Carbs carbs and more carbs

Author Message   Ted Broderick Advanced Member Username: tbrodes Post Number: 102 Registered: 02-2008 Posted on Thursday, October 15, 2009 - 10:39 am:    Guys, Got the boat all winterized over the weekend. Engines ran great the final run. But, my starboard carb. (Q-jet) is running rich. Gas flow out of the exhaust, just seems gassy-er. I'm thinking of a rebuild or just buying new. Quickly typed into Ebay marine quadrajet, and a bunch came up around 235-250 bucks. Cheaper than I had thought. I have 1990 454 with I'm assuming original stock carbs.I think I want to keep Q-jets just for ease of install. Looking for guidance on how to go about my carbs,and any tweaking adjustments.   makomark Senior Member Username: makomark Post Number: 1669 Registered: 09-2008 Posted on Thursday, October 15, 2009 - 12:08 pm:    Ted: Lots you can do to improve over what you have. be warned ahead - it takes time to get things optimal. Before tearing into that starboard carb, I'd check to make sure the fuel pump diaphragm isn't ruptured first. If you are willing to invest the time, I'd suggest obtaining two "bibles" on the topic: one by Doug Roe and the other by Cliff Ruggles. You can get them much below retail by searching amazon and other www sites. The theory, background, and must dos are covered in both. The marine specific items aren't clear but inferred; I believe I can help you with most. If you would rather defer to a professional, I'd endorse Cliff to rebuild what you already have. though I haven't used his rebuild services personally, I've bought his parts and have been impressed. All that I've steered his way have provided nothing but Positive comments. Whether you do it or farm it out, I believe fixing what you have is much better than replacing it unless absolutely necessary.   Ted Broderick Advanced Member Username: tbrodes Post Number: 103 Registered: 02-2008 Posted on Thursday, October 15, 2009 - 01:23 pm:    Mark, Thanks for the quick response. Interesting that you mention the fiel diaphram. Never thought of that, nor do I know how to check it/how hard it would be. The boat is on the hard currently and I dont plan on yanking the parts until the spring. Just ordered both books! Look forward to reading them. So it sounds like you think I would be better off having the carbs rebuilt instead of new. Whats the methodology behind that? Thanks, looking forward to the dialogue   makomark Senior Member Username: makomark Post Number: 1671 Registered: 09-2008 Posted on Thursday, October 15, 2009 - 01:54 pm:    Doug Roe's words capture the thought much better than mine but here's the thought process for rebuilding what you have: GM supplied those engines and owned RPD at the time - RPD owned the Q-jet. GM's R&D center (test facilities) drawfs any marine OEM's similar centers, probably even in aggregate. Though the marine Q-jet is an "old" casting, all of its tuning parameters (rods, jets, bleed holes, springs, etc) can be optimized to suit a specific application. Who better to do this than the vertically integrated company who's reputation stands on the end result? As far as "new" q-jets, there aren't many new RPD q-jets left. The closest would be the edelbrock-owned ones and they are all "newer" (APT-styled) castings. the point is these products come from a source without that huge R&D complex so the likelihood of them being tuned for your engine are small. As far as the "remanufactured" products, the devil is in the details. For example, Mercruiser used several different casting numbers for big blocks and small blocks over the years. Look how many unique parts numbers a "remanufacturer" has available for a product line. I've never seen a reman house that offers as many carb numbers as what was factory original/available. Though there may be subtle differences between several castings, the point is one or two "reman'ed" part numbers can't match the total performance spanned by over 10+ different "OEM" part numbers - some compromises had to have been made. Another benefit of rebuilding what you have is that you have the opportunity to know EXACTLY what is in that carb. Using this info, you can "tune" the carb to be uniquely application specific, if desired. Here's what I learned from Crusader's tech support lead long before they moved to SC...I asked how lean I could rejet the carb on the 454's that were "new" at the time. he said I couldn't - voids warranty. After a few more calls, the short story goes like this: "We can't control what hull the boat builder installs this engine in. We need to have reliable products. The reliability accomodates 'worst-case' conditions. We stand behind our products." My interpretation - "our carbs are jetted on the rich side to ensure we won't have a lot of warranty claims for melted pistons due to lean conditions. If your boat is light weight, you can probably lean the curve without problems." The first mod I made was to change the operating point of the power system. It was significant. My mods, in total, have reduced cruise consumption 25% over factory settings.   Tom Toth New member Username: jubilee Post Number: 1 Registered: 10-2009 Posted on Thursday, October 15, 2009 - 08:14 pm:    Mark, In reading your post you mentioned changing the operating point of your power system are you refering to the spring on the power piston? I rebuilt my Q's using Cliff's rebuild kit and followed book and had awesome results. I was wondering though if changing to a softer spring would help at cruise or change primary from 70 to 69. I have no nozzle drip and have control at idle screws. Do have some minor fuel floating both sides at idle though. Looking to reduce this more and get better cruise mpg. 1986 454/350 fwc p 990 hrs. vacum @ 710 is 19 s 1025 hrs. vacum @ 710 is 18.5 pertronics ignitor 2 rebuilt mallory's with new springs to original curve timing set digitally @ 10 props scanned plugs and wires new   Drew Robertson New member Username: andante Post Number: 2 Registered: 03-2009 Posted on Thursday, October 15, 2009 - 09:01 pm:    I have 1992 Carver 350MY with 454s and have noticed a "raw" fuel odor while underway at various power configurations and in the slip at