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Re: [GMCnet] Injection versus Carbs [message #73921 is a reply to message #73914]

Mon, 15 February 2010 14:40

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma:

Senior Member

emerystora wrote on Mon, 15 February 2010 13:42

On Feb 15, 2010, at 12:33 PM, Bill Freeman wrote:

>
>
> $2175 for "Affordable" fuel injection, plus a lot of work installing
> all that new stuff? It might run perfectly as installed but from
> reading this forum many seem to require a substantial amount of
> additional tuning. Some fuel injection conversions apparently never
> run right.
>
> $15 for a couple of metering rods and 30 labor minutes to put them
> in sounds a lot better to me. If you re-tune a q-jet for 5000 feet
> I expect it would run good enough from sea level to 10,000.
>
>
> --
> Bill Freeman
> 78 Royale 73 Sequoia
> Colerain, North Carolina
> http://tinyurl.com/yx7nra

I think that you would still be too lean near sea level and too rich
above 7500 feet. Of course, than might be "good enough" for you
depending on how much traveling you do away from 5000 feet.

Emery Stora
77 Kingsley
Santa Fe, NM

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IF you tuned it properly for 5000 feet, you WOULD be to lean at sea level and still to rich at 7500 and higher. Tuning a Q-Jet is not as easy as just changing rods or jets. Until I started using a wide band O2 sensor and an LM-1 FA ratio gauge, I had no idea how much altitude plays in FA. I had no idea how much changing rods or jets had on FA. I had no idea that changing the idle screw can change the FA in both primary and secondary circuits. Just as an example, I spent most of October and November trying to tune a Q-jet that has an adjustable part throttle. There are an incredible number of variables when working with a Q-jet. Any minor changes to any of the primary circuits effects performance at WOT...yes even changes to the idle effect WOT. I finally got my carb (a Q-Jet from a 81' chevy PU with 454) set so that I had a highway lean burn of about 15.5/1 going down the road at 60mph, no wind, flat run, 11 to 15 inches of vacuum. That was in Menomonie Wisconsin at an altitude of 970ft. I am now in Texas along the gulf coast at sea level. Just the change of 900+ feet changed my FA from the 15.5/1 to 14.7... under nearly the same driving conditions. Imagine the change that can take place from 5000 to sea level...or 5000 to 10,000 ft.

You could go to a altitude compensating carb, but those are tuned for an automobile and have an extra power valve in them. This adds another whole dimension with several more variables than the standard Q-jet.

After working with a q-jet for several months now, I'm going to MPI for my cad. Instead of pulling the top of the carb for jet changes, changes will be made from my lap-top..maybe even in real time. JMHO

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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[Message index]

