Hello,
This post ended up being a bit longer than planned, but I wanted to give adequate back story on everything I had done so far.

I have a 1971 Ford F600 dump truck with a 300 i6 that I have been working on. The truck has not been on the road or ran at all in the greater part of a decade, but it did start and would run (thought not very well) before I started monkeying with it. The exhaust manifold was cracked in several places so I ended up replacing that, the intake manifold, and the carburetor.

The carb that was on the truck when I started was a Carter YF, however I don't think it was original to the vehicle (Autolite maybe?) Mainly, the truck was originally equipped with a manual choke but this carb was an automatic. The automatic choke (thermal) was not hooked up as there was no port on the exhaust manifold. The cable for the manual choke was left dangling in the engine compartment. Needless to say, the choke did what it wanted to and the vehicle was hard to start. I installed a manual choke conversion kit and it worked much better. It would start right up with choke fully closed and then I could open it back up in a short amount of time.

This all was before I replaced the manifolds. I installed a new intake and exhaust manifold. The new intake manifold had a different bolt pattern for the carb then the old one (holes were further apart) and had an EGR port which I blocked with a freeze plug. Since the old carb wouldn’t fit back without modifcation and wasn't right to begin with, I decided to replace rather then rebuild it. I talked with the folks at UREMCO about which Carter carb I should get that was manual choke and would fit my bolt pattern. The advised me a part number which I then ordered from Summit. Though I was told this carb had slotted holes that would fit both hole patterns, it didn't and I ended up having to wallow out the holes anyway.

With everything installed, I gave it a try, and the truck fired right up. With no more cracks in the manifold and a new gasket, it sounded much better then it did before. The problem is that when I open the choke the engine dies instantly. It will only run with the choke valve fully closed, but seems to run well in this position. I tried adjusting the mixture screw from all the way in to all the way out with no noticeable difference. I checked the tightness of the manifold screws and they seemed secure. I sprayed starting fluid the intake, the vacuum hoses, and the base of the carburetor and didn't notice any difference in idle. I measured the vacuum at the port on the intake manifold to be about 16" Hg while idling with the choke on, and 20 or more when I step on the gas. When I open the choke, the vacuum drops to nothing (but the vehicle “is” about to die) and I have to give it quite a bit of gas to get it back up again.

One point of confusion for me on this carb was that it had two apparent vacuum ports on the throttle body whereas the old one only had one in which the distributor vacuum advance attached. One of these ports pulled the same vacuum as the manifold port and the other didn’t seem to pull any. Later, while propping the vacuum gauge so I could see it from the cab, I realized the other port only pulled vacuum when the throttle was revved. I moved the vacuum advance over to this port.

Another thought is that I had a week spark, so I went ahead and replaced the spark plugs and coil (which I had planned to do anyways) but the truck runs exactly the same. I was not able to notice any obvious vacuum leaks, but there are other places that they could be, such as around the brake booster. However, this much seemed to be working OK before. My next thought goes towards the new rebuilt carb. Can something be working with it to make it behave like this? A problem with the idle circuit? I took it off and blew carb cleaner throught the mixture screw hold and it passes to the otherside. I do have a rebuilt kit for the carb, but didn’t want to have to open it up unless I really had too. If that is the case, what are some t hings that I should be looking for? Are there any other issues I may have overlooked? Am I reading enough vacuum or do I have an obvious leak? Any input would be helpful.
Thanks

 

Welcome in, pal. Wow. A lot of stuff here. Congratulations on bringing Lazarus back from the dead.

The guys have put up several well thought out lists of things to do to get iron like yours back on the road. They will be in to repost them soon.
Meanwhile, get rid of all fluids in that motor: antifreeze, oil, and especially fuel. Drain the fuel tank and replace all soft lines and filters to the carb. Also, get some Seafoam or Marvel Mystery Oil to add to the tank and crankcase to free up any stuck rings or valve stems. Get it up to temperature and run it. It will start to heal itself.

Your vacuum numbers are okay. Hook up the vacuum advance to the highest port on the carb, the one above the throttle plates. And make sure the vacuum advance diaphram is not ruptured by sucking on the line at the carb port.

These motors are tougher than old Army boots and will survive a lot of neglect as you have discovered.

 

Welcome to the forum. I don't know much about the six's. But like CougarJohn said, the other guys will get to you soon.

 

When you changed the plugs and they looked kind of a dark to a light tan color is normal and adding new may not show any noticeable improve.

But black carbon fouled will be more noticeable. Possible causes bad plug wires to a weak coil. Also a full inspection of all dizzy ign wires, check for any broken or frayed points ground wire. All screw are tight in dizzy and condensor wire is not rubbing inside dizzy housing may cause it to short.

Points in good shape not pitted or burnt up with uneven melted metal build up making it impossible the set correct gap.

Check dizzy cap for any build up of carbon on contacts & check that the carbon button in the center of the cap for being in good shape a long with the rotor.
Remove plug wires one at a time looking into each wire socket hole for green corrosion build up in there or on the plug wire end terminal tips .
Replace with a new cap if in doubt.

A compression test should be done first so you'll know if any low cylinder you'll know why is may not be running at it best.

To me it sounds like the idle circuit is plugged in the carb. Did you look into the carb to see if any gas is being squirted down the throat of the carb with engine turn off.

This use to work way back in the day sometimes. If possible reb engine up 2,500-3000 then put hand over carb throat opening and choke off all air then remove hand fast to keep engine from dying out. Repeat this 3 or 4 times and see if it will dislodge any blockage in the carbs idle circuit.
This takes a little learning to get the hang of it tho.

Also the main jet maybe plugged so, I'd pull it apart and shoot starting fluid through it the ports looking for blockage.

