Nikki Modification finally

Engine related articles specific to induction (carby, EFI etc.)
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troyrotor
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Post by troyrotor »

Once you move the point up by making the new slot you will have more travel, this is where you have to change the arm setup so it starts from higher up the chamber. I can't remember exCtly what I did to the spring I thought I had a spare plunger but I'll have to pull on of my carbs apart to see what needs to be changed.

Unless I chop a photo to show you exactly what to do
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geminilover3236
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Post by geminilover3236 »

Hey, hey, hey...
The carby is back together and waiting to be bolted up. tonight hopefully. waiting for gaskets.
Basically. i figured out what you meant about the plunger and I have some pici's.

- With full throttle, the plunger doesn't go all the way down. So modify time. I pulled out the connecting arm from the throttle lever and drilled a new hole inbetween the two. Bent the arm to line up with the arm that connects to the plunger. This was pretty much spot on from what I could tell.

Arrow indicates turn axis of the throttle lever, as you can already see the new hole gives it a bigger leverage.
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and here you can see it with the rod connected
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Will post results of how it goes.
I'm running a 30/70 Cam on a 1600 with 4-2-1 extractors to a 2" system and electronic ignition (however I think it needs a recurve).

Jetting? Just the main power jets are we thinking to change? Im thinking the primary will need to be a tad bigger.
troyrotor
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Post by troyrotor »

awesome mate so you actually made sense of my mumble?

sounds like she will get up and boogie then, the jets i looked at changing the couple jets that differ from g161 to g200 i think there is 2 or 3 that need to be changed. the info is at the start of the thread
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geminilover3236
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Post by geminilover3236 »

Yer, seemed to all make sense. Once I saw how the plunger didn't go down it all came together.

Just got it bolted up and running.
She's pretty lumpy down low but that could be the cam, I only just put that in too. My biggest issue is there is no down low power AT ALL. Like I have a pretty steep driveway to get up to get out to the street and I can't do a hill start on it :S. It just really bogs down. I made it up just... but was on idle revs and had the pedal 1/4 - 1/2 open so that the secondary wouldn't open up and smother it. This poses a bit of a problem to driveability. However, after about 2900rpm it pulls really hard. And I think it was suffering fuel starvation at like 6000rpm but that doesn't matter atm. I think thats to do with the fuel supply.

Primary Jet - 113
Secondary Jet - 175
The one marked 46, Thats now a 48.
The one marked 80, is now 90
Everything else is the same.

I definitely need to regain some of this low down so it can be driveable. I also noticed it running quite hot. I managed to get up my driveway with one of the intake manifold hoses off & air filter off causing an air leak. Not sure whether it was the higher idle or lean mixture that gave it a bit more go. Hmmm. Probably going to grab some drill bits tomorrow and start drilling them out and seeing what works. I'm just going to be playing with the Primary and Secondary Main Jets (113, 175). Any suggestions would be grass.

*edit
Just had a thought, could it be beneficial to make the secondary open LATER so that we still retain some down low performance from the pimary being able to open up a bit more before the secondary cuts in. Still have it open to full though. (modified linkage)
Last edited by geminilover3236 on Mon Feb 28, 2011 11:44 pm, edited 1 time in total.
geminilover3236
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Post by geminilover3236 »

Okay, flooding the topic here but... I am trying to identify what circuit each jets belongs to. this is what I've got. I have marked the ones I don't know with a ? followed by a number. If you know what it does then can you please post it up.
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troyrotor
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Post by troyrotor »

I think you will find that it's not the jeti g that is causing the no low down power. It will be something else, are your solenoids working properly? Also maybe the choke not completely open, other than that I would say flush the carb out again. When running at idle place your palm over the top face of the carby and it will suck your palm down and cover your hand in fuel haha but should suck any junk caught in the jets out. Also the hot temp may be from your cam. If this fails try standard jetting see what happens
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geminilover3236
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Post by geminilover3236 »

Ladies & Gentlemen... we have lift off!

She's purring like a kitty. A mean angry kitty ready to rip you apart!
Turned out the timing was way out. 1 or 2 BTDC :|

Anyway, today I went to bunnings and bought some super small drillbits. packet said ranging from 0.6mm - 1.6mm so I was like perfect for the pimary. Bought it got it home then realised that at about 1mm they start to skip ahead leaving 1.16mm, 1.4mm, 1.6mm. That cost me $40!

However, spoke to a carby bloke at a place called Moto Carb in Nerang, they seem like really great blokes. Gave me a run down of what he'd do to get up and going well. I explained all the mods I'd done to the carb (thanks troy) and he was impressed, especially about the fuel pump plunger to account for mechanical secondaries.
He said;
- First things first he would get the dissy recurved, set the timing to 10, 12 btdc (run 98 ofcourse).
- Do away with the vacuum advance system all together as with a high initial timing it would cause issues when cruising along.
- Then after the ignition side is taken care of, move onto the carby. He recommended running it on the dyno and then seeing what it shows us and then possibly move onto changing jets however he didn't seem to think that much change would be needed and really only the main power jets would need to be played with and still then, very small increase. The emulsions (I'm a bit hassy with theses), but he said they would more than likely NOT change these at all.

