Does it brake up at the same RPM?
Is it barking out the exhaust or the intake?
Is it barking out the exhaust or the intake?
“New” Intake
- Thread starter Ishiftem
- Start date
Congrats with the intake Dan
If you've swapped out ignition, sounds like fuel. Fuel pump? Fuel pressure? Carb float level etc.? Process of elimination, best of luck sorting it Dan
If you've swapped out ignition, sounds like fuel. Fuel pump? Fuel pressure? Carb float level etc.? Process of elimination, best of luck sorting it Dan
Hope it's not cam or valve train, wiped lobe maybe?
What about valve springs ??? Strong enough?? Is oil pressure sufficent at higher rpm to keeps lifters pumped up?? Just some thoughts that might cause the vacuum concern???
When you say it could be something stupid Dan mine was when I was on the dyno. Something got stuck in a secondary Jet. Tried a different carb and problem went away. Everything was fine to a certain rpm and then broke up and choked. Cleaned it out found a piece of carb gasket from a metering plate went through it and stuck.
There's NOTHING hyd.in Dan's valve train as this is a pure race engine.I suspect valve train issues but could be wrong.
Ok ,did not know what he had as far as lifters. Thinking valve train also.
Valves tight in guides hanging up.
oil flow to heads.
oil flow to heads.
James: Not the same rpm. I would say exhaust but didn’t want to be next to it at 6500 to verify.
Taylor: pressure steady 5.5. Floats doubtful but maybe? Wiped lobe oil looks great. No metal on plug after 25 pulls. Thanks! The intake will only get better if I raise the plenum.
Dave: will check springs
Tim: carbs will be taken apart and scrutinized.
Dons: yes valvetrain is a suspect.
Tom: guides are actually a little sloppy.
The autopsy begins now. Findings to follow!
Taylor: pressure steady 5.5. Floats doubtful but maybe? Wiped lobe oil looks great. No metal on plug after 25 pulls. Thanks! The intake will only get better if I raise the plenum.
Dave: will check springs
Tim: carbs will be taken apart and scrutinized.
Dons: yes valvetrain is a suspect.
Tom: guides are actually a little sloppy.
The autopsy begins now. Findings to follow!
Sorry to hear Dan……..
You said you changed plug wires, did you replace coil wire?
Yep. Also took a pair of jumper cables and grounded the intake to the battery.
Nothing yet. Loosest valve was .002 off. None tight. Cut the filter open and it looked fantastic. Worst leak down on a cold engine was 4%. Cam timing 2 degrees retarded so I’m going to advance it as long as it’s out but that’s not the issue. Nothing wrong from the intake to the pan so it’s gotta be electrical or fuel some how. Plan is to clean the carbs and put it back together in the car using all my fuel supply and electrical and see what happens.
Dan, we had a similar issue with a BBC Super Stock engine on the dyno. The springs were fresh and were the same as what had come off.
I'll spare you all the gorey details and get right to the meat and potatoes of it: shimming the springs to actually 'stack up' a couple of coils at max. lift got things calmed down and life was good again. Valve spring surge can be a real mother to track down. We had some inside help from a NHRA Pro Stock crew member, so that shortened the learning curve up a bit.
P.S. Take a couple of intake and exhaust springs off and look at the underside of the retainer and the valve lock outer surface for any signs of fretting or chatter. We didn't recognize it at first but looking back, it was there. We 'looked' but we didn't really 'see', if you know what I mean.
I'll spare you all the gorey details and get right to the meat and potatoes of it: shimming the springs to actually 'stack up' a couple of coils at max. lift got things calmed down and life was good again. Valve spring surge can be a real mother to track down. We had some inside help from a NHRA Pro Stock crew member, so that shortened the learning curve up a bit.
P.S. Take a couple of intake and exhaust springs off and look at the underside of the retainer and the valve lock outer surface for any signs of fretting or chatter. We didn't recognize it at first but looking back, it was there. We 'looked' but we didn't really 'see', if you know what I mean.
Working in a dealership ,we installed a lot of rebuilt engines from consolidated engines. Sometimes they would not run right and a guy from their business would come out and shim weak springs because of the warranty .
That honestly has crossed my mind. I took off the springs I had because they had a ton of passes on them. Pressure wise they were in great shape but they were PSI and I have heard they hold their pressure right up till they break. Anyway, The old springs were set up about .065 from coil bind. These new ones are about .125 if I remember right and have about 25 pounds more pressure on the seat.Dan, we had a similar issue with a BBC Super Stock engine on the dyno. The springs were fresh and were the same as what had come off.
I'll spare you all the gorey details and get right to the meat and potatoes of it: shimming the springs to actually 'stack up' a couple of coils at max. lift got things calmed down and life was good again. Valve spring surge can be a real mother to track down. We had some inside help from a NHRA Pro Stock crew member, so that shortened the learning curve up a bit.
P.S. Take a couple of intake and exhaust springs off and look at the underside of the retainer and the valve lock outer surface for any signs of fretting or chatter. We didn't recognize it at first but looking back, it was there. We 'looked' but we didn't really 'see', if you know what I mean.