Author Topic: mikuni settings for fl250  (Read 619 times)


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mikuni settings for fl250
« on: February 18, 2022, 04:17:54 PM »
Recently restored a FL250 and need some advice on the carb. I had the engine but the carb was long gone so I purchased a mikuni VM30. This appears slightly larger than the original but the machine runs unfortunately it runs, I believe, rich. I rebuilt the engine, new bearings, ported head otherwise stock setup with DG exhaust.
My question is does the mikuni come with the right size jets for this setup and is that my reason for the sputtering, excessive exhaust etc. I also have small amount of oil coming in the exhaust pipe, drips noted. I am using synthetic oil mixed to 20:1 and I suspect this is too much for synthetic.
Any assistance is appreciated.


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Re: mikuni settings for fl250
« Reply #1 on: February 20, 2022, 12:27:45 PM »
I find 32:1 to be a good balance between protection and smoke. If you are rich jetting, at least you can run it to dial it it.  I don't know what jet is in that carb or what is needed. If it happened to be jetted well for an FL250, it no longer would be with the porting and pipe. You need to test and dial it in. Remove the plug and look at the porcelain around the electrode. If it is wet or black, it is too rich. That does not tell you where in the throttle range it is rich at. However, if that rich, you are now safer to do tests at specific throttle positions. Start with running full throttle. shut off the engine at the same time as letting off the throttle. Once stopped, check plug again. If it got lighter, then you are lean on the main jet and it is burning off excess fuel left from other throttle positions. If it is wet or black, drop the main jet and repeat. When you get to a dark chocolate brown, start doing the same with half throttle. If rich, lower the needle by raising the clip. If lean, raise the needle. I would then double check the main again and you could drop to more of a milk chocolate brown. If the slow jet is too big, initial start off will be sluggish. Running full throttle for a bit, stopping, then starting again, it would be crisper. That is because the excess fuel would be burned off during the full throttle run. If the slow jet is too small, after revving the engine, the RPMs will hang before dropping back to idle. You may have seen this effect when forgetting to turn on the fuel.