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Tune 4G15 Carburetor


Iroshw
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Hi guys,

I have Mitsubishi C62A (known as ASP Model 1991). It has 4G15 engine and very powerful. But I'm not happy with the fuel efficiency of this car. And there is a black smoke as well. I just surf the new and found this car does 14km/1ltr (average). But my one is doing nearly 8km/1ltr (without AC).

I was searching a solution through net since I'm really really tired with garages. I took my vehicle to a lot of place to solve this issue. But so far no good result.

I found some instructions from a forum. This is about tuning the engine (4G15). Please check this and let me know your feedback since I'm going to try this on Saturday :).

1) Warm up engine first(run 5-10 mins)
2)Shut off engine
3) Back out on the idle speed screw until it justt doesn't touch the throttle linkage. Then screw it in back about 11 turns (what this does mean actually?)
4) Screw in the A/F mixture screw until it stops(do not force tighten)
5) Screw out the A/F mixture screw 2 full turns
6) Start the damn car. It will run like its choking. As long as it's running it's ok.
7) Now turn in the A/F screw until engine dies. If this happens, turn out the A.F screw half turn at a time to bring it back. (try to start the car of coz) (what this does mean?)
8)Continue to turn out the A/F screw at half turns every 3 seconds. Engine will pick up speed. Continue to screw out until the point engine runs worse. When that happens screw back in half turn every 3 secs to the point engine runs smoothest.(do this by ear or watch engine vibration) (what this does mean?)
9) Now set the idle speed. Go on the air conditioner. Watch the tachometer. Turn in the idle speed screw until rpm is around 900 to 1000 rpm.
10) Now it's ready to rumble..

black smoke also caused by KO piston ring (what this does mean?).. check the compression

screwsqr2.jpg

Guys, please let me know your feedback, is it ok if I follow this to tune my engine? Only problem is my AC is not working. So will it be a problem for me to follow these steps since it says that I need AC to be on during the process. Please advise.

Will this help to get a good fuel efficiency and stop black smoke?

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Before you attempt any adjustment in the carb it is better to spray a crab cleaner down the barrel with engine revved up to ensure that you do not have carbon deposits that may mess up the adjustments later on. Also for the carb shown (4G15s came with a conventional carb too) adjusting the A/F mixture at idle will not have a major impact on fuel consumption. I do not think you get black smoke on idle. Make sure you have good clean spark plugs before you begin the procedure. Also make sure your ignition timing is correct (hope this must have been checked and set correct)

As for the steps you need not worry about 2 and 3 (11 turns must be a mistake anyway. It is to set the throttle opening roughly to idle setting and 11/2 to 2 turns will do) since the car must be idling fine now. But if the idle speed increases while you adjust A/F you can back it off a bit. After Step 1 note the current idle speed. Go to step 7 and go on turning the A/F screw by 1/2 turns until you feel the onset of engine stalling. This is the lean mixture limit. Then back off the A/F screw (Step 8) until engine idles smooth at around 800 RPM or more. If the idle speed is more adjust the idle speed screw a bit and repeat the Step 7 and 8 once again.(You can do this adjustment ignoring the settings for AC). Before doing the adjustment and after the car has warmed up, feel and smell (health hazard but only if you do it everyday) the exhaust for steam and unburned fuel. After the adjustment compare the results.

However as I mentioned before this will not solve your problem of black smoke at high revs.

Edited by Rumesh88
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Before you attempt any adjustment in the carb it is better to spray a crab cleaner down the barrel with engine revved up to ensure that you do not have carbon deposits that may mess up the adjustments later on. Also for the carb shown (4G15s came with a conventional carb too) adjusting the A/F mixture at idle will not have a major impact on fuel consumption. I do not think you get black smoke on idle. Make sure you have good clean spark plugs before you begin the procedure. Also make sure your ignition timing is correct (hope this must have been checked and set correct)

As for the steps you need not worry about 2 and 3 (11 turns must be a mistake anyway. It is to set the throttle opening roughly to idle setting and 11/2 to 2 turns will do) since the car must be idling fine now. But if the idle speed increases while you adjust A/F you can back it off a bit. After Step 1 note the current idle speed. Go to step 7 and go on turning the A/F screw by 1/2 turns until you feel the onset of engine stalling. This is the lean mixture limit. Then back off the A/F screw (Step 8) until engine idles smooth at around 800 RPM or more. If the idle speed is more adjust the idle speed screw a bit and repeat the Step 7 and 8 once again.(You can do this adjustment ignoring the settings for AC). Before doing the adjustment and after the car has warmed up, feel and smell (health hazard but only if you do it everyday) the exhaust for steam and unburned fuel. After the adjustment compare the results.

