Cylinder vs crankcase (reed) induction
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7408
Location: Victoria, Australia
Mon Oct 28, 2019 6:27 pm quote
swa45 wrote:
I discovered that the Malossi bellows fit perfectly inside the MRP 'Dumbo' hose (or any 60mm flexi hose). I cut it back, to shorten it and to get rid of the angled bit on the end, and then 'screwed' it into the 60mm hose. Perfect fit, unlike when I tried with a stock Piaggio bellow. Fitted between carb and frame, it works a treat and so much better than with the Dumbo metal frame connector.
Every Malossi rubber bit I have bought seems to made of some super-stiff rubber, and the bellows appear to be around 10% smaller than Piaggio ones.

You can get the hose that they make the Dumbo out of from hydraulics/hose supplies places. I got some in black rubber which I think looks better, but you can also get it in clear as well. I got some 50mm and 65mm.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1295
Location: UK (South East)
Mon Oct 28, 2019 10:25 pm quote
Correct Ginch, the Malossi bellow has a slightly smaller diameter, but that worked in my favour, as it 'screwed' into the 60mm hose perfectly. I had to use boiling water to soften it, but once on, it's a lovely tight and solid fit to the frame. The Piaggio one collapses inwards when attempting to insert it into a 60mm hose.

I'm only using the Dumbo hose because I'd already wasted my money on the Dumbo and it's perfect for the PWK35, which has a 59mm filter connection. The problem with the Dumbo is the metal frame connector, not the flexi hose. It doesn't fit the frame very well. it's way too long, and it's orientation is totally wrong for my carb and manifold.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1295
Location: UK (South East)
Sun Nov 10, 2019 2:12 pm quote
Time to try a new exhaust
I had always intended on changing the BigBox v1.0 to a BigBox Sport or a PD box, as I think the old pipe is a bit clogged up. Decided to do it now, rather than springtime 2020, but when I went to install it, there was no way that it would fit with the centre stand, at least not without some modification. I think with the engine shifted by 1cm to the right (for wide tyre), the interference is made worse.

Anyway, while I think of a plan, I just wanted to post a photo of the two exhausts side by side. The new Sport has a much longer and fatter downpipe than the original BigBox, and presumably that's where it gets the performance characteristics that are 'like an expansion chamber'. Hopefully it will be an improvement with my setup.

pipes2.jpg

Molto Verboso
1980 P125X, 1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
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Location: Staten Island, NY
Sun Nov 10, 2019 2:45 pm quote
What's the clearance on that pipe? Who makes it? It looks almost like the sip road xl which drags on bumps when leaning left all the time.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7408
Location: Victoria, Australia
Sun Nov 10, 2019 6:24 pm quote
They also hit at the front over big bumps, speed humps etc.

MRP make a plate that moves the centre stand forward, not sure if it's just for the older models or P's as well... have a look and maybe you can come up with something similar.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1819
Location: London UK
Sun Nov 10, 2019 7:48 pm quote
Hard to believe a box doesn't fit. Does look to go much further under. Is it just touching the spring bracket?

Would imagine if the rear shock is slack it will hang down lower at the front.

With the extra fat down pipe it will go better and on a reed inlet, even better still.

Hows the jetting coming on?
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1295
Location: UK (South East)
Mon Nov 11, 2019 12:21 am quote
swiss1939 wrote:
What's the clearance on that pipe? Who makes it? It looks almost like the sip road xl which drags on bumps when leaning left all the time.
Swiss, it's a BGM pipe. They do two versions, the Touring and the Sport. A friend uses the SIP XL on a small block 187 and yes, it does ground out from time to time, mainly on curbs. The Sport is no bigger than the original BigBox in terms of the box itself, but the downpipe extends much further forward. It's fat as you can see in the photo, so to Ginch's point, the downpipe itself can also be an issue. I'm hoping that my 11 inch rear tyre gives me some precious clearance.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
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Location: UK (South East)
Mon Nov 11, 2019 12:31 am quote
Ginch wrote:
They also hit at the front over big bumps, speed humps etc.

MRP make a plate that moves the centre stand forward, not sure if it's just for the older models or P's as well... have a look and maybe you can come up with something similar.
Cheers Ginch, MRP does make a plate for the PX/T5. Yet another overpriced gadget to avoid annoying problems! I'll try to get creative, but if I need to fit one of these, it won't be on this scooter, which I'm only using to jet the carb and test the engine as a whole. The intended scooter for this engine is still in grey etch primer, so during the build, I will factor in mods like this.
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
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Location: UK (South East)
Mon Nov 11, 2019 12:42 am quote
Jack221 wrote:
Hard to believe a box doesn't fit. Does look to go much further under. Is it just touching the spring bracket?

Would imagine if the rear shock is slack it will hang down lower at the front.

With the extra fat down pipe it will go better and on a reed inlet, even better still.

