Help an old man tune a new to me 340
- Thread starter HS Duster
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Our 70 340 is right at 18* BTDC
what is the initial timing in gear? if it's not 15 deg BTDC @ 800 RPM it's not enough.
I'd be shooting for 16-18 degs at least. probably 20
The top hole is where it should be. Closest to the carburetor, right?
Initial timing is at idle.
As you increase rpm, the mechanical advance inside the distributor increases timing. You limit the amount of mechanical advance by stopping the weights from moving further out. You do that either by welding up the outside of the slots or by installing a limiting plate from FBO. The plate "limits" how far out the weights can move. You want total timing (inital plus mechanical) to be 36ish or less.
I use an FBO plate and it works great for me.
As you increase rpm, the mechanical advance inside the distributor increases timing. You limit the amount of mechanical advance by stopping the weights from moving further out. You do that either by welding up the outside of the slots or by installing a limiting plate from FBO. The plate "limits" how far out the weights can move. You want total timing (inital plus mechanical) to be 36ish or less.
I use an FBO plate and it works great for me.
It has to be disassembled. There are slots in the distributor governor. The length of those slots determine how much mechanical advance the distributor has. The old racers trick is to weld those slots up a little and file them to a specific shorter length, so that the distributor only advance as much as you need. I have a hot slant 6 in my 64 Valiant, for example. SLant sixes don't need anymore than about 30-32 degrees total timing. I run mine with about 22 initial timing at idle. I shortened the governor slots up in the distributor to provide about five distributor degrees, which is about 10 at the crank for a total of 32.
I GUESS you could, but that would be a major PITA. Plus, you could easily drop something into the distributor with it being way in the back. Just pull it.
MOPAROFFICIAL
If it has tits, it's a liabilititty.
If its timing being too little at idle or off idle... test it.. advance it and do some part throttle acceleration , low speed drives, and if it's better... there ya go, weld up the beginning of the slots or thread a short screw to take up the slot , the weight rests stationary on the screw. Keeps the advance springs working in the correct range or rpm/advance rate
If you want to do it the poor man way though, pull the heavy spring out and only leave the one stock lighter spring in. It should give you about 18° at idle and not affect your total timing from where it is, as in.. set it to 32-35 degrees full advance.. and with the heavy spring out it will idle with 18 or so degrees timing.
If you want to do it the poor man way though, pull the heavy spring out and only leave the one stock lighter spring in. It should give you about 18° at idle and not affect your total timing from where it is, as in.. set it to 32-35 degrees full advance.. and with the heavy spring out it will idle with 18 or so degrees timing.
There is NOTHING wrong with the Edel carbs that could cause your problem. The cam must be fairly mild to idle with 15" of vac & only drop 100 rpm going into gear with so little initial timing. With more idle timing, the rpm drop will be even less, maybe only 50 rpm.
The plugs are too cold, could be your problem. Try some NGK 5 heat range. With cold plugs, the deposits do not burn off because the plug electrode never gets hot enough to do so. Spark energy is bled off by the deposits causing a misfire.....
The fact that the carb idles & makes 15" of vac tells YOU it is reasonably well adjusted.
* Warning sign*. The change from ported to man vac adv should have changed the engine sound & rpm. No change could mean the vac adv diaphragm is leaking or the carb's T slots are not in the correct place when idling.
Try this simple test:
- loosen met rod piston covers, swivel slightly so pistons are in view. Tighten covers.
- adjust initial timing to about 20*, not critical.
- warm up & put in gear. Pistons should go down & not move. If they move, you need softer springs.
The plugs are too cold, could be your problem. Try some NGK 5 heat range. With cold plugs, the deposits do not burn off because the plug electrode never gets hot enough to do so. Spark energy is bled off by the deposits causing a misfire.....
The fact that the carb idles & makes 15" of vac tells YOU it is reasonably well adjusted.
* Warning sign*. The change from ported to man vac adv should have changed the engine sound & rpm. No change could mean the vac adv diaphragm is leaking or the carb's T slots are not in the correct place when idling.
Try this simple test:
- loosen met rod piston covers, swivel slightly so pistons are in view. Tighten covers.
- adjust initial timing to about 20*, not critical.
- warm up & put in gear. Pistons should go down & not move. If they move, you need softer springs.
Well I figured something out this morning. I set up my crude method to find #1 TDC with a little more precision than I did the first time. The white mark on the balancer the previous owner had on is actually 15*. I rotated the engine multiply times with my wire in #1 and when I got to absolute top of the stroke, it lined up with another mark 15* ahead of the white mark he had. So what I thought was 0* was actually 15*. I haven't been into the distributor yet, but I think it may be set up properly. All that now leads me to carburation for that 1600-1800 skip/miss possibly.
Remark your TDC(obviously). But also add a mark that will show you if the balancer spins. Prev owner may have marked TDC correctly, but then balancer spins(elastomer let's go).
Hope that makes sense
Hope that makes sense
I have actually been running about 15* all along and didn't know until the exercise I went through today to fine #1 TDC. I bumped it about 17-18 and tried it and no change. Still rough comes in about 1600. I tried more jet and metering rod changes with no help. I almost to the point to jet me another carburetor. Is there anything else in the ignition system that could cause this?
Just for kicks, check the firing order. 1-8-4-3-6-5-7-2. I forget which two but there are two that can get crossed and make it run rough and not pop or backfire. I THINK it's 6&8 but I wouldn't sweat to it.
Make sure to go thru the new carb. ANYTHING new nowadays has or should be gone thru.
No-one close you can borrow carb from?
No-one close you can borrow carb from?
Those 1407s are a known issue. I had one I went through multiple times and couldn't do anything with it. It had issues with running way to rich. Nothing I could do changed it.
I wonder if a 1405 would work for him? That's what's on mine, so far so good.
Lots of 05 come up for sale here.
Hate to buy a new carb and it not be the problem.
Lots of 05 come up for sale here.
Hate to buy a new carb and it not be the problem.
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