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86 T5,
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I have 2 older Vespas, an 86 T5, and a recently rebuilt 80 Smallie.
I've noticed that when I shift from 4th to 3rd, or 3rd to 2nd, on the T5 there is very noticeable engine braking. I don't do it a lot.
On the Smallframe there is very little engine braking when I downshift. The scooter has plenty of power. But I wonder if this signals a possible problem with either compression or clutch?
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Ossessionato
LXV 150 3v ie. Midnight Blue (Sold) Now Honda Zoomer X
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T5 revs more so gearing is lower?
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Hooked
Rally 180, TS 125, PX 150 and a lot of smallies
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Rally 180, TS 125, PX 150 and a lot of smallies
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What flywheel are you using? When I was racing I noticed I had more engine braking with a stock ET3 than an HP4.
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If you're talking about engine braking on downshifts, that's a function of your gearing. Braking when you let off the throttle is affected to some extent by compression.
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Also, 2 strokes by nature will not compression brake as well as a 4 stoke.
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86 T5,
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I believe it is the different gearing, if I drop from 4th to 2nd, there is noticeable braking. I tried to do a quick compression test and found that with the spark plug fitted in the center of the head, (on the Pinasco kit) that I will have to partially drop the motor just to fit the tester. So I'll wait on that
I have a PLCcorse clutch in the scooter and its touchy as far as adjusting. A few turns in on the adjuster, and the clutch engages even with the clutch lever pulled. A few turns out and it's slipping in 4th gear. There is about a 1/4 inch of sweet spot on the adjuster.
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Are you comparing engine braking on a 100cc to a 150 or 200cc?
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86 T5,
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The Smallframe is 135 with the new top end, the T5 is 125.
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That's interesting...
Engine braking is created by three factors, the effort the engine needs to expend to suck air passed the closed throttle, the compression stroke and the effort to push air out the exhaust. Clearly the third is not in play. The second should be minimal in similar displacement and compression ratio cylinders. I wonder about the first, what are the carbs?
The feel of the braking could be influenced by the steps in ratio between the gears as you noted by going down 2 gears. How does the gearing between the two setups compare?
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86 T5,
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The gearing for the smallie is short 3rd and 4th, the T5 is standard T5 gearing, really quick in lower gears but going up hills or against a stiff wind I have to drop back into 3rd to stay in the power band.
T5 is really a sweet machine (knock on wood) runs like a champ. I can get to 9000 rpms in 3rd and shift to 4th and I'm going 65. It idles nice and slow, which might help explain the engine braking.
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