Holley Cruising Lean Out: Stumped...
James Drinkwater
Got a Holley 650 double-pumper on "Dad's hotrod" with some probs tuning.
Upon depression of the throttle, my fuel/air ratio gauge shows that the
mixture goes way lean and the engine goes into lean misfire and dropped
power. Eventually it richens back up as the RPMs slowly increase. Not
talking about the accelerator pump, just giving it a little more gas while
driving.
Bought the carb from my machinist in the original box in like-new
(visually) condition. Here's what's new and ruled out: high-volume fuel
pump, fuel filter, fuel regulator and pressure gauge, float needles & seats,
jets (just to be sure), 6.5" power valve (like the original). both
squirters appear to pump fine but the problem occurs when you slowly roll
into the throttle and it happens really quick (very throttle sensitive).
It's a moderate, street performance SB Chevy that makes about 10.5" vacuum
at idle. I know the PV should move up to 8.5" but rolling into heavy
acceleration (vacuum below PV opening point) doesn't overcome the lean
condition either.
Two last things are that idle mixture is pretty un-responsive to idle
mixture screws, even when idle speed is as low as the engine will reliably
rev. Second, main jets were very, very rich at stock 67's (primary) and
still a tad on the rich side with 65's.
Dirty passage somewhere? Higher vacuum power valve needed and drill the
PVCR's? I'm a little stumped.
Best Regards,
Drink
'87 TransAm (No computer controls)
Holley 650cfm double-pumper
Victor Jr. single plane
186 heads, fully ported with 2.02 valves
218/228 roller cam
1.6 magnum rockers
10:1 KB pistons
Mallory Comp9000 distributor
Hooker SuperComp headers
3.73 gears
jim
James Drinkwater wrote:
>
> Hi Guys,
> Got a Holley 650 double-pumper on "Dad's hotrod" with some probs tuning.
> Upon depression of the throttle, my fuel/air ratio gauge shows that the
> mixture goes way lean and the engine goes into lean misfire and dropped
> power. Eventually it richens back up as the RPMs slowly increase. Not
> talking about the accelerator pump, just giving it a little more gas while
> driving.
> Bought the carb from my machinist in the original box in like-new
> (visually) condition. Here's what's new and ruled out: high-volume fuel
> pump, fuel filter, fuel regulator and pressure gauge, float needles & seats,
> jets (just to be sure), 6.5" power valve (like the original). both
> squirters appear to pump fine but the problem occurs when you slowly roll
> into the throttle and it happens really quick (very throttle sensitive).
> It's a moderate, street performance SB Chevy that makes about 10.5" vacuum
> at idle. I know the PV should move up to 8.5" but rolling into heavy
> acceleration (vacuum below PV opening point) doesn't overcome the lean
> condition either.
> Two last things are that idle mixture is pretty un-responsive to idle
> mixture screws, even when idle speed is as low as the engine will reliably
> rev. Second, main jets were very, very rich at stock 67's (primary) and
> still a tad on the rich side with 65's.
> Dirty passage somewhere? Higher vacuum power valve needed and drill the
> PVCR's? I'm a little stumped.
You didn't say anything about float adjustment. A low float level would
match the description of the problem. Late ignition timing would also
contribute to the problem.
-jim
> Best Regards,
> Drink
>
> '87 TransAm (No computer controls)
> Holley 650cfm double-pumper
> Victor Jr. single plane
> 186 heads, fully ported with 2.02 valves
> 218/228 roller cam
> 1.6 magnum rockers
> 10:1 KB pistons
> Mallory Comp9000 distributor
> Hooker SuperComp headers
> 3.73 gears
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Gary - KQ6RT
rated in two different systems. I forget which is which, but one is inches
of mercury and the other is inches of water. Divide your gauge reading by 2
then subtract 1 and round off. I figure you probably need a 5.0 power valve.
Gary
"James Drinkwater" <jdrin...@satx.rr.com> wrote in message
news:45d74c48$0$24706$4c36...@roadrunner.com...
James Drinkwater
Revs don't drop upon hard braking (like I think you'd see with low floats).
I have clear sight plugs and it looks good.
I tried timing from 6-8 at idle and tried total timing and it came back to
roughly the same idle time. Today I used the vacuum gauge and best vacuum
gave 20+ idle timing. When I ran it up the road, surprise... ping! Just
backed off down to 15deg. We'll see how that fares without the vacuum
advance connected (and work from there).
Still, idle mixture screws are fairly unresponsive. I wonder if the
secondaries are open too far. But, if that were the case, wouldn't closing
them a bit be an erred solution to different problem?
Drink
"jim" <"sjedgingN0sp"@m...@mwt.net> wrote in message
news:1171738...@sp6iad.superfeed.net...
James Drinkwater
wouldn't be an issue on the interstate when the revs and vacuum are up.
