'89 GSX-R 750 where has been swapped '90 GSX-R 750 engine with carbs.
Carbs are '90 stock Mikuni BST38SS with dynojet stage 3 jet kit. (I have drilled one lift hole larger on the slider and drilled main air jet, as listed on instructions)
Airfilters are K&N RU-2922, as listed on dynojet stage 3 jet kit. They have been washed and oiled.
Exhaust is full vance&hines SS2R.
I have never been able to test these 38mm carbs with stock jetting.
Dynojet kit is E3335.
There is constantly sudden cut-offs when accelerating. First gear goes fine, but after that problem gets worse. See video and you get what I mean.
Tried so far:
- Ultrasonic cleaned carbs.
- On first start, bike didn't want to rev at all. Changed needle to the second most richest position (step by step) (instructions says to put to the second most leanest position).
- After changing needle position, adjusted mixture screws.
- After mixture screw adjustment, synced carbs.
- Changed main jets. Instructions says that 150 is the correct one.
-> Started with 150 main jet. Stuggling a little bit to rev past 9k and also same cut-offs.
-> Changed to 155 main jet. Struggling badly to rev past 9k.
-> Changed to 146. This is the current state and the best one so far.
- Changed new spark plugs. Tried with NGK CR9EK and CR10EK (current).
- Tested spark. It seems good strong blue.
- Measured coil resistance, both are ok.
- Fuel lines are replaced.
- Battery is charged.
- No visible air leaks.
- Carbs diaphragms seems ok.
- Float level adjusted.
- Fuel tank filter cleaned.
Does this seems more like fuel issue or spark issue?