Hithere, I have Dual IDF 40s and I have the following tradeoff. When I set timing for best (fastest) idling I get about 15deg BTDC or a a little earlier than the 10deg BTDC that the manual calls out. When set at 15degC the car does not hot start as the starter pushes against the explosion. If I set it to 10deg it'll idle well, but slower but runs a little hotter than I would like. The question is if this trade off is just the reality of things that need to be accepted, or is there some tweaking that could help.
I have hooked up the vacuum advance to the vacuum advance port of the carb, but do not see it moving when idling or revving the engine. The vacuum advance does respond when sucking on the tube.
Thanks for any advice you can give.
Arved
Idling timing 40IDF
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Arved
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sptcoupe
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Re: Idling timing 40IDF
I'm not quite sure I understand, but you don't use the timing advance to set the idle speed. Use the idle speed screw, which is typically set up on the rear carb.
Set the timing for 10 BTDC, and then use the screw to set the idle to 800-900 rpms. Once you have the idle at 800-900 rpms, check the timing again to ensure it is still 10 BTDC. If not, reset it again, and use the screw to adjust the idle to 800-9-- rpms. But don't set the idle using ignition timing.
The coolant temp (is that what you mean by "runs cooler") will normally rise until the temp hits about 200 -205 degrees, then the fan should come on and the temp should drop to about 180 - 185 degrees (depending on what thermostat you are running.
Set the timing for 10 BTDC, and then use the screw to set the idle to 800-900 rpms. Once you have the idle at 800-900 rpms, check the timing again to ensure it is still 10 BTDC. If not, reset it again, and use the screw to adjust the idle to 800-9-- rpms. But don't set the idle using ignition timing.
The coolant temp (is that what you mean by "runs cooler") will normally rise until the temp hits about 200 -205 degrees, then the fan should come on and the temp should drop to about 180 - 185 degrees (depending on what thermostat you are running.
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fiatfactory
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Re: Idling timing 40IDF
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Last edited by fiatfactory on Mon Jul 01, 2019 11:38 pm, edited 1 time in total.
nothing to see here... move along.
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Arved
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Re: Idling timing 40IDF
Thanks so much for your answer! let me clarify:
I adjust idle speed by using the idle adjustment screws. I do find that when moving to an earlier timing, the engine speed picks up, the idling is generally smother, and I believe more efficient. I then adjust the idle screws back to the 800-900 rpm as you suggest. With this timing the car (engine coolant temperature) is lower and the car in general runs to my complete satisfaction. However it will not hot start reliably as the cylinder pressure builds before TDC.
When going by your suggestion, the car will idle well but with more idle screw, hot start well, run well, but the engine coolant is a little hotter than I like.
This may be a design trade off for this engine. Any insight is appreciated.
Arved
I adjust idle speed by using the idle adjustment screws. I do find that when moving to an earlier timing, the engine speed picks up, the idling is generally smother, and I believe more efficient. I then adjust the idle screws back to the 800-900 rpm as you suggest. With this timing the car (engine coolant temperature) is lower and the car in general runs to my complete satisfaction. However it will not hot start reliably as the cylinder pressure builds before TDC.
When going by your suggestion, the car will idle well but with more idle screw, hot start well, run well, but the engine coolant is a little hotter than I like.
This may be a design trade off for this engine. Any insight is appreciated.
Arved
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Arved
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- Joined: Sun Mar 03, 2013 8:20 pm
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Re: Idling timing 40IDF
Hey Steve, fantastic to know what to do with my cranks breather. Right now I just have a filter there. How difficult is this to set up and get running smoothe?fiatfactory wrote:IDF 13/15's don't have a vacuum port for vacuum advance pickup... the small tubes coming off near the accelerator linkage are a crankcase breather re-circulation port.
SteveC
My IDF40s look like the ones shown in this diagram: https://www.thesamba.com/vw/gallery/pix/682351.jpg and I have hooked up the vacuum advance to the ports labeled as such.
Thanks for your help
Arved
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fiatfactory
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Re: Idling timing 40IDF
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Last edited by fiatfactory on Mon Jul 01, 2019 11:37 pm, edited 1 time in total.
nothing to see here... move along.
