30 replies to this topic

[marcus626LX]

Hello!
I'm from Sweden and I have a Mazda 626 lx, GC from 1984 with a 2.0l FE carby engine.
My problem is that the idle is a bit rought (spell?)
If i hook up a timinglight gun (don't really know what they are called) for setting the timing and idle, the idle is first lying steady on 1000rpm and then i jumps down to 800rpm then back up to 1000rpm and it does this 3 or 4 times then it's steady at 1000rpm for a couple of seconds before it does it again.

To get the timing right i had to rotate the distributor as far as it goes to the right to get the timingmark line up correct. Which seems to be to much, i thought that i only were supposed to rotate it a little bit from center position.

There is a rust hole in the pipes that goes from the airfilterbox to the exaust.

What i have changed:
spark plugs
spark leads
ignition coil
rotor
airfilter
fuelfilter
carby
battery (now have a banner running bull at 80Ah)
alternator (changed this because it was draining my battery)

i have cleaned all earth points from rust and paint and applyed copperpaste on them.

does anyone know what could be wrong?
please! give me some tips! i'm going crazy here

ps. sorry for my english

edit:
i have a manual choke.
i have tried to adjust the valves by "tried" i mean that i followed haynes instructions, but i'm not sure if i did it right. It seems that it runs a little better then before, but i could be wrong.
I have a leak in my exaust system, its right underneath the backseat before it goes around the gas tank. The leak is where two pipes get together (dont know what else to call it). The are fitted with a clamp.

[marcus626LX]

isnt there anyone that can help me? please?

[silver_1987_626]

Hi-
Firstly I would advise you to check ALL your vacuum hoses to check that there are no leaks, as this can cause an erratic idle.

Because you have a carburetted car, you may have a problem with your automatic choke. There is a thing thats called a 'fast idle cam' attached to the choke that makes your engine rev higher when the choke is in operation. If the temperature diaphragm in the choke is faulty (as in intermittent, will work then wont...) then this could cause your idle to increase then decrease when the car is cold, which may explain your 1000 then 800 business.

Failing that being faulty, check your 'slow fuel cut solenoid' as this 'clicks' in when your RPM is lower than 2300rpm. If this is clicking out intermittently, it will cause your engine to 'stall' then pick up again, then stall then go etc. The fault would be caused by the RC network or the switching transistor in the 'computer' if this is found to be the problem.

Best advice I can give is to go buy a Haynes service manual for the car, and trace through all their suggestions.

If you have any more problems / questions, gimmie a hoy!

al
ps I'm in Australia, so I wasnt awake when you were online

[marcus626LX]

silver_1987_626, on Mar 14 2006, 07:04 PM, said:

Hi-
Firstly I would advise you to check ALL your vacuum hoses to check that there are no leaks, as this can cause an erratic idle.

Because you have a carburetted car, you may have a problem with your automatic choke. There is a thing thats called a 'fast idle cam' attached to the choke that makes your engine rev higher when the choke is in operation. If the temperature diaphragm in the choke is faulty (as in intermittent, will work then wont...) then this could cause your idle to increase then decrease when the car is cold, which may explain your 1000 then 800 business.

Failing that being faulty, check your 'slow fuel cut solenoid' as this 'clicks' in when your RPM is lower than 2300rpm. If this is clicking out intermittently, it will cause your engine to 'stall' then pick up again, then stall then go etc. The fault would be caused by the RC network or the switching transistor in the 'computer' if this is found to be the problem.

Best advice I can give is to go buy a Haynes service manual for the car, and trace through all their suggestions.

If you have any more problems / questions, gimmie a hoy!

al
ps I'm in Australia, so I wasnt awake when you were online

hehe, its 3 in the morning here now and i'm still up

thank you for your help.
do you have any tips on how to check the vacuum hoses?

i have a manual choke, sorry that i didnt mention that in my first post :-/ does any of your choke-tips still apply?
i also forgot to mention that i have tried to adjust the valves by "tried" i mean that i followed haynes instructions, but i'm not sure if i did it right. It seems that it runs a little better then before, but i could be wrong.

thanks again.

