Just installed a freshly rebuilt 400 into my 1979 Ford F150 4x4 over this past weekend. It was bored .030", the crank turned .010", stock compression (mid 8's) pistons and moly rings installed, Crane Energizer 266H Cam (.508" lift, 266 duration), beefier valve springs, both heads completely rebuilt, a Cloyes double roller timing chain and gears, Edelbrock Perfomer intake, Edlebrock 1406 Carb - Everything new (including a stock distributor).

My issues are: temperature too warm (stock gauge reading at the "L" on Normal, was at the "R" before rebuild and w/ 160,000 miles on original 351M), backfiring through carb accompanied by hesitation up to about 35 mph when cold going through all 3 gears (C6 trans) - goes away after you get up to cruising speeds, and also seems to load up - like driving at a sustained speed of 50 MPH, then goosing it, it will hesitate before kicking in.

It is my belief that this is mainly all attributed to timing issues. I have a new 3 core radiator on it's way to handle the temps, but think if the timing is straightened out, probably won't be necessary. I set the timing chain and gears straight up when installed, and currently have the harmonic balancer also set at "0" (TDC), because this is where it idled the best at up through 2500-3500 RPM's (or so). The carb has not been touched, other than the idle. I have had a few of these carbs in the past, they always seem to run excellent with no tinkering from me.

I have my vacuum line hooked up from my distributor (vac advance) going into the LH side of the carb (driver's side). Just curious if anyone else has a similiar set-up, and where you have this line hooked up to (maybe I have it wrong?) Also, where is everyone running there timing at with a similiar set-up? I am currently right at "0" as mentioned. Once warmed up, the truck runs pretty strong, although I think I lost some low-end torque from this cam. Hopefully I will get the timing, and/or carb lined up, and it won't be as sluggish from 0-1200 RPM's as it currently is. It has a smooth power band though, but not appropriate for a 4x4..................Any thoughts, suggestions, they will certainly be appreicated.

 

Sounds like your static timing is slow and you might be hooked up to manifold vacuum for the advance. New engines will tend to run on the hot side until things loosen up a bit. Also, retarded timing can increase temps. If you pull the vacuum advance hose from the carb at idle, is there vacuum at the port? If so, find the ported vacuum connection and hook it up there. Shouldn't be any vacuum at idle, and increase as you start to open the throttle. And try setting your timing around 8° to 10° BTDC. Also, double check your firing order and route the #8 plug wire away from the #7 wire.
Hope this helps.
Greg

 

I agree the vacuum advance is the culprit. I run almost the same setup (same Carb) on the front of the carb there is two vacuum ports, my vacuum advance is on the left( looking at the carb).

 

I have been told by many that the radiators in these trucks arent the best and cant handle very much more engine buildup b4 they start to overheat. They used the old down-draft style radiator. Down-draft radiators are not as efficient as the more modern cross-flow radiators used in the '80 and up Ford trucks. Although its still a down-draft, the Modine Max-Cool #545 is a great bolt in upgrade. As for timing, I dont have any timing marks on my motor so I cant tell you what mine is actually at, but I have tried just about every combination of base timing, advance sensitivity, timed port/ full manifold vacuum and I have found full manifold vacuum seems the run the best on my mostly stock 351m. I also have my advance sensetivity set to full. But know that the weather is warming up I am probably going to retune the whole thing again soon (allong with the holley truck avenger that I just cant seem to get perfectly tuned). Plus I hope to soon have a new cam and possibly a fuel injection kit on it. Just my $0.02

 

Looking directly at the front of the carb, I have my vacuum advance hooked up to the right hand side. This is different from where snow fighter is running his apparently. I switched sides this evening before leaving from work, and the idle dropped way down, and the truck ran worse. About 2 miles down the road, I switched the vacuum line back over to the original side it was on (driver's side). Idle picked up right away, and it drove better than it was on the other side. Per Mac's suggestion, I pulled the vacuum line from the carb (after it was hooked back up on driver's side), and I believe there was quite a bit of vacuum there - I couldn't feel anyhting, but as soon as that line is plugged back in, idle goes up considerably, and instantly. So, the two of you seem to be on the same track perhaps, and maybe I should hook the vacuum advance line up to the LH side, and start advancing timing? It is really most bothersome when the engine is first started and "cold". Wants to hesitate and backfires through the carb if I take off at a normal speed. You really have to crawl to prevent this from happening, and by then the carb seems loaded up, and you end up having to stomp it a little to get everything cleared up anyway.

