Author Topic: Yamaha Ls2 misfires  (Read 329 times)

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Offline Montoya

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Yamaha Ls2 misfires
« on: May 10, 2018, 12:00:20 PM »
Hi guys. I hope someone can help me out with my Ls2. It fires occasionally on left cylinder. When passing 5k rpm, it tends to hang on, but is not giving full power. The ignition and point gap is spot on. New coils, pointers, spark plugs, condenser, wiring and battery. Carbs are cleaned up, synchronized and perfect adjusted. No vacuum leak anywhere, crankshaft and seals are all new. I just can't imagine why this cylinder is making som much headache.. Anyone with  a suggestion?

Offline Montoya

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Re: Yamaha Ls2 misfires
« Reply #1 on: May 12, 2018, 10:43:42 PM »
I managed to make the left cylinder a little bit more alive. The carburetor piston was not lifting as much as the right one. However, the bike has a lack of power. it has no more power at wide open throttle than half way. it just makes more noise from the carbs. When going uphill and giving som more throttle and the power decreases. Just that typical sound from the carbs and the speed gets lower and lower. It has´t always been like that, so I know the main jets are OK. #70
Any suggestion why full throttle isn´t making any more power than half throttle? Sounds like just about to go out of fuel..

Offline 5port

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Re: Yamaha Ls2 misfires
« Reply #2 on: May 14, 2018, 09:41:49 AM »
Just that typical sound from the carbs and the speed gets lower and lower. It has´t always been like that, so I know the main jets are OK. #70

It sounds like your jetting is too rich? It could be a combination of things like blocked air filter, starter enrichment, jets, needle and/or idle mixture screw.
 Just because the jets look OK doesn't mean that they are!   Firstly, many jets are modified or partly blocked with gum or corrosion.  ::)  You are best to get new genuine jets!  Secondly, some carb makers make different types of jets that will fit but are different!  :o You are best to get new genuine jets.  :)  Also, having checked which type and size of jet you need, you might get them from the carb maker supplier cheaper than Yamaha.  Cheers

5port     
5port

Offline Barnett

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Re: Yamaha Ls2 misfires
« Reply #3 on: May 18, 2018, 10:21:27 PM »
Do you use in line fuel filters? If so check them for flow? Tank breather hole clear? Did the problem suddenly occour or has it got worse over time? Are your spark plugs a health colour and are they the same colour? what type of air filter does the Ls2 use, paper or oiled foam? As it is the left side have a look at the choke, ( fuel enritchment assembly), is it sealing shut propperly? loads of things to check, step by step, you will find it!
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