Running rough

[AceOfDiamonds0]

I've had this same issue before and it seems like it was around the same time last year so i don't know if the weather being colder has anything to do with or not.

 

When i first start up, it won't stay started unless I give it gas. When i give it gas it pops out of my carbs quite a bit. Not just a pop here and there, it pops and stutters until it "clears out the carbs" almost like the carbs are loaded up with fuel. Occasionally even while I'm driving around it pops once or twice when accelerating, stutters and is then fine.

 

I've played with the air fuel mixture screws both rich and lean it still pops. I've changed the plugs and set the gap at .042. I cleaned the points on my distributor cap and I've also played with the timing a bit. I'm starting to think maybe a vacuum leak? When i come to a stop my rpms drop and in rare cases it will die but not very often.

 

Its quite frustrating so any input is welcome. Aside from rebuilding the carbs and everything else under the hood I'm stumped!

[AceOfDiamonds0]

Forgot to mention the important stuff. I've got an L28 with triple 40 DCEO's, MSD ignition. Also what fuel pressure should I be running? Right now I've got about 3lbs.

[datzenmike]

Unless you have replaced the distributor with a later EI unit you have the gap way too wide on the plugs. 0.032 will be easier for the coil to fire. 0.042 would be okay with a high voltage matchbox dizzy.

[AceOfDiamonds0]

I couldn't honestly tell you what distributor I've got but I do know its not the factory one for the L28.

[datzenmike]

Look under the cap... does it have points?

 

If points 0.032"-0.035" gap.

 

L28? The 240Z should be an L24. Maybe engine swapped?

[I'm BLUE]

With fire extinuguisher in hand or close by ... And engine running ... Lightly spray intake sealing surfaces .. gaskets .. hoses etc

If a change in rpm or idle ... You have a leak.

 

Carbs can create leaks as well.

 

What fuel pump do you have ??

 

If EFI ignition check/clean connections to module.

Fuel pressure is correct.

 

I sure hope you have a EI dizzy with those tripples.

 

Time the engine ... Turn it as high as you can without it pinging.

You'll be sitting likely around 12-15 degrees.

 

You really need a sun engine analyzer to tune dcoe, Carbs to that last degree .. :)

 

Always run brand name gas and never to the bottom.

 

L28 into 240z is a fairly common swap.

[AceOfDiamonds0]

It is the L28. I bought it over a year ago with almost all of the mods that are in there that the guy i bought it from put in. He said he was a British auto mechanic and raced the TR6's until the Z's came out and then started racing them which doesn't seem too far fetched because he still had a TR6 in his garage next to the Z.

 

There's no points under the cap I'll take a picture of it in the morning and post it. I'll also try finding a vacuum leak as well and update tomorrow.

[datzenmike]

Maybe list all the differences/changes/mods on your car. I see '71 240z, so it's natural to assume you have an L24 and suggestions for it are based on it.

 

Did you re-jet the carbs for the larger displacement motor? It might be running lean and in the cold thios is magnified. It could be a lean backfire.

 

Usually a lean mixture produces a very light colored spark plug. In some cases it is shiny white. Check yours after a long drive when thoroughly warmed up... normal will be tan.

[EricJB]

What do you mean MSD ignition? Just a blaster coil or a 6/6al box? I would agree that it is a lean spit. And it's probably one carb thats doing it. If the carbs are out of sync, the one that opens first is usually the one that spits. After you get everything adjusted correctly, if it still does it, you might need to go up 1 on the idle jets.

[datzenmike]

Probably SUs.

[I'm BLUE]

yeah could likely be lean.

I've got an L28 with triple 40 DCEO's, MSD ignition.

 

The accelerator pump rods tend to gull/stick ... make sure they are operating correcting as well.

DCOE's ... I tend to clean/inspect/rebuild when I get them.

 

Distributor adjustment and timing is a pretty big deal.

 

Do you have the flat-top piston f54 block or dished f54/n42 L28 block ?

[AceOfDiamonds0]

Ok so I dont know for sure what jetting is in the carbs, I do know the guy adjusted the timing trhough the oil pump and it sits about 13 degrees last time I checked which was a few months ago.

 

No box so I'm assuming just a blaster coil, but I'm still not sure what that is. I know I know, I still have a lot to learn but thats why I'm on here asking.

 

I do have the N42 head on there, the bottom end was balanced. Milled heads, 9:1 compression, mild cam, and 2" mandrel bent exhaust. The headers, a friend of mine said they are some triflow or something like that, that is supposed to be really good but again thats just what a friend of mine told me.

 

I looked around for vacuum leaks but didnt find anything outstanding, I was a bit busy today so I couldnt really spend a lot of time looking or tinkering with it.

 

[datzenmike]

[AceOfDiamonds0]

So I couldn't find a vacuum leak at all. I guess I'll just try running it richer and see if it is just a lean backfire. I'll also set my plugs down to .040 and see if that doesnt help any.

 

What is the difference between larger and smaller plug gap? Is it just a stronger more solid spark if the gap is smaller. If larger gap maybe more of the spark is exposed to get a better burn?

[datzenmike]

Wider gap gives a longer spark to light the fuel. The problem is that you still need the voltage to do so. Old style points are no good above about 0.032" or so but the newer EI dizzy (that I see you have) has enough extra voltage to allow the gap to be increased by about 0'010".

[AceOfDiamonds0]

This is what all 6 of my plugs looked like after being thoroughly warmed up and I drop it for at least a half hour.

http://i1341.photobucket.com/albums/o758/AceOfDiamonds0/2012-11-07_18-28-55_554.jpg