Thu Jun 23, 2022 3:08 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Location: Madeira Island
Thu Jun 23, 2022 3:08 am linkquote
Hi,

Sorry the long post but wanted to put everything I can remember together

Current setup running fine for around 700-800 kms? But as I referred on another thread, on my last ride it bogged for around 200 meters, didn't die and managed to wake it up, then rode +10 kms back home normal as if nothing had happened. I think the spark was isolating. Just as a reminder a couple of weeks I pulled the spark plug for the 1st time and it was black, easily cleaned with a rag - this tells very little but all clues tell I'm running too rich WOT

Setup: BGM 177 ported 3 window engine, extended intake crank, var advance electronic ignition, fast flow tap, drilled carb, Sip road 3.0. For the setup I think Idle jet is fine, 2.91 ratio: 55/160; Main jet stack is 160/BE3/140

So I'm waiting to arrive a BGM main jet set, 10 pieces to experiment:
115-118-120-122-125-128-130-132-135-138

Bottom line: Could I leave it as it is? I guess so but as believe its really *too rich*, my plan is to clean the spark, jet down, ride it to heat, change for a new plug and make a plug chop WOT/Cut ... with a smaller main. My question is, make it with the 138 or skip it already to the 135 considering the spark pictures and behavior so far? is this too risky? 138 would be safer but don't want to spend much time on this... what would you do?

Ps: I don't know the brand of the installed main jet and as I'm aware there may be differences on the real size between manufacturers, 1st thing I'll try to compare it with the new ones... maybe with a needle or something, any clues?


Spark before / after clean



Last edited by PSMA on Thu Jun 23, 2022 3:59 am; edited 1 time in total
Thu Jun 23, 2022 3:55 am

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
 
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
Thu Jun 23, 2022 3:55 am linkquote
I would jet it based on the engine behavior now. Your plug is telling you too rich but you can now dial it in finer by finding the peak performance and then bumping it a wee richer when you find that jet for insurance.

*edit* to answer your specific question I'd do one jet size at a time. Once you start skipping you make things uncertain. Of course, if you're cutting plugs that gets really annoying fast - but it's no big deal if you jet from engine behavior like I suggest

Last edited by xantufrog on Thu Jun 23, 2022 5:05 am; edited 1 time in total
Thu Jun 23, 2022 4:45 am

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Thu Jun 23, 2022 4:45 am linkquote
What spark plug is that?

Based on the color it's too rich. If you're running a 160/BE3 with a 140 main you are definitely too rich. I'm surprised it's revving out at all.
Thu Jun 23, 2022 6:03 am

Ossessionato
2007 Stella 225
Joined: 02 Nov 2019
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Location: Rochester, Minnesota
 
Ossessionato
2007 Stella 225
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Thu Jun 23, 2022 6:03 am linkquote
What 2T oil are you running synthetic or Dino? Correct %?
Thu Jun 23, 2022 6:20 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
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Lucky
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Thu Jun 23, 2022 6:20 am linkquote
It's the 160 AC, SoCal. That's leaning out the main & atomizer both.

OP, you need to get a 120 Air Corrector, then try again. You're too lean at mid-range with 160-BE3, then too rich on the main to make up. 160-BE3-140 is basically the perfect Seize Stack.

You might be OK at WOT, but once it's good and warmed up, you roll off the throttle and seize it on the off-ramp. And the BGM is not forgiving in that scenario. The Nicasil will delaminate above the exhaust port and it's game over for that jug. Sadly, I've got the receipts (plural!) for that move.

The air corrector is effectively a multiplier that affects the mixture across the entire throttle range by controlling how much air is allowed into the jet stack. If it's higher (large hole) it allows in more air, leaning the mixture. Smaller hole == less air == richer mixture.

For tuned motors, you should always have at least a 140 AC. Consider that 160-BE3-98* is a stock PX or Stella stack. Increasing every single flow point through the motor is going to increase the fuel needs through the entire throttle range, not just a ~50% increase in main jet diameter (which translates to a 70% increase in area).

