I have a 351w from a 69' Mustang with gt-40P heads and I just can't seem to get it to run right. I am running a mild cam that was put in by someone else so I don't know the specs and a truck avenger 670 de-jetted to 60 primaries and 72 secondaries. I have a holley electric fuel pump regulated down to 4.5 pounds. I am running autolite spark plugs with a .45 gap and MSD 6 ignition, rev control anmd 8.5 wires. It runs like crap. I thought I had it tuned perfectly before I started running the buggy, there were no misses and it ran at 160 degrees with no problem. Then I put in the shafts and started driving it and now I have some problems. For starters, at idle it sounds like it's dropping about three cylinders. First I thought this was a vacuum leak but I only have two vacuum ports out and I have replaced the intake manifold so it's not that. I checked all the plugs but have not replaced the wires because none of them looks bad. When dropped into gear it drops so low in the rpms as to barely stay running. It stutters badly at takeoff but will run like a champ once it gets over 2500 rpm in forst gear While running any stab over the throttle is met with more sputtering. When shifted into second or third(c-6 with manual valve body) it just sputters all over the place unless it gets over three thousand rpm's. If I put it in low and try to power over something it just won't go.The msd is a second hand unit but I have tested it according to MSD and it seems to be fine.It's also running at about 190 to 200 with a 160 thermostat but that may be because it's over 100 out and I have a high flow water pump and a regular thermostat instead of a high flow. I had the carb tuned by someone who is supposed to be a carb expert but he could have put bananas in the secondaries and told me it was right and I wouldn't know. I have started thinking I may have a stretched timing chain as the timing has always been erratic since I got it running. I seem to recal when I had it on a stand that one side of the chain was tight and the other side had noticeable slack in it. I would rather not pull the entire front of the buggy apart only to find out it isn't the chain.The motor was given to me and I don't know enough about motors to have checked things like the timing chain when I put it together. Anyone have any thoughts? This buggy is ready for the rocks if I can just get the motor running right.
Posts by Butler
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When Cragrat and I started it the first time we tried the 302 firing order and turned over manually and it definitle has a 351 firing order.. The idle isn't bad per se, it just sounds like a bad wire or plug on three cylinders. If the firing order was that far off I would expect that the idle would sound a lot worse or not start at all. It runs awesome over 2500 rpms, though. It also doesn't sound like a lopey cam would sound.It only sounds like three or so cylinders. I could live with the idle but the heat and the stuttering off the line is unacceptable. At this point I am very tempted to take the motor out and completely tear it down. It would be faster that troubleshooting every damn thing. CAn anyone tell me how to wire an msd coil without using the ignition box? Then I can check the MSD while it's running. Like I said, it was a second hand unit and I would like to definitely rule that out.
Checked and adjusted the fuel pressure to 6 pounds. Put a vacuum gauge on it and it shows a reading of about 9 in hg but bounces up or down 2" at idle rapidly. I'm told this indicates a vacuum leak but the low vacuum pressure is nothing to worry about since it may be a factor of the unknown cam. I have changed the manifold gaskets twice and have used the thickest I could find which is a fel-pro product that is more of a rubber than a metal and is still fairly thin. In looking at the block from the side it almost appears that the block and the heads have different mating angles ground into them. Remember it is a 69' 351w block and the heads are from a 97 explorer 5.0. I am trying to find the 1/4" thick gaskets that I am told exist but have had no luck so far. I used an unlit propane torch and then wd-40 sprayed every where to check for a vacuum leak at the top end and have noticed no difference, As far as the fuel bowls, none of those settings have been changed from the factory, should they have been when the jets were changed? In any case, I am going to a less complex ignition setup on Monday, I will be changing all the wires as well(two were bad originally so I still have the other seven wires) So we'll see what that produces. Supposedly the engine had five thousand miles on a full rebuild when I got it so I can't believe that there is something majorly wrong in the bottom end including the chain. One other thing, when I changed the plugs the explorer heads call for a .54 gap I believe. A ford builder told me this is way too much and suggested I go with a .45 gap. The original heads had a .40 gap. When I bought these heads I had the valves opened up quite a bit(and these are already a high flowing head) but I can't find the paperwork to tell me the exact size. Will the valve size matter for what I am trying to do(troubleshoot)? After I have done everything listed above are my next steps to go to a thicker intake gasket and pull the front apart to check the chain?
As far as I know I bought the heads used from a guy on e-bay and they came directly from a blown up exploder. They still had the stock plugs in place and they were rusted pretty good indicating to me, at least, that they had never had any work done. I had a valve job done with I believe new guides and the seats ground and that was it. No machining was done to the exterior faces. Again I am looking toward the msd due to the box being a used unit. To listen to the exhaust at idle there is distinct popping three times and then it smooths out. To me it sounds like three cylinders missing in a row. This is not consisitent however. It will smooth out occasionally for one or two cylces which sounds like some sort of timing or ignition problem to me. I'll up the ante. I need this fixed asap and I'm willing to offer the famed hundred dollar reward if someone can figure it out.
I am using an MSD but with this dizzy you have to use the box. I am going to a different setup in any case. I will check the wires and chain tonight. I don't think the block had any millwork done but I'm going to find out tonight. I think I may have figured out one of the sputtiering off the line. I spoke with a bona fide carb shop today and told him about de-jetting it he said I was nuts. He would never use 60 primaries in anything but a v-6 with a two barrel. Tonight I will re-jet and take it for a spin. I think I am facing several problems here. The sputtering off the line, the bad idle, and seriously low vacuum. The idle and the sputtering may be related to the vacuum so where do I start to look for that? The motor was in decent shape to look at so who knows if the rings are bad. I had a valve job done on the heads so I don't think I have a sticky valve. Maybe a worn guide? I think I had them done too.
O.k. I bought a third set of wires(ones I didn't have to assemble) and put them on. and changed the jets back to the stock size. It runs MUCH better. The three cylinder miss at idle *seems* to be gone and the stumble at takeoff as well but I didn't drive it because it was getting too late and driving it involves pulling my trailer out and the whole nine yards.It sounded fine before I drove it last time though as well, so tomorrow I will get the final verdict on that. I also hooked the vacuum advance back up mostly because the vacuum cap came apart in my hands and I didn't feal like looking for a new one. This cap was the one I took off to perform the vacuum test so it wasn't leaking through there. I pulled the cap and watched the distributer as I turned the crank in opposite directions. I can turn the crank about 10 degrees the opposite direction I was turning it before the rotor starts to move so I'm guessing the chain is cooked. Thoughts?
I hope your wrong about that for my wife's sake. She said when It comes time to re-build this motor I can go full roller and whatever else it takes to get me up and over 400 horses. I am just not prepared for that right now.Ramboss429 said:
Oh and I'mnotright, I don't have power brakes.1 - 8 of 27 Posts
