TOPIC:

This bike was work in progress when I bought it in 91. I got real sick in 99 and lost my equal librium completely, so the bike has been sitting since. Before I parked it I put a Dana ignition on it woth new coils, they are green HO coils. Vance & Hines 4-1 headers, air pods. I believe the stock jets were 97.5 main and 15 pilots as I found them in a jar. The bike has now 117.5 in it with 17.5 pilots. I remember it running rich at good throttle. I believe the needle are on 3. I have 115's and 120's spare. How many sizes as a rule should I go up from stack with alters? What is the starting rejet rule? I would like to start the process over from scrath as I don't remember where I left off

Post edited by: vach, at: 2007/04/28 23:20

I rebuilt my carbs today and tonight, while looking for some replacement rubber parts, I found this site. He has what looks like a pretty good rule of thumb for calculating where to jet your carbs:
www.motorcyclecarbs.com/Jetting_Rules_of_Thumb_W43C551.cfm

Well I guess I'm pretty close then. It say's up 2 jets for 4-1 headers and 2 up for pods. Up 4x2.5 -1 jet size = 7.5. I'm running 117.5's 10 up from the 97.5. Looks like I should try 115 mains. It say's up one pilot every 3 mains so, I'm good there. 17.5 from a 15. Cool. Does anyone know what rpm band the pilots go to and the mains start? There was a link but I can't find it. I want to do a new plug reading.

rbrewrr wrote:

I rebuilt my carbs today and tonight, while looking for some replacement rubber parts, I found this site. He has what looks like a pretty good rule of thumb for calculating where to jet your carbs:
www.motorcyclecarbs.com/Jetting_Rules_of_Thumb_W43C551.cfm

I found the info, Though i would like to know the stock position of the needle jet, I may have messed with it.

From the theory of operation that I've read (here, manuals, and elsewhere) the main jet only has full effect from about 3/4 to full throttle. The needle controls the flow through the main jet from about 1/4 to 3/4 throttle or thereabouts. At idle and just a bit above to around 1/4 throttle the pilot jet supplies the fuel.

So, I would suspect the pilots first as below 2000 RPM seems to low for the needle to have much effect (this isn't an exact science). The next question to answer is whether the mixture is too rich or too lean when it bogs.

WRT to synchronizing. All a sync does is match the slide openings so the same amount of air is being drawn into each cylinder. It does not affect the fuel delivery per se. That said, proper sync results in a smooth running engine. Unless the adjustment screws are bumped loose, you shouldn't need to resync every time you take the carbs apart. It would be wise to check it once your problem is solved.

I found the info, Though i would like to know the stock position of the needle jet, I may have messed with it.

From the theory of operation that I've read (here, manuals, and elsewhere) the main jet only has full effect from about 3/4 to full throttle. The needle controls the flow through the main jet from about 1/4 to 3/4 throttle or thereabouts. At idle and just a bit above to around 1/4 throttle the pilot jet supplies the fuel.

So, I would suspect the pilots first as below 2000 RPM seems to low for the needle to have much effect (this isn't an exact science). The next question to answer is whether the mixture is too rich or too lean when it bogs.

WRT to synchronizing. All a sync does is match the slide openings so the same amount of air is being drawn into each cylinder. It does not affect the fuel delivery per se. That said, proper sync results in a smooth running engine. Unless the adjustment screws are bumped loose, you shouldn't need to resync every time you take the carbs apart. It would be wise to check it once your problem is solved.