For comparison, I have an almost identical build in my VBB right now: 3-port SprintV motor, SIP RoadXL, 60mm cut crank, BGM 177 w/ a 1.5mm base spacer and seriously ported transfers. Port timings are TD124/ED174/BD24 and a 0.8mm squish. B8 spark plug.

I'm running 120AC-BE4-128MJ right now, so MUCH richer across the board, other than my main. I could put a 140 in for giggles and see how it does, but I'll be surprised if it revs out at all.

Lastly, I'd strongly suggest pressure testing your motor if you haven't already. If you have any air leaks, you'll never really jet around them successfully and eventually, it will come back to bite you.

Once you get it dialed in, though, you'll have a solid 17-18 HP build that'll go until you wear out the cruciform.

* someone check me on 98. I'm on a roll here!
Thu Jun 23, 2022 7:06 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Hooked
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Thu Jun 23, 2022 7:06 am linkquote
SoCalGuy wrote:
What spark plug is that?

Based on the color it's too rich. If you're running a 160/BE3 with a 140 main you are definitely too rich. I'm surprised it's revving out at all.
Its a NGK BR9EIX

It revs fine all the way up, 70mph easily even in a light uphill
Thu Jun 23, 2022 7:08 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Posts: 194
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Hooked
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Thu Jun 23, 2022 7:08 am linkquote
Christopher_55934 wrote:
What 2T oil are you running synthetic or Dino? Correct %?
Castrol Power 1 racing 2T fully synthetic
2% and a bit, maybe around 2.3-2.4%
Thu Jun 23, 2022 7:19 am

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
 
Moderibbit
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Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
Thu Jun 23, 2022 7:19 am linkquote
PSMA wrote:
It revs fine all the way up, 70mph easily even in a light uphill
That's why I wouldn't jet based just on color. It looks too dark, but there can be many reasons for that. If you're riding well now and revving out clean, and your goal is to go from that color to tan, I bet you'll seize it (because you are currently very far from tan). I don't know why it's so dark, but if it's riding so well I'd proceed systematically with caution when leaning it out
Thu Jun 23, 2022 7:28 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
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Lucky
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Joined: 16 Jun 2011
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Thu Jun 23, 2022 7:28 am linkquote
xantufrog wrote:
That's why I wouldn't jet based just on color. It looks too dark, but there can be many reasons for that. If you're riding well now and revving out clean, and your goal is to go from that color to tan, I bet you'll seize it (because you are currently very far from tan). I don't know why it's so dark, but if it's riding so well I'd proceed systematically with caution when leaning it out
I'll say it again: it needs a richer Air Corrector and atomizer before the main gets leaned out.

Thu Jun 23, 2022 7:35 am

Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
Joined: 12 Jun 2008
Posts: 8848
Location: Atlanta, GA
 
Moderibbit
1980 P200E - "Old Rusty", 1976 ET3 Primavera
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Location: Atlanta, GA
Thu Jun 23, 2022 7:35 am linkquote
chandlerman wrote:
I'll say it again: it needs a richer Air Corrector and atomizer before the main gets leaned out.


Just to keep things straight - I'm not disagreeing or giving counter-advice to you! You know a lot more about tuning than me. I'm just saying when/if they start pulling that main jet down they should proceed with caution and listen to the bike!
Thu Jun 23, 2022 7:35 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: 04 Aug 2014
Posts: 194
Location: Madeira Island
 
Hooked
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Joined: 04 Aug 2014
Posts: 194
Location: Madeira Island
Thu Jun 23, 2022 7:35 am linkquote
chandlerman wrote:
It's the 160 AC, SoCal. That's leaning out the main & atomizer both.

OP, you need to get a 120 Air Corrector, then try again. You're too lean at mid-range with 160-BE3, then too rich on the main to make up. 160-BE3-140 is basically the perfect Seize Stack.

