Tuning Panda 30 carburetor tune

[gordinir8]

About a year ago i installed a weber 30 250DGF from fiat panda 30 in my tuned engine. Now while on temperatures up to 28-30 Celsius the engine operate fine i have noticed that during hot summer days when i let the engine at idle for a few seconds for example at stop light then it is suffering to gain rpm. I have to slowly press and release throttle and little by little engine starts to rev up otherwise it dies. Removed air filter duct and let the carb breathe free and it improved a lot. I believe that when stopped at idle hot air is getting to the intake because car is not moving and engine suffer to breathe. I removed the standard 650cc intake duct and installed a bigger 60mm duct and bigger air filter and there is some improvement but not like when the duct is completely removed. I am sure that it has to do with jetting but have no idea about what to replace. The jet sizes my carb has are standard as per @Bleeding Knuckles list taken from another post of mine.
Thomas

Jet sizes where like this..
Panda 30 standard in (brackets.)
Air Correction Primary - 1.90 - (1.90)
Air Correction Secondary - 2.00 - (2.00)
Primary main Jet - 1.12 - (1.10)
Secondary main Jet - 1.00 - (1.00)

 

[Bleeding Knuckles]

Hi Thomas, sorry to hear about your problem, Before you try changing jets I would adjust the mixture to make it very slightly richer - turn the mixture screw anti-clockwise (out) a very small amount and remember how much! You say that your engine runs better without the filter duct - try running it without the filter ducting too (all of the time) Remember that you will be changing the volume of air that the carb is drawing in and making the mixture slightly more lean too. Let me know what happens when the temperature is 28-30deg C, we can then think about changing jets if necessary. My engine is running at 712cc in a high state of tune with a wire gauze filter and runs well, but the jetting has been changed to accommodate this.

 

[gordinir8]

Ok I'll try and open the mixture screw a quarter at a time but I prefer to let the filter and duct in the engine if possible. I'll wait for the hot days to come and let you know.

 

[Bleeding Knuckles]

Hi Thomas, I have looked back over the past posts about your engine build and have come up with the following - only adjust the mixture 1/4 of a turn no more, if you have a hot camshaft and reduced the weight of the flywheel the engine will become lumpy and resist initial acceleration because you have moved the torque curve up the rev range. To help with this problem (I Have it too) increase the engine tick over to 1000 rpm minimum. This may sound high but it will help the response of the engine. This problem is very obvious with my engine running a 9.8:1 C/R and worse still with my 'Hot' engine running a 10.5:1 C/R. When the air temperature is high you have the problem of hot air getting drawn in and compounding the issue. You may still need to go up one stage with the Primary Main Jet and Secondary Main Jet, I can give you the figures and where to obtain them when needed.
Ian.

 

[gordinir8]

Ian thanks for getting your time with my problem. What I was thinking was that because of hot temp, air density is low so less air, less compression, more fuel thus struggling to rev up because of reach mixture under hot conditions, but you are telling me to step up main and secondary jets! I thought that this will make it worse but obviously you know better than me and I'll follow your instructions. (Tuning carburetors was never my strength point) So I will open needle by 1/4, increase tic over to 1000rpm (usually I am increasing it at summer a bit for better cooling) and then if still necessary ill go for the jets which I believe I should do anyway because this is a stock carb on a tuned engine and I am afraid that it might running lean. If those jets are on the diagram above tell me the numbers and I'll go to our local Weber dealer and buy them.

 

[Bleeding Knuckles]

Hi Thomas, A pleasure to help, Don't worry about the mixture adjustment as it is small and can be reset if required. I would wait and see how the engine runs with the small mixture change and the tickover increase. Take the plugs out and check for good combustion anyway too.
The jets you May need are (primary main) from 1.10 up to 1.12 - (secondary main) from 1.00 up to 1.02 the part numbers I used with my weber supplier were 7380111200 and 7380110200.
Ian.

 

[gordinir8]

Hi Thomas, A pleasure to help, Don't worry about the mixture adjustment as it is small and can be reset if required. I would wait and see how the engine runs with the small mixture change and the tickover increase. Take the plugs out and check for good combustion anyway too.
The jets you May need are (primary main) from 1.10 up to 1.12 - (secondary main) from 1.00 up to 1.02 the part numbers I used with my weber supplier were 7380111200 and 7380110200.
Ian.

