carb jetting????????????

[advantage21]

i have an 850 holley double pumper with 80s in the mains and 78s in the sec runnin a little to fat on the top end should i change mains and secs or just go down on the mains anyone got any suggestions.

[Nucking futs]

When you say mains are you talking the front (primaries) or the rear (secondaries)? the primaries should always be smaller then the secondaries.
I have a demon 850 and i was running a tad fat too. Mine came with 93sec. and 85 prim. went down to 87/82 but havent had a chance to run it yet.

[Squirtin Thunder]

i have an 850 holley double pumper with 80s in the mains and 78s in the sec runnin a little to fat on the top end should i change mains and secs or just go down on the mains anyone got any suggestions.
What Holley 850DP do you have ???
Check this out to get a baseline;http://www.mortec.com/carbtip1.htm

[advantage21]

i have a 4150 and by the numbers off the carb and from the tech sheet off the holley it show having 80 in the mains and 78 in the sec with 6.5 power valves. I have never touched this carb had some pump work and put on a new manifold over the winter and now i am looking for a little more top end.

[Squirtin Thunder]

i have a 4150 and by the numbers off the carb and from the tech sheet off the holley it show having 80 in the mains and 78 in the sec with 6.5 power valves. I have never touched this carb had some pump work and put on a new manifold over the winter and now i am looking for a little more top end.
There are lots of 4150s carbs which one do you have ???
Modle #

[advantage21]

the model # is 4781-5 on the air horn

[Squirtin Thunder]

First off I would try advancing your timing 2* That may help.
If not check your PV. You may want to go a set smaller. But I would read the whole deal on the Mortec site to give you better insite of what might be happening.

[Oldsquirt]

That is an 850 DP with 4-corner idle. Mortec shows his jets as being the stock setup. It also has 6.5 power valves in primaries and secondaries. Earlier versions of the carb were jetted "square" with 80's.
Jim, changing the PV to a different number only changes WHEN they come on. Doesn't change the quantity of fuel flowing through the PV portion of the main metering circuit. AT WOT, they need to be "ON".

[Squirtin Thunder]

That is an 850 DP with 4-corner idle. Mortec shows his jets as being the stock setup. It also has 6.5 power valves in primaries and secondaries. Earlier versions of the carb were jetted "square" with 80's.
Jim, changing the PV to a different number only changes WHEN they come on. Doesn't change the quantity of fuel flowing through the PV portion of the main metering circuit. AT WOT, they need to be "ON".
Thats why I said go to the larger #, it will stay on longer. It will turn on at 9.4" of Vac and turn off at 9.6" of vac, instead of turning on at 6.4" and turning off at 6.6".
I tried to jet up on mine and it just got super rich, went from 80 to 81, just in the secondaries !!!

[steelcomp]

When you say mains are you talking the front (primaries) or the rear (secondaries)? the primaries should always be smaller then the secondaries.
I have a demon 850 and i was running a tad fat too. Mine came with 93sec. and 85 prim. went down to 87/82 but havent had a chance to run it yet.
Futz...why such a drastic jet change??? More than 6 sizes is getting out of the calibration range of the carb. A "tad" might mean trying two sizes at a time in the direction you want to go. Baby steps, my friend. :coffeycup

[steelcomp]

Thats why I said go to the larger #, it will stay on longer. It will turn on at 9.4" of Vac and turn off at 9.6" of vac, instead of turning on at 6.4" and turning off at 6.6".
I tried to jet up on mine and it just got super rich, went from 80 to 81, just in the secondaries !!!
Dude, you just shouldn't post stuff when you don't know what you're talking about. PV's don't "turn on and off". They are open, or closed. At WOT, PV's are open. At a certain vacuum, they are closed. When throttle is opened, and vac drops below that point, they open. They don't close again untill vac comes back up to the PV value. Under some cruise conditions, the vac might first drop, allowing the pv to open, and as rpm climbs it might rise again to close the pv, but not at WOT. Beside, Advantage 's problem is a too rich condition, which having the pv's stay open longer would only make worse.

[Squirtin Thunder]

Dude, you just shouldn't post stuff when you don't know what you're talking about. PV's don't "turn on and off". They are open, or closed. At WOT, PV's are open. At a certain vacuum, they are closed. When throttle is opened, and vac drops below that point, they open. They don't close again untill vac comes back up to the PV value. Under some cruise conditions, the vac might first drop, allowing the pv to open, and as rpm climbs it might rise again to close the pv, but not at WOT. Beside, Advantage 's problem is a too rich condition, which having the pv's stay open longer would only make worse.
So I was thinking of my condition !!! Oopppppppps
Open close turn off and turn on same mother ****in thing.
Hows that Lake Boat coming ???
Are you going to make CBBB ???

