I have a 69 F250 Camper Special, with a 390/C6 that is knocking under moderate load. I can reproduce the knock by slowly accelerating up a gradual hill. It is not heavy knocking, but I can hear it and I didn't hear it before I made some "improvements"

It has an Edelbrock 1405 carb, a RV cam (of unknown maker), new coil, distributor, points/condenser and plugs, stock intake and exhaust manifolds and the stock exhaust system, single. (BTW, Thanks BBB for your description of routing a dual exhaust, I've got a quote for a custom 2 3/4" dual system with a FlowMaster 70, dual-in/dual-out muffler, for $500. That sounds high to me though.)

This truck always smelled VERY rich so I decided to do some snooping. Here comes the "IMPROVEMENTS", I found two rubber nipples, next to the distributor vac advance on the carb, which were both cracked and very brittle. After replacing them, I dialed the idle mixture screws all the way in (~3 1/2 turns) and then backed them out 1 3/4 turns (someone said 1 1/2 - 2 turns is a good rule of thumb). I re-set initial timing to 12 BTC (this is where it was prior) and adjusted the idle to 550rpm. This change really helped starting the truck, before I had to give it full choke and tap the pedal a couple of times, which created a nice blue cloud after stumbling to life (believe me I tried every other method of starting it, no choke, no gas pedal, one tap on the pedal, etc it had to start semi-flooded). Now it fires right up with little to no choke or pedal.

Took it for a spin, and put my foot into it a couple of times. It has excellent throttle response, way better than before. No problems accelerating. It goes off real strong, however when I'm slowly giving it gas up a hill it starts to knock, like coffee percolating. This goes away when I floor it. I never heard any knocking before. I've read a bunch of threads and can't determine if my symptoms are due to timing advance or a lean condition. I'm guessing that I've leaned out the idle mixture too much, but I'd like a more knowledgeable opinion...

I look forward to your thoughts and suggestions.

Doug
69 F250
Camper Special

 

The coffee percolating noise would most definitely be detonation. Either retard your timing to about 6 BTDC or run higheer grade gas. I would recommend running higher grade gas. Also you could change your thermostat to a lesser rating.

 

Doug, something that has been on my mind lately is heat, it is 94* here today. What kind of air cleaner do you have ? Lots of older trucks have an open air cleaner, including my 390 powered 71. Every time I open the hood the heat is pouring out from there. Would we be better off if we ran a closed air cleaner with a couple of snorkle hoses connected to the grille? Kinda like what T-bolts came with is what I had in mind. Maybe a somewhat cooler intake charge would get rid of that slight ping. The air the engine breathes from under hood has got to be frightfully hot! DF

 

You may need to back the initial back to 10 and reduce the vacuum advance a little. Take a 3/32 allen wrench and pull your vacuum hose off the canister, insert the wrench and see if it locks in. If so turn the wrench counter-clockwise 1/2 turn and test drive. If the pinging stops, go back in 1/4 and see if the pinging returns, if not, stop. It is right. If the first 1/2 turn doesn't do it, go another, and go back 1/4 if it stops. You want to keep as much timing as you can and just stop the ping.

If the wrench doesn't lock, get an adjustable vacuam advance. I have a Standard brand advance for an '84 460 F250. It works great.

 

Thanks for the tips... I found that my diaphram for the vacum advance was cracked. Can that cause the knocking? I'm confused, from what I've read, to much advance causes knocking, but if my diaphram is cracked and not pulling the advance on my distributor, that means I'm getting no advance. So why would it still knock?

I'll try and pick up a new diaphram assembly tomorrow and install. I'm very curious to find out what will happen.

Thanks again for your suggestions.

Doug

 

It could be, Doug. A broken diaphragm will cause a vacuum leak through the ported vacuum source on the carb. This would lean out your mixture on part-throttle and cruise, causing the pinging. Now would be the perfect opportunity to do what Bill said and get a new adjustable vacuum can. You'll love being able to tweak it right on.

Barry

 

Thanks, I'll look for an "adjustable Vacuum Can" tomorrow @ the parts store. What exactly should I ask for. My local store was baffled when I asked them for a Vacuum advance assembly for a Ford 390. They only had Standard Brand vacuum advance assy for the 302. Will the one for the 460, like Bill has, fit my Dizzy? While I'm buying, should I get the Petronix kit that eveyone in this list talks about and get rid of my points?

Thanks for the advice and insights.

Doug

 

It is for an '84 460 F250. I am 99.9% sure that this one will fit all V8 distributors, anyone?

