Hi everyone:

I have a great mechanic that knows Z's who built my car and has done some recent work on it. He's totally perplexed by this problem.

Last year, the car would bog with light acceleration. In attempt to fix it this year, this is what has been done:

1. oil change
   
2. oil filter change
   
3. new spark plugs
   
4. install of an electronic fuel pump
   
5. install of electronic ignition
   

After this was done, the car ran beautifully. Smooth acceleration, no stalling on stops, for two trips - driving home and the next morning on the way to a golf course out of town. Two things happend - I filled the car with premium fuel (as usual) and we had a flash rain storm. On the way home the car started to pop and bog. The popping never happend before this.

I took the car back to my mechanic. Perplexed, he tested the fuel pump and put in new wires. Afterwards, it ran fine to a trip back to the gas station. Filled it up, then we have the problem again. it pops and bogs and stalls out on stops.

Bear with me, I'm still getting to know the car; my mechanic is the expert. I'll learn quick and I am super motivated to fix this and drive my Z.

Some info on the engine:

71 240 Z

Triple Weber Carb set up on a 280Z motor

82 280Z plugs

Racing cam

Flat top pistons

I have a video while driving - sorry that it is poor quality.

Anyone have any ideas?

Haven't watched the video but the first thing that pops in my mind is dirty fuel tank

Does sound lean, for one reason or another. Similar to the issue with my L28, but I still have the stock EFI.

Did you get the fuel from the same gas station. Could be water in the fuel.

In a driveway/garage, in neutral and you rev, does it make the same popping sound? Is it only at 2500 rpm or 2500 rpm and up? Is the popping coming from the carbs or exhaust? It might be easier to hear if you take the air-filters off (if its the carbs).

My guess would be to check your timing, webers like a lot of advance (like 13-15 at idle, 32-34 all-in)...I would also second the opinion on checking/replacing fuel filters if that wasnt already changed recently. Lastly, start really digging into the world of weber dcoe's. I find it fun and really not as intimidating as I use to think it was.

When I said dirty tank, I picture you stirring up crap during fill up and this crap initially getting sucked into the sending unit. After sitting for a period of time the crap falls out and things are good again.

Have you peeked inside your tank.

Hi guys:

Thanks for the replies!

1. I disconnected the fuel pump line going to the carbs and pumped fuel into a plastic bottle. From what I can tell, the fuel looks clean.

2. I went to two different gas stations to answer Olzed comment.

3. TBone028, popping is coming from the carbs from 2500 rpm and up. It's coming from the front the most.

4. The carbs were rejetted. There was a flame coming out of that front carb and with the new jets, it runs a bit leaner which solved the flame problem.

Perhaps as a precaution, changing the fuel filters is my next step. Thank you guys!

The other thing that would have jumped out at me was the rain storm.

I would have suspected moisture under the dizzy cap would have caused the misfires .

Ignition issue

Some success last night. The new spark plugs were black - carbon all over. I replaced them, went for a 45 minute run and the car ran awesome. No issues whatsoever. Afterwards I took a look at the plugs. Black all over and scored somewhat. See below

What could be the cause? Should I get different plugs with a different heat range?

So all the plugs looked the same?

If they did, then it's something that effects all of them at the same time like ignition being weak, too much fuel pressure , etc.

prob to much fuel..