Hows the jetting coming on?
Jack, I'm still getting bogging beyond 1/2 throttle, particularly on hills, and it doesn't want to wind up to high revs in 4th. This is despite dropping the main to 140, which seems low enough, all else considered. I'm trying two things now: changing the exhaust and bypassing the pump (temporarily). It feels like the old BigBox may be a bottleneck (it's 5/6 years old and has covered many thousands of miles......must be clogged) or the pump is over powering the float valve.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1819
Location: London UK
Mon Nov 11, 2019 1:03 am quote
Did you drop the float level a few mm lower than its supposed to be?
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
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Location: UK (South East)
Mon Nov 11, 2019 1:24 am quote
Yes I did but no noticeable change. I'm experimenting with non-pumped fuelling in order to rule out the pump from being the issue. I'll do this with the old vpipe on, just so that I'm not makes two changes at the same time.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1819
Location: London UK
Mon Nov 11, 2019 1:33 am quote
Try it but doubting the pump will make any difference. If it was there would be more issues at low rpm. And the odd puddle on the floor.

That carb needs the smaller atomiser. Think this is the root of the issue.

Did you say there were no smaller tapered needles left? A definite sign.

EDIT: Here's something I only just thought of. Are you sure you have a 2 stroke carb? The 4 stroke ones run much richer
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
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Location: UK (South East)
Mon Nov 11, 2019 3:36 am quote
Jack, I'm not getting any puddles or other signs of over-fuelling, leaks or flooding, and it starts first or second kick every time. I have noticed that it races a bit when first started from cold, but that condition very quickly goes away. It's as if there is a bit of air in the system whilst the pump kicks into action.

There is a smaller taper, the 'A' range of needles, but I haven't come across a single reference point amongst Vespa or Lambretta forums where an 'A' is being used. The vast majority are Bs and several are Cs.

As far as I can tell, the PWK AirStriker carbs are all two stroke, seemingly aimed at the dirt bike and ATV market in particular.
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1819
Location: London UK
Mon Nov 11, 2019 7:20 am quote
A quick search says they are also on 4 strokes. Is the same carb but just some different parts.
To rule it out, post two pictures of the carb. One from the front with the throttle half open and the same from the engine side.
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P/Rally200
Joined: 07 Apr 2019
Posts: 9
Location: sweden
Sat Jan 18, 2020 12:22 pm quote
I was sondering Swa45 why you did,nt go with the Pinasco VTR?

Im starting a VTR build in the next couple of months. Just some final research before i splash out
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1295
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Sun Jan 19, 2020 4:52 am quote
I considered it for a long time, but after all, I decided that the Malossi MHR was tried and tested with great power potential. I also got a really good deal on the MHR. The VTR looks great, but I cannot tell you any more than that
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
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Mon Mar 16, 2020 4:58 am quote
Time on my hands......
I'd booked a long weekend off work, but we didn't travel due to the threat of compulsory quarantining in Croatia . I decided to dust off the Vespa and have another crack at getting the BigBox Sport to fit. I'd put the scooter away back in November with it still spluttering at just past 1/2 throttle despite going all the way down to a 142 MJ, which for this setup is a bit small.

After an hour of manhandling the exhaust and moving the stand springs around, I got the BigBox on pretty good. I couldn't get it all the way up the cylinder stud, but there's only ~3mm to go. Out on the road, it was immediately obvious that it was a MASSIVE improvement over the old 2013 BigBox. It wound out cleanly in 1st, 2nd and 3rd, and quite frankly I ran out of road and balls in 4th. I got home, went straight back up to 158 MJ and went for another ride. Still clean all the way through the gears, with none of the spluttering. Unbelievable turn of speed. That old exhaust must have been very clogged and generally not up to the job for an MHR221 with a big carb and reeds. The BigBox Sport most certainly is up to the job, despite the fit and finish being below par.

I have a 160 main to try, but I'll probably need a couple of bigger ones to get it rich at the top, then work back down. The PJ will also need to go up a size or two, as it was hunting when warm and not coming down quick enough from high revs on the stand. I seem to remember dropping it to 40, but I think a 42 or 45 will be better. Going to keep the BGN needle at 3rd clip, which seems to work well with the no.6 slide.

Big grins r us. This is going to be fun !!
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1819
Location: London UK
Mon Mar 16, 2020 9:26 pm quote
You were right to be cautious. Sounds like its going just like it should. Be sure its actually spluttering at WOT before deciding on the final main jet. Believe it or not but 160 is possibly still a bit small. Pilot jet at low 40s sounds about right. If you post some sound recordings from riding we can all have a listen.

The blocked exhaust is a classic, so hard to find for sure. Going to roast it on the BBQ?
Molto Verboso
One or two fun scoots....nothing too precious
Joined: 17 Jul 2013
Posts: 1295
Location: UK (South East)
Tue Mar 17, 2020 12:38 am quote
Yes Jack, I will cook it, paint with POR-15 high temp, and keep it for another project. The old BigBoxes were built really well and I hate to throw things away.

I need to grow some when it comes to riding this scoot. An indicated 65mph is probably only 60 in reality, which translates to 6000 RPM for my setup. I really want to push it beyond 8000 in 4th (80+ mph), assuming it will get there, but it just feels wrong on a Vespa
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