Cold start troubles with Weber 500 carb

[jefferybond]

Hi folks,

Now that the weather has got colder, I'm having trouble with cold starts on my 3.5 RV8, fitted with Edelbrock 1404 carb (weber 500).

In the summer, it always used to start just fine with full choke, then immediately backed off to half choke as soon as it fired. Now that it's cold, the only way I can get it to fire is with no choke, and no throttle either! Obviously with no throttle it doesn't run, but you can very gently tickle the throttle to get it to run.

Once it's going but still cold, any slight throttle opening causes it to die. After about 30 seconds of this palaver, it all starts to rev and idle normally. Once it's warmed up (even slightly), it starts and runs just fine.

So far I've tried a new cap and rotor arm, fiddling with the idle mixture, fiddling with the accelerator pump, all with no improvement. Even had the plugs out and they are a nice light grey colour. Fuel consumption and power is very good too.

Any ideas? Is it just a symptom of the cold weather and a big carb?

Jeff

[sidecar]

Hi folks,

Now that the weather has got colder, I'm having trouble with cold starts on my 3.5 RV8, fitted with Edelbrock 1404 carb (weber 500).

In the summer, it always used to start just fine with full choke, then immediately backed off to half choke as soon as it fired. Now that it's cold, the only way I can get it to fire is with no choke, and no throttle either! Obviously with no throttle it doesn't run, but you can very gently tickle the throttle to get it to run.

Once it's going but still cold, any slight throttle opening causes it to die. After about 30 seconds of this palaver, it all starts to rev and idle normally. Once it's warmed up (even slightly), it starts and runs just fine.

So far I've tried a new cap and rotor arm, fiddling with the idle mixture, fiddling with the accelerator pump, all with no improvement. Even had the plugs out and they are a nice light grey colour. Fuel consumption and power is very good too.

Any ideas? Is it just a symptom of the cold weather and a big carb?

Jeff

It is not normal for this carb, I run the same carb with no choke at all and I can start my motor in cold weather but I do have to jab the throttle for a minute or so so that the eccelerator pumps richen the mixture up, after that it's OK

questions:-

1.What sort of fuel pump are you running, does it run all the time that the igintion is on or does it only run when there is oil pressure?

2. What are your pilot air screws set to?

3. Has the carb been calibrated with different jets and needles? (The fact that your plugs are the right colour would suggest that someone has re-calibrated the carb as the plugs are quite often black with the standard setup!). If it is none standard what are the jets and needles?


You could just try opening the pilot screws 1/4-1/2 a turn to richen the idle up a bit but make a note of what they are set to now. (I think that mine are around 2+1/2 but I'll check when I get home).

Pete

[jefferybond]

questions:-

1.What sort of fuel pump are you running, does it run all the time that the igintion is on or does it only run when there is oil pressure?

Facet red top. Also have a filter king regulator set to about 4psi. Pump runs while cranking OR oil pressure present.

2. What are your pilot air screws set to?

About 2.5 turns out. This seems to give the best idle when warmed up.

3. Has the carb been calibrated with different jets and needles? (The fact that your plugs are the right colour would suggest that someone has re-calibrated the carb as the plugs are quite often black with the standard setup!). If it is none standard what are the jets and needles?

Yes, I bought the calibration kit since it needed richening up from the stock settings (strange I know, since the stock settings are normally rich) after some mild head and manifold porting. It does have nice tubular headers and a free flow exhaust though.

I'm running 0.089 main jet, and a 68/52 needle. I.e. cruise mode is roughly stock, power mode is ~ 4% richer than stock.

You could just try opening the pilot screws 1/4-1/2 a turn to richen the idle up a bit but make a note of what they are set to now. (I think that mine are around 2+1/2 but I'll check when I get home).
Pete

Tried all that too. All that does is make the idle worse once it's warmed up.

I think the problem didn't exist last winter before the head/manifold porting (ie, just matching up to the gasket line). Maybe the larger ports have dropped the intake velocity a little bit, which causes the fuel droplets to drop out of suspension when it's cold?

As I said, once it's been running for 30 seconds it all starts to behave again.

Thanks!

Jeff

[sidecar]

questions:-

1.What sort of fuel pump are you running, does it run all the time that the igintion is on or does it only run when there is oil pressure?

Facet red top. Also have a filter king regulator set to about 4psi. Pump runs while cranking OR oil pressure present.

2. What are your pilot air screws set to?

About 2.5 turns out. This seems to give the best idle when warmed up.

3. Has the carb been calibrated with different jets and needles? (The fact that your plugs are the right colour would suggest that someone has re-calibrated the carb as the plugs are quite often black with the standard setup!). If it is none standard what are the jets and needles?

Yes, I bought the calibration kit since it needed richening up from the stock settings (strange I know, since the stock settings are normally rich) after some mild head and manifold porting. It does have nice tubular headers and a free flow exhaust though.

