Moped Questions (Running In & More)
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(34 posts, started )
#1 - Jakg
Moped Questions (Running In & More)
Well i've got two questions relating to my lovely moped - a 2001 Gilera DNA 50cc (Two Stroke). 'tis a twist-and-go, if that helps.
Firstly - My bike seized, the piston melted (lack of Oil). I fitted a new Piston & Bore set, new (second hand) oil pump and now it works.
HOWEVER the new piston needs to be run-in, and according to my bikes manual I need to run it at 80% throttle max for 1,000 miles before it's properly run in. I want to get this new piston and bore working as well as possible so I want to Run it in properly.
ATM the bike feels a bit crap. Before it would have a top speed of ~80 KM/h, however now it feels a little less powerful accelerating from 0-10 KM/h (Although it's a twist and go, 'twas always utter shite at those speeds, though. Now it's just a bit worse). Between 10-45 KM/h it feels as punch as it always did (at least as punchy as a 50cc could be!). However it now won't accelerate much past 50 KM/h. The cyliner and bore has done a grand total of about 15 miles, so it's still very VERY new. It needs a "cooling pipe" for the cooling-thing-me-jig aparently, so atm it's running rather cool (the previous owner had a "brainwave" and removed the thermostat from the engine. So it now permantly runs a bit cool). When assembling the bike I noticed that between the airbox and the carbouretta (sp?) was a tiny plate that seemed to serve no purpose but to reduce the flow (plat was the full width of the tube with largish holes in it). My bike is already de-restricted, however in my infinite wisdom i decided that i didn't need the plate and removed it. I'm wondering if this was a stupid decision?
#2 - Bawbag
First of all, sounds like quite alot of money to be spending on the engine, did you ever consider just bolting another engine on there?

As for the plate, you can only test the differnce between leaving the plate on and taking it off, I would have thought that more airflow into the carb would be more air and less fuel, which could be your problem.

The seizing thing, do you have to mix your petrol with oil yourself or is there a seperate tank?
#3 - DrDNA
Well, if it was between the carb and the air filter then it makes the most sense that it's a further restrictor. If it seemed to be blocking a fair amount of air from coming through then it may be worth upgrading your main jet to match the increase in air with a little more fuel. It'll create a richer fuel mixture (as opposed to what would've been a leaner one) that will help your engine to run even cooler.

As for breaking-in the new parts, there many different opinions on this, but most commonly it's recommended that you limit your throttle usage to around 70-80% for the first 100 or so miles, but also including shorts bursts of full-throttle tossed in from time to time. You essentially want to stress the rings in a wide-variety of situations, but mostly taking it fairly easy.

If you find the bike seems to lack a bit of power, keep in mind that the rings and piston will create a better seal as they wear into conformity, so you might be experiencing a tiny amount of blow-by. Also, it is a 50cc, so if you aren't riding at 100% throttle then you'll notice it. Obviously, if it hasn't improved much once everything is broken in then it's worth investigating.
#4 - Jakg
Firstly I looked into a new engine, and it wasn't cheaper than a new Piston+Bore set (£50).

And as for the Oil/Petrol thing - It has a seperate tank, but as the Oil pump was new(...ish) and the oil tank was full of crap which i tried to clean, my Dad advised me it was best to try to mix a little bit oil with the petrol as well just to "loosen things up".

I think i'll try adding the restrictor again to see what happens tomorrow.
#5 - Tweaker
Also some mopeds are prone to a lot of carbon build up inside the exhaust pipe... specifically in the catalytic converter. It kind of looks like a clogged artery so to speak, and it will greatly decrease your power. But I am convinced your bike is screwed up because of the actual engine changes.

Still, this is something to look out for. I had 2 mopeds that had this problem, both 2-stroke which are pretty messy. As a temporary fix, draining the whole pipe with paint thinner will dissolve most of the build up, but it's never better than a brand new pipe.
#6 - Jakg
Quote from sidi :Jetting may be your answer.