However as I mentioned before this will not solve your problem of black smoke at high revs.

Thank you for the comment Rumesh. I actually used a Carb Cleaner few months ago. It actually worked but only for a few days.

The problem is, it is difficult to touch and see the A/F screw since it is located at the back of the Carb close to the Car dash wall (from inside). Can touch the screw by hand but can't see it. And, do I need to screw it to rightside (clockwise) or ?

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Hi

3) Back out on the idle speed screw until it justt doesn't touch the throttle linkage. Then screw it in back about 11 turns (what this does mean actually?)

This is to keep the engine idling without keeping the leg on accelarator padel,

7) Now turn in the A/F screw until engine dies. If this happens, turn out the A.F screw half turn at a time to bring it back. (try to start the car of coz) (what this does mean?)

when turning Af screw in you are leaning the mixture (means you reduce the amount of fuel to a given air intake), when you keep on turning it in engine will die means there is not enough fuel passes throught idle circuit,so that is why they wanted to back it half after engine die, if not car will not start it back

8)Continue to turn out the A/F screw at half turns every 3 seconds. Engine will pick up speed. Continue to screw out until the point engine runs worse. When that happens screw back in half turn every 3 secs to the point engine runs smoothest.(do this by ear or watch engine vibration) (what this does mean?)

turn the af screw out , then engine will start increaing it's rpm , each and every turn you must give few seconds to engine to adjust itself for new settings, stop it somewhere when you feel engine has sufficient rpm and doesn't shake it self or stumble

(if you have a rpm and vacumm guage you should get maximum vacum and your normal idle speed)

as a tip because you are new do this ,

Keep a full glass of water on the engine bay and watch it should not spill or shake much

then try to gas it at once hard it should not stumble or jerk , asssume this is fairly good


black smoke also caused by KO piston ring (what this does mean?).. check the compression

you got worn piston or rims or leaking valve seats or guide , keep the finger inside the tail pipe and see if it is oily then you have a engine repair to be done

if you have oversize carburator main jets none of these will work better you got o reduce them to a lawer size

thanks

regards

sumith

Edited by Sumiya
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Thank you for the comment Rumesh. I actually used a Carb Cleaner few months ago. It actually worked but only for a few days.

The problem is, it is difficult to touch and see the A/F screw since it is located at the back of the Carb close to the Car dash wall (from inside). Can touch the screw by hand but can't see it. And, do I need to screw it to rightside (clockwise) or ?

If you have cleaned it recently no need to do it again. The difficult part in this adjustment is as you said accessing the screw without actually seeing it because of the air cleaner obstructing the view. In fact Mitsubishi recommends the use of a special tool for this. If you can get a small piece of a hacksaw blade cut and filed to requied size, that is the best. For Step 7 turn clockwise and 8 the other way. Try Sumiya's tips above.

BTW has anyone meddled with this carb before?

Edited by Rumesh88
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If you have cleaned it recently no need to do it again. The difficult part in this adjustment is as you said accessing the screw without actually seeing it because of the air cleaner obstructing the view. In fact Mitsubishi recommends the use of a special tool for this. If you can get a small piece of a hacksaw blade cut and filed to requied size, that is the best. For Step 7 turn clockwise and 8 the other way. Try Sumiya's tips above.

BTW has anyone meddled with this carb before?

Rumesh: I think YES. Since as per the 4G15 manual Main Jet screw is sealed with a special cover, but mine is open and there is no sealed clip. Simply means someone has played with it and lost the seal. I bought this 2 years ago. Actually this car is really fast but the problem is Fuel efficiency.

Also noticed that sometimes when I accelerate (say I'm in 4th Gear) I can see the RPM goes up but my car is still at the same speed. But when I accelerate slowly it start increasing the speed. And I feel that the car picking up has gone down too.

