Acts like valve float at 4K WOT ??
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
Acts like valve float at 4K WOT ??
New problem. Had a misfire that turned out to be crud on spark plug so cleaned them all up and reset gaps. Now engine runs fine and strong but during WOT when I hit 4k or higher it starts misfiring like valve float is the best way to describe.
Feels like electrical issue more than fuel but not sure. So need ideas.
First guess is could it be possible if plug wires touch each other you can get shorting between wires? Also what about coil if its going bad? Points are new and set correctly. I had issue with secondary air valve on Qjet sticking but pretty sure I solved that but maybe its still sticking. Valves are set for solid lifters and never had issue with that before so can rule that out.
All comments appreciated. THX
Feels like electrical issue more than fuel but not sure. So need ideas.
First guess is could it be possible if plug wires touch each other you can get shorting between wires? Also what about coil if its going bad? Points are new and set correctly. I had issue with secondary air valve on Qjet sticking but pretty sure I solved that but maybe its still sticking. Valves are set for solid lifters and never had issue with that before so can rule that out.
All comments appreciated. THX
Pro
Joined: Jan 2016
Posts: 502
Likes: 103
From: Reno Nevada
New problem. Had a misfire that turned out to be crud on spark plug so cleaned them all up and reset gaps. Now engine runs fine and strong but during WOT when I hit 4k or higher it starts misfiring like valve float is the best way to describe.
Feels like electrical issue more than fuel but not sure. So need ideas.
First guess is could it be possible if plug wires touch each other you can get shorting between wires? Also what about coil if its going bad? Points are new and set correctly. I had issue with secondary air valve on Qjet sticking but pretty sure I solved that but maybe its still sticking. Valves are set for solid lifters and never had issue with that before so can rule that out.
All comments appreciated. THX
Feels like electrical issue more than fuel but not sure. So need ideas.
First guess is could it be possible if plug wires touch each other you can get shorting between wires? Also what about coil if its going bad? Points are new and set correctly. I had issue with secondary air valve on Qjet sticking but pretty sure I solved that but maybe its still sticking. Valves are set for solid lifters and never had issue with that before so can rule that out.
All comments appreciated. THX
If you are running a distributor, a small crack or even a scratch in the distributor cap can do funky things to spark at speed. Same things with plug wires, boots, etc, etc. If something is arcing, you should be able to see a small burnt spot wherever it is arcing if you look close.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
had that happen took me two weeks to find it in a dark garageCross # 5 and 7 by accident? easy to do
Sometimes just moving wires around can fubar one up if they are old
Go one cyl at a time usually something simple.
How olds the fuel pump, oil smell like gas at all?
Last edited by cv67; Jun 7, 2016 at 11:05 AM.
Race Director
Joined: May 2006
Posts: 18,742
Likes: 2,583
1. do a fuel pressure test
2. what do you mean "valves are set for solid lifters", are they hydraulic or solid?
3. The points are new and set, does that mean the dwell is 30 degrees and you set the initial timing and made sure the mechanical advance isn't sticking?
4. Did you adjust the tension on the secondary air valve spring, if so how much tension did you apply 1/2, or 3/4, or 7/8 of turn?
5. Do a primary and secondary coil resistance test.
2. what do you mean "valves are set for solid lifters", are they hydraulic or solid?
3. The points are new and set, does that mean the dwell is 30 degrees and you set the initial timing and made sure the mechanical advance isn't sticking?
4. Did you adjust the tension on the secondary air valve spring, if so how much tension did you apply 1/2, or 3/4, or 7/8 of turn?
5. Do a primary and secondary coil resistance test.
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
My guess is an ignition problem. I would change those plugs. I have found as my plugs break down my engine will start breaking up at progressively lower RPM's.
Check the basics. If your dwell is not set correctly it will cause exactly what you are experiencing. If there isn't enough time for the coil to charge at higher RPM, you will be losing spark. Cap and rotor would be on my list to replace or at least check. And finally old wires could do it.
Check the basics. If your dwell is not set correctly it will cause exactly what you are experiencing. If there isn't enough time for the coil to charge at higher RPM, you will be losing spark. Cap and rotor would be on my list to replace or at least check. And finally old wires could do it.
