I have a 71 240 F100 that I bought not to long ago. The truck was barely running when I got it, but since the rebuilt YF carb from Discount, cap, rotor, wires, coil, plugs & points, its running and now I need a little advice.
It loads up from about 3K up on the road. At idle it runs a surprisingly steady needle at 18in. Dwell is 33 and timing is 6BTDC. I don't know what the dwell and timing numbers should be but when I got it they were 40 and 10BTDC. It seems to run better at 33 & 6BTDC though so I left it there until I can find out what the dwell and timing should be.
When I hit the gas rapidly from idle in the driveway, it will start stumbling but it doesn't stall, eventually, it will catch up with itself. If you milk it, it will sound half way decent throughout the RPM range, maybe some mild popping, and no big backfiring through the exhaust or carb. No smoke through the exhaust at all. But running it on the road I can go alright until the upper RPM band, say 2K-3500, I don’t have a tach so that is a guess, and then it starts breaking up and stumbling all over itself and I have to shift way to early.
Now I notice that the timing does not advance until 1500RPM and then starts advancing out of range of the scale.
Shouldn’t I be getting a gradual increase in advance throughout the idle-2500RPM range?
The distributor is a dual-diaphragm type and the vacuum hose that is farthest away from the dizzy goes to full vacuum and the vacuum hose nearest the dizzy is going to the DIST port on the carb. I don’t know if this hose routing is correct. When I draw a vacuum on the hose farthest from the dizzy, there is no resistance. Is the diaphragm blown?
I have replaced most of the things that I wanted to replace without starting to buy things that may not need like a new distributor.
Just wanted to run this through here and see what you all think. Thanks. James

 

Hi James, sounds like your dizzy is way out of wack and the vacuum advance is ruptured. I’d get a new dizzy along with a vacuum unit. The port on the outside goes to ported vac. and the inside one goes to manifold vac. Point gap is .027” and dwell of 35 – 40 degrees.

Barry

 

Sorry, I don't have any answers for your questions, but I also own a 71 240 F100 that I am starting to tune up. Could you tell me what you set your curb idle at? The Chilton book I have shows 850/650 and I am a little confused about that.

 

If I read that correctly the vac hoses are backwards on the advance.

The high rpm stumble could be plug wires.



Tom

 

Am at work and don't have any reference stuff but I would guess 850 is for a stick and 650 is for an automatic (in drive).

Barry

 

OK, here’s the latest. I switched the vacuum lines so that the inside goes to manifold vac and the outside goes to the dist port on the carb. It did not make a difference, but I guess it wouldn’t if the dist was shot.
I have no references for figures; here is what I have so far:

Curb Idle? For both auto and manual to also help out Pramos.
Timing?
What hose to plug off to set the timing?
Dwell: 35 to 40
Point Gap: .027

Could someone fill in the blanks here??

Tapenick, the plug wires are new 7mm Beldens A new coil and new Autolite 45’s.

Also, I have set the idle mixture with a vacuum gage. I backed out the screw 1-1/2 turns and the started the truck while it was at operating temp. I turned the screw out until the vacuum rose and stabilized then I slowly turned the screw in 1/8 of a turn at a time, waiting for the engine to stabilize each time I turned, until the vac just started to drop. Then I slowly backed the screw out until I just got the highest vac reading while counting turns. Then I divided the turns by two and turned the screw in by that number. Does that sound right?

I set the choke by holding the throttle open maybe 1/4 open and turning the choke until there was a 1/8” gap from the choke plate being closed. The engine was cold (for Florida, which was about 58 this morning. Does that sound about right?

Is there any way to check to make sure that the vac advance is working properly? What should the dist port vac read at idle? At 2K RPM? Should I be getting advance right off of idle or is it normal for vac not to start coming in ‘til 1500 RPM. If I draw vac at the dist port side, should I see the timing start to advance?

Questions, questions…I know. Thanks for all of your support. I will try to give you all of the info that I come across. Poor ‘Ole Red….. I know he’ll run well once I get this licked. The vacuum gage is rock steady and it burns no smoke or leaks no oil. Sounds great until I hit the gas….

 

go to autozone $34 for a new dizzy with piont's already set at the proper gap with core, I put mine in at autozones parking lot!!!

umm I thought the gap was 18-21 on a 360 points umm what size motor you got bub?? I might be wrong on the gap though

71 f-250 4 speed with a 360 with the death knocks

 

Seems if switching the vacuum lines didn't make a difference the vacuum advance must be bad? One's supposed to retard the timing and the other is supposed to advance it... if those are working backwards I'd think you could tell it.

If you manually pull a vacuum on each line can you hear the engine speed change?

As for setting the idle... you did it exactly like I've heard except for the divide by two part. I thought you were supposed to set it for max vac and leave it right there? Can anyone confirm?

 

Yeah, you should have left the mixture screw at the highest vacuum level.

Ok, here's what the 850/500 spec. is, F100's have a throttle position solenoid. For a manual transmission, 850 is the higher idle speed with it energized, 500 is the lower idle speed with it de-energized. For a F100 with an auto, the spec is 600/500.

The F250 - 350 doesn't have a solenoid so its spec. is 550 with an auto and 600 with a manual trans.

That dwell I gave earlier is for the F100 with a dual-advance vacuum unit. The F250 – 350 runs a single vacuum advance (no retard) and its dwell is 34 – 39.5 degrees or a point gap of .025”. Spark plug gap on all F100’s is .032" - .036", on the F250 – 350 it’s .028" - .032”.

Initial timing for all 240 engines in all trucks is 6 degrees BTDC. When you set it, disconnect and plug the vacuum line(s) to the dizzy.

These different specs. are for emissions and out of the 1971 Ford Truck Service Specifications book.

Ya know, a <a href="http://motorhaven.autoanything.com/"><a href="http://motorhaven.autoanything.com/"><a href="http://motorhaven.autoanything.com/"><a href="http://motorhaven.autoanything.com/"><a href="http://motorhaven.autoanything.com/">shop manual</a></a></a></a></a> is not a bad idea if you intend on keeping your truck for a while. The online store has them on CD plus it has a lot of other stuff too like the dealer’s brochure. Ok, enough of a plug.

Barry

 

Sheesh I see another question there. The ported vacuum starts to come on during light throttle and shuts off at idle. The manifold vacuum is on all the time.

I think we've answered them all now.

Barry

 

Thanks all. I'll leave you all alone, for a little while. Thanks again.

 

I read the whole thing, and had a thought. I dont think this came up, but did you un-plug the vacuum advance hose and plug it up when you set the timing? If you did not it will be set way retarded. Also, I usually run my dwell at about 28 degrees. Just a thought.

 

I had a high idle (under load) stumble with my '72 300. It had symptoms like those described,retarded timing, or even lean fuel (plugged off main jet). the points and condenser only had about 6K on them, about half life, but I found (finally) that the condenser was shorting through its case to the rotor on occasion. A new condenser fixed it. I don't know if I'd run my dwell anything below about 33 deg. From wht I know about ignition, anything lower than that and you start running pretty short burn times, and can start using more gas, etc. Never tried it though.