Rattle at very light throttle. ??

[Canadian1968]

With all my problems fixed hopefully. I have been driving the charger around quite a bit. The car is running pretty well as far as I am concerned. The only thing I notice is that when I get up to approx 2500 RPM,  and this is only under Light throttle, very light actually, I hear ratttle from the engine, as soon I take my foot off , it goes away, and basically the weight of my foot is all it takes to make it come back.  But if I give it bit more gas, it does not make the sound. Like I said, only very light throttle.

Any Thoughts? It sounds like detonation but so light and if I put more load it goes away??

[Back N Black]

It sounds like detonation, you may have to play with the timing. 

[firefighter3931]

Where is your timing set ?

The problem could also be a lean condition in the carb based on your description. On the tip-in transition from the idle circuit to main circuit. This is based on your description that the rattle occurs only at very light throttle then disappears after the accelerator is pressed deeper 


Ron

[maxwellwedge]

Try it with your distributor vacuum plugged and see if it goes away. If it does you can dial in your vacuum advance to where it is workable....

[elacruze]

Try it with your distributor vacuum plugged and see if it goes away. If it does you can dial in your vacuum advance to where it is workable....

If you have an adjustable vacuum can on your distributor, turn it out (counterclockwise) one turn at a time until it goes away. If you take out more than about 4 turns, you may need to have it recurved.

[Canadian1968]

Well we are in the middle of a crazy heat wave here in sounthern Ontario.  But I will test some things out as soon as I can bare the heat lol !!

I have the MP Electrontic conversion kit, I am pretty sure I read that it has an adjustable vaccum advnace.

[Canadian1968]

I just went and turned the nut inside the vacuum advance. I turned it all the way out ( counterclock wise) Then turned it back in 1 1/2 turns, and took it for a drive around the block.  The noise is still there. Same situation, if I lay into the gas a bit its fine, only on slight accell and decell. Hard to say if it is any better or not. 

Should I try and pull my base timing back a bit, its at 15 degrees right now.

[firefighter3931]

What is the total timing and at what RPM does it stop advancing ?   


Ron

[SUPERSTAR14]

An engine typically wont "ping" under light throttle, "pinging" usually occurs under load when combustion chamber temps are high. I would bet you either have excessive rod bearing clearance, main bearing clearance or I have also seen piston to cylinder clearance issues cause the noise you are describing. Hope I didn't ruin the day for ya.
-Pat

[firefighter3931]

An engine typically wont "ping" under light throttle, "pinging" usually occurs under load when combustion chamber temps are high. I would bet you either have excessive rod bearing clearance, main bearing clearance or I have also seen piston to cylinder clearance issues cause the noise you are describing. Hope I didn't ruin the day for ya.
-Pat

It will ping under light load if the carb is going lean on the transition from idle to main jets. 


Ron

[elacruze]

An engine typically wont "ping" under light throttle, "pinging" usually occurs under load when combustion chamber temps are high. I would bet you either have excessive rod bearing clearance, main bearing clearance or I have also seen piston to cylinder clearance issues cause the noise you are describing. Hope I didn't ruin the day for ya.
-Pat

It will ping under light load if the carb is going lean on the transition from idle to main jets. 

yep. Decrease air bleed size? What carb?



Ron

[SUPERSTAR14]

An engine typically wont "ping" under light throttle, "pinging" usually occurs under load when combustion chamber temps are high. I would bet you either have excessive rod bearing clearance, main bearing clearance or I have also seen piston to cylinder clearance issues cause the noise you are describing. Hope I didn't ruin the day for ya.
-Pat

It will ping under light load if the carb is going lean on the transition from idle to main jets. 

yep. Decrease air bleed size? What carb?



Ron

I just went and turned the nut inside the vacuum advance. I turned it all the way out ( counterclock wise) Then turned it back in 1 1/2 turns, and took it for a drive around the block.  The noise is still there. Same situation, if I lay into the gas a bit its fine, only on slight accell and decell. Hard to say if it is any better or not. 

Should I try and pull my base timing back a bit, its at 15 degrees right now.

Perhaps we have a "play" on words here.......Obviously an engine can ping under light load, but what I read was A rattle noise at light throttle, very light throttle, as per the first post. Then he also stated on accell and decell in another post.
That is why I responded the way I did. "Light throttle" and "light load" in my book mean two different things.

