carb

[kennystag]

Hi all,
When I take the air filter hose of the carburettor, the engine runs like a bag of bones and stalls.GP150, why do you think this is happening.
Cheers
Stag

[Storkfoot]

You are letting too much air in which gives you a lean mixture. Why are you taking it off?

[kennystag]

Took it off to clean the air filter. I think it is a bit more than just that, I am going to have to rejet the carb but not sure as yet, I fitted a 22mm jetex recently with a new expansion exhaust. I will have to give it a good road test, when I ever get her out of my workshop, to see how she runs and what to do next.
Stag

[Rich Oswald]

A 22mm Jetex is not a particularly good match to an expansion exhaust.

Rich'

[kennystag]

A Jetex carb is ok, what I can make out Just a matter of tuning.

[Rich Oswald]

A Jetex carb is ok, what I can make out Just a matter of tuning.

I agree Jetex carbs are ok, just not with an expansion.

[kennystag]

Is this your opinion or fact, if so what are the problems with the pair, do the company that make the jetex say no good for xyz exhausts .

[Storkfoot]

^ I tend to agree. If I had a standard 150, I wouldn't personally go bigger than a 42 Clubman.

There is a possibility that you are running too weak at the bottom end of your throttle progression and that, when you take the filter off, it sends it really lean which is why you stall. Be careful when you road test it.

[kennystag]

Thanks for that advice.

[Donnie]

Jetex and expansion, usually a big no no, though when i had the chopper with a tuned 175 i ran a jetex with one of the taffy vietnamese copy pipes and worked well (other then the pipe being crap viet metal and cracking and rotting through in very short order).

But yeah if you are on a standard 150 it's gonna be crap.

A couple of things that worry me are that youve not defined what exact exhaust you have and that you obviously havent rejetted to suit

[CHRIS in MARGATE]

If it's a 150 with expansion try a 50 pilot and a 108 main jet. I'm not saying that's the answer but it might be a good starting point.
You must check your plug to make sure it's a good chocolate brown.

[kennystag]

When and if I ever get her out my workshop, I will road test and see what it is needing doing carb wise, she ticks over very well, and starts first kick, that is a good starting point, but we will see how she goes.

[kennystag]

Chris,
What else carb jet parts would you get if it was your Lammy, as I am about to order the jets you recommended.
Cheers
Stag

[burnside]

What expansion exhaust is it...and is your GP150 standard or kitted?

[kennystag]

sterling

[kennystag]

Sorry forgot to say it is a standard 150cc with 22mm jetex and Sterling expansion exhaust.

[burnside]

So standard settings for a GP150 with 22mm carb are 50 starter, 45 pilot, 118 main, 5899-4 atomiser and 7895-2 slide. Normally with an expansion you would be looking to go up on your main (would probably start at 130 and work down) and possibly pilot as well. What's your current setup?

But as others have said a 22mm carb really isn't suited to an expansion exhaust, just isn't big enough to get sufficient air and fuel in to get the best out of the pipe. And Jetex can be a bit hit or miss as well, you either get a good one or a crap one and nothing much in between, but using Dellorto jets and ensuring the float doesn't stick can go a long way to help.

The other thing to consider here is that whacking an expansion pipe on a standard 150 will not actually give you much benefit at all, expansions are suited to tuned setups to allow them to rev higher and get the full potential of the kit. All you will probably get here is just more noise. It's like sticking a pair of high end trainers on a fat bloke, will make him look more sporty but won't actually make him run any faster....if at all

[kennystag]

Thanks burnside,
After the negative comments on the jetex with my exhaust you have explained to me why they do not match. .
Cheers Mate
Stag

[burnside]

Those guys know a lot more than me about this stuff, I just read up a lot and do my homework. End of the day there isn't really a quick fix for poor Lambretta performance, you have to look at the setup as a whole and get components that compliment each other. A 22mm Jetex is essentially a re-made standard GP carb, suited to standard set ups.

[CHRIS in MARGATE]

I think the 130 main will choke it. ( But I might be wrong !)
I have seen 128 on a 200 cc and 122 on 175 cc


Buying lots of jets gets expensive as well.

Any other opinions so we can save this guy some money.