Bad Idle. Tapping noise...

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Bad Idle. Tapping noise...

Postby grim_b » 08 Dec 2005, 11:03

God that sounds terminal :(

OK, so recovering from the brain beating that I got from my spark plug problems. I now have idle problems and the car seems to choke when accelerating.

I have also noticed that during the choke I hear a "tink, Tink" noise. I think it sounds like the needle in the Carb rattling? is that possible? ( I am not describing the rattle I get from behind the speedo, its a new noise )

I am thinking that Doive may be right about the condenser, but where is that? I found that there is a remote part to the coil that is bolted to the head on the clip that holds the coil in place... Is that it? (I took a picture, but havent posted it yet. edit soon)

Any more ideas people? could it be idle mixture now that the points and plugs have been adjusted?

Thanks all. Remember it needs to be relative easy for my brain to grasp it :oops: :D
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Postby Neilyman » 08 Dec 2005, 11:14

Sounds like a fuel mixture problem. The `tinging` noise could be `pinking`, I think that points to running lean? Someone will correct me if I`m wrong :)

The condensor is in the dizzy, the round barrel shaped silver thing with 1 wire on the end.
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Postby grim_b » 08 Dec 2005, 11:32

Ok,

I will have to get the old color tune out again.
Do you happen to know what that is connected (with one wire) to the coil then? I also think that my condenser is outside of the dizzy? is that possible?

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Postby grim_b » 08 Dec 2005, 11:34

Sorry,

Thought of another question.....

When changing the idle mixture (The little screw on the front of the carb) is it clockwise for weaker or is it anti-clockwise?

Cheers again.
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Postby Neilyman » 08 Dec 2005, 12:01

I`d go for the main jet underneath the carb, 1/2 a turn anticlock. `Cos you say it bogs out when you accelerate, idle screw won`t affect that!

I wouldn`t have thought the condensor was outside the dizzy, but stranger things have happened :) The wire is connected to a terminal inside the dizzy.
The `barrel` has a tab/screw, fastened to the base inside the dizzy.

Is the colds start thingy on the side of the carb tight?
It`s the long thing with the coloured plastic cover., Mine was loose one time........the car ran like a dog.
Just a thought ;)

I take you have got a Stromberg carb?
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Postby grim_b » 08 Dec 2005, 12:25

Yes got the Stromberg.
I have never changed the main jet in any way, as I have never removed the cap to get at the adjuster. I suppose it could be that the engine was set up wrong by the last owner? Somehow compensated for all the settings being wrong by adjusting the mixture to compensate?

Now that I have reset all the plugs to 1mm and the points to .38mm, I am seeing that the mixture is now screwed with the K&N replacement and all.

I don't mind making a tool to set the mixture, but will this have to be done with the engine running? I will obviously read the manual, but your real life experiences are so much better as some great tips can be found here :D

This cold start thingy? is that the yellow thing? I really need to sit down and have a good read don't I? :?

Cheers.
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Postby grim_b » 08 Dec 2005, 12:26

Bit more info.

The bogging occurs during bitting point or just after. if that is relevant at all?
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Postby Doive » 08 Dec 2005, 15:13

Grim, you have the Bosch dizzy which has the condenser nailed onto the side of it, not like the nice tidy Delco ones which are all enclosed. The condenser is fitted to the positive side of the points and is earthed through the dizzy body. What it basically does is momentarily holds the voltage across the points as they open to prevent arcing, then allows a controlled collapse of voltage which creates the high tension voltage in the coil, so giving you your spark. Without the condenser the points would arc and break down, so all spark is lost as the coil voltage depends on rate of change of current.

Anyway. In my experience a condenser is either knackered or it isn't, so if yours was the car just wouldn't go at all. If she is bogging under load, I'd say that is either bad mixture or timing problems. For the timing, do a quick test. Run her up to speed and go out for a drive. Get to about 20 mph in second, then drop her into 3rd and bury your foot. Listen for a sound like teaspoons hitting the inlet manifold in time with engine rpm, this is pinking and is very bad for the engine if allowed to continue. Retard your timing slightly in degrees until it goes away and the car idles smoothly. You will be able to judge for yourself when it is right, trust me!
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Postby grim_b » 08 Dec 2005, 15:40

Would my timing gun help here then? Is that a case of just losening off the dizzy and giving it a bit of a turn?

