Holley 4175 Idle Circuit Problem

[Jeffrey Knox]

I have a boat with a 93 OMC Chevy 5.7L(350) motor that uses a Holley 4175
spreadbore carburetor. I bought the boat used several years ago and has
always run well at full throttle but at idle it seamed awful rich. If a lot
of time was spent on the water idling, when I would remove the boat from the
water the back of the transom would be black. I decided to see if I could
lean out the idle circuit to solve the rich idle and found that the idle
screws were turned all the way in. Turning them out only makes the rich idle
condition worse. Pulling the plugs out they are all flat black. Over the
past 3 weeks I have been trying to troubleshoot this problem and have not
made much progress.

I sent a detailed message to holley tech support and got an answer, leaking
metering gaskets. I replaced both primary and secondary gaskets with no
change. I have 2 different Hollley carburetor books and have read both cover
to cover again trying different things but nothing I have done has made a
difference with regards to getting the idle circuit to function.

I hoping some can point me to something I have over looked or maybe some
other methods of troubleshooting this problem. I will detail the best that I
can what I have done so far to troubleshoot this problem and the carb
itself.

The Carb.......

The carb is a Holley list #80328-1, 4175 spreadbore, with vacuum secondary.
The fuel bowls are side hung with no external float adjust. The primary
metering block is more like a 4160/4150 block, it doesn't have the
accelerator pump check ball in the block like most 4165/4175 most do, it has
it under the accelerator pump discharge nozzle like a 4160/4150. The jets
are size 62 and the power valve a 3.5. The metering block has the number
10959 stamped on it, it is not the reverse idle screw type as far as I know.
It uses the transfer tube with 2 o-rings for the accelerator pump fuel
transfer and the anti-pullover style nozzle #31. The secondary is a metering
plate setup, plate number 34R-9716B stamped #55.

What I have tried.....

I have gone over almost all the following items at least 3 times. I may not
have them in the exact order I tried.

Power Valve. I replaced the power valve and went as far as putting in the
power valve block-off plug to see if power enrichment circuit was leaking.
No change. Vacuum is around 11-13" at 800-900 rpm. I am in the Denver area,
5800 feet above sea level so vacuum will be about 3" lower than what it
would be at sea level, or so I have been told.

Fuel bowl level has been checked in both primary and secondary.

All air bleed passages and metering passages have been cleaned with carb
cleaner and compressed air.

Various combinations of throttle plate position and idle screw have been
tried. I also tried opening up the secondary throttle blades slightly which
allowed me to close the primary throttle plates but that made no difference
either. Pulled idle screws out, they don't look damaged.

Main Jets appear to be pretty close on WOT, after caursing around the lake
at 4600 rpm I can pull the plugs and they all have that picture perfect look
you see from most spark plug reading brochures. It was suggested that I try
small jet size 10 down to 52, to see if it had any effect on the idle
circuit or the transition slot which is slightly uncover on the primary, no
change.

I checked with a straight edge to make sure the metering block and the main
body was not warped. Same on the secondary side metering plate.

I wondered if maybe I had weak spark or maybe low compression so I did a
compression check, all cylinders were within 5 pounds of 150. I
disconnected the ESA(Electronic Shift Assist), this basically interrupts the
spark from the coil momentarily allowing it to engage the drive unit
smoothly when you put it in gear, just to make sure it wasn't cutting in on
its own. I put a HEI distributor in just to make sure it wasn't a ignition
problem, no change.

Thats is where I am at right now. Does anyone have any suggestions of
something I may have over looked or done wrong? Any ideas on how I can try
to isolate the problem to at least the primary or secondary side?

Thanks in advance to all who reply.

Jeffrey
jwk...@ix.netcom.com

[Mark Sullivan]

I just got through with the same type issue with my Spread bore Holley. Finally
gave up and took the carb to a place that specializes in fine tuning race
engines. They basically tore out the idle circuit and built their own at a cost
of around $400. They told me that Holley performance carbs in their "mid-line"
are notorious for this. Their advice was that Holley is great if you don't do a
lot of idling, or if you replace the idle circuit. Otherwise, get an
edelbrock. They did suggest completely closing off the secondaries at idle.
The downside is that the plates could potentially stick, but it might lean it
out a bit.

Mark

[milwau...@hotmail.com]

Are you sure this is a carb problem? I'd borrow a known to be good carburator from someone
and see if the problem goes away.
Does the motor have a long duration cam? If so an over rich exhaust at idle is normal.
Red
Red's Garage
.

[Carl G. Craver]

What plugs are you running?
OMC recommends Champion RV15yc4 plugs for this
engine (and all small block GM and Ford) to eliminate
the problem you are describing.

The original plugs RV8YC were just not hot enough to keep them
from fouling during idle.

Try this first.
Carl G. Craver
Evinru...@msn.com

Jeffrey Knox wrote in message <6pbv9o$1...@sjx-ixn11.ix.netcom.com>...

[Daniel]

Hi Jeffrey
Problems like this get really old. One item you might check is the fuel
pump pressure. (I might have over looked it in your message) Had a
similar problem. At Idle the pressure was to high and would over power
the float and run rich a idle. Above idle, the engine used enough fuel
that the engine ran OK.
Also, a bad needle and seat could cause this.

