Any help please with running problem

[prog54]

Hi, using a Dellorto 25 with the jets supplied for 2 stroke and it starts first time and runs fine upto about 1/4-1/3 throttle, if i accelerate from about 40mph onwards it seems to have lagging spots as if occasionally riding into head wind and if I really open throttle it back fires.
Any ideas please.

[johnnyXS]

Is it backfiring at the inlet or in the exhaust ?
This could be an electrical problem , Timing issue or carburation.

A little more information would be helpful like how did it run before you changed the carb. Have you checked the timing lately ? Have you fiddled with any of the electrics or timing ?
It would be a good idea to check all your electrical connections, stator to coil ,coil to plug etc and maybe change your spark plug before blaming the carb ... that said if its a new carb you are going to need to tune it to the engine .
HAve a read here http://www.lambretta.co.uk/downloads/carbsetup.html

[MickYork]

Agree ^. Sounds more electrical than carb'. Suspect stator then the CDI (after changing plug of course).

[prog54]

Cheers guys. I will get plug changed and electrics checked to start with.
I can't tell while riding if it's exhaust or inlet but this back firing has only recently started whereas the dip in power ie the head wind effect has been for a little while.
I did have the carb tuned some months back and the scoot runs like a dream except for this higher speed (40-50mph) or half to full open throttle.
thanks again

[prog54]

OK I have now done several plug checks and rechecked timing at 19btdc. Whilst checking the timing with strobe at approx 4000 revs the timing arrow on flywheel moves back and forth between 19btdc and about 14btdc any other rev amount it seems to be constant on 19btdc.
currently running 25 ml dellorto, sr 185 and original series 2 tv175 exhaust
Any ideas

[Fat Trucker]

Sounds like pick up box breaking down.

[Warkton Tornado No.1]

I was wondering why there appears to be no information regarding the type of ignition you are using. As for the retard, it may be incorporated or an addition, for all anybody knows, unless they already have that information.

Surely, if the full specification were shown, somebody with a similar set-up might be able to offer an insight into their own experiences with what you have.

I am trying to help, this is just a constructive comment, which I hope is not taken the wrong way.....

[prog54]

Sorry Warkton Tornado No.1 I don't have a clue as to what you are talking about but I am sure you are trying to help.
type of ignition? "As for the retard, it may be incorporated or an addition"? these two points are a puzzle to me.
As I said I accept your comments as constructive if only I knew what you meant by full specification.

[MickYork]

Is it a points system or electronic ? if electronic what make are the components ?

Basically some electronic ignition systems (after market) have a separate or built in, "auto retard" system. This allows the timing to shift depending on rev's. It may be that you have this system on your scooter, hence the wavering timing.

It would be helpful to know all your carb' settings (jets, atomiser, slide, etc). The size and type of barrel would also be needed, as well as exhaust (standard, expansion, etc).....basically the spec' of the scooter.

[hullygully]

"original series 2 tv175 exhaust", with a SR185 & 25mm Delly! ! presumably to retain some originality in looks , but after adding the kit & carb why restrict the setup, when you could use an Ancillotti or clubman type exhaust, still retaining the look but giving some much needed engine exhaust outlet

[prog54]

Ok I understand now.
Ignition is via a standard electronic set up supplied by Scooter Restorations everything locked when set up, no automatic advanced or retard that I know of.
I am not interested in performance just outward looking originality where possible thus the series 2 exhaust.
I do not know what jets are installed only that when the 25ml carb was ordered from Beedspeed they set it up with the sr185 and exhaust being given.
It is only recently that this power reduction/missing has occurred and only when checking timing did I notice the wavering at about 4000 revs,it's as if it fires on ever other pulse, either side of this is fine and it pulls and runs smooth with a chocolate brown plug colour and a constant reading of 19btdc.
This set up has worked absolutely fine for 3 years it is only recently that the problem has been happening.
If it is electrics what is the best part of the electrics to start changing first.
cheers

[coaster]

I would agree that it could well be the pickup or CDI breaking down. the CDI is very easy to change and I would advise buying a cheap Indian one for use for testing purposes (replace it with a Ducatti if it cures the problem) for an outlay of £10 it is worth keeping one wrapped up in the tool box as a get you home spare. The pickup will need a flywheel puller and a soldering iron but it is reasonably straight forward. Scooter Restorations or Scootopia would be your best bet for a replacement.

http://www.ebay.co.uk/itm/LAMBRETTA-12V ... 3f509264ca

[Warkton Tornado No.1]

Sorry to have been a bit abrupt or technical, but you are getting good advice now & I would bet that the contributors are correct. The red herring was in presuming that you had a retard in the equation somewhere because of the variance in timing.

You have a common or garden 'static' Indian electronic ignition that, in my opinion, is failing. As others have said it is probably the CDI, but don't forget the stator pick up or possibly, though unlikely, a bad earth.

Good luck.

[prog54]

Thanks everybody for your help so far.
I have run the scooter again before replacing parts and noticed that when the flywheel moves back and forth at 4000 revs there is a clicking sound coming from the regulator, could this be a fault with regulator or is the clicking as a result of the pick up box failing. All cables are connected and sound.
The cdi unit is a ducati blue which I understand are quite reliable.

[coaster]

..................there is a clicking sound coming from the regulator

There are no moving parts in the regulator (or CDI) so difficult to imagine how it should be making noises Also. the regulator has no connection with the ignition circuit, separate coils are involved. Have you checked to make sure the flywheel isn't hitting the pickup?

[prog54]

Your quite correct Coaster, I have followed the cables from the flywheel which go to the cdi and then to the regulator and spark plug, from the regulator to the loom. So, logically thinking it's either the pick up, which is not hitting flywheel, the cdi or the plug.
I will start with the plug then cdi then pick up. It has got to be one of these.
Thanks everybody for the help I will report back what I find.
cheers

[prog54]

Solved.
Changed plug, no difference. Removed cdi and rubber sleeve, checked and noticed that a green wire that went to the loom was on but not very tight, clamped it with pliers reassembled and run, no missing and flywheel stationary.
Thanks for everybodys help which eventually made me remove cdi.