You might be OK at WOT, but once it's good and warmed up, you roll off the throttle and seize it on the off-ramp. And the BGM is not forgiving in that scenario. The Nicasil will delaminate above the exhaust port and it's game over for that jug. Sadly, I've got the receipts (plural!) for that move.

The air corrector is effectively a multiplier that affects the mixture across the entire throttle range by controlling how much air is allowed into the jet stack. If it's higher (large hole) it allows in more air, leaning the mixture. Smaller hole == less air == richer mixture.

For tuned motors, you should always have at least a 140 AC. Consider that 160-BE3-98* is a stock PX or Stella stack. Increasing every single flow point through the motor is going to increase the fuel needs through the entire throttle range, not just a ~50% increase in main jet diameter (which translates to a 70% increase in area).

For comparison, I have an almost identical build in my VBB right now: 3-port SprintV motor, SIP RoadXL, 60mm cut crank, BGM 177 w/ a 1.5mm base spacer and seriously ported transfers. Port timings are TD124/ED174/BD24 and a 0.8mm squish. B8 spark plug.

I'm running 120AC-BE4-128MJ right now, so MUCH richer across the board, other than my main. I could put a 140 in for giggles and see how it does, but I'll be surprised if it revs out at all.

Lastly, I'd strongly suggest pressure testing your motor if you haven't already. If you have any air leaks, you'll never really jet around them successfully and eventually, it will come back to bite you.

Once you get it dialed in, though, you'll have a solid 17-18 HP build that'll go until you wear out the cruciform.

* someone check me on 98. I'm on a roll here!
Thanks Chandlerman for feedback, a lot for me to digest for sure

So if I understand you correctly I may be rich on top due to the 140 (dark plug) but lean in the mid range due to the 160AC?

Fact is engine has been (and still is) running great in these 1st 700kms, so I'm afraid of changing too many variables. The only thing was that bogging in the beginning of the ride. Vespa was off for around 2 hours, before running and while idling I did twist the throttle a few times, maybe this was the reason?
Thu Jun 23, 2022 7:50 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: 04 Aug 2014
Posts: 194
Location: Madeira Island
 
Hooked
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Thu Jun 23, 2022 7:50 am linkquote
xantufrog wrote:
Just to keep things straight - I'm not disagreeing or giving counter-advice to you! You know a lot more about tuning than me. I'm just saying when/if they start pulling that main jet down they should proceed with caution and listen to the bike!
I heard you both, many thanks for feedback. Also check my last post above.
What still puzzles me is that a 24SI carb comes stock with a 160AC ... and a BE3. All that was done was increase the stock 118 main jet o a 140, how can that lean out anything?

Cheers



Thu Jun 23, 2022 7:53 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5991
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Lucky
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Joined: 16 Jun 2011
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Location: Nashville
Thu Jun 23, 2022 7:53 am linkquote
PSMA wrote:
So if I understand you correctly I may be rich on top due to the 140 (dark plug) but lean in the mid range due to the 160AC?
Yep, but it's both the 160AC and the BE3 mixer. Your bogging off-idle is probably actually LEAN, not rich. It's starved for fuel until you get the throttle open and it transitions to the main jet, at which point it may be just fine at WOT, but that's it.

If you're ordering jets and want to get it dialed in Just Right, get a 120AC, a 140AC, BE1, BE5, and BE4 atomizers, and main jets from 125-135 (125, 128, 130, 132, 135). Yes, that's a $50 jet order, but 1) it's better to have more than you need, since shipping will cost you the same as a couple jets; and 2) $50 is cheap compared to a new BGM 177.

There's a pretty common jet effectiveness chart for side draft carbs, but I've never seen one for si carbs, so here's one of my infamously crude drawings that shows the same thing for the SI. There's room for improvements, I'm sure, but the role of each jetting component is fundamentally correct.