[silver_1987_626]

Well, yes, the manual choke will make a difference. The manual choke also has the fast idle cam, but it is held by your choke cable, so it will not move. Now that I am saying this, what I told you about the choke wasn't entirely correct as I think about it- the fast idle cam on an auto choke will only 'reset' as in, lower the revv's of the engine if you tap the accelerator, as it is spring loaded and has tension on it from the auto choke. Anyway, you need not worry about that.

Checking the vacuum hoses is simple really. Firstly look for obvious signs of fatigue, such as cracking, hardening (as in, becoming brittle at the joints), sloppyness on fittings etc etc.

Probably the most important one is the ignition vacuum advance hose that runs to the diaphragm on the distributor. This will adjust your ignition advance depending on load and comes straight off the manifold, so any leaks here are a problem. I don't know exactly, but it could cause your car to 'hunt' at idle (meaning go up and down). On mine it simply makes the idle faster if I remove it.

Basically just check they are all connected, and if not (and you can't for the life of you work out where they go) plug them with a bolt. Another way to check the hoses is to use a 'stethescope' - just stick a piece of hose next to your ear and listen with the other end. Check for wooshing noises around joints etc.

Another thing I just thought you could try is the actual idle mixture. Have you by any chance changed it recently? If this is set too rich or too lean, the engine will hunt at idle. It is a simple task to set it near enough to okay, or if you want to pay, a shop can measure your emissions and set it accordingly.

If you havn't touched it at all, perhaps the idle bypass jets are blocked in some way (fuel is trash nowdays...). A complete carburettor overhaul is a simple task, a rebuild kit costs about $60 AUD. Inside are seals for EVERY variation of the Nikki dual downdraft carburettor (ours). It has a new needle and seat, float, gaskets galore, etc etc. A good carby clean out using 'carby clean' solvent might just solve your problems - if the float level in the carby fuel bowl is wrong, you may be running out of fuel or if one of your jets is blocked you may not get idle mixture fuel etc etc...

Anyway, a long list of things to check. If you need more help, just ask!
al

p.s. The valve clearences must be set when the engine is HOT! If they are done cold they will be wrong (metal expands remember). Set both intake and exhaust to 0.3mm when the engine is hot- work fast!

[marcus626LX]

silver_1987_626, on Mar 15 2006, 02:25 AM, said:

Well, yes, the manual choke will make a difference.  The manual choke also has the fast idle cam, but it is held by your choke cable, so it will not move.  Now that I am saying this, what I told you about the choke wasn't entirely correct as I think about it- the fast idle cam on an auto choke will only 'reset' as in, lower the revv's of the engine if you tap the accelerator, as it is spring loaded and has tension on it from the auto choke.  Anyway, you need not worry about that.

Checking the vacuum hoses is simple really.  Firstly look for obvious signs of fatigue, such as cracking, hardening (as in, becoming brittle at the joints), sloppyness on fittings etc etc. 

Probably the most important one is the ignition vacuum advance hose that runs to the diaphragm on the distributor.  This will adjust your ignition advance depending on load and comes straight off the manifold, so any leaks here are a problem.  I don't know exactly, but it could cause your car to 'hunt' at idle (meaning go up and down).  On mine it simply makes the idle faster if I remove it. 

Basically just check they are all connected, and if not (and you can't for the life of you work out where they go) plug them with a bolt.  Another way to check the hoses is to use a 'stethescope' - just stick a piece of hose next to your ear and listen with the other end.  Check for wooshing noises around joints etc.

Another thing I just thought you could try is the actual idle mixture.  Have you by any chance changed it recently?  If this is set too rich or too lean, the engine will hunt at idle.  It is a simple task to set it near enough to okay, or if you want to pay, a shop can measure your emissions and set it accordingly.

If you havn't touched it at all, perhaps the idle bypass jets are blocked in some way (fuel is trash nowdays...).  A complete carburettor overhaul is a simple task, a rebuild kit costs about $60 AUD.  Inside are seals for EVERY variation of the Nikki dual downdraft carburettor (ours).  It has a new needle and seat, float, gaskets galore, etc etc.  A good carby clean out using 'carby clean' solvent might just solve your problems - if the float level in the carby fuel bowl is wrong, you may be running out of fuel or if one of your jets is blocked you may not get idle mixture fuel etc etc...

