250 build questions

At a lot of my refuling locations​ I suspect that the octane is less than advertised. And in the remote areas 85 octane can be $4 + a gallon when local gas is around $2.65 I'd like to error on the side of caution. I've built hi torque v8's with small duration cans and had detonation problems so bad I killed 40% of the power killing the timing to stop the pinging then had over heating problems​. I'll stick to 9.0-9.25 to 1 even if I'm leaving a lot on the table, but I'm leaning towards the Schnider 248/256 cam or the Jones 248 cam. Thanks again for all the input! 16° initial timing made a small improvement but it's really hard starting now??? I had never hooked up the "white wire" on the ds2 today I did to the start side of the starter relay it would only crank, so it's disconnected and I'm back to 10 initial

Howdy All:

I forgot to mention, I'm at 5,000 ft. elevation here in Idaho Falls.

N Smith- Sounds like you have a plan that you are comfortable with and it sounds great.

I'll be real interested to follow your build with the new tranny. So keep it coming.

Adios, David

Nevadasmith":2tbayumi said:

I'm leaning towards the Schnider 248/256 cam or the Jones 248 cam. Thanks again for all the input! 16° initial timing made a small improvement but it's really hard starting now??? I had never hooked up the "white wire" on the ds2 today I did to the start side of the starter relay it would only crank, so it's disconnected and I'm back to 10 initial

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Both cams would be a good choice.
The Schneider has more exhaust lobe duration and lift which is not as important at high elevation because of the reduced exhaust gas volume.

Which piston are you going to use?
Would you consider an Autotec piston that has the correct compression height for a zero piston to deck and correct dish volume so you don't have to do any machining to the block or head to get a 9:1 compression ratio?

As previously mentioned, it sounds like the present engine is being choked by the exhaust system.

Sorry to bring back an old thread...quick update then a newish question...so I haven't gotten around to building my new 250 still running a stock never been apart 74 Maverick motor. I did do a new exhaust 2" down , under the starter goes to 2-1/4" then a flowmaster 40 series. Then turns out between leaf spring and frame. Solved my top end woes, and lost almost nothing on the bottom end..
So after a trip to the lake 8 miles each way. 4 washboard 4 asphalt. My Carter BDS carb, whent to a stuck open float condition. It never ran right anyhow. So 6.25 gallons of gas in 8 miles home, fouled all the spark plugs....my kid will probably never ride in the bronco again..... 3000 rpm second gear 10 mph backfiring through the carb and the exhaust..... I'm done with the Carter BDS.....
I was looking for a 300i6 yf1 carburetor, when I found a motocraft 2150, free, boiled it ,kitted it, vintage inlines adapter. Bolted it on. It is a 1.08 of a 1977 2.8L pinto... It runs rich at idle and lean every where else..... has any one else used a 2100/2150 carb on a 250 at 4000-8000 feet elivation? On a 1.08 carb what size main jets did you end up going to? What size should I order as a starting point?.... before you ask I'm a dumbass and didn't look when I was rebuilding. I sorta thought a high reving, better flowing 2.8 would be about the same a a slug 4.1L..... so what did you do???? Thanks in advance!

congrats on installing the bigger and better sized exhaust system for your 250 and also on picking up the 1.08 Motorcraft carb that's about the perfect size for a 250 engine. With it being rich at idle first make sure the wet fuel level is set correctly and also check your fuel presure too. Then make sure that the choke is fully open before doing the idle mixture is set to the best lean idle setting. If you don't have a vacuum gauge you should get one it will be a big help in getting the tune up dialed in. I can't advise you on the size jets that you might have now though but that's the real beauty of those Autolite / Motorcraft carb's you can pull the top off and check fuel level, jetting, and economizer valve rating, all with it still bolted onto the intake. When it's set up right it will also give you the best in MPG of most any other 2V carb. Good luck