I will of course doublecheck my firing order, and look at the #7 and #8 wires specifically. This actually reminds me of a similiar problem I had with this same truck about a year ago when the original engine was still in it. It ran bad when first starting out (hesitation, etc), then seemed to gradually get worse at all speeds. Turns out that I had a bad spark plug wire. These are all new as of now, but who knows...........I will keep everyone posted, as I am sure many people are following for theor own knowledge. If anyone wants to continue throwing some suggestions my way, or can tell me where their similiar set-up is timed, hooked up to the carb, etc, please do so. I will be in touch, thanks for the responses so far.

 

When running manifold vacuum to the advance:
Yes the idle will probably increase and if the static timing was slow enough to start it'll increase quite a bit and seem to run a lot better (at idle). Especially if it's running too rich. The problem comes when you try to accelerate. Just when you want the timing to increase to prevent a stumble, it decreases as the manifold vacuum drops. Granted, ported vacuum will never read higher than manifold vacuum at the same throttle opening. The benefit comes when the timing advances as the throttle is opened. If it seems to idle a lot better with manifold vacuum try setting the static timing faster and using ported vacuum for the advance. Aim for about 36° to 38° total advance (static + vacuum + mechanical) at 2800 to 3400 rpm.

As to the #7 and #8 plug wires, if they are run alongside each other one can induce a spark in the other even if the wire is good. When #7 is firing #8 is just coming up on compression and with the lower compression the plug is easier to fire. (Yes, cylinder pressure makes a difference on how much voltage it takes to jump the plug gap.) That's why you should route them away from each other.
Hope this helps.
Greg

edit: skip, I just saw your other post about your emissions sticker saying static timing at 4° @500rpm. That's to help with emissions. The engine will probably like a lot more. When we had inspections, I'd set the timing down to the factory specs for the sniffer and pass with flying colors. Of course it would run like I can't say what (off idle stumble) but afterward I just reset it to where it ran good.

 

A Final Update: After warming up the truck this morning, I removed the vacuum advance line from the carb, plugged both carb ports as well as vacuum advance line, and advanced the timing (from where it was - "0") to about 13 degrees BTDC while the truck was running. I tightened down the distributor, re-installed the vacuum line to the passenger side of the carb (opposite of where I had it originally), and plugged the other port to the carb. I did not have to adjust the idle, it stayed up where it should be. I accelerated a little keeping an eye on the "new" timing mark and did see the timing mark moving further advanced as more fuel was given (before it was staying at "0").

After a short test drive, everything was super! No loss of power after a gear change, no hesitation, no backfiring, noticeably improved torque. The temperature gauge actually came down as I was driving to about 3/4 of the normal range - exactly where it stayed before changing engines.

I let it sit for about 5 hours to see how it would react cooled down as this was my biggest problem before. It drove excellent, with no more stumbling and backfiring through the carb. The weather has been in the 40's and 50's the last few days since this Motor was dropped in, now we are at the beginning of a warming trend, so I will have to monitor the temps still. The new radiator did make it in today, (2 days early if you can believe that), so I will just leave it boxed up until I need it or find time. I am tired of turning wrenches, and need a short break to enjoy the new engine a little.

Thanks very much to all who have taken the time to answer my questions (and so quickly at that!) and those who have been following for their own reference. I do have all this information in books, but most of it goes right over my head, and I appreciate the common sense approach and terminology that was expressed to me through this forum. As I get the tank filled up this Friday, I will begin to keep a log for calculating gas mileage and post some information concerning this rebuild with the components I used for others who may be interested. As for torque, I am happy with the way the truck is running now, and at the least I have not lost any torque over the stock 2V engine that was in there last week. HP however is noticeably better, and was my goal when I decided to rebuild an engine for this truck - just to get a little better performance over stock. MPG will be the make or break decision for many others, so I will have something in about 3-4 weeks to report. Thanks again!

 

Since you already have the new radiator, I think you should put it in when you get a good opportunity. The new radiators are quite a bit better than the old stockers. They usually flow better and cooler.