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Rumesh: I think YES. Since as per the 4G15 manual Main Jet screw is sealed with a special cover, but mine is open and there is no sealed clip. Simply means someone has played with it and lost the seal. I bought this 2 years ago. Actually this car is really fast but the problem is Fuel efficiency.

Also noticed that sometimes when I accelerate (say I'm in 4th Gear) I can see the RPM goes up but my car is still at the same speed. But when I accelerate slowly it start increasing the speed. And I feel that the car picking up has gone down too.

That is exactly what I wanted to know. Once the seal is taken out you cannot put it back but that is not a problem. However, in that case how do you know if the main jet adjustment is correct or not? BTW what were your ECO test results at both idle and 2500 RPM. That would give you a clue.

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Rumesh, I did an ECO test a few weeks ago and did Fail :(. I really need to get this thing fixed to take the 2nd test.

And, as per this image there are three screws. But actually there are 4 screws including the main jet. Two as showed in the pic and there is another, can see it. I can remember one garage guy screwed it to set my idle RPM also the other two screws. But he didn't touch the main jet.

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In that case make sure idle is set with the correct screw (one near the carb bottom). Leave the other one backed off a bit for it is of no use now without AC. If the idle is set at a wrong point, a correct setting will improve on your ECO results, but that alone would not be enough. After doing the idle setting properly be prepared for the main jet adjustment too if you want to get your ECO test passed. But take your time to observe the improvements. How about your plugs after a good run? Do you find carbon deposits on the ceramic tip?

Any vacuum hoses removed or plugged up?

Edited by Rumesh88
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sorry to go bit OT. Is this the carb that garage guys called as "bothal carb" where piston is placed horizontally ? My 1994 Lancer CB2 has the same and looks similar to above. My mechanic said it's hard to keep the tune of these types of carbs. Is this true? what would be the best replacement if i were to change the carb? I'm facing bit of idle related issues with may carb.

Edited by hrm
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To my knowledge they use this term to identify both horizontal and vertical piston types. It is not harder to tune these carbs compared to more common "fixed venturi down draft types" but you need to monitor the exhaust gases to determine the exact tuning to the OEM specs. Thus an ordinary mech may find it difficult. In fixed venturi types as the name suggests the fuel metering is fixed hence all you need to do is to set the idle speed and the air/fuel ratio at idle. What exactly is your issue at idle?

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To my knowledge they use this term to identify both horizontal and vertical piston types. It is not harder to tune these carbs compared to more common "fixed venturi down draft types" but you need to monitor the exhaust gases to determine the exact tuning to the OEM specs. Thus an ordinary mech may find it difficult. In fixed venturi types as the name suggests the fuel metering is fixed hence all you need to do is to set the idle speed and the air/fuel ratio at idle. What exactly is your issue at idle?

Thanks Rumesh88 for the reply.

The issue is when I take the car to the mechanic they set the idle to 750 rpm and it will remain there fine at that moment. If I turn on the AC idle goes up to like 900. But when the AC is off idle come down to about 600. Like wise idle keeps changing time to time. Sometimes when I start the car after a drive as soon as I start, idle stays very low like 150 and car starts to wobble. Then I had to press gas a bit and then it comes to some speed like 600 and this will change again time to time.

When I told this to my mechanic he said the carb.s door is not been functioning well. What's actually wrong with the carb?

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@hrm

If that is the case, the piston may not be moving freely on its (linear) bearing particularly towards the end of its travel. Can be the door but some what unlikely. This piston is supposed to move horizontally by an amount proportional to the vacuum. Trying to clean the carb from top by spraying carb cleaners may make the matters worse sometimes if the dissolved gunk ends up on the piston mechanism. Best way to clean the piston mechanism of these carbs, if at all necessary to do so, is to remove the mechanism and wipe all the deposits clean with petrol. One should take extreme care is re-installing the piston to prevent damage to the needle. Do you have same problem at cold start? How was your eco test last time? What were the CO reading at idle and 2500rpm?

Edited by Rumesh88
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@hrm

If that is the case, the piston may not be moving freely on its (linear) bearing particularly towards the end of its travel. Can be the door but some what unlikely. This piston is supposed to move horizontally by an amount proportional to the vacuum. Trying to clean the carb from top by spraying carb cleaners may make the matters worse sometimes if the dissolved gunk ends up on the piston mechanism. Best way to clean the piston mechanism of these carbs, if at all necessary to do so, is to remove the mechanism and wipe all the deposits clean with petrol. One should take extreme care is re-installing the piston to prevent damage to the needle. Do you have same problem at cold start? How was your eco test last time? What were the CO reading at idle and 2500rpm?