The standard DNA carb has the usual "Hyper2" brass washer in the inlet area. When this washer and the rubber air inlet snorkel into the air filter box are removed, the carb needs rejetting with a larger main jet and pilot jet. We used 36-38 pilot (standard is 32) and 74-76 main jet (standard is 56) when we fitted a LeoVinci ZX exhaust system.

Copied from http://www.taffspeed.co.uk/page41.html

Hope that helps.

Right. And how does one "Jet"? That block of texts might as well be in Klingon for all the sense it makes to me :X

@ Tweaker. I actually had the exhaust in my hands the other day, and was thinking of doing the same thing and then thought "nah, i don't need that!"
#7 - wheel4hummer
Put a throttle body on the thing and get a megasquirt.
#8 - Jakg
Oh no not a big bore - the old cylinder was a "race tuned" Athena one, the new one is a standard one I think.

I'll order this cooling pipe than i'll put the plate back in and go for a ride!
#9 - jibber
Quote from Jakg :Oh no not a big bore - the old cylinder was a "race tuned" Athena one, the new one is a standard one I think.


And you don't think that might explain the loss of power?
#10 - Jakg
Quote from jibber :And you don't think that might explain the loss of power?

I dont think the cylinder was really any better than what i have now, it seems like it can still pull hard from 10-40 but 40 upwards is crap (KM/h).
#11 - jibber
Back in the day when we used to tune the engines of our mopeds, a bigger cylinder (call it "race tuned" versions if you want) was what really gave you a boost of power... especially at top speeds.

Was the old cylinder bigger in displacement?
#12 - Jakg
They were both 49cc.

Put the little restrictor thing back on, 'tis so cold out there that it barely starts, though.
#13 - Syfoon
The plate is a restrictor. Whack it out.

My little 125cc had one in the carb and they were never built to have them. Ran much better without it in.

Not sure about 50cc 'ped engines. I only know the NSR125 engine. Can't imagine they'll be much different, but meh.

I'd personally say it's a jetting problem. But check the sparkie is good and your air/fuel screw is turned to where it should be.

When running it in, keep it at a very sensible RPM for about 200 odd miles. Big pain in the arse, but you'll have a good running 2st engine until it pops again.

*re-reads some posts*

Don't pin it. It'll be poor above a certain speed because it's all new.

Ride it like a granny with 1 gammy eye and a false leg. Otherwise you'll just kill it and it'll run like a bag of spanners for half the time it would if it's run in nicely
#14 - tristancliffe
Best way to run an engine in is to use it - that includes full throttle and high revs to generate sufficient gas pressure to bed the rings in (which only work properly with gas pressure), low revs full throttle, medium revs part throttle.

Don't thrash it. ALWAYS let it warm up before using full throttle. Your running cool issue WILL reduce reliability on a 2-stroke, so get that sorted. Running an engine cold not only reduces power, but also increases wear as it decreases piston:liner clearances.

ANYONE who says run an engine in by NOT using full throttle at all is a twat, and that includes the manufacturer (who, after all, are merely covering their own backs). Do the girly "must not rev it" bedding in will merely make your rings leak, and you'll lose cylinder pressure and power - and it will not recover without some hard thrashing later in life, so just avoid it in the first place.
#15 - beefyman666
I was always told not exceed a certain RPM when running in a 2 stroke. I stuck to around 6-7k RPM on my last 125cc bike but still used 100% throttle at times.

With a twist and grovel its slightly different, as the 'clutch' on pull away takes a little more revs than normal, still I don't think you'd need 100% throttle.

Just don't be a twat for a few hundreds miles and you'll be OK.
#16 - Christopher Raemisch
Quote from tristancliffe :Best way to run an engine in is to use it - that includes full throttle and high revs to generate sufficient gas pressure to bed the rings in (which only work properly with gas pressure), low revs full throttle, medium revs part throttle.

Don't thrash it. ALWAYS let it warm up before using full throttle. Your running cool issue WILL reduce reliability on a 2-stroke, so get that sorted. Running an engine cold not only reduces power, but also increases wear as it decreases piston:liner clearances.

