Devon Murray

So I finally finished up my 79 Rx7 "restomod", is it ever finished?, idk. But I have driven two full tanks of 91 on it now and have been having more fun than i ever had thought i could. I've had some hiccups and was wondering if anybody could help me.

To start the Nikki is stripped, The only vacuum i use is for the dizzy.. I have upgraded to the later electronic ignition, timing is set to the specs on the hood, i cant get it to idle lower than 1500, 2k rpm. but i believe that is because i didnt have a dial gauge to set the initial throttle opening screw at 1 degree per the manual. i just backed it off and screwed it in till i saw the throttle plate move. its doesnt bother me at all. mpgs are just tanked. again dont really care.

Here's the issues though, First pulls of the day are great! Seriously this rx7 is WAY faster than all my other ones. But after about 20 minutes of hard driving on and off the interstate, When doing hard pulls, the carb will straight up hit a wall it seems. almost like i have a rev limiter. ill get up to about 4500k rpm in 1st and ease into the mechanical secondaries and itll pull great till 6k. then it hits this wall, i havent had this issue yet with a nikki. then if i shift up to second it will pull fine again till about 6k again but it will cough and spit to get there. my 83 gsl had a bad fuel filter once but i was able to pull through 3rd gear before that hindered anything. I do plan to change the fuel filter even though it was replaced 3 years ago and the car has only driven 400 miles since then.

I am thinking maybe just maybe I am having vapor lock issues like Uncle Tonys Garage on YT has told me about older muscle cars still running carbs, that the new gas is different then what they had back in the carb days and the seals and pumps are no bueno for todays fuel. our fuel pumps boil the fuel and cause it to vapor lock our carbs. hes saved tons of old classic hot rods with that simple fix. he uses a 3 port vapor fuel separator. one port runs back to the tank and allows the fuel to free flow without being boiled. maybe i got all of that wrong. would be awesome to hear from the greats on the forum. i can get a driving video of the problems if you want a better visual of whats happening.

j9fd3s

iTrader: (3)

i would change the fuel filter first. step 2 would be to look at either the ignition, or to test the fuel pump when its hot

t_g_farrell

iTrader: (1)

Yeah, change the filter above all else.

What fuel pump are you running?
Are you running the return line back to the tank?
Is it clogged?

If it seems to get worse as it warms up I would suspect ignitors or some other ignition issue as well. I don't know what you did for the ignition so details there might help as well.

Devon Murray

I'll get the fuel filter changed asap. thanks for your wisdom j9. I foorgot to add i am running a GM HEI on the leading and factory ignitor on the trailing. I am using artic silver thermal paste. do you think maybe the GM HEI is getting hot? is that a "thing"? for testing the fuel pump when its hot do you mean by just installinga FP gauge and running the engine hard then checking if its stable? seems like thats how i would do it. never tested a pump before

Devon Murray

didnt see your post till i posted my response TG. sorry, The fuel pump is probably still the original pump from 78, the car has 55,xxx miles on it. fuel filter was changed 2 or 3 years ago when i bought the car but only have driven it 4-500 miles since then. I have an N249 dizzy, GM HEI bolted to the side of it and using thermal paste for my leading ignitor, 1 off the shelf napa 12v coil for the leading, and all the trailing is left factory beside using a 12v coil from an FB ignition. all the points stuff has been removed


edit and yes i am still running the full factory fuel system. factory 79 hardlines feed and return line. i have the oneway valve still also. vent for the tank is open. FBVS is open.

t_g_farrell

iTrader: (1)

GM HEIs can handle heat pretty well but any igniter failure (OEM or other) typically involves heat and the failure will get faster and faster until it stops working.

I would suspect the pump is having an issue. I would drive it until it exhibits the symptoms and compare the hot pressure and flow rate seen to what it is on first startup when its cold. The FSM talks about how to do both of these I think.

GSLSEforme

Post a pic of your leading HEI setup. This may or may not have anything to do with your driveability complaint. Knowing the size of the HEI module and of J109 and the pad on side of distributor it mounts on,there would be a good amount of surface of HEI module not mounted to anything. These modules in oe applications are mounted with their entire base in contact with distributor housing to transfer heat from module to distributor housing to keep them cool.

wankel=awesome

What coils are you running?

Devon Murray

The primary coil is a Napa brand 12v coil. Trailing coil is factory from an 83. And yes if these GM modules need a full mounting surface then that is most likely my issue. Only about a 2/3 of the module has a "heatsink" where I have it right now. I have a plate of Ally just haven't found time to rig it up. drove it very hard yesterday and had no issues. Few coughs on the way to 7k from 5500. But it was every once in awhile. The other day I would try and run at a light and when it would get to 5k or 6k it would hit what I've only heard described as a "wall". To me it's like a rev limiter. Here is a video of yesterday drive. I guess let me know if it sounds alright.


the fun really starts around the 15 minute mark.

go for a top speed pull at 17:00

Ran out of straight at 110. Had to hot the corner at the end at 80mph haha. She's handles like my old mx5 haha