Sending unit is re-installed minus the sock, along with an inline filter before the pump and all new rubber lines. Seems to have a little more fuel pressure, however the problem is still there. Got to about 4850rpms before it ran out of steam. The only things I can think of doing in the mean time are replacing the rotor, cap, and installing the re-curve kit I have. Otherwise all the other ignition components are new. At this point I think I'm done throwing parts of it. I'm going to wait unit the winter when I finally do a cam swap, since that will officially eliminate any weak valve springs, and will definitely add a subtantial amount of power and top end. I plan on giving the heads a little home port job too. Thanks again for all the help guys. :beer
Andy please remember to let us know what you find later on, some of us have our suspicions :laugh: . Good luck with it and enjoy the rest of the summer. I hope to have at least one of the Cats back on the street next spring:TU:
Will do John. At this point, I'm thinking it's either something in the valve train, or that's just all the motor has in its current configuration. We'll see next spring I guess.
Andy, I still think it would be worth it to put a vacuum gage on the engine to see if you are building enough vacuum to close the power valves at the point it lays over. The engine can start to build vacuum at the top of the rpm range under load and would close the power valves if you get to the vacuum amount stamped on the power valve. Even at wide open throttle, 6.5 Hg is very little vacuum to generate in an engine with a strong vacuum signal. Once the power valves closed it would be lean and lay over like you described. If you don't want to use a gage, you could also test for this condition by replacing the power valves with a power valve blocker and jetting up 7-10 sizes. In either case, you want to replace the power valves with those that are higher then the vacuum reading you get at WOT under load at the top of the rpm range, but lower then the reading at idle in gear. I was also wondering how you set the rear float level. It could be too low if you do not use the secondary throttle rod to open the float valve when setting the level. It would not be able to recover fast enough in that condition and would run out of fuel. HTH - Cheryl
I'll see if I can borrow a vacuum gauge from someone. To set the float level I did nothing more than remove the sight plug, and raise the float level until fuel started to dribble out. Could you go over the proper procedure? One other thing I came across was an article someone posted on here not too long ago. The article mentions that Buick rated the lifters at 6000rpms, BUT that number is only attainable if no more than 20 weight oil is used. Otherwise pump up may occur. I'm running 10W-40 synthetic. How likely or unlikely is it that this is my problem?
I just read a nice article in Car Craft about lifters. Here's a summary: With lifter preload set at 0.020", and using springs not suitable for hi rpms, separation between valvetrain components can occur, valve float results, and the lifters will pump up and take up that extra 0.020"..... it's possible that could keep the valve from closing completely, killing the power. On the flip side, a leaky lifter or using too much spring pressure, will result in lifter bleed-down (compresses too much) and the valve will not open fully.
Andy, Open sight window Turn secondary throttle shaft enough to increase idle (should be enough play to do) Continue to hold secondary throttle shaft slightly open until the fuel bowl level drops and recovers Release throttle shaft and adjust secondary float level until the is a slight fuel drip from the sight window Repeat procedure until no adjustment is needed for the secondary fuel level to recover to level where there is a slight drip from the sight window The bowl on the primary side uses fuel for idle. This allows you to see where the float level is set because it is constantly opening and recovering because of the fuel used for idle. The secondary bowl only uses fuel as the secondary shaft is opened. Meaning it is static unless operated. You have to get the valve to open and close to assess the level. That is why you have to move the shaft until the level falls and recovers. I hope that makes sense. Cheryl
So Andy, did the cam and springs fix the problem? will it rev past 5000 now:laugh: Also what rpm was you shifting at when going with the 69 chevelle
If you haven't installed the ducts yet You'll like it when you do. I had that same set-up on my Dodge ram, and though I felt it killed the low end a bit, once I got up to about 45mph it was a whole different animal. Effects of ram air are probally minimal, but it sure loved that cold air.
Sorta. It will easily pull to 5k now, whereas before it struggled to even get to that point. But revving it beyond 5k is pointless. Since I didn't touch the heads, peak HP is still probably relatively low in the power band - maybe 4500rpms? That's about what the dyno simulations say, and that's what my butt dyno says. I've been shifting at 4700-4800rpms. Just past peak HP, and it puts me at peak torque shifting into 2nd gear. The ducts haven't been installed to get a true "ram air" effect. They've been located to pull cooler air though. That's one thing on my to do list. I've also been debating ditching the Spectre setup all together and going with a much larger air cleaner. I had the Spectre setup apart the other day and that filter is kinda puny. Without the "ram air" effect I'm not sure if that thing is capable of supplying enough air.
Bingo, that's EXACTLY what I was thinking Devon. I had this very problem, the car just nosed over under WOT once I reached terminal velocity. Couldn't figure out what the deal was. Some guy at the track said, how much fuel is in your tank? I said I think like a quarter or less. I filled it up and it stopped happening. I had 2 or three runs where it nosed over then after filling the tank it stopped. The pickup was running dry with the remainder of my fuel pinned to the rear of the tank under WOT. Stupid question maybe but is the tank at least half full?
At times yes, and at times no. I don't think it was a fuel issue as I had consistent pressure readings during a run. I can also say it wasn't valve float. This was my old setup last year, and I think I had two problems. The first being that's simply all the motor had. I did a little digging, and I think the cam in it was a Sealed Power replacement. That particular cam is significantly milder than even a stock Nailhead cam (by roughly 13* duration @ .050). So I think that's all it had in it. In addition, the 6.5 PV's that I thought were in the carb were actually 2.5's. So it's also highly likely that the PV's were partially or fully closing too. This would also explain why the plugs looked so good even when I had the larger jets installed. The current setup (with a Comp Cams Thumpr) will pull past 5k, but seems happiest just shy of that. Until I port the heads any more worrying about high RPM potential is really a moot point. If I can beat up on a built Chevelle in my current configuration I'm happy. :TU:
