Carburation problem

In a fit of enthusiasm some 8 yrs ago I fitted a reconditioned motor, & installed a set of 240Z carbs, which I had reconditioned by specialists, in place of the 260Z flat-top carbs. However, I had no sooner got the carbs back but the car went into storage due to changes in circumstances & has remained since, I came very close to selling it at one point but decided to keep it & am now glad I did.

Now I'm in the process of trying to get it mobile again, going over the whole car & refreshing or replacing anything that looks tired.

I've been trying to start it but the front 3 cylinders & sparkplugs are totally black dry sooted & fouled. Even #4 plug gets affected. I've tried balancing the carbs carefully & leaning the front one right off but all to nil effect, there doesn't appear to be enough lean adjustment & the plugs just keep on heavily sooting up so the car struggles to run at all & then stalls. Motor is fresh, not even run in.

So it's got to be the front carb at fault, surely. Maybe it was reconditioned with the wrong parts, not that there are many parts in the things. Before I pull the carbs off, has anyone struck this before?

Any advice or leads would be really appreciated, it's driving me nuts. The Xmas/NY break will give me a chance to work on it.

Thanks for your help guys, I'll try all those suggestions over the weekend. NGK it is, BP6ES if I recall correctly.

Float in the front carb has filled with fuel and "sunk".

I had my front carby float stick open once. It was a simple matter of taking the float chamber lid off (four screws) and bending the small metal tab so that it will engage the fuel valve sooner. I suspect this is not the case for you however as you did not complain about fuel leaking from the throat of your carby, which is what I experienced.

If I were you I would replace all the plugs with NGK BP"5"ES (5 means hotter, and many people on this forum have agreed that the hotter plug is better for a road car). At the same time I would also replace your leads, just to be sure it's not them. It is also possible that your dizzy needs a new cap, so I'd replace this at the same time. If you have ever considered putting an electric dizzy on the car, this would be the perfect time. Everyone here agrees they make a big improvement to the engine.

I'd also suggest checking the valve clearances on your engine. If you haven't done it before it is probably better to get someone to show you rather than trying to learn from a book.

If your front three cylinders are still running rich after this then I'd be taking it to a specialist again.

May I suggest you start with checking the choke function ie moves freely and not stuck closed, then I would check that the float level is correct, that the needle and seat function ie moves freely and stops fuel entering the float chamber when closed. Make sure the float actually floats and is not sinking and that it does not have fuel in it. Check the piston moves freely and is not seized. Make sure that there is no other source of fuel for those cylinders like from a vacuum line etc.

Black soot indicates inefficient combustion process so do not discount that there may be a vacuum leak in the front three cylinders too.

Tight or leaking exhaust valves will cause a fine black mark to form on the electrode surface of a spark plug but not usually at idle and it is not a soot but more a stain.

Spark at the cylinders is easily confirmed. New plugs would be great however you will foul anything you put into the cylinder until you fix the problem so perhaps just remove and clean them and then replace them when the problem is fixed.

Failing all of the above, strip and inspect. Happy hunting.

May I suggest you start with checking the choke function ie moves freely and not stuck closed, then I would check that the float level is correct, that the needle and seat function ie moves freely and stops fuel entering the float chamber when closed. Make sure the float actually floats and is not sinking and that it does not have fuel in it. Check the piston moves freely and is not seized. Make sure that there is no other source of fuel for those cylinders like from a vacuum line etc.

 

Black soot indicates inefficient combustion process so do not discount that there may be a vacuum leak in the front three cylinders too.

 

Tight or leaking exhaust valves will cause a fine black mark to form on the electrode surface of a spark plug but not usually at idle and it is not a soot but more a stain.

 

Spark at the cylinders is easily confirmed. New plugs would be great however you will foul anything you put into the cylinder until you fix the problem so perhaps just remove and clean them and then replace them when the problem is fixed.

 

Failing all of the above, strip and inspect. Happy hunting.

Actually yeah, try these things before buying new plugs and leads, it might save you some cash! Good tips there

Wayne G's suggestion of a vacuum leak is something I hadn't thought of. But also the suggestions of the carb float filling & sinking - hmmm - you see during the hours I have spent trying to start & run the car if anything the sooting up seemed to get worse.

Yes, thanks, I'll go for the hotter plugs seeing as they've been found to better suit road cars.

By electric dizzy, are we talking a Pertronix kit to eliminate the points? But I've seen discussion about 280ZX dizzys on this forum too, but don't know whether they just plug in or require electrical modifications?

All the above advice is a huge help, thanks to everyone taking the time out with such detailed postings, I've already got a much clearer idea what to do next.

Fantastic forum, very much appreciated.

280zx dizzy is what we are talking about (they were the first Z here in aus to have electronic not points) and is reasonably cheap and simple to install. I am one of the people who had their tacho stop working though, so there is a possible downside. Here is the sticky thread on the topic. Very easy to to, even someone with zero experience like me could figure it out.

http://www.viczcar.com/forum/index.php/topic,5211.0.html

Thanks stevo_gj, for the sticky, I had had a quick look but hadn't found that; much appreciated, 4 helpful pages of discussion there.

So Z people prefer using 280ZX parts to a Pertronix? (I'm presuming Pertronix do one for the early Zeds). I've put a Pertronix into the dizzy of my Mustang & am most happy with the results.

I'll have a look around & see if I can find a 280ZX set-up (complete, as noted in the sticky).

Many thanks!

Did you get the car sorted? What did you find?

Hi Wayne, nice of you to ask, no luck so far & I ran out of holidays & am now back at work. I spent several days digging drainage ditches around my house to mitigate the surface water that kept running into my garage & carport during all the incessnant rain which overwhelmed the drains, when I had planned to work on the Zed.

I didn't find any obvious vacuum leak though, but just didn't get to pull the carb off to check the float which is another possible cause for all the sooting up.

Hopefully I'll have time over the next weekend or two.

Thanks for your interest, regards, John

Hi, does it run points or electronic ignition?

ScootaG, it has factory standard points (but all new incl condenser, cap & leads). I've tried very hard to balance the carbs & set them up according to the standard mid-settings so they should both perform the same in theory, yet the black soot in the front cylinders is excessive.

The flood emergency here in Brisbane took precedence & it wouldn't have been pleasant standing in the surface water seeping through the undercroft where the car is, & to mitigate that water I got busy ditch digging. I'll try to get back on the car over the next week or so as the problem is too silly & very frustrating.

Regards, John

Just out of curiosity have you checked that both carbie pistons fall in unison, to check this out remove air clnrs lift pistons with fingers & release pistons at the same time, they should reach bottom same time .Check that you have equal amounts of 20Gde oil in piston wells about 11mm below top.If you want quicker response from carbs thru rev range use ATF but you will use a little bit more go juice.

                                            Regards: Alan. 

Thanks for the advice Alan, I actually picked up on your same comment (I think it was you) to another complainant. So yes I checked them for that & they seem fine. The last things on the list of excellent advice from you & other enthusiasts for me to try is for either a big vacuum leak, or leaky floats, but due to work, young family plus house reno committments I just can't find time. I also have another classic car, a Mustang, & seldom find time to ever drive that so the poor old Z hasn't much of a chance of getting a look in. However, what I've done is to print out all this top advice so that I can methodically work through all the possibilities again, that's if I ever get a day to myself, & fix it. Many thanks.

Check the piston travel by lifting them with your finger or a screwdriver placed under the piston. It is quite common to find the pistons have been placed on the wrong carb's, this can result in the needles binding in the jet. If they don't return to the fully closed position try fitting the front piston ass'y in the rear carb' and visa versa.

Also check the fitting of the needle in the piston. The flat underside of the needle boss should be flush with the bottom face of the piston.

Cheers

Gordon Dobie

Thanks Gordon, hadn't thought of testing that; could be part of the issue. I'm just in the process of hooking up a temporary exhaust system as I've now replaced the rusted headers - rusty & pitted along the gasket flange - so I can get back on to examining the car's sooting issues while running it without deafening everyone, assuming I will get it to start.