 

df, I've been wondering about that kind of setup, too. They are commonly referred to as "cold air induction" arrangements, as they are designed to draw air from outside the engine compartment as opposed to inside it. I'm adding headers, so I'll really concerned about finding ways to minimize preheating of the intake air.

I have a 96 Mercury Sable whose intake consists of flexible tubing that runs from the intake manifold to the left front corner of the car, with a square filted mounted in line. I'm thinking of lifting a similar intake system off a late model wreck and trying to adapt it to draw air from just behind my radiator.

Of course, there's always the classic "solution" to reducing underhood heat buildup -- have louvers cut into your hood.

ksd
69 F100 Explorer lwb 2wd FE 360 C6 3.25:1. WANTED: straight/clean styleside long box w/aux fuel tank for 67-69 F series.

 

Bill & Barry,

I went out and found an adjustable Vacuum Advance kit from CraneCams (part# 99606-1). I could find a Standard brand kit. So, the install went smooth but the restart was terrible. Way to much advance to start it, then I flooded it and couldn't get it started for a while. Then, backfires through the carb and still having trouble keeping it running long enough to adjust the initial timing. 30 mins later and a few swear words later, I got the timing reset to 10deg BTC, down from 12deg, and then reset the idle, and the idle mixture, which was now WAY to rich. Barry, you were right about the leak into the carb from the diaphragm. I got that dialed in and took it for a spin.

Pings on the hill @ full throttle, get out turn the adjuster a couple of turns and WAM! no more knocking @ full throttle. It wasn't exactly that easy, I made baby step adjustments, until the knock was gone, then backed off the adjustment and it knocked, so I knew I was there.

I'm completely impressed with you guys. I've got the alan screw in my glove box just in case I get a batch of bad gas and have to adjust out some more advance.

Now that I have the Vac advance my engine should have had all along, I feel like I'm driving a hot rod. I'm wondering how many people are driving around with a cracked diaphragm and don't know it. This must have been like this for a while, as the guy I bought it from told me after the engine rebuild it still didn't have much power, and that was when the timing was set @ 12deg BTC.

I bought the Petronix kit, but did not want to put it on until I figured out the vacuum problem. Do you think I'll have the same start-up problems after I put the Petronix on?

Thanks again.

Doug

 

I'm glad we could help. There is nothing like a good tune.

 

The Pertronix upgrade is easy, I bought the Pertronix coil too just to be safe. I've heard nothing but good things about them and have had no problems with mine.

As far as the guy looking for a cold air intake, I've seen several of these that came stock in the junk yards. they are plastic hoses that run from pass side front just to the side of the rad, to just aside the battery, then a flexable host to connect to the air cleaner. Probably better than trying to fab one up.

 

OK,

I'm not running, this is frustrating. It starts just fine and will idle with the choke for about 1 min, then when I turn the choke off, it will idle down and run for a little while, maybe 1-2 mins, then just stop. If I try to catch it with the throttle it just pops in the carb. I then can start it right up again, but when it drops back down to idle, it dies again.

I thought I had this licked, when I got rid of the ping. All I did was replace a vacuum advance diaphragm and re-set the timining and idle screws. It has to be either one or the other right?

I have the timing set @ 10deg BTC and the idle mixture screws set @ 1.5 turns open. Am I starving the carb or is there to much advance @ idle? Or is there something else I'm missing?

 

The first thing I'd do is get some B-12 carb cleaner and remove the idle screws completly and spray it directly into the screw holes, then re-check the float level and clean the inside jets too. Then I'd richen up the idle and keep going until you get a solid idle. You might have to play with it for a while to get it right. It might help to use a vac guage to the intake and try for highest vac (about 17~20 is good).

Don't forget that the plugs tend to get dirty while doing this, so it might be a good idea to clean them every so often.

Older carbs tend to leak air thru the throttle shaft holes when they wear out and a some carbs tend to warp because of air cleaners pulling at the center and also warp at the base. I'd do a careful inspection for flatness and then clean everything.

 

That's a good idea about cleaning the idle jets out. You might want to check the fuel filter, too. I know it wasn't giving you grief before but a big enough chunk will shut things down right away.

My uncle uses an unlit propane torch to check for vaccuum leaks. He opens it and moves the torch head around the usual suspect areas. When the carb sucks in some propane, the idle will slow substantially or stop. Of course, this will only work if you can get the thing to run.

I had similar problems with my car this last spring and it turned out to be the ignition--new spark plug wires and cap and rotor fixed it. Not likely that's the case with yours, but a rich running carb can hide a lot of other problems. Meanwhile you're getting lousy gas mileage. What kind of wires did you put on there? The unfinished universal ones that require you to crimp a fitting on the end? Those suck--I found out the hard way--and they might be part of the problem if you're using them.