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Confused on Jetting
- Norseman
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04 Sep 2007 19:59 #168595
by Norseman
Confused on Jetting was created by Norseman
Well, I’m not sure if anyone can help me with this based on the description only, and I know there has been much debate on jetting. But here goes (sorry about the lengthy text).
I bought the bike with air pods and a 4:1 Supertrapp exhaust. The jets were 130 mains and 37.5 pilots. I returned the bike to stock airbox and removed the EPA-mandated system, capping all the carb vents since I have an aftermarket non-vacuum petcock. Mikuni 34's, new carb holders, deep-cleaned carbs with new gaskets/o-rings, valve clearances set exactly at nominal, new plugs, air screws at 1.5 turns out, tuned with Morgan Colortune and synched with Morgan Carbtune.
Start-up and idle was terrible, so I was advised to increase the pilot jets to #40 and keep the #130 mains, which I did and it helped. Stock mains are supposed to be 122.5 and stock pilots are to be 37.5. I seem to remember the rule says for a 4:1 exhaust, go up one size on the mains, stay stock on pilots. Add pods and you go up 2 sizes on mains and 1 size on pilots. That translates to 3 sizes up on mains to #130 and 1 size up on pilots to #40.
In my quest to identify the source of my misfiring problem (seems to be the original coils), I pulled the plugs today. All four look to be in identical condition; ground electrode and central electrode are a nice tan, but there was build-up of soot at the bottom of the threads and its collar at the bottom. They did not look like the samples of a well tuned and efficiently burning plug I have seen depicted.
My question is this: it seems I am burning somewhat rich and I'm getting some popping in the exhaust upon deceleration/downshifting. Since I returned to stock airbox but kept the 4:1 exhaust, should I go down to #125 mains and return to 37.5 pilots?
I realize I’m talking about “rule of thumb” here, and no one can answer finitely without observing and testing the bike, but am I using sound logic here?
Post edited by: Norseman, at: 2007/09/04 23:38
Post edited by: Norseman, at: 2007/09/05 00:06
I bought the bike with air pods and a 4:1 Supertrapp exhaust. The jets were 130 mains and 37.5 pilots. I returned the bike to stock airbox and removed the EPA-mandated system, capping all the carb vents since I have an aftermarket non-vacuum petcock. Mikuni 34's, new carb holders, deep-cleaned carbs with new gaskets/o-rings, valve clearances set exactly at nominal, new plugs, air screws at 1.5 turns out, tuned with Morgan Colortune and synched with Morgan Carbtune.
Start-up and idle was terrible, so I was advised to increase the pilot jets to #40 and keep the #130 mains, which I did and it helped. Stock mains are supposed to be 122.5 and stock pilots are to be 37.5. I seem to remember the rule says for a 4:1 exhaust, go up one size on the mains, stay stock on pilots. Add pods and you go up 2 sizes on mains and 1 size on pilots. That translates to 3 sizes up on mains to #130 and 1 size up on pilots to #40.
In my quest to identify the source of my misfiring problem (seems to be the original coils), I pulled the plugs today. All four look to be in identical condition; ground electrode and central electrode are a nice tan, but there was build-up of soot at the bottom of the threads and its collar at the bottom. They did not look like the samples of a well tuned and efficiently burning plug I have seen depicted.
My question is this: it seems I am burning somewhat rich and I'm getting some popping in the exhaust upon deceleration/downshifting. Since I returned to stock airbox but kept the 4:1 exhaust, should I go down to #125 mains and return to 37.5 pilots?
I realize I’m talking about “rule of thumb” here, and no one can answer finitely without observing and testing the bike, but am I using sound logic here?
Post edited by: Norseman, at: 2007/09/04 23:38
Post edited by: Norseman, at: 2007/09/05 00:06
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