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-   -   Carb question. 850 vs 800 (https://www.offshoreonly.com/forums/general-q/344032-carb-question-850-vs-800-a.html)

MILD THUNDER 03-24-2017 08:23 AM


Originally Posted by cabin fever (Post 4540403)
My guage was acting up (think its a bad gtound) but it was flickering between 5-7

I would def not set fuel pressure using those electric gauges. Are you running a psi regulator ?

GPM 03-24-2017 09:22 AM

7 might make it run rich at idle

cabin fever 03-24-2017 10:14 AM

No im not. I read that the carb is set up using 6.5# of psi.

The back float was the one that was set high. Front was right on the money.

I fixed the ground on the gauge so when i run it again ill have a better idea. Ill plumb a mechanical gauge in line if i need to

The boat ran great the one time i used it in the fall with 800 carb.

Baja Rooster 03-24-2017 12:02 PM

My QF850m came with a mech gauge already plumbed into the carb line. I'm surprised that yours didn't.

cabin fever 03-24-2017 12:07 PM

I didnt even get a carb line.

Unlimited jd 03-24-2017 12:44 PM

Was the boat sitting at a similar angle on the trailer as it sits in the water? Might want to double check float levels when it's in the water. I know a few guys that store there boats with the bow WAY up. And don't be too surprised when the 850 doesn't make much difference with the performance. Then again you don't really know what this motor did with an 800

GETTINBYE 03-24-2017 01:04 PM

Also off the top of my head I think QF sets their fuel bowl level middle of sight glass and not at the bottom just trickling out like Holley.

cabin fever 03-24-2017 01:41 PM

Thanks guys. Ill report back in a few weeks when i get it out to fire up again. She leaves on tuesday for some fiberglass work and get my new platform installed.

It does feel like 1 step forward 1 step backwards right now. Ill get it ironed out though.

Mr Maine 03-24-2017 03:15 PM


Originally Posted by cabin fever (Post 4540176)
I have the worst f'n luck! I could fall into a barrell of boobs and come out sucking on my thumb!

Make sure itis tightened evenly and not over tight. They are very sensitive to this or they wont idle or run right.

Bought the quick fuel 850. Installed

Week later finely got the time to fire it up

Ran like complete dog chit! Black smoke so bad it covered the back of the boat. Wtf?

After a minute or 2 it came out of it and idled fine. While looking through the sight glass, seemed the float was adjusted a little high. While adjusting the float my son was talking to me and withouht paying attention i stripped the threads on the f'n float bowl!

Of course since its the black diamond bullchit a new bowl was the price of a kidney and bj. I ordered 2 new polished bowls for less then 1 black one. Fixed and ready to fire up again


I must say after it came out of the horrible rich condition it idled like a champ.

Probablly be another week or so before i can get back to working on the boat. In the middle of a kitchen remodel, that like the engine rebuild is way over budget and doesnt seem to end. Happy wife/happy life.

I did get my new aluminum swim platform yesterday. Cant wait to get it installed.

Make sure the carb is tightened evenly and not to tight. They are super sensitive to this. They wont idle and will puke gray black smoke if they are over tightened or warped.

KAAMA 03-25-2017 07:35 AM

Here's an experience I had that you guys might find interesting....back around 2002 or so, I had a pair of naturally aspirated 540cid engines built with some lightly bowl ported 310cc Dart aluminum heads, and hyd roller cams 236*/244* on 114* lobes with only like 8.2-8.5:1 comp ratio....engines made about 630hp @ 5400-5500rpm on Tom Earhart's dyno.

We were using a Holley 830cfm carb with Annular Discharge and 4-corner idling. I remember Tom Earhart saying something like, in all the years he had been dyno testing engines, he had never seen a carb "follow so well" as what he witnessed that day as he dyno tested my engines. At least the Holley 830cfm w/AD seemed to have fit my application very well to about 5600rpm, at least in this reference.

I would think a Holley 800cfm on a 509cid engine should be adequate for a hi-perf marine engine, but I am no expert....I just kill bugs for a living.


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