Hello everyone,

I was driving my 300 CID equiped F-100 to work today and the thing snaped the roll pin that holds the timing gear on the dizzy. Needless to say their was a huge exhaust pop and a back fire through the carb. Anyway, I figured out what was going on with the roll pin and bought a new one. I then proceeded to TDC and set the dizzy accordingly. So I go to start the thing and she fires right up, no problem. But when I apply a small amount of throttle the thing coughs and sputters and nearly rips itself off the engine mounts.
After seeing the said display I think about it for some time and come to the conclusion that somthing in the old carter YF must be damaged. So I open the thing up and inspect; I turn up nothing. Than I inspect the exhaust; other than the big hole blown out of the muffler their is nothing wrong. Then I pull the side cover and the valve cover. No bent push rods no punctured lifters nothing.
So that's it I'm dry for ideas, I still think it may be the carb due to the fact it idles fine and opperates normaly through part throttle. However, I've been wrong before so I'm begging all of you for your help. This truck is my daily driver and I have no back-up. On top of this I am a poor college student and can't take it to a mechanic or get a new engine. Thanks in advance for your help.

Joe B.

 

It sound's like you are 180 out on the timing but then again it idles ok .
The is no power valve to blow out on the yfa but the ball check valve for the excelerator pump may have been knocked loose from the back fire .
There should be a small ball and a weight on top of the ball .
open and close the throttle and see if you have a healthy shot of fuel if not that may be the problem .

 

Other than the carb - which is the prime suspect...

You pulled the diz - correct firing order...153624 ?

You set the timing - with the correct mark on the ballancer?
- using the right timing plate ( sometimes
there is one on both sides of the timing cover)

Did you replace the diz cap/rotor? Maybe you're getting some arc-ing in there.

You said it fired right up. Does it idle smooth or rough?

I'm running out of ideas... I'll keep thinking about it...

'hope you didn't jump time

 

Thanks for your replies,

I get a pump shot so the accelerater pump works; anyway, it would smooth out after a few seconds once the fuel supply caught up. It idles as well as it did before all this happened. Also I completely went through the carb (I still think it's the problem due to the fact its been rigged for so long). Would it be posible for the cam to jump time like that? It just doesent seem like I had a catastrophic enouph of a failure to cause that. What is the likelyhood of that even happening? Thanks for the help.

Joe

 

you would have to break a tooth off of the timing set in order to get it to jump time .
If it has a fiber cam gear that is really the only way I can think of it jumping .
If the engine has not been rebuilt I would say that it is the stock metal to metal gear set .
the dizzy may be off on 1 tooth too , from when you removed the dizzy from the engine and put it back in .

 

do a test on it with a vacum gauge. If the needle jumps all over you have vale train problems, like bent valves. Would you stake your life on the fact that your firing order is right? Are you sure that is the way that the rotor spins? Try starting it up with one spark plug unhooked at a time, until you find the problem cylinde(s).

 

Sounds kinda like a vacuum leak. Maybe some vacuum line/s burst from the backfire or unseated from their fittings? Check around for something like that, especially on the larger ones like PCV or brake booster lines.

 

You did not indicate what year you have - but for now, I'll guess it has a cat.

Is it possible in the backfire, you severly damaged the cat (it is upstream of the muffler that you indicate has a big hole)? If so, it could be causing your exhaust to be clogged - the old bananna-up-the-tail-pipe thing. At idle, you can get enough exhaust out. AT any RPM, it can't handle it and dies.

I once pulled a cat of my wifes 84 Mazda 626, it had a lot of debris from the cat crumbling. It was blocking of 1/3 of the air passage way.

Good luck

Jerry

 

you have your vacum advance hooked up incorrectly, or if it is new, you may have been sound the wrong dizzy. It ahould run just fine with that vac. line off Try it, let us know what you think.

 

Thanks for the replys everyone,

I have a duel diaphram dizzy on that 1972 F-100. It seems the backfire blew the retard portion of the advance/retard unit so when I went to give the truck throttle the advance advanced too much. But now I have a new problem. I bought a dura-spark dizzy and control unit from the junk yard. I wired everything up correctly and tryed to start it up. I'm getting spark and the thing starts to catch but it wont fully start. Firing order is correct and I stabed the distributor at TDC. The only problem I can find is the positive terminal on the coil tests at 6.85 Volts (I don't see a ballast resistor. Did Ford hide these somehow?); but when I pull the wires and test them I get battery voltage. If anybody has run accross this please enlighten me. Thanks again everyone.

Joe