ANYONE who says run an engine in by NOT using full throttle at all is a twat, and that includes the manufacturer (who, after all, are merely covering their own backs). Do the girly "must not rev it" bedding in will merely make your rings leak, and you'll lose cylinder pressure and power - and it will not recover without some hard thrashing later in life, so just avoid it in the first place.

Your manual is wrong Jack. Don't bring in alot of heat into the engine but the only way the rings are going to seat is if there is gas pressure pushing them against the piston wall. I don't know how your engine is exactly but most engines from the factory now have scoring on the piston wall to help bedding and from what I read MOST of the bedding in happens in the first 20 miles.

Just get the engine nice and warm, give it a hard pull, run at a steady slowish speed for a bit and give it another hard pull. The key is to create lots of gas pressure, without alot of heat so keep the revs down.

I know when my neighbor bedded in his ceramic rings they would do first gear launches for the first few miles to get the chamber pressures up, without having too much heat.

Rejetting would mean you buy a little nozzle, unscrew the old one, and put the new one in. The nozzle should be living in the carburetor.
#17 - CSU1
put expensive oil in the engine and use treatments and the like for the oil/bore and stop fannying about and thrash it, you'll have more fun
#18 - Jakg
Right. A jetting issue - what exactly does that mean?
#19 - tristancliffe
It means you are either supplying too much or too little fuel for the engine at a given rpm (i.e. the mixture is rich or weak). Rich is bad for economy and emissions, but can give the most power (as long as it's not too rich), whilst weak is really bad - bad emissions, poor power, coughing and spluttering, no really fuel saving (really!), and the potential for detonation (knocking) and ultimately pre-ignition or piston/value failure.

Combine one of those with lower engine temps (removed thermostat), and your engine has the potential to be a mini time-bomb, just waiting to pop.


Oh, and ignore CSU1's advice. He knows not what he says. Use cheaper oil for the running in period (you WANT some wear to start with), and then do a couple of changes in quick succession (say a month apart) with better oil to flush out the bits and provide some protection. Decent oil does not mean thinner (or thicker), or with flashy (but pointless) gimmicks like Magnatec.
#20 - Jakg
Right, thanks for the help.
#21 - Osco
how does your sparkplug look?
fix the jetting, you don't want it running lean on break-in. when removing the restrictor, always check your jetting, air-screw on the carb and check your sparkplug. Is the exhaust restricted too?

you might want to check your clutch springs and transmission rolls (don't know the word in english, vario)
#22 - 11SuLLy11
Run it in on a Dyno ? if you don't want to toodle around for ages lol
#23 - Christopher Raemisch
Quote from 11SuLLy11 :Run it in on a Dyno ? if you don't want to toodle around for ages lol

Dyno a moped?!
#24 - beefyman666
Quote from Christopher Raemisch :Dyno a moped?!

Why not? Fair enough Jak shouldn't bother dyno'ing his 'ped but if one has a 'ped/scoot, churning out enough ponies then why not?

Saw a video clip a while back of a Piaggio Zip, with a 70cc bore kit with all the bells and whistles churning out 21bhp. That's mad for such a small engine. After the dyno run on the video, it had a small drag race against a Yammy R1 and blew it off the start line but shortly got owned.

I miss my little 50's.
Started off on a Kawasaki AR50, wrote that off after 6 months, then got an Aprilia RS50. I refused to get a twist and grovel. Aprilia had mild bits done to it, normal derestriction, sports exhaust, better air filter. That hit an indicated 72mph (it was beyond redline) down a steepish hill near Wymondham.

Good old times.
#25 - pearcy_2k7
Ive got a pug speedfight and its a nightmare have to warm it up for 10 mins before i take it our or i have grannys overtaking me n their zimmerframes. Can't wait to hit sweet 17 (16 sucks) and get a proper moter, and not freeze my nipples driving 2miles and notbeing able to feel my hands. Beats the bus though i suppose.
rant over/

Jak have you tried cleaning the carb? i recently just got mine done as it was stalling all the time, it made a massive gain in torque and top speed...
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Moped Questions (Running In & More)
(34 posts, started )
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