jet sizes for double carbs

[retro]

I want to make sure all bugs are out of my car and i have just fitted the old girl with a set of speco double strommies.

What i would like to know is when i re jet them what size air and fuel jets will be best for average power and economy??

FYI the car has a 25/65 cam, unleaded head and minor head work if this makes a difference.

As i said im only after average power, if i wanted speed a red motor would have already been installed.

[FB MAD]

G'day Retro,

Information you are after seems hard to come by.

I'm working on tripple stroms on tripple Speco manifold for a hot grey down the track so have been trying to find out the same info as you with some results.

The standard grey main metering jet size is .051 ( .050 in FX Grey's ) so that's the starting point.

Someone on another forum advised another forum member with a similar question as yours to use size .046 to .048 jets on a standard to mild grey with twin strommies.

Venturi restricters in the carbies for twins would help also.

Apparently venturi restrictors from one of the Holley carbies are able to be fitted to the grey carbie but I can't find out which model holley the restrictors are from.

Problem I've found is finding where to get smaller main jets from.I've asked around and no one seems to know whether anyone is doing them anymore nor anyone that may have any.

I think I'll have to solder up the hole in a standard main jet and redrill with a number drill to a smaller size to do my tripple strommies because I can't find a supplier of smaller jets or even blank jets to redrill.

Stewart ( parisian 62 ) is working on tripples for his grey so maybe he might be able to add more to what I've said re jet sizes,suppliers etc or maybe another forum member might be able to advise also.

So in a nutshell,

.046 to .048 main metering jets and/or venturi restrictors and make sure your carb butterflys are syncronised together when opening and I'd say they'll most likely work OK.

Oh, and make sure the throttle shafts aren't worn in the carb base as this can also give some tuning problems as well.They can be rebushed if they are worn so that repair is no problem.

Hope this helps,

Cheers,

Terry.

[Thommo]

Apparently venturi restrictors from one of the Holley carbies are able to be fitted to the grey carbie
but I can't find out which model holley the restrictors are from.

The restrictors are a 'Redline' product to suit Holley carbs.
They will need to be adjusted in diameter by
filing them like you are gapping piston rings.
The restrictors are split down one side,
allowing them to crush a little, then spring back to size when fitted.
Mine are glued into place with arildite.
Im sorry I dont have the part# for them.

I hope this helps.

Cheers
Jeff

[parisian62]

I stumbled across this on the Redline website...

http://www.redlineauto.com.au/Holleycar ... spares.htm

on the page above they have the following listed...14-35 Venturi Sleeves To suit 7448 Holley 350cfm 2 Barrel Carb. When fitted, these sleeves increase air speed through the carburettor venturi and help prevent flat spots, particularly on small cubic inch engines. Increased air speed through the carburettor also assists low down acceleration. Main jet sizes must be reduced to maximise fuel economy and prevent overrich idle. Metering block power valve holes can also be swaged down from 0.060” dia. To 0.030 dia. Pack of 2

American Autos have them listed for $9. I go past Redline on the way home and will buy a set and post up a pic.

My other port of call was going to be http://www.carburettorservice.com.au/ for some advice...

Retro...give them a call on 9747 4066 and see what they say...

regards
Stewart

[retro]

the way i feel about the car at the moment, it may be on ebay soon. The more i see the chop top fj cartoon in the hot rod annual, i want to get out the angle grinder on one of my fjs.

When i get the urge to punish myself, ill get the info from some where and post for all.

[Harv]

Gents,

Apologies in advance for dragging up an old post , but some queries over on the FE/FC forum got my interest (probably 'cause my hands are still carbony from overhauling Strombergs ). The post over on the FE/FC forum relates to carby venturi restrictors:
http://fefcholden.org.au/forum/index.ph ... 575.0.html

The theory of fitting restrictors appears to be backed by factory experience. The HD and HR X2 motors (179 and 186 reds respectively) ran twin Stromberg BXUV-2 carbs with 13/32” venturis, which are smaller than the Stromberg BXV-2 carbs used on the same motors (15/32” venturis) in single-carb mode. I guess on the greys, running Stromberg BXOV-1 carbs (11/32” venturis) that there are no smaller B-series Strombergs to go to, and that the venturi restrictors are the way to go when running twins (or at least they help).

