Back carb backfire!!

[dohc]

Hi guys,

I need a hand. I'll give you a bit of back ground first to try and set the scene and make it a bit easier to help me.

I've just swapped the L26 engine out of my auto parts car (both 260Z 2+2) into my daily driver (5 spd manual). This engine has the good SU's and when I stopped my parts car (about two weeks before doing this swap) and it ran fine. The old engine had the flattops but I don't think that's relevant...

Now that I've got it into my daily driver, all hooked up and ready to go but turn the key and it won't fire. It turns over fine, all the electrics are good but still no life.

I've checked the fuel pump (electric) no problems, after trying for a bit the plugs are damp with petrol so I've ruled that out (plus you can still here it clicking over and see the fuel filter in the engine bay fill with fuel). I've checked the leads and while cranking the engine atleast the back four leads are sparking (my arms aren't long enough to crank nad reach the front two ).

After trying for half hour and trying a multitude of things, and cleaning everything I could think of the back carb coughed. It didnt sound like the engine fired, but just the back carby coughed and put out a bit of smoke. Nothing else happened....?

The only change between the two cars was the Auto to Man trans and I can't see how this would effect the runnign of the engine? The timing hasn't moved and I'm pretty sure the carbs weren't knocked in the swap, but I think it would still start even if they were out a little?

Anyway I'm boned. I can't for the life of me figure out where to go next :stupid:

Any info or suggestions would be great

Cheers,

Ross.

[smg1404]

Make sure that you are nor 180 degrees out of time... The timing marks will line up just like everything is right but you will be firing the plugs on the exhaust stroke instead of the compression stroke...

[Mike]

Agreed, flip the wires around 180 degrees on the distributor cap and see what happens.

I had this same problem. Ends up that my engine rebuilder put the distributor shaft in 180 degrees off!!

I fought with the thing for at least 2-3 days and was terribly pissed. Then a friend came over and said... "Man, it sounds like the timing is totally off"

We flipped it around and it started right up.

Worth a try.

[AxtellZ]

Another idea- the auto cars may be wired such that it won't start with the car in a drive gear. Perhaps thats another thing to check out? I'd still check out the previous comments first tho..

Good luck!

[dohc]

Turns out you guys were right. The previous owner had put the dizzy in 180 degrees out of whack so when I swapped the leads during the engine change, it all went to hell.

I've moved the leads around 180 deg and it gave a few wet sounding pops but still wont start. I think I've managed to flood it:classic:

I'll let you know when I get it going

[dohc]

Crap. I've done the above and waited for awhile incase it was flooded and then tried again. Nothing. Played for a while and it turns out one of the wires in the dizzy had worn through and was shorting on about every second rotation.

Replaced that and now it is sparking again, it's definatly getting petrol but all I get is the occassional wet sounding pop?

Does this sound like a blockage somewhere or like it is still an ignition problem? As the engine was running when I pulled I'd be surprised if it was a carb fault.....

Another though I had was that it was a weak spark failing to ignite the fuel that has been sitting for a while. I've ruled that out by draining all the dregs from the tank and replacing it with fresh fuel. I've also swapped the coil over from my parts car to this one to rule that out.....

I'm fresh out of ideas again, it all appears to be working this time but just won't ignite!

Cheers,

R.

[biker]

By the looks of it you are pretty frustrated all hte options with electricals.

I was playting around with the carbs last week and accidently blocked off the vents.

Try checking the following:

Plenty of air getting through to the throats such as clean filter, no blockage to carby.

Are the breathers on top of the carby clear (definitely required on Round Tops)

Next port of call would be the valves if you are sure that you are getting spark to the plugs. (Taken one out and had a look while turning the motor over?)

[dohc]

Still no joy....

I've now cleaned the plugs off again, just to be sure and even swapped out the dizzy cap incase it was stuff (it looked like it has a whole bunch of hairline fractures running out from one pin.... What else can be wrong??

Thanks for the further ideas Biker. I've had the air cleaner off the whole time so I could watch the carb and on these SU's the breather pipes out the top of the carbies have been blocked off with a brass plug... The plug has always been there, so I assume it was a mod at some point?

I'll have to pull a plug and watch it turn. I'll see if that gives me any ideas...

Thanks all for your help, we'll get there soon.

R.

[Mike]

Okay, here are a few ideas:

1) Make sure you have spark.

a) Remove the main wire from the distributor cap (center wire) and place it near a metal surface. Crank the engine. You should see sparks. Put the wire back.

Remove spark plug #1 and place it on a metal surface. Crank the engine. It should spark. Repeat for all plugs.

c) Check the firing order on the wires from the distributor cap. You'll have to check a manual for this info. Check both the cap and the plugs to make sure they are connected properly.

2) Make sure you have fuel.

a) Remove the aircleaner.

Check for proper operation of the SU pistons.

c) Crank the engine.. do you smell gas?

d) Buy some starter fluid and use just a little to see if the engine is trying to start but has no fuel.

e) If the SU's have sat for some time or if they are way out of adjustment... tighten the mixture nuts all the way down and back them off about 3 full turns.

3) Make sure your engine has compression.

If you have tried all of the above.... something basic is missing. These cars operate on a very basic scientific theory. So, it's probably something simple. If there is fuel, air, and fire... it should ignite and SOMETHING should be happening.

If nothing is happening.... the fuel might not be good? Starter fluid should help determine this.

[dohc]

Ok lets see if we can narrow this down a bit. The more I wrestle with this problem in my head this morning the more that the option of bad fuel comes up.... I can't understand if it is, the fuel is less than a month old, and I've left fuel before for over six months with out a problem?

Anyway, I'll run over what I've done in relation to the above...

1. a) Check, strong and regular especially after it ran through my arm for a rotation or two

Check, not strong but I'm not familiar with how far this spark should jump.

c) Check, and double checked. From the top of my head its 5 3 1 6 2 4, but I've been running from the manual for that one.

I've also removed the plugs and cleaned them, and regapped them to be sure, all looks fine....

2. a) No air cleaner the whole time to try and help air flow and let me see into the carbs.

Not sure how to check this but I've moved them up and down manually and they slide freely, no obstructions that I can see...

c) Yes, and I can watch the petrol filter fill with petrol as the pump turns over. The plugs were also damp with petrol when I cleaned them. The return line is putting out a good deal of petrol and each carb is getting a good supply as well.

d) I think I'll have to give this a shot, I'll nick some fresh fuel from my g/friends BMW and see if that helps.....

e) I'll have to try this next if I can't get a fire from the BMW fuel. They only sat for a couple of weeks between cars, is that long enough to jam up?

3. I'll check compression tonight as well and report back.

I thing it will turn out to be something small and stupid that I've missed, but only having an hour or so of light each night to work on it I haven't spotted it yet. I've never had this much trouble with any car, and I've worked on EFI car's before (and loved it ).

Ah well, I'll try again tonight and see what the hell I can find out.

Thanks all,

Ross.

[biker]

Hey dohc

Hope you are not dsylexic but you have got the firing order quoted wrong. My memory serves me as the order is 153624, not as you quoted earlier as 531624

Foolish me also once had the wires in backwards on the dizz and running anti clockwise. Took me an hour to realise that the rotor in the carby runs clockwise menaing that everything was out of whack

[2ManyZs]

The way I was told to remember the firing order of a straight six is 15(is too young)36(is too old) and 24(is just right). Works on all inline sixes......course that was 20 odd years ago when I was still in high school...

guess it would now mean 15(is your grandchild)36(is just right) and 24(is a fantasy). :stupid: :disappoin