Dyno session w QF 850 "marine" carb LEAN
 

I had a new 502 short block I sold to a customer, he provided a set of port matched dart 325s, mild hyd roller cam, Vic Jr intake, carb spacer and Quick Fuel 850 ,marine carb, all new stuff in boxes. I assembled this combo and put it on my dyno. Right off the batt, hp/tq numbers were WEAK and afrs were LEAN. Floats set aggresively high, fuel pressure almost 7lbs. so initially we had some fairly cold, dense air (1200 feet dry air density "DA") with 55 to 60 degree intake air temp at carb. We were seeing numbers in the 15-1 to 17"s. Throttled shop air supply, turned up heat to get air temp motor was seeing into mid 80s (like it would in a boat), DA was now in the 2600 to 2900 range, CF went from 3 or 4 % to 6 ish, AFRS went into the 14 to 16 range. BSFCS in the .420-.450 range (too good to be true for a 9.5-1 motor). Out of the box this "marine" carb's initial calibration is what I would call "blow up lean". It had 82 primarys, #70 mid bleeds, #28 hi speed bleeds, w 6.5 PV. On secondary side no PV, #94 jets and same bleeds as primary. The Jet numbers seem "reasonably" large enough, keep in mid though, the circuits that feed them , internal circuits can make those jets act small or large. So we started adding jet which in turn gained hp/tq. Went from 82's to 93 primarys, went from 94 to #100 secondarys. One step before the 93/100s, our HP flattened out around 580/585, our tq was about identical. With the biggest jets mentioned, we gained another 10 ft lbs of tq and hp at least maintained (tells us were in happy range) our afrs were between 12.8 and 15-1 (#8 cylinder at worst spot), remember, I have individual cylinder 02 sensors and this is a NON fire swap cam (they seem to even this stuff up). I did NOT spec any of this top end.
Being this is getting much more restricted exhaust, the afrs will probably drop about a point in boat, would probably be ok. I could have put #25 high speed bleeds in BUT I didnt have any that small to try at this time. Sooo, we progress, now its time to drag my dyno brake like a guy drivinga boat at part throttle. So being my dyno is manual, I drag brake form idle to 5000 progressively loading it and giving it more throttle/higher load, ie, 250 ft lbs at 2500, 350 at 3500, on up. Do a graph, holy fawk, part throttle is between 14-1 and 17-1 (hottest/coldest cy;inders). I graph/correlate torque vs MAP, convert map to vacuum, my 6.5 PV isnt opening even at 400, almost 450 foot lbs of tq! Wrapped this up for the day that day, needed some #25 bleeds, 58/63 bleeds and a 8.5 PV to go any further. End of day yank mufflers off, we see 590 hp/595 ft lbs tq, of course, afrs are even leaner but hey, its FUN!

Day two, I consult with my dyno partner/carb expert Norm over coffee, I decide to take primary metering block to him. He mods the whole jet circuit (opens up jet feed from .135 to .158 with drill then a reamer, wire gauges the low bleeds in plate, mods them slightly, mods circuits, feeds etc). He also supply's me with more testing supply's, ie, appropriate bleeds, power valves, some modded 100 Main jets that would be like 104's. I really have hard time wrapping my head around how opening up a feed hole from lets say .140 to .160 is going to do SQUAT when its feeding a jet that's about .105 ID BUT it does! Soooo, back onto dyno, make open header pull, before anything else (how I ended day previously) to establish a new baseline vs where we ended. #25 hi speed bleeds in rear/#63 mid bleeds in front, 8.5 PV . Motor is LAZY, RICH, and down 25-30 hp even with open headers . Graph afrs, into the 10s to 14-'s, FKNG IMPOSSIBLE. We didnt mod THAT much stuff! THEN I remember, I used vaseline to get bleeds to stick to screwdriver , I look, sure enough, still plugged with GOO (we all make stupid mistakes lmao). Clean that **** out, re pull it, miraculously we are still a little on rich side, powers down a tiny bit. I do some part throttle drags, motors wailing and blubbering, bsfcs into the sixes at PT, well, at least now we can start PULLING jet back out instead of trying to max them out on a little piss ass 600 hp build! (shouldn't be necessary). I end up going back to #70 bleeds in front, #90 then #88 primary jets, I rejet the rear, keeping in mind #8 is on fire at wot like most these open plenum deals, I stagger jet rear down from 100s to 98/96. Thing makes almost 600 ft lbs tq, same hp at 590. AFRS at wot actually close up a little and are between 12-1 to a little over 14-1, dragging it at part throttle, Im in a range of 13.5 to 12.5 average (still have hot and cold cylinders). I leave the # 25 bleed in rear, if customer feels its too rich in the boat, that could go to a #28 or 32, possible primary's could go down to 87 or maybe a 86.
The point of THIS write-up is to show how important PROPER carb tuning is on a marine application. IF you slapped a set of anybody's decent aluminum heads, intake, cam etc on a 502 and you bolted THIS carb on out of the box, you would most likely see ALUMINUM when you pulled the plugs on water after 20 minutes to get a reading! Smitty

