I just bought another rx7 and after putting a few hundred miles on, it has developed a loud rattle when I really get on the gas. I'm not exactly sure where its coming from seeing how it doesn't do it when I have it in neutral sitting in the driveway. It only happens when I'm in gear and it will do it in every gear. A little car background: 1985 GS with street port, RB street port exhaust, holley carb, msd ignition and coils. Any ideas?

 

Most likely it's an exhaust rattle. Check your heat shields to see if they're bent or missing any bolts.

 

when you say it happens only when in gear, are you driving? if so, check driveshaft u-joints. i had the same problem with a 280-zx.

 

If all that fails check your timing. my car did the same thing under full throttle it mite be to mutch advance on the trailing. it sounds pretty violent I assume. If don'tnt have access to a lite just bump the trailinvacuumme thing on the dizzy. It would be the one closest to you when standing on the driver side. loosen the two screws and push it in a little. In mexperiencece the nock usually means too mutch advance. So by pushing thvacuummdiaphramam thing in your retarding the timing. If you cant get right take in to a pro.don'tt try and set it to the stock timing if your motor is ported it wont fly

 

I didn't even think about a knock, I was thinking rattle. Your leading timing is just as critical as your trailing. If either is over-advanced, it will cause a knock. The generally agreed-upon max advance for our cars is 24* leading and 16* trailing. Whatever advance the leading timing is set for, the trailing should be 8* less.

 

I'll give another vote for timing. Sounds like a loud rattle/gurgle when you floor it. Fix it fast...

 

Ok, I finally had some time yesterday to get at my car. I put the car up on stands, put it in gear and reved it up. The noise was coming from the engine so I was going to push the trailing vacuum thing on the dizzy in but it was all the way in already. I don't have access to a lite so to be sure that timing was the problem I disconnected the trailing coil and took her for a drive. Problem solved, the noise is completely gone. My question now is am I ok just driving it on the lead plugs alone for awhile? I don't seem to have any power loss. Another question while I'm thinking of it: while I was checking for loose parts on the exhaust I noticed a small open ended copper tube about 1/8 inch diameter coming off of the bottom front of the Holley that goes down and is wrapped around one of the header pipes. What is it for? BTW, thank you for the help.

 

You can drive around for a while like that. If you hear any pinging, ease off the throttle. I stabbed the distributor one tooth off once and ran 50* advance for a while until I had the time to re-stab it. I wouldn't recommend it, but the engine survived (eventually blew an apex tip due to wear). Get your hands on a timing light ASAP. Set the leading to 24* and the trailing to 16* and I think you'll be surprised how well it runs.



Distilling your 'shine.

 

this too is what i'm running. and mine also starting this rattling noise but i immediately knew what it was. a spark knock in a rotary sounds totally different than one in a piston engine. retarding the timming wasn't making it go away. one day i decided to take a look at the plugs, and when i pulled the trailing out, they would screw out so far then get tight. i consider myself lucky cause when i finally did get them out, the ceramic on both trailing plugs was broke at the tip, but didn't get left inside the engine. the knock was gone after replacing these plugs. needless to say, i have my timming set dead on the marks now.