Pro
Joined: Jan 2016
Posts: 502
Likes: 103
From: Reno Nevada
Agreed. If it was a fuel injected system, I would suspect a lean condition which is typically fuel or air leakage conditions. On a carb setup, what you are describing is more likely a spark issue in my experience.
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Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I had one that was doing that-- solid lifter cam. It was going flat. Pulled good until about 4k then started going stupid. Everything looked good until I pulled the intake and looked at the cam. It was going away so slowly that I didn't see any big adjustment changes in the valve lash. Little here, little there.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
Cam going flat is a possibility since I'm using solid lifters. Using Mobil 1 synthetic which should protect well. Cam has probably seen around 25k miles.
Might just replace pump since they are only $30 and not to hard of a turn a round. Cant hurt. I'll check cap and wires also...
Might just replace pump since they are only $30 and not to hard of a turn a round. Cant hurt. I'll check cap and wires also...
Instructor
Joined: Apr 2001
Posts: 242
Likes: 3
From: New York, NY USA
I too had this problem with 69BB w/HEI and QJET. Checked all ignition stuff and it checked out so went to fuel. Heard a lot of ideas when I posted on the forum but the right answer came from Lars - He told me that using two fuel filters (e.g. the inline AC GF432 and the one on the inlet on the QJET) was probably the issue. I took out the one on the inlet on the QJET and all was fine - It's cheap and easy so I'd try that. Good luck
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
I knew about that Qjet fuel filter issue also so I only run the regular long one inside the chamber and its less than a year old so pretty sure its OK but maybe I could take out and leave empty for testing. The GF432 is a possibility I forgot about and its been around 4 years since I put a new one on so maybe...
Timing is perfect, valve lash settings are perfect so things seem to point to cap or pump. Will attack this weekend. Still spinning the tires under 4K though....
Timing is perfect, valve lash settings are perfect so things seem to point to cap or pump. Will attack this weekend. Still spinning the tires under 4K though....
Last edited by Surfer69; Jun 8, 2016 at 07:12 PM.
Burning Brakes
Joined: Oct 2003
Posts: 1,090
Likes: 74
From: New Carlisle IN
I had kind of the same issue with my 73. It was a coincidence, but I had tried installing a HEI distributor. Things went wonky from there. I tried reinstalling the points distributor, change carbs, change fuel pump, change timing chain, replace gas tank and lines and nothing worked. I finally started to tear the engine apart and found some scoring on a couple of cylinders. Next I found the cam had been wiped. Many lobes were flat or lopsided from wear. The car had been used since 1994 as an autocross car by both my dad and myself. It was beat on pretty hard!
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
OK so looking at dist cap I see the rotor blade has worn a grove into almost but not all the little contact metal things inside. The groove is exactly the thickness of the rotor blade as if the rotor was too long or something is crazy loose.
The cap is not the chevy black stock one but the heavy duty tan or beige one that someone here had said was a good one. Something is not compatible so I will go find the basic black one and see what happens. Also I noticed the rotor blade thing can pivot if it wants too like move counter clockwise maybe 10 degrees if you physically move it with hand force, is that normal?
Nevermind, now I see the rotor cap stop on both sides of the blade, one has been completely broken off. So I think we found the problem. I don't know how I got two incompatible parts together but I will go back to basic stock stuff.
I'm surprised this thing still ran at all and very strong at that. THX All
The cap is not the chevy black stock one but the heavy duty tan or beige one that someone here had said was a good one. Something is not compatible so I will go find the basic black one and see what happens. Also I noticed the rotor blade thing can pivot if it wants too like move counter clockwise maybe 10 degrees if you physically move it with hand force, is that normal?
Nevermind, now I see the rotor cap stop on both sides of the blade, one has been completely broken off. So I think we found the problem. I don't know how I got two incompatible parts together but I will go back to basic stock stuff.
I'm surprised this thing still ran at all and very strong at that. THX All
Last edited by Surfer69; Jun 10, 2016 at 09:37 PM.