Dan
**To reply via E-mail, change "AT" and "DOT" in email address to the correct
"symbols."

-----Original Message-----
From: Jeffrey Knox <jwk...@ix.netcom.com>
Newsgroups:
alt.autos.sport.nhra,rec.autos.misc,rec.autos.rod-n-custom,rec.autos.tech,re
c.boats
Date: Saturday, July 25, 1998 1:53 AM
Subject: Holley 4175 Idle Circuit Problem

>
>Thats is where I am at right now. Does anyone have any suggestions of
>something I may have over looked or done wrong? Any ideas on how I can try
>to isolate the problem to at least the primary or secondary side?
>
>Thanks in advance to all who reply.
>
>Jeffrey
>jwk...@ix.netcom.com
>

--

[Mark Sullivan]

Carl...this post is very interesting. Could you elaborate? I've been running
plugs that are one number hotter than stock and the problem still exists. How
much hotter than stock are the plugs you're recommending?

Mark Sullivan

Carl G. Craver wrote:

[gee...@inreach.com]

Hi there!

The comment about too high fuel pressure was a good one. Here's
another. If you have the black nitrophyl plastic floats, replace them
with brass or hollow tan plastic floats. The black nitrophyl floats
are notorious for soaking up gas and sinking.

Also, bad float valves can cause flooding problems. Have you replaced
them? I suggest buying a Holley brand rebuild kit instead of individual
float valves, as the cost of the kit is relatively low, and will have
two float valves in it as well as many useful gaskets. DO NOT buy an
off-brand kit. ONLY HOLLEY KITS! Everything else is overpriced and
poor quality.

Read my Holley carb tuning page at
http://home.inreach.com/geewhiz/carb.htm , and email me if you have any
questions.

Gerard
--
BOB Oil Recovery System: http://www.bob2000.com
-----------------------------------------------------------
Geewhiz Homepage: http://home.inreach.com/geewhiz/4277.htm :
Fast Ford cars, ATV's, Rockets, & A Tribute to My Late Father

[gee...@inreach.com]

Man, I think you got ripped off! Did they say what they did to the idle
circuit? On a carb that is in good condition with good, tight throttle
shafts, there is really nothing you can do to the idle circuit of a
Holley, especially if it idled well when in newer condition. You could
have bought a brand new carb for $400.

Closing the secondaries completely works ok only if your engine idles
slow and smooth. By closing the secondaries as much as possible, this
means you must open the primaries more to make up for lost airflow.
Opening the primaries TOO much at idle gets the primaries into the
transfer slot, which totally overrides the idle feed ports, making for a
rich idle. This also occurs if you open the secondaries into the
transfer slots.

One thing people don't realize about Holley 4 barrel carbs is that the
secondaries flow fuel and air all the time, no matter what the engine
speed is. This is intentional, to prevent the fuel in the secondary
bowl from becoming stale. Since it's flowing anyway, take advantage of
the secondary idle circuit's idle air and fuel flow to help keep the
primaries butterflies below the transfer slots for mixture
adjustability.

Read my Holley carb tuning page at:

http://home.inreach.com/geewhiz/carb.htm for more info.

Gerard
--
BOB Oil Recovery System: http://www.bob2000.com
-----------------------------------------------------------
Geewhiz Homepage: http://home.inreach.com/geewhiz/4277.htm :
Fast Ford cars, ATV's, Rockets, & A Tribute to My Late Father

[gee...@inreach.com]

You guys are playing with fire by putting hotter plugs in an engine that
obviously has a problem. Fix the problem that's causing the fouling,
and don't try to crutch it along.

In boats especially, running hotter than normal plugs is a recipe for
disaster. Under sustained loads as seen in boats, the tips of hotter
plugs will get hotter than stock, and send your engine into preignition,
destroying the entire engine.

Gerard
--
BOB Oil Recovery System: http://www.bob2000.com
-----------------------------------------------------------
Geewhiz Homepage: http://home.inreach.com/geewhiz/4277.htm :
Fast Ford cars, ATV's, Rockets, & A Tribute to My Late Father

>

[Carl G. Craver]

gee...@inreach.com wrote in message <35BB7B...@inreach.com>...

>You guys are playing with fire by putting hotter plugs in an engine that
>obviously has a problem. Fix the problem that's causing the fouling,
>and don't try to crutch it along.
>
>In boats especially, running hotter than normal plugs is a recipe for
>disaster. Under sustained loads as seen in boats, the tips of hotter
>plugs will get hotter than stock, and send your engine into preignition,
>destroying the entire engine.
>

Normaly I agree totaly with this, fix the problem that's causing the
symptoms. However, I'm not recommending this OMC is. There is
a service bulletin on this problem.

OMC has recommended this for their engines for years.
I ALWAYS go with what the manufacuer recommends. In the
latest OMC Parts & Accessories catalog (the book they tell us to
use for spark plug recomedations) they recomend RV15YC4 plugs.

Carl G. Craver
Evunru...@msn.com

[gee...@inreach.com]

Of course, if the manufacturer recommends a particular heat range, you
should use it. But to stuff hotter plugs in an engine that has a carb
problem is just plain stupid.