454 mag backfiring won’t rev up.
08-12-2021, 12:39 PM
#21
Registered
Pull the valve covers and take a look. Fellow boater had one last year doing the same along with "hard start". Found 3 broken rockers.
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SB (08-12-2021)
08-12-2021, 12:57 PM
#22
Platinum Member
Platinum Member
iTrader: (6)
to me the video sounds like its got a dead hole
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SB (08-12-2021)
08-12-2021, 01:09 PM
#23
Registered
iTrader: (1)
Manufacturer's Part Number:
11-232-3
Part Type:
Camshafts
Product Line:
COMP Cams Xtreme Marine Camshafts
Summit Racing Part Number:
CCA-11-232-3
UPC:
036584038474
Cam Style:
Hydraulic flat tappet
Basic Operating RPM Range:
1,000-5,000
Intake Duration at 050 inch Lift:
218
Exhaust Duration at 050 inch Lift:
224
Duration at 050 inch Lift:
218 int./224 exh.
Advertised Intake Duration:
262
Advertised Exhaust Duration:
268
Advertised Duration:
262 int./268 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.505 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.515 in.
Valve Lift with Factory Rocker Arm Ratio:
0.505 int./0.515 exh.
Lobe Separation (degrees):
112
Charter Member
08-12-2021, 11:12 PM
#25
Getting back to checking fuel press, Having a metal line from pump to carb does make it more challenging. There's a couple of different options.
1. Cut out section for a "T" and install a gauge there. This is a PITA since you would need flaring tools and fittings. Very easy to screw things up.
2. Remove fuel line from carb and rig up some hose/ fittings to connect end of fuel line to carb with a "T".
Both of these options will most likely mean disturbing the alignment of the fuel line to the carb. Even a small amount of mis-alignment will make threading the fuel line back into carb inlet a PITA and possibly lead to cross-threading the fuel line fitting.
3. Get another metal line, cut out a large section in the middle and use hose to attach the 2 ends. Install a "T" and gauge and make this your "test line". This would be the best option since your original line would remain un-molested and would be easy to re-install once troubleshooting is done.
As a rudimentary test, you could do what my father (auto mech) showed me when I was a kid. Disconnect fuel line at carb and slip hose over flared end of fuel line ( add hose clamp). Place other end of fuel hose in a 16oz Coke bottle (glass) and have someone start eng. Coke bottle should fill rapidly at idle speed (don't rev eng), like less than ~30 secs. Can't determine fuel press this way but it will be obvious if fuel flow is restricted. You should see strong surges of fuel into the bottle.
In regards to option 2, loosening the fitting at fuel pump may allow the metal fuel line to be rotated slightly to help avoid bending the the fuel line too much.
1. Cut out section for a "T" and install a gauge there. This is a PITA since you would need flaring tools and fittings. Very easy to screw things up.
2. Remove fuel line from carb and rig up some hose/ fittings to connect end of fuel line to carb with a "T".
Both of these options will most likely mean disturbing the alignment of the fuel line to the carb. Even a small amount of mis-alignment will make threading the fuel line back into carb inlet a PITA and possibly lead to cross-threading the fuel line fitting.
3. Get another metal line, cut out a large section in the middle and use hose to attach the 2 ends. Install a "T" and gauge and make this your "test line". This would be the best option since your original line would remain un-molested and would be easy to re-install once troubleshooting is done.
As a rudimentary test, you could do what my father (auto mech) showed me when I was a kid. Disconnect fuel line at carb and slip hose over flared end of fuel line ( add hose clamp). Place other end of fuel hose in a 16oz Coke bottle (glass) and have someone start eng. Coke bottle should fill rapidly at idle speed (don't rev eng), like less than ~30 secs. Can't determine fuel press this way but it will be obvious if fuel flow is restricted. You should see strong surges of fuel into the bottle.
In regards to option 2, loosening the fitting at fuel pump may allow the metal fuel line to be rotated slightly to help avoid bending the the fuel line too much.
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SB (08-13-2021)
08-17-2021, 02:28 PM
#26
Registered
Did you update your valve springs when you changed your Cam? This cam does require stronger springs and that backfire could be from some valve float along with a lack of fuel on the secondary's. You could try bumping the jetting on the secondary's up too. I am running the exact same cam in mine and it runs great. I am running 4" through hull exhaust however.
08-19-2021, 03:19 AM
#27
Sorry I haven’t responded lately, been working a lot and it’s been raining every day for almost the past week so I haven’t worked on it in a few days. But...
-no dead cylinders all have 185 psi
-pulled valve covers before, no lost lobes, no broken springs, no broken rockers.
-I do have full roller aluminum rockers, had to put valve cover spacers on to make them fit. They don’t hit cover now.
-pulled line at carb to verify it was getting fuel, with ignition off I jumped the relay to turn it over, it pulses out pretty hard. Didn’t fill up a bottle, but from that it looks healthy.
-I got a whole timing set with the cam, came with new springs. I’m not sure valves would float at 2300 rpm even if they were stock.
-It had a pamphlet on different ways to install the small timing gear on the crank, I did not advance or retard, just set to zero. Someone not on here asked that.
I bought a plastic piston stop tool to verify TDC, going to check that as soon as it stops raining.
Stupid question but on a Quadrajet how do you change jetting on the secondarys? It’s just the secondary metering rods and hangers correct? I didn’t see any secondary jets when I went through it. I did change primary jets from 68 to 70 before I started. I have multiple sets of secondary hangers and rods. But the Carb rebuild kit said to adjust secondary’s you bend the hangers, not sure how I feel about that.
-no dead cylinders all have 185 psi
-pulled valve covers before, no lost lobes, no broken springs, no broken rockers.
-I do have full roller aluminum rockers, had to put valve cover spacers on to make them fit. They don’t hit cover now.
-pulled line at carb to verify it was getting fuel, with ignition off I jumped the relay to turn it over, it pulses out pretty hard. Didn’t fill up a bottle, but from that it looks healthy.
-I got a whole timing set with the cam, came with new springs. I’m not sure valves would float at 2300 rpm even if they were stock.
-It had a pamphlet on different ways to install the small timing gear on the crank, I did not advance or retard, just set to zero. Someone not on here asked that.
I bought a plastic piston stop tool to verify TDC, going to check that as soon as it stops raining.
Stupid question but on a Quadrajet how do you change jetting on the secondarys? It’s just the secondary metering rods and hangers correct? I didn’t see any secondary jets when I went through it. I did change primary jets from 68 to 70 before I started. I have multiple sets of secondary hangers and rods. But the Carb rebuild kit said to adjust secondary’s you bend the hangers, not sure how I feel about that.
Last edited by Reg119; 08-19-2021 at 03:24 AM.
08-19-2021, 06:24 AM
#28
Good compression, accurate cam timing, sounds like the "air pump" is working. The fuel portion of the equation is somewhat crossed off by swapping the carb and checking fuel pressure and volume . I'm curious about the ignition box, in my pea brain it seems like it's happening at the exact same rpm. Can you borrow a HEI distributor ( or even a points style) to eliminate the possibility of inaccurate spark ?
08-19-2021, 06:27 AM
#29
Registered
iTrader: (1)
Increase sec jetting by using smaller (thinner) metering rods.
i would suggest reading articles or getting s book on the subject.
i would suggest reading articles or getting s book on the subject.
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Helmwurst (08-19-2021)
08-19-2021, 06:34 AM
#30
Registered
iTrader: (1)
Nit saying it’s your problem. Just mentioning it.
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liberator221 (08-19-2021)
