Tune up questions
here are the specs:
5.9 magnum. cam: oregon regrind 214/221*, 480/482", 110LSA. hughes spring kit. airgap intake. holley 600VS.
Currently 12 base timing and 34 total. Mopar electronic ignition, old orange box.
Car runs alright when cold, but when hot it wants to stall in drive. It also does not want to go past 4000rpm, at which point it loses power and backfires through the exhaust.
Ideas?
I run 12/34 in my hi-pressure 367 combo too, and with the VA modified to 22* on the spark-port, set to come in quick and fast; and with the Airgap and a 750DP.
IMO, timing is NOT your problem, (unless the engine is in detonation which is hard to imagine at 34* and 4000rpm).
12* is plenty enough power to idle on. Mine, with a 230*cam, will idle down to 550 @5* advance, easy enough, and still pull itself all 'round the parking lot, at 900ft elevation.
and; I doubt you have a valvespring issue. Springs don't come and go.
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>>IMO; More than likely you have a fueling issue, or overheated sparkplugs.
My first guess is a partial venting issue, and the pump is unable to pull fuel up.
Second is a hot carb boiling the gas; but on an AirGap? IDK
Third might be; LA is near sealevel. What elevation are you at when the engine dies, compared to when you started your trip?
Fourth is some combination of the above
Fifth is see note-1 below.
Note-1
But, if your secondaries are cracked, as in not fully closing; well, if you have a cam smaller than the old Mopar 292, as you do, then, I'd fix that first. What can happen if the Secondaries are cracked, is that the Primary throttle opening has to be nearly closed to keep the Idle-speed in check. When you close the primary throttles like that, then the Transfers lose signal, and may stop flowing altogether. Hence the lean-backfire out the exhaust followed by a stall.
Make sure the Secondaries are fully closed but not sticking.
Then open your primaries to make up the difference,
then reset your mixture screws to in the middle of their range, somewhere between 1/2 and 3/4 turn. If you can't get a decent idle in that adjustment window ,
then open or close the Primary throttles, to change the Transfer slot fuel delivery, until you do.
If the Idle speed gets to be too high, just retard the timing a lil.
This assumes;
the PCV is correctly plumbed to the front of the carb, and is working and
that all the air that the engine is getting,
is coming in past the Primary throttles, AND
that the fuel-level is correct, stable, and not polluted.
>If this makes your exhaust stinky, well that's a new challenge as your engine is wanting some Idle Bypass-air. This is somewhat normal , but your modest cam size, should not require it.
Note-2
When an engine, at WOT, stops revving at a particular rpm; Generally it can be traced to one of;
1) Valves not closing on time;
all or many of them. The reasons for this could be;
1) insufficient valve-spring pressure leading to lifter pump-up and valve float which is, valves not closing.,
2) could be tight guides, not enough valve lash, or could be cam-timing seriously out to lunch.
3) AFR going extremely rich;
The reasons for this could be; the choke system is stuck on, the air-intake system is failing, the float-valves arenot holding, or the exhaust system is severely restricted
4) a serious change in elevation, or
5) sabotage,
Note-3
This is seriously easy to diagnose. Just run the rpm up to the sticking point, then back off the throttle some.
a) If the engine then continues to rev past the sticking point, then:
it ain't valve springs or anything to do with valve-timing.
b) but if you can't coax the engine to rev any higher, at the reduced throttle setting and yur still in first gear, then it's gotta be fueling.
Note-4
a 600 Vsec with a a 214/221/110 cam, should run perfect at your near sealevel elevation, with the factory jetting, which IIRC was like 64 or 66 Primary mains, and about 6 numbers higher on the Secondaries...... don't be trynta run 72/80s, lol.
I suppose that if your PV diaphragm was ruptured, that could deliver gas straight into the intake; but this would be all the time, and NOT intermittent.
Note-5
If you say that you are running 12* at idle but then hook the VA up to get 30, that means you must be getting 18* from the can.
This then means that your engine is getting those 18* all the time at Part throttle. So say you are just cruizing around town at say 30mph= 2000rpm in Second gear with 3.23s. Say your mechanical advance is up to; 12*initial, plus 8* centrifugal plus 18* in the can= 38*. There's nothing inherently wrong with running 38* under this circumstance..... IF your fueling is correct!. But chances are, with a cam that small, It's already got a lot of power at that rpm, and so, the Primaries are gonna be on the bottom of the transfer slots and the mains are still shut off.
So what happens in that situation, is that the engine is running lean for extended times, and the spark plugs are prone to overheat. That's not good.
Notta chance would I (me personally) run that engine with the VA hooked directly to Manifold vacuum! Just something to think about.
Note-6
The thing is this;
yes, at 30* idle timing the engine will be smooth, and
yes with 18 extra degrees of timing at low load Part-Throttle settings, the engine will make more power, and be more responsive. I get that.
But there are better ways to make that happen, which begins with a two-stage timing curve..
And your 5.9 should have plenty of cylinder pressure, such that, with 18 extra degrees, the throttle, at low load, will always be, nearly closed and the engine running on the Transfer slots. The fuel-delivery curve on those transfers cannot easily be changed to accommodate this crappy situation.
If I'm right that you have 18* in the can, just put it on the sparkport, and readjust the T-slot sync to use the proper Mixture screw setting, and CHECK FOR OVERHEATED PLUGS, which you may have to throw away.
Finally, In terms of advertised numbers, which is what you engine sees for most of it's not-WOT life,
Your 214/221/110 cam probably has advertised numbers near
262/268/110. compared to the factory 5.9cam, which I have recorded as
250/264/110, So then, your Hughes cam is not that much bigger than the factory cam. The factory cam is pretty good for a 5.9 streeter, once you retime it away from the truck ICL of 119*, to something like, in at 106*. I mean it won't be all that fast in the quarter, but with a well-matched compression ratio, it could be a killer stump-pulling streeter....... Which I'm sure, so would be the Hughes that you have.
In closing
Well this turned into a bit of a long post and riddled with opinion, so, to satisfy the keep it brief self-appointed brevity police, I better say this;
I'm just guessing.