Hey guys. Been trying to get the mix right. Mild 327 - Offy 6x2 manifold. Running progressive linkage so basically just running two middle carbs. I am down to 39 jets and 69 power valves. Front four plugs foul up really quickly then the car starts to run rough - I have a basic MSD setup. The back four plugs don’t get anywhere near as sooted up. I am gradually getting longer runs between cleaning plugs. Thought I would ask the question before I change jets again because they ain’t cheap here in Australia. Sent from my iPhone using The H.A.M.B. mobile app
You've got two more headaches then me. Plugged a port in each carb. I made a holder for lathe so I could braze and drill main jets till my mix is right using an O2 sensor to read. (Fastest way I got jetting down). Also make sure ALL butterflies close completely. Sent from my VS988 using The H.A.M.B. mobile app
Solder works well for closing jets up, then drill back out to the size you want. When you get it running right, order the correct jets. Find someone with a Air/fuel ratio gauge you try, it will quickly dial in your mixture. As for the front running rich, block off the two front carbs with sheet steel or aluminum under the base gaskets. If the plugs clean up, look at the carbs to see why they are not shut off when not in use.
^^^^^my guess would be that the four secomdaries are leaking. At idle have you placed your hand over the carbs to see if there is vacuum present. The slightest leak is going to pull fuel thru. Have you considered blocking off all 4 secondary carbs and tuning to the primaries first then adding in the secondary carbs after it is running well on the two?
Yes the secondary carbs do draw some air even though the blades are fully closed off. Thanks guys. I think blanking the secondary carbs may be what I have to do to isolate a problem that may be there. Sent from my iPhone using The H.A.M.B. mobile app
Don't they make thicker plates for secondary carbs? See if you can get some of those to close off the outer four when the throttle isn't stomped.
Nice intake. Feel your pain. Have the same with a 283. Have the highest power valves I could get, and have only 1 of 1 idle vales open in each carb. Seems to be working well for now...
YES. In 1955, there were some guys on our racing team that soldered the jets, then drilled them around .042", IIRC. But when they left the soldered jets in, the solder gave way and/or simply eroded the newly drilled holes! (in time, not overnight...) Find the right sizes, replace with the correct new brass jets.
Sorry, no advice about the carbs, but is that a legit Western Australia license plate? It's a great one!
Surprised to hear about solder in the jets giving way, the floats in my carb are soldered together and are holding up fine.
Make yourself up a vacuum gauge set with a gauge for each carb. That too is a great way to see each. Got that tip from a guy in the Keys who is always out with a graffiti coupe. He gives his rod a steady pounding. Sent from my VS988 using The H.A.M.B. mobile app
The secondary’s are Big 97 secondary carbs so I guess they have the correct plates? Good suggestion though Sent from my iPhone using The H.A.M.B. mobile app
Nice my car is going good - I just need to get the plugs to stop fouling so quick. You are adjusting your idle mix on just one screw per carb? Sent from my iPhone using The H.A.M.B. mobile app
Interesting thing is all four secondary carbs pull a small amount of air. Back four plugs are good - if all eight were like that I would be happy. Sent from my iPhone using The H.A.M.B. mobile app
Yes - on a progressive linkage that does not come on a this point. Just trying to get the primaries right Sent from my iPhone using The H.A.M.B. mobile app
Yep, I closed one idle screw on each of the 4 carbs, and use the other to adjust for idle. Got it dialed in ok, starts right up and pulls hard (though a get an occasional backfire on acceleration when the accelerator pump linkage falls out on one of the carbs and it leans out those cylinders still working on that), though haven't synced via a Guage yet so hopefully even more to come. Sent from my SM-G960U using The H.A.M.B. mobile app
Kind of oranges to apples comparison. The jets have fuel flow through them....erosion is possible/likely. Floats are surrounded by fuel but the flow, if any, is minimal and not through an orifice. Erosion is extremely unlikely. I may be all wet but that’s my take on the differences involved. Ray
Stock jetting should only be changed when raising compression. I’ve run multiple carb systems since 1962 and unless I changed to higher compression the stock jets remained. The air to fuel ratio stays the same no matter how many you use. Depending on the way the manifold was built one or two maybe increased or decreased to get proper plug readings. Same with accelerator pump nozzles. Occasionally I had to change the cam or lever on the pumps. The best information I ever received was from Howard Johansson after I bought a cam for my GMC and running multiple carbs on my 6’s. Even after moving to over 12-1 and running Bonneville did what he taught me how to tune gasoline ever change.
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