First off, Hello everyone! I'm fresh owner of my first rx7 and at the same time newbie to the forum. Been reading threads here for awhile but this is my first post. Unfortunately about a issue caused by myself

So, I was driving long distance with my rx7, and had to stop for gas. Unluckily it was only gas station inspan of like 80km. And the gas station didn't carry e98. Well out of the circumstances I filled the car up with E95 thinking the difference in octane is not too big. Well it apparently was

So after driving for another 40km or so the car started prefiring alot, aka knocking I guess. After while it died down and didn't start until cold. Well I had to just let it cool down and drive with rinse and repeat till I got to next gas station where I emptied the tank and filled her up with E98 but the problem continued. And the engine starts to die down after 10km or so. Odd part is that it does not seem to matter if I let it idle till warm or start driving cold the problems start at around the same time

Well, judging from sound of it, it sounds like it could be a fuel delivery issue. And I thought ethanol maybe have eaten off something. So First off I started easy and changing out fuel filter and inspecting in tank fuel sock. After that the car drove and pulled hard for good 40km or so. Lot more than before. Then the problem started again. After this I did compression test.

I bought a "rotarytronics" tester off eBay, which gives raw numbers and corrected numbers, which should be 250rpm and at sea level. All the Results are in BARs

1. Housing
RAW : 6.5 - 6.4 - 6.9
Corrected : 7.1 - 7.0 - 7.5

2nd housing (one closest to firewall)

RAW : 6.5 - 6.4 - 6.3
Corrected : 7.0 - 6.9 - 6.9

To me, the numbers seem decent. After all the engine has 140 000 km droven and the numbers are pretty similiar. Also I read out of these forums that the 2nd rotor housing wearing out faster is to be excepted

So I guess my question here is, should I really open the engine regardless before trialing and erroring and just causing some damage that can't be fixed with just a rebuild. or is there parts on carburetor that ethanol could damage or cause problems when warming up, or anywhere else for that matter. I myself am new to wankel engines and carburetors so all help would be greatly appreciated. Thank you in advance

 

Welcome to the forum!

I know you said you checked the sock for the fuel tank, I assume you inspected the tank thoroughly inside? The problem you describe seems to match others' experience here where the fuel pickup in the tank progressively becomes blocked due to a buildup of contaminants. I've also read of other people here having blockage right at the carb inlet screens.

Could you perhaps be confusing misfires or stuttering due to fuel delivery with knocking? Pre ignition only occurs on a rotary with very misadjusted timing afaik. I run low octane 89 fuel and never have any problems in my 83 GSL, 12a with stock ignition.

I definitely wouldn't take the motor apart at this point!
Edit to add: those compression numbers look pretty good to me.

 

Thank you for answer!

That could be, at the time I filled her up with e95 it was also the first time I filled tank to the brim. That could pick up trash from the tank and cause blockage I guess. But mystery here is that why the problem occurs only when I have been driving for awhile. When "cold" car responds to throttle Great

 

The mechanism of failure for the tank pick up getting blocked is that as the fuel pump pulls fuel from the tank the sock gets progressively blocked until it starves the engine. After the suction is gone with the pump turned off, the obstructions float away... At least that's the theory and what people here have experienced with older compromised fuel tanks. That's why it can coincide with a cool-ish engine.

​​​​​​Was the fuel filter looking dirty/clogged? And how is the new one?


​​​​

 

Sounds reasonable, thank you.

I guess I have to check the new filter and drop the tank again. Old filter was filthy but it was very old too so hard to tell.

Last time when I removed the tank I took the sock out completelly to test it out. It seemd clean enough tho. But I guess the trash doesn't stick to it

When I think about it I guess the tank had some rusty slush on the bottom but don't they all? Well i think my next move will be to empty the tank and clean it thoroughly, have to look around for a bit on how to do that effectively. Maybe make new fuel lines and change the sock too while I'm at it. If that doesn't work I guess I have to do what Ive tread a bit and take the carburetor apart but let's try easier route first.

I'll update how it goes

 

There are a bunch of threads on here about cleaning the tank...most seem to have found a shop to clean it and re-line. I recall one guy doing it himself, cleaning with some acid and then recoating with a POR15 product.

Here's a thread that seems relevant:

https://www.rx7club.com/1st-generati...ing-up-744586/

Edit to add: maybe you could test the fuel delivery independent of the tank to identify the problem before all of that work? Something like running the pump into a bucket for a good lock duration, simulating a good long drive and see if it does clog up. Also check the screens in the carb inlet.

 

Hello, Tought id update. Upon inspecting new filter i installed. i found bunch of sand inside!?

i removed the tank, drained all the fuel and ended up just cleaning it with regular hose water because lining in tank was actually in good condition. so i ran water through the tank for a while and let a hot airgun dry it for a few hours. after that i put some fresh gas in with high 2 stroke oil mix and slushed it around to "coat" the tank and prevent rust if that makes sense. I also shot compressed air through all the fuel lines and got some grime out with that too. after that i filled her up to brim with new gas along with new fuel filter. car has ran great ever since with no problems!

I think the fuel station that i filled the car up before problems started must have had a faulty underground fuel tank that leaks. this because the sand i found inside the tank was very fine, something that you dont find in ground normally. This is kind of sand that is used to "surround" underground structures such as pipes and cables etc to protect them from rocks in normal earth content.

so that was something new, but im glad i got it sorted out thanks for the help!

 

That's great! I'll bet your car is a nice unique one to have in Finland. Thanks for updating, it really is helpful when people reply with the resolution.

 

Yes forsure, havent seen one in person ever until i got mine. For now i plan to enjoy it for the remaining summer and do bit of bodywork during winter, sandblast all the axles and suspension arms and give it some fresh bushings + check the body for all the starting rust spots and recoat the underbody. altought the body is in very good condition, especially compared to my other same era japanese cars. but id rather keep it that way so better get it done.

also found out that they dont measure emissions here for rotary engined cars, so i plan on getting rid of the airpump and get the racingbeat exhaust for it, as i heard that the catalytic converter isnt really a good thing for rotaries. also have to look into OMP if its worth keeping or not. maybe offtopic but if i dare to ask how does this platform like urethane bushings for rear axle? does it give too harsh of an ride or is it acceptable? also as a newbie to this platform im open to all the suggestions for mods, im looking forward to getting on tinkering with this car. Ive heard alot about electric waterpumps, fans and lighter flywheels and whatnot. i guess electric cooling parts are cool mods to simplify the engine bay a bit but really dont see alot other advantages with that. but have to do more research. i dont intend to make this a full on race car as i have different platform for that (mr2). Just some mods to embrace the feel and reliability of this odd little carbied wankel machine.