you can try bigger jets, did your timing get to far advanced some how.why not just .shift at 4950 rpms. with out a cam or head work your not going to make any more power or go faster plus your engine will stay together longer.even with all my mods my best times are at only 5250 rpms. just my thoughts. oh yea your valve springs could be your real problem most likely e sorry about spelling . a
What power valve(s) is in your 850 and how much vacuum are you pulling in gear at idle? It may be getting enough vacuum to close at the top end. Power valve(s) that are 1-2hg lower then the vacuum you get at idle should be used. Cheryl
Timing is still the same as it has been. PV's are 6.5's, don't have a vacuum reading to give you, but the cam is fairly stock so it should be a pretty decent number. If this is all it's got, I'm fine with that. I'm just trying to determine if there is a problem, or something I should be worred about (like valve springs).
The only way to determine that with certainty is to test them, either with a hand held spring tester on the car, or off the car on a bench tester. Otherwise it's all conjecture. Devon
some times with the ethanol fuel it will lean the motor out, you need to jet the carb up 1-2 sizes just to stay the same. why not try going up 2 sizes on the secondarys just to see what happens. if the valve springs are stock and have been on the motor all those years seems like they have to be weak. like Devon said you have to check them.
Sorry to sound ignorant, but can you explain the procedure for testing them on the car. Perhaps a link to a tester? Something like this; http://www.summitracing.com/parts/MOR-62390/?rtype=10? Normally I run 91 octane w/o ethanol, with a few gallons of 110 mixed in. I actually just re-jetted, and went down 3 sizes in the primaries and secondaries, and put in smaller shooters (31's). Felt like it had the slightest bit more top end, actually made it to about 4850rpms before it nose dived. And the valve springs are probably stock replacements, however they should have been replaced when the heads were rebuilt about 12k miles ago.
Andy,,, I think you are running out of fuel,,, and I dont mean lean jetting... I think that for what ever reason , the fuel supply is running out.... and there is nothing wrong with the engine, carb or timing or cam and or valve springs.... jmho :laugh: Start at the tank sending unit.... remove the sock at the end of the pipe, blow compressed air thru it,,,, [i found a dirt dauber nest in mine there] then proceed on up to the fuel pump/carb .... I am thinking you will find a clogged line, defective pump, rubber hose with a hole, sucking air,,,, something....:Brow: :Brow:
That's the idea, but I don't know how well or poorly the in-car testers will work on your engine, sorry! Devon
They are a little bit difficult to use because of our offset/stubby rockers. Because of this they are not as accurate on our "Nails" as opposed to straight across rockers. But, they will at least identify the weak one or ones. If you find one or more that ARE weaker than some of the others then you at least know what you have to do. I know that it's been mentioned previously, but have you checked the hose coming out of the tank yet???? They can suck air & not leak fuel. Had it happen to myself causing the same symptoms. Tom T.
Andy, it depends on just how the test was made.... 5-7 psi at idle at the carb will be the norm for the mechanical pump,,,, but it will drop off going down the road... a carb can work well with just 3-4 psi...and most will..... with that said, then there is the trip from the tank to the carb... with the factory pump, there is suction from the pump all the way to the opening of the tank unit that picks the fuel up...and at any point along that line a pinhole can get in there and induce air along with the fuel being sucked in... and bubbles in the fuel will completely mess up a carbs metering...and there can be other restrictions,,, corrosion, debris, collapse, kinking,,, bad filter,,,plugged filter, ect... There needs to be a test reading at idle, hot idle, normal speed, high speed, the speed where the shut down occurs,,, and so on... some times a pump that works normally at one speed and temp will not work right at different speeds and temperatures... I once saw a fuel problem that nearly drove the owner crazy untill he finally decided to remove and look in the tank... he found a red shop rag in there, it would float away and then move over and cover the fuel pick up... and then move away again... and I myself was hunting a shut down problem on a ford dump truck and found a piece of a shop rag inside the carb float bowl .... the owner was cussing ford , holley carbs,,, ect... but the problem was human induced... fuel problems are like others, you have to start the process of elimination,, know that you have good fuel, in a clean tank, with a good, solid, clean fuel line and filter, to a good clean, properly working carb.. and so on... and I wondered about the ability of the air cleaner to handle large amounts of air... I am amazed that the factory will have a 425 in. engine breathing thru a 1 1/2'' hole in the snorkel with dual exhausts.... and have baffles inside the can to muffle noise... After the ign. system and the fuel system is checked and the exhaust system , then and only then I would start looking into the cam/valve springs/timing chain system.....
Hi, first time posting. At the risk of stating the obvious, you haven't got the rev limiter set on your Pertronix have you?
yup-yup opened up a 'rebuilt' 401 a few years ago to find a red shop rag sitting in the pan-strange that it wasn't all sucked to the screen
I was going to suggest that myself. I think they come set to 5000RPM but he said at no load he can get higher. I would not rule it out though. Pat
On one of my project cars, I have a small lawn mower gas tank mounted under the hood, just to move the car around. You might want to try that to eliminate original fuel tank and lines as a potential cause of the problem. The original Q-jet air cleaner on my blue car chokes the 425 at higher revs.....it's VERY noticeable on the street!
I'll re-check the lines from the tank. They looked good at first inspection, I guess I'll just replace the rubber portions. I believe I can check in the tank via the access hole in the truck. I'll do that as well. I don't think the air cleaner is causing a restriction, but I'll make a run or two without that and see what happens. And the rev limiter is set at 5700 or 5800rpms. When I first put it in the car, I accidentially set it at 4700, so I know what it feels like when it hits the chip, and it definitely isn't. At the beginning of the summer I actually turned off the limiter function to make sure that wasn't the problem. Thanks for all the help!!! I really do appreciate it.
The sending unit will come out through that access hole. Pull the whole thing out & check the sock also.
I pulled the sending unit. Tank is clean and in good shape. The sock is black, but is in good shape and doesn't seem to be an issue. Should I replace the sock before I re-install the sending unit? Is there a source for them? Also, is there a source for the cork sending unit gasket? Mine is still intact, however I figured I might as well replace it while it's out. Or would a thin bead of RTV suffice?
I took the sock off of mine and installed a good inline filter...just one less trouble source......and the inline filter is easier to get to.....
