rough running mid-range 70 TLRB Yamaha

[zappaddles]

I have a low hour 2003 TLRB 70 HP Yamaha that has very rough running between (approximately) 1150 rpm and 1350 rpm; feels like it's running on 2 cylinders. I have a new gas tank, new fuel line and bulb, new fuel filter and have just had the carburetors professionally removed, cleaned, re-installed and adjusted. The carb work was done in response to the same symptoms as are still present. Before I take the engine back in(and be w/o the boat during prime season) I'd like ot hear from other Yamaha owners who might have had the same problem and what their final fix was. Thanks for the help.
Zap

 

[mtsinner7868]

Re: rough running mid-range 70 TLRB Yamaha

I have an 05 F40. After cleaning the carbs I have a mid range problem too. Idles perfect and top end is sweet. Just getting from one to the other in about the same rpm range is the problem. Talked to our local yam tech and he insists it's the idler jet(s) on the carb(s). So I will be taking mine apart again here pretty quick and clean the hell out of the jets and see what comes of it. Also he mentioned to make certain the port on the top of the carbs under the plate dealing with the idle jets are clean ! Things may look clean and you may be able to see light through them but that doesn't mean they are all the way clean and performing as necessary. Also if there was any fuel line you didn't replace you may want to consider doing so. Crap may be coming off the inside of it. You can clean the carbs a hundred times and still end up with the same problem a hundred times.

I'll report back once I finish. Maybe before I head out fishing this weekend or just after...... can't miss fishing ! Zap, you should consider doing the carbs yourself. They are not difficult in the least to tear into and only took me a couple hours...... probably about 5 minutes short of what I should have spent on them :facepalm: Also I have some fuel line to replace too before going completely mad.