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New lambretta gp200 engine wont rev smoth its a tho the choke is on it isn't as if I put choke on while riding it splutters and stops. only done 18 miles help please

Posted by steve on

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Gregg Mahin

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  • Motorcycles Master
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Hi, Steve if your bike is still under warranty take it back to the dealer, engine "BOG" is mainly caused by a rich air and lean fuel condition but it can also be caused by a lean air and rich fuel condition this situation rarely occurs and is only caused by the misinformed weekend warrior that owns a toolbox. If the bike has been sitting for months or years you will have to completely disassemble the carburetor and submerge the parts (except rubber parts) in "Carburetor Dip" It usually comes in a gallon bucket with a wire mesh basket that can be purchased at any automotive store. If it is not the above scenario then the following explanation will apply.
The more you open your throttle the more vacuum you are creating in your carburetor venturi and your intake manifold. When you are operating at higher RPM any unmetered air that leaks into your system can become more obvious.
Unmetered air is the air that is getting into your system after the fuel has been delivered. If you have unmetered air getting into your system between the butterfly/slide of the carburetor and the cylinder head this will create a lean condition.
All of the rubber components of the fuel system like vacuum hoses and intake manifold that you mount the carburetor to are made of rubber. If none of these components has been changed they are more than likely highly degraded and probably cracked in places to allow unwanted-unmetered-contaminated air into the combustion chamber. Check all of your vacuum lines and vacuum plugs for carburetor synchronization. The vacuum plugs are in the head just after the rubber intake manifolds. The petcock has a vacuum line as well as part of the emission system.
1. Check the intake manifold for fissures.
2. Ensure the bands used to tighten the manifolds down on the intake are secure and have not bound up the manifold.
3. Make sure air box fittings are not warped and fit completely over the carburetor.
Your airbox is metering air and is the first step in the process of consuming air and fuel. The system requires the resistance of the air filter in order to get the proper vacuum to "SUCK" the fuel out of the float bowl and create the proper venturi effect.
Improper mounting and sealing of the airbox will create a small lean effect. This might seem like no big deal but you are inviting dust and debris in your engine that is doing slow damage by not having proper fitment. Fix it so you know it's not contributing to your issue. Pick the low-hanging fruit first.
Do not go and start adjusting anything at this point. It ran fine before. There is something wrong with the assembly or a component. Do not adjust your floats. Get it back to where it was. The moment you start tweaking everything is the moment you lose OEM settings which are a must-have for fine-tuning and maximum performance.
Fine-tuning your carburetor and multi carb syncing come at the very end following the proper procedure established by the Carburetor Gods.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
http://www.ilambretta.co.uk/forum/viewtopic.php?f=6&t=3716
http://50.18.170.78/forum/topic138436
https://masolartva.files.wordpress.com/2015/09/lambretta-service-manual.pdf
https://www.gtbbeximl.com/index.php?main_page=product_info&products_id=830891
https://www.scooterhelp.com/serial/gp200.sil.manual.html

Posted on Aug 09, 2020

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5 Related Answers

robotek

Graeme Ross

  • 1512 Answers

SOURCE: misfire & spluttering when warm

Hi wayne

Not knowing what you have checked or done already, I would first remove the spark plug from the bike and check it fir a carbon deposits. If it has not had a new one for a while, Just get a new one and replace it. Before I drop the oil for a service(as it can dirty up the oil), I also like to run a fuel system cleaner additrive(I use a Nulon product) to my bikes every few thousand kays, just to keep everything tip top. If you still have misfire problems, then it will most likely be a faulty sparkplug cap, ignition lead or other ignition part. Change out/clean spark plug with a wire brush first. I think that will fix it for you. If you still have problems,happy to talk to you more about it.

regards
robotek

Posted on Nov 20, 2008

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Anonymous

  • 126 Answers

SOURCE: wont run /idle

i'd start with removing the carbs and giving them a thorough cleaning as when bikes sit for so long, the carbs begin to get gummy/varnished from the old gas.

check for blocked holes in the pilot jet & main jet and look for "hard & dried up" gas in passages. be careful of the float bowl gasket as to not tear it or you will need a replacement.

Posted on Mar 06, 2009

tombones

  • 3567 Answers

SOURCE: My 125cc single cylinder (pulse adrenaline) cuts out at junctions

Since the bike is new, chances are strong that fuel IS the problem.
Also chances are that the carb is perfectly fine. Since the bike is new I'll bet yoy have washed it several times already. The dealer may have washed it also. Fuel is the problem because bikes do not run well on water.

Drain the carb. Remove the water trap bowl on the bottom of the petcock, (gas valve). Look at the gas in the bowl. Any water in the bottom of the bowl? Drain a cup of gas from the petcock. any water in the cup? I am very hopefull this will fix the problem. With a new bike and a clean carb and fuel system not much else should be wrong.

Posted on Mar 21, 2009

Anonymous

  • 23 Answers

SOURCE: GSXR 750 Slingshot wont rev past 5000rpm, with or without choke

I have seen this before a few things to do too make sure. First take the air filter out and shine a light use your fingers to move the slides up and down I suspect the springs that go on the slide is not seated in center you can tell from the slide going halfway and hanging up. Next, the boots on the slides only go on 1 way there is a notch on the carbs for them. I would guess this would fix you up if not we can get deeper into it with air-fuel mix screw settings.good luck

Posted on Mar 25, 2009

Anonymous

  • 226 Answers

SOURCE: 1984 aspencade starts w/choke and revs up, runs smooth. Take off

My 'wing won't run unless it has been warmed up some. I would suggest that you r&r your carbs to make sure the jets in the bottom are working correctly. They tend to get plugged up, especially after sitting & the aluminum flaking off inside... Rick

Posted on Apr 14, 2009

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