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Setting Mixer And Idle In Ke70?


abatom

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I've started another topic because I've created another issue. Though someone may know how to do this properly. I was playing around with my idle and mixer screw on my carby today as I've messed things up in the past. I'm not 100% sure what I'm doing. I have a small bump at low RPMs, and I think I created it by messing with these screws. I realize this could be a myriad of things but I'd like to focus on this for now.

 

On my 4KC carburetor there are three screws. A Fast Idle Screw andIdle Speed Screw and a Mixer Screw. (Photo below, couldn't find a better diagram).

 

How do I coordinate the adjustment of these three screws to set these correctly. Where should the idle be when setting the mixer screw for example? What do I do with the Fast Idle Screw? etc. etc.

 

post-20082-0-77736100-1388926473_thumb.png

Edited by abatom
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I think one will be idle when the choke is on, but I gave my stock carb away years ago....

 

So one idle speed screw should screw onto a choke quadrant, and gives you idle when the choke is on.

 

The other idle screw will push on the body and give you idle when warm.

 

With the car warmed up, set the idle when you want it, say 700rpm. Screw the mixture in and out in half-turn lots until you get the fastest idle speed. Then re-adjust the idle with the idle speed screw. Then you can play with the mixture in 1/4 turns to get it how you want it.

 

If you screw the mixture right in then take it out one & 1/2 turns that will be a good starting point.

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Thanks.. I have another question if anyone is interested. It's about setting the timing.

The car was running fine until I started fiddling around with the timing. I also installed a timing chain recently. The car ran fine after that, so this problem has started since my bright idea to reset the timing .

 

Here it goes... I am using a timing light. When my number one cylinder is at top dead centre, the notch on my flywheel is at around 5 degrees before top dead centre. I marked the wheel with white liquid paper. I then hook up the timing light to number one cylinder ( it works) and kick the engine over. When pointing the light at where the mark is, the white mark is nowhere to be seen at the 0 to 10 degree (prior to tdc) mark. But if I direct the light back around the wheel (anticlockwise, prior to tdc or 0) the white mark is at around 35 degrees or more when the light locates it. In other words, the spark happens at least 35 degrees from top dead centre. Maybe even further.

 

What is this telling me. Is the vehicle sparking too soon? Seems to be, but this is where it runs at it's best. If I set it to 5 or 10 degrees from tdc it just conks out. Why would this be? The vehicle is nowhere near top dead centre or when the number one cylinder notch spaces the contact to make it spark. I've set the gap correctly, several times.. I'm at a loss to explain it.

 

Thanks

Edited by abatom
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You can set it without the timing light to check everything, it won't be running.

 

Take off the dizzy cap and turn the ignition on. Rotate the motor with a spanner on the crank pulley until #1 is at TDC and note where the rotor points to. It should be around #1 lead, or maybe quite a bit before that in your case. Turn the crank back to about 20deg before TDC then approach TDC and note the points rubbing block moving around the dizzy cam.

 

Set the crank pulley on about 10deg before TDC, then turn the dizzy so the points are just opening. Wth the ignition on they should give a spark.

 

Do it a couple of times until you have the points just opening, then tighten the dizzy. Put the cap back on and fire the motor up. (don't forget about the spanner on the crank pulley!) If it won't idle, increase the idle speed until it does.

 

Then see if it drives OK. After that you can put the timing light on and fine-tune it to whatever timing advance you'd like. Rev it to 3000rpm with the light and see what the max advance is. That really needs painting more white marks on the pulley out to 40deg before TDC, as the max should be 36. They will run with more advance, but I don't know if they have any more power or whether the spark tries to push the piston back down at 45deg BTDC.

 

You can generate a spark advance curve if you have a tacho, as I did here in the electronic dizzy work I did a while back.

 

http://www.rollaclub.com/board/topic/42407-the-girls-ke70/page__st__45

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Before I changed the timing chain it was at about 5 degrees.

 

oops... the dizzy drive is off the cam so the ignition timing depends on the cam timing.

 

If you touched nothing in the ignition system, and had read the advance with a timing light before you did the cam chan, then the only answer is that changing the chain changed the ignition timing.

