Hi everyone
I wasn't sure if I should post this in the Technical section or Other section so moderators if you see fit go ahead and move this if you wish. I am fixing up a friends' vintage Yamaha FZ 750. Issues it had were:
Leaking fork seal - fixed.
stalling when hot and near impossible restart - found out the valve clearances were way to tight - reshimmed and adjust all 20 valves to spec.
Cleaned carbs and replaced needles and seats in all. All jets and passageways cleared. Vacuum diaphragms all good and function well. Float levels are set dynamically with clear tube to indicate actual fuel level, as far as I can tell it is within spec of 8.3 mm below lines of float bowls.
At least now the bike does not die when it heats up and seems to restart ok, but it really has a hesitation issue at 2500 - 3000 rpm at any throttle opening. It seems it can't get out of it's own way until you drop a gear and get up over 3k then takes off and runs like a Banshee, and fuelling feels just fine up at higher revs. It has a Vance & Hines 4 into 1 aftermarket exhaust and I am sure that is not helping. Idle mixture screw are currently at 2 1/2 turns out, idle is quite lumpy with popping in exhaust on decel. I tried dropping the needle clips down from center to lowest notch, and this did nothing to help, so I returned them to the stock center position. As far as I can read the jetting numbers in carbs are stock jets, and it pulls so hard at high revs that I think at least the mains are spot on. It just seems to be low speed anything below 3k that it sputters and really makes in-town riding a chore. I did a leak down test of all cylinders when I did the valves and they all show less than 8% leakage so pretty sure no mechanical issues. I'm pretty sure there is no vacuum leaks around carb boots = sprayed with brake clean all around no change in idle. I had a better idle with the idle screws out 5 1/2 turns but went up a mountain road and it would hardly stay running when I stopped so must have been way too rich. I also synced the carbs numerous times and am confident they are all even across the board. Also new spark plugs put in. I'm getting real tires of these carbs real fast, can someone help me out?
I wasn't sure if I should post this in the Technical section or Other section so moderators if you see fit go ahead and move this if you wish. I am fixing up a friends' vintage Yamaha FZ 750. Issues it had were:
Leaking fork seal - fixed.
stalling when hot and near impossible restart - found out the valve clearances were way to tight - reshimmed and adjust all 20 valves to spec.
Cleaned carbs and replaced needles and seats in all. All jets and passageways cleared. Vacuum diaphragms all good and function well. Float levels are set dynamically with clear tube to indicate actual fuel level, as far as I can tell it is within spec of 8.3 mm below lines of float bowls.
At least now the bike does not die when it heats up and seems to restart ok, but it really has a hesitation issue at 2500 - 3000 rpm at any throttle opening. It seems it can't get out of it's own way until you drop a gear and get up over 3k then takes off and runs like a Banshee, and fuelling feels just fine up at higher revs. It has a Vance & Hines 4 into 1 aftermarket exhaust and I am sure that is not helping. Idle mixture screw are currently at 2 1/2 turns out, idle is quite lumpy with popping in exhaust on decel. I tried dropping the needle clips down from center to lowest notch, and this did nothing to help, so I returned them to the stock center position. As far as I can read the jetting numbers in carbs are stock jets, and it pulls so hard at high revs that I think at least the mains are spot on. It just seems to be low speed anything below 3k that it sputters and really makes in-town riding a chore. I did a leak down test of all cylinders when I did the valves and they all show less than 8% leakage so pretty sure no mechanical issues. I'm pretty sure there is no vacuum leaks around carb boots = sprayed with brake clean all around no change in idle. I had a better idle with the idle screws out 5 1/2 turns but went up a mountain road and it would hardly stay running when I stopped so must have been way too rich. I also synced the carbs numerous times and am confident they are all even across the board. Also new spark plugs put in. I'm getting real tires of these carbs real fast, can someone help me out?