Holley secondary main jets?

[Nambo]

My fuel ratio meter tells me my primary jets are fine but if I hold the throttle full open, and hold it there for a while, so its not the accelerator pump, my mixture is too rich at 11 to 1.
So I am figuring it needs smaller main jets for the secondaries.
Any body know where they are?
If they dont use there own jets, how can I lean the secondaries whilst leaving the primaries as they are?

[V Mad]

What mixture are you trying to achieve and why?

[mike@thenook]

What are the main jets you have fitted?

If they are 51 (512) you should change to 48 as the 51 is for 3.5 RV8 - this will affect the mixture over the whole rev range. I had the same problem with mine, idled fine but was too rich on the road - fine now though.

[Nambo]

What mixture are you trying to achieve and why?

On the primaries I have 14.7
On the secondaries I am looking for 13 in order to have more power, less fuel consumption, and less piston rind wear.

[Nambo]

What are the main jets you have fitted?

If they are 51 (512) you should change to 48 as the 51 is for 3.5 RV8 - this will affect the mixture over the whole rev range. I had the same problem with mine, idled fine but was too rich on the road - fine now though.

If I make the jets suitable for secondaries,, then its going to be running far too lean on the primaries, the mixture is just right at the moment until the secondary bores ope then its too rich.

[73stagman]

The secondary jets are a "plate" are they not. Unless you have a modified jet plate.
Presumably you have a 390 holley which is a singe pump 4160 type (I think).....
I believe you can buy these Holley parts from Real Steel...you can also buy a kit which lets you change the jets using main jets rather than having to change the plate
If you search on Holleys website you can down load an exploded view of your carb showing where the various bits are...its not an easy search though from memory

[73stagman]

The real Steel PDF parts list is here somewhere..... I think!

http://www.realsteel.co.uk/section6.pdf

and this is your exploded view

http://www.holley.com/data/TechService/Technical/4150%204160%20Exploded%20View.pdf

[Nambo]

The secondary jets are a "plate" are they not. Unless you have a modified jet plate.
Presumably you have a 390 holley which is a singe pump 4160 type (I think).....
I believe you can buy these Holley parts from Real Steel...you can also buy a kit which lets you change the jets using main jets rather than having to change the plate
If you search on Holleys website you can down load an exploded view of your carb showing where the various bits are...its not an easy search though from memory

Cheers, Am I right in thinking changing the main jets will affect the mixture on the primaries?, or do the main jets only effect full throttle with an intermediary system metering for partial throttle openings like on a motorcycle?

[73stagman]

Sorry Nambo.... I chickened out of the Holley Carb and went for an Edelbrock.... my Holley carb is sitting in bits in covered in dust in a cupboard in my garage. It was just too hard to get anybody in the UK interested in trying to help get it sorted out.. even for my Rover V8

I did do a LOT of searching and trolling the internet and found the info I have put here but I cant help with the actual settings....

[73stagman]

I do know that the vacuum secondaries only operate when the engine creates enough vacuum to operate the secondar butterflies. The Edlebrock it is all linked mechaincally but in theory the Holley should be better at managing the throttle opening versus engine vacuum. ie the edlebrock can dump the full fuel load when the car doesnt really need it ie when you floor the throttle in the garage the Holley wont open the secondary throttle because there is no load on the engine you may even have to put a paper clip on the secondary shaft connector link. Mark its position then when you take the car out on the road, floor the throttle to full load just once, then, stop, pop the bonnet and see if the clip has moved!
This might also be why you think you are running rich at higher revs because the secondary plate butterflies haven't opened to let in the air but the fuel will be getting squirted in

[Nambo]

I did put a paper clip on the rod and it did move but as I had it on there for a while I cannot be sure it didnt just vibrate down.
I was holding the car flat out in second when I saw 11-1 mixture, if the secondaries dont open then, I dont know when they will, sure went fast anyway!
I have the smaller jets so might try them anyway.
Even if it was just using the primaries, the fact at mid range its nearly 15 then goes to 11 at full throttle, this would indicate an intermediary metering system else it would be the same mixture throughout the throttle range wouldnt it?

[73stagman]

Like I said Im no Holley expert but I guess the theories remain...
if the meter shows its getting richer at higher revs then its clear its not getting the air for the fuel....(or its getting more fuel than air)...
so either the secondary jets are too big or the secondary butterflies are not opening far enough or easily enough so.... you either need to change the secondaries for smaller jets or change the spring to a lighter one which allows the secondary butterfly to open sooner.....
As for the primary jets go with the flow from the guys who have done all this before!

[flying farmer]

When I had my Holley fitted (pre efi days), I was running 53 jets in primaries and secondaries with the strongest spring available in the vacuum secondaries to stop them opening too soon.
If the mixture is correct then you get a weak stumble as the secondaries open at low revs. This is because the air gets in before the fuel has time to pull off the jets.

The 390 Holley is about 25% too big for the Stag engine anyway, and this means that the secondaries can open at quite high revs, ie about 5000rpm with the strongest spring fitted, anything less than the strongest spring out of the Holley spring set just meant a flat spot at progressively lower revs on my engine.

If you are not getting a flat spot as the secondaries open then your mixture is probably too rich on the primary circuit. My memory is a little vague about it now but I seem to remember quite a few progression drillings in the primaries, and due to the size of the carb the stag engine probably isn't running fully on the main jets until motorway speeds anyway.

I had quite a few problems with the engine stumbling as it came off the idle circuit and onto the main jets. Again the problem is caused by the carb being too big for the engine, and the way that it is usually cured is by upping the jet size. This gives a good cruising mixture but as the revs build it goes too rich again which is probably what you are seeing rather than the secondaries being the problem.

There is a cure for this which I was fortunate enough to read about while on holiday in the USA, in a hot rodding magazine. It was aimed at weekend drag racers with carbs too big for smooth street driving during the week.

The basic idea is to drill a very small hole in each primary butterfly. This lets extra air into the engine at idle. The weakened mixture then has to be compensated for by opening up the idle jets. Having done this you now have a very high idle speed, and the throttle stop is then backed off to restore normal idle speed.

If you drill the holes too big you can't get the idle speed back down again, and have to solder up the holes in the butterflies and try again. Guess how I found that out! Think I terms of a 1/16 I drill, not a 1/8 to begin with.

The end result of this is that the engine runs on the idle jets to a higher rpm than it normally would, and by the time it moves off the idle circuit onto the progression drillings there is enough airflow for the carb to start working properly. I managed to get my mixture spot on throughout the rev range and it transformed the driveability of the car. When I swapped to efi using the same inlet manifold all I gained was 1mpg on average, and no improvement in power output.

The Holley can be made to work well, but it is a shame that you can't buy them correctly tweaked.

Incidentally, the 53 jet size I quoted at the beginning was with cold air ducting to the air cleaner. Sucking ambient under bonnet air means the required jet size varies from 53 on a cold morning to 50 on a warm day and possibly as little as a 48 in very hot weather. Cold air was ducted to the Strombergs for a reason!

Neil

[73stagman]

See. I told you I wasnt an expert!

[mike@thenook]

There are only two changeable jets on the 390 but 73 has hit on the other point regards the secondaries - they only open when there is load, not just when you rev it stationary.
I can try and load a copy of the 390 manual if you don't have it?

Cheers