I'm running 0.089 main jet, and a 68/52 needle. I.e. cruise mode is roughly stock, power mode is ~ 4% richer than stock.

You could just try opening the pilot screws 1/4-1/2 a turn to richen the idle up a bit but make a note of what they are set to now. (I think that mine are around 2+1/2 but I'll check when I get home).
Pete

Tried all that too. All that does is make the idle worse once it's warmed up.

I think the problem didn't exist last winter before the head/manifold porting (ie, just matching up to the gasket line). Maybe the larger ports have dropped the intake velocity a little bit, which causes the fuel droplets to drop out of suspension when it's cold?

As I said, once it's been running for 30 seconds it all starts to behave again.

Thanks!

Jeff

Sounds to me like you know what you are doing and haven't just lobbed the carb on to the engine! (So that's me done then!)

I think that you might be right in that the porting has lowed the velocity a bit. I noticed that my carb needed a fair mount of re-setting when I went from standard heads to stage III jobbies.

You could always pour a teaspoon of juice down the carb before cranking it over!!!! Only joking.

Maybe you need to jab the throttle 3 of 4 times before cranking just to give is something to burn for the first few seconds?

Good luck sorting it out!

Pete

[Eliot]

>Maybe you need to jab the throttle 3 of 4 times before cranking just to give is something to burn for the first few seconds?

Thats what i was going to suggest also.

[jefferybond]

>Maybe you need to jab the throttle 3 of 4 times before cranking just to give is something to burn for the first few seconds?

Thats what i was going to suggest also.

OK, maybe that's the next thing to try. I don't normally pump the throttle, because of fear of flooding it, I'll give it a go tomorrow once it's cooled down properly!

Cheers,
Jeff

[kiwicar]

On the first Rangy I had I fitted a boxer manifold onto it but only had two choke mechanisms set up to work, it could be a pig to start on cold damp days, I used to poor a kettle of boiling water over the inlet manifold where the whole lot crossed over in the middle, started a treat then .I would thikn with a loverly ally manifold this would work even better.
Mike

[Robrover]

I once had the same problem - not starting from cold but once it did start it ran ok. I also thought it was the Edelbrock carb and played around with jets and settinds. Turned out to be not getting a full 12 volts at the plugs at start up due to a duff coil.

[minorv8]

I let the fuel pump fill the float chamber and then press the pedal 2 or 3 times everytime when starting from cold, be it spring, summer or autumn. You will not flood the engine. My engine then starts within 1-2 seconds.

If it is really cold like around 30 deg Fahrenheit, it might not start right away. It then needs a couple extra shots from the pedal. I don´t have the choke connected. When the engine is warm, just turn the key, that´s it. OTOH, if I don´t press the pedal, it will need a lot of cranking to get it started.

My ignition is Mallory Unilite+MSD 6AL. More often than not, like Robrover suggested, poor starting may be due to electrical gremlin, not the fuelling.

[mgbv8]

I do the same Minor. A few seconds to make sure the fuel is up. 3 pumps on the pedal and she bursts into life in any weather. When its really cold I have to tickle the throttle for a few seconds to get the rpm up to about 1200 and then she smooths out and will pretty much idle from cold.

[jefferybond]

I once had the same problem - not starting from cold but once it did start it ran ok. I also thought it was the Edelbrock carb and played around with jets and settinds. Turned out to be not getting a full 12 volts at the plugs at start up due to a duff coil.

The coil was new when I built the engine, but that was several years ago now. Maybe I should try a new one?

Jeff

[CastleMGBV8]

Also worth checking that you have good clean wiring connections to the coil, and a good earth on the engine, it can only need a small voltage drop to effect starting.

Kevin.

[jefferybond]

I tried the pumping the throttle trick earlier (with no choke) and it fired right up!

Problem is that I changed two things at once! ie, the starting method, and also I moved the accelerator pump lever one hole richer, so I don't know which of the two did the trick! Doh.

Thanks for all the advice chaps!

Jeff

[Eliot]

I tried the pumping the throttle trick earlier (with no choke) and it fired right up!

Problem is that I changed two things at once! ie, the starting method, and also I moved the accelerator pump lever one hole richer, so I don't know which of the two did the trick! Doh.

Thanks for all the advice chaps!

Jeff

They are related, because all you are doing is pumping fuel from the accel pumps. You can move the linkage back and you should find that it still starts ok.
Ive recently rebuild a chrysler 440 that had no choke on it - 3 good stabs and a little tickling after startup was good enough.

[jefferybond]

On a slightly different subject, which is usually the best position for the accelerator pump linkage on a 3.5l rover v8?

I was running on the outermost hole (shortest pump stroke), but the middle hole seemed to work OK too and might have actually improved the cold start behaviour, although on this position I could make the engine stumble if I jabbed the throttle open and then quickly shut again (which is kinda expected!). I could still snap open the throttle normally and the thing would pick up very well though.

Jeff