And I bet it goes over 600hp

IF I had put some 89 in , hooked a msd box up we would have seen about 605 to 610 with open headers, never did though, very close to 600 though! The customer was told he would "blow his drive up IF he went over 600 hp" so, were keeping it at 595 ish, LMFAO!

It wasn't long a go some were bagging on the Vic Jr intake ? if I recall.........so stock Merc 502 dimple rods and forged crank, what rpm @ the 590hp pull

Not my favorite intake. 5800 w mufflers, 5900 w open headers. I would have liked to tried a performer rpm, would have probably made 10 less hp on top and picked up 30 to 40 ft lbs of tq where it coulkd be used. I did a overlay of the best open header pull vs best open header pull of Jeff Hoekstras 502 w chinese valeko heads and MPI intake I heavily modded, Jeff's 502 kicked this motors ass from top to bottom! Now, to be fair, jeffs had more cam so its not a real good comparison but even with his bigger cam, he out torqued this motor EVERYWHERE.

Norm doing his "magic"
https://cimg0.ibsrv.net/gimg/www.off...207f34d9d6.jpg
https://cimg0.ibsrv.net/gimg/www.off...1e6b20f282.jpg

Was there a hand written note in the box when he gave it back........:D.......he didn't like my C&S carb

Yep. Most "newer" carbs have way too much emulsion circuit area. Usually, only 2 in each channel are needed depending on the application. To make things worse this usually causes light load rich conditions (automotive) and high load lean conditions.

Sounds like you are getting it sorted out.

This one was pretty much too lean everywhere but at dead idle, i was just shocked how far off it was out of the box. If a average joe skipped the dyno tune, didnt bother to put a 02 meter on boat, went out and drove this, unless it just broke up to point they knew it was lean, i strongly feel motor would get damaged in a fifteen minute drive trying to get good ol fashioned plug readings! Clearly this carb was really meant for a stockish bbc, not something modded in the 600 hp range! I would have chosen a bigger carb , smaller heads and prob a fire swap cam had i been one picking the parts combo, Smitty

That's hard to believe but very good to know. Did you happen to reach out to a QF tech just to hear their response. That definately could ruin a guy's day with such a basic build. Wonder what an out of the box (smaller) 950 hp holley would have done. Shops/individuals on this side of the state use them a lot with very little tunning in the 500-650 hp range. Amazing how far off that 850 QF was. WOW.... I understand you didn't spec anything and got what you were handed but who woulda ever thought.

Btw Thanks for the thread. Always good info and helpful to others.

x2 !!

Possibly with 100 less hp this would have been ok, i continue to be amazed when norm.mods something a slight bit how.much it changes. He wire gauged the bottom idle feed jets at .037, drilled them to .039, really no difference in size. I cant believe that and making the fuel feed hole size to jets about .020 bigger when they are already .035 bigger than the jets makes jets flow so much more that i went from too lean to rich enough i had to go back down 5 jet numbers AND had afrs i was looking for, Smitty
As far as contacting QF, i never bother doing anything like that anymore if i can just make something work even if it takes a little bit. I do have a friend who couldn.t make a different QF carb work the way he wanted on a sbc powered hotrod car (a BRAWLER, marketing hype) and went around and round with them on the phone. I had a different qf 1050 here i use as my "dyno" carb to.make peoples stuff work right when they have problems (its had various mods), he stuck that on temporarily and his idle/drivability problems went away BUT he could have simply paid norm to straighten it out. I never heard outcome of what he did, he only tested with.my then i got it back, he was getting a different carb or sent it back to them I think.

