drt-rcr

I have been working on this truck off and on for a couple months. I know this isn't a truck board but there are some pretty sharp people here as far as engines go. The trouble has been a VERY rich midrange/offidle. Idle is okay and top end is fair. This has been the case with three different carbs. It's an 86 chevy that originally had a Q-jet with the electronic enrichment valve on the rt front of the carb. It also had a computer controlled dist. I changed carbs to a Q-jet from a 79 van I parted out and got same results. I also put on a new 750 holley I bought for my 406 project and again same result. On the holley I set the floats at idle but didn't check after that.
I found out thursday that it was a computer dist. and decided to try with a standard hei.
I put every thing back to original except for the dist. plus I added a new set of wires and plugs plus cap and rotor. I was really hoping that the dist or the computer was bad but no change. Last night I was racking my brain trying to figure this out and I came up with this idea.
IF, the return line from the fuel pump is some how restricted, then the pump could be putting out more than enough pressure and volume at midrange to overpower the needle and seat thereby flooding the carb. At idle the pump is either bleeding off enough excess or it just doesn't have enough volume/pressure at idle to override the needle and seat.
I'd like to put a fuel pressure gauge on it but I don't want to cut the hard line to the carb.
Has anyone experienced this and/or is this a reasonable conclusion?
I hope someone out there can help because I'm really getting tired of this thing in my garage keeping me from working on my bird.

Thanks,,,,, Matt

P.S. I checked compression last night just looking for anything strange and every cylinder was within 5 psi of 210. Isn't that rather high for a stock truck engine? I was expecting something more like 160 or so.

86 chevy truck with HP 305 (engine code H). Possibly the same engine that might have been found in one of our third gens.


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Former Dirt Late Model racer and Third gen lover.
91 V-6 bird with 406 in process.

[This message has been edited by drt-rcr (edited December 30, 2000).]

Vader

Dirt,

I think you have a good theory. Unfortunately, you'll either have to cut into the fuel line or rig an adapter to test fuel pressure. If you have some spare fittings and a 'T' you can probably make it happen without resorting to the tubing cutter.

If you do find a pressure problem, you'll have to cut in somewhere to install a regulator anyway, but that is only a possibility. I'd try the fitting method first.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
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drt-rcr

Okay,
That wasn't the problem. I had a steady 6psi the whole time I ran it. It still runs like S***. Unless someone has any real good ideas it's going to get parked till the weather warms up and I have absolutely nothing better to do than work on it. (that may never happen).
Thanks,,, Matt