My typically awful drawing


Side Draft jetting effectiveness for reference

Thu Jun 23, 2022 8:01 am

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
Joined: 16 Jun 2011
Posts: 5991
Location: Nashville
 
Lucky
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Joined: 16 Jun 2011
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Location: Nashville
Thu Jun 23, 2022 8:01 am linkquote
PSMA wrote:
I heard you both, many thanks for feedback. Also check my last post above.
What still puzzles me is that a 24SI carb comes stock with a 160AC ... and a BE3. All that was done was increase the stock 118 main jet to a 140, how can that lean out anything?

Cheers
Legit question. Answer is that the stock jetting assumes stock throughput and tuning for optimal efficiency (Stoichiometric Ratio) of 14.7:1 air:fuel ratio (AFR). When building a tuned motor, you're aiming for an AFR of 12.6:1.

So think of the motor as a pump. You increase the volume being pumped (cylinder size, crank stroke), and potential throughput (max RPM's). You're moving more air (and with it, more fuel) than stock.

Thus, the requirements for more fuel in the mixture increase further as the amount of air being pulled through increases, the amount of fuel you need to add increases to keep up with it.

Does that help?
Thu Jun 23, 2022 8:48 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Thu Jun 23, 2022 8:48 am linkquote
Very elucidating chandlerman, it makes sense. Your drawing with the overlapping influence of the various components is also very interesting.

Thanks!
Thu Jun 23, 2022 1:03 pm

Addicted
Joined: 29 Nov 2020
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Addicted
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Thu Jun 23, 2022 1:03 pm linkquote
Some quick bits.

Broken record sound here:
You should really take advantage of that threaded CHT port you have. That CHT... Port... Threaded. CHT. Safer... Jet with it -- it's so. damn. responsive. Seize insurance.. More fun to ride. CHT.
Honestly, they should come included with any kit.

Really suspect your mechanic is a bit of a fibber. If it's revving out well with that mj, I'd bet you're getting a kind of artificial 128 or so (un-drilled float bowl channel). If true, you won't feel any difference dropping a size or two down from your 140.

Watch this at around 8:30.
"It's not about getting the right color!"

Thu Jun 23, 2022 1:26 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX172 Quattrini and some motorbikes
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Jet Eye Master
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Thu Jun 23, 2022 1:26 pm linkquote
chandlerman wrote:
Yep, but it's both the 160AC and the BE3 mixer. Your bogging off-idle is probably actually LEAN, not rich. It's starved for fuel until you get the throttle open and it transitions to the main jet, at which point it may be just fine at WOT, but that's it.

If you're ordering jets and want to get it dialed in Just Right, get a 120AC, a 140AC, BE1, BE5, and BE4 atomizers, and main jets from 125-135 (125, 128, 130, 132, 135). Yes, that's a $50 jet order, but 1) it's better to have more than you need, since shipping will cost you the same as a couple jets; and 2) $50 is cheap compared to a new BGM 177.

There's a pretty common jet effectiveness chart for side draft carbs, but I've never seen one for si carbs, so here's one of my infamously crude drawings that shows the same thing for the SI. There's room for improvements, I'm sure, but the role of each jetting component is fundamentally correct.
CM jet diagram needs a rev2. Main jet goes from just off idle to WOT on an SI as does AC
Thu Jun 23, 2022 1:31 pm

Jet Eye Master
PX221 MHR, O tuned PX200, PX172 Quattrini and some motorbikes
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Thu Jun 23, 2022 1:31 pm linkquote
PSMA wrote:
Thanks Chandlerman for feedback, a lot for me to digest for sure

So if I understand you correctly I may be rich on top due to the 140 (dark plug) but lean in the mid range due to the 160AC?

