Starting after top-end rebuild and new carb

[loadedscooterist]

Hi Nick, No offence taken and its good to see others helping those less knowledgeable so many thanks!!!

Paul, I have the other slide (e.g. the 200 as I think I made the decision to use the 150 one when I got the option) so I am going to try that as a first port of call and then report back findings.

[nick b]

defo put the 200 slide in but possibly put a smaller jet in to start with my other lambretta is a standard gp 200 [so I haven't had to mess about with setup etc] it has a sh22 carb and the main jet is a122 if the main jet is to big it is very swampy as you go through the gears and only feels right on high revs

[loadedscooterist]

Hi Nick, First point of call is the other slide with the 5899-2 Atomiser which is sitting on my desk with a 45 pilot. The main I plan continue to use the 112 (as it was fine running and a good colour on the plug). My main need is to get it starting better.

[HxPaul]

Its safest to start with a jet thats to big.If you start with one thats to small,you run the risk of seizing the engine.

[loadedscooterist]

Hi Paul, yes agree. Just want to get the thing started so will revert to the 118 I started with as well.

[johnny650]

there is some excellent advice in this thread and obviously you are very near getting your settings dialled in.

First of all you should only need to use zero throttle with full choke to start within 1-2 kicks . if you need to give it some throttle to start, or it takes more than 3x kicks, then your start mixture or delivery is wrong or you have an air leak or some other fault.

.it does rather sound like your engine is receiving too much fuel at start up and idle settings.

You might try screwing the idle mixture screw in to 3/4 turns out and then increase gradually by 1/4 turn at a time until it starts with less than 4x kicks . You will probably need to clean and dry the spark plug before each test.
If you kick the engine over 4x times and it doesn't start then there is no point in continuing ...You'll simply either flood the engine and plug or break the kickstart eventually


Set the idle speed as low as possible. if the idle speed is set too high then the slide will be high and the engine vacuum will start to draw fuel from the Atomiser and main jet which will make adjusting your idle mixture impossible. The Idle mixture screw should be set with the idle speed set as low as is practical yet still achieve a stable tickover.

When you set your mixture screw you need to bear in mind that all it does is increase or decrease the amount of combined starting and idle fuel and air . It does not alter your air or petrol ratio. In other words screwing the mixture screw in or out does not alter the idle air or the idle fuel alone .

The idle air supply is supplied by a fixed jet as is the idle fuel .........so to vary the ratio of idle fuel to idle air (ie to richen or weaken the idle mixture ) you must do it by changing the pilot jet size. To richen the idle mixture increase the idle jet size and then adjust the quantity of idle fuel/air with the mixture screw .

If the engine cuts out shortly after starting then I would check that there is no oil on the sparkplug (leaking drive side seal or rings) Also check that the choke is re-seating perfectly. The slightest leak from the choke will supply too much fuel and gradually flood the engine at idle.

[nick b]

I would also start with a 118 it sounds about right but have you checked yourtiming and your spark it might not be the carb that is causing the problem

[johnny650]

dead right Nick....I recently found my timing 2x degrees out and I would have sworn it was correct . i'd checked it several times .
An incorrect points gap can vary the timing significantly if its a points ignition system

[loadedscooterist]

Hi both, that was plan C that you have uncovered! I am going to go with the carb setup first and then failing that it was going to be timing. I have a strobe gun and a willing accomplice so that is a good one to check as well.

[loadedscooterist]

Spark seems ok but wondered if there was a good way of measuring the quality and strength of a spark?