idle. Inspection of the Tygon tubes on the fuel pumps for evidence of fuel would be one of the first checks, would it not? And if fuel is indicated the pump(s) should be replaced, correct? Thanks, DR   makomark Senior Member Username: makomark Post Number: 1673 Registered: 09-2008 Posted on Thursday, October 15, 2009 - 09:51 pm:    Drew: You have the diaphragm inspection down correctly - I ommitted that in the last reply to Ted - sorry about that. Tom: I found my power system was starting before she was planing. I used the edelbrock springs and settled on the "gold" one if memory works right. I'm not sure about the floating - flooding? If you get the power system where you need it and you are happy with WOT, then I'd be swapping primary rods. I found the most economy in modifying the basic settings to work with my installation - Optimizing the system as they say. getting the dribble to stop from the secondaries made a huge difference; figuring out why it was happening was the hard part. On the idle, I'm convinced all marine big block chevy's need the idle bypass air mod though I've never seen one on a stock carb. I've done the mods to a "test" carb but haven't swapped it in yet. I'm starting with 0.050" but wouldn't be surprised if I wind up at 0.080" (emails traded with Cliff).   Al Advanced Member Username: knuckle47 Post Number: 727 Registered: 09-2007 Posted on Friday, October 16, 2009 - 10:51 am:    Mark, All of this discussion has stimulated my thinking that I may be better of with the Q-jets instead. It sure seems like you have come upon a myriad of potential. I looked into the books you mention and found them as well as a similiar one for the Carter/Edelbrock series. I am wondering what you think of the potential enhancement of the existing setup I have versus the ones you guys are discussing....?   makomark Senior Member Username: makomark Post Number: 1681 Registered: 09-2008 Posted on Friday, October 16, 2009 - 01:51 pm:    Al: If i were standing in front of your engines, I'd be more inclined to "tune" the 1409's than to go back to the stock setup. That's mostly so you don't have to undo what has already been done beside spend $$$ to get the parts. IF you do that and don't get what you want, then maybe contemplate the return to the original setup. I suspect you operate as I do: manuever thru the harbor, cruise to fishing grounds, and troll. these are the main operating modes with very little, if any, in between. that gives you three points to optimize three (mostly) independent subsystems. If I remember correctly, you can adjust all the metering devices much quicker on the 1409's. As long as you are comfortable with the 1409 theory of operation and know how to check to make sure your mods didn't just drive your A/F super lean, take that vacuum/timing data, figure what you have and where you need to go and then buy that edelbrock mod kit(s) and have at it.   diver dave Advanced Member Username: diver_dave Post Number: 460 Registered: 08-2008 Posted on Friday, October 16, 2009 - 02:44 pm:    I've got the 1409 strip kit, 99% complete; will let go for a song...   Ted Broderick Advanced Member Username: tbrodes Post Number: 104 Registered: 02-2008 Posted on Sunday, October 18, 2009 - 09:18 pm:    very interesting!! I think I am just going to send them to Cliff this winter. I am no good at small motor skills and small parts (missing my left hand). Better left to the proffesionals on this job. I thought I could yank the water pump out of my 1961 Triumph TR3b, well once again after 2 horus, covered in grease and cut knuckles, I decided to call a british car mechanic an hour away. Told him I had the parts...long and short of it, 300 bucks and he'll come get the car in a covered trailer and he'll put in my electronic ignition (gotta love lucas....) There we go! I know Cliff will want particulars of the engine and that type of stuff. Mark what are your jet sizes, and anything I should tell him/steer him towards? Just not sure how to go all about it. Thanks guys, this thread has been great thus far, as has this entire forum!! Some of the best reading of the day is here for me!   Fastjeff Senior Member Username: fastjeff Post Number: 6969 Registered: 09-2003 Posted on Sunday, October 18, 2009 - 09:48 pm:    Lucas electrics! Ugh. Wanna know why Brits drink warm beer? 'Cause Lucas makes their refrigerators! Jeff   makomark Senior Member Username: makomark Post Number: 1707 Registered: 09-2008 Posted on Sunday, October 18, 2009 - 09:53 pm:    I think you'll find those books interesting. I'm still finding little jewels and I've had Roe's book over 15 years..... As far as what to tell him...I'd give him the info on the engines and tell him what you want them to do. Let him know if you spend a lot of timme trolling, or running 50 miles, or whatever you do. I believe he runs each carb on a real engine after he's done and before it ships. Must be nice having a dyno close by. Two items come to mind as far as specifics, one may be a bit late (in the year). First is to get him to add some bypass air. If the carb is apart, it takes about 15 minutes. The other would be to adjust the power system so it is off during cruise. You need to know what vacuum the engine cruises at and he can't do much without that data point. On mine, I set it up to start "two inches later" on the vacuum scale. Most of the engine info is in the owner's manual. If he need the cam info, its readily available. Now that I think about it, he probably has a standard question list.   Fastjeff Senior Member Username: fastjeff Post Number: 6970 Registered: 09-2003 Posted on Monday, October 19, 2009 - 07:05 am:    At cruising speed on a boat, there is no vacuum to speak of, so the 'economy' circuit of a carb is not being used. It might come into play at low trolling speeds, however. Jeff   makomark Senior Member Username: makomark Post Number: 1708 Registered: 09-2008 Posted on Monday, October 19, 2009 - 11:12 am:    I can tell you for a fact that my power pistons are Down (economy mode) at cruise rpm. They don't start to richen things up until the air valves start to open. Cruise vacuum is nominally 8" Hg.

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