Thanks for that, maybe tonight :D
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Postby Neilyman » 08 Dec 2005, 18:49

I use the second method...I don`t even own a timing gun. :P
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Postby Doive » 08 Dec 2005, 18:56

But that's because you'gve been doing it since before the rest of us were born mate :P

Grim, a timing light is ideal. I set mine once with a light and have never managed to get her to run as sweet again by hand. Set up the light with the engine warm, mark the pulley and block with tipp-ex or white paint so the light picks it up better, point and adjust until the marks line up. Rev the engine a few times, still pointing the light and make sure the mark moves around the pulley to show the vacuum advance is working correctly.

Hmmm. I'm just thinking here - you had a problem before with one of the manifold pipes leaking didn't you? If that wasn't sealed up right it is possible the vacuum advance wouldn't be working properly, so causing the engine to run extremely retarded under load. Engine experts, is this possible?
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Postby Herbie_Flowers » 08 Dec 2005, 19:05

Doive wrote:But that's because you'gve been doing it since before the rest of us were born mate :P

and before timing lights were invented :P
Doive wrote:Hmmm. I'm just thinking here - you had a problem before with one of the manifold pipes leaking didn't you? If that wasn't sealed up right it is possible the vacuum advance wouldn't be working properly, so causing the engine to run extremely retarded under load. Engine experts, is this possible?

it would be extremely advanced under load if it wasn't sealed mate :wink:
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Postby Doive » 08 Dec 2005, 19:43

See I couldn't picture it in my mind, I'd rather ask someone who knows better than I do than give Grim wrong advice! Does the inlet not create more of a vacuum under acceleration, so giving more advance? No, I'm trying to work it out in my head, and it's beginning to hurt.
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Postby Herbie_Flowers » 08 Dec 2005, 21:10

LED time eh Doive :lol:
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Postby grim_b » 08 Dec 2005, 21:51

Ok,

Well, not being able to find the timing light tonight, I did it by hand. I still have a semi rough idle, but i am not sure where that is originating from? I still think a gasket has gone somewhere, but what do I know?... :oops:

I took her out for a stretch after the hand timing and it seems a bit better if not running faster? hmm, must clear that garage out and find the light tomorrow. :?:

I'm afraid I got lost at Herbie's post but kind of grasped Doive's... but I am kind of :? confused :? at this vacuum again. (I got lost last time too)

I think what I really need is a person saying "This is the Dizzy. Watch out for not getting your points gap wrong" kind of book... The Haynes is ok, but its not the kind of book read in bed is it? [gif]smiley of oilslick type bed [\gif]

I will let you know how it goes in the morning.
Cheers all. :D
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Postby Herbie_Flowers » 09 Dec 2005, 00:25

right, how's this Grim.
look at a clock face. imagine the hands to imitate the crank going around and around. we'll say 12 o'clock is Top Dead Centre. the static timing (engine not running) of a chevette is 9 Degrees Before TDC. so if we put that onto our clock it will be on the number 11. as engine revs increase so the timing has to move so we can get an earlier spark. this is called ignition advance but in effect you are retarding the ignition - moving it even further from the 12 o'clock position. the maximum advance on a chevette is 12.5 degrees so this number combined with the already 9 degrees BTDC means the spark can occur at 21.5 degrees BTDC - say the 10 o'clock position. clearer?
Last edited by Herbie_Flowers on 09 Dec 2005, 15:38, edited 1 time in total.
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Postby jayen4 » 09 Dec 2005, 02:45

Herbie , The chevette engine does NOT turn anti clockwise (as you stand in front of the car)!! :) As far as I know,it was only some of the old Honda engines that turned anti-clock. And,by the way, Grim,have you checked that the oil in the dashpot is topped up ?? Will the engine rev cleanly,when the car is stood still ??
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Postby Doive » 09 Dec 2005, 03:14

Having had a look at a trusted source, I think I've fully grasped what vacuum advance is all about. Basically when at idle, your engine is sitting with the basic timing of 9 degrees BTDC. What this means Grim, is that when your piston is 9 deg below TDC on the upstroke, the spark is allowed to cross the plug and ignite the mixture. This advance ignition is allowed because the mixture takes time to ignite, so by the time it has burned sufficiently to create power the piston is past TDC and so makes the most of the energy.

