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Discussion Starter · #1 · (Edited)
Long time, no post. But I've done it! CV carbed 87 Sentra 1.6L SOHC!
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Well documented, getting her jetted tomorrow..... Hopefully.
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Runs alright, especially considering that I have no real "professional" automotive training, just a love for Datsun/Nissan cars.

The carbs came off of a Yamaha FZR1000, completely a "parts only", "deconstructed and stripped" BDS 37mm Mikuni carbs I was incredibly lucky to find on KSL (craigslist in Utah... maybe it's Mormons, fxck if I know lol)...
Anyways.

It runs. But.... Not as well as I hoped. According to the narrow band air fuel mixture gauge I have installed (I don't really know how much I trust it, it was $20 on eBay. And NB sucks so badly compared to WB. But whatever.)
Long story short, it kinda flops around between being too rich or too lean. Which is a massively huge improvement from it dying going downhill, when applying the brake, etc. Fuel pressure stays between 2-3psi, sometimes jumping to 6 for WTF ever reason.
Bought a oil catch can (Amazon) for $20, six port vacuum manifold kit (eBay) for $20. So vac diagram goes as follows...

★Valve cover, right side: small NAPA cone filter
★Valve cover, left > Vac hose to Oil Catch In
★Oil Catch Out > inline PVC Valve
★PVC Valve > Vac hose to 6 port mani, Large Left Port
★Intake runners 1/4" fittings (post carb. Right before head. Design flaw, i think) > port 1,2 and 4,5 (1/4")
★port 3 > dist vacuum with inline vac delay valve (is this necessary...?)
★port 6 > plugged
★Right Side vac Mani > brake booster
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So the VMani actually has 8 ports: 2 large on left and right, 6 small in the middle.
I also had thoughts about the size of the VM.. 1"X6" Seems small, almost like i should instead build one like this, more ports obviously. This container is solid aluminum, easily 3"X10"

These behemoth 37mm carbs have 1.075mm Main Jets...
So
I bought 4 packages of main jets, ranging from .88mm to 1.5mm.
Retrofitted a dizzy with a vacuum advance, a loooooong time ago. Which i now regret, as these carbs allegedly work best with the Crank Angle Sensor of the correct year for my car.

I know this was a mouthful, but I'm rather proud of it. Super happy, just wish I knew how to best tune this, jets and all.

If anyone has any knowledge that I may use to my benefit, I'm all ears.


Thanks for your time!♥ Hood Motor vehicle Automotive design Automotive lighting Automotive exterior
 

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Discussion Starter · #4 ·
Hey, congrats on your effort and result. Looks good. Hit a few web sites to pick up some tuning tips.
Thanks, man!

I think it has officially become a "you live and learn" type hiccup, because I jumped the gun. There were 4 slow pilots at 0.175mm i drilled to 0.2mm, because I thought "since I changed the main jets from 107.5 to 130.... Might as well hit these, too".
With a drill, like an idiot haha...
Now it really has stumbling issues. LOLOL.
You live...
You learn.

I'll definitely try a few more things before spending "X" amount on 4 slow jets. I think my fuel filter has a bunch of schmutz in it; and taking the carb off one last time and hitting that with cleaner for good measure would be a great idea as well.

@rogoman , for the life of me, i cannot find any single bit of anything regarding an E16 with CV carbs. Just me. Maybe I should base my jetting off of perhaps an L16 Datsun...? What do you think?
 

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Thanks, man!

I think it has officially become a "you live and learn" type hiccup, because I jumped the gun. There were 4 slow pilots at 0.175mm i drilled to 0.2mm, because I thought "since I changed the main jets from 107.5 to 130.... Might as well hit these, too".
With a drill, like an idiot haha...
Now it really has stumbling issues. LOLOL.
You live...
You learn.

I'll definitely try a few more things before spending "X" amount on 4 slow jets. I think my fuel filter has a bunch of schmutz in it; and taking the carb off one last time and hitting that with cleaner for good measure would be a great idea as well.

@rogoman , for the life of me, i cannot find any single bit of anything regarding an E16 with CV carbs. Just me. Maybe I should base my jetting off of perhaps an L16 Datsun...? What do you think?
What you might want to consider is modifying your carbs to use removable jets. Drill each carb jet out to some larger size; then tap the holes out so that a removable jet will screw in. Over the years I've worked on holley carbs, which use removable jets, by replacing jets during tuning runs. I've got a large assortment of jets for many different size holley carbs.
 

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Discussion Starter · #6 ·
Oh! They're totally removable! Lol i removed them and bored out the size from .175 to .2 haha, my bad.
(The idle is FANTASTIC by the way lol)
Only reason I drilled the slow pilot out was to give it more fuel. And now it bogs in the mids. But maybe I'm closer, who the eff knows.
Check this out, though.....And I quote:

"If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner."
If the engine is "dry" and flat between 2k to 3k rpm, lower the fuel level.
That's what I am effing dealing with right now. Call me inexperienced, lol i don't care, but I had no idea that float level controlled throttle responsiveness. No goddamned clue.
It's weird being on a Yamaha forum to figure out how to work these Mikunis, buuuuuut I believe that I accidentally stumbled on the most detailed, accurate information that I've found to date.
 

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Oh! They're totally removable! Lol i removed them and bored out the size from .175 to .2 haha, my bad.
(The idle is FANTASTIC by the way lol)
Only reason I drilled the slow pilot out was to give it more fuel. And now it bogs in the mids. But maybe I'm closer, who the eff knows.
Check this out, though.....And I quote:

"If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner."
If the engine is "dry" and flat between 2k to 3k rpm, lower the fuel level.
That's what I am effing dealing with right now. Call me inexperienced, lol i don't care, but I had no idea that float level controlled throttle responsiveness. No goddamned clue.
It's weird being on a Yamaha forum to figure out how to work these Mikunis, buuuuuut I believe that I accidentally stumbled on the most detailed, accurate information that I've found to date.
On the holley's I did mess with the fuel level but making the level too low caused bog problem during take-off in the drag cars; had better results with the pumpers. If your carbs have removable air bleeder jets, you might want to mess with those; I did for awhile but with mixed results.
 

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Discussion Starter · #8 ·
So it was the fuel filters causing my bogging. But it still needs more air.
Some jet needles for Mikunis come with small grooves on the top of them to adjust how lean or rich the mixture will be with use of an E-Clip. Mine only has one groove. Some have five.

My setting seems obvious to me that it's "the middle", OEM setting that is best suited for a 1000cc bike. But now that they're on a 1597cc car.... Perhaps asking a motorcycle mechanic what needles to purchase that are adjustable instead of fixed may be a window to achieving full tuning and responsiveness....?
 
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