[ScorpionBoy]

sorry to start a thread on this, but i am a carb noob. they suck.
but anyway, i wanted to check my understanding for setting initial timing.
i have 2bbl and mallory vacuum advance dizzy.
should a miracle occur and i get the carb running like it should, i would then set the idle per spec for having an auto (rolling with a C5 though i have not picked up the rig to count bolts etc).
I remove the vacuum line from the dizzy.
I plug the vacuum port on the dizzy.
I then set the timing with the light. I am thinking around 10 btdc.
for fine tuning i will have to get it under load and advance it til it pings.
then back it off a few degrees.
does this sound right?

 

[ScorpionBoy]

bump

 

[Robs79BBbronco]

I remove the vacuum line from the dizzy.
I plug the vacuum port on the dizzy.

:doh0715:

plug the vacuum line coming from the carb.other than that, sounds like a plan.10 deg. is a good # to start with.:toothless

 

[ScorpionBoy]

:doh0715:

plug the vacuum line coming from the carb.other than that, sounds like a plan.10 deg. is a good # to start with.:toothless

:doh0715: oh shit! you can tell i haven't tried yet. thanks.

:histerica

that is pretty funny now that i re-read.

 

[redbeast9]

Your on the right track, with my experance most 335 blocks will run best with a base timing of 10-12 deg BTDC. You can also use a vacum gauge to find a good base timing for your engine. Good luck.

 

[Gearhead2012]

I've got a bigger cam in mine, as of recent, and I'm trying to decide on a good timming point. The cam is ground with 4* of advance into it, and it's installed straight up, so it's basically installed 4* advance. Should I keep it at around the factory 11* mark? I'm looking for best performance...right now it's set around 14 or so...but, I'm getting a wierd popping noise through my exhaust...not a back fire, or a misfire...just a fairly audible "pop" for lack of better words. Thanks.

 

[ScorpionBoy]

thanks all. good advice. i have my vacuum gauge ready to go so i will dig in tomorrow.

 

[redbeast9]

I've got a bigger cam in mine, as of recent, and I'm trying to decide on a good timming point. The cam is ground with 4* of advance into it, and it's installed straight up, so it's basically installed 4* advance. Should I keep it at around the factory 11* mark? I'm looking for best performance...right now it's set around 14 or so...but, I'm getting a wierd popping noise through my exhaust...not a back fire, or a misfire...just a fairly audible "pop" for lack of better words. Thanks.

Sounds like you might have some detination going on there?:shocked Might need to retard the timing some. I would sugest trying 8* and go from there since you have 4* built into the cam. Also use a vacum gauge to see where you pull the most vacum at idel verses timing. Remeber its better to have the timing retarded a touch than to be to far advanced. Good luck.:thumbup

 

[bmc69]

I've got a bigger cam in mine, as of recent, and I'm trying to decide on a good timming point. The cam is ground with 4* of advance into it, and it's installed straight up, so it's basically installed 4* advance. Should I keep it at around the factory 11* mark? I'm looking for best performance...right now it's set around 14 or so...but, I'm getting a wierd popping noise through my exhaust...not a back fire, or a misfire...just a fairly audible "pop" for lack of better words. Thanks.

That barely audible pop in the exhaust when decelerating is indicative of LATE timing..not enough advance. Having the cam advanced does not mean that your base timing need be retarded to compensate. Advancing the cam lowers the RPM point where the engine 'peaks' in terms of maximum torque but should have little effect on your base timing (exception..advancing the cam also increases your dynamic CR..which itself can require less advance if pinging occurs...not the same as exhaust popping due to late timing though) All that said..11 or 12 degrees base timing is usually plenty..?

 

[mostly_broncos]

You said 351c did you mean a 351 m?


for an 351 m I like 14 degrees base 34 degrees max in by 2500 rpm with around 14 degrees of vacuum advance , maybe you can get away with 20 degrees vacuum advance. use ported vacuum for the advance.

14 degrees is plenty for a good idle and as soon as you crack the throttle the vacuum advance clicks in and gives you a nice kick in the pants.

Thats for 87 octane, if you want to run super you could run up to 44 degrees maybe total timing but I don't see any real benefit to it that would outweigh the cost of an extra 30 cents a gallon.





A 351c is a different animal. If its a stock 2barrel cleveland with 9.5 to 1 compression try 4 degrees initial 34 degrees total in by 2000 rpm with maybe 10 degrees vacuum with full manifold vacuum to the distributor .

Here you set the initial timing low so it starts easy but once its running the vacuum being hooked up will give you 14 degrees still at idle. It shuts off without dieseling too because when you kill it the vacuum goes away and if it won't shut off at 4 degrees advance you have other problems.


Assuming that doesnt ping you can add a little to the base timing till you do get a ping then back off a bit.

All thats assuming you run at least 92 octane.

 

[Runnin'OnEmpty]

Gearhead, the only thing I can add to BMC69's excellent post, is to try to eliminate the popping with the vacuum advance. Try turning the adjustment screw inside the VA port clockwise, and see if that helps.

If no joy, then get a Crane dist advance kit and put weaker weight advance springs in the distributor.

Double check the initial timing too; you shouldn't be getting exhaust backfiring with 14* initial advance (even with an advanced cam). That's if the distributor is advancing as it should.....maybe the weights are sticking...?

 

[ScorpionBoy]

A 351c is a different animal. If its a stock 2barrel cleveland with 9.5 to 1 compression try 4 degrees initial 34 degrees total in by 2000 rpm with maybe 10 degrees vacuum with full manifold vacuum to the distributor .

Here you set the initial timing low so it starts easy but once its running the vacuum being hooked up will give you 14 degrees still at idle. It shuts off without dieseling too because when you kill it the vacuum goes away and if it won't shut off at 4 degrees advance you have other problems.


Assuming that doesnt ping you can add a little to the base timing till you do get a ping then back off a bit.

All thats assuming you run at least 92 octane.

hey, thanks a bunch. it is a 351c 2V (H) motor.
i run 91 octane, highest i can find around here.

 

[Gearhead2012]

cool, thanks for the advice. I'm gonna try dropping the timming back some, I'll just have to play with it...could totally be something different too...like a bad, or weak valve spring too. I'll eventually pull the valve covers off again, and check the torque on everything anyway. It only does it at a steady throttle...not accelorating (at least not that I can hear open header)...and not decelerating...which says bad vacuum advance, or the weights. I'll check it out...thanks again

 

[Gearhead2012]

well it runs like a top now. I marked the numbers with chalk before I checked the timming...and, turns out it was set at like 22 degrees...at idle. Oops. Backed it down to about 12-13...and all is perfect now. I guess when I set it initially, I couldn't see the numbers well enough...