I assume that the restrictors work by decreasing the venturi diameter, giving better vacuum to the main metering and power systems (with twin carbs, the air flow down the carb is slower than a single carb, and vacuum signal or "suck" to the metering and power systems decreases). They would thus not effect the idle system, which takes vacuum signal from the throttle body (below the venturi). Interested to hear that they help acceleration flat spots, as the accelerator pump is purely mechanical - I assume they do this purely by better atomisation. Anyone with some anectdotes of before/after installation?

Rod's interest is in hearing how the carb restrictors were fitted. From Jeff's post, it looks like they need to be filed back to an interference fit then epoxied in place. I assume that they are fitted into the main body after removing the air horn and throttle body. Can someone describe how these are fitted please?

Cheers,
Harv (1st year apprentice Stromberg fiddler).

[Harv]

Hmmm.. think I understand now why the venturi restrictors need to be filed back when fitting to grey motor Strombergs. The restrictors (or venturi sleeves) used are made for Holley List 7448 carbs (a Holley 2300 carb, 2 barrel 350CFM). The Holley 7448 carbs have a 1 3/16” primary venturi, which is bigger than the Stromberg BXOV-1 (1 1/32” venturi) - so to get the sleeves to fit a grey motor carb, they have to be reduced in diameter (filed back).

The sleeves are still available from American Autos (part number 14-35) and from Barnes Performance (http://barnesperformance.com.au/shop/pr ... eves-p-197).

Some interesting info (mainly relating to their use in the 7448 Holley) here:
http://www.google.com.au/url?sa=t&sourc ... XMQmc1Kr3g
Note the recommendation to size down the main jet and power valve for the Holley (the increased venturi speed is going to give more vacuum at the main and power circuits). I assume for a Stromberg you would go from the FJ-EJ 0.050" main jet back to the FX 0.050" main jet, and change from the FB-EJ No. 65 drill power bypass jet back to the FJ-FC No. 57 drill jet. Interesting to hear if anyone has had to jet back after fitting the restrictors to ease up on the fuel side.

[Thommo]

Gday Harv
I cant give you any 'before & after' comparisions, as mine were fitted to the triples during the build.
My idle is still too rich, but it doesn't do much idling.
Jets in mine were 48's in either end carb, 50 in the middle.
I have the redline / holley restrictors fitted.
The carbs were built by an old fella who used to run the same set-up back in the day.
It runs a treat, No flat spots, no problems at all.

When the motor was built and fitted, I had it dyno tuned, they recurved the dizzy as well.
For the rest of the engine specs, just click on the 'My Old School Sedan' link on the bottom of this post

Cheers
Jeff

[Harv]

Cool

"it doesn't do much idling" made me laugh - sounds familiar!

Cheers,
Harv.

[browny]

g'day what size jets would you use for double carbs say if any size was available, if i ever get my lathe set up at home i could have an attempt at making some, just a thought

[Harv]

Browno,

Don't bother making main jets for Stromberg - you can order any size you want from Rocket Industries, who are the Aussie supplier for Stromberg Carburetor Company.

This may be of some use for the right sizings:


Cheers,
Harv.

[browny]

no worries thought couldnt get smaller size's all, good

[choppedfan]

Browno,

Don't bother making main jets for Stromberg - you can order any size you want from Rocket Industries, who are the Aussie supplier for Stromberg Carburetor Company.

This may be of some use for the right sizings:


Cheers,
Harv.

Well heres a quick update for those who play with grey motors and think one carb isn't enough I rang Rocket Industries this morning looking for smaller jets for the triples I'm setting up and was told even though they appear on their online catalouge they no longer stock them

Good news is I found a set following Stewart's (Parisian62) advice from the Carburettor Service Company (02 97474066) when I ordered mine this morning I asked how far the size range goes and he told me he has them all the way down to size 41.

Now I've got something to play with Boxing day

Mick