Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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07-07-12 09:12 AM - Post#2245397
I bought a rebuilt carb for my boat 2 years ago (3.8L 229 cid V6 90 deg chevy - Mercruiser 185 it's called in marine world)
It has worked decently, but is very rich at cruise. I suspect the primaries because these ebay guys try to sell a one-fits-all carb for 3.8/4.3/5.0 and my plugs look charcoal bbq'd after a long cruise at 3300 rpm.
So Mercruiser manual specs .066" primary jet and .036" rods
so my question is - would those be unstepped rods?
also any suggestions where to buy such parts?
and what would be the next richer set?
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
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motorman
Super Senior Member
Posts: 5017
Loc: south western pa.
Reg: 01-25-00
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07-07-12 12:22 PM - Post#2245464
In response to Mike73
I bought a rebuilt carb for my boat 2 years ago (3.8L 229 cid V6 90 deg chevy - Mercruiser 185 it's called in marine world)
It has worked decently, but is very rich at cruise. I suspect the primaries because these ebay guys try to sell a one-fits-all carb for 3.8/4.3/5.0 and my plugs look charcoal bbq'd after a long cruise at 3300 rpm.
So Mercruiser manual specs .066" primary jet and .036" rods
so my question is - would those be unstepped rods?
also any suggestions where to buy such parts?
and what would be the next richer set?
what is the number stamped on the carb 
| retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way |
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Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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07-08-12 11:30 AM - Post#2245722
In response to motorman
no numbers stamped anywhere I can see -
but I got the parts out
jets are marked 71
rods are B 36
so looks like I just need some 66 jets
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
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motorman
Super Senior Member
Posts: 5017
Loc: south western pa.
Reg: 01-25-00
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07-08-12 11:35 AM - Post#2245724
In response to Mike73
no numbers stamped anywhere I can see -
but I got the parts out
jets are marked 71
rods are B 36
so looks like I just need some 66 jets
here you go. http://www.carburetion.com/quadrajet.asp
| retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way |
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Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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 07-08-12 01:22 PM - Post#2245759
In response to motorman
thanks!
$43 for 2 pair shipped  , but at least they have them... 
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
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 4dr 57
"6th Year" Silver Supporting Member
Posts: 2734
Loc: The Texas Hill Country
Reg: 11-10-04
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07-08-12 05:47 PM - Post#2245845
In response to Mike73
Mike, here in Texas at the Southern part of the world, there was a Carb Shop owned by a guy named Mike, too. He was good with Q-jets. He told me one of the easiest things to overlook was the 'cam' in the center of the carb horn. I remember replacing my worn one, but no too well. So I'm just passing it on because he was reliable:ex racer.
Stanley
| Wife: "Don't race the Police car, Stan!" |
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 carbking
Senior Member
Posts: 1151
Loc: Missouri
Reg: 06-14-03
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07-09-12 07:53 AM - Post#2246066
In response to Mike73
To really be sure, you NEED to locate the identification number on your rebuilt carburetor.
Often, Rochester would use the same fuel jets, but different air jets. You really need to know the actual number before guessing on rods/jets.
On Rochester Q-jets manufactured AFTER about January of 1968, the number will be STAMPED in a vertical line on the center section just above the secondary throttle shaft arm. Units from 1968 through 1975 will be 7 digits, beginning with 70. Units from 1976 will be 8 digits, beginning with a 170.
And Stanley (post directly above this one) is correct on the plastic cam. This is the cam that controls the opening of the secondary rods. They should ALWAYS be replaced when rebuilding a Q-Jet.
Jon.
Good carburetion is fuelish hot air!
The most expensive carburetor you will ever buy.....is the incorrect one you attempt to modify!
If you truly believe "one size fits all", trying walking a mile in your spouse's shoes! |
Edited by carbking on 07-09-12 08:00 AM. Reason for edit: No reason given.
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Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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07-09-12 01:41 PM - Post#2246177
In response to carbking
ok...confused now. I am getting these jet and rod sizes from my Mercruiser service manual.
is there a circumstance where I should be going with parts other than those?
btw, I am not rebuilding. This carb was just rebuilt. It might have 20 hours run time.
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
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Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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07-09-12 01:50 PM - Post#2246182
In response to carbking
On Rochester Q-jets manufactured AFTER about January of 1968, the number will be STAMPED in a vertical line on the center section just above the secondary throttle shaft arm. Units from 1968 through 1975 will be 7 digits, beginning with 70. Units from 1976 will be 8 digits, beginning with a 170.
yeah, I've got about 6 Qjets around here - and every one has a number like that except this one.
I have an OMC manual that has the same engine with a Qjet and lists the factory spec carb as 17082515 - same thing but with a spring choke instead of elec choke.
I have been referencing this "tuning paper"
http://members.shaw.ca/crussel/quadrajet/QJet _Tuni...
and comparing the Jet Area vs. Rod Area and Resulting Area chart.
the Mercruiser recommended 36 rods in 66 jets have a result of .00240332
which seems right as I'm sure this is the smallest engine to ever be fitted with a Quadrajet at 229 CID.
36 rods in 71 jets gives .00294132 which seems bigger than even any big block factory jetting.
for example, the Pont 67 400 MT w/A.I.R. GTO is 70/38 - not even as big a spread, and it's the biggest spread I can find of any factory setup 1967-1980 on their chart
I gotta think tiny 36's in big ol 71 jets is just way wrong for a 229 cube motor
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
Edited by Mike73 on 07-09-12 02:16 PM. Reason for edit: No reason given.
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Mike73
Senior Member
Posts: 710
Loc: Ontario, Canada
Reg: 01-31-00
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07-14-12 08:30 PM - Post#2248268
In response to Mike73
wow, it's like a new motor with the .066 jets.
starts nicer, idles better, and gets around 15% better fuel economy at cruise.
no more overwhelming gas fumes after shutdown.
73 Laguna Coupe 400/400
Bayliner with a 229CID Chevy V6 |
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