Motorcraft 2100 1.21 on 2.8

[PetesPonies]

No you are incorrect. Cold air will not help fuel atomization. See what you are missing is the knowledge of how a carburetor functions. What the problem is you have a small engine, that is capable of pulling "X" amount of air into it. A different filter or intake will not force more air into the engine. The air is drawn in by the vacuum created by your pistons. A power adder will force more in, but that's the only way. You now have a hole in your carburetor that is hour glass shaped. It creates the vacuum signal that will pull the fuel out of the nozzle and cause it it atomize. Sense your carb has a hole that is larger than your engine needs, air will be drawn through without a proper vacuum signal created. The way it works is air has to speed up to get through the venturi,. the air moving faster lowers the pressure and a vacuum is created. Since your engine is pulling less air in, the air does not have to speed up as much to get through the venturi, thus little vacuum is created and the fuel, is not drawn out correctly nor is it mixed correctly. This is the vacuum signal that the carburetor creates. You have a poor vacuum signal, thus the textbook problems you are having.

 

[BichoBII]

yes i understand that, atomization is not the correct term, but i understand colder air has more density and should drag more fuel to the engine than the hotter thinner air im running on without the stock air box/duct... i think so...

 

[PetesPonies]

You are correct it is more dense and can support more fuel. But I don't believe your problem is too much fuel, actually the opposite. But the fuel you have is not properly mixed.

 

[BichoBII]

yes im hoping for more fuel with colder air. went to try the cold air duct i improvised today, got more throttle response, but still knocking under load at low rpms... input from someone using the 1.21 would be great...

 

[PetesPonies]

You are trying to make a carburetor that flows 25% more air react properly with a small engine. I would say the 2150 at 1.08 was a bit large, but understand the one Ford used is a feedback carb. Therefore, they ( computer ) had some control over things. It was also a known stop gap . . fuel injection was on the way. Look at the size carb that was used on the 2.8l when it wasn't a feedback design.

 

[PetesPonies]

By the way, your engine is probably flowing about 230 cfm at WOT. That 1.21 carb is 351 cfm.

 

[BichoBII]

Its all great info man, i appreciate it, but for now i need to know what did those guys with 1.21 on their 2.8's do to get it running good. I am looking for a 1.08 (or smaller), but until then, 1.21 is what i got

 

[drgrcr]

Here is what I am using, I run a 1.08 with 46 jets, a #65 power valve, I set the timing using the max advance, that is bring the engine rpm up until the timing quits advancing (vacuum advance disconnected) and set the timing at 36' degrees it idles at around 15' degrees. Then I use a hand held vacuum pump connected to the vacuum advance on the dist. pump it down to 10'' of vacuum and adjust the vacuum pot for and additional 15' degrees. So, say the vehicle is cruising at 65 mph engine rpm is 3100 and manifold vacuum is at 12'' then the timing will be around 32' + 15' total of 47' degrees. Carb power valve is closed so it the carb is pulling on the main jet & intermediate circuit. It will be a little lean but works well. The truck gets 18 to 21 mpg around town. No spark knock on 87 octane fuel.

oh yeah, the egr valve is disconnected, and the air pump is non functional, and the cat is removed.

I am in the process of building another engine that will have 10 to1 compression, port work and 2.9 valves. And plan on tuning it to run on 87 octane fuel in 100' degree weather at 3300' altitude with occasional trips to 600' elevation. Will keep ya posted.

Oh yeah, vehicle is a 83 Ranger, auto trans, 3.08 axle ratio. A/C (gotta have it in Arizona) does not run hot, great little truck.

 

[BichoBII]

3.08! I thought my 3.45s were tall, what tire size are you running? Im on 235s and i can't make a turn in 2nd gear without knock. And 15 degrees is a lot, guess i can go up there with larger jets, i thought i could go up only to 12 degrees to compensate for altitude. My timing light died, so ill do some tests by feel and keep posting the results, thanks!

 

[BichoBII]

BTW Wich side turn to reduce vacuum advance?

 

[drgrcr]

Counter clockwise will reduce vacuum

 

[kimcrwbr1]

The main problem with using the 1.21 venturi is the fuel does not atomize properly and puddles in the intake manifold. Maybe you could rig the choke to stay partially closed to richen up the mix a little. I`m running #43 jets with good results. This spacer will save you alot of greif with vacuum leaks on the base of the carb felpro#60529
http://www.ebay.com/itm/Fel-Pro-Car...Parts_Accessories&hash=item5aee4ba101&vxp=mtr

 

[drgrcr]

Is the vehicle a south american or US?

 

[BichoBII]

US. That choke plate idea sounds good, will try it soon. I remember when I rebuilt the carb there was a piece of mig welder wire, bent in v shape, inserted in fuel passages i think. I removed it since it was not part of the carb, but now i think it could be there to improve atomization.......?

 

[BichoBII]

I think i dont have leaks, although that gasket looks much better than the one i have, will look around for it