Check my logic on this one. At cruise (2,500-3,000rpm) the vacuum's from
15"-20" and the PV's out of the picture. It goes lean with even a slight
increase of throttle. Heavier makes it worse.
Drink
"Gary - KQ6RT" <kq6rt(NoMoreSpam)@sbcglobal.net> wrote in message
news:SBIBh.6469$o61....@newssvr19.news.prodigy.net...
Steve Austin
Maybe you aren't talking about the accelerator pump, but you should be
looking at it.
jim
James Drinkwater wrote:
>
> Floats are correct and have fiddled with 'em up and down to no avail.
> Revs don't drop upon hard braking (like I think you'd see with low floats).
> I have clear sight plugs and it looks good.
The lean problem with very light acceleration still sounds like low
float level or late timing. Although bad thermostat (engine too cold) or
bad gas could be a part of the problem. How old is the gas in the gas
tank.
> I tried timing from 6-8 at idle and tried total timing and it came back to
> roughly the same idle time. Today I used the vacuum gauge and best vacuum
> gave 20+ idle timing. When I ran it up the road, surprise... ping! Just
> backed off down to 15deg. We'll see how that fares without the vacuum
> advance connected (and work from there).
Did advancing the timing help or was it still lean? If its still lean
that could be the cause of the ping. You may have to live with some ping
given the nature of modern gasoline. You need to get the timing right
before you mess with the carb. Don't assume timing marks on vibration
damper are correct.
> Still, idle mixture screws are fairly unresponsive. I wonder if the
> secondaries are open too far. But, if that were the case, wouldn't closing
> them a bit be an erred solution to different problem?
The idle mixture shouldn't have much to do with the problem you
described. Is it getting too much gas at idle or not enough?
-jim
Eugene Blanchard
stupidly) connected the vacuum advance to manifold vacuum rather than the
carb pre butterfly outlet. It killed the engine response like yours.
Have you checked your ignition timing at idle (about 8 degrees) then up to
3000 rpm to see what the advance is doing - should be about 30 deg total
advance or so?
My rule in troubleshooting - if it looks like a carb problem: check the
ignition system. If it looks like an ignition problem: check the carb.
Works 90% of the time.
You never said if you have a HEI distributer or points. If it's points check
the gap.
James Drinkwater wrote:
--
Eugene Blanchard
http://www.catsasskustoms.com
Parts, Performance, Passion
News for Motorheads
James Drinkwater
that can't be it. Let me describe the situation better. Interstate cruise
is the most obvious.
So, there I am on the interstate cruising along at about 60mph. The
engine's revving and the mixture's doin' alright. If I press a little on
the accelerator smoothly to get up to 65 or 70, it goes way lean and holds
in a lean condition until I get up to the desired speed and ease out of the
throttle a tad to hold it.
I'm not "kickin' it" to need the pump shot or so heavy that the vacuum
drops enough that I'd need the Power Valve; just a little more throttle. If
I do continue to roll into the throttle for heavier acceleration, it don't
see the PV overcome the lean condition.
Perplexing, huh?
Drink
"Steve Austin" <saus...@twcny.rr.com> wrote in message
news:45d79695$0$28119$4c36...@roadrunner.com...
James Drinkwater
Timing didn't correct the lean condition. I installed a new Tstat and the
engine gets up to 195deg max. I drive the T/A regularly and the gas is
fresh. This fresh engine (still dialing in the carb & spark curve), oddly
enough, doesn't ping when it leans out; the power just drops until it
sputters.
I threw in the idle mixture problem in case it's indicative of something.
I can turn in the idle mixture screws a 1/2 turn or more until it makes a
difference and the revs drop off hard.
Thanks for the reply,
Drink
"jim" <"sjedgingN0sp"@m...@mwt.net> wrote in message
news:1171758...@sp6iad.superfeed.net...
Steve Austin
for a lot of it with pump shot. Check the pump cam to see if anybody
has messed with it (stock and in stock locatation). Make sure the check
ball is still there (under the pump nozzles). Make sure it has the 50cc
pump. I like the actuating arm to be on the cam when throttle closed
(as long as you still get full travel).
Eugene Blanchard
troubleshooting suggestions/comments:
Your idle circuit is not working right. You've stated that it is
unresponsive to the idle mixture screws. Are the tips of the screws sharp
or dull? If you screw in an idle mixture screw in too far it can dull the
point. Are they the correct ones for length? Some screws are shorter than
others. Maybe you have the wrong length ones. I know that there is a
difference in length for emission vs non emission idle screws.
Could be that the main jets were rich to compensate for the idle circuit is
not working... You may have to open up the carb to find out why the idle
circuit is not working.
BTW what model Holley is it? Could it be one made specifically for racing?
James Drinkwater wrote:
--