Howdy guys, I'm working with my Ford 200 L6 and i got a weber 32/36 on it. It smells kinda gassy at idle. I had an extra Holley 5200 (holley version of the weber for those who aren't familiar) and i believe its for the Ford Cologne 170 V6. Using proportions, I got pretty much all the same jet sizes i currently have, except my air correctors. i was given the jet sizes that I currently have, i did no calculation whatsoever These are the calculated values. So should i jump up my air correctors? Currently i have 180/160 for the primary/secondary Thanks
jets usually are proportional the the (airflow) size of the carb. The carb doesn't know or care how big the engine is, the ratio of fuel to air needs to be the same for all engines. There are some differences due to other factors, though.
So like for my case, what differences should be for the 170 carb and my 200 carb? So how do I know if my jet sizes are correct-ish without a wideband?
For jetting, look at the base ring. It will run hot or even surge at cruise when too lean. Start out rich and jet down. https://www.dragstuff.com/techarticles/how-to-read-plugs.html
Adjust the idle mixture screw, play with it enough to get a feel for how the engine sounds, etc when you adjust it slightly rich or lean. What I'm trying to tell you is that if you think jetting should depend on engine displacement, you need to do some more reading about how carburetors work, because you don't understand the basic principle of air/fuel ratios, and how carburetors achieve that ratio. It has nothing to do with engine size.
I remember reading posts by @gimpyshotrods on here, he seemed to have a s**tload of information on webers and ford sixes. Search for “weber” posted by gimpyshotrods, lots of information.
A good start would be to return the carb to the stock configuration, assuming it's been monkeyed with. A friend had one of those Webers on a 200 six in a Falcon about 30 years ago, I'll ask him next time I talk to him if he remembers if he changed parts in the carb.
I've heard of that guy! Also, a funny circular reference, as I believe that he got the jet numbers that he is using from me.
Idle jets (small): https://www.pegasusautoracing.com/productselection.asp?Product=1587 Idle jets (large): https://www.pegasusautoracing.com/productselection.asp?Product=74409 I believe that there are two jet body sizes. I would have to check my Holley 5200 spare and see what it has. It might have the fat ones, which, I believe, are the same body size as down/sidedraft Webers. Idle instructions: http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm Jer Pac part numbers: http://www.redlineweber.com/html/application_guide/performance_main_and_air_jet_kit.htm
Hey man! What do you know?! Haha. Yeah the car runs great and i cant seem to get the idle mixture screw in more than about 3.75-4 turns out. Reading on webers, it says it should be 2ish turns out. Thats a big part of why I think I'm running rich/lean with the jets. Since I'm backed out, either its not getting enough gas or I'm not getting enough air. And this would explain the weird smell i get from the ewww exhaust (either rich or lean) Also my speed screw is tightened in a lot more than recommended and im only getting an idle of about 500rpm (i haven't tached it yet) and 12 degrees of timing See what I'm trying to get at?
So let me get this straight, if it has absolutely nothing to do with engine size, then I should be able to take that 170 V6 Holley and slap it on my 200 L6 and have no issues b/c the carb jet sizes have nothing to do with displacement? That can't logically be right. A larger engine requires more fuel and air. A carb will only allow so much to go through it, yes i get that part. But solely playing with the idle mixture screw can't allow the engine's needs to be met. Thats why jet sizes are increased for larger engines and downsized for smaller engines. The jets restrict how much gas goes in, and thus larger jets allows more gas in and vice versa. And to being Gimpyshotrod into this, I don't know if it is pure luck, but when you do the proportion math like as I posted, i got pretty much the exact jet sizes he gave me in the first place. That much tells me there, that at least for the most part, jet sizes are mostly proportional to engine size, until the carb can't deliver what's needed. Right?
It’s all about air flow, change air flow , change the jets.. more air going in will need more fuel to keep things right. Going by displacement will give you an approximation, but all engines aren’t created equal. The same carb on a stock engine won’t be jetted right for the same engine that’s been modified to get more air in . It’s not as simple as referring to a chart but a chart might get you into the ball park.
Gimpy, those Weber idle adjustment instructions are really good at explaining how (and why) to adjust idle mixture screws. It looks like Weber use different size jets for the idle circuit itself and they emphasize that about 80% of driving is done on the idle circuit (or just off idle) in the transition area of the carb and they have taken a careful approach to get this dialed in closely.
