Motorcraft 2100 1.21 on 2.8

[BichoBII]

Hi everyone, i bought an 84 bII about 8 months ago, and have been dealing with PO bad repairs, at first i noticed it was running cold, never reached op temp, found out there was no tstat, so instaled a 180°, temp gauge goes to the middle, but then started knocking under load. Then learned a little about carbs, realised my bII have been durasparked, with a 1.21 venturis 2100 motorcraft, and jets where size 41... so started going up (btw, im at around 9200 feet), reached 51 and spark plugs came out black, so went down to 46-47 until plugs were mostly tan, but i still get knocking under load or slightly heavy acceleration. At first i set timing to 10 btdc, but felt better at 12, guess its ok because of altitude. Im running 3.45 gears, 235 tires, and airbox is missing, so breather is taking air right over left exhaust manifold. I know its a bunch of things, but it would be great to find someone with similar setups, mostly jet size for 1.21, i know 1.08 is the correct carb size for the 2.8, but have heard of people running strong with the 1.21, besides its hard to find one here in Ecuador, so im trying to make it run as best with what i have. Any input is very appreciated, thanks!!!

 

[kimcrwbr1]

At higher altitudes you want to run leaner (smaller jets) the problem with a 1.21 venturi is the engine is not pulling enough cfm`s to atomize the fuel properly. The pinging is because it is too far advanced. You can try setting the base timing at 6 degrees base and then connect the advance to manofold vacuum then adjust the idle needles out for the highest possible rpms or vacuum pressure. I would put the 41 jets back in also. Ideally if you can find a 1.02 venturi to go with the 41 jets and you would be in fat city.

 

[BichoBII]

Hey thanks for the response! I've tried retarding the timing until almost lost any acceleration and there still was some knocking, so guessed it was more like a mixture issue...

 

[85_Ranger4x4]

I took the intake tube off of my 2.8 because it was all busted up with the stock 2150 and it ran like crap once the engine bay warmed up, really boggy with no power. Thew the tube back in (with a fresh layer of duct tape for good measure) and it ran a whole lot better.

I am at 1200ft, it may be exaggerated with higher altitudes.

 

[BichoBII]

Thats great! haha, I mean for me, i should try making some sort of cold air intake. If 1.21 doesn't pull air right on the 2.8, then hot air will make things worse... It will be almost impossible for me to get the stock air box, so i'll have to addapt or build something...

 

[wildbill23c]

I have the same issue with the whole air filter housing missing and the oil cap hose that's supposed to be attached to the filter housing is just open, what's the proper way to fix this, I know having that thing just there in the open sucking in unfiltered air has got to be very bad for the engine, and the actual air filter on the carburetor I kind of wonder about as well it kind of looks like a knock off of a K&N.

 

[BichoBII]

On the mc2100 there's a port on the top rear passenger side you can use, but i think the best choice is to put a cap with air filter

 

[wildbill23c]

I have the MC2150 and the vehicle is in the shop right now so I can't go out and mess with it, but I'm thinking a filter as well or at least until I can find the original air filter housing.

 

[drgrcr]

Hi everyone, i bought an 84 bII about 8 months ago, and have been dealing with PO bad repairs, at first i noticed it was running cold, never reached op temp, found out there was no tstat, so instaled a 180°, temp gauge goes to the middle, but then started knocking under load. Then learned a little about carbs, realised my bII have been durasparked, with a 1.21 venturis 2100 motorcraft, and jets where size 41... so started going up (btw, im at around 9200 feet), reached 51 and spark plugs came out black, so went down to 46-47 until plugs were mostly tan, but i still get knocking under load or slightly heavy acceleration. At first i set timing to 10 btdc, but felt better at 12, guess its ok because of altitude. Im running 3.45 gears, 235 tires, and airbox is missing, so breather is taking air right over left exhaust manifold. I know its a bunch of things, but it would be great to find someone with similar setups, mostly jet size for 1.21, i know 1.08 is the correct carb size for the 2.8, but have heard of people running strong with the 1.21, besides its hard to find one here in Ecuador, so im trying to make it run as best with what i have. Any input is very appreciated, thanks!!!

9100' wow! what drive mode does it spark knock at?

if it is knocking during part throttle, you can retard the vacuum advance by adjusting the vacuum pot, stick a 1/8 allen wrench in the hole where the vacuum hose connects to the dist. and turn it clock wise to reduce the advance at part throttle. The original dist. curve was calibrated for for more advance to compensate for egr flow. When the egr valve is removed or the port becomes plugged with carbon the engine will spark knock.

I am really surprised that it knocks at that altitude. Must have really bad gas in Equador? low octane?

 

[BichoBII]

Thanks for the reply, I did some tests with vacuum advance disconnected and still knocked under load, so im more inclined to a mixture issue. The comment about the airbox/duct reminded me this happens only at operating temperature, when engine is cold it feels stronger, so i think theres a good chance this is all because of the missing air intake, gonna try adapting some sort of hose and will post the results soon.

 

[dangerranger83]

One thing that has been happening is bad fuel us being sold by gas stations, had it on my local news about stations around me with it. Run a bit more octane and see if that helps.

Sent from my rooted SPH-D710 using Tapatalk 2

 

[PetesPonies]

A 1.21 is too large of a carb. When that happens, you cannot flow enough air through the venturi to make it function as it should. Therefore, you will actually run lean. people wrongly thing a large carb runs rich. Wrong, you cannot create the vacuum needed to draw out the fuel, because the venturi is too large.

 

[BichoBII]

About the gas, we have 89 and 91 octane here in ecuador, im running 89, will try 91. Yes its true about the carb, i want to get a 1.08, but its hard to find one here, in the mean time i need to get the 1.21 running as good as possible, ive read about people using them on 2.8's and running ok, so why can't I.

 

[PetesPonies]

Lean fuel mixtures promote detonation.

 

[BichoBII]

I gradually went up till 51 on jet sizes, but the current 46 brought best results, never got rid of knocking and plugs where black, so im going for the air intake for know, cold air should improve fuel atomization...