[steelcomp]

Jim, I know you were trying to help, but you were giving advice that was just wrong. Sorry.Open close turn off and turn on same mother ****in thing.
In that sense, maybe so, but as you were using as an example, they don't open, then close...(turn on,, then off again) they stay open. When they open, as Old Squirt posted, has no effect on WOT fuel mixture.
I won't make CBBB as much as I'd like to. Trying to make dyno test last week of this month, and that'll be pushing it. I'm spending a lot of time out of town. I'm hoping to have the short block and heads assembled this weekend. I have one carb done, (I can do those in the evenings) and the other is almost done. Manifold still needs port matching, and I need to build new fuel system. I still need to set the intake in the boat, then assemble the boat. I'll do my best to be at Ming in Sept. and may be running sooner. It would be nice to test and tune before Ming.
Why don't you bring your boat to Ming...take a run down the 1/4 mi? Or who knows, maybe I'll make a late summer trip to the river.
Wanna race? :rolleyes:

[Squirtin Thunder]

In that sense, maybe so, but as you were using as an example, they don't open, then close...(turn on,, then off again) they stay open. When they open, as Old Squirt posted, has no effect on WOT fuel mixture.
Won't make CBBB as much as I'd like to. Trying to make dyno test last week of this month. I'm hoping to have the short block and heads assembled this weekend. I still need to set the intake, then assemble the boat. I'll do my best to be at Ming in Sept. Maybe be running sooner. It would be nice to test and tune before Ming.
Why don't you bring your boat to Ming...take a run down the 1/4 mi? Or who knows, maybe I'll make a late summer trip to the river. Wanna race? :rolleyes:http://www2.***boat.com/image_center/data/520/2311river2.jpg
http://www2.***boat.com/image_center/data/520/2311Pict0565.jpg

[steelcomp]

http://www2.***boat.com/image_center/data/520/2311river2.jpg
Yeah...I'm pretty bummed I won't be there, but there's always next year! :D

[Squirtin Thunder]

Jim, I know you were trying to help, but you were giving advice that was just wrong. Sorry.
In that sense, maybe so, but as you were using as an example, they don't open, then close...(turn on,, then off again) they stay open. When they open, as Old Squirt posted, has no effect on WOT fuel mixture.
I won't make CBBB as much as I'd like to. Trying to make dyno test last week of this month, and that'll be pushing it. I'm spending a lot of time out of town. I'm hoping to have the short block and heads assembled this weekend. I have one carb done, (I can do those in the evenings) and the other is almost done. Manifold still needs port matching, and I need to build new fuel system. I still need to set the intake in the boat, then assemble the boat. I'll do my best to be at Ming in Sept. and may be running sooner. It would be nice to test and tune before Ming.
Why don't you bring your boat to Ming...take a run down the 1/4 mi? Or who knows, maybe I'll make a late summer trip to the river.
Wanna race? :rolleyes:
I plan on being at Ming in Sept. All I have to done is pass my pysical. I will be setting up for Octs race at Ming with the SCSC. I will be working on not breaking the 80mph speed limit.

[Nucking futs]

Futz...why such a drastic jet change??? More than 6 sizes is getting out of the calibration range of the carb. A "tad" might mean trying two sizes at a time in the direction you want to go. Baby steps, my friend. :coffeycup
went to an 89 not a 87. thanks for the typo catch.

[steelcomp]

I will be working on not breaking the 80mph speed limit.LOL!
Boat's lookin good. :D

[steelcomp]

went to an 89 not a 87. thanks for the typo catch.Figured you knew better. :D

[djdtpr]

who knows, maybe I'll make a late summer trip to the river. Wanna race? :rolleyes:
Scott bring that thing to Blythe Labor Day i am sure we can line ya up with a race or two heck if ya promise not to smoke me too bad ill even run ya. :rolleyes:

[steelcomp]

Scott bring that thing to Blythe Labor Day i am sure we can line ya up with a race or two heck if ya promise not to smoke me too bad ill even run ya. :rolleyes:
You a funny boy, Deej. :cool: I'll race ya, but I think the promise will have to go the other way. :D I might be ready for Father's day...I'm hoping so, but not ready for you. Blythe sounds like fun, or CFW. I'm still running my na motor. Lots more power and some boat mods, but wait 'till next rear. That'll be the "other" motor. :D :devil:
When you coming back to Ming?

[djdtpr]

Ill be back at ming in October we are still getting the boat dialed in right now.We have pulled some good #'s but there is still alot left,so far we have only messed with the motor we still have setup to start working with but its real close right now.I am going to run 8.50-8.99 bracket and BGJ hopefully.

[SmokinLowriderSS]

Since this thread is now under FULL HIJACK STATUS, :cry: I'd advise reducing the main jet sizes (all 4) by 2 sizes and then check. if you are only "A Tad" rich, then just drop them all by 1. Don't worry about the power valves. They won't alter the actual jetting mixtures under normal conditions. They are "tunable" but for other things and conditions. :smile:

[advantage21]

sounds good i will try that and let you guys know how it goes thanks.

[steelcomp]

Since this thread is now under FULL HIJACK STATUS, Guilty as charged...sorry :redface:

[SmokinLowriderSS]

Is OK steelcomp. The FBI "anti-hijack" :2purples: team has been called off. :wink: :wink:

[steelcomp]

Is OK steelcomp. The FBI "anti-hijack" :2purples: team has been called off. :wink: :wink:
Whew!! I can stop packing. :D

[SmokinLowriderSS]

:D :D :D :D