Hello,
If after other checks of the intake system it is found necessary (preferable) to change the size of the main jets, I strongly recommend to check the flow rates of the old ones first - in case that the current main jets have been there for a while. This is particularly true if you have older Max that might still have the original jets in place. This can be done for example as follows:
1) Remove the main jets.
2) Check the size of the thread and get maybe 5 cm long flexible plastic / rubber hose of the size where you can just screw the thread of the jet in tightly. Do so for the first one.
3) Get an empty pet bottle of Coke or something.
4) Drill a hole through the bottom. The hole must be suitable for the hose to just be able to get in a little.
5) Using hot glue gun, silicone or something like that seal the joint between the bottle and the hose to be watertight.
6) Get some tool that you can temporarily squeeze the hose so that you can control the water flow from the bottle.
7) Get a watch where you can see seconds running.
8) Get a measuring cup that shows let's say tens of ml (millilitre) until 200 ml or so.
9) Now you have connected the hose into the bottle and the jet into the hose. There is a nice channel for water to pass. Then put the squeezer tool to squeeze the hose while you fill up the bottle with water. Make a marking to the bottle to show the starting water level (at this stage the water should not let run through yet).
10) Hold the filled up bottle above the measurement cup and take the watch near you. Release the squeeze and let the water to run from the bottle through the hose and the main jet into the measuring glass for exactly 60 seconds.
11) You can check each jet 2 or 3 times and write down the readings. 60 second flow amount tells you the Mikuni or Keihin main jet size equal (160 ml means jet size 160 etc.).
12) Perform the check for each of the old jets. Fill the water up until the marking you made for the first run.
WHY TO DO THIS?
When the jets are there in service for a long period of time, they start to wear. This means that the fuel passage becomes larger and the actual flow rate becomes bigger than the nominal size says. Further, due to the wear can happen in different way in each jet, it is possible that there is difference between the carburettors' flow rates.
Even if you have a clear direction in your mind (richer or leaner) where to proceed, it is well worth of checking the actual flow rates first. Then you will have more accurate starting point and idea of what could be the suitable size. The flow rate can increase CONSIDERABLY due to wear.
If after other checks of the intake system it is found necessary (preferable) to change the size of the main jets, I strongly recommend to check the flow rates of the old ones first - in case that the current main jets have been there for a while. This is particularly true if you have older Max that might still have the original jets in place. This can be done for example as follows:
1) Remove the main jets.
2) Check the size of the thread and get maybe 5 cm long flexible plastic / rubber hose of the size where you can just screw the thread of the jet in tightly. Do so for the first one.
3) Get an empty pet bottle of Coke or something.
4) Drill a hole through the bottom. The hole must be suitable for the hose to just be able to get in a little.
5) Using hot glue gun, silicone or something like that seal the joint between the bottle and the hose to be watertight.
6) Get some tool that you can temporarily squeeze the hose so that you can control the water flow from the bottle.
7) Get a watch where you can see seconds running.
8) Get a measuring cup that shows let's say tens of ml (millilitre) until 200 ml or so.
9) Now you have connected the hose into the bottle and the jet into the hose. There is a nice channel for water to pass. Then put the squeezer tool to squeeze the hose while you fill up the bottle with water. Make a marking to the bottle to show the starting water level (at this stage the water should not let run through yet).
10) Hold the filled up bottle above the measurement cup and take the watch near you. Release the squeeze and let the water to run from the bottle through the hose and the main jet into the measuring glass for exactly 60 seconds.
11) You can check each jet 2 or 3 times and write down the readings. 60 second flow amount tells you the Mikuni or Keihin main jet size equal (160 ml means jet size 160 etc.).
12) Perform the check for each of the old jets. Fill the water up until the marking you made for the first run.
WHY TO DO THIS?
When the jets are there in service for a long period of time, they start to wear. This means that the fuel passage becomes larger and the actual flow rate becomes bigger than the nominal size says. Further, due to the wear can happen in different way in each jet, it is possible that there is difference between the carburettors' flow rates.
Even if you have a clear direction in your mind (richer or leaner) where to proceed, it is well worth of checking the actual flow rates first. Then you will have more accurate starting point and idea of what could be the suitable size. The flow rate can increase CONSIDERABLY due to wear.
