Trouble Timing my 340

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pj_elia

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I'm having trouble trying to get my 340 timed properly. When I go to set full advance near 38 BTDC at 4000 rpms, the car does not want to idle well near 15. When I do get it to idle, it backfires and coughs flames when trying to start the motor. That is with the vacuum advance connected to manifold vacuum trying to get more advanced idle timing while limiting full advance. When I advance timing to get good idle speed and easy starting, full advance goes to 60 and beyond.
The motor has unknown pistons,I believe they are stock height. An early set of Edelbrock performer heads, the .508 lift hydraulic purple shaft, a torker 340 single plane manifold, mopar performance distributer. The PO claimed difficulty setting timing and carb issues before he let it sit for 8 years and then sold it to me. The motor had a barry grant 750 double pumper race carb. Since it was leaking and had been sitting for years I replaced it with a recently rebuilt 4160 type holley (600 cfm) just to see if I can get it running decent. Also, the exhaust is fairly restrictive 2.5" to 2.25" dual.

Any ideas what I should try next or ideas on how best to tune this set-up?


Thanks,

PJ
 
With the Torker intake and .508 cam, 15* initial should not be a problem. I think you need to check that TDC on the balancer is true TDC. Ring may have slipped?
 
20* initial minimum with a 508 cam IMO.

You're going to have to limit mechanical in the distributor to hit your total number. If it's still advancing to 4K, you need to put different springs in it to speed up how fast mechanical comes in.
 
crackedback said:
20* initial minimum with a 508 cam IMO.

You're going to have to limit mechanical in the distributor to hit your total number. If it's still advancing to 4K, you need to put different springs in it to speed up how fast mechanical comes in.
Click to expand...

I was wondering if this was going to be the answer. I have no experience with radical cams or high performance motors. Is that what most people do when running this cam?
 
Yes and 38 is too much, I would try 34 - 36 unless its low on compression \ I run only 32 on my 10 to 1 cause it ping sometimes at 34.

The exhaust is causing no problems with low speed and idle. I would look towards vacuum leaks, maybe the intake gasket or brake booster if power brakes.

20 degrees at idle will be of big help and all in by 3,000, with the aluminum heads you shouldn't have to worry about gas knock
 
OldmanRick said:
With the Torker intake and .508 cam, 15* initial should not be a problem. I think you need to check that TDC on the balancer is true TDC. Ring may have slipped?
Click to expand...

I did a quick check with a screwdriver in the cylinder head. It seemed to be right but obviously I could not tell if it was off by some degrees. Its a newer balancer, but I didn't think it could be off like that.
 
pj_elia said:
I did a quick check with a screwdriver in the cylinder head. It seemed to be right but obviously I could tell if it was off by some degrees. Its a newer balancer, but I didn't think it could be off like that.
Click to expand...
It may not be off. Just wanted you to make sure because when there's issues with timing in what should be a "normal" range i like to go there first.
 
dodge freak said:
Yes and 38 is too much, I would try 34 - 36 unless its low on compression \ I run only 32 on my 10 to 1 cause it ping sometimes at 34.

The exhaust is causing no problems with low speed and idle. I would look towards vacuum leaks, maybe the intake gasket or brake booster if power brakes.

20 degrees at idle will be of big help and all in by 3,000, with the aluminum heads you shouldn't have to worry about gas knock
Click to expand...


Ok, so mechanical stop for the distributer and check the intake for leaks. I'll check for leaks tomorrow and try to figure out how to add mechanical stops for the distributer.

Thanks, I'll reply back with results.
 
I welded the slots in the distributor. What do you think? Did I go too far? I figured, I could file away more if I have too. Haven't put it in yet.
2012-09-06_21-20-26_948.jpg
 
By the way, I found out the distributor is a stock one (3656763) and that's why it has soo much advance. Probably around 24 or more degrees. I didn't take the time measure. Now I'm thinking I might not have closed them up enough !?
 
Hard to say, you don't want much advance, I would leave it be if the rotor moves a little, even if you run 25 degrees at idle and 34 total.

Lock out timing works good sometimes - if the gas octane is high and the rear gearing is low (4.10) but then cranking the motor over the start it kicks back unless you retard the timing or cut the power to the spark till its spinning over good and then turn out the sit park - ignition.

