Jump to content

JS21-1 Injectors

Recommended Posts

I continue to work on the injection angle and from various sources, have acquired 8 JS21-1 injectors, which are the recommended stock injector for my motor, in its original state. My difficulty is deciding "best bang (or in this case injector) for the buck". Here is how I see the options (feel free to inform if I have missed any)


1. Pick the best looking 4 and run them. Pros- no additional money needed. Cons - one additional concern when the motor will not run after rebuild

2. Take them to be tested somewhere, run the best 4. Pros - should be free or inexpensive. Same Cons

3. Buy rebuild kits to replace wearable parts, self install, then take them to be tested somewhere, run the best 4. Pros - is the cheapest way to semi-trustworthly injectors. Cons approx $25 for 4 $50 for 8 plus price to test bench (test benching to get the best 4 out of the 8 and to understand the flow).

4. Throw some of the old injectors in an "emergency injectors" box and purchase 4 new injectors from China  Pros - new injectors Cons - $50 for 4 and ordering from China "You pays your money and you take your chances.

5. Send the injectors to an injection specialist to be rebuilt. Pros- USA, expert and will flow match all injectors (and advise if increasing the flow would be wise, since the pistons are 1mm overbore) Cons - $80 for 4, $160 for 8.+ shipping

  • Like 1
Link to comment
  • Replies 3
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

  • 4 months later...

 Is it possible to change injecor nozzles for higher flow? I have been reading about injectors and mpg, in many ways mpg is improved by running lean (with knock sensor), but then I read of instances where "too lean" explodes the engine. After research and Ratsun advice, I am forgoing both new cam and new header; keeping the fuel injection, and the 1.00 overbore.

Is it possible and a good idea, for someone focused on mpg and longevity


Please Advise

Link to comment



What ever your engine came with for injectors is good enough. If you were to heavily modify your engine so that it breaths more air (a turbo is a good example) it's possible that your stock injectors might not be able to keep up with the extra air and add enough gas and go lean. Too lean under load can cause damage to engines. Heavy load requires a rich mixture of low 13s even well into the 12s, than a perfect 14.7 to 1.  The extra gas that cannot possibly be burned due to lack of enough oxygen, absorbs heat from evaporation, cooling the combustion chamber and reduces or prevents pre ignition. At full throttle that's a good thing.


Lean, above 14.7 part air to one part fuel, assures there is more than enough air for any amount of fuel so it's burned completely but increasingly lacks power because less fuel. At light throttle this doesn't matter much. It's easy on fuel economy but as it gets leaner and leaner it starts to become harder to fire. You certainly don't want less than 14.7 to 1 at light throttle and cruise. Anything below 14.7 to one the fuel just goes out the tail pipe.  

  • Like 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.