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4.9 Wont idle by northstar
Started on: 09-05-2013 08:48 PM
Replies: 11 (288 views)
Last post by: trotterlg on 09-07-2013 02:25 PM
northstar
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Report this Post09-05-2013 08:48 PM Click Here to See the Profile for northstarClick Here to Email northstarSend a Private Message to northstarEdit/Delete MessageReply w/QuoteDirect Link to This Post
Transplanted a 95..4.9 Into my 86 se...got rid of the fuel injection.milled the intake to receive a mechanical Carb. The Carb is brand new..I can't get it to idle..only if I crank the idle screw all the way in.it will stay running at about 3k rpm..any ideas? Thanks c-note
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trotterlg
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Report this Post09-05-2013 08:52 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
What carb? I have a Qjet running on my 3100 and it is great. Larry
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northstar
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Report this Post09-05-2013 09:19 PM Click Here to See the Profile for northstarClick Here to Email northstarSend a Private Message to northstarEdit/Delete MessageReply w/QuoteDirect Link to This Post
Edelbrock...brand new..at low rpms it seems to be flooding and running on not all 8 cylinders..but when I throttle it up a little the whole engine comes alive and sounds fantastic..
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Zac88GT
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Report this Post09-05-2013 09:23 PM Click Here to See the Profile for Zac88GTClick Here to visit Zac88GT's HomePageClick Here to Email Zac88GTSend a Private Message to Zac88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
What fuel pump are you using and what to do you have the pressure set at?
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northstar
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Report this Post09-05-2013 09:33 PM Click Here to See the Profile for northstarClick Here to Email northstarSend a Private Message to northstarEdit/Delete MessageReply w/QuoteDirect Link to This Post
The original fiero pump
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trotterlg
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Report this Post09-05-2013 09:54 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
You are likely just pushing fuel past the float needle because of so much pressure, that carb only needs about 3 psi and you are hitting it with 50 or so. Larry
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trotterlg
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Report this Post09-05-2013 09:57 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post

trotterlg

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My solution was to build a little pressure relief valve that bypassed any pressure over about 5 psi, just put a "T" in the line and the relief valve in the return line. Mine works really well. Larry
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northstar
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Report this Post09-05-2013 10:09 PM Click Here to See the Profile for northstarClick Here to Email northstarSend a Private Message to northstarEdit/Delete MessageReply w/QuoteDirect Link to This Post
Larry that sounds like the answer. I'll check on my gas flow tomorrow, thank you for responding'''c-note:
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Arns85GT
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Report this Post09-06-2013 09:57 AM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
There are two potential issues.

The first one is the stock v6 fuel pump. Way too much pressure. The easy fix is to install a bypass fuel regulator like the Mallory 3 port. You adjust it down to 6 psi, 7 max, and you are in business.

Second issue is the integrity of the seam between the carb flange and the receiver. Easy to check with a bit of WD40 around the seam.

The Edelbrock is actually a little big for the motor. You may have idle issues with that volume of carb.

Call Edelbrock and find out if you need to adjust your primary circuit. The engine actually uses a little less than 500 cfm (487) max so your Edelbrock may be rich.

Arn

Actually the potential for a vacuum leak around the base is pretty high

[This message has been edited by Arns85GT (edited 09-06-2013).]

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trotterlg
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Report this Post09-07-2013 12:40 AM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think it will run well when he gets the fuel pressure down. The problem I had with the Qjet idle was that my cam was too big to get much idle vacuum, so I had to drill the idle ports out some. This is a known problem if you idle with low vacuum, (mine idles at about 10 inches MP at 1,200 rpm) but it is an easy fix. Good luck, I am betting it runs really well when you get it sorted out. Larry
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Arns85GT
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Report this Post09-07-2013 12:08 PM Click Here to See the Profile for Arns85GTClick Here to Email Arns85GTSend a Private Message to Arns85GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
The stock cam on the 4.9 produces about 18" at 600 rpm and gets up to about 20" at 800.

That is plenty for most applications.

I know from experience though, that milling and modifying is hard to get a tight vacuum seal, and my money is still on a vacuum leak.

Arn
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trotterlg
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Report this Post09-07-2013 02:25 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
The way it is discribed the fuel pump is just pusing too much fue past the float valve when the thing is at idle. As soon as he starts using some fuel things are good. Hope he tells us what the problem really was. I also have found I need about 12 to 15 degrees of static advance for mine to idle, and I don't know what he has done for ignition. Larry
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