When the throttle is first cracked open under load, maximum vacuum is generated and so with our Bosch dizzy the vacuum causes the base plate on which the points are mounted to spin round relative to the cam on the dizzy drive, so altering the time in the cycle at which the points operate, in effect changing the position of the spark. This means the spark occurs earlier in the cycle, that is longer before TDC, and so the ignition is actually more advanced at this point. Apparently the engine can cope with more advance here as it has something to do with relative speeds of gas flows and chamber pressure or somesuch clever stuff that's miles beyond me. Must have something to do with the weaker mixture taking longer to burn.

As the engine progresses towards wide open throttle the vacuum reduces, and so the vacuum advance mechanism in the dizzy returns towards it's rest position of 9 degrees BTDC. The whole idea behind vacuum advance is to maximise the power available and to ensure a clean burn all through the rev range - disconnect your vacuum pipe and go for a drive to see the difference.
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Postby grim_b » 09 Dec 2005, 09:55

Wow, you people never stop amazing me. :shock:
Ok, so I now understand how the process works and have driven to work today (1.5miles) with no choke :D I am not sure if that is a good thing, but it saved me having to worry about losing power when pulling away / out at junctions. :) Noubt more scary than pulling out onto a roundabout and finding that the car wants to slow down to a crawl.... :shock:

The engine didn't want to start without a bit of choke (say, 1cm) and then started missing after about a minute. I put the choke back in and let her tick over for a few minutes. I then started driving to work.

The car still bogged like Doive said in his "20mph - 3rd gear" test, but I think this was just the car hadn't warmed up?

I think I will still have to do the Light test on the timing, but at least I know if the car warms up, I can drive her. :)

Is it worth trying to find a replacement vacuum? just to make sure mine is fine? I have removed the pipe from the carb and blown down it and I could here what sounded like a diafram folding noise on suck and blow?

Also does no-one know what the thing connected to the + of my coil is? I described it earlier in the thread, but it was just mentioned as not my condenser. (Cheers Doive) :)

Thanks again to all for the descriptions given here. I look forward to problems in a way as I just know you guys and girls can advise me on it :D
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Postby Harry Flatters » 09 Dec 2005, 14:00

Grim, have a look at this website, which has got some nice basic info and a good cross sectional animation of a car engine.

If take the dizzy cap off and suck on the vacuum tube, you should be able to see the baseplate with the contact breakers on move slightly.

The other way to check is attach the timing light, point it at the timing mark and rev the engine. As the revs increase, you should see the mark on the crank pulley move away from the mark on the timing case, then back towards it. If it doesn't do this or only does it at very high revs the vacuum isn't working.

I think I can just about see the thing on your coil in the photos in the other thread. If it's the black wire from the coil +ve, looks like a small metal canister, is bolted to the block on a clamp, and has no other wires going to it then it's another condenser fitted for radio interference suppression - you can do away with it but you might hear the engine on the radio! Might be worth disconnecting temporarily to check it's not faulty.

Apparently the engine can cope with more advance here


It's more like the engine wants different amounts of advance at different operating conditions / revs.

If your engine needed such a small amount of choke it may point to an over rich mixture or carb fault. If it's running very rich it'll want to bog down as it gets warmer (plug fouling).
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Postby grim_b » 09 Dec 2005, 16:30

Harry Flatters wrote:Grim, have a look at this website, which has got some nice basic info and a good cross sectional animation of a car engine.


I forgot about that site, never thought of the engine on there :)

I read the ingnition section as well for good measure. It was just what I have been looking for. Again, another sign that this forum can help anyone :D

I will have a more indepth look over the weekend, but I am very happy that this car can run sweet again. :)

Thanks.
Grim. :wink:
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Postby Harry Flatters » 09 Dec 2005, 17:17

Grim, where in Hants are you?
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Postby shuvit-tim » 09 Dec 2005, 17:26

i have an AA 'how it works' book which is excellent at explaioning how each of the components in a car works and how to maintain them
when all else fails, rivets, cable ties and bodge tape will see you through

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Postby grim_b » 09 Dec 2005, 17:46

Harry, I am in Basingstoke chap. :D
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Postby Harry Flatters » 09 Dec 2005, 17:51

Shh.... I'm not here. :lol:


No, apparently you're in Basingstoke!

So am I, on Sunday......

.... for my GF's brother's birthday - suspect any looking at / advice rendered to a certain Chevette may not go down too well......
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