Vacuum Or Carb

[Toby the Dancing Bronco]

My 74 (302-435/D20) was running like the factory would have been envious of, but last week started to fall flat on its face under acceleration. Idles fine, rev's fine, put it under load and it looks for a curb real quick. A friend told me it was probably the accelerator pump (original 2bbl), but when I kick the throttle, gas shoots out in 2 pretty even streams. No obvious leaks around carb. As it is 30 years old, I removed the air pump and plugged the air rail ports near the exhaust valves and tuned it right. Ran great. Can't find any obvious vacuum leaks, but there is something not right some where. Any suggestions, or a link to a good current site on vacuum routing? Thanks!

 

[NMBronco77]

Howdy,

The first place I would look is at your ignition system. Got a coil or coil wire breaking down? Open the hood at night and have a friend put your truck under load. (stand to side, not in the front) Look all around the coil, distributor, spark plugs and the full length of the spark plug wires. Many times you will see a spark at night that you would not see during the day. It may help you locate the problem. You should not be able to see any spark anywhere. It's all supposed to stay in the wires, ya know what I mean?
You can have all of the gas you want, but if you can't ignite it, it is just gas. A weak spark can make for a weak truck.

Hope this helps,

NM77Bronco
(Pat R)

 

[NMBronco77]

Also,

I have had a 302 that ran like that. It turned out to be a bad coil. See if your coil is real hot. It might be because it is shorting out between the turns inside, creating exsessive heat. Your coild should not be TOO hot to the touch.
It should be putting out a nice blue spark. If it is not, then make sure that you have 9v to the +side terminal. (12v on start curcuit, 9v on the run) If you do then maybe you need to look at a new coil. They're pretty cheap.

Pat

 

[Toby the Dancing Bronco]

Thanks. Just so happens that it is night right now, and I think I will try both of those things. Oddly enough, when I put new wires on it a couple months back, the new coil wire was too short to allow leaving the coil on the fender well. I Put it back on the intake manifold (seems like a stupid place to put electricty... next to the carb, but I didn't design it..)
Well, I let it run for a few minutes and couldn't see any spark leak, but that coil got pretty hot. I put a new ignition module in when I did the other stuff, too, and should have put a new coil on it at the same time, I'll bet. I'll get one tomorrow and try it out. Thanks!

 

[Broncoholics]

If that doesn't fix it try sucking on the vacume advance line on the distributor and see if your tounge will stick to the end of it. If no suction then it has to be replaced.
If you run points check inside the distrubutor cap, there is a small silver canister (ignition module). If this goes bad the engine will run bad only under load (while driving), it will rev and run at idle perfect all day untell you drive.

 

[Seabronc]

There is no danger from the electric being next to the carb, unless you are leaking fuel and arcing at the same time, but it has happened . For a carborator, there is a possibility that your power valve is bad and floods the engine. Do you have a gas smell under the hood when this happens :unsure: ?

Good luck,

>-

 

[Toby the Dancing Bronco]

Thanks for the assistance, as once I got the new coil on the fenderwell, and a new wire, it is running like it should. Now, on to the transfer case rebuild!

 

[Broncoholics]

Must have been the wire. b-(

 

[Guest]

Alright!!
I am glad that I was able to help!!
I used to troubleshoot vehicles for a living. Many problems have specific symptoms. Weak spark = weak truck.
Good luck!!

Pat in LA,NM :wacko: