Standard 150 li + Dellorto sh1-18 problems

[Covboy]

So I'm having problems starting my 6v S2 li150 (S3 engine). When it eventually fires the initial tickover is very slow, whatever the throttle position..it sounds BLOBBY. It then picks up and revs normally after about 20 seconds Also max speed was 45mph (gps app) and acceleration had flatspots/ slower than normal.
The airbox has been drilled, the baffle has also been cut out of the airscoop.
There is plenty of clean fuel getting through, and the carb is clean.
New slide.
The original set up was choke 50 / atomiser 5899-1 main jet 105 / pilot jet 45. Ie standard li150

So I put in some jets from a sx150 - set up is now:

same choke 50 / atomiser 5899-5 main jet 102 / pilot jet 45.
It accelerates much better, top speed is now 53mph but the starting issue remains.
I then removed the rubber air hose and it's starts first time now without the blobby / boggy initial 20 seconds.
So I guess it's getting the air petrol mix correct at the start up phase that's critical here....
I don't want to run the carb open mouthed - suggestions please ( and an explanation / reason as to why your suggestion should / work - I would like to understand the rationale as I'm still trying to learn about setting these buggers up!!)

[johnnyXS]

have you checked to see if the rubber hose is collapsing and restricting the air flow when you open the throttle wide open ? some of the cheap Far Eastern hoses are extremely thin walled and collapse with the vacuum created by the carb venturi when you blip the throttle or put the scoot under load. https://youtu.be/C3Ng32ioTjY
Initial throttle response is governed by a combination of the pilot jet, slide profile and the atomiser air jets.
Not sure what the bore diameter of the 5899-5 atomiser is but the 5899-1 is only 1.5mm . The 5899-2 is larger at 1.75mm
Are you using the correct 150cc slide with the cut out ?

[Covboy]

Hi Jonny

Thanks for the prompt reply. The slide is the correct one. The YouTube clip is interesting - the hose is a new SR one and feels sturdy but I'll check to see if it colapses tomorrow.

Cheers

[Meds]

Here's a few things to look at.
Is your choke operating correctly. If it's sticking on or in a half cocked place that could cause problems.( You should be able to see it operating with the air hose off.)
What's your timing set at, my electronic kit is is out by 3 degrees from static to running & caused all sorts of problems when trying initially set up my LI150. ( my static set up was 19 deg, but was actually 16 deg when running).
I have an 18mm carb that just won't work cleanly, it's too badly worn but looks great. I changed all of the jets, had it chemically cleaned and replaced the slide, it didn't make any of difference.
The combination of all 3 issues had me tearing my hair out as I couldn't narrow it down
The simple thing is if someone has a working carb, jetted similarly see if you can try it.

[johnnyXS]

thats a good suggestion about the choke Meds.

They are a very crude assembly and I had a helluva job setting my choke up to work properly.
It either wouldn't open fully or it wouldn't return off fully or it got stuck part open occasionally grrrrr

Eventually I threw away the cheap plastic tap assembly and bought a proper metal one (expensive) and adjusted the length of the metal bend tube because the new choke cable was too short and finally had it working properly.
Now mine will start second kick every time however long it has been left.

[Covboy]

Hello
Thanks meds and Jonny
I can see the choke opening and closing through the air hole when I operate the lever, and the rubber hose does not colapse...next step is to try another carb.

I think points etc are probably ok as when it is running it pulls nicely now and reaches the best top speed I should expect from this set up.

Steve

[johnnyXS]

you say that normally it is really difficult to start when cold but it starts immediately when you remove the carb hose !

That could mean that there is an air restriction....... or the idle mixture is too rich


When you get it started and the engine is warmed up ,how does it idle ? have you tried putting a bit of choke on when its idling ? That will tell you whether the idle mixture is too rich or weak .You may need to reduce the idle jet and adjust the air mixture screw

Just had an idea . have you checked that the choke is working properly when the hose is fitted and neither the choke or throttle cables are fouling on the hose ? worth a check.

When you start from cold you aren't using any throttle are you ? there should be zero throttle and full choke. If you apply the slightest throttle it will screw up the cold start system

[Covboy]

Jonny - I think you may have the answer . Out of habit I always seem to open the throttle as I kick down.
Just tried starting it like you recommend, no throttle whatsoever and it picks up everytime....thank you

[johnnyXS]

we all do it especially if it doesn't start first or second kick ....

Its the same with cars, they should all be started with zero throttle but many of us 'give it a bit of throttle ' to help it along .

Hope that is all it is anyway good to hear that its starting ok .