Not sure about the gearing on the car or the engine specs or tranny set up but lets say at 2500RPM you are going 50MPH on flat ground, lift off the accelerator just enough to release the load or back off entirely and then pick it up with light throttle to match speed but before a load is placed on the engine is that when you hear the noise? If so I would suspect an internal rattle vs pinging. If you are hearing the rattle as you start to increase the load on the engine then pinging could be the problem, and can be easily resolved.  Engine noises can be described many ways depending on who hears them and who describes them.
-Pat

[Canadian1968]

I went and check my timing, the hold down bracket was loose and I was running up around 23 degrees base timing!!

I reset the timing to 15 degress and reset idle mixture for highest vacuum at approx 800 RPM.   By approx 2000 RPM all my timing is in at 45 degrees ( I still have the canister nut only turned in 1 1/2). I took it for a spin, it sounds MUCH better, but I can still hear it slightly when I really listen for it.   I ran out of day light but I think I just need to bring back by timing a bit more?? 

[ottawamerc]

45* is still too much total advance your base seems ok but you need to limit to 35*-38* total.

Scott

[maxwellwedge]

The 45 probably included vacuum advance. Set the total advance with the vacuum plugged.

[firefighter3931]

As mentioned above.....too much total timing. It will detonate at 45* 

Did you disconnect the vac advance when setting the timing and did you check the total with vac advance connected ?


Ron

[Back N Black]

Hook up your vacuum advance to manifold vacuum, then it will not be a factor at WOT.  Then you will have a cooler idle temp and a smooth cruise.

[Canadian1968]

Yes I set the base timing with the vacuum disconnect. The 45* is with the advance hooked back up. So I to be around 35*.

Does Turing the adjusting nut determin how much advance or how fast it comes in???

[Chryco Psycho]

Do you know what advance spings are in the dist ? I have seen lighter springs allow too much advance low down .
I would run without the vacuum advance at all .

[Canadian1968]

Back at it tonight. First thing I did was Disconnect the vacuum advance . With that plugged I get a total of only 28* at approx 2200 rpm .

I then took a few degrees off base timing to 13* . Now with vacuum running I am hitting 40* . I didn't take it for a ride was getting to dark. But this is still to much??

And what a out with it plugged and only running 28* is that enuff for city driving seems pretty low.

The distributor is a new mp conversion unit the springs are whatever it came with

[MSRacing89]

Back at it tonight. First thing I did was Disconnect the vacuum advance . With that plugged I get a total of only 28* at approx 2200 rpm .

I then took a few degrees off base timing to 13* . Now with vacuum running I am hitting 40* . I didn't take it for a ride was getting to dark. But this is still to much??

And what a out with it plugged and only running 28* is that enuff for city driving seems pretty low.

The distributor is a new mp conversion unit the springs are whatever it came with

28º total is not enough.  I would run your initial up to 19º or 20º, reset your idle, your total will now be around 35º.  Throw the Vacuum advance away and you will be happy.  The only slight, and I mean slight advantage to vacuum advance is at very light load cruising at highway speeds.  That is strictly related to a possible fuel savings, not enough to run it IMHO.  Times have changed and so has the quality of gas!

[Canadian1968]

I won't have any problems running that much advance??

I don't have the manual in front of me but I thought suggested timing was around 7* mark.  The engine is stock except for electrical upgrades. Why is 15* suggested for base timing all of a sudden . Is this due to the change in gas we use today??

Curious.

[Canadian1968]

I took the car for a spin with the timing dropped down to 13*.  Same problem, I pulled the car in the drive way and pulled out the timing gun, my total advance was up around 42*.

Sooooooooo. I blocked off the vaccum advance, bumped the timing up to 20* and gave it rev, climbs up to 35* @ a bit higher RPM. I didn't have anyone else with me to watch the Tach, just goin by ear.

Again, time is short after work so I will have to wait till tomorrow to take it for another spin.

[Canadian1968]

Blocked off the advance. Set  timing to 18* , idle mixture and idle speed. Went for a drive and its gone!! With just the mechanical advance it pull me up to around 37*.

Thanks for all the help guys ! 

[MSRacing89]

Blocked off the advance. Set  timing to 18* , idle mixture and idle speed. Went for a drive and its gone!! With just the mechanical advance it pull me up to around 37*.

Thanks for all the help guys ! 

Nice work.  Simple fix and you are all good now!