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Messages - Thoppa

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Citycom 300 / Re: Airbox and exhaust changes
« on: March 08, 2015, 03:15:13 AM »
Another update - found a K&N that was suitable to fabricate into a re-usable air filter for the Citycom. It's from a Silverwing 600. Some tests specs :

and some images

and my new filter

other side

I fitted a new CR8EIX to see how she runs but I can hear she is leaner - the purr has a dry rasp now. So next up is to modify the FI to suit. I put the air temp sensor in the freezer for an hours and it was reading 5.5K ohms. It reads 2K at room temp, and the maximum is 18K according to the manual. So I'll try adding resistance in series and see how that goes. The FI also has a CO adjustment but I need the factory diagnostic tool for that - maybe a trip to the dealer will also be necessary.

Oh, and she takes off on small throttle openings now.  ;D


Citycom 300 / Re: Airbox and exhaust changes
« on: March 03, 2015, 11:57:47 PM »
And here's the flare... I bodged the first tube - too small a donut - but managed to overcome that error in the end.

Add 15mm tube cut in half at the sides

Smooth and round - tip for using epoxy putty is to keep cleaning your fingers, and then when you want to smooth it, keep them wet.

The difference in throttle response is very very noticeable ! I've never had to add a bellmouth before - every FI bike already had them. For example, the ER6 has bellmouths on the air inlet at the bottom of the pic below. And the throttle bodies have bellmouths that protrude into the airbox through the two holes at the top of the pic.

Why Sym didn't design the airbox with a bellmouth is beyond me. The difference is so noticeable - it makes no sense to throw away a performance gain like that. I guess they don't have experience designing high-performance machines so perhaps they simply don't know?

Citycom 300 / Re: Airbox and exhaust changes
« on: March 03, 2015, 12:45:43 AM »
Yeah, I read Kiwiscoot's long thread and he said the same - engine just keeps loosening up. Good news !

However, I'm an inveterate meddler and I have a degree in mechanical engineering, with decades of experience in tuning carb bikes, so it is somewhat guided meddling. I've modded two FI bikes - an XT660 and an ER6F.

If you look at the intake port, which is effectively the velocity stack, you'll see a very small rounded edge.

To get smooth flow into the velocity stack, the curve of the bellmouth should be 1/4 of the pipe. The pipe is just over 40mm so it should have a curve of radius 10mm. They gave it 2mm. Flow from the airbox into the engine should be much improved by simply adding a correctly sized bellmouth and it's a certainty that using a correct bellmouth will improve throttle response.


Citycom 300 / Re: Finally, a high flow air filter
« on: March 02, 2015, 11:52:04 PM »
Audioguy - how did that filter work out for you ?

Citycom 300 / Re: Airbox and exhaust changes
« on: March 02, 2015, 11:41:51 PM »
Thanks for that. I'd prefer to keep using paper, but they are disposable, and cost US$28 here, and that's supposed to be every 6,000km.

I've never run a machine until it dies before so I have no idea how much an effect the filter type has on engine life. I have used K&N and DNA filters on other machines without problems but then again, the longest was about 30,000kms using a K&N in an XR250.

More air flow might mean the fuelling gets messed up from being too lean? The DNA filter Audioguy posted about flows three times the volume.

DNA FCD air filter flow: 202.00 CFM (Cubic feet per minute) @1,5H2O corrected @ 25degrees Celsius
SYM stock paper filter: 62.10 CFM (Cubic feet per minute) @1,5H2O corrected @ 25degrees Celsius

Well, my guess at the maths is based on this
.... Airflow (m3/min) = (Engine Size (Liters) x RPM) x VE / 2000 the engine is 263cc or .263 litres, let's say rpm is 6,000 , and VE is 0.90 for a 4 stroke, that's a maximum flow of .263 x 6000 x 0.9 / 2000 = 0.71 cubic metres a minute. 0.71 x 35.3 = 25 cubic feet per minute. Pulsation factor is 2.1 so that means 50 CFM @ 6,000rpm.

So does it need a less restrictive filter ? Try it and see.

I've been experimenting with a taper on the port for the connecting pipe inside the airbox. I added some 6mm rubber tube, tied in a loop with fishing line inside, to make a C shape around the port. I filled the area to make a smoother, wider and more tapered port. That changed the induction noise to a deeper note - a purr - and the throttle seems to have more initial response.


I'm looking for a better pad for the front too and it seems the EBC sintered pads are likely to give the biggest boost, but with greater disk wear. The EBC organics get recommended too.

For me, the back brake is hugely powerful and can stay 100% stock. It's the front that is too feeble for my liking - no initial bite and no ultimate stopping power either. However, both brakes together works brilliantly.

With a motorbike, I'm used to putting the front on first to get the front tire loaded, then using the back as an extra. But on this back heavy scoot, that method doesn't seem to matter at all in the dry so the two at the same time works well. I haven't tried heavy braking in the wet yet though.

Hi all,

After commuting on a Citycom for a month, I decided to start modifying it. I've done this a lot on motorcycles.

I've been running the modifications for around 800kms and all is good so I thought I'd share. When I got the scoot, she had under 4,000kms, and she's now almost 6,000 ready for a big service.

I've put all this info and other stuff on my blog if you're curious.

I opened up the airbox and checked out the pipe connecting the airbox to the throttle body. It's long and twisty and has a much larger diameter (42mm) than the airbox air inlet tube (33mm). The pipe could do with a better flare into the airbox.

