Any ideas on why i get a breif deceleration while accelerating either at part or full throttle?

It is an intermitent problem for sure.

It can happen when applying throttle at any RPM, you give her gas, say at 3500, she will accelerato to maybe 4200, then fall back to 4000 for a second then pick up again,.

Otherwise the engine is running very smooth, no jerky action during these episodes.

Does it sound like a timing advance problem? its not just the tach malfunctioning, I can hear the enigine fall off in revs for a few seconds, but again it is internmitent.

This is in my 71 with stock carbs, only mod is header and exhaust.

Probably more likely to be a fuel related problem, is your fuel filter clean? When was the last time it was changed? But it wouldn't hurt to check the condition of the spark plugs (Clean? Color? Gap?) and check the timing as well.

Thanks Carl, I was just thinking about the fuel filter, although its probably been only 3000 miles since I changed it, but i'll look at it today, and maybe examine the plugs as well..it seems like the problem began when we got hit with real hot weather I wonder if theres a connection?

If the symptoms go away when the hot weather does, it could be related.

If you swap out the current one, cut the top off and look inside. Maybe your fuel tank/lines are full of crud or rust and it's plugging the filter. Fram sells a fuel filter (#G3359) for 240Z's.

Yesterday I took a couple of long crusises in the car. In the morning temperatures were in the low eighties and she ran just fine. I took another drive in late afternoon when it was in the 90's and she still was ok, so i guess this really is an intermitent thing.I put about 130 miles on the car without incident. But I 'm thinking the fuel filter scenario sounds likely. I dont beleive the gas tank has ever been out of the car for any type of cleaning or reseal. I will check the filter again before the summer is over. I have read somewere that cold weather can definitely affect your gas filter, although I'm not real sure why. I still wonder if hot weather can be a factor...

For less than $5 you can replace the fuel filter, cut the old one open and see what amount/kind of crap is in there. It will tell you a lot about the condition of your fuel tank.

Just a technical tidbit............Scientifically speaking, the term decelerartion is not used! It's actually negative acceleration, the opposite of positive acceleration!!! Acceleration is defined as the rate of change in the velocity of a moving body. Everyone wanted to hear that one.......right!! :nervous:

Just a technical tidbit............Scientifically speaking, the term decelerartion is not used! Everyone wanted to hear that one.......right!! :nervous:

Wrong!

That reminds me of something I saw at a local car show. Maybe this belongs in the 'Z plate' thread but there was this '41 Willys with a blown big block Chevy with the liscense plate: IDOXLR8

But I 'm thinking the fuel filter scenario sounds likely.

I use one of the clear glass inline filters that contains a replaceable element.

This makes it very easy to inspect the filter. It's quite obvious that my gas tank has some rust and getting it cleaned up and resealed properly is on the todo list.