-----------------------
Rough quotes I was given:
Distributor Advance Recurve - $165
Dyno & jets played with - Budget for $400 (wasn't keen to give me a figure for that, his words "Budget for $400")
-----------------------

-----------------------
My Setup: (that I told them)
- 30/70 Cam
- Nikki
+ NO Choke
+ Mechanical Secondaries
+ Shaved Ventury notches
+ Modified Fuel Plunger (to combat bog when secondary opens)
+ 113 Primary Jet, 175 Secondary Jet
- Extractors, 4-2-1, 2" system
- Distributor, Electronic RB with RB Coil.
-----------------------

Concluding & Other Thoughts;
- He seemed to have a lot of faith in the old Nikki, and saying when done right they are great in comparison to a Weber.
- If he were to have modified the carby, he said he would not have done mechanical secondaries but modify the vacuum system to allow it to open sooner. He did run over how he'd do it but my mind has failed me. Something about having it crack open a little bit when you put your foot down but then the rest needing to be opened by the vacuum. It sounded like a good way to do it and once right it would have the carby operating to its maximum.
- I won't be doing this any time soon as I have very little money's.

All the best and hope this helps anyone else.
geminilover3236
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Post by geminilover3236 »

Updates:
Took her out for a burn last and put it through it's paces.
Had a few issues with sometime (don't think it was pinging), but it was sort of spluttering and jumping at around 5000rpm. Got one major backfire too when I reved it's head off. Was experiencing what felt like fuel starvation at 5500rpm. But that went away when I put the vacuum advance back on? (coincidence?)

Pulled it off this morning and change;
- Jet marked #4 from a 48 back to a 46.
- Increased float level slightly so it was right on the line
- Drilled out the primary to 116

Put it back together and took it for a run. Felt much more driveable and able to rev a lot higher. I took it up to 6000rpm no worries. But, it did feel ever so slightly less powerful than with the old jets which is strange because I didn't think that the 48 jet would have made much of a difference when the car was under Load (what is the purpose of that jet? I thought it was to do with the idle circuit)
terocket
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Post by terocket »

how much power yu gettin outa yur engine?? and nice write up helpin heaps lookin at wat fuel system to run atm lol
geminilover3236
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Post by geminilover3236 »

Well, without having it on a dyno or anything, it definitely feels like it's got heaps more.

I actually have a bit of an update with this. I just recently bought another gemini, a coupe of a bloke that races gems and he is running the nikki on the 1600. He got his built by a bloke for about $500. Along with making it flow better and jetting it, He also modified the fuel bowl somehow so that it could hold 15mm more fuel and this seemed to stop fuel surge. Caution though, don't just bent the tab so that the fuel level is higher (what I did) because this will make fuel overflow into the throats of the carby and flood the engine. I notice when I'm on steep hills idling, this happens.

To get decent power from this modification, you definitely need to couple it with some mods to the timing advance curve. whether you maintain the stock cam or switch it for another or get it reground. Recurving the dissy makes all the difference. You can get this done professionaly for about $165.

If I were to do it again, I would modify the vacuum secondaries so they open earlier instead of making them mechanical, especially with a 30/70 cam, there isn't much power until about 3000rpm.
gemiracer
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nikki carb

Post by gemiracer »

That is correct 32/36, guy that does a lot of the gemini series carbs is named ian stewart at carbtech at redcliffe, i can post the number if anyone wants it ...this guy certainly knows his stuff as far as any carb is concerned, and is very much involved in motorsport, so you know his attention to detail is what you would want when handing over your hard-earned (not trying to be an advertisement, but i can definitely vouch for the guy). The extra capacity of the bowl was an afterthought that was cooked up at home afterwards (and is probably not so important to any one doing this for road use,partly because when we did this, we were limited to a standard fuel pump, that could not supply the volume needed when flat on the gas halfway through a fast left hander when the old gemini was almost inverted!!, and when we were allowed to fit a bigger pump and use a regulator, this totally cured the initial issue that we were chasing in that area previously, but if you still use a stock pump it is definitely useful) But yeah carbtech certainly does all the other good stuff that make these carbies work extremely well for what they are. BTW, we find that on our racecar the float still does need to be set just below flooding level to remove all trace of surge on hard left handers, we do this by putting different thickness shims under the needle and seat, and i set my level approx halfway between the white line and the top of the window.
geminilover3236
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Post by geminilover3236 »

Okay, so I was pulling apart a nikki carby from a TC. I was down to the throttle bodies and found that the diameter of the throats is different to the other nikkis I had.

TC Nikki:
Primary - 28mm
Secondary - 32mm

Other Nikki's:
Pimary - 29.5mm
Secondary - 34mm
tudorsi
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Post by tudorsi »

thanks for this helped heaps!
geminilover3236
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Post by geminilover3236 »

tudorsi, that's great to hear! Let us know what jets you are running if you can.

Update:
just ported a manifold, it hasn't been 'port-matched' to the carby though so further gains can probably be made there but I just got rid of that bloody seperator in the middle between the primary and secondary and smoothed it all out with the dremel and sand paprer and a few hours.
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tudorsi
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Post by tudorsi »

geminilover3236 wrote:tudorsi, that's great to hear! Let us know what jets you are running if you can.
Not sure exactly, I have just picked up a 1980 TE sedan and have not done any work yet but am thinking of doing this to make the carby run better as it is running pretty rough at the moment
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