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Arved
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Re: Idling timing 40IDF
Thanks so much Steve C. Yes I am pretty sure I have an IDF 70. Thanks for the clarification.
Arved
Arved
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Nut124
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Re: Idling timing 40IDF
OP, did you get your bugs worked out?
I run 40DCNFs and have dealt with similar problems. Moving to 44IDFs this winter.
What I did is this: The manifold I have has a brake booster fitting. I put a T in the brake booster hose for the Dist vac advance line. The problem is that in an individual runner manifold setup, like 2x40IDF, the vacuum signal is very oscillating and will make the distributor vacuum advance diaphragm swing crazy. The fix I used is a "dampening circuit". I placed a restrictor piece in the vac advance hose, a solid piece of brass. I drilled a small, hole, a numbered drill bit, very small, in this brass block. I then used larger, 3/8 or so hose from the restrictor to the vac advance diaphragm. This completes the dampening circuit.
The key is to have a small orifice at the vac source and a considerable volume (of hose) at the distributor end. This will dampen the vac oscillation.
Low speed driveability will be greatly enhanced when properly using the dist vac advance.
For top end you must verify the total advance at approx 3500rpm to be about 38 degrees or so. If you feel that the engine is running hot, it could be because of retarded spark under load. This can seize exhaust valves.
Just my experience,
Good luck,
nut124
I run 40DCNFs and have dealt with similar problems. Moving to 44IDFs this winter.
What I did is this: The manifold I have has a brake booster fitting. I put a T in the brake booster hose for the Dist vac advance line. The problem is that in an individual runner manifold setup, like 2x40IDF, the vacuum signal is very oscillating and will make the distributor vacuum advance diaphragm swing crazy. The fix I used is a "dampening circuit". I placed a restrictor piece in the vac advance hose, a solid piece of brass. I drilled a small, hole, a numbered drill bit, very small, in this brass block. I then used larger, 3/8 or so hose from the restrictor to the vac advance diaphragm. This completes the dampening circuit.
The key is to have a small orifice at the vac source and a considerable volume (of hose) at the distributor end. This will dampen the vac oscillation.
Low speed driveability will be greatly enhanced when properly using the dist vac advance.
For top end you must verify the total advance at approx 3500rpm to be about 38 degrees or so. If you feel that the engine is running hot, it could be because of retarded spark under load. This can seize exhaust valves.
Just my experience,
Good luck,
nut124
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Nut124
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- Your car is a: 1978 124 Spider 1800
Re: Idling timing 40IDF
OP, another thing,
The initial advance, 8 or 10 degs, must be observed w/o the vac advance connected.
Nut124.
The initial advance, 8 or 10 degs, must be observed w/o the vac advance connected.
Nut124.
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Nut124
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- Your car is a: 1978 124 Spider 1800
Re: Idling timing 40IDF
OK, just to clarify,
The idle timing of 8-10 deg is not to be based on the smoothest or stongest idle. The only purpose of this test is to set the full power advance to 38deg or what ever the spec is. The centrifugal advance mech inside the dist will add the 28deg or so by 3500-4000rpm.
If you set the idle timing based on best idle quality w/o the vac signal, then you will have majorly advanced spark at full power, pre-ignition, poor HP and over heating, bad news.
The car will idle better when the proper vac advance signal is connected. This will increase the actual advance at idle and light
loads. At full throttle there is little or no vac and the vac advance is effectively zero, and the total advance is set by the mech centrifugal system in the distr.
I hope this makes some sense?
Nut124.
The idle timing of 8-10 deg is not to be based on the smoothest or stongest idle. The only purpose of this test is to set the full power advance to 38deg or what ever the spec is. The centrifugal advance mech inside the dist will add the 28deg or so by 3500-4000rpm.
If you set the idle timing based on best idle quality w/o the vac signal, then you will have majorly advanced spark at full power, pre-ignition, poor HP and over heating, bad news.
The car will idle better when the proper vac advance signal is connected. This will increase the actual advance at idle and light
loads. At full throttle there is little or no vac and the vac advance is effectively zero, and the total advance is set by the mech centrifugal system in the distr.
I hope this makes some sense?
Nut124.