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ITS car hits a flat spot between 7,000 and 7,800...what gives?

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ITS car hits a flat spot between 7,000 and 7,800...what gives?

Old 07-05-07, 08:58 PM
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ITS car hits a flat spot between 7,000 and 7,800...what gives?

Pretty much as the title. Last race my ITS car has developed a flat spot where it feels like it is draging the brakes (what it feels like, not what is happening). Then it clears out at about 7,800 rpm or so. Any thoughts.....

90 Rx-7 13B
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Old 07-07-07, 02:40 AM
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Originally Posted by bean13 View Post
Pretty much as the title. Last race my ITS car has developed a flat spot where it feels like it is draging the brakes (what it feels like, not what is happening). Then it clears out at about 7,800 rpm or so. Any thoughts.....

90 Rx-7 13B

Let me take a shot try changing your plugs

or you 6th ports arnt opening?
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Old 07-07-07, 08:48 AM
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Could be a variety of things. If you don't have any kind of fuel control you can expect mixtures in the 10:1 range in that area. That combined with a weak spark and you have misfire issues. Pretty common. Without data it's hard to diagnose. Plugs, wires, 20 year old coils/ignitors? You're past peak torque (peak fuel consumption) so it shouldn't be a fuel supply issue.

New problem or something that's always been there? Change anything before the weekend?

When you going to bring that thing down here and let me set it up for you?
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Old 07-07-07, 08:35 PM
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Humm....

The plugs were new a few races ago....wires definitly could be...I will change out the ignitors too. No, this has just shown up the last race. It is a stock fuel system.

Oh beleive me...if I have the time and money you would be the first person I take it too. I know you would take care of it.... Once I get everything figured out and have some good showings on the car it will prolly be for sale. If I was going to get serious with it , I would definitly have you tinker with it. Once I am out of grad school I am planning on selling it to move into a formula series of some sort.

My freind had the same issue with a heavily street ported "track car." I still dont think he has it fixed either.

What plugs would you reccomend? I have stock 3rd gen in it now, that was what Mazda told me to use, what are your thoughts?

oh yeah, the only thing I changed was I wired the VDI open...I would think that would make it better, not create a problem.

Thanks guys!
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Old 07-08-07, 12:29 AM
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The stock plugs in the stock heat range work fine. I never could justify the expense of the fine wire plugs. I've also test the EGV plugs on the dyno and there was no difference in power at all. They're cheaper than the stockers so they're a good option IMO.

The VDI shouldn't make a difference unless you somehow wired it in the low rpm position. Then I could see it being soft up top but not just in one area.

Dunno...
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Old 07-08-07, 09:24 AM
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hum, to cover my ***...teh VDI in the open position should be turned counter-clockwise, or against the lower ot the two stop tabs. (opposite of how it was at idle or engine off)
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Old 07-09-07, 01:14 PM
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I just checked out your website....very nice. Looks like you have a well developed car and biz....I am sorry to see you in a Miata though
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Old 07-09-07, 02:09 PM
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this is just fyi...

we ran the stock plugs, usually 9's all the way around, and had no trouble, they even last a decent amount of time.

my opinion is that the race plugs would be "better" mainly due to the colder heat range.
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Old 07-09-07, 03:19 PM
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Yeah, I have always ran the stock plugs as well, first time this ever came up.

racing beat suggests a BR10EIX I think...any thoughts on that.

As for the weak spark, my lame "test" is that I took all the plugs out and lined them up on the strut bar and put a cordless drill on a spare CAS - distributor, whatever, and they all seem to have the same healthy spark....is this a waste of time or am I actually ruling out weak spark as an issue.

Thanks guys!
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Old 07-09-07, 03:48 PM
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ok, so to add to my own question....the hack drill idea only spins the CAS to 3k rpm. I am trying to really cobble up a way to spin it a bit faster....more to come on my hillbilly diagnosis....maybe if I use some duct tape somewhere......
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Old 07-09-07, 04:25 PM
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well, i spun it from 7000 to 9000 and I saw no difference in the spark at any time. Any other thoughts.....man this gets frustrating.
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Old 07-12-07, 09:21 PM
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Testing spark the way you are doing it isn't telling you anything really. Since you aren't dealing with combustion pressures or turbulence there isn't much doubt you'll get a decent spark. And you only need to spin the CAS to 4000 rpm to show 8000 engine rpm. The CAS spins at half crank speed.

I've ran all 7s, all 9s, pretty much everything but the seriously expensive plugs and never had a spark issue. I'm guessing spending a bunch of money on the "race" plugs won't solve a thing.
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Old 07-12-07, 11:42 PM
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humm...ok. Thanks for the advice as always..

Also, I meant I spun the CAS to 8,000 on the tach, i dont know the actual rpm of the CAS, just so I dont look like a tool.

Thanks!!!
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Old 07-13-07, 12:38 PM
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Originally Posted by C. Ludwig View Post
Testing spark the way you are doing it isn't telling you anything really. Since you aren't dealing with combustion pressures or turbulence there isn't much doubt you'll get a decent spark. And you only need to spin the CAS to 4000 rpm to show 8000 engine rpm. The CAS spins at half crank speed.

I've ran all 7s, all 9s, pretty much everything but the seriously expensive plugs and never had a spark issue. I'm guessing spending a bunch of money on the "race" plugs won't solve a thing.
yeah i wouldn't expect race plugs to fix this problem, i might expect a little more power or less melting or something
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