What is the rpm at idle and does the LED turn off when revving up engine?

 

Idles at 800 rpm ,did not turn off when revved to 4000 rpm

 

Need to lower the value of R4.
Try something around 60K.
Do you have more of those 120K resistors?

 

Yes

 

Connect two 120K resistors from pin3 to ground and try again.
Once the rpm reaches the trigger frequency the LED should be ON and stay ON until the rpm drops a little below that frequency.

 

You did it! It kicks on a little early 1500 rpm and stays on until the rpms hit 800 then goes out.

 

Good now we know the circuit is working. Is you preference, closer to 2500 and or what?

 

Yes I would like to get it between 1800 and 2500

 

Replacing R4 with a 43K resistor should be about right.

 

Or adding one more 120K resistor from pin3 to ground should get there also.

 

I ll try it.and the output should trigger the relay

 

I ll try it.and the output should trigger the relay

Correct.

 

Added another resistor and it now switches the relay at 2500rpm.many thanks for working with me. Can I leave it on the breadboard or have a pcb built.its probably going to be a one only

 

Your welcome
I wouldn't leave it on the breadboard.
If it's only one unit I recommend installing on a perfboard for reliability.

 

Ok ill let you know how it turns out

 

Take a look and let me know if this looks right

 

Can't tell exactly from the photo because the wires are obstructing the view.down on pins1and 2.
Looking at the terminal numbers on the perfboard, 2 and 4 should be at ground and the blue wire on 5.
On a perfboard none of the holes are connected to each other which requires jumpers on the bottom or top side of the board for continuity.
Show a photo of the other side of the board.

 

I jumpered 2 to 4 .and ordered a pair of snippers to clean it up a bit

 

You don't appear to be using enough heat when soldering, as some of those connections look like possible cold joints.
All the joints should have smooth solder around them.
And the 5th top joint from the left on the bottom row is not soldered. Shout it be?

 

I jumpered 2 to 4 .and ordered a pair of snippers to clean it up a bitView attachment 345426

OK, didn't know that board had common vertical traces.
Still can't tell if it’s correct though.
Would definitely try cleaning it up then give a test.