24 replies to this topic

[Gatti]

Hi fellas,

 

I have been playing around with the tune of my car as at times the idle will set high for 10 seconds or so then settle to 1000rpm.

 

All the engine work was done by another owner so I don't know the exact cam specs but it has more lump at idle than a 35/75

 

I have put new spark plugs in it and had a look at the timing with a light.

 

It also has an electronic dizzy.

 

I have tried it at 6 and 10 degrees but it doesn't make a difference to the idle issue and actually idles rougher and seems to be struggling.

 

When I first put the light on it the timing was below the markings on the engine so I'd say around 15 or 16 degrees.

 

What is a good timing starting point for a large cam?

 

I don't know if the dizzy has been re-graphed, but does that make a difference at idle?

 

I have also ordered a vacuum gauge so I can check the balance of the carbs but it is due to arrive later this week so I can check them yet.

 

 

 

 

[hanra]

Vac leak leak? Sticky accelerator linkage?

[claysummers]

Mechanical binding somewhere between accelerator pedal and throttle butterfly plate. A butterfly could be slightly missAligned and dragging on the Venturi wall. What about a stronger return spring?


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[Gatti]

Thanks, I was wondering if it was the return spring as well. 

 

I'll tighten it up so it has more tension and see if that helps.

 

One question for you gurus, when a dizzy is re-graphed does the reading still stay the same at idle and the re-graph only effects the advance as the revs increase?

 

I had a look online and couldn't find the answer.

[claysummers]

Correct.

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[Gatti]

What idle speed should the motor be at when checking the timing?

 

Is 10 degrees a good start seeing as it has a decent cam?

 

I was told it is a stage 4 Crow Cam by the previous owner.

 

Camshaft Specifications;
Advance Ground on Cam; 1 deg, Lobe Separation; 110 deg, duration @ .050 inch INT = 226 deg EX = 226,  Total duration INT = 304, EX = 304, valve timing INT 43/81, EX 83/41, Valve Lift  INT = 0.423 inch, EX = 0.423 Power range 2500-5800 rpm. Install straight up on timing marks.

[claysummers]

Low as you can get it to comfortably idle but best way to set static timing is by ear.

Try it around 13 deg lightly clamped so you can still turn the dizzy but won't move with vibration. Load motor up in top gear. So low revs up slight incline and floor it. If it pings badly back it off bit by bit. Repeat until just pings lightly a couple times. That s my method.

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[caterham2]

Bear in mind that even the "best" of harmonic balancers  wll frequently move the outer on the inner and thereby give you a dodgy static timing point. Best result as advised by a previous answer is to lightly clamp the distributor and move it while running at idle. As you advance the revs will rise, so drop the idle speed back at carbs and retry till the motor accepts the sweet spot you have now arrived at. Road test carefully with a 9/16 spanner in your pocket, listening for pinging etc, making slight adjustments till running cleanly. This is the way I set my 202 which has a pretty mean cam in it. As for the "stage 4" crap you were told, means as much as a twit in a shop years ago overheard telling  a customer he needed a "mild full" cam W.E.T.F.T.I. All the foregoing assumes carbs in good nick, no wear on shafts, and balanced, engine mounts good, linkage coming forward from firewall in good order, no air leaks or cracked hoses, PCV valve if fitted not snotted up.

Edited by caterham2, 02 June 2020 - 11:51 PM.

[warrenm]

With a cam with the specs you have above, I would use 14° at idle & no more than 28°/30° total & check the items that caterham2 mentioned. 

[Gatti]

Thank fellas


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[DMLC71]

Has the dizzy been graphed to match your cam?

I can’t imaging an 8 deg dizzy with your cam spec set at 14 deg would perform.

 

cheers Dazm

[I'm a Red Motor fiend]

Static timing means jack shit. Set it at say 14 as Warren said then check the total at 3500 rpm and set it to 28-30.
Read your plugs and give it a bit more if it needs it and can take it.
If you haven't verified if your balancer has slipped or not, this will also be a good indicator.
After set, your static will land on whatever it may be and if it is only say 8-10 and it won't idle nice, you need the dizzy regraphed again.

[Gatti]

Thanks.

 

I had a bit more pf a play with it today.

 

With initial timing at 14 degrees its at 30 degrees at 3500rpm so the dizzy seems fine.

 

I think it it the linkages not re-setting all the way back because if I give it a rev then push the linkages closed the idle is fine.

 

I'll work out why it's sticking or fit a stronger return spring.

[Gatti]

I actually managed to track down the owner that had the motor built in my car a few weeks ago and as luck would have it he sent me the cam sheet today.

 

It's even bigger than I originally thought

 

[I'm a Red Motor fiend]

👍 sounds good.

[jd lj]

I'd be more inclined to be looking at your carbs than the ignition. Looking at your carbs in your other thread your return spring set up needs some work. The spring isn't pulling straight. I make stainless steel return brackets that attach to the top of the dcoe carbs but I haven't tried one on the Weber copy carbs so I'm not sure if they'd fit. The hex bar linkages aren't great quality.

Have you checked for vacuum leaks?

Leaking spindle seals can sometimes cause a lazy idle syndrome like yours.

Do your idle mixture screws have O rings on them, what's their condition? Sometimes air can leak past the threads of the idle mixture screws. This can be eliminated by putting some thread sealer or grease on the threads but to do so you'd have to remove the screws and then reset them.

