Hello all, this is my first post and am really glad I found this board. Anyway I bought my 1st 4 wheel drive, its an '87 bronco with the 351 H.O. and holley 4 bbl. The engine has about 6,000 miles since its rebuild and runs great except for some hard starting. Basically it will crank and crank (maybe 10 seconds) then when it starts has kind of a diesel knocking sound (if that makes sence). I pulled the distributer cap and it and the rotor look good (they were replaced during the rebuild). I changed the plugs and it would start great for a day or two, no gas and only turn over a couple times. Then it would start going back to its old habbits. Since the plug replacement I failed emmisions and traced it to a bad egr valve. Replaced it and passed emissions. The hard starting persisted and wasn't sure if maybe the old egr failure had possibly fouled the new plugs. This time I replaced the plugs and the wires and double checked the timing. Again it started great for a day or two, then back to hard starting. The strangest part is that when the truck is nice and cold and I get in and hit the gas to engage the choke it will fire right up, but when its warm and you restart its always hard. could my problem lie possibly with the vacuum advance or even carb tuning? The holley wasn't rebuilt on the rebuild. I did set the floats to the correct level and toned the idle down. Any ideas? sorry for the novel of a post but wanted to make sure I gave the best info I could. Thanks in advance for any suggestions!

 

just remembered, I also replaced the coil.

 

I experienced the same problem and discovered it was a combination of corrosion inside the primary battery cables (first start was fine, heat then 'loosened' the corrosion) and a bad ground.

 

Thanx, for the reply, I'll take a look at that. Never thought of something that simple, but its usually the simple things that end up being the culprit.

 

Well, cleaned up the post and checked the cable and problem still there. Anyone else have some ideas?

 

Sounds like it's running rich. I'd say you need to fully tune the carb, but start by testing your vacuum at idle. What do the spark plugs look like after a couple of days?

 

The plugs seemed to look ok (I used the picture of plugs on the haynes manual for comparison). I do think that the carb may be the problem. I know a little about holleys but i'm no expert. Is there a link to holley tuning somewhere? I did notice that when I was getting it to pass smog that the secondary float was set way high, and the idle mixture screws had way different setting. one was screwed half a turn out, and the other was 3 1/2 turns out. I set them both at 2 turns out off of some advise from a friend. I should probably just pull it and rebuild it. Thanx for the help!

 

oh, and about the vacuum at idle, do you have a link explaining exactly what to do, and what it should be? I'll dig through the haynes manual but you know how vague it can be at times. Thanx

 

Yes, the text in my previous post IS the link to the vacuum diagrams.

The instructions with the rebuild kit will tell you how to tune the carb.

 

sorry, still getting used to this board, didn't realize you included the link. Thanx for the help