Anyway, a long list of things to check.  If you need more help, just ask!
al

p.s. The valve clearences must be set when the engine is HOT!  If they are done cold they will be wrong (metal expands remember).  Set both intake and exhaust to 0.3mm when the engine is hot- work fast!

I think that i need to change some vacuum hoses.
Should i change all that shows a little hardening?

If i disconnect the ignition vacuum advance hose it doesnt make any noticble diffrence, any ideas on what could be wrong with that?

I havent touched the idle mixture setting but i have taken apart the carby and cleaned it with the help from the haynes book.

When i'm going to adjust the valve clearences, should i remove the spark plugs? thats what i did last time.
I took of the valve cover to polish it (maybe you would like to see it?) and before i put it back i adjusted the valve clearences.
I called a friend whos friend is an mechanic and he told me that it is not that important that the engine needs to be warm, but maybe he was wrong?

Thanks again for all your help

Here is a picture of my engine:
where the...
green arrow marks what i think is the ignition vacuum advance hose
blue arrow marks how much i had to turn the distributor, doesnt seem right to me
red arrow marks the pipe that has a little hole

[silver_1987_626]

Hi
Now that I see your distributor is so far twisted, I think I can give some different advice.

Firstly, while I remember, YES it is VERY important that the valves be done when the engine is HOT! The valves and rockers and head and seats ALL expand and contract at different rates- we have an alloy head, which has STEEL valves in it and STEEL rockers, springs, clips etc. Because the temperature coefficiants are different between Aluminium and Steel, we MUST do the valves when the engine is HOT- that is when the clearence value was specified for. No one has ever published a 'cold' valve clearence for our engine- no one has done the sums to calculate the contraction of the different metals. When the engine is hot, all parts are at their largest, and the clearances are to be measured then. I am an engineer, so that's why I feel its important to follow specifications. Often mechanics will do the 'best effort' to finish the job on time for the customer, or take an easy way out if it is all too hard- I have a friend who is a mechanic as well, and I know what he (and everyone else where he works) is like... Oh, and yes, it is a hell of a lot easier doing clearances with the plugs out- compression... I can do mine with them in, which is NOT a good sign... My sisters is impossible to turn over by hand when the plugs are in there.

Anyway, before you go ripping off vac hoses, try this. Set your engine to TDC (no real need to, just its easier if you screw up something). Make sure that your rotor is pointing to the number 1 lead (so you know you are on compression stroke). Because ignition fires 6 degrees BEFORE TDC, your rotor should not be exactly in the middle of the no.1 lead, it should be (one spline of the distributor gear) after it. I hope you understand what I mean- if the engine IS at TDC, it should have already fired for that cylinder- understand? I can see that you have it severely advanced or retarded (by the twist, I can't remember which way advances or retards off the top of my head). The distributor will work on 3 splines of the drive gear because you can rotate it to compensate. It should be on the middle oadvancedf the three. I have drawn a picture to help you, but I can't upload it because my university blocks port 21. I will send tonight.

Rocker cover looks cool- how'd you do it? Regarding the other small hole, don't worry. They are 'air injectors' for the exhaust, simply for emissions junk. Same with that silver hose you obviously replaced. A lick of paint and the engine bay will look great! Tell me if you need more info.
Al

P.S. I'd paint your radiator black as well, helps with black body radiation, cools more efficiently than silver. Heat transfer 2904 tells me that

[marcus626LX]

thanks for all your info.
I will comment it when i come home from school tomorrow (that will be in 12h from now).
just wanted to ask you if could add you, if you have, msn or icq?

[silver_1987_626]

I forgot to add in the last post about your carby- you said you cleaned it all out- did you replace all the gaskets? They MUST be done if you take it apart or else it will leak (as in, air will suck in where it is not supposed to). Happened to mine when I made my own gaskets, the material (which was supposed to be fine for petrol...) went hard, and carby was not as smooth as it should be. PM me for msn addy.

al

[marcus626LX]

silver_1987_626, on Mar 15 2006, 06:51 PM, said:

Hi
Now that I see your distributor is so far twisted, I think I can give some different advice.

