Spark plug problem

I’ve got a problem, when my engine got hot, if I stop it, I just can’t start it again, I have to change the spark plug and then it’s ok, it start at the first kick. Can you tell me what the hell is this??

My engine is a PX150 with a Malossi 166 Cylinder kit, the jets included in this kit for the carb and a SIP Performance exhaust, my spark plug is a Bosch W3AS Silver and I ride with SIP
full Synthetic oil at 4% (maybe a bit too much?).

I hope it helps!!

hello,

I think should be a 30. A classic PHBH or something from Mikuni or Keihin if you want go esoteric.
If you want to go for reed conversion you need a massive enlargement of the inlet port and you want be able to go back to rotatory any more.
You could use Malossi reed block, they are quite cheap in comparison with the other. The only thing a found against Malossi manifolds is that construction is not very precise and need some modification. It happened to me with normal Malossi manifold and Malossi reed too. Maybe I was unlucky?!
Some will reccomand you a full crankshaft if use reed. What I can say is that I have tried and…you can keep your original crankshaft with no modification at all. If you really want to change it go for a Worb 5. I found them extremely well balanced.
As far as your question what you should buy first I think your 20 carb is really too small for the Malossi and with a bigger carb your engine will cool out better too. You know from the carb the engine doesn’t get just fuel but a mix of fuel and fresh air.
What about your hot starting problem?

:roll

Air corrector jet : 160
Mixer tube : BE4
Main Jet : 115
Starter Jet : 52140 ;D [:D]

hello,

your plug seems correct, but try a normal W3AC and let us know.

I think for your engine a W4AC would be too hot.

Let us know. If it doesn’t work we will think of something else untill it will work!

[:roll:]

For the timing, see my post named TIMING, Beerace said to me to retard the timing to the stop, I did it but I think in the wrong way, I put it back to IT and then no problem, it starts. Now I moved it to just after the A and my Vespa runs very good!
IT is 18° - A is 20° - should the stop higher than 20° or lower than 18°?

hello,

what carb are you using ?

OK I’ll try this weekend, thanks for the answers, guys[:D]

Thanks, it 's very pleasant to see that we can count on guys like you when there’s problem

hello,

I am not sure, but it doesn’t hurt if you try.

Maybe your plug it’s too cold for your engine.
On Bosh scale means you have a small number.
Try with a higher number.
For example you have a 3 AC go for a 4 AC.

Good luck and please let us know for experience.
Would be of help if you tell us your engine specif.

[:roll:]

Mikke,

Just curious, what jet size came with the kit?

Regards,

Brian.

hello again,

if you want to do a favor to you and to your engine and not spending too much buy a normal manifold with a 28 or 30 PHBH.

In my experience the Malossi kit is the most powerfull but also the most sensitive kit available for the px 125 - 150.

[:roll:]

Mikke,

SIP has advised me to use 130 main jet and work my way down to 118 with a setup of Polini177, 24mm SI and SIP pipe.

maybe jet size is your problem, maybe some of the guys could comment.

Regards,

Brian.

A classic SI 20/20, I plan to buy something better but I don’t know if I’m gonna buy with reed valves or with the conventionnal manifold, I don’t have enough information about all that, I think with reed valves I have to change also the crankcase?
Do I have to buy a 28 or 30 mm? In fact all the information are well gone as I something good.
I plan to buy some parts but I can’t buy all this at the same moment which parts do I have to buy first?

hello,

forgot about the oil.

For me 4% is too much. Maybe the doubble you should use.

Go down to 3%. Or 2%
I don’t know SIP oil. What they suggest?

For my engines when I use Castrol TTs I go 3%, 2%
When I use Bell-Ray, my favourite , I go 2%.

The more oil you have on the mixture the leaner the mix will be.
Oil is ticker then fuel and will block it from the jet.

You will have more oil but you will run leaner.
I know most people think leaner and reacher in term of oil ratio, but it is not the oil %. It is reffered to air fuel mix ratio.

So change % with a new W3AC and let us know.

[:roll:]

hello,

I.T. mark 18 degree

A. mark 23 degree

I always double ceck my timing dynamiclly with strobo using marks on the fan and fan cowling.
It happened to me sometimes the two values are not the same.
The most advanced I will use with your kit, and considering your level of tuning, would be around 19, 20.
More than this and you risk to overheat and make a hole in your piston.
Try to go about 1mm from I.T. mark toward A. mark.

[:roll:]