Thanks Ian, one last thing, are those two jets on the diagram I have posted on my first post?

Thanks

 

[Bleeding Knuckles]

Hi Thomas, the Primary is yes, the secondary is not - note part number 7380111200 and 7380110200 hope this helps.
Ian.

 

[dangfiat]

Just a guess (and possibly a bad one)... but are you maybe getting vapor lock when you idle on a hot day?

I can't think of why you'd be so on a knifes edge with the jets that a few degrees would cause the hot air to run lean. Almost seems like the fuel is vaporizing. I know "the hobbler" and others run a return line for just this reason

Again, could be wrong. Just a thought

 

[gordinir8]

Just a guess (and possibly a bad one)... but are you maybe getting vapor lock when you idle on a hot day?

I can't think of why you'd be so on a knifes edge with the jets that a few degrees would cause the hot air to run lean. Almost seems like the fuel is vaporizing. I know "the hobbler" and others run a return line for just this reason

Again, could be wrong. Just a thought

All thoughts are welcome, I hadn't think of it. Sunday we had 28c plus and I had problems again, increase idle as advised and opened idle screw by one turn (quarter didn't made any change) and it was a little better. Problem is that I can't install a return line, there is no clearance for it except if I fabricate a special union, now it is plugged.

 

[dangfiat]

I know the Hobbler here and a few others ran the return from the carb back around the engine to "tee" into the fuel line just before the pump. I might try that myself

 

[the hobbler]

I know the Hobbler here and a few others ran the return from the carb back around the engine to "tee" into the fuel line just before the pump. I might try that myself

Yes, I have a 'return' fuel line on my FZD carb. I have run a fuel line from the carb, round the back of the big 'cooling-air-intake-hose' (inside some fuel line as protection) secured by a couple of 'P' clips to a METAL "T" junction, in the engine bay, but before the fuel pump. I secured the "T" piece with rubber-lined 'P' clips holding the fuel lines iether side of the 'T' piece against the side of the engine bay. I have never suffered any 'hot-start'problems
When I was doing my apprenticeship on M/Benz cars, the 220SE and 230SL had just come onto the market. Both of these cars had a 6-cylinder engine with a simple '2-plunger' pumps for their fuel-injection system and a 'constant-flow' fuel system, with the fuel being delivered by an electric pump that delivered (if my memory is correct) about a gallon per minute. As the fuel was constantly flowing , you could feel the difference in temperature over a 'non-return'system---the fuel lines were quite cold.

 

[Bleeding Knuckles]

Hi Thomas, We have had our first + 28deg C day today so I thought of having a test, The engine I have in the car has a 3.5ltr alloy sump with no oil cooler fitted with my carb running as standard except for the slightly larger jets as previously mentioned. The one difference is that I use a Pierburg E1F electric fuel pump running at 0.10 bar (1.45psi) I don't have flooding problems at any time. There was no change even when the oil temperature reached 100deg C. If you are suffering from fuel vapour and cannot fit a return line you could try an electric pump. I would check the delivery amount from your fuel pump anyway. Look at the Pierburg service info sheet for number 7.21440.51.0 if you need any info let me know.
Ian.

 

[gordinir8]

Hi Thomas, We have had our first + 28deg C day today so I thought of having a test, The engine I have in the car has a 3.5ltr alloy sump with no oil cooler fitted with my carb running as standard except for the slightly larger jets as previously mentioned. The one difference is that I use a Pierburg E1F electric fuel pump running at 0.10 bar (1.45psi) I don't have flooding problems at any time. There was no change even when the oil temperature reached 100deg C. If you are suffering from fuel vapour and cannot fit a return line you could try an electric pump. I would check the delivery amount from your fuel pump anyway. Look at the Pierburg service info sheet for number 7.21440.51.0 if you need any info let me know.
Ian.

Ian Thanks for the update, i was out today and i slightly had this problem one time only but i wasn't driving in traffic etc but i tell you that because of increased idle speed close to 1000rpm i think that this helps a lot. ill see what i can do for the return line, it is something i wanted to put from the first time i installed this carburetor.