At cold start no big issue. It happens when the engine turns hot after some driving. Eco test failed at first time. Then I got the air filter cleaned and adjusted the idle a little bit then got passed. Let say barely passed. CO level is close to 4.0 at idle. At 2500 it is very less 0.2 or something

Edited by hrm
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This means you already had the answer with you. I do not know why our mechs do not make better use of the eco readings. In your case it is not difficult to adjust the carb because you need to get only the idle mixture screw set, but it may not be perhaps possible if the piston fails to home in at idle position due to restricted movement. You can test this if you make sure the car idles at 600 (or whatever stable speed without AC) before you stop the engine after a drive. Now when you restart the engine it should idle at the same stable speed. If u try to rev the engine just before stopping, as many of us got used to, the piston may get stuck at a random position thus giving you trouble when you restart and idle. If you observe this behavior of the carb, get your piston mechanism cleaned so that it moves freely all the way. At the same time get the carb needle too checked for damage.

Thanks a lot machan for the insight !! will check them soon

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Dear Rumesh,

I'mm having a Lancer CK2 with 4g15 engine. But the carb of it gives a lot of problems. It has cold start problem. Until the car gets heated, it cannot be driven and gives knocking. and the fuel consumption is very bad (8.5 - 9 km/l in Colombo without AC). Fuel cannot be adjusted further and if done so, it also leads to knocking when accelerating in first and second gears.

Vacuum lines of the carburetor is also wrongly connected for sure. There are two green colour Vacuum Control valves and bothe of them were bypassed and no line is connected to the auto choke.

I'm also thinking of replacing the carb and thought to order one from alibaba.com.

Please help to overcome this problem.

Thank you

Kusal

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Dear Rumesh,

I'mm having a Lancer CK2 with 4g15 engine. But the carb of it gives a lot of problems. It has cold start problem. Until the car gets heated, it cannot be driven and gives knocking. and the fuel consumption is very bad (8.5 - 9 km/l in Colombo without AC). Fuel cannot be adjusted further and if done so, it also leads to knocking when accelerating in first and second gears.

Vacuum lines of the carburetor is also wrongly connected for sure. There are two green colour Vacuum Control valves and bothe of them were bypassed and no line is connected to the auto choke.

I'm also thinking of replacing the carb and thought to order one from alibaba.com.

Please help to overcome this problem.

Thank you

Kusal

I'm sure Rumesh will provide his expert commentary very soon.

In the meantime the first course of action is to have your carburettor serviced and rebuilt. In the forum Mr Dhammika Fernando at Cotta Road has been mentioned a few times in a positive light for this sort of work. I'm sure others will weigh in with their own choices.

Do not import Carbs through Alibaba. What you are likely to get is a chinese clone. What you need to do is get yourself a genuine carb repair kit and rebuild the car replacing worn components. While you do this, you can check out the vaccume lines and the solenoids which activate them. I believe they are electronically controlled in the CK2 4G15.

The behaviour you mentioned sounds similar to what happens when the jets are either the wrong size or are blocked, and this gets better when the engine warms up.

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I'm sure Rumesh will provide his expert commentary very soon.

In the meantime the first course of action is to have your carburettor serviced and rebuilt. In the forum Mr Dhammika Fernando at Cotta Road has been mentioned a few times in a positive light for this sort of work. I'm sure others will weigh in with their own choices.

Do not import Carbs through Alibaba. What you are likely to get is a chinese clone. What you need to do is get yourself a genuine carb repair kit and rebuild the car replacing worn components. While you do this, you can check out the vaccume lines and the solenoids which activate them. I believe they are electronically controlled in the CK2 4G15.

The behaviour you mentioned sounds similar to what happens when the jets are either the wrong size or are blocked, and this gets better when the engine warms up.

This i highly recommend through my experience.. I was experiencing some what similar issues with my carb and non of the cleaning and using non genuine carb repair kits did work. Ultimately got myself a genuine card repair kit (Mind you its expensive) and got the problem solved.

