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It's a 2002 Yamaha vstar 650 classic. Engine quit running overnight. Wouldn't even idle. So far I've fixed the intake leaks, a stuck diaphragm, unclogged two of the jets, replaced the needle valves and o-rings, replaced cracked vacuum hoses and had the carb professionally cleaned. New spark plugs, air filter and fuel filter. Needle valves set and throttle synced by local shop. The engine was running with clogged jets and intake leaks and now that they've been fixed the bike will only idle. When the throttle opens its dies out from what I'm guessing is overly lean? It was running extremely lean prior to being cleaned. The rear cylinder now only heats at half the rate of the front cylinder. The choke used to kill the bike at idle and now when the choke is applied it doubles or triples in RPM. (Better fuel air mixture?). Restricting the intake by the air filter increases RPM. Covering the intake entirely kills the engine so I'm assuming no intake leaks. Fuel can be seen clearly entering the venturi through the jets and doesnt look like its evaporating entirely. I'm an aircraft mechanic and I'm not used to this style of carb. I talked to the local bike shop and they recommended a total carb rebuild. I don't know if this will fix my problem. Any ideas on anything else that can cause bogging when the throttle open? Float levels, bad jets, bad fuel pump? I'm trying some stuff at home before spending money at the local shop. Any help is appreciated.

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    Welcome to Motor Vehicle Maintenance & Repair! – kyle_engineer Aug 24 '18 at 18:25
  • You say you replaced a diaphragm, so it sounds like you have CV type carbs? If you have CV carbs, can you see if the slides are actually going up when you open the throttle and it starts to bog? Is the bike rideable? If the rear cylinder is only heating at a low rate it sounds like that cylinder isn't burning, could be spark or fuel. Have you confirmed that you have spark in that cylinder? – Eric Aug 24 '18 at 18:27
  • Before you get completely fixated on the input side, do you have a blocked exhaust pipe? If the engine suddenly quit running, something suddenly changed. You mention about 7 "problems" you have "fixed", but most of those couldn't have happened "suddenly" - and certainly they didn't all "suddenly" happen at the same time. IMO it's tIme to apply the old advice, "If you can't find the problem where you are looking, then you are looking in the wrong place". – alephzero Aug 25 '18 at 9:48
  • It is a CV type carb. The slides can be seen moving as the engine accelerates. It's not drivable because it doesn't output enough power to get it going in first currently. Fuel and air have been confirmed entering the rear cylinder. No after of back firing. Hot exhaust can be felt coming out both pipes. I assumed the exhaust wasnt the problem since both had air rushing out. The spark plugs are new but I'll check them anyway. I figure the rear cylinder is firing because it warms up just not quickly. I'm gonna mess with it for 2 more days before dropping it off at the shop. – Nick P Aug 26 '18 at 23:20

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