[rebel-builders] High EGT

[Kim Kimball]

To clarify - there are no main jets. The primary jets are removed. An additional plate is added between the main metering plate and the float bowl. That plate has a shaft that has two slots cut halfway through that lines up right where the main jets would go in the main metering plate. The shaft is rotated by a lever that leads via cable to the cockpit. By exposing more or less of the slot the mixture is leaned or enrichened. It's possible that the full rich position is still not rich enough. To fix this, I would have to widen the slots which is easily done.

Another thing that came to mind just today is that I replaced the 650 carb body with a Proform 750 carb body that eliminates the choke tower. I didn't really want to go up to 750 but it was the only direct replacement carb body I found that gets rid of the choke tower. If this 750 carb is flowing more air than the 650 like it should be then the secondary metering jets would be too small to keep up with the extra air. And possibly, the mixture plate slots were also designed for a 650 carb and aren't large enough for a 750. I plan to call the guy that made the mixture plate and talk to him about it.

Thanks all for your inputs!!! Keep it coming.

Mike

----- Original Message -----
From: Ken <klehman@albedo.net>
Date: Saturday, July 28, 2007 12:23 pm
Subject: Re: [rebel-builders] High EGT
To: rebel-builders@dcsol.com

Guys report 20+ to 100+ hours from O2 sensors that are fed with
avgas.
TCP or Decalin fuel additive should increase that. However I would
not
trust the reading when used on short individual exhaust stacks as
puffs
of air will travel back up the pipes between exhaust pulses. Even
a
$30. narrow band sensor with a multimeter will give a lot of info
but
you'd need decent length exhaust pipes.

With the leaning block one should be able to estimate rich or lean
of
peak though. Full rich should be rich of peak at all throttle
positions.
If leaning does not increas EGT then the main jets are definately
too small.

Ken

Dave Ricker wrote:

Mike

I don't know if I'm out in left field here but would a wide band

O2 sensor

(exhaust sniffer) be useful here to tell you what mixture you're

getting at

various points on the power curve? I know the car guys use them

to get their

ECU maps right when adding a turbo, basically the issue there is

to make the

most power but not go lean at any point to keep from burning pistons.

They usually go with stand-alone fuel injection/engine management

systems like

the 034 but air/fuel ratio is the same whether it's a carb or EFI.

Google "wide band oxygen sensor". Just had a thought, I don't

think these

things like lead so you'd have to be running MOGAS but you have

done some work

with it haven't you?

I think a wide band is under $200.

Dave



Mike Kimball wrote:

Yeah, I know about the power valve for enrichment. Only problem

is, I don't

have one. One of the mods that the manufacturer of the cockpit

mixture>>control specifies is to remove the power valve and block
off the hole with a

supplied plug. I'm thinking the enrichment I am getting at max

power must

have something to do with the secondaries. Just guessing

though. I have no

real idea what causes enrichment between 4000 RPM and full

throttle. I may

experiment with removing my mixture control and try a bunch of

jets in the

stock config for the carb to see what happens. I may even see

what happens

if I put the power valve back in. Oh, the life of the experimenter.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On

Behalf Of Ken

Sent: Friday, July 27, 2007 3:24 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] High EGT

Mike

Most automotive carbs that I've had did have some kind of enrichment
circuit to richen up the mixture at high power settings which does
indeed drop EGT while allowing more power to be developed. Sometimes
called the "power valve". I'd consider the lower egt at max

power to be

normal. Perhaps you are a bit lean prior to the enrichment

operating. I

don't know whether the enrichment starts when the secondaries

open or

before that on your carb. Adventures like yours are part of the

reason>>that I kept my engine internally stock and deferred
decisions about

whether to do mods for the next engine.

My vacuum pump is OK but my horizon has become unreliable. Kind

of wish

it was just my pump...

Ken

Mike Kimball wrote:

I could

live

common with

cruise>>>

power.

to adjust

conservative profile.

and colder

preignition/detonation>>>than I was before.

decided to

engine started to

noticed that I

and the engine

4500RPM>>>

static

pitch but I

know

various RPMS.

Holly>>>

somehow

engine>>>wouldn't even stay running at max power with a setting
just slightly lean

of

it to stay

rest of the

acceptable all

plate to allow

advance>>>

past

to 4500RPM.

any vacuum

have fried

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--
David A. Ricker
Fall River, Nova Scotia
Canada






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[Dale Fultz]

Mike there is a lot that could actually play into this situation that you
have. With out knowing what all was done when you assemble the engine
could be some of it. As an example just because your timing light is saying
the distributor is firing at 14 degrees doesn't necessarily mean it's
actually 14 degrees internally. When you assembled the engine did you
check to make sure TDC was TDC with the piston to your reference pointer for
timing. Next there can be so many variations for the timing of the camshaft
to crankshaft reference done with a timing dial. Changing the timing to make
it advance more in my opinion won't help the situation. If you get to much
advance when the cylinder fires the piston is to far down into the cylinder
yet and you will be trying to push it back down (we have seen all this on a
dyno) this is one place that if some is good more is better. Next it would
be helpful to know where you put the sensor for the water temps??? Are the
fuel preasure readings consistant throught the power ranges you are
checking??? As you are finding out there are so many variables with a V-8 of
the type you have installed.
Just a couple more ideas for you to hash around.. Dale




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[Mike Kimball]

I did check that the zero point on my harmonic damper is truly TDC on #1. I
carefully found TDC without looking at the damper marks, and when I was done
it was pointing right at zero. I also comfirmed correct timing chain
installation: the CAM specs for intake valve opening says it should start to
open at 5 degrees BTDC and that is exactly where the intake valve starts to
open. My temp sender for coolant is on the water pump. Admittedly, not an
ideal location, but without drilling a hole in my intake manifold my only
other option is in the thermostat housing which is a tall one with a
radiator cap. That might be better and I may move it there. Since I am not
running a thermostat (I made a plate with a 5/8 hole to restrict flow) the
readings should be a reasonable representation of the overall coolant temp
since the coolant is always cycling. Everything seems to be pointing to a
lean mixture right now so that is what I am fiddling with to try and address
EGT.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Dale
Fultz
Sent: Sunday, July 29, 2007 6:58 AM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] High EGT

Mike there is a lot that could actually play into this situation that you
have. With out knowing what all was done when you assemble the engine
could be some of it. As an example just because your timing light is saying

the distributor is firing at 14 degrees doesn't necessarily mean it's
actually 14 degrees internally. When you assembled the engine did you
check to make sure TDC was TDC with the piston to your reference pointer for

timing. Next there can be so many variations for the timing of the camshaft
to crankshaft reference done with a timing dial. Changing the timing to make

it advance more in my opinion won't help the situation. If you get to much

advance when the cylinder fires the piston is to far down into the cylinder
yet and you will be trying to push it back down (we have seen all this on a
dyno) this is one place that if some is good more is better. Next it would
be helpful to know where you put the sensor for the water temps??? Are the
fuel preasure readings consistant throught the power ranges you are
checking??? As you are finding out there are so many variables with a V-8 of

the type you have installed.
Just a couple more ideas for you to hash around.. Dale




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[Dale Fultz]

Mike you need to get the sending unit out of the water pump!!!! With it in
there all you are reading is the temperature of the water returning from
the radiator... You need to have it where it exits the engine thermostat
housing is the best place or side of the head would be better.. I think you
will find your water temperature is a little higher then you think it is and
you also probably have a lean condition.. If you are lean now this time of
the year when the air is terrible for performance you will really be lean in
other times of the year when the air is better to burn in the combustion
chamber... JMO Dale N269DF




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