If all else fails send it back..
Orich
O

 

1st off, 2X Orich.

I think your problem is also the POS carb you bought. Or because you are mixing parts. Take it back to where you bought it and have them look up their part number for whichever application your intake manifold came off of. If you don't get a reading on a vacuum gauge unless the choke is fully closed then you have a bad vacuum leak somewhere. You should be able to hear it. Unless maybe a gasket is partially covering it enough to stop the sound but still let air past it. Now some 300 intakes back then took a spacer plate in between the intake and carb. If your intake requires one and you are bolting a carb directly to it that could be your problem. What did your intake come off of?

 

Thanks everyone for the replies. I was able to play around with it a bit this weekend and I think I found the (or a) problem. I am going to attempt to post a few pictures this time.

It turns out I did indeed have a large vacuum leak. I had checked the torque on the intake manifold bolts and they were all good, so I didn't think I was leaking there. However, when I looked underneath the intake manifold I saw that it was not lining up properly with the gasket and I had a "catseye" crack there.


I tried to see if I could loosen and push this section down, but it wouldn't budge and I ended up tearing the gasket, so I took the whole setup down that is when I noticed there was an inherent alignment problem between the intake and exhaust whenever the two are bolted together. I held the gasket up to the engine block and it matches perfectly, so the problem is between the two manifolds.



The only way to get it close to lining up is to loosen the bolts between the two and make a severe crack where they join. I attempted to try and cheat a little bit and leave these a bit loose while reinstalling the manifolds, pulling the right side down just enough to cover and then torquing the two together. This was disastrous and now I have an audible exhaust leak on top of the problem. My plan is to send this image back to Steven's specialty parts where I got both manifolds and see what they think.

This was the only new intake I was able to find at the time for this truck. The guys at Steven's told me that that the carb bolt holes would be further apart then my original and that I would have to mill the holes out on the carb throttle plate in order to fit. This much I expected. But they didn't mention nor did their pictures online show the extra hole for the EGR which I ended up covering with a freeze plug. Below is the original intake:

Here is the intake from Steven's:

Here is the hole plugged:

And here is the whole thing before I started:

And here it is almost back together:


If this intake doesn't work out what other options are out there? I looked a bit at the offenhauser intakes, but at the time they were months out of stock (but available now I think) If I were to get that, can I adapt the 1 bbl carb to fit them? I have seen the adapter in reverse but wasn't sure if I could downgrade back to a 1bbl. I am not really looking to by a 4bbl or even 2bbl carb for this truck at this moment.

Anyways, thanks for the advice so far. I look forward to seeing you comments.

 

Looks to be the wrong gasket as it's not even lining up??
Orich

 

not sure if it matters, but you have the HD exhaust manifold.

 

Gembone,
Yes I am aware this is the HD manifold. This is an F600 and it was originally equipped as such.
Orich,
When I held the gasket up to the engine block both the intake and and exhaust holes seemed to line up ok.

 

wasn't sure if you were aware. I also don't know if that might use a different gasket, although doubtful.

I know when I did my 300, I had to trim the gasket to 'port match' the manifolds. It wasn't as bad as yours though.

 

I figured I could separate the intake and exhaust portions of the gasket and make it work but I was worried about not lining up well to the ports on the engine. If you look closely at the last picture you can see I am barely catching the tabs on the intake manifold with the washer.

 

That gasket looks so far off that it could be the wrong one.
A lot of guys don't use the exhaust part of the gasket. They use copper high temp permatex instead. Apparently that is what Ford did. Might want to research it.

 

Seems to me the problem is you're trying to use a later model L/D EGR intake with prolly an older model H/D exhaust manifold. Looks like you'd have to have their mating surfaces milled down.

 

OK guys, I have been hung up with some other stuff but am finally trying to get back to this. I sent the manifolds back to Steven's. They came back and told me that the flat on the intake was indeed milled out of square and sent me a new one along with my original exhaust. When I got them back, I bolted them together and to my surprise they still seemed just as badly out of alignment! I called back Steven's to make sure they QC'd they new intake or just grabbed another out of stock. They told me they checked it and made sure it mated to my exhaust and test fit it to an engine block they had...So naturally the next thought is what am I doing wrong. The fellow I was talking to told me that I shouldn't bolt the intake and exhaust together and should instead install the intake first using a dowel in what I guess is an alignment hole and then follow with the exhaust and then bolt them together. At least thats how I interpreted it. Afterwards I went and looked at the shop manual and it clearly states to bolt the two together "finger tight" and then install. Anyways, I went ahead again with the later approach but keeping the nuts so loose that I could easily move the intake independently of the exhaust. I was able to use this alignment hole that I overlooked before along with the leftmost bolt hole to perfectly align the intake to the ports. I started to run into issues when I did the exhaust. I put the rightmost bolt in alright, but it was already clear that the left part of the exhaust needed to come up a lot before the bolts would even go in. I started tightening the nuts that bind the two together to see if it would raise the exhaust up. It closed up enough to start all of the bolts, however, there is still a crack big enough to put a fingernail in on the left side of the junction between the manifolds, while the right side is tight. I am right back to the same alignment issue as before, just moved to a different place. I stuck my old cracked manifolds back together just to check them out and they align perfectly right off the bat. What am I missing here? They verified there was a problem with my first intake....sent me another one that they tested...but it looks like the exact same part....If it wasn't unpainted I would have thought they sent it right back... Are the ports on these engine different in later model years? Is something still not right in my assembly? Did they send me another bad part...

 

Man oh man what a pisser. I don't know what to tell ya now.
How well of fit does the gasket fit on the old exh. manifold as the gasket don't fit or line up on the head ports in your picture.

Damn may be keep checking ebay for the correct one as Steve can't solve your problems and but keeps trying too.
Orich