Interesting. I run quick fuel 850s on warmed up 502s and had none of these problems. I have my jet sizes written down at home but I’m 78-80 primary and 85ish secondary. 12.5 cruise. I don’t have the rest of the numbers off the top of my head. Have her a little extra on the secondaries for 7/8 cylinders since of course I’m reading all 4 cylinders on each side in the boat.

How warmed up, cylinder heads?, Cam? Intake etc, thanks

You've got a good guy there "Norm". To bad but before to long not many of the carb wizards will be around as technology is changing so rapidly. First thing I probably would've thought of was the needle and seat size but that was ruled out in your first thread from everything you mentioned. I've talked to Norm on the phone a couple of times. Full of knowledge without a doubt and very pleasant to boot. Fortunately for your customer he was on site. Likely saved him some $$$ in the long run.

Cant blame your for not calling a tech. They are hit and miss these days also.

EQ heads. Kept compression low for blowers (which I haven’t added yet). 8.7:1. Comp cams. .243/.251 .627/.632. Merlin x intakes. 2 1 inch spacers. Daytona ignitions. Dyno tuning was done in full marine trim. They were quite rich when in the boat. Had to lean them out some

“marine” carbs
 

OP - I like that you put “Marine” in quotes. I bought two new QuickFuel “marine” carbs. 1 season and all the linkage was rusty.

We debated needle and seat change, that was Norms first comment BUT IMO we were using less than 300 lbs per hr fuel, barely over 250 and I was seeing lean part throttle also so felt it was overal calibration, Smitty

Man messing with carbs to get a good AFR results,4 carbs to tune , I don`t miss those days ... have a truck full of bleeds and jets etc . If I added up all the fuel I used tuning I`d probably could have gotten EFI 5 years ago. :D
Not sure what you got going on there , seems strange to have it so lean with such large jets.

simple jet plate mods though brought jets into range , post is just to share what I found and what I did plus to help understand they are rolling the dice if they bolt stuff together and NEVER at least look at the afrs. A little rich, waste gas, alot rich, well can wash the rings, alot LEAN, game over! A local guy put roots blown 509s in his 38 or 42 fountain (never saw the boat), wanted me to help check "tune" on the water. Dual 4bbls, 8-71s. I told him my hourly rate and that he would need to get some 02 bungs put in SOMEWHERE so I could get some readings. Said he'd just do it himself and look at plugs (I did NOT have anything to do with building his motors or picking his combo). Called me up this fall, said he took it out and everything was "fine", put it in boost for about 15 minutes around 4200 to 4500 and for some reason motors started breaking up. Opened hatch and there was oil blowing out his breathers. I just shook my head. I told him he probably hurt the motors, he wanted to argue with me. So after it kinda sank in that they MIGHT be hurt he asked IF I could fix/ tunes his motors at my shop, dyno them, etc if they were hurt. THEN informed me hed like to come "hang around" anytime I was working on them (he's retired}. I said your welcome to come see them apart, see them run on dyno but I cant have you standing here all day every day. I decided I was kinda "booked" up at that point, not worth the aggravation!! second or 3rd time he's hurt these motors from what I heard!

Wonder if that's the same guy I sold my 8-71's to? Almost sounds like same GUY... ahhhh

You spent 3 days of people time making the tune right. If you know better, he would definitely be money ahead starting with the best carb possible for the app.

Point is the carb theoretically should have been right for the build but didn't but articfriends was kind enough to share info with us and got to the bottom of the issue and shared. There's got to be a ton of 850's on top of 600 hp engines without issues. I've been running carb performance engines for years and never ran into what he did.

should have put a Dom. on it.:D

True but keeping under 600 hp. My next builds in the works as I gotta get this 12 meter out of the shop and on the water. will interesting and will post dyno. 496 or 540 with 4150 970 cfm pro systems and holley 2 circuit 1150. Who knows we'll see. Just depends what heads I strap on. Any info is good info. Will have both with adequate ported intakes. Wished I had my NOS bow tie blocks but is what it is. Good bad indifferent will post. Would like to go the 548 route but will see what future brings. Regardless will be dyno' with both. Fk. I just wanna get on the water. Lol.

my guess would be the 496 like the 4150 pro systems 970 and the 548 be liking the 1150.

Any Mark 4 bow tie blocks around pm me.

John