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Discussion Starter #1
Need your input!

Got my 347 stroker running and have driven it to a recent car show in California andit did fine. BUT, I have a slight miss.

It's hard to describe (and I am pretty good usually at diagnosing engine problems but this one is kinda strange).

My car starts great and with the cam I have of course it has a hell-of-lope to it, so the idle is pretty shakey anyway, especially with the A/C on. But I deal with it.

When I drive it (somewhere around 2,500 to 3,500 RPM) it appears to get a girgling kinda miss. If I really get on it it smooths out (I think). The damn thing has SO much power it's hard to tell for sure but I don't think I am realizing it's full 450 horses quit yet.

I tried rejetting the carb and richening it up a notch and in some ways that appeared to help it but now I'm not so sure. I've played with the timing some by advancing and retarding it and that hasn't helped much either.

I have a NEW set of Jacobs wires on it and just put new plugs in it but I may have a cracked plug or a wire that is breaking down at that certain RPM, that's about the only thing I can think of at this point. SO, I guess I'll change the wires and plugs and see if that fixes it.

What do you think? Any ingenious ideas?

Here is the specks on my motor
http://www.inficad.com/~moneymanager/newengine.htm

Doc the moneymanager
http://moneymanagment.info/347completed.jpg
 

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The 347 has a sound all it's own from what I have heard. A friend of mine said he could tell the difference at the California speedway when a 347 went bye as compared to anything else. Are you sure it is a miss or could it just be the sound of the engine.
 

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Is this problem in the 2500 - 3500 range there when you are driving like an old man (slow to moderate acceleration - cruise type driving) AND when you are driving hard, or just one or the other?

With the big cam your carb may be trying to open up the secondaries on you in moderate driving and it is flooding the engine a little since you really aren't driving hard...or conversely.....it might actually need more fuel when you hit that RPM and it isn't getting it. I would adjust the secondary springs first and see if that helps.
 

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Discussion Starter #6
You might have a point there. It's such an unusual sound and feel it's really hard to tell but it sure feels like a "bluberring" kind of miss. Almost like it's getting either too much gas or not enough, I can't tell which. But when you get on it more it goes away and pulls like HELL!

I'm gonna put it on a DYNO and find out for sure. I'll post my findings when I do it.

Thanks
"Doc"
 

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Discussion Starter #7
It accelerates fine from a stop and then when it gets into that RPM range kinda like crusing along at a moderate speed just waiting to shift into a higher gear or waiting to accelerate more, that's when I feel it.

Your idea of adjusting the secondary springs might be it, I'll try that when we put it on the DYNO and see if that helps it.

THANKS, that's a good suggestion that might just be it.

"Doc"
 

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You havent been playing with that NITROS have you? ::

With 450 HP, I imagine at 2500-3000 RPM your motor just isn't "clearing out"... You may be gassing up a plug or two... I'd try a new set of Autolites.
 

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Discussion Starter #9
Yes that may be it as well. I have a new set in it now but as you suggested I am going to change them and the wires again and give it a try. Who knows? That might just fix it.

Thanks
"Doc"
 

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A day at the dyno will reveil a lot. for what it's worth, Iv'e read that those new Nippon Denso irridium (sp?) plugs are suppose to be fantastic in hi hp motors. In more then one case I have read that those plugs made all the difference. From running like crap, sputtering and spitting with platinum to flat out running fantastic with nothing more then a plug change to irridium plugs. In one case, it saved them from putting in a big ignition system! And this was a case where a super charger was used.
 

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Check those Jacobs wires. Since Jacobs have been sold, their quality has decreased. I have a set (my third set!!) that is being replaced. One wire opens up at temperature and when in a certain position that, interestingly, corresponds with the position of the engine under acceleration. Man, tht took a couple of hours to find with an Ohmmeter. My Jacobs Pro Street also failed. The new people are nice, easy to deal with and great about replacing these things but there is just too much failure. Plus their tech. hotline doesn't return calls so there is some frustration there. It wasn't that way when Dr. Jacobs still owned the company in my opinion and experience. When I get the replacement wires and Prostreet I'll replace them with Taylor wires and an MSD spark box of some sort.
 

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Sounds like a lean condition. Typically steping up one 'notch' wont do much. You also said it seemed to help some, so I would go another jet or 2 up in the primary side.
Maybe the secondary could come down 2.
What do you have installed right now?
 

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As others have suggested, there is no better money spent than on a actual dyno tune. Many spend thousands of dollars and don't invest a few hundred to correctly tune it.

Is your carb brand new, or has someone been in it? Could be a lean condition at that rpm, or rich condition. I would also suggest checking the idle vacuum and vacuum readings in the 'miss' zone. Check your power valve and insure that it is at least 3" lower than either.
 
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