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4K-C Timing and Jetting DCOE 45


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It will run poorly and you will struggle trying to get small enough chokes.  You need to dramatically increase the airflow to make it work. 

This was a thread I posted years back with some suggested settings on various applications. I can’t open the thread, not sure why, but if you can it may help


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Yeah, a waste of a good carb without more compression, some porting and a good cam.

This is what you're after-



Leave the timing at 8deg and see if it pinks with 98octane. I doubt it will with stock compression.

Get good fuel usage figures before you fit it, then again afterwards. I'n dying to see how much difference it makes!



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Look down a throat and read the size of the choke.  Should be 25 to 35 cast in the alloy.

"Weber emulsion tube numbers were assigned chronologically, as each design was introduced. It is not linear (a smaller number does not necessarily mean a leaner or richer mixture). The F7 will richen the low end and initial throttle response. The F2 will lean out the low end and initial throttle response (F11 and F16 also lean out the low end, to a lesser extent). The F9, F11, and F16 are the most common sizes. F2 and F7 are recommended when using alcohol fuel."

You can see the mains and the air correctors are too big when a 140 170 is running a 2litre Celica.

K motors will run with plenty of advance, so 12deg is fine.  In the end too much advance will lose power, so you will have to sort that out last.

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What does it drive like at the moment??  What does it easily rev to in 3rd gear?? I would expect the compression and cam are holding it back.

You should drop the chokes down to 27 or 28, according to the Weber chart, and drop the jets too, but you will probably just end up with a smoother bottom end and better fuel economy. If it will get up to the revs where it is using the carb you have you probably won't get the top end any better. To make the carb really work you'll need a cam & a head job too.

Find a long uphill where you can hold your foot flat in 3rd from say 60 to 110kph and time that with a stopwatch. Use that as a base time and get a cam cut for it. Time it again. Do a head job and time it again, then finally change the carb stuff.

If you spend money on the carb now you'll be trapped with you've got, as the new jets will be wrong for a hot cam or a porting job, so do the carb last. You might find you can build the rest of the engine to match that carb.

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It may be that the bigger carb setup is feeding the motor everything it needs by half-throttle & the motor can go no faster.

Can you beg/borrow/steal a pair of 28s or 30 chokes, or a pair of 34s.  Just swapping chokes will tell you if it has all the top end it can handle with 32s and big jets, or do those jets need a bigger choke. If 34s make no difference then you've reached the limit of the motor.  Its the only way to see if it can be improved without spending cash just to find out you need a head job. Do you have a motor race circuit neaby??  Those guys carry all sorts of Weber parts with them.

A dyno printout will tell you, but there goes $120.


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