HI all, just had my carbs tuned, they were way out of wack. Now since i have gotten the car back it has been dieseling after i turn it off, what causes this? Before i take my car back and yell i kinda wanna know what the hell is goin on if ya know what i mean!

My car did not do this before i had them tuned.

Thanks,

Paul:ermm:

Two main causes for "dieseling" are idle too fast, and/or timing is a bit too advanced.

If it's idling more than 800 it will do it. If the idle is Ok, double check your static timing..

Haven't i also heard that carbon build up in the cylinders adds to the dieseling, by providing a source of ignition, or something like that??:stupid:

It can, as well as severely fouled plugs, but that is usually in more extreme cases. It could also be that his carbs weren't tuned as well as he thought, but I didn't want to say that...... :cross-eye

From experience with my Z. It used to diesel when I bought it, it was contributed to by a few things.

Vacuum Advance. L's will diesel badly if they have the vacuum advance detached. My car has triple delhortos, so there is no easy way to attach the vacuum advance so I had to work around it (read on). But, if you have the standard carbs make sure the vacuum advance is working and not leaking.

Idle. My car would diesel if the idle was about 1000rpm (or more). If you have a working vaccuum advance this shouldn't be such a problem.

Fuel. Crap fuel will make it diesel. Unleaded fuel will promote dieseling. 240's where designed to run on Leaded petrol and LRP is not as 'good' as leaded, despite what the fuel companies say. Forget LRP, run it on premium unleaded, it will save you money now and in the future as I get more MPG out of premium. So go premium. LRP doesn't help VSR at all there are numerous studies to prove that.

Fuel Cat's. I fitted a fuel cat to my Z. It's Voodoo majic, many people will dish me for this but it actually helped my run-on. I also fitted it to help VSR. I used a tin based one

- Fuelstar.com.au -. They used these (tin cats) in the war to help the mighty merlin engines run on crap fuel so they must do *something*.

OzLime240Z

My Mechanic told me that after adjusting the carbs to run evenly, that he could not get the front carb to idle below 900, he said that the one carb looks like it could be on it's way out... rebuilding might be neccesary down the line. My knowledge when it comes to carbs is very minimal. Is it out of line for me to ask to have this readjusted? Or does someone just have a pair of new 72 SU's theyed like to donate:love: Yeah riiiggghhhht.

I find it hard to believe that your mechanic can't get ONE carb to idle below 900. You should be able to bring it down so far that it will almost die.

I also saw dieseling when I used the 'cheater' idle screw to keep my idle above 1000rpm. I did this because it ran like crap before I knew how to adjust SU's. The cheater idle screw, located on the very top of all the linkage, should never be used. Carbs that are balanced and adjusted correctly should not need this screw.