Firstly, while I remember, YES it is VERY important that the valves be done when the engine is HOT! The valves and rockers and head and seats ALL expand and contract at different rates- we have an alloy head, which has STEEL valves in it and STEEL rockers, springs, clips etc. Because the temperature coefficiants are different between Aluminium and Steel, we MUST do the valves when the engine is HOT- that is when the clearence value was specified for. No one has ever published a 'cold' valve clearence for our engine- no one has done the sums to calculate the contraction of the different metals. When the engine is hot, all parts are at their largest, and the clearances are to be measured then. I am an engineer, so that's why I feel its important to follow specifications. Often mechanics will do the 'best effort' to finish the job on time for the customer, or take an easy way out if it is all too hard- I have a friend who is a mechanic as well, and I know what he (and everyone else where he works) is like... Oh, and yes, it is a hell of a lot easier doing clearances with the plugs out- compression... I can do mine with them in, which is NOT a good sign... My sisters is impossible to turn over by hand when the plugs are in there.

Anyway, before you go ripping off vac hoses, try this. Set your engine to TDC (no real need to, just its easier if you screw up something). Make sure that your rotor is pointing to the number 1 lead (so you know you are on compression stroke). Because ignition fires 6 degrees BEFORE TDC, your rotor should not be exactly in the middle of the no.1 lead, it should be (one spline of the distributor gear) after it. I hope you understand what I mean- if the engine IS at TDC, it should have already fired for that cylinder- understand? I can see that you have it severely advanced or retarded (by the twist, I can't remember which way advances or retards off the top of my head). The distributor will work on 3 splines of the drive gear because you can rotate it to compensate. It should be on the middle oadvancedf the three. I have drawn a picture to help you, but I can't upload it because my university blocks port 21. I will send tonight.

Rocker cover looks cool- how'd you do it? Regarding the other small hole, don't worry. They are 'air injectors' for the exhaust, simply for emissions junk. Same with that silver hose you obviously replaced. A lick of paint and the engine bay will look great! Tell me if you need more info.
Al

P.S. I'd paint your radiator black as well, helps with black body radiation, cools more efficiently than silver. Heat transfer 2904 tells me that

ok, then it will be hot when i try to adjust the valve clearences next time.

I think that your picture will help alot but i get the ide, atleast i think so

I have wetsanded the rocker cover with 80p, 100p, 120p, 180p, 240p, 400p, 500p, 600p and finally 1000p.
But i didnt put enought time on each paper, but it's ok.
Then i polished it with 2 types of wax, the first one was a polish wax and the other was a shine wax.
After that i applied regular car hard wax.

i followed this guide:
http://www.supraforu...ad.php?t=274253

I havent painted my radiator as in "now i'm going to paint my radiator", the paint and dust got on there when i painted the area behind the bumpers

Today i discoverd another problem, or a reason to why theres so much water in my trunk.
There seems to be a rust hole under the trim for the rear glass and i think that i have to remove the glass so that i can get to the hole, but i dont know how to remove it, do you know?

btw; here is a link to my project thread on a swedish car forum:
http://www.zatzy.com...ad.php?t=191941

[marcus626LX]

silver_1987_626, on Mar 16 2006, 08:40 AM, said:

I forgot to add in the last post about your carby- you said you cleaned it all out- did you replace all the gaskets? They MUST be done if you take it apart or else it will leak (as in, air will suck in where it is not supposed to). Happened to mine when I made my own gaskets, the material (which was supposed to be fine for petrol...) went hard, and carby was not as smooth as it should be. PM me for msn addy.

al

no i didnt change all the gaskets only the one between the carby and intake manifold.
Then theres only the one between the airhorn and carby-bodie that needs to be changed, right?

[silver_1987_626]

The carb is in three sections, with a spacer and a pre-heater on the manifold. See my pic. All gaskets should be replaced if you have had the carburettor in pieces. Do an overhaul- get a kit and do all the seals in it, its an easy (but kind of time consuming) job.



The distributor should be installed like this when the engine is at TDC. It will work the way you have it, but you get no adjustment because you are one spline out.



al

p.s. There is no need to 'quote' my post to reply, just press the 'add reply' button under the post.

[marcus626LX]

thank you i will take a look at this, at my car tomorrow.

[silver_1987_626]

Great! I await your response in eager anticipation!

al

[marcus626LX]

hehe, just dont hold your breath