30/31 idle and power jet. Which is which???

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30/31 idle and power jet. Which is which???

Post by fluxcap on Wed Jul 24, 2013 2:11 pm

Been reading on this for a few days, and found no definite answers about which location is correct for which jet.

Picture stolen from thesamba.  The person who made this picture believes the power jet is the rear (rear of car) angled jet, and the idle jet is the front (straight) jet.




There is a post here from Rob of rob and daves vw-resource.com website which says the same as the picture.
http://www.shoptalkforums.com/viewtopic.php?p=602362#p602362

However, on Rob and Daves actual vw-resource.com writeup, they say the opposite.
http://www.vw-resource.com/jets.html#30

"On the H30/31 carburetor, there are two brass jets on the right side (right is right of car). The angled one (points slightly towards the rear of the car) is the idle jet. The other one (pointing straight out to the right side of the car) is the power jet, which feeds additional fuel at high throttle/high rpm. The power jet is needed to correct a tendency for the air correction jet to work TOO well at max airflow - it leans the mixture off too much and the power jet corrects this."

John at aircooled.net also says the opposite of what the picture says.
http://vwparts.aircooled.net/Solex-Kadron-Brosol-and-Bocar-Idle-Jets-p/solex-idle-jet.htm

"The Idle Jet and Power Jet are physically interchangable, but are different sizes. These are often switched on carbs by guys that think the idle jet should be small and the power jet should be big! Make sure the Power Jet (50, in the ANGLED location) is to the rear, and the Idle Jet (65, out the side) is in the front."

I have a 65 and a 50 jet, where the heck should these go???  study 

Ever since I've had the bus, the 65 has been in the rear angled location, and the 50 has been in the front location.  Just wondering if this is correct, or if they need to be switched around.  Bus has been running good, but ran pretty hot last time I had it out (oil light came on at idle, dipstick very hot), so I did a tune-up (valves, oil, timing, carb) but when following the "2 screw" carb adjustment instructions, I didn't get all the responses (increase/decrease rpms) the instructions said I would get when tinkering, and I'm wondering if this could be why.  

Anybody got a definitive answer.

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Re: 30/31 idle and power jet. Which is which???

Post by vw57drvr on Wed Jul 24, 2013 2:22 pm

Did you see this from Vw-resource? Last sentence.

"There is an pilot (idle) jet on all carburetors too - these are normally left at 55 for most carburetors (28, 30, H30/31 and 34 series), on any engine size (since it's only feeding the engine at small throttle settings anyway). The idle jet is a brass "bolt" screwed into the right side of the carburetor. On older/2 carburetors it has the idle solenoid screwed into the back of it. On the /3 and /4 carburetors - it looks like a bolt with a tiny silver plug in the center. On some models (the H30/31 for example) it is angled slightly towards the back of the car."
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Re: 30/31 idle and power jet. Which is which???

Post by fluxcap on Wed Jul 24, 2013 2:36 pm

Yes, I did see that!  Just confused, cause the vw-resource page says the one angled towards the rear is idle, but then Rob from that same page, says the opposite thing in another post on the shoptalk forums.  And then aircooled.net is also saying the opposite.  Makes my head spin, lol.

However, I did find this diagram of a 31pict3, which I think the 30/31 is modeled after and it does indeed show the idle as the rear angled jet, and the front jet as the power/auxiliary jet.  



I'm think I'm just going to leave it as it was and do some more test driving to see if my tune up helped it run any cooler. Right now I've got the idle jet set as the 65 which is what vw-resource says the carbs usually came with and is also what aircooled.net suggests (though I think John has the locations incorrect).



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Re: 30/31 idle and power jet. Which is which???

Post by pwmcguire on Thu Jul 25, 2013 2:30 pm

I had the same issue, I could not figure it out. I thought of asking Clyde to pull a new one out of the box and look. My solution was to go back to a 34 pict 3 with a stock 034 distributor. It's the best running engine I ever had and no gas smell from the Exaust.
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Re: 30/31 idle and power jet. Which is which???

Post by fluxcap on Thu Jul 25, 2013 2:34 pm

Yeah, I ran that combo on my bug before I got duals and like it. The bus is a single port though, so want to try to stick with the 30/31. I took it for a spin yesterday and the oil light never came back on, but the dipstick was still hot, though I could hold it. Gonna pull the sparkplugs soon and see what story they tell.

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Re: 30/31 idle and power jet. Which is which???

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