what will be the main reason for a car sort jerk while accelerate..?

it happen when i gas on to reach a normal speed to 60-80km/h

 

* engine model 3k (4 speed)

Ignition breakdown- take the bonnet of and go for a drive at night. Look for green sparks jumping off the coil or leads.

 

A- Clean the top of the coil and the dizzy cap, (inside and out) wipe the leads and clean the plugs. Spray with CRC 556 or WD40 or similar, then try it.

 

B- Take the plugs out and compare them, look for a pug that is darker or dirtier than the others. If so it might be that plug, that lead or that pole on the dizzy cap. Swap them around and follow it. Make sure they have the correct gap and the points and timing are correct too.

 

C- Check the points and change the condensor. If there are no obvious sparks jumping off the coil or no dirty lines showing tracking on the top, swap the coil and swap the ballast resistor.

 

That will all eliminate the electrical side of misfires. After that comes carb... enough fuel to cruise, but not enough to feed acceleration. See how you go with the electrics first.

Ignition breakdown- take the bonnet of and go for a drive at night. Look for green sparks jumping off the coil or leads.

 

A- Clean the top of the coil and the dizzy cap, (inside and out) wipe the leads and clean the plugs. Spray with CRC 556 or WD40 or similar, then try it.

 

B- Take the plugs out and compare them, look for a pug that is darker or dirtier than the others. If so it might be that plug, that lead or that pole on the dizzy cap. Swap them around and follow it. Make sure they have the correct gap and the points and timing are correct too.

 

C- Check the points and change the condensor. If there are no obvious sparks jumping off the coil or no dirty lines showing tracking on the top, swap the coil and swap the ballast resistor.

 

That will all eliminate the electrical side of misfires. After that comes carb... enough fuel to cruise, but not enough to feed acceleration. See how you go with the electrics first.

 

Had check all that u had suggest...run it this morning to work..its totally jerk to off when running...the engine off when i try to accelerate..it jusz run when i adjust dizzy timing to higher...please help..

Take off the aircleaner top and look down the carb. Open the throttle quickly and see if petrol squirts down into the carb.

Take off the aircleaner top and look down the carb. Open the throttle quickly and see if petrol squirts down into the carb.

 

my carb is nikki model that has shown petrol level.. i hd check that its full..and i jz clean up the carb with carb cleaner..its start slow now...

I wonder if the Nikki is not jetted down enough or has the wrong choke size to run a 3K...

 

When you check for petrol squirting down the throat, read the number off the choke in each throat. Should be 27 to 33 or so.

I wonder if the Nikki is not jetted down enough or has the wrong choke size to run a 3K...

 

When you check for petrol squirting down the throat, read the number off the choke in each throat. Should be 27 to 33 or so.

 

u have an instruction on how to check it...??

Some carbs have the size stamped on them, so you can see the number when you look down the throat.

 

The chokes (also called "venturi" becasue that's the effect they have) can sometimes be pulled out by themselves to measure the diameter of the hole, or sometimes are part of a larger fitting. You just pull the carb to bits.

 

You can measure the chokes one way or the other, or you can find out what the Nikki came off and Google that specs of that carb.

 

If the hole is too big it will not give enough air velocity at low revs to pull fuel in properly, and if it is too small the low revs are great but it won't rev so high. (it gets 'choked')

 

If nothing else, you need to spend a couple of hours on the net learning how carbs work and what parts of a carb is important. There is some great stuff around. You should be able to confirm that your carb will work for your motor, and which part of the rev range it will be good or bad at. My inch & 1/4 SUs are smaller than most guys use, and I know they are good at low revs but no good at 6500rpm. They were lean on my motor (designed for a smaller one) when I got them and I had to modify them to get them right. You might have to do the same.

 

If you have had the carb on for 6months and it ran fine, then the problem is probably elsewhere, but if you've just fitted it then it is most likely the trouble. You can see that you have to know plenty about how a car works just to explain to us when is wrong and what the car is doing.

had a similar issue, timing was off, so reset everything and car is smooth as now

nice tips dude..will check it ASAP...its been 2 years the carb sit on my ke20..it had this prob since i use it last few years..

 

* slow start but run normal..

* easy start but run poor (jerking)

 

what i do is only tune the dizzy...and change the contact & plug every month..if not..it would't run me to work...

 

 

BTW rthy..how do you reset everything..?

Edited July 10, 201313 yr by jasonke20

.its been 2 years the carb sit on my ke20..it had this prob since i use it last few years..

 

Well, if the problem has been there since you fitted the carb, it will be the place to look.

 

Check for inlet leaks by spraying an aerosol all over the gasket where the carb joins the manifol and the manifold joins the head, do it with the motor running.

 

If that doesn't change anything have it dyno tested so they can measure the fuel mixture while under load and see if the carb jets are making it rich or lean. Then you know where to start to modify the carb.

 

Any idea what the carb was off??

 

One other thing to look at, when you change the points and plugs, have you changed the condensor or coil?? Either could cause the problem.

You need to buy a timing light.

Well, if the problem has been there since you fitted the carb, it will be the place to look.

 

Check for inlet leaks by spraying an aerosol all over the gasket where the carb joins the manifol and the manifold joins the head, do it with the motor running.

 

If that doesn't change anything have it dyno tested so they can measure the fuel mixture while under load and see if the carb jets are making it rich or lean. Then you know where to start to modify the carb.

 

Any idea what the carb was off??

 

One other thing to look at, when you change the points and plugs, have you changed the condensor or coil?? Either could cause the problem.

everything had been change accept the coil...i didt much sure if it has breakdown or else..jz mention that it become hot after a ran..

.jz mention that it become hot after a ran.

If the timing is too retarded it will run hot... also running lean makes it hot, or poor cooling system.

 

You need to buy a timing light.

Gav is right....

had a top overhaul my engine last few days..no more jerk and it run smooth but a common prob still there..the engine hard to start..it start slow..is it starter prob..? already change starter carbon..any tips on how to check or service instead of change a new one..?