351c issues MAYBE

[Jayro]

Hey all,

To be honest not 100% sure I've got a problem but just wasn't right tonight. So engine is a relatively fresh build 351c. Nothing crazy.

Not having any issues. Took it out tonight and noticed when I went to merge onto the freeway and I opened right up and there was like a metal/rattle noise seemed to be coming from engine bay passenger side. Only at WOT. Done it a few times but then not again.

Then when we went to come home it wouldn't idle well. I generally idle at around 900-1100 rpm. Tonight coming home it was JUST not stalling at traffic lights and revs were about 600rpm. Can temp affect this as it is a bit chilly tonight around 10 deg C

2 issues could be totally unrelated maybe. Just seems odd I've had no issues then both these tonight.

Thanks in advance all

Cheers
Jase

 

[Steve McMahan]

The first thing sounds like detonation. What is your initial and all in timing? Also, what is your compression ratio? Since the engine is newer, you may need to do further carb refinements and tuning.

 

[giantpune]

Thats what I thought, too. Detonation during load/acceleration. My guess is too much timing at that RPM+vacuum+load combination.

 

[Don C]

Probably two issues. I would pull the spark plugs, see what they look like and make sure the gaps are correct.

After the engine is warmed up the colder temperature shouldn't have any affect, unless your choke was closing due to lack of heat to the thermostatic spring.

More likely need to check intake manifold bolt torque and carburetor gaskets. After the first few runs it's not uncommon for some things to loosen up and start leaking vacuum.

 

[basstrix]

Agree with the others that the rattle sounds like a classic case for detonation. The 2nd situation could be that one cylinder is mis-firing, aka missing. As Don suggests, I'd pull the plugs and inspect. You're looking for one plug that's fouled or damaged. The quick way to check for a misfire is to pull each plug wire with engine running and listen for change is RPM. I don't recommend unless you have the insulated tongs used for this purpose.

You'll also need to check and re-set your ignition timing. Where is the vacuum advance connected? If it's connected to timed/ported vacuum, it's probably getting too much advance at higher RPMs.

 

[Bill Kanode]

Agree with the others that the rattle sounds like a classic case for detonation. The 2nd situation could be that one cylinder is mis-firing, aka missing. As Don suggests, I'd pull the plugs and inspect. You're looking for one plug that's fouled or damaged. The quick way to check for a misfire is to pull each plug wire with engine running and listen for change is RPM. I don't recommend unless you have the insulated tongs used for this purpose.

You'll also need to check and re-set your ignition timing. Where is the vacuum advance connected? If it's connected to timed/ported vacuum, it's probably getting too much advance at higher RPMs.

Here is a trick that I learned as a diesel mechanic instructor in the Army. Back then I felt the exhaust manifold for the cold port but now I use an infrared thermometer. With a cold engine start it up and let it run for a few seconds then with the engine off quickly measure each port temperature for a cold (dead) cylinder. It is easier to find with your hand if headers are installed as the tube will stay cold longer.

 

[AcesArneson]

Hey all,

To be honest not 100% sure I've got a problem but just wasn't right tonight. So engine is a relatively fresh build 351c. Nothing crazy.

Not having any issues. Took it out tonight and noticed when I went to merge onto the freeway and I opened right up and there was like a metal/rattle noise seemed to be coming from engine bay passenger side. Only at WOT. Done it a few times but then not again.

Then when we went to come home it wouldn't idle well. I generally idle at around 900-1100 rpm. Tonight coming home it was JUST not stalling at traffic lights and revs were about 600rpm. Can temp affect this as it is a bit chilly tonight around 10 deg C

2 issues could be totally unrelated maybe. Just seems odd I've had no issues then both these tonight.

Thanks in advance all

Cheers
Jase

Did you replace your harmonic balancer during the rebuild? Sounds like maybe it is old and the rubber between rings has dried to the point it has slipped. You will never get your timing right again with that balancer if it's bad, it will need to be replaced if that is your issue. This is an issue that usually pops up right after a rebuild because the engine has likely sat for a long time during the process without being used.