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Discussion Starter #1
We installed a JR s/c on my 93 Miata late last summer, and I knew something wasn't quite right, but with winter coming on I parked it and figured I would tinker once it was warm enough to mess with it.

After a long winter trapped up to the windows in snow, I finally dug it out last week and have been driving and tinkering. I have a few issues though:

It's idleing too high, 1500rpm or so. It's also surgy with the power delivery. It's not at all consistant or smooth, it's lurchy. It also feels like I'm missing most of the power I should have, but sometimes it feels fine. Vacume leak?

It's also detonating a bit, only at higher rpms, above 4500 for the most part. As long as I drive it gently I don't hear anything amiss, but gentle driving sort of defeats the purpose. I'm thinking its running lean, but whats the best way to fix this? More fuel? Retard the timing? Both??
 

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hi chicky! haven't seen you around on tp.com.

i just installed one on mine last week. just need a basic rundown on what you have.

iirc, you had the standard kit. is there an adjustable fuel presure regulator on the car? what sort of timing controls are you using? power card? what is your timing set to?

it *sound* like you aren't getting enough fuel. answer the questions above and i think i can help you.
 

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Did you check for vacuum leaks? That can cause weird idle. I also found that unplugging the switch to the dummy throttle body took care of the crappy cold surge I was getting until I fixed the connections on the timing control.
 

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Discussion Starter #4
Hi KFJ - I posted the same thing on TP too...

iirc, you had the standard kit. is there an adjustable fuel presure regulator on the car? what sort of timing controls are you using? power card? what is your timing set to?

it *sound* like you aren't getting enough fuel. answer the questions above and i think i can help you.
Did you check for vacuum leaks? That can cause weird idle. I also found that unplugging the switch to the dummy throttle body took care of the crappy cold surge I was getting until I fixed the connections on the timing control.
Well, I bought it used - so I'm assuming it was a basic kit, but I'm not sure. I haven't done a thing as far as tuning yet - just been driving very gently. No timing controls to speak of. I called FM about something else, and while I had the guy on teh phone asked about a few things, and he reccomended their voodoo box for the timing, said it should solve the issues. But he also told me how to check for a vacuum leak. I'm fairly certain thats at least part of the issue. We haven't checked yet as my husband is working insane hours and until this week hadn't been home during daylight hours for over 2 months.

Louis (husband) thinks the throttle body is suspect - apparently during the install the one that came with the s/c was installed, and he wants to put my stock one back on to see if thats part of the issue. The guy from our local club that assisted with the install thinks it's a fuel issue, and wants me to buy his blueprinted 1.8L injectors and install those to deliver more fuel.

I would (in a perfect world) like to fix this without spending a fortune. I'd also love to get it fixed before heading to the Gap at the end of the month.
 

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ok, i'm going to run through a lot of stuff here. my knowledge is in turbochargers, but i am familiar with s/c's too.

if you have no timing control, the base timing on the car should be set at 6-8 degrees (depending on the highest octane you can get in CT). the voodoo box is one option to control timing.

if the timing is correct, as a few have mentioned, check for vacuum leaks. that idle is pretty high. does the idle "bounce" up and down? or stay at 1500? a good way to check is let the car idle and spray just a little bit of wd40 or some aerosol lubricant near vacuum line connections, where the throttle body meets the supercharger, where the dummy throttle body meets the intake manifold and the hose connections on the crossover tube (the tube that spans in front of the engine from the throttlebody to the intake manifold. you don't need to spray a lot, just short bursts. if the idle increases noticably after spraying near one of these areas, you found your leak.

your kit should have an adjustable fuel pressure regulator(AFPR). it will look sort of like a an aluminum flying saucer from a cheesy '50's b-movie. it will be on the passenger side of the engine compartment. it will have two hoses coming out the bottom and a smaller vacuum tube out the side. if this isn't there, you need one. if you DO have one, and you are detonating, you may have a weak fuel pump. sometimes the addition of an AFPR can exaggerate a weakening fuel pump. 1.8 injectors WON'T help if the pump is going bad.

i hope i'm not sounding condescending, i don't know your familiarity with the car.

if you need pictures of what i'm talking about, let me know and i'll shoot pictures of mine for comparison.
 

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Discussion Starter #6
Ok - finally had some time to tinker today and here is what we did. Set timing to 7, adjusted idle to about 750-ish when idling, checked for vacum leaks on a few obvious places and compression is also fine. I've been running 93 octane - and after todays timing and idle fixes I can run it to 5k rpm without hearing and pinging or popping or detonation. (with traffic I wasn't able to run it up any higher) The issue I'm having now is the power delivery is.. for lack of a better word, lurchy. Maybe surge-y is a better description? It seems fine between 3k and 4k, but lower than that it's really laggy and lurchy. Is this a result of the timing fix? I still think I'm not getting enough fuel, and I know I still need a timing control.

Thanks for all your help :)
 

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Unplug the pressure sensor on the dummy throttle body. This oftentimes will help a little if you don't have timing control.
 

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Is the throttle cable nice and tight? I think the lurchiness you describe is more due to the timing. Not really a surge, more like the low end response is dull due to the timing retard. Get some form of timing control on it (I use a Bipes), this will let you raise the timing back up to regain the low end.

Why are you only running it to 5k rpm? :)
 

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Discussion Starter #9
Scott - at this point I might just try to beg JD to tinker with it when I'm in TN for RATG.

Greg - I'm only running it to 5k because I don't want to blow anything up quite yet. I got darn near to 6k today without any detonation that I could hear, but I don't want to push things too hard. I do need a Bipes or something, just trying to allocate limited funds between 6 different projects at the moment.
 

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Discussion Starter #12
I snagged a Bipes from the Mnet classifieds and its now installed. But, we forgot to fix the timing (long day-brain fart) so I haven't driven it yet. Today I'm going to put the timing back up from 6*, the Bipes needs tuning though - if I read everything correctly. Any tips or tricks for that?
 
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