Cheaper and simpler to just do what you are doing.
 
oh and remove one of the two stock springs to speed up the the advance, 4,000 rpm is way too late unless its got 2.45 gears and 11 to 1 compression, lol
 
Look at the plate,it will have a number on it., double it for crank degrees. here's a list of dist degrees and slot length.

Mopar slot lengths
3 0.295
4 0.310
5 0.325
6 0.340
7 0.355
8 0.375
9 0.390
10 0.405
11.5 0.420
12 0.435
13 0.445
14 0.460
15 0.475
16 0.490
17 0.505
18 0.520

Whatever mechanical you want, divide by 2 and make the slot the length it says above.
 
I also just stretched the weight springs a little on each. I will see how it goes. Hopefully I'll have time to get it back in tomorrow. I am wondering what noticeable benefit will I get with a performance distributor other than adjustability. If I get this to work well, I'll probably leave it. It also has an MSD ignition and coil.
I plan on taking this car (71 demon 340 4sp) more towards a daily driver than a street/strip car. The battery was moved to the trunk and has a super loud high flow electric fuel pump that's really annoying. Once its running well, I'll have to change the fuel pump for something more quiet.

Paul
 
crackedback said:
Look at the plate,it will have a number on it., double it for crank degrees. here's a list of dist degrees and slot length.

Mopar slot lengths
3 0.295
4 0.310
5 0.325
6 0.340
7 0.355
8 0.375
9 0.390
10 0.405
11.5 0.420
12 0.435
13 0.445
14 0.460
15 0.475
16 0.490
17 0.505
18 0.520

Whatever mechanical you want, divide by 2 and make the slot the length it says above.
Click to expand...

Neat, I took the easy way out and got an MSD E curve dist but its overpriced for sure
 
crackedback said:
Look at the plate,it will have a number on it., double it for crank degrees. here's a list of dist degrees and slot length.

Mopar slot lengths
3 0.295
4 0.310
5 0.325
6 0.340
7 0.355
8 0.375
9 0.390
10 0.405
11.5 0.420
12 0.435
13 0.445
14 0.460
15 0.475
16 0.490
17 0.505
18 0.520

Whatever mechanical you want, divide by 2 and make the slot the length it says above.
Click to expand...


Thanks for the reference. It currently has L17 stamped on it so it has a whopping 34 degrees of advance! No wonder. I was expecting more like 20 degrees. This was never going to work as is.

Thanks for your help.
 
pj_elia said:
I also just stretched the weight springs a little on each. I will see how it goes.

Paul
Click to expand...

That is how springs fall off those little posts

Adjustably is the nicest part about MSD dist, the E curve has dials / switches to electrically the timing curve.

Another thing is where the rotor points when its firing, sometimes it can be off. Getting an MSD dist insures the rotor phasing is correct.

Question is , do you have an extra $250 - $400 laying around, I sure don't now. I'm worst off then 8 - 12 years ago, who isn't, lol
 
No problem. I'd make the slot around .355-.375 for 7-8 degrees on the plate, 14-16 mechanical.

If you have a tru value or other good hardware store, they may have a selection of micro springs. If the ones you have now are those huge ones, get something a bit lighter.

Good luck
 
dodge freak said:
That is how springs fall off those little posts

Adjustably is the nicest part about MSD dist, the E curve has dials / switches to electrically the timing curve.

Another thing is where the rotor points when its firing, sometimes it can be off. Getting an MSD dist insures the rotor phasing is correct.

Question is , do you have an extra $250 - $400 laying around, I sure don't now. I'm worst off then 8 - 12 years ago, who isn't, lol
Click to expand...


I don't have the extra cash. I feel guilty enough spending money on myself when I could put it into my children's college saving's account. The few dollars and work I put into this demon will hold its value. I'm not going overboard at least until my son is old enough to help me build it.

Good point about the springs but they look like they are on there pretty good. I'll check them out more carefully. They seem lighter than I would expect stock springs to be. The ends wrap around the posts fully. Looks like they would have a hard time falling off. Also, they didn't seem to be colored, they have a coating of surface rust.
 
crackedback said:
No problem. I'd make the slot around .355-.375 for 7-8 degrees on the plate, 14-16 mechanical.

