engine breaks up at about 4200rpm's?
Thread Starter
6th Gear
Joined: Jun 2006
Posts: 6
Likes: 0
engine breaks up at about 4200rpm's?
i got a 69 350-350, when i take off i can only rev to about 4200 and it starts to break up.. and need to shift. Anybody have any clue what could be the prob? ive replaced the carb, coil, points, condencer, i dont know what else it would be.. the engine has had a total rebuild and it did it before that to.. HELP!!!!!!!
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Originally Posted by blu69sting
i got a 69 350-350, when i take off i can only rev to about 4200 and it starts to break up.. and need to shift. Anybody have any clue what could be the prob? ive replaced the carb, coil, points, condencer, i dont know what else it would be.. the engine has had a total rebuild and it did it before that to.. HELP!!!!!!!
Thread Starter
6th Gear
Joined: Jun 2006
Posts: 6
Likes: 0
Not sure if im running out of fuel.. it just kinda pops and wont go any more till i lower the rpm's i had a 850 holly on when i got the car.. it was dumping to much gas in it and got in the oil.. solved that.. (engine rebuild and new carb* but the edle is a 650 i think.. and it does the same thing. HOw much is the hei distributor?? im guessin alot?
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
The points distributor is a good unit. Make sure the upper and lower bushings are not worn out, and the coil is giving a hot spark. If anything, you may convert it to electronic ignition, (I like the Crane unit). If not the distributor, look for a fuel flow/pressure problem, like pinched fuel line or clogged filter/sock in the tank.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
If the problem occured before and after an engine rebuild, and the same distributor was used, I'd look there first. Then fuel delivery (fuel filter?), then I'd look for a broken valve spring(s).
Le Mans Master
Joined: Nov 2004
Posts: 6,128
Likes: 21
From: North Alabama
Interesting thread. Mine was already converted to HEI with a recurve kit and different springs. Engine has 385 miles on it and just the last couple times, right around 45-4800 rpms it breaks up like that. Sounds like a back fire, popping. Not flattening out. Its a new issue. 
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
My '69 350/350 does a similar thing. I can slowly accelerate through the entire RPM range, but at WOT it starts cutting out around 3500-4500 RPM, depending on the starting speed, what gear, etc. If it's in the garage under no load-- it can rev high no problem. So that makes me think I'm maybe running out of gas at WOT under load. I'm going to hook up a fuel pressure gauge and duct tape it to my windshield to see what happens at WOT under load.
Unfortunately I have a Holley 4165 so it's not easy to direct connect a fuel pressure gauge to only the secondary feed, since it's fed through a tube from the primary bowl.
So maybe you should try removing your fuel filter and monitoring your fuel pressure. It could be your fuel pump just can't quite keep up when your foot's to the floor. Also you could try keeping your secondaries closed and running on primaries only. If it doesn't cut out-- it's probably your secondaries are too lean-- maybe increase the jets, or the fuel pressure is too low when the secondaries are also sucking gas.
Unfortunately I have a Holley 4165 so it's not easy to direct connect a fuel pressure gauge to only the secondary feed, since it's fed through a tube from the primary bowl.
So maybe you should try removing your fuel filter and monitoring your fuel pressure. It could be your fuel pump just can't quite keep up when your foot's to the floor. Also you could try keeping your secondaries closed and running on primaries only. If it doesn't cut out-- it's probably your secondaries are too lean-- maybe increase the jets, or the fuel pressure is too low when the secondaries are also sucking gas.
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Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by blu69sting
Not sure if im running out of fuel.. it just kinda pops and wont go any more till i lower the rpm's i had a 850 holly on when i got the car.. it was dumping to much gas in it and got in the oil.. solved that.. (engine rebuild and new carb* but the edle is a 650 i think.. and it does the same thing. HOw much is the hei distributor?? im guessin alot?
Burning Brakes
Joined: Jun 2000
Posts: 892
Likes: 0
From: GA
Similar issue here... it was my cam. Exhaust lobe was rounded badly. Right around 4000rpm... starting backfiring and sputtering. Had a slightly rough idle as well. That is what I got for thinking I knew how to adjust rockers... NOW I know... but it cost me... live and learn. Good luck with your toubleshooting...
