Just wondering, did this engine run good before ? If so, did anything take place that may help explain why it now has a problem ?

 

Well, right off this morning, I will thank everyone for the input so far. I put a normal dizzy back into the motor to get away from the huge spark advance from the MR gasket recurve kit. Those things didn't work well for my brother or I, but atleast they are cheap and easy to install. I gave it a shot. Next, the engine is supposed to be really built, for an iron headed truck engine, 10.5 compression, big cam (flat tappet comp), roller rockers, D3 heads with 2.190 and 1.710 valves, straight up cam timing, ported/polished heads, and more that is already posted. The builder was trying to check the lift on all of the lobes but he said that with the engine in the vehicle it was very difficult and got only half done and gave up. Found no problems yet but said that he thinks he will have to tear it down and he WILL fix it when he finds the problem. The engine is brand new and has always been weak at best, or tired is maybe a more complete explanation. I thank you for your time and look forward to the replys, but it looks like a cam shaft to me at this point.

 

Yeah... sounds like your running out of ideas "in the truck". Just had a thought though... pushrods... new I assume, and pardon such a basic thought here, were lengths verified? bent maybe???

 

not sure. I thought of that and I will definitely look into the pushrod verification when the motor is tore down.

 

Sounds like too much timing. Do yo still have your stock distributor your could try? I know my 460 hates anything over 38* at 3000 with no load (pulling about 18" - 20" so don't know why yours would need that much.

 

I did reinstall a stock dizzy and that didn't change any symptoms except for the pinging quit. thanks the MR gasket recurve kit didn't do justice for me if anyone wants my 2 cents.

 

Well I got my rig back from the machine shop and it had new plug wires, no oil leaks, new cap and rotor, and it will set me back in the seat now. not sure it is 500 horsepower but it does good. I raced my brothers 7.3 powerstroke and beat him. I think with headers now it will do very well. I have been tuning on my Holley 670 truck avenger and got the flat spot gone off idle and now it has one that is about 2500 rpm right when it starts drawing fuel out of the venturies. I did some research and it turns out that the first gen truck avengers had a notorious flat spot at low rpm and holley will replace them at no charge with the new gen 2 that is better. I think I will quit messing with it until I talk to holley tomorrow.

 

glad to hear the shop got it working better for you. Thanks for coming back and letting us know.

Let us know about that gen2 holley too will ya?

 

Yes thanks everyone for the input it sure helped me so far. I think there is room for improvement but Holley said that those gen 1 TAs didn't run right and they will replace it with a gen 2 at no cost if I send it back, Already have the post office flat rate box too. Next is headers and that should wake it up then the new carb too. It is getting tolerable and best of all is all of the oil leaks are fixed. But I will let everyone know how the carb swap goes.

 

I am reading so much about headers it raises a question. I have a donor 1986 460 I am putting in my 1973 F 350. I was just going to use the stock headers and put in a new system from the headers back. Am I making a mistake not putting an after market set on the engine. I am planning to tow only and not extra large trailers.

 

Well, I have never personally owned a 460 with headers, but my neighbor had a 429 police interceptor that was built up and turned into a 460. It started life out with headers and glass packs and then evolved into mufflers and manifolds and that made great improvement on lowend torque which was awesome since the motor was in a 79 f250 4x4 that was used to tow. I thought my engine would run good with manifolds since his did but he must not of had build up that mine has. His truck did very well with a stock cast iron intake and a set of iron manifolds, so I bet you will be fine but a good aluminum intake will help some on performance and a set of headers should make a noticeable difference too if you are budgeted for it, the other thing I would recommend on a 1986 motor is put a straigt up timing set in it.

 

Well I got my Gen 2 holley 670 TA in the mail last monday and jetted it, adjusted the kickdown, got the idle and choke set for our 5* coldstarts in the mornings and it seems way better than the old TA. The flat spot is totally gone, it idles better, It is snappier, and, my favorite, it has noticeably more power. I thought there was something wrong with that carburetor and I was right, those things are defective from the factory. I couldn't get it to run right and I knew I was better with carbs than that. There is a slight hesitation when the vacuum secondaries open, at WOT, You feel the motor slightly flatten out then the roar gets a little louder and she really sets you back in the seat. I think for optimum performance, It needs a lighter spring in the secondaries but I will leave it the way it is, up here where the air is thin and vacuum is a little low, I thought that would be a consideration for factory calibration, but I think where those secondaries stay closed longer, it might keep fuel mileage up a little and when offroading, it will be easier on the u-joints, but overall, I'm happy with the setup. I think with headers, it will really run. If anyone has a 1st gen TA, send it back for the upgrade.

 

You need a HEAVIER secondary spring if you can feel a flat spot before they kick in.

http://www.holley.com/data/Products/...199R8219-2.pdf

Get a 20-15 kit and perhaps a 20-59 quick change cap if you don't like disassembling your carb all the time to change them.
Be careful the o-rings stay in place if you get the 20-59. A little dab of vaseline will hold them in place.

 

Well, thanks for the input, but the secondaries are staying closed until the engine makes vacuum off of the open primary then they open the secondaries, and mine flattens out slightly, not because it leans out, but because there is something wrong with the engine and the manifold vacuum actually drops as the RPMs increase, like a plugged exhaust. So, there fore, there isn't enough vacuum to open the secondaries like they're supposed to. I appreciate your input and am not trying to citicize your post, only merely clarifying the details that are not yet widely known about my situation. If the engine was correct, then yes it would be opening the secondaries too soon and leaning out but it is in need of headers to start with and god only knows what after that!! However, I put a screw in the secondaries linkage to open them sooner and the problem fixed itself then. I assumed upon that test that the secondaries needed to open with less vacuum, which explains the problem, and supports my theory that the spring is in fact too heavy and holding the linkage shut a little longer than optimum. I could be wrong, but based on my scenario, the engine's low vacuum condition is causing a flatspot by not opening the throttle soon enuogh.

 

Well I'm back. Installed my L&L chassis exit headers tuesday. Went well I had a slight motor mount issue that I had to resolve to gain clearance on the passenger side but after that thi install went smoothly. The headers are a little tight with the cooler lines on a C6 but they look like they will fit with a little creativity. Next thing was the performance. Seemed to gain a noticable amount of snappiness off the bottom but seemed to almost flatten out up high, possibly a carb issue now that the manifolds are no longer restricting it, but I didn't drive it enough with uncorked headers to tune it. However, it did seem to eliminate the hesitation when the secondaries open so now we have an even power curve until it flattens out which is cool. I am still not a fan of headers but they do improve the situation. I agree with the previous discussions that headers are necessary and the L&Ls are my recomendation at this point. I have heard some bad and even had a few bad experiences myself but they are a nice header. When the exhaust is hooked back up, I will tune some more and repost. Thanks for all of the good info, none of it has led me astray yet.