The inlet tube in the front of the airbox cover is removable so out it came. However, the circular hole this left was still much smaller than the 42mm pipe, so I trimmed out all the plastic and added some epoxy putty to smooth the new intake. This gave a similar intake area to the 42mm diameter pipe. Like this :

and the square ridges too

After that, I removed the tab of plastic on the inner half of the airbox, since this another way to restrict the air intake to less than the 42mm pipe.

And then finally, to smooth the intake area as best as I could, I added some foam filler and a layer of epoxy putty to the cavity. Like this :

It's very subjective, but the throttle feels like it has a slightly better response. For sure, there is now some induction noise which makes the scoot sound more like it has an engine. It isn't loud at full throttle, and sounds good to my ears.

When the air filter is due for replacement, I may consider fabbing my own using a K+N filter.


I didn't want to pay big bucks for an exhaust because the engine clearly isn't going to deliver significantly more power and the CVT means that power would only be noticed on top speed runs. The main reasons to change the exhaust were the looks and the weight.

So I got an exhaust for a Honda CBX 250 (?) and an interface from Taobao, figuring that they were so cheap (US$40 plus US$20 shipping to here in Hong Kong) I could give them a go and not be unhappy if they turned out to be trash.

The interface with sizes :

The exhaust :

And the ad:

I was surprised to find they were good. The interface inner diameter was 1mm too tight so that got filed down to fit. The outer diameter was 2mm too small so I added some thin steel pipe split along its length for clamp tightening. The exhaust bolted on without interfering with the original exhaust mounts or sticking out from the side of the machine. It fitted very well in fact. I got very very lucky with that. :)

The exhaust sound is very deep but much too loud for me without the decibel killer fitted, and sounds kind of farty with it, and the exhaust didn't seem to make any change to the performance. That was really surprising - I'd expect that it would have less back pressure and that would either cock up the fuelling, or knock torque off the bottom end for a small gain at the top. But actually, no obvious fuelling change at all - just more noise.

However, the original with its bolts weighed around 8kgs and the replacement weighs 2.5kgs, so that's significant, especially since the 5.5kgs reduction is unsprung mass at at the back of an already back-heavy machine. It also looks much better to me, so it's a keeper.

I recently checked the spark plug, after about 750kms, to see if it was running too lean. Surprisingly, it's not. So that's great, although I'll wait until I've seen how a new plug colours to be sure. Fuel economy has averaged at a little over 32km per litre, which is a slight improvement, but I wouldn't assume that is only these changes.

Before :

After : 

I've also been slowly re-spraying the silver parts with either black or graphite paint. The first things I did were the grab handles and side panels, and I've also done the rear clamp, rear shocks, front forks and I did the wheels with black spokes and graphite rims. I'm very pleased with the look.  ;D

EDIT Forgot to say - I removed the AISV stuff -it adds air into the exhaust below 3,500rpm when slowing down on a closed throttle. That caused some pops and it affects emissions, not performance, so off it came. And the pops stopped.  ;D

Air comes from inside a low frame tube on the spark plug side of the engine, through a rubber tube into an air filter can, and through another rubber tube into the Air Injection Solenoid Valve. When the AISV is open, the air flows through another rubber tube into the head where there is a reed valve. The output from the valve flows out of the head and through a metal tube to the exhaust port. So I removed all the rubber tubing and filter can, plugged the frame tube, plugged the AISV but left it electrically connected, and plugged the head entry to the reed valve. This came off :

So overall, I'd definitely recommend the airbox mod but the exhaust hasn't made much difference.

Cheers !

Citycom 300 / Re: Strange, but forgot to double check.....
« on: February 27, 2015, 11:55:45 PM »
Did you do a continuity check to see if the bulbs are wired in parallel or in series ? I'm sure you know that if they are in series, then one dies opening the circuit so the other can't work. Seems unlikely given they are 12V bulbs but worth a check anyway ?

Citycom 300 / Re: Citycom turning radius?
« on: September 27, 2014, 01:36:00 AM »
I found a Greek site called Scooternet who did a full test and say the radius is 2.3m, which sounds about right.

Citycom 300 / Re: Citycom turning radius?
« on: September 24, 2014, 07:46:23 PM »
It seems the new GTS 300i with a 278cc engine (LN30W1) has a turning radius of 2.6m according to the manual I found here : (it's in Chinese unfortunately but page 38 has "the minimum turning radius" or "最小迴轉半徑")

Despite many searches and finding a manual in English, I still can't find the Citycom's turning radius. I emailed SYM in Taiwan too but no reply.

Can anyone with a Citycom and a 3m tape measure check for me ? It's easy to do - just point the scooter straight out (perpendicular) from the kerb and do a 180 turn on full lock until the scoot comes back to the kerb. Measure the distance along the kerb and that'll do it.

Many thanks to the kind soul who'll put me out of my misery...


Citycom 300 / Citycom turning radius?
« on: September 20, 2014, 06:49:59 AM »
Hello all,

I'm thinking about getting a Citycom and would like to know the turning radius?  I know the 300 GTS is 2.5m from the manual, but the Citycom manual doesn't say.

The other scoot I'm looking at is a Kymco People and that is 2.2m - can the Citycom do this?



EDIT : I bought one. The turning circle is 4.25m, so turning radius is just over 2.1 metres. That's pretty nimble - a Honda PCX150 is 2.0m.

First impressions. Comfy, very comfy. Power is adequate. Storage is awesome. I miss a clutch for pulling out of junctions. Front brake is very disappointing - glazed pads? She's only had one owner who did just 4,000kms in 4 years. There's a bit of minor rust - already fixed that with Jenolite and Hammerite. Chassis flex is something I'm gonna have to get used to I suppose, and combined with the light front end, the handling is "entertaining". But the comfort, wow. 

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