Check your fuel levels. On genuine dcoe's you want the fuel level to be 25mm down from the top of the carb body as measured in the rear emulsion tube well. With the engine idling use a mirror and torch to look down the throats and see if any fuel is dripping off the auxiliary ventruis, if there is the fuel level is probably set too high.

Remove a progression hole cover and look at the position of the throttle plates in relation to the first progression hole. Can you see the top edge of the throttle plates through the first progression hole? Can you see the back edge of the throttle plates through the first progression hole? If so the air and fuel can go through the progression hole even when your throttle plates are closed. You can alter the position of the throttle plates at idle with the idle speed screws and air bypass screws.

The throttle plates could be binding in the barrel if they're not set correctly.

James D

[Gatti]

I'd be more inclined to be looking at your carbs than the ignition. Looking at your carbs in your other thread your return spring set up needs some work. The spring isn't pulling straight. I make stainless steel return brackets that attach to the top of the dcoe carbs but I haven't tried one on the Weber copy carbs so I'm not sure if they'd fit. The hex bar linkages aren't great quality.

Have you checked for vacuum leaks?

Leaking spindle seals can sometimes cause a lazy idle syndrome like yours.

Do your idle mixture screws have O rings on them, what's their condition? Sometimes air can leak past the threads of the idle mixture screws. This can be eliminated by putting some thread sealer or grease on the threads but to do so you'd have to remove the screws and then reset them.

Check your fuel levels. On genuine dcoe's you want the fuel level to be 25mm down from the top of the carb body as measured in the rear emulsion tube well. With the engine idling use a mirror and torch to look down the throats and see if any fuel is dripping off the auxiliary ventruis, if there is the fuel level is probably set too high.

Remove a progression hole cover and look at the position of the throttle plates in relation to the first progression hole. Can you see the top edge of the throttle plates through the first progression hole? Can you see the back edge of the throttle plates through the first progression hole? If so the air and fuel can go through the progression hole even when your throttle plates are closed. You can alter the position of the throttle plates at idle with the idle speed screws and air bypass screws.

The throttle plates could be binding in the barrel if they're not set correctly.

James D

 

Thanks mate.

 

I found today it's definitely the linkages because if I give it a rev and return them by hand the idle is correct.

 

I was thinking of pulling them apart and rotating the spring connection so it is more upright which will give the spring more tension which might help get it to return properly. (I'd rotate it to the right as shown in the photo)

 

[jd lj]

Look at how the spring attaches to the manifold, see the indirect line of the spring.

[warrenm]

I looks like a healthy cam. 

I'd give the accelerator cable bracket a bit of a bend to get the cable to pull straight.

[Gatti]

Thanks for everyones help, I've sorted it today.

 

I used a door latch bracket I had sitting around to make a better mount for the spring onto the manifold and I also fitted a new slightly stronger spring. 

 

I also moved the spring lever along slightly to centre it up.

 

 

I also had a different 3 way splitter for the vacuum lines sitting around so I fitted that as well to get the hoses away from the spring (I'll buy proper hose for it now I know it works)

 

 

The end result is I give it a rev and it settles straight back into idle 

[jd lj]

I'm glad that you made some progress.

As for your vacuum lines, I'd put screw in plugs into two of the holes in the manifold and only run the vacuum line to one runner. Your brakes will still be fine and doing this will stop the dilution of the manifold vacuum level between all three runners. Which will probably improve the progression circuit. Most Holden 6's with a decent cam tend to have low manifold vacuum which contributes to a poor progression circuit.

[Gatti]

I'm glad that you made some progress.

As for your vacuum lines, I'd put screw in plugs into two of the holes in the manifold and only run the vacuum line to one runner. Your brakes will still be fine and doing this will stop the dilution of the manifold vacuum level between all three runners. Which will probably improve the progression circuit. Most Holden 6's with a decent cam tend to have low manifold vacuum which contributes to a poor progression circuit.

 

I was wondering about that.

 

It has the XU1 large diaphragm booster on it. Does that need the extra vacuum?

 

If not I'll plug one of them up.

[jd lj]

No, XU-1 booster doesn't need any extra vacuum. Ideally measure the manifold vacuum level at idle first to see how much you actually have. This must be taken from just one runner and with a one way check valve in the hose to stop the gauge fluctuating wildly. If the vacuum is around 20hg or higher then leave the hoses as they are but below 20hg plug up two of the holes. It's common for pur engines to be down around 12-15hg.

[claysummers]

That looks better Matt. Don’t forget to nip the fasteners up after a run in case the threads bed in a bit with vibration.


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[LC-GTR-1969]

Nice cam you have there, similar to my cam. Glad you got the binding issue fixed..

 

On timing matters- I run 29 degrees locked and runs fine with 12:1 comp and pump fuel. I would try what Warren recommended, re-graph dizzy so it has around 16 degrees advance- 14 static and all in by 3500rpm with about 30 degrees. 

 

If your compression is on the low side (ie less than 10.8:1), you could benefit from even more static timing. Have you done a compression test? If you are at 150psi per pot or lower, you might find a locked dizzy will surprise you with the improved response. Not ideal though but its easy and cheap to test, big cams and lowish dynamic compression seem to like lots of static timing, the overlap and reversion can contaminate the charge which makes it burn less efficiently hence liking/needing a little more spark time than usual.