temperature when being tuned so the ideal mixture will be found at this temperature.

 

I will leave as is as long as i am not going to cause damage to the carbs. Do you envisage any damage occuring?

 

Ian

[stevefoster]

I would say as long as the spitting isn;t too bad and you nurse her during warm up (you should anyway of course until the oil is warm) then leave it.

 

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

[Petrolhead]

Also if they are out of ballance they can spit more

 

NE7Club Web Site

R5 no 65 😬

I am after low level tyre rack and jerry can box for Mino

[strongy]

Recently had a rolling road session on my 1700 ss and asked the very same question. I was told that with Webers "they all do that sir when they are cold". Something to do with having no choke.

 

As long as it runs well at normal temp thats all I worry about.

 

 

Strongy, Fekkin working

[Firemang]

Cheers all will leave then as they are 😬

[wonkey eyed barmaid]

firemang,

how does the car run on the new jet setup...

 

45 F9 idle

115 main

35 pump

correct 🤔

 

im planning to fit the idle and pump jets, as above, tomorrow. my mains are already 115.

 

have you given it a good run - high rpm etc. no probs?

[Mick Day]

Spitting back of course can lead to fires in the air cleaner; seen it happen once & rapidly controlled without damage by quick use of an extinguisher.

 

You all carry one don't you?

[blade_runner]

I thought an engine running too rich can spit back when cold, due to a rich mixture taking longer to burn, its still burning when the inlet valve opens but maybe i'm mistaken. 🤔

 

'Pinky Pics' here

[stevefoster]

My Throttle Bodies did spit back when too lean when I was mapping her. during warm up.

Initially all was fine but the change from summer to winter ambient temps caused this.

In my expereince the mixture for spitting measured with a wide band O2 would be at something like 16+:1.

Ideal light throttle load mixture is 14.7:1.

Under full power 12.5:1.

 

Too high a mixture I suppose >16:1 at high rpm / load would quickly melt a piston.

Under light load and careful revving it would be fine. Esp as it warms up and all is ok.

 

Of course the severivty depended on the load.

My problem was a warm up map. Once warm no problem. The only difference for me once on EFI was that I could now change the numbers in the coolant compensation map.

 

I am sure putting a wide band on your 7 and driving through it would give similar results.

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

 

Edited by - stevefoster on 12 May 2005 13:23:05

[Normans_Ghost]

A lean mixture will cause this spitting, not rich. I've seen flames (long ones) spitting out of carbs (which is why I never get in front when starting a webber's car from cold with no air cleaners on) but never seen an air cleaner catch fire as with the air cleaner on the flame gets damped a lot.

 

Advanced ignition timing can also cause this.

 

Webers do have chokes it's the cable that's missing on 7's. It's the small lever near the engine side of the carb, moves from front to back in an arc. May have a little union on the end of the lever usually doing 3000 revs with viabration.

 

Having spent money on a head conversion you should have the carbs setup on a rolling road with someone who knows how to jet webbers. The mixture may be fine at tickover but may be very lean higher up the rev range. If so, could end up burning a hole in a piston!

 

Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here

[wonkey eyed barmaid]

im always scared to check the mixtures at high revs.

screw in colourtune.

rev to 3k....

 

get too scared to stare down colourtune window incase it explodes in my eye

 

 

firemang,

if im correct, you said in a previous thread that you changed your pump jets from a 50, down to a 35. you said it started easier on the 50's.

maybe 35 was too big a jump, and its now running lean on throttle opening scenarios?

try swapping the 50's back in, and see if the symptom goes.

 

then maybe consider a half-way house pump jet - a 40 or 45?

 

im just about to fit a set of 35 pump jets, on yours and redlines advice. if i get spitback or lean running i'll let you know.

 

grant

[Firemang]

Have been speaking to a guy at work about it. He used to be a mechanic (still is on his days off) and is in to his Land Rovers. Got a short wheel base whith a massive American Lump in the front!!!

 

The spitting back when cold is normal on Webers according to him.

 

Whats is happening is that the fuel is being mixed in cold carbs and drawn through a cold inlet manifold. This causes the fuel not to be atomised properly with the air. The cold mixture is going into the cold cylinders and not burning properly which causes combustion to be still taking place when the inlets valves open causing the spit back. THis is why we have chokes but we don't seem to use them????? I suppose if it really bothers be I can always hook up the chokes for starting.

 

Granteuk,Nverona I am using the same jets as the others have used after the conversion and the car runs and starts better. The previous pumps were to rich as before the change it was blowing out black smoked when the throttle is pulsed. It stil does to some extent so maybe to rich still. As the Car will change and improve over the next 3000 miles I may just leave it then put it on the rolling road. As the others have had there cars on these jet settings i can't see why mine should be different and causes any damage? Or will I?

 

 

Ian

[wonkey eyed barmaid]

i think you'll be fine. as you say -others are using this setup.

it was just a guess given the lean running.

but if its only a cold-engine thing. i wouldnt worry.

 

changed my idle jets yesterday. car ticked over and revved a lot sweeter on the smaller jets.

will do a test drive today, then change pumps, then test again.

 

its in scotland again. for the FIFTH day in a row