If you aren't sure of the transfers duration then enter 125-130 for race engines or 115-120 for street/trail engines.
If you have to lower it so much that it causes too much of a weak zone off idle then you should just buy a needle with less taper angle.ģ) Go to the last sheet (click on the velocity tab at the bottom left of the screen) to find out the maximum air velocity to enter at B7 of the jetting sheet. But be aware that the needle position also affects the transition of power off idle. Of course you can lower the needle by repositioning the clip higher in order to lean out the mid range, or do the opposite to richen the mid throttle jetting. If not then you need to adjust the beginning of the ideal jetting graph (the grey line) so that what it shows is what you experienced. You need this info to be able to verify if the programs jetting graph is showing you the same thing. Something between those two extremes is desirable. If it runs fine but drops power when you quickly open the throttle then it is too lean there. If it is irregular and/or sputters occassionally then the needle is too rich at that setting. Ride at a steady speed on a flat road, or on an inclined road if the bike wants to accelerate much at those settings. 5mm (.02") at a time till the jetting is right.Ģ) Mark your throttle body and throttle grip so you can see when riding what the correct throttle opening is for 1/2 and 3/4 slide open. In that case put in the rich jet and then lower the shroud. For small carbs you may need to lower the needle shroud if one main jet size is too rich and the next smaller size is too lean.
Click here to find out the best way to size the main jet. 15 to get 3, so if the slide at closed throttle is more than 3mm open then the idle jet may be too big.ġ) Make sure your main jet is correct. Example: for a 20mm carb you multiply that by. 10% for piston port) indicates the idle jet is too big or the needle jet is wallowed out and letting too much gasoline past it during idle. Anything over 15% of the carb size (for reeds.
#Dellorto phbh 28 main jet crack#
If you have to make the idle mixture too rich for idling in order to help compensate for weak throttle response as you crack the throttle open then you either have the needle clip in too high a position or you need a skinnier needle or fatter needle jet (the brass hole the needle slides into).Īnother way to tell is by how open the slide is for a normal idle. The idle jet that gives the best idling and power is the right one. I say "may" because the only true test is how the engine runs up to 1/2 throttle. Then turn the slide stop screw till you have a normal idle speed. If it is more than 2 turns then you may need a smaller idle jet. If it is less than 1+1/2 turn then you may need a bigger idle jet. This should result to be within 1+1/2 to 2 turns out. Then turn clockwaise the air screw till the idle speed starts to drop off rapidly and return the screw position to just before that.
Then turn the air screw till you find where it idles the fastest, then readjust the slide stop for the same fast idle. Turn in the slide stop screw till you have a fast idle. If you hover the mouse pointer over a cell with a red corner then a message will pop up telling you about that cell.Ġ) First make sure your real life idle jet is correct.
#Dellorto phbh 28 main jet how to#
Here's how to use the spreadsheet: Enter data into all the light blue cells of the spreadsheet and the program will graph the jetting.
Near the bottom of this page are the links to the needle and needle jet info that you will need to know such as the inner diameter of the needle jet of your carb. Jetting DellOrto Carbs Jetting DellOrto CarburetorsĬlick here for my page verifying the jetting calculator for DellOrto carbs (except SHA).īelow is a screenshot of my spreadsheet for DellOrto carbs.
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