Fact is engine has been (and still is) running great in these 1st 700kms, so I'm afraid of changing too many variables. The only thing was that bogging in the beginning of the ride. Vespa was off for around 2 hours, before running and while idling I did twist the throttle a few times, maybe this was the reason?
You cannot run that kit on an AC160. After 700 miles, If you take off your cylinder there will already be detonation damage. Your spark plug has what looks like detonation markers.
Fit an AC120/BE4 and it will last for ever (several years in reality but a forever in 2 stroke years).
Thu Jun 23, 2022 2:19 pm

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 08 Stella (for now)
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Lucky
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Thu Jun 23, 2022 2:19 pm linkquote
Jack221 wrote:
CM jet diagram needs a rev2. Main jet goes from just off idle to WOT on an SI as does AC
I'll update accordingly

I figured there would be updates. I didn't think the MJ went that far down, but getting to a solid guide is part of why I did it.
Fri Jun 24, 2022 12:18 am

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
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Hooked
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Fri Jun 24, 2022 12:18 am linkquote
Jack221 wrote:
CM jet diagram needs a rev2. Main jet goes from just off idle to WOT on an SI as does AC
Ok. It would be interesting to make a rev3 where you could easily read the influence of the different atomizers. Maybe replacing the atomizer block by 5 colored lines representing higher/richer lower/leaner ?
Fri Jun 24, 2022 12:35 am

Hooked
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Fri Jun 24, 2022 12:35 am linkquote
Ray8 wrote:
Some quick bits.

Broken record sound here:
You should really take advantage of that threaded CHT port you have. That CHT... Port... Threaded. CHT. Safer... Jet with it -- it's so. damn. responsive. Seize insurance.. More fun to ride. CHT.
Honestly, they should come included with any kit.

Really suspect your mechanic is a bit of a fibber. If it's revving out well with that mj, I'd bet you're getting a kind of artificial 128 or so (un-drilled float bowl channel). If true, you won't feel any difference dropping a size or two down from your 140.
Thanks for feedback and the video Ray. You're correct and just made up my mind, it hurts anything unless my wallet, I'll get that CHT.

Had to google to find what is "fibber" He drilled the float bowl chamber to 3 mm! Engine is eating fuel like crazy, if I close the fuel tap it takes less than 30 seconds *at idle* to kill the engine.
Fri Jun 24, 2022 12:37 am

Hooked
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Hooked
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Fri Jun 24, 2022 12:37 am linkquote
Jack221 wrote:
You cannot run that kit on an AC160. After 700 miles, If you take off your cylinder there will already be detonation damage. Your spark plug has what looks like detonation markers.
Fit an AC120/BE4 and it will last for ever (several years in reality but a forever in 2 stroke years).
Ok, I'll address the subject with the mechanic, get the CHT and a set of Air correctors/atomizers to play with ... should be fun. Thanks!
Fri Jun 24, 2022 5:41 am

Hooked
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Fri Jun 24, 2022 5:41 am linkquote
PSMA wrote:
What still puzzles me is that a 24SI carb comes stock with a 160AC ... and a BE3. All that was done was increase the stock 118 main jet o a 140, how can that lean out anything?
chandlerman wrote:
Legit question. Answer is that the stock jetting assumes stock throughput and tuning for optimal efficiency (Stoichiometric Ratio) of 14.7:1 air:fuel ratio (AFR). When building a tuned motor, you're aiming for an AFR of 12.6:1.
I'm quoting myself again, I understand the richer target AFR of 12.6:1, still, trying not to look obsessive with the subject, while browsing Scooter Center I found this item PN: BGM1770NEJ https://www.scooter-center.com/en/carburettor-tuning-kit-nozzle-set-bgm-pro-for-vespa-px125/150-with-bgm-pro-177-cylinder-kit-main-jet-set-secondary-jet-mixing-tube-air-correction-jet-bgm1770nej?number=BGM1770NEJ

Quoting Scooter Center:
"Carburettor tuning kit - Nozzle set -BGM PRO for Vespa PX125/150 with BGM PRO 177 cylinder kit- main jet set, secondary jet, mixing tube, air correction jet" ... "The tuning set refers to a conventionally built engine with BGM177/187 and so-called box exhaust system"

What does it include?:
Main air correction jet: 160
Mixing tube: BE3
Main Jet set: 115-118-120-122-125-128-130-132-135-138
Auxiliary nozzle: 55/160

