Holley 390 jet size estimate...

[Jono FD3]

Hi guys, I'm going to set up the carb and timing properly (hopefuly on the local college's rolling road) early next year, but was wanting to know, what sort of size jets would be required as a starting point?? Not sure what is in there at the moment, but think it's running rich but can soon check that by pulling a plug to check the colour!

Engine spec is:

Rover 3.5
9.75:1 C/R
Offenhauser 360 manifold
Ported heads (std SD1 Valves)
RC87 cam
Std rockers & lifters
K&N pancake filter with Extreme top filter plate

Cheers
Jono

[j.johnson23]

Presume your running a Holley 390(8007).You need to take front float chamber off and remove the jets,if you are running a bigger cam you may need 52 or 53 jets,but either will get engine running decently.Important to rolling road it somewhere decent as you need the timing and mixture to be bang on to get best power\economy.Last thing you want to do is run too lean as it is worse than running too rich.
If you decide to rebuild the carb, a Holley trick kit from Real Steel will give you everything you need except for jets.
They are relatively easy to rebuild if you take your time-hard work is in the cleaning.

[mgbv8]

Presume your running a Holley 390(8007).You need to take front float chamber off and remove the jets,if you are running a bigger cam you may need 52 or 53 jets,but either will get engine running decently.Important to rolling road it somewhere decent as you need the timing and mixture to be bang on to get best power\economy.Last thing you want to do is run too lean as it is worse than running too rich.
If you decide to rebuild the carb, a Holley trick kit from Real Steel will give you everything you need except for jets.
They are relatively easy to rebuild if you take your time-hard work is in the cleaning.

Just to clarify!!
You do mean Remove the front jets to replace them with the size 52 or 53 jets right?

[j.johnson23]

Have a look at them first,some come with 51 jets and some come with the 52 jets.
The other thing to do is check that the primary throttle blades are not open too far at tickover.If they are open too far the slots in the carb will be exposed causing the rich mix you have.
Open the secondarys slightly to get the tickover you want without opening them too much or you have the same problem again.
If that still does not increase the idle enough then you need to look at drilling holes in the blades to get idle to where you want it.
Plenty of info on the internet regarding all of this,it just takes a little time to take it all in.

[Darkspeed]

If not already done make sure you fit a secondary block kit so that you have the option of changing the jets in the secondaries.

A QC vac spring chamber is also nice as will a range of accell pump cams

Andrew

Make sure that if you use a low line filter cover that the element is larger than 3" otherwise the cover will block the air inlet to the carb

[j.johnson23]

Good point about secondarys,although a rolling road test will tell you how far out you are.The spring housing will save you a lot of hassle.
One important thing I forgot was the float settings,make sure the floats are ok and that height setting is to Holley specs.Too high a fuel level will cause a rich condition.