ok here we go something that im sure many people have been waiting for.
this is a bit of a guide on moding your stock carbi to flow more like a weber but with more control. (well i think anyway) no fights please.
bit of an intro, my name is Troy im from the gold coast 19 years of age.
i have a 79 td wagon with a pretty heavily modded 1600. and i needed a decent carbi to suit so i thought i would give the nikki a second chance at life.
i had a spare so i didn't care it was all trial and error. but i had a fair bit of success.
ok lets get started shall we.
so here is the list of mods i wanted to achieve
general reshaping of venturis and tidy up.
removal of choke (optional) haha
larger volume accelerator pump
probably some others that ill remember half way through writing this.
here is a list of what ive done to my "poer house" i mean power
Engine Type: G161z
Engine Mods: Bored 020thou
G161 Pre emission head (TX big valve)
Port and polished head
Ported inlet manifold and carbi
High lift cam very lumpy idle
Flat top pistons
Shaped pistons to suit head clearance
hardened Double valve springs
rejetted nikki carbi, with mechanical secondaries and full reshaping with disabled vacums. bigger ac pump
bosch fuel pump
fwd gemini/rodeo hall effect dissy, bosch ignition module and twin gt40r coils
and a 2.25 inch exhaust single muffler straight tip.
so first i started off with a stock 1600 carburetor. all g series carburetors are the same except jets and the secondary aux venturi is taller.
see photo. 1600 and 1800 are the same height but different sizes.
i stole this from Lok15 hope he dont mind ill just buy more stuff from him
first off i strongly recommend getting a carbi rebuild kit, i got mine from super cheap, cost like 12bucks i think they are getting harder to find but ebay has them for 45 i think. anyway you need this so fork out and buy.
so first up we want to take the hole thing apart and clean everything we can with carbi cleaner or kero. i used petrol i think works the best just try to keep all rubbers and diaphrams dry.
we want everything spotless and remember what you took off and where it came from, write it down if you have to.
and unless you are totally re-jetting we want to clean these to, fine peice of wire and carbi cleaner will do. any blockages and your car could run like dump. some stock jets will still be used. write down what went where so you know what jet is what. and watch out for the ball bearing and rod in the AP (accelerator pump) jet.
Once this is done its time to start cutting.
This is a aux venturi there are two of these one for the primary and one for the secondaries.
and this is the modified ones,
what I did was file down the extra lug that supported the other side, that isnt needed. Also the supported side I reshaped rounded on the top and sharpish on the bottom aswell as just giving them a general polish maybe a reshape for sharper edges on the bottom.
The main thing to remember is that a bigger hole is not better, the purpose of a venturi is to increase the airs velocity to suck the fuel through.
Next I reshaped the butterfly shafts to increase flow. This is my modified one I simply filed the rounded shaft down thinner and gave it smooth edges. One shaft had support on both sides of the butterfly so I completely removed that and kept the side with screw thread side. I also filled the extra thread on the screws to sit flush with the now much thinner shaft.
and here a butterfly fitter to shaft. (secondary)
next we want to ensure that both butterflys are actually opening to full, this is a big problem with nikkis. Place the butterflys and rods back in the body and file these lugs that work as stoppers. We want to just file the ends off so the butterfly is able to rotate to completely straight.
so I wanted to have mechanical secondaries like a weber so when I put my foot down it does what I want, the usual vacuum system needs the revs to operate before it will completely open.
So what I did was first I had to disable the vacuum system. In the vacuum diaphragm there is a spring you need to remove. you need to peel the diaphragm off the rest of the unit and take out the arm that is connected to the diaphragm and remove all these components. Leaving us with the inside of the secondary lever looking like this.
we also need to block the vacuum tube that operates this diaphragm, I used a piece of spare gasket and covered the hole and screwed the top cover back over the top sealing the hole. If not done correctly this will cause a vacuam leak and idle may be compromised. Other options could be maybe an epoxy filler or plug. Be creative.
Finally I used a small amount of wire to tie the levers together. Hard to explain but you will see what needs to be done. There is a tab that you can bend to time the secondary's opening time this is located where the diphragm lever was attached. We want to time it so that the secondary reaches full opening at the same time as the primary butterfly. Trial and error you will figure it out. the secondaries should be begining to open at arounf 1/3 throttle and reach full at the same time as the primaries.
This shows the linkages but doesn't show the wiring.
and this is the butterflys at full throtle
I then port matched the top ventury section of the carbi with the butterfly body. I used a small flappy wheel on a drill, the aim is to only alter the bottom section just to match where it lines up with the base. And give it a smooth polished finish, crack out the elbow grease and some wet and dry.
in my carbi I totally removed the whole choke setup, and filled the holes with epoxy for better flow.
I find the car starts perfectly fine even on cold mornings just hold a bit of throttle until she starts to run smooth and let warm up, kinda gay for street driving. But still good.
I tried a few things to make a larger Acelerator pump volume but im still working on that. We want a larger volume and travel so when you boot it we dont lean out and dig down, this symptom happens when the AP is blocked. But with the mech secondaries there is an excess of air flow for the stock pump. The extra travel works best say when ur sitting at like 80km/h and put your foot down there is still enough travel in the pump so leaning out doesnt occur and we get a smooth powerfull acceleration up to 110km/h(on the road boys).
Now putting it all back together, hopefully you have a good memory or wrote it down we want to put everything back with new gaskets seals and washers, from our rebuild kit. The kits come with a new needle and seat and adjustment of the fuel float may be needed, I tune my float to run on the line of the glass when the car is idling.
ok well here is the hard part that I have no idea. I'm currently running a set from a g181z carbi I have no idea if they are good or not. I'm hopefully going to chat to a carbi bloke about new jets. Ill start a thread on here see if anyone can help out on sizes. But I would recommend if you went to the trouble go see an expert and get them to jet it right, to your engine, its going to make a huge difference.
Here is my top section of the carbi together. You can notice there is a lot more clearance in there for better flow.
Mine I put on 2 days ago and i've noticed quite a power increase and much smoother running. My car actually idles now. I seem to have more low and high up power. I've got to do some timing cause I haven't been able to get any revs out of the engine lately much before the carbi mods. I'm expecting some good power from this carburettor.
so yer hope this helps everyone wanting to give their Nikki a bit of a kick.
I'm open to feed back to on any thing I haven't explained properly or anything I can add.