I have a 1968 c10 that I been working on for a while now, it has a 350small block with a 7,000 rpm limit cam starting at 3,500 rpm 3 speed transmission, runs like a top until you get it up to 65 then the entire truck vibrates and won't go past 65 it has a 3:73 gear ratio in the rear end, could it be that I need to go lower to maybe a 2:93 or do I just need to put an overdrive tranny in it or? It's running 4,000 RPMs at 65.
there are a LOT of things that it could be...and we need a lot more info on your engine combo..got pictures.....lets go over a few things first..do you have a remote starter button.. this is going to help.. COLD ENGINE.. DISCONNECT the IGNITION COIL or distributor so NO SPARKS CAN BE CREATED..... disconnect the fuel line going into the carb...extend the fuel line into a clean.. clear plastic soda bottle..use the remote starter button to crank the engine for 15 seconds.. use a watch.. or have somebody count.. while you Observe the pulses of fuel from the end of the fuel hose into the clean clear plastic 2 or 3 liter soda bottle.. you want to see fuel pulses start instantly... and continue unchanchanged ... each pulse the same as the others... not diminishing.. you will also want to use a pressure gauge on the end of this circuit.. to verify the fuel pump is not leaking back into the tank thru dirty check valves....after you have verified at least a PINT of fuel more to come later.. describe your entire set up please...and photographs..
No I don't have a remote, starter button its getting plenty of fuel.I have checked and the pulses of fuel are the same each time it has all new fuel lines.New fuel pump about to post pics, it's a carbureted 350 early to mid 80s model engine/transmission from a k5 blazer. 4 barrel edelbrock 850 thunder series square flanged carb has electronic ignitionPictures I have is when I had a Holly 750 on it but it has the exact same set up nothing has changed.
dylan...need a LOT more info..i was tired when i posted.. missed the volume of fuel..how much timing max... at 3200 RPMs.. or where does it stop advancing.. you say electronic ignition.. but what kind.. and who curved it.. or straight out of the package..which heads... which valve springs.. who adjusted the valves.. there is just so much to think about with too little info to give you a decent answer..click my user name.. repost your question over as chevyhiperformance forums.. there are a lot more members there who get more sleep than i do.. list everything.. you could have too much timing advance... if there is too much advance curve.. at high speeds.. the engine could be detonating.. one guy could not get his 512 mopar to rev beyond 4400 RPMs. seems the engine builder had set the built in rev limiter low to protect the engine as the owner did not believe in break in timeyou could have too tight a valve adjustment and are floating the valves. or the lifters are pumping up.. there might also not be enough spring tension to slam the valves closed at high speeds... you could have too much carb for the heads. and for the exhaust .. the jetting could be wrong.. and there still could not be enough fuel.. i forgot to mention that you need to find at least a half a pint in 15 seconds.. i used to full flow test the fuel systems for ten seconds. but i find 15 seconds works better. just because you get a few pulses does not mean anything.. i had one guys fairlane that after 7 seconds it would start to get less.. and by 15 seconds it was down to drops... when i used my brake bleeder vacuum pump on the fuel line from the tank.. i could pump 23 inches of vacuum in this line that should be open.. found the line was full of sediment.. like somebody had poured dirty dusty fuel into the system.. and it was smashed flat in several places...how about the electrical system.. can it keep up with the needs of the ignition system ..?? some ignition systems pull well over 10 amps.. thats a LOT to draw thru a 68 chevy pickup wiring harness... you might need to do a few mods.. to supply the ignition with increased amperage either directly off the starter.. or off a terminal block from the battery or off the terminal block behind the battery...in a 68 chevy truck.. the big wire goes to the starter. but there is a small wire off the positive cable.. goes over to the terminal stud on the inner fender.. from there across the core support to the horn relay usually.. then in thru the bulk head connector to the ignition and several other places.. that like almost 16 feet of wire.. before it comes back thru the firewall.. and the ignition switches can burn..and don't forget.. the NEGATIVE Side has to be hooked up also.. negative battery terminal to the engine block.. but a small one to usually a ground connection on the inner fender next to the battery.. where it supplies power to the body.. the core support for the headlights and all the rest of the body...there also needs to be a ground strap from the back of the cylinder heads to the firewall... i think that an 850 is probably too much carb.. but it might work.. but there are probably a bunch of other small things wrong that are easily fixed without spending a TON of cash...