If you have a tru value or other good hardware store, they may have a selection of micro springs. If the ones you have now are those huge ones, get something a bit lighter.

Good luck
Click to expand...


Would you believe it if I told you they are at .365. No joke. I just measured them and one side was .355 and the other was .365. I evened them up,came up and looked and your chart and thought, "wow that just might be perfect". Then I read your post and got some confirmation. Looks like I'm ready to give it a go.
 
Sounds like its ready to go.

Don't oil the weights or if you do just a tiny tiny bit and use grease if you do , the mist of the oil can mess up the reultor or points Might want to double check the gap is about .008
, its electronic I'm guessing, if its points, well those might be pitted - worn
 
So I put back together and back in the car and now I have some more questions. I had it idling around 1100-1200 without the vacuum advance connected, I didn't get any more mechanical advance as I revved it. With vacuum connected, it advanced around 24 degrees!? Does that mean the weights are stuck? Also, at around 1100 rpms, I'm getting around 7 in of vacuum with some shake to the needle. Its got roller rockers and I'm guessing they are not adjusted right. The PO said they needed to be adjusted and some might be too tight. I checked the carb base gasket for vacuum leaks and found none. I ran out of spray to check the intake gaskets. I'm going back to tinker with it in a little bit to see if I can get it to idle lower, measure vacuum and get a better measure of total advance.
 
Sounds like the weights are all the way out at 1,200

Stretching the springs over did it

Forget about the vacuum advance for right now - my engine doesn't even use one.

That engine will run much better at 34 degrees, if the weights do close once the engine is shut off, set it for 34 revving it at 3,000 rpm - just the make certain the weights are all out--you did gun it to 4,500 or so to make certain the weights aren't sticking.

I like wearing gun shooting muffs around my ears to lessen the noise

It might work fine, my old dist came all in by 1,500 and stayed there pretty much at idle and the weights back off so the engine would start easy.

If you sure the weights are all out at 1,200 then again, rev it to 2,500 - 3,000 and set it for 34. It will idle better and once settled down, shut it off and re start, if it doesn't kick the start back, its test drive time if those valves are set right - it has adjustable rockers ?
 
dodge freak said:
Sounds like the weights are all the way out at 1,200

Stretching the springs over did it

Forget about the vacuum advance for right now - my engine doesn't even use one.

That engine will run much better at 34 degrees, if the weights do close once the engine is shut off, set it for 34 revving it at 3,000 rpm - just the make certain the weights are all out--you did gun it to 4,500 or so to make certain the weights aren't sticking.

I like wearing gun shooting muffs around my ears to lessen the noise

It might work fine, my old dist came all in by 1,500 and stayed there pretty much at idle and the weights back off so the engine would start easy.

If you sure the weights are all out at 1,200 then again, rev it to 2,500 - 3,000 and set it for 34. It will idle better and once settled down, shut it off and re start, if it doesn't kick the start back, its test drive time if those valves are set right - it has adjustable rockers ?
Click to expand...

Well you are pretty much right on with what I ended up doing. I disconnected the vacuum advance and set timing at 35 full advance. I did rev it up and got no further advance so I think they are all out very early. It starts up pretty easily. Some slight blowback occasionally. It runs OK like this. I did not get to open it up much to really test it. I can't get it to idle less than 1050 rpms and the manifold vacuum is at 7 in, which I think is low. I did not find any intake leaks. Its got roller rockers and I'm thinking adjusting them might be next. Then comes some guage/wiring issues to get fuel, temp,and headlights working so I can test it better driving in public. It has 4.30 gears in the rear and is a 4sp manual car so keeping RPMs up is going to be the rame of the game for this car.
 
You could adjust the valves with the engine running, just wear old clothes. Back each screw off till you hear it clicking and tighten till the noise stops and then just a bit more 1/4 to 1/2 turn. Can do it with the engine off, just takes longer

I wished my 340 had 4.30 gears, its got 3.91's and when gas was cheaper I like them more. Now that I don' drive the car as much with $4 plus fuel, I wished it was easier to buzz that motor. Hanging out on the freeways burns lots of fuel, lol
 
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