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Looking for best MPG on 454

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akdale:
Hi all,
Cliff's book should be in my hand this afternoon so I will have that to refer to, but there is no substitute for real time input.
I have been lurking and reading this site for a while, and have not quite located the info that I an seeking.

I have a 1984 31' class A Pace Arrow Motorhome.
I estimate that the weight is about 14,000 lbs.
It is on a P30 chevy truck frame.
The engine is a 454 that appears to be untouched although I am not sure if the factory put in a light cam for the motorhome application.
The tranny is a 3 speed turbo 400 which I would like to change to a 4 speed. (That is not in the cards yet until I can find a reasonably priced stand alone computer to manage it.)

When I bought the coach, (about 1500 miles ago) I found that I was getting about 4.5 MPG.
Looked at the carb and found that someone had tried to improve the economy by removing the choke plate..  They also Jammed the secondary air closed where they could not function so I suspect that when the manual secondaries opened, it was sucking fuel through the jets like a straw and just running super rich without the proper air mix.
There were so many vacuum leaks that the exhaust was not black.

I put a kit the carb re-using the jets and metering rods that were in it.
I also attempted to use JB weld to patch the leaky bowl.  Maybe worked for 5 minutes.
Going to tap and plug them this time.
Engine is not running bad.
No Bog
Secondaries working great.
With the dog house open, I can see them open all the way.
(I have to be careful when they open all the way---The duelies break loose and she starts getting sideways.....  ;)
Idle slightly rough with a intermittent miss.
Timing is at 6 BTDC  Supposed to be at 4 BTDC. (Vacuum disconnected and plugged from Dist.)
Mechanical and Ported vacuum Dist.
13-14hg Vacuum at 800rpm idle
Smog still hooked up.


Carb number= 17084502 2373HNX
Jets=73
Primary rods=49M
Secondary rods=DH
I do not have the Bleed and passage info.

The question that I have is,
What is the recipe that will get the most MPG from this setup.
(Driving like Granny) I am rarely into the secondaries.
Thanks,
Dale

429bbf:
dale i built a carb for a buddy of mine for a ford motorhome about the same specs as you have. i used a 17085212.according to your no.170845## yours is a california model. heres how we set this one up.idle tubes .034  idle down channel restrictors .056 upper air bleed .068 lower .062 idle bypass air .075 mixture screws .060  jets are .075 needles are 58s   single main air bleed carb in air horn .052 acc.discharge .026 holes for 4 barrel wells .040 secondary needles EF i adjusted the throttle plate stops to 90 degrees and bent the linkage so he could run on the primaries untill the very last amount of throttle pedal  then the secondaries will start to open. it used to have a holly at 4-5 mpg now hes running 8-9 the APT is set about 4 turns up and the idle screws are out about 8 turns. runs like a dream.hope this helps dean

akdale:
Thanks Dean.
Quite an improvement.
Looks like you have less fuel at cruise/mid range than I do now?
Dale

429bbf:
dale i dont know if your carb has the top limit on the APT.i had his set about 3 turns down and he said it seemed lean just before the 4 barrel was opening . so i had him raise it 1 turn and he says now he very seldom uses the secondaries. hope this helps.when i got done adjusting things the primaries were about 90 percent open before the sec.started to open.

akdale:
I have the adjustable lower limit.
I think that the only way for me to adjust the rich limit is to bend the hanger.

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