It's also interesting, it is not universally true that more air in always = bigger jet. More velocity may simply pull more fuel from the well. For example, dual exhaust over a restricted stock system "should" mean bigger jets due to a leaner cylinder charge, better scavenging. This may be necessary, though not always. Give it whatever it wants based on the plugs etc.
Wouldn't it be easier to just jet down one size and see how it acts? Numbers in charts are just starting points since all engine are slightly different, altitude, Barometric pressure, humidity, worn engine, fuel type, all play a role in how they run. Start with a jet thats damaged or way to big, solder it shut, drill out smaller then you need and try it. Keep drilling till it runs right, then hunt down a factory made jet with the same size hole you drilled.
When you take a carburetor from a smaller engine and install it on a larger one, you need to readjust that carb to get the same idle speed. If part of that adjustment involves cranking in the throttle stop screw to increase the idle speed, the relationship of the throttle plates to the fuel transfer slots/ports in the carb throat changes, which changes the A/F ratio. Even running with, without, or a different air cleaner will result in A/F ratio changes. A different engine may also need a different "diet" due to cam timing, overlap, intake manifold differences, etc. Simple math may get you close in this instance, but it's not usually the case.
Stop for a moment and think about your question. If I had 2 engines, 1 bone stock and the other with everything thrown at it (a roller cam, 13:1 compression, ported heads, etc.), would they take the same carb and same jets for those 2 combinations? Absolutely not. It's about matching air flow and fuel flow with the parts combination inside the engine to get in that specific A/F ratio mentioned above. SPark
So my proportion thing im talking about is for stock engine to stock engine. I understand cam/compression/atmosphere/etc all has to do with it. I'm simply trying to get into the ball park using jet sizes from a smaller but similar engine. This is what I saw when I asked the same question on the fordsix site and the guy posted about his 170 L6 holley 5200. My air correctors are smaller than his and he's running 10:1 compression on a stock bottom end. So my guess, with the higher compression than mine, but smaller engine size should put me about what I should be at. So i think i should start with either what he has, and work my way up, or start maybe 5 higher on both. I'm just trying to get closer to what it should be, and based off what I just saw on the fordsix I think my air correctors are a little small, which explains my gassy smell. (I would think) What do you all think? I'll pull my plugs next and take a picture but which one should i pull for the L6? The center ones naturally run rich and the outers naturally run lean. Should i just pull 2 and 5 then since they should be in the middle?
If you're opening the throttle too far at idle, it exposes the transition circuit. The idle mixture screws then have little effect on mixture. The transition circuit supplies fuel for part throttle, and will be over fueled at idle. Figure out why it won't idle with a reasonable throttle adjustment, then come back to mixture adjustment. On engines with lumpy cams needing fast idle, one solution is to drill a small hole in the throttle blade near the idle jet to provide the necessary idle air without opening the blade too far.
Use this chart to compare cubic inches to your engine to find a starting point then use your sparkplug readings to make changes if needed. Whoops, this is just the first page, there are 6 more that will not load......
Your carb might be new enough that the idle mixture screw is in air circuit, not the fuel and that might be causing you some confusion. We normally think the idle mixture screw affect the gasoline flow, but the EPA 'improved' hoe the idle mixture is adjusted in the '70's. The jets are sized the amount of horsepower your engine makes, a 350HP 327 chevy will be jetted very nearly the same as a 350HP 454 chevy. They'll both take the same amount of fuel and oxygen.
Once the air/fuel ratio is correct, a carb will work on different engine sizes. The smaller carb on the bigger engine will restrict getting the highest HP. In reverse the large carb on the smaller engine will work a very low speed but flood the engine with too much air when opening up. Changing compression ratio does more harm to tuning than any other modification. Moving from 8.5-1 to 10.5-1 will definatly need a jet change.
Not true , the len GTgth of the orifice is as important as the diameter of the orifice , hence you will find 2 jets drilled the same size numbered differently.....check a holley jet chart , also the chamfer of the orifice ma makes a difference
Is there a way you can find a part on that PDF near 3300 cc or 200ci? When i look at the jets for the 32/36 DGV its much smaller all the way around than what I currently have.
The Jalopy Journal
