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Discussion Starter #1 (Edited)
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.
 

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Just got off the phone with Chris - he won't be able to get back on til later tonight. He has MSD ignition box and distributor - he doesn't know if there is a ballast. I think he should try the propane trick to look for vacuum leaks - but I'll tell him to check fuel filter as well. Any other ideas? He said it also got hot pretty quick - 5 minutes to 200*. Not to surprising becasue it was probably 100* at his house though.

???
 

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sounds like ignition to me, excpe the idle part.
check base timing, and see how it advances, and when.
BUT,
I'd also check to see if the secondarys are hanging open some, or possibly the rear flats are high, and dribbly down the carb.
 

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Jrod-13 said:
sounds like ignition to me, excpe the idle part.
check base timing, and see how it advances, and when.
BUT,
I'd also check to see if the secondarys are hanging open some, or possibly the rear flats are high, and dribbly down the carb.

I told him to go buy propane torch and to check to make sure his electric fuel pump isn't flooding his carb like you mentioned. He said once he gets above 2500-3000 rpm it runs like a champ. I asked if he had black smoke coming out the pipe and he said no - but you never know.
 

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I'd end up saying its your jetting. Sounds like your running lean. May also be your cam causing that choppy of a idle.
 

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ImNotRight said:
since you don't know what cam is in it, it kinda sounds like you are running the wrong firing order. --

http://www.mustangandfords.com/techarticles/28738/index3.html

3 and 4 and 5 and 7 are switched between the two.
This was my guess. Wrong cam. It's possible you have a cam made for a 5.0 H.O. in your motor. No biggie if thats the case.

Easiest way I can think of to find out is to pull the valve covers, roll the engine over a couple of times, and watch the firing order via the cam.
 

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Butler said:
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.
He says there may be 3/8" of slop in the chain ...
 

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Discussion Starter #10
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.
 

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Pretty simple. Go get a GM 4-wire HEI module from napa or wherever.

two of the wires are the mag pickup, the other two wires are the coil. Just run a couple screws into some bare metal to ground the module and you're good to go for testing. You can mount it anywhere for testing purposes.

If it runs fine, then yea.. MSD. I did run into one that just plain wouldn't work right for some time. Ran like shit. (GM HEI w/ remote mounted coil) But with a MSD dizzy it now works just fine. Wierd.
 

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Butler said:
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...
What's this "We" crap ? :flipoff2:
 

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You didn't say where it was you had your ignition timing set. Start at straight up (0 degrees), and slowly move forward. The carb was obviously taken apart to rejet it, are all the base plate screws tight? Your float level is properly adjusted? No other places where there might be a vacuum leak (manifold gaskets, etc.)?

A very useful tool I started using recently is one of those laser thermometers, you can find out which cylinders are acting up by measuring the exhaust temp on the manifold or headers one cylinder at a time, beats the hell out of spitting on your finder and touching to find out what's hot and wha't cool.
 

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Discussion Starter #14 (Edited)
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?
 

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the heads/block doesn't matter. a 302 head is a 351 head is a 302 is a 351 head (as far as exterior demensions are concerned).

Now where things like that can happen, is if the heads or the block where milled down considerably at rebuild time. Then, yes, the angles can be off a bit if the intake wasn't milled down at the same time.

A quick note, the 69 block already starts with a shorter deck height than 72+ blocks. "the 351 is 9.480 inches for '69-70 and 9.503 for '71-current"
That isn't enough to cause problems, but if for some reason the heads were milled also, it definetly is a start.

Spark plug gap is NOT dictated by the head. Gap is completely dictated by what the ignition can handle. The larger, the better, and the MSD can ignite quite a large gap. MSD's instructions go something like open the plugs up .005" at a time untill performance drops off, then close again. I just put everything at .055" and not messed with it. I'd say you definetly should open them back up, as .040" is WAY small. The stock duraspark could handle that without breaking a sweat.

A quick/easy way to tell if the chain is worn is to pull the dizzy cap off and turn the crank back and forth a little bit. The rotor should move almost immediatly with the crank. The more you have to turn the crank to get it to move, the more your chain is worn. (of course turning it backwards is what will show the slack)
 

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Discussion Starter #16
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.
 

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What type of distributor are you using? A duraspark, or something else? You can bypass your MSD, it only takes a few minutes of rerouting the wires, if it still runs like crap you can rule the MSD out.

I don't like the sound of how your heads line up with your manifold, but if there isn't a vacuum leak it shouldn't be a problem. Your valve clearances are all correct? If the heads or block have been milled down any you aren't going to be able to tighten the rocker arm nuts as far down as before.
 

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Discussion Starter #18 (Edited)
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.
 

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Never done the check with propane, I always use carb cleaner. You can spray it every where and actually see where it is going. As opposed to propane.

How about a blown brake booster? Clamp it off and see if it helps.

after that, if you think you have low comp, go buy a $20 compression tester and start testing. It can only be so many things, ya know.
 

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I had the same problem that you are describing with an old 318 in a farm truck of ours a few years back. It end up being the timing chain jumped. I put in a new timing chain set, and timed it and it ran good after that.

I had this same problem about 2 months ago with a 1991 F150 with a 302 in it. Idled like crap, but when it got up to 2,000 rpms it ran just fine, or so it felt/sounded. I did a compression check on it and cylinder 4 and 8 were dead.
 
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