 

So you have pulled the cam 'forward' in relation to the crank, the valves will be opening and closing earlier and the points firing earlier. Changing the chain made quite a difference! I expect the valve timing is now at factory spec, which you could check by measuring the valve opening times, and the dizzy just gets adjusted to 10deg advance.

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Hmm.. I probably have pulled the cam forward in relation to the crank. I believe I lined it up correctly though, the keyway on the camshaft in relation to the dot on the camwheel should have allowed that I would assume.

 

OK, thanks, but I didn't completely understand your last paragraph.

(The valves will be opening and closing earlier and the points firing earlier ) Is this good or a bad thing? Do I need to go in and readjust the chain again?

 

(Changing the chain made quite a difference! I expect the valve timing is now at factory spec) I'm assuming from this it sounds like I did it right. Is that correct?

 

which you could check by measuring the valve opening times, and the dizzy just gets adjusted to 10deg advance.

Is that using the timing light? Not sure what you mean here. I have adjusted the dizzy several times now.

How do you measure the valve opening times?

 

 

Initially things ran fine. Drove about 100km in it the other day and it went well. After fiddling with the mixer and idle screws I now get a little miss at idle speed. Also the idle speed won't come down, it stays quiet high. This to me sounds like a carby problem or an air leak (of which I can't find). Just making sure it's not connected to the timing chain I did recently.

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You can measure the valve timing with a circular protrator on the crank pulley. You can buy big round protractors, or just print one off the web and stick it on a sheet of something firm like aluminium or perspex.

 

Take off the tappet cover & take the plugs out.

 

Set up the protrator at TDC, and rotate the motor until say, #1 exhaust opens. That will be when the tappet gap vanishes and you can't wiggle the rocker. Keep slowly turning the motor with a spanner or pushing the car in 4th gear, and the inlet will open just before next TDC. Suddenly the inlet rocker can't be wiggled. After that TDC you will have the exhaust close and the rocker come loose.

 

Somewhere on the web will be those figures for a stock cam.

 

If you have a lot of advance it will cause a high idle, and advancing the cam with a tight chain would do that. Knock it back to 10deg and wind the idle speed screw up if you need to before you go chasing air leaks.

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Thanks both. The timing mark for TDC is between the two marks at the front. It's a small notch on the back of the pulley.

I'll do that alltez, will post how it goes in a week or so. I'm taking a break from the car.. much needed.

 

A few hours later....

 

I've just been thinking about my timing being advanced too far. That certainly explains my idle problem and my inability to adjust the idle speed.. Would you know if this would also explain a small bump I feel at around idle speed. It seems to be at regular intervals. If my timing has been advanced too far and my fuel air mix is incorrect then could it cause that miss, or bump at idle speeds? Your answer above has got me thinking altezz.

 

Cheers

Edited by abatom
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Sure- there are quite few things that can cause a miss at idle, because the motor is not under load.

 

The cam chain whips back and forth instead of being tight on one side because the valve springs are alternately pulling and pushing on the rockers as the cam lobes go past, and that causes the valve timing and the ignition timing to dance about. As well as that, the compressing of one cylinder will slow the crank, and make the "pull" side of the chain loose, then that cyl fires and the chain snaps tight.

 

That changes the idle speed in revs per second, not maybe showing in rpm, but those fluctuations will send pulses up the inlet system and play around with air velocity going through the carb. The air has no inertia at 800rpm compared to 5000, so it is going down a port, then stopping dead, then moving down again.

 

Any of this could make a spark too advanced to fire so it tries to run the motor backwards, or too retarded so it doesn't burn, or have a lean pulse through the carb...

 

Just listen to any hot cam at idle, compared to when it is under load. My twin SUs are very grumpy at idle, with an occasionaly miss just as I load the motor as I let the clutch out too quick without enough revs. I reckon its just the relationship between two carbs and a cam, but it is beautifully smooth when driving..

 

Anyway, once you get the ignition running cleanly from 10dg to 35 or so, you can then really see if the carb has a problm.

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