		[GMCnet] Injection versus Carbs By: Richard Lister on Mon, 08 February 2010 10:01
		Re: [GMCnet] Injection versus Carbs By: Mr ERFisher on Mon, 08 February 2010 10:10
		Re: [GMCnet] Injection versus Carbs By: GeorgeRud on Mon, 08 February 2010 10:17
		Re: [GMCnet] Injection versus Carbs By: Ron on Mon, 08 February 2010 11:08
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Mon, 08 February 2010 11:14
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Mon, 08 February 2010 12:25
		Re: [GMCnet] Injection versus Carbs By: k2gkk on Mon, 08 February 2010 12:35
		Re: [GMCnet] Injection versus Carbs By: Mr ERFisher on Mon, 08 February 2010 12:46
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Mon, 08 February 2010 18:31
		Re: [GMCnet] Injection versus Carbs By: Larry on Mon, 08 February 2010 22:00
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Tue, 09 February 2010 07:19
		Re: [GMCnet] Injection versus Carbs By: bill schurman on Mon, 08 February 2010 13:11
		Re: [GMCnet] Injection versus Carbs By: Ron on Mon, 08 February 2010 14:31
		Re: [GMCnet] Injection versus Carbs By: Ken Burton on Tue, 09 February 2010 02:11
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Tue, 09 February 2010 06:40
		Re: [GMCnet] Injection versus Carbs By: tgeiger on Tue, 09 February 2010 09:51
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Wed, 10 February 2010 07:57
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Mon, 08 February 2010 15:30
		Re: [GMCnet] Injection versus Carbs By: USAussie on Mon, 08 February 2010 16:23
		Re: [GMCnet] Injection versus Carbs By: Larry C on Thu, 18 February 2010 09:06
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Thu, 18 February 2010 11:17
		Re: [GMCnet] Injection versus Carbs By: Gary Worobec on Thu, 18 February 2010 11:33
		Re: [GMCnet] Injection versus Carbs By: Chr$ on Mon, 08 February 2010 16:48
		Re: [GMCnet] Injection versus Carbs By: Chr$ on Mon, 08 February 2010 16:49
		Re: [GMCnet] Injection versus Carbs By: k2gkk on Mon, 08 February 2010 18:12
		Re: [GMCnet] Injection versus Carbs By: Rick Williams on Mon, 08 February 2010 18:45
		Re: [GMCnet] Injection versus Carbs By: David L Greenberg on Mon, 08 February 2010 19:55
		Re: [GMCnet] Injection versus Carbs By: George Beckman on Mon, 08 February 2010 20:14
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Tue, 09 February 2010 13:25
		Re: [GMCnet] Injection versus Carbs By: Richard Lister on Tue, 09 February 2010 14:36
		Re: [GMCnet] Injection versus Carbs By: George Beckman on Tue, 09 February 2010 20:50
		Re: [GMCnet] Injection versus Carbs By: GeorgeRud on Tue, 09 February 2010 15:04
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Tue, 09 February 2010 15:54
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Tue, 09 February 2010 17:03
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Wed, 10 February 2010 05:41
		Re: [GMCnet] Injection versus Carbs By: klassic kampers on Tue, 09 February 2010 17:34
		Re: [GMCnet] Injection versus Carbs By: Bob de Kruyff on Tue, 09 February 2010 18:35
		Re: [GMCnet] Injection versus Carbs By: Sandra Price on Wed, 10 February 2010 11:18
		Re: [GMCnet] Injection versus Carbs By: tgeiger on Wed, 10 February 2010 14:37
		Re: [GMCnet] Injection versus Carbs By: ljdavick on Wed, 10 February 2010 14:45
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Sat, 13 February 2010 08:20
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Sat, 13 February 2010 09:01
		Re: [GMCnet] Injection versus Carbs By: emerystora on Sat, 13 February 2010 09:47
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Sat, 13 February 2010 15:47
		Re: [GMCnet] Injection versus Carbs By: Ron on Sat, 13 February 2010 16:14
		Re: [GMCnet] Injection versus Carbs By: Surbo on Sat, 13 February 2010 17:45
		Re: [GMCnet] Injection versus Carbs By: Ron on Sat, 13 February 2010 17:57
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Mon, 15 February 2010 13:33
		Re: [GMCnet] Injection versus Carbs By: emerystora on Mon, 15 February 2010 13:42
		Re: [GMCnet] Injection versus Carbs By: Larry on Mon, 15 February 2010 14:40
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Mon, 15 February 2010 15:31
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Tue, 16 February 2010 07:49
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Wed, 17 February 2010 17:34
		Re: [GMCnet] Injection versus Carbs By: GMCWiperMan on Wed, 17 February 2010 17:57
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Wed, 17 February 2010 19:31
		Re: [GMCnet] Injection versus Carbs By: Ken Burton on Wed, 17 February 2010 20:23
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 21:46
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Wed, 17 February 2010 22:01
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 22:34
		Re: [GMCnet] Injection versus Carbs By: klassic kampers on Thu, 18 February 2010 14:22
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Thu, 18 February 2010 09:09
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Thu, 18 February 2010 07:49
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Thu, 18 February 2010 08:38
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 20:57
		Re: [GMCnet] Injection versus Carbs By: Surbo on Mon, 15 February 2010 14:09
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Mon, 15 February 2010 14:38
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Tue, 16 February 2010 07:38
		Re: [GMCnet] Injection versus Carbs By: Carleton Douglas[1] on Wed, 10 February 2010 14:53
		Re: [GMCnet] Injection versus Carbs By: jimk on Wed, 10 February 2010 22:18
		Re: [GMCnet] Injection versus Carbs By: Richard Lister on Tue, 16 February 2010 10:55
		Re: [GMCnet] Injection versus Carbs By: bryant374 on Tue, 16 February 2010 12:21
		Re: [GMCnet] Injection versus Carbs By: Bill Massey on Tue, 16 February 2010 13:24
		Re: [GMCnet] Injection versus Carbs By: psakw on Sat, 13 February 2010 21:58
		Re: [GMCnet] Injection versus Carbs By: emerystora on Sat, 13 February 2010 22:07
		Re: [GMCnet] Injection versus Carbs By: rallymaster on Thu, 18 February 2010 11:45
		Re: [GMCnet] Injection versus Carbs By: g.winger on Thu, 18 February 2010 14:11
		Re: [GMCnet] Injection versus Carbs By: Larry on Thu, 18 February 2010 15:08
		Re: [GMCnet] Injection versus Carbs By: wally on Thu, 18 February 2010 15:33
		Re: [GMCnet] Injection versus Carbs By: Larry on Fri, 19 February 2010 13:44
		Re: [GMCnet] Injection versus Carbs By: wally on Fri, 19 February 2010 14:44
		Re: [GMCnet] Injection versus Carbs By: Larry on Fri, 19 February 2010 19:05
		Re: [GMCnet] Injection versus Carbs By: GMCWiperMan on Fri, 19 February 2010 19:23
		Re: [GMCnet] Injection versus Carbs By: Keith V on Sat, 20 February 2010 10:12
		Re: [GMCnet] Injection versus Carbs By: GMC_LES on Sat, 20 February 2010 16:45
		Re: [GMCnet] Injection versus Carbs By: WD0AFQ on Sat, 20 February 2010 17:35

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