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:
O2 sensorMike
I don't know if I'm out in left field here but would a wide bandgetting at(exhaust sniffer) be useful here to tell you what mixture you'reto get theirvarious points on the power curve? I know the car guys use themto make theECU maps right when adding a turbo, basically the issue there issystems likemost power but not go lean at any point to keep from burning pistons.
They usually go with stand-alone fuel injection/engine managementthink thesethe 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'tdone some workthings like lead so you'd have to be running MOGAS but you haveis, I don'twith 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 problemmixture>>control specifies is to remove the power valve and blockhave one. One of the mods that the manufacturer of the cockpit
off the hole with apower mustsupplied plug. I'm thinking the enrichment I am getting at maxthough. I have nohave something to do with the secondaries. Just guessingthrottle. I mayreal idea what causes enrichment between 4000 RPM and fulljets in theexperiment with removing my mixture control and try a bunch ofwhat happensstock config for the carb to see what happens. I may even seeBehalf Of Kenif 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] Onpower to beSent: 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 maxoperating. Inormal. Perhaps you are a bit lean prior to the enrichmentopen ordon't know whether the enrichment starts when the secondariesreason>>that I kept my engine internally stock and deferredbefore that on your carb. Adventures like yours are part of the
decisions aboutof wishwhether to do mods for the next engine.
My vacuum pump is OK but my horizon has become unreliable. KindI couldit was just my pump...
Ken
Mike Kimball wrote:
common withlive
cruise>>>to adjustpower.
conservative profile.and colderpreignition/detonation>>>than I was before.decided toengine started tonoticed that Iand the engine4500RPM>>>pitch but Istatic
various RPMS.know
Holly>>>engine>>>wouldn't even stay running at max power with a settingsomehow
just slightly leanit to stayof
rest of theacceptable allplate to allowadvance>>>to 4500RPM.past
any vacuumhave fried-------------------------------------------------------------------
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