Carb / Brake Master Clearance issues... Ideas?

[Vae Victus]

I'm working on my '70 FJ40, and I have put a Racer65 Carb 2F on. The PO had put a single diaphragm booster (along with the firewall rib adapter), and front disc brakes, so we added a dual master brake cylinder for a little redundancy in the system.

Problem is, the new carb hits the MC on the secondary diaphragm. This is the 2nd attempt at a smaller MC ... It all fit until I realized I was missing the insulator under the carb which raises it another 1".

Here are my options:

1. Shorter MC. Use a compact MC shorter than 6" - but I haven't found one that works yet.
2. Modify the secondary diaphragm on the carb if possible (it is the part that is making contact with the MC).
3. Go back to a single circuit MC. Loses the safety factor of dual circuit.
4. Go back to the OEM-style carb for this model year. (rather not since I've bought this one but it's a near last resort)
5. Remove the booster and run a larger bore MC like TheCrazyGreek suggested here (not 100% confident in this option so it's like the last option for me)

Creative group here. Love to have input on the options.

 

[Vae Victus]

You can see the MC hits the secondary diaphragm.

Using (not the right insulator/spacer) you can see how far off I am from being able to mount the carb.

The length of the MC must be 6" or shorter if this is going to work.

 

[thorslc1977]

You've tried a stock Fj40 MC? If that doesn't work I think OEM style carb is best solution. Sell or keep for trail part the carb you have now? I believe I saw a 69 - 70 Aisan carb in good shape in Classified parts section

 

[Vae Victus]

No I've not tried the original MC. I can go back to a single circuit MC, but trying not to.

 

[subzali]

Do you have a thin booster like a mini truck or fj60? Can’t tell from pics.

 

[Vae Victus]

Yes it is not the fat dual one - but it is mounted on that 5" spacer that pushes it past the rib in the firewall.

 

[RockDoc]

Some of us have gone "kinky with the linky" to move the master towards the fender.

Bronco brake booster link in an FJ40

 

[B y r o n]

Maybe a shorter MC adapter like this one.

 

[Bear]

Vae,

Just a thought. Would you be able to lower the carb with its secondary diaphragm by slicing the bottom insulator in half?
Or cut out part of the firewall rib and make a shallower brake booster adapter?

 

[tornadoalleycruiser]

Different master? Say 80 series? Designed for 4wdb but I recall 91 and 92 had rear drums

 

[65swb45]

I don’t know if I’m tempting fate by sharing this, but under the category of I remember a guy, pre-internet days, with this issue who made a plenum spacer shaped like a parallelogram to ‘jog’ the carb away from the MC. It was one of the fugliest things I ever saw, but he swore it worked just fine.

I would just use a 1F carb.

Rebuilts available.

 

[Vae Victus]

Man, great options guys! Thank you.

So going to look at the 80 MC first. Thought I had the right one but that one is shorter.

Cutting the spacer in half - might work... good idea.

The Bronco MC custom angle bracket. Nice engineering and fab work.

Shorter MC adapter won't work - have the firewall rib to deal with.

If I wanted to spend a grand I could use an electric booster but, nah.

.. and yes, switching carbs to one without the secondary diaphragm or back to the proper carb would always work.

I'll report back.

 

[Downey]

I would have stacked factory insulator blocks (or made a tall adapter spacer) to get the diaphragm above the master cylinder. Why?? because the additional spacers would actually add to the plenum chamber value of the intake manifold, giving greater performance.

 

[Vae Victus]

Good thought Downey.

Can someone explain why the throttle valves are hanging going open without the spacer? Is it a clearance issue, a temperature issue, amoressure/volume issue.... I don’t understand the purpose of the spacer/insulator.

(I know it keeps the fuel from vaporizing prematurely due to too high temps but that’s not all it does surely)

 

[tyama]

i put a aisin MC/booster from a 96' geo metro. Fits & works well.
best, ty

 

[bikersmurf]

Hydraulic booster would fit where the spacer is.

 

[Vae Victus]

Hydraulic booster would fit where the spacer is.

I would need a PS booster.... Not currently an option. Good idea though.

 

[Vae Victus]

So I've run out of known options for short dual master cylinders. The shortest I can find is 6 1/4" I need 5 5/8" to ensure clearance. If anyone knows of one....

An option is to mess with the height of the carb spacer - either to lower it to raise it. Not crazy about doing that. Stock spacer (which I just bought because I had NO spacer) makes the vacuum advance hit the master cylinder.

NOTE: Why did the carb stick open without the carb spacer in place? Was that the reason? I don't understand what the spacer does for a carb. It is just for fitment and clearance, or does it serve a mechanical purpose? I was hoping it would solve the mechanical sticking issue.

I guess I need to find an F carb. Wish I could buy a new one, but looks like rebuilds are it ATM.

 

[Downey]

Sure is starting to smell like TBI conversion time to me ?????

 

[liko]

Went with geo metro as well, but i have 4 wheel discs. Works awesome.