Engine idles but hesitates around 3000rpm timing suspected

[Jordon]

So after getting the car to start and keeping idle without stalling I started to try and fix my hesitation problems

 

So far I have:

*Replaced the spark plugs, mechanical points, ignition leads and coil. (After I did all this I noticed easier starting, less stalling off idle when throttle is applied and no more popping.)

 

*brought cylinder 1 to top dead center, verified by shining a light in and moving the cylinder back and forward until I got it as close as I could. I then pulled the rotor cap off and checked to see that the rotor was pointing at #1 spark plug. I then marked a new timing mark on the balancer as the stock one was nowhere to be seen

 

*checked then checked again to make sure I got my firing order right and the plugs were in the respective places.

 

*I then started the engine, got my timing light hooked up and had a look. Now I'm lost, the mark I made was at least two inches past the 20 degree timing mark, the engine idles well at this point. If I try and retard the distributor it starts to run rough, the same happens when I try to advance it. When I rev the engine at this point either progressively or suddenly it will hesitate and then stall if I keep the throttle applied.

 

Fuel has been checked and my fuel pump is rooted but I am keeping the fuel level up manually

 

Really stuck at the moment.

Thanks for your help in advance.

[Miles]

And your car is a (yr)   ________________.

 

Carb or FI?

 

Other details?

[Jordon]

Sorry, totally forgot all that

 

It's a 1973 240z. 2.4 stock engine and it's carburetted. Manual transmission.

[Miles]

The popping and stalling (lean sag) suggests a too lean setting for the carbs.

 

Assuming that you have SU carbs:

 

Try adjusting the  the carb mixture:

 

There is a mixture adjustment  wheel  at the bottom of each carb. It has click stops as you turn it.

 

1. With the engine off:  On each carb turn the adjustement wheel  all the way counter clockwise (looking top down) until it stops.  This is the max lean position of the carb and your starting point for adjustment. Mark each adjustment wheel so you can count the number of turns.

 

2. With the engine off:  Next turn each adjuster clockwise (looking top down) 2.5 turns.  You are now 2.5 turns in the rich direction. This is your starting position to fine tune the mixture.

 

3. With the engine running. Play with the mixture adustment until the popping and stalling (lean sag) goes away. This should be somewhere between 2.5 and 3 turns out on each mixture adjustment wheel. In the end,  one carb may have to be adjusted richer or leaner then the other until you reach the best setting.

 

If you are not familiar with SU carbs you need to purchase the ZTherapy video "Just SUs".  The video will explain exactly how to adjust and rebuild the SU carb.

 

Your carbs may need to be rebuilt. You may have other issues, but the above procedure should get your engine running in most cases.

[Jordon]

Thanks for that miles, I have the car idling great now but I am still having the hesitation but it has moved way up to around 5000rpm. I will get the video and have a go at rebuilding the SUs

Thank you again.

I spent so much time thinking it was definitely the ignition because I had fuel and just overlooked the carbies being out of tune/needing a rebuild.

[daddydonuts]

If you have SU's then Miles is correct, I would also check the float bowl levels... they need to be the same. If that fails, I would look at replacing the points ignition...I put a pertronix electric ignition in my 73 and it took all of the timing, idle and hesitation issues out of that engine...plus it is budget friendly

Edited July 16, 2013 by daddydonuts

[Jordon]

I may also have an issue with my float bowls then. I have round top SUs, right now I am just waiting on a replacement float I have just been keeping them topped up manually.

 

I eventually would like to go the pertronix route but that will have to wait till after I sort out the carbies now.

 

Thanks again guys, I will post again after I have the carbies sorted as to whether that solves my problem completely.

[Tony D]

" I then marked a new timing mark on the balancer as the stock one was nowhere to be seen"

 

Oh no, my good son, this is not how it is to be done!

 

Dial indicator, or TDC stop will get you to a "Mark your balancer point"--mere eyes will only get you...ah..."about 2" from where it should be"!

 

Getting your timing to a KNOWN value will enhance all the above suggestions from Miles, et al...