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28/36 Weber Jetting


Evan G

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ok tomorrow ill be remove the top cover of the carby to find out what size my jets are.

 

once the top cover is removed, do the main & sec jets stick out?

 

can anyone offer me some advice?

 

i might even swap the pri to the sec? runs real lean in the prims and real rich in the sec?

 

edit - is it anything like a 3k/4k carby?

Edited by Evan G
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orite cover off.

 

prim 125

secs 155

 

air correction

 

primary says 195

secondary says 150

 

so i swapped jets and air correction jets prim to sec. got more pick up when cruising but still rich. gets stoich at 4500rpm then lean after that

 

 

i reckon ill swap the jets back and run a 140/140 jets

 

do i need to change my air correction jets?

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  • 1 month later...

orite a little wtfable update.

 

was getting 16L/100km on the gor with 130;s pri and 155 secs

 

got home and put 120 pri and 140 secs in her.

 

 

now my o2 sensor is showing lean in 4th @ 60kph at 2000rpm. stays lean for a couple of seconds then goes rich at 3000rpm. then starts to get stoich around 5 grand. then lean till 6 grand?

 

 

even when crusing around goes lean in the pri for a couple of secs then straight to rich....??

 

ryan is running a 32/36 water choke weber, 160 secondary and a 70 primary WTF!

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So.. idle jets do the low work, up to 3000rpm, so bigger idles will cover the low leaness. Mind you, it could be an air leak doing that! ..or even the float level too low...

 

Its looks like the carb had stock Fiat 124 jets in it when you started. 125/195/50 & 155/150/70. I think that's all for economy on the primary and power on the secondary. They were probably pretty dead until the scondary opened.

 

When you swapped them over you had 155/150/50 and 125/195/70, which gave you rich low down and lean up top.

 

Then what happened on GOR? Did you swap the air jets back, to get 130/195/50 & 155/150/70?? or were you cruising on 130/150/50 & 155/195/70 when you booted it?? That would be worth 16L/100!

 

..and now are you on 120/195/50 & 140/150/70?? Lean, then rich in the middle, then rich at top? The 120/195 combination looks very lean.

 

What jets do you have to play with?? Can you go back to stock and get some solid readings?

 

I know with the SUs there is a couple of seconds delay in the gauge reading, and they are always changing up and down as the car responds to the road loading, not the accelerator position. So its hard to get definate data, but basically the differences are in a slight throttle push at 2000rpm can give either stoich or lean, depending on the needle, and top end 100kph plus can vary on the needle. Cruise can vary by needle and setting. So idle is always easy to set, off-idle acceleration is always richer when you boot it, and over-run/cuise is lean. It varies a lot with how much accelerator input you give it, just a very slight push usually goes lean, but a bit more richens it, so it takes a lot of driving to really get a pattern.

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Actually Evan, stick it back to stock Fiat jets and set the idle according to page 42-43 in the pdf document. Keep the vac advance on, (does nothing at idle) throttles closed off completely and 400rpm on the idle screw only, then take it up to 2000rpm on the idle screw.

 

That might show up any vacuum leaks, and the number of turns on the idle screw to get the smoothest idle shows the suitability of the idle jet size.

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I'm running 150 primary air correction and 195 sec air jets with a 130 pri and 155 sec on the GOR

 

i reckon it has to do with the air correction jets, my carby guy said they only kick in in the higher rpm?

 

ill have to read thru that weber tuning guide agian.

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I'v recently put a new carbie in my KE55 and was looking for someone who could help me out with a minor thing. My old Carbie created pressure for an air hose that went in to the head of my engine. This pressure kept oil from coming up through this hole. When I got the new Carb it didn't have a pancake on the top, so there was nowhere to put the hose. I just got one of those cheap little filter things from SCA or wherever. Turns out these don't create any pressure downward and so the useless little thing is now full of oil. Oil is also being sprayed through the engine bay.

A friend thought a little one way valve would do the trick, if I could find one nice and easily. Anyone run into the same problem? And if so, how did you fix it?

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Micmac, don't KE55s run PCV systems??

 

My KE70 motor has two vents in the tappet cover, the rear one going through the PCV valve to the inlet manifold. This creates suction that clears the oil fumes out of the crankcase & sump. To let air IN to replace the fumes being sucked out the other vent on the tappet over sucks clean air from the air cleaner.

 

Evan you're right, the air correctors have more effect at high revs. The idle jets get you going up to a couple of thousand revs, then the main jet system. I thought the air jets were about main fuel jet + 60, so a 130main fuel needed a 190 air jet as a starting point.

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from memory (I ran one of those for some time on a 4k with a huge cam) there is an idle adjustment on the secondary as well as the primary - have a look, it might be open too far.

 

there is primary and secondary idle jets as well, one either side in a jet holder about halfway up the carburetor.

 

I'd block all the vac ports and get it going then work out what you have and where you want it to go.

 

I had mine idling very consistently at 800rpm with that carburetor, but it took some dramas to sort vacuum leaks out on the inlet manifold first.

 

Robert.

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