SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: king295 on April 12, 2017, 11:32:25 AM
-
Looking for some baseline jetting suggestions as I will be ordering jets for my carb in the next few days and wanted to get a read from you guys on where to start and the ranges I should get.
Boat:
19ft shallow v with a berkeley pump and diverter
Motor Setup:
454 BBC
Edelbrock Victor Jr. intake
Holley 850 carb (previously said 750)
Dooley air scoop
Don't know the exact cam but it is mild
OT Rewarder headers
Any suggestions / baselines are appreciated.
-
Pri.73
Sec.81
P.v. 5.5
Try this and see if it works for you
Sent from my SM-G930T using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)
-
With the limited information this is what I'd recommend.
I believe that with a mild combination you can start with the original jets for the carb. Post the list# for carb you have and we can tell you what was originally in it.
You didn't state if it has vacuum or mechanical secondaries.
If vacuum, I'd recommend going to the light "yellow" secondary spring and a 4.5 power valve, with stock jets to start.
If mechanical, again I'd recommend the 4.5 power valve with stock jets to start.
Good luck with the build.
-
You got that without a list number?
Skills.
GT
Pri.73
Sec.81
P.v. 5.5
Try this and see if it works for you
Sent from my SM-G930T using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)
Sent from my SM-G900V using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)
-
Well my lack of knowledge is apparent... here are pictures of the carb, perhaps this will help? If not, what am I looking for? Thanks for all the replies thus far, where I lack in knowledge I make up for it with beer on the water this summer.
Sent from my iPhone using Tapatalk
-
Number should be on the choke horn. If it's a 4779 it's a 750. If it's a 4781 it's an 850.
Kinda looks like an 850 to me.
Sent from my iPhone using SoCal Jet Boats
-
So same question but with an 850 then?!....
I plan to rebuild the motor next year which will require a bigger carb. Can I make this work without losing power?
Sent from my iPhone using Tapatalk
-
If the carb hasn't been touched, it probably has size 80 main and secondary jets and a 6.5 power valve. You should probably change to at least a 5.5 power valve. They only come in 1/2 sizes. (4.5, 5.5, 6.5, etc.)
As far as jetting goes, run what's in it and check the color of your plugs. If they show a medium brown color it's good. If they're light gray or white, too lean. If they're black, too rich. You get the gist.
Holleys website sells all the parts for it.
You have an 850 double pumper.
Sent from my iPhone using SoCal Jet Boats
-
Depending on what you do to your motor when you rebuild, an 850 double pumper will be plenty. Just have to get on the lake and do a day of testing and tuning. I'm getting ready to do the same as soon as my motor comes back from the machine shop.
Sent from my iPhone using SoCal Jet Boats
-
Dual power valves, both 6.5".
Primary jets would have been 80, secondary probably 78.
I would go 80 square with a 5.5 power valve on the primary and a 4.5 on the secondary.
This will get you silly close.
The one thing to keep in mind is that a jet does not need to pull a gear. You have to think of the fuel curve in reverse. The engine has virtually no load until the impeller loads up, like over 4,000 rpm.
Staggering the power valves makes for a smoother transition.
JMHO...
Sent from my SM-G900V using SoCal Jet Boats mobile app (http://r.tapatalk.com/byo?rid=201)
-
Thank you Steveo909 and GT Jets, I owe you both a few cold ones!
-
To truly read spark plugs for an air/fuel indication an otoscope is needed. New plugs must be used and after a few hard pulls/passes the engine needs to be shut down ASAP. To really see deep down inside the plug shell at the color ring captured on the porcelain cone, you need an otoscope ( lighted magnifier) to truly see it, the naked eye with natural or florescent light is not enough to truly see the color ring. Color on the plug tip or shell base can only tell one thing….problems, not an air/fuel ratio indication.
-
To truly read spark plugs for an air/fuel indication an otoscope is needed. New plugs must be used and after a few hard pulls/passes the engine needs to be shut down ASAP. To really see deep down inside the plug shell at the color ring captured on the porcelain cone, you need an otoscope ( lighted magnifier) to truly see it, the naked eye with natural or florescent light is not enough to truly see the color ring. Color on the plug tip or shell base can only tell one thing….problems, not an air/fuel ratio indication.
Sent from my SM-G920V using Tapatalk