Simple Street Performance Mod for F5a / F8b

[Alto Boy]

Guys......what I have done as far as remapping the vacuum supply to the secondary diaphram is a simple, cheap and very effective performance mod that will give you heaps of get up and go for suburban driving.

Here is a link to my Gallery http://www.tamon.org/gallery/v/members/ ... f5cfa85dbf

Checkout the last 2 photos

1. Go to Repco and buy 1 metre 1/8th vacuum hose and a T piece 3 way splitter to join all 3 hoses.

The longest hose runs from the back of the carby to 1 end of the splitter this is exactly 21cm long, then cut another piece 8.5cm and join that from the splitter to the diaphram, next cut another piece 6cm long this runs from the splitter to the vacuum advance on the distributor.

I have spent countless hours trying to restore the lost power my car suffered after an exhaust change......I still can't fix the top end speed but this mod has given my little F5a a new set of balls for street racing or just having fun around the suburbs.

Total cost $10.

Bear in mind if your second stage is not working it could be either your daiphram needs replacing or the Forked fuel feeder pipe supplying fuel to second stage is blocked.

If you are in Brisbane or near by, I am happy to show you how to do the mod and check your second stage and diaphram for free.

I hope you have fun with this inexpensive but very effective modification.


Seeya......Greg.

[stevan_istheman]

Thanks mate.
I thought it was much more complicated than that but oh well, i'll give it a go on my F8B when it's running.
can't wait!

[Jermaine]

how do u tell if the secondary isnt opening?

[Alto Boy]

Honda Dude......1st and most common problem is Diaphram leaking.....to check this, you will still need a piece of vac hose.....there is a short hose running from the right side of the daiaphram back to front of carby.....disconnect this at the diaphram end and connect hose long enough to reach your mouth.

While the engine is stopped, you need to pull on the lever your accelerator cable runs to and pull it fully forward, while holding it in that position, suck on the tube you'ved connected to the diaphram and and you should see the little spring loaded leg pulling the second stage on....put your toungue over the hole of the tube you have in your mouth and if the diaphram slowly springs back into fully out position, you diaphram is leaking and more than likely your second stage is not working.

The other fail safe way is just make my mod and if you can't feel a difference.....then you've only spent $10.

Seeya....Greg.

[Jermaine]

i can tell u know its not opening

[gremlin]

the simplest way to check i could think of was just to get someone to give the car a good rev and watch. if the secondary opens, it works, if not it doesn't.

[Jermaine]

or use your hand and open the throttle on the carby

[gremlin]

lol yeah that'd do it.

[Alto Boy]

Dude....I have no idea whether it's working or not......you asked how to tell if it's working or not.....and I told you how to check it.

Something I DID leave out was......when you disconnect the short hose from the diaphram to the carby, you will either need to put a screw in the end of that tube to seal it off or while you're at Repco get a 1/8th blocking cap.....this is a little rubber cap to seal the nozzle sticking out from the carby that used to supply vacuum to the diaphram.

Hope this helps.


Seeya....Greg.

[Jermaine]

yeah and i said its not workin but with a spelling mistake my bad

[Brayden]

the simplest way to check i could think of was just to get someone to give the car a good rev and watch. if the secondary opens, it works, if not it doesn't.

The secondary is designed to only open when the engine is under load, and creating more vacuum than it does when free-revving.

[Jermaine]

and that means?

[gremlin]

what i gather from what brayden said is that the secondary is designed to open only when driving (putting load on the engine) and that free revving not under load (not driving) isn't going to open it fully/at all.

hmm, mine still opened fully (i presume it was fully open because it looked fully open and i could hear the induction sound become somewhat more fierce), perhaps mine's not setup properly? Oh well, does the job anyway.

[ceej]

Just in reply to Greg (sorry i haven't kept you up to date...) I have had the setup on an off. I have cleaned the carby up, run cleaner through the fuel system and played with the hose lengths... It runs smoother now, but still seems to be "snapping" open and hence leaving a flat spot in the rev range (very annoying when trying to take off from lights ...Even more annoying when wogs pull up next to you and laugh at the boy and you are wanting to show em up )

Any way, i will keep trying cause i am liking the way that i can drive on half throttle at the same speed as i would be on at full... And then when i need to burn something i just slam the foot down

[Alto Boy]

Ceej....this is why I reccomend getting 1 metre of hose, so you can experiment.....try lengthening the tube from diaphram to the splitter by 1 to 2cm and look at the way I have run the T piece, the second photo in my album shows exactly the way each hose connects to it's relevant component......the upright leg of the T connects to the distributor, the top of the T connects the vacuum supply from the back of the carb to the diaphram.

If this is how you have already connected it and you are still getting too much suction, then connect the T sideways so the distributor gets the most suction and the diaphram gets less.

Trial and error.....mine works perfectly, the only time I get a small flat spot is when I've been coasting in gear and then reaccelerate, sometimes I get a small delay.