Fuel Tank Failure & Briggs 61102 Upgrades

Minimichael

Minimichael

Well-Known Member
#21
#21
jeep2003 said:
One of my bikes i cut the bracket and raised it up an inch or so and it eliminated the need for a pump. But i used a tecumseh carb with the inlet low on the side.
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Did the Tec carb have a diaphragm pump built into it, or a bowl? I wanted to like the diaphragm style but found it just couldn't respond quickly. That one also had an inlet at the bottom.

I may someday switch to a crossbar tank if I ever find one, but I think I still like the idea of having a little background fuel pressure in the lines.
 
Minimichael

Minimichael

Well-Known Member
#23
#23
f4radar said:
Nice upgrade but for some reason that 45 on the exhaust looks unnecessary.
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f4radar is right, that 45 fitting on the exhaust was unnecessary after all.

The more I worked with the flex pipe the more it loosened up. I've also swapped out the cheaper galvanized pipe for stainless, which is even more forgiving. And I learned again this kind of twisty pipe also slides sideways on itself, just a tiny bit, so the hose ID is actually slightly adjustable, too.

The remaining nipple and collar fitting are still aluminum and holding up just fine. The galvanized pipe on the other hand got splotchy and frosty looking from the heat. This automatically looked like crap, and automatically justified the price of the 304 stainless. (Still not bad at $35/5ft.)

So not counting all the R&D costs, or all the gas back and forth from McMaster-Carr, or the stopping at Starbucks... this header could have cost about $36 (and that's even including the $7 fancy lock washer and $7 exhaust hanger.) I'm happy.
 

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Minimichael

Minimichael

Well-Known Member
#25
#25
I make them from materials I've found online. You can purchase different cast manifolds from eBay, Amazon, and Alibaba. They're for scooters, I think, and do come in a variety of shapes. And I've settled on a few shapes I like. The hose can be radiator hose, though I prefer the higher performance "racing" silicone ones. The holes in the inlet casting have to be shaped to fit the block's, but the other end of the casting always fits your standard slide carburetor. I've considered making and selling them, but so far I've only done them for 2 and 3hp blocks.

I really appreciate the versatility they offer in terms of length and positioning, which the prefab steel ones, when they're even available, do not provide.

Like what if you don't want your carb sticking straight out the back?
 
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M

MICHAEL JOE

New Member
#26
#26
Minimichael said:
I make them from materials I've found online. You can purchase different cast manifolds from eBay, Amazon, and Alibaba. They're for scooters, I think, and do come in a variety of shapes. The hose can be basic radiator hose, though I've come to prefer the higher performance silicone ones from the racing world. The holes in the casting have to be shaped to fit the block's, but the other end of the casting always fits your standard slide carburetor. I have considered making and selling them, but so far I've only done them for blocks of 3hp and lower. I'll be doing a Briggs 5hp very soon tho, and maybe then I'll find enough interest to justify making multiples. I also like the versatility they offer in terms of length and positioning, which the prefab steel ones (when they're available) do not.
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Thanks I have some 5hp Briggs flatheads that I would like to put a Pred. 212 carb. onto the flathead.
 
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Minimichael

Minimichael

Well-Known Member
#28
#28
In our last thrilling episode...

We had the #112 main jet securely positioned within the Nibbi PE24 carburetor ...and it was running decent, on the bench. But on the road it didn't make it down the driveway. The engine was just starved for fuel. Lots of gasping...

So I've switched out the 112 jet for the biggest main jet that came in the box -- the #115 -- and now this newly accessorized beauty powers the bike more smoothly and faster than before. There really is a smoothness to these engines with a slide carb installed. The throttle response is also more immediate, but it still feels soft. And while soft acceleration is nothing new for this mini (it originally came with a 1hp model 6S), it's clear that the engine is still starving. So I've sent away for a few larger main jets, and this mini-series will continue... So stay tuned for more tuning!

Thanks btw to jeep2003 for the point about the flat-faced air filter being restrictive. I still love the look of the flat one, but swapping it out to a cone let me adjust the air screw down nearly half a turn! Thanks again, jeep2003.

Here's some final walk around pics of the old farm find, along with a couple from way way back...
 

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Mr. Pink

Mr. Pink

Well-Known Member
#31
#31
Does the carb jiggle around much using the rubber coupling on the intake manifold?
Will that be your permanent setup, or just a prototype mock-up?
 
Minimichael

Minimichael

Well-Known Member
#32
#32
Mr. Pink said:
Does the carb jiggle around much using the rubber coupling on the intake manifold?
Will that be your permanent setup, or just a prototype mock-up?
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It is permanent... for now anyway. Yeah it's remarkably steady during operation. I'm also happy it kind of insulates and prevents heat transfer to the carburetor. Actually I did expect to need a brace of some sort, but it hasn't worked out that way. The more important thing is manifold capacity and that naturally limits lengths.

So no it really doesn't bounce around or even vibrate. I have made longer ones and with more turns without a problem. Having higher grade silicone helps. And there's silicone with special fuel resistance coating, but I have had great results with regular untreated as it is already rated for petroleum vapor.
 
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Minimichael

Minimichael

Well-Known Member
#33
#33
The bigger Nibbi main jets got here (#'s 118, 120, 122, and 125). For reference, I wanna say I read that the Nibbi jet sizes are based off the Keihin standard rather than mikuni, tho I could be wrong.

Anyway it's a beautiful day in Chicagoland. Here's the project, idling on the #40 slow and #118 main jets. I hope to take it riding this evening and see where the bigger jet puts me...
https://flic.kr/p/2nMyTDA
 
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Minimichael

Minimichael

Well-Known Member
#36
#36
On jet size and needle positions...

