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 Post subject: Idle Mixture Screws
 Post Posted: Tue Jun 05, 2012 11:31 am 
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Hey all, been a while since I've posted. Mainly cuz everything that could possibly go wrong, has. And most of them have happened multiple times. I am finally getting ready to run the 555 (assuming I finally got the rings to seat). My question is: Would it be a terrible idea to adjust idle mixture screws according to idle EGT? I know you dont always wanna tune based solely on EGT but I am really really really gonna try n setup this carb (APD 1150) to NOT dilute the oil. I already know my fuel pressure is too low downtrack so I ordered some extra bypass pills for my Enderle pump. So now I need to adjust the idle and thought watching the EGT at idle would be the easiest way. Not to mention if I adjust it pretty hot at idle, I could build heat a lot easier. I'm just ready to go racing again!

Any help would be greatly appreciated.
Thanks
Brad

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 Post subject: Re: Idle Mixture Screws
 Post Posted: Tue Jun 05, 2012 12:13 pm 
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Ya have to be careful and not get an alky carb too lean at idle cuz that will likely create problems in the shut down area, ie, it'll want cut off if you're in neutral after the stripe. Of course with a belt drive and bypass setup it's likely to flood and cut off then anyway. I have seen real lean idles cause a slight stumble at the "hit" also. A lean out valve is a better choice IMHO.

As far as milking the oil goes, I get some condensate in the valve covers but in the shut down area after the last run of the day I cut the water pump off, then drive it back to the trailer to make sure it's "good n hot", ie, at least 200* before I load it up! Then I pull the breather/evac tubes off once it's in the trailer and just let it air out and it does fine. And BTW, I run the same synthetic oil "forever"!!! O:)

The biggest problem I see with methanol and extended oil change schedules is that there's a sludge buildup that settles in the oil pan over time and there's only two ways to get that out.

1. Get the oil out of the engine when it's good and hot, like after the last round in a race.

2. Pull the pan and clean it out a couple of times a year.

Either way, I usually put the same oil back in minus about a half a quart left in the bottom of the jugs that has that sludge in it. Oh, and the longer you leave it sit in those jugs, the more of crap falls out to the bottom.

With synthetic oil I run @ $11 a quart, I damn sure ain't gonna throw it out after every other race! [-X

Your Mileage May Vary! ;-)

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 Post subject: Re: Idle Mixture Screws
 Post Posted: Wed Jun 06, 2012 11:30 am 
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Okay. Thanks for the info.
Mine does fine during shutdown, but it just seems to use WAY too much alky. I thought the i/m screws would be a good place to start. I'm gonna clean out air bleeds and try it.
It seems like a while back Rupert told me a good way to set those i/m screws to fit your combo is to let it get up to heat, deck it from idle and if it stumbles back em in or out (dont remember which). Basically do it until it decks without hesitation. I remember I did that with that carb of his and he was right, made all the difference in the world!
Anyway, one other question. I have been told in addition to doing the things you are talking about, I should squirt some marvel mystery oil in it before I load it up. Ur thoughts?

Thanks again for the help.

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 Post subject: Re: Idle Mixture Screws
 Post Posted: Wed Jun 06, 2012 4:18 pm 
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Brad the Mystery oil can't hurt if it's compatible with methanol. :-k Some oils aren't BTW. WD-40 is a good one for this as it IS compatible with methanol and will also help prevent rust in both the carbs steel parts and the cylinders. And I also roll the engine over a couple of times a week with the starter between races too.

But back to my original post, the best way to dry them out is make damn sure it's "good-n-hot" before you shut it down and it doesn't hurt to have the throttle cracked open either to allow whatever condensate that's in the plenum/runners a way out.

And in case you don't already know this, I NEVER START MY ENGINE ON METHANOL UNLESS I HAVE ENOUGH FUEL AND TIME TO FULLY HEAT CYCLE IT, IE, GET IT TO 200+* BEFORE SHUT DOWN. I've never pulled one down that didn't have "some" rust pits in the cylinders!!

RE: Fuel use? My 18* SBC with dual Rupert 750s will use right at 2.5 quarts per pass trailer to trailer. My fuel cell holds 4.2 gallons and last Sunday we made 4 passes and a cold start warmup drive around on about 3 gallons of methanol.

And another thing about the excessive fuel use, if you're running 10 to 12psig fuel pressure down track, then what happens when you shut the butterflies in the shut down area? If you said that the engine gets flooded with methanol because the needles are blown off the seats, then you'd be correct unless you've got a vacuum referenced regulator on that thing. ;-)

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