I had damaged plug wires on top of a bad carb and fuel figure dropped to 4-5 kmpl in city.

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<blockquote class="ipsBlockquote" data-author="kusalk" data-cid="272881" data-time="1424708011">Dear Rumesh,

<p>I'mm having a Lancer CK2 with 4g15 engine. But the carb of it gives a lot of problems. It has cold start problem. Until the car gets heated, it cannot be driven and gives knocking. and the fuel consumption is very bad (8.5 - 9 km/l in Colombo without AC). Fuel cannot be adjusted further and if done so, it also leads to knocking when accelerating in first and second gears.</p>

<p> </p>

<p>Vacuum lines of the carburetor is also wrongly connected for sure. There are two green colour Vacuum Control valves and bothe of them were bypassed and no line is connected to the auto choke.</p>

<p> </p>

<p>I'm also thinking of replacing the carb and thought to order one from <a href="http://www.alibaba.com/product-detail/Mitsubishi-Proton-4G15-carburettor-MD192036_157009818.html">alibaba.com</a>.</p>

<p> </p>

<p>Please help to overcome this problem.</p>

<p> </p>

<p>Thank you</p>

<p>Kusal</p>

</blockquote>

<p>100% agree with The Don's comments above. In addition to the vacuum lines there should be two coolant lines to the auto choke. The coolant serves to warm the wax pellet inside the auto choke which in turn turns the idle cam and switches the three vacuum lines connected it to provide the cold start boost. If this is not happening you need to get that part attended first. All the vacuum lines should be connected to their proper ports before a tune up on the carb can be done. Depending on the condition of the main jet you may have to do a rebuild as Don has suggested but before doing all that you need to get the your vacuum/coolant lines connected and working and to re-assess the overall situation. AFAIK Mr. Dhammika will not undertake carb repairs/rebuilds but you can ask and get his advise. Once you get all the mechanisms working then go for a tune up.</p>

Edited by Rumesh88
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You can use this site to get a vacuum diagram of your car https://partsouq.com/en/catalog/Mitsubishi

Go in a region and select the model and look for CK2A. Then select the model code. Vacuum diagram is in ENGINE \ EMISSION CONTROL.

Most of our basses will mess-up the vacuum lines. So take it to a reputed guy. Also make sure the vacuum lines are not blocked. Once I found a small metal ball in a vacuum line.

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Thank you very much every body.

I tried several times cleaning and putting carb repair kit bought from Panchikawaththa but not worked. Actually I have no idea about the fuel jets. Water lines to the choke are connected properly but in this model, there is only one vacuum line in to the choke and it also kept open. One of the rubber hoses is blocked using a small metal ball.

I found the emission control vacuum lines from the link given above and corrected some of the lines but not the line for the choke and lines from the air cleaner.

With all these problems and considering your suggestions, I'm thinking of getting advise from Mr. Dhammika Fernando. I found his number form somewhere in the forum. If he is not undertaking repairs, who do you guys suggest to show the carb for cleaning and tuning?

Thank you guys again

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This must be your auto-choke

If you intend to get it tuned from Mr. Dhammika best thing is to get his recommendation for a mechanic.
Note the two black arrows. That the auto-choke travel from cold start to warm up. Yes you should have only one vacuum connection to the choke.
Edited by Rumesh88
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Hi Guys,

I met Mr. Dammika and he corrected all the vacuum lines. According to him, the carb has to be replaced since a small portion of the needle of the piston has been cut.

Now the timing, ignition etc are OK. Talked to another guy for repairing or replacing the carb and still waiting to fix an appoinment

Mr. Dhammika is a highly professional person and his work is highly methodical unlike other basas.

Thank you very much for you all for directing me to the correct place

Kusal Suraweera

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Hi Guys,

I met Mr. Dammika and he corrected all the vacuum lines. According to him, the carb has to be replaced since a small portion of the needle of the piston has been cut.

Now the timing, ignition etc are OK. Talked to another guy for repairing or replacing the carb and still waiting to fix an appoinment

Mr. Dhammika is a highly professional person and his work is highly methodical unlike other basas.

Thank you very much for you all for directing me to the correct place

Kusal Suraweera

Not clear as to why your carburetor needs to be replaced because the piston is damaged. I'm pretty sure you get the piston as a part of the (genuine) carburetor repair kit.

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