Tuning this particular carb for this particular 2hp has been trickier than I expected. I've identified the better needle settings, tested all the jets, and found all the sweet spots for the air screw and idle screw for the different main jets... But this Nibbi has still been more difficult to read than your usual Keihin or Mikuni. I am getting closer, but the settings have gotten weird...

With eight main jets from 108 thru 125, I'd had high hopes for the largest four, but while they might have improved certain upper power bands, they would also include multiple other bands of sputtering. The bigger jets were just too rich. Strangely enough, I found that if I also richened the needle jet by raising the needle position those sputtery bands started to fill in. This allowed me to venture back to the smaller main jets while keeping the needle in position #5. So now I'm now back down at the second from smallest main jet (#110) and road testing pretty well, so long as the needle stays in its highest position (#5). NOTE: I've even raised the needle to extremes, with as many as 4 shim washers, and with success... So go figure.

As a final approach, I've ordered one smaller main jet (the 106) and two larger slow jets (42 and 45). The #40 works here, but I want to see if I can fill in the lower band more, and maybe even bring the needle back down a bit. I've also resolved not to adjust any higher than a "realistic" needle setting (like 5, plus one shim). While raising the needle seems to smooth out all the bands so beautifully, the sky can't be the limit, and Nibbi doesn't sell different needles...which I also think is curious.

This bike is unique, in that it has a little 2hp engine and huge 72 tooth sprocket. It's a bike with little torque but fun top speeds. In other words, there's no reason not to floor it for much of the ride. And I'd heard racing carbs (like flatsides) are designed for this all-or-nothing fuel delivery, so I had hoped this Nibbi "Racing" carb might be a good fit (plus the colors were a good match). And in fact, the Nibbi's slide throttle valve is so wide, and the slide travel is so short, that it kind of operates like a frickin barn door for fuel. So I'm into it, and I'm not cutting my losses just yet.

But if I can't smooth out the whole throttle range with one of the 9 main jets in my extensive inventory, and one of my 4 pilot jets, and a needle shimmed above #5... well then I'll just switch carbs. Stay tuned...

https://flic.kr/p/2nMRsHn
 

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Minimichael

Minimichael

Well-Known Member
#37
#37
PXL_20220925_004544695.jpg
Tuning this Nibbi PE24 has been tedious, not very satisfying, and only somewhat enlightening. Here are some notes from this afternoon...

Tuning today ...got two bigger pilots 42 and 45 and one smaller main 106 to test out... Trying clear up sputtering especially in low to mid cuz very short fat slide valve gives all or nothing... For pilot jets: swapping #40 out and go right to 45... Okay, 45 too much, cuz air screw needs 4-1/2 turns out, just to start engine... This thing is touchy... There's sweet spots all over the dial, depending on jet and screw in place, but the sweet spots are also real narrow windows... Had needle at #5 but now back at #3 for shits and giggles ... #42 pilot better than the 45...42 is good, with 2.25 turns on air screw... #42 pilot's air screw sweet spot is barely 1/16th turn left or right... For main jetting: #106 has no upper end, 108 only a little more... And always sputtery in mid throttle... Going back to needle 5 for sputter, and better now... #'s112...115...118 showing more and more top... Nice "whirring" combusting sound at top end when reach full throttle, best so far at #118... Still sputtery on many throttle transitions especially from low to mid range... 118 saw some backfiring in mid to upper when laying on throttle as bike climbed in speed, ...got too rich? More balls tho, so on to 120... Thinking that needle always at 5 really limits later adjustment (does Nibbi suck?) Hold on cuz maybe needle setting window is also super narrow? Keep going with mains and then revisit needle, still at 5... Now #120 very sputtery at mids, but solid feel at top. 122 harder to get past sputter into full top, and then...a bit soft and gurgley? #125 now, and it just won't start... Back to #120 now, cuz was most solid at top... Next try find better needle # for 120... Bike is fast and fun and sounds great at top speeds, and top rpms not too fast either... Some sputtery acceleration mids are still there tho...

It's like this carb has very narrow sweet spots for adjustment, at least for this application. Now that I know a 42 slow jet works, and a 118/120 is main, I only have the needle left to clear up the rest of the sputters? I'm not so sure. I've noticed a higher idle helps, if only because it buries the lowest end of the problem. I might be learning this engine can't do what the carb expects? At 105cc, the engine falls within the carb's rating of 100-150cc, but maybe their flow is mismatched or something?

But tomorrow's another day...
 
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Minimichael

Minimichael

Well-Known Member
#38
#38
Despite having my doubts about this carb, I was able to find a very best needle position setting, and those trouble spots are mostly gone. Raising the idle woke things up a bit, too. And now both carb and engine seem to be more or less in sync. The bike is more lively, much faster, and accelerates really well through the upper band (and remarkably quietly, too).

Fun side fact: After selecting the 3 best main jets, I planned a final course of needle/shim combinations to road test, just to know I'd exhausted every option within the range I'd narrowed to. (Because as of last night, I wasn't particularly happy with any results so far.) I set up for the first test combination on my list, and went to bed. Well not only was that very first configuration today's overall winner, but the darned thing started on the first pull of the afternoon!

For posterity, final specs are: #42 pilot, 2-1/4 turn air screw, #120 main, Needle at #5 (richest) plus 1 needle shim. The box came with four main jets 108 - 115, and pilots 35 and 40. Nibbi doesn't sell different needles, and shims aren't part of the design either.
https://flic.kr/p/2nP6C6g
 
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