Noisy 351 Cleveland

[Jayro]

That's weird. It does the rattle accelerating down hill and stops as soon as you lift your foot but up hill it sounds normal under acceleration? I am stumped but I will think about it some more.

Those things with the missing vacuum lines were used for emissions controls. Without vacuum lines connected they do nothing. It's not the source of your problem.

Ok thanks. So am I right in assuming if it was timing related it would be doing it under load such as going up the hill?

 

[Stevieray]

I agree with many here which think it is a timing issue. Jon Enheart rebuilt my original 4300D years ago and after installation I was having issues getting the timing correct. Jon taught me to toss the timing light and time according to maximum vacuum. With the recent engine rebuild, I had my balancer rebuilt so I now trust the timing marks when I did my first start up. I was in the ball park. Fuel octane also has a lot to do with it. Go with the highest and use 100LL Av gas if you can get access to it. Have your timing wrench with you and take her out on the back roads. Keep working with slight timing changes until you lessen the pings during hard acceleration. I can scan the steps Jon provided me and post them if you think that may help.

 

[Stevieray]

See attachments. Hope this helps

 

[Stanglover]

Ok thank you. Going over it now. Apologise for the dumb questions but just checking if there is any issue with these items seemingly being uncapped?

First my friend, there is no such thing as a "dumb question" on here. You might get some dumb answers, though!!!!
This is how I learned much, no most of what I sort of know now and that's thanks to all the great, knowledgeable members on our Forum.
Ask away.

 

[Stanglover]

Oh sorry old pic. I’ve replaced the plugs and leads View attachment 62476

I agree with many here which think it is a timing issue. Jon Enheart rebuilt my original 4300D years ago and after installation I was having issues getting the timing correct. Jon taught me to toss the timing light and time according to maximum vacuum. With the recent engine rebuild, I had my balancer rebuilt so I now trust the timing marks when I did my first start up. I was in the ball park. Fuel octane also has a lot to do with it. Go with the highest and use 100LL Av gas if you can get access to it. Have your timing wrench with you and take her out on the back roads. Keep working with slight timing changes until you lessen the pings during hard acceleration. I can scan the steps Jon provided me and post them if you think that may help.

Good point on using a vacuum gauge.
Jayro didn't mention what carb he has on that engine, not that that seems to be the cause, but would help to know.

 

[Jayro]

Good point on using a vacuum gauge.
Jayro didn't mention what carb he has on that engine, not that that seems to be the cause, but would help to know.

Mate It’s a Holley and I’m told it’s a 600

 

[will e]

Ok thanks. So am I right in assuming if it was timing related it would be doing it under load such as going up the hill?

In my experience the greater the load the better chance of pinging. So if it only makes the noise going down hill under acceleration and not up hill under acceleration I cannot see how it could be early detonation.
When you accelerate down hill does it make the noise right away or take a few seconds? I am wondering if your float levels are causing the issue, if you are leaning it out going down hill that could cause pinging. Check the float levels, it's an easy check for a weird problem.

 

[Stanglover]

Mate It’s a Holley and I’m told it’s a 600 View attachment 62483

It looks to be an older style 4V with the larger secondary vacuum thingy (motor).
Also I'm guessing there are quite a few mods done to the motor before you got it. Any chance you can back track to the PO and find out what has been done? It would really help you moving forward to know exactly what's what. That would be my plan of attack anyway.

 

[Jayro]

In my experience the greater the load the better chance of pinging. So if it only makes the noise going down hill under acceleration and not up hill under acceleration I cannot see how it could be early detonation.
When you accelerate down hill does it make the noise right away or take a few seconds? I am wondering if your float levels are causing the issue, if you are leaning it out going down hill that could cause pinging. Check the float levels, it's an easy check for a weird problem.

I am being told similar to what your saying that it’s odd to be doing down hill not up. It’s instantaneous. The second either flat ground or down hill that I accelerate when doing over 50mph this noise starts and the instant I lift my foot it stops.

The engine is running rich so I have booked it in on the 4th for a dyno time to make sure either way that it’s running right.

Im also being told it’s quite possible that it’s a loose baffle in a muffler?

 

[pepperdog]

Hey guys,

So had the car out for a long run yesterday after getting it back from the shop getting the C4 serviced and all the transmission leaks fixed. All good it seems on that front.

Still got what appears to be a tear main seal leak to sort which will get done in the coming weeks.

However my main concern is the engine. Don’t get me wrong, starts and runs fine. Not Smokey or anything. Runs smooth. BUT once I’m doing more than 50 mph and the second my foot hits the accelerator it has a filthy rattling noise. The second I lift my foot that noise stops.

Any suggestions?

Cheers
Jase

just wondering if you have considered a faulty mechanical advance in the distributor if applicable MSD distributors are notorious for jumping around

 

[Stanglover]

It's a mystery for sure............... can't wait for the finale'.

 

[Jayro]

I’m actually getting suggestions over here that the issue will be a lose baffle in a muffler.

Anyhow getting the tune done in 2 weeks to make sure timing etc is sorted then look at edgy if the noise is still there. Will certainly update on how it goes

 

[71ProjectJunk]

Mate It’s a Holley and I’m told it’s a 600 View attachment 62483

Take the air cleaner off and look at the top front part of the carburetor, where the choke is. There is a list number there. It will say "LIST-" and a number. That looks like an 0-80457S, but who knows until you get the number of it. The "list" number will let you know exactly what carburetor you have.

 

[Jayro]

Take the air cleaner off and look at the top front part of the carburetor, where the choke is. There is a list number there. It will say "LIST-" and a number. That looks like an 0-80457S, but who knows until you get the number of it. The "list" number will let you know exactly what carburetor you have.

I did get a pic mate. This mean anything?