This leaves me completely puzzled, even understanding all your responses, which I respect and read carefully. Is Scooter Center tricking their customers leading them to seize their own Cylinder kits?
Fri Jun 24, 2022 6:52 am

Lucky
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Lucky
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Fri Jun 24, 2022 6:52 am linkquote
PSMA wrote:
This leaves me completely puzzled, even understanding all your responses, which I respect and read carefully. Is Scooter Center tricking their customers leading them to seize their own Cylinder kits?
If I were an evil and cynical person, I'd say that made perfect sense in terms of helping drive more cylinder kit sales, but I suspect the answer is much more mundane. The vast majority of people never learn more about jetting than the main jet, so they see no value in buying a bunch of jets that they never expect to use anyway. I would not be surprised at all if SC either did market research or used to offer a kit with multiple AC's and atomizers which just didn't sell very well.

As it is, they probably actually do reduce the number of seized cylinders by encouraging the people that buy the kit to use a "known good" atomizer and AC which will work pretty well with a stock-ish setup, and assume that the true tuners know what they need and will buy it specifically.

And I fully expect to do multiple iterations of the jetting chart. Look for a proper electronic version with the first round of corrections, and I'm going to do some testing with an AFR to measure *relative* change in mixture for different jetting changes (ACs & Atomizers) at standard throttle positions (idle, 1/4, 1/2, 3/4, WOT), but won't be able to get to that for a week or so. That should let me estimate the relative effect of those changes and better scale the graph. I'm still thinking about how best to visualize that. I think I know, but it might be a little confusing to people who don't read instructions.
Fri Jun 24, 2022 11:55 am

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Fri Jun 24, 2022 11:55 am linkquote
That kit's for jetting with an un-drilled filter. The stock heart above the jets acts as an air corrector(?).
They also recommend replacing a drilled filter from a previous setup with a stock one

Warning about the CHT:
The threaded CHT sensor will give you different temperatures vs the more common thermocouple under the plug.
Had a hard time at first! Kept having to turn back and check everything, since the temperature will shoot under sustained load. The under-plug sensor responds very differently.

I'll see a 20F or so max CHT change with one size mj in either direction. "So far" I can ride for hours at 350F -- 10 minutes at 400 by accident. No scoring on the piston..."So far."

BTW I had a similar 200m episode like your first post here. Poured oil at a gas station with the fuel tap on reserve.
Fri Jun 24, 2022 1:15 pm

Jet Eye Master
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Fri Jun 24, 2022 1:15 pm linkquote
PSMA wrote:
I'm quoting myself again, I understand the richer target AFR of 12.6:1, still, trying not to look obsessive with the subject, while browsing Scooter Center I found this item PN: BGM1770NEJ https://www.scooter-center.com/en/carburettor-tuning-kit-nozzle-set-bgm-pro-for-vespa-px125/150-with-bgm-pro-177-cylinder-kit-main-jet-set-secondary-jet-mixing-tube-air-correction-jet-bgm1770nej?number=BGM1770NEJ

Quoting Scooter Center:
"Carburettor tuning kit - Nozzle set -BGM PRO for Vespa PX125/150 with BGM PRO 177 cylinder kit- main jet set, secondary jet, mixing tube, air correction jet" ... "The tuning set refers to a conventionally built engine with BGM177/187 and so-called box exhaust system"

What does it include?:
Main air correction jet: 160
Mixing tube: BE3
Main Jet set: 115-118-120-122-125-128-130-132-135-138
Auxiliary nozzle: 55/160

This leaves me completely puzzled, even understanding all your responses, which I respect and read carefully. Is Scooter Center tricking their customers leading them to seize their own Cylinder kits?
As Ray said. BGM jet kit relies on using an undrilled original Vespa air filter. And what they fail to mention is that with this ensemble fitted and jetted for WOT operation, it will be heavy/spluttery low down and be not so fun to ride. Which is why you have come to us.
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