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Main jet question
Hi, I have a 83 750e I just got finished putting together. I put a Wiseco 816 kit in, 4-1 exhaust, supertrapp r series canister w/6 disks, pod filters, 85" 700 cams. My bike started right up and with a little tuning is running strong. My carbs are the bs32ss, they have been drilled and the main jet has been changed to 140. I think this is too big. With what I've stated, what is a good main jet size I should start from? I got better response with my air screw turned out 3t. Thanks for any bodys help!Tags: None
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The general "rule of thumb" for jetting increases will ask you to go up 3 to 5 sizes for an exhaust system and 4 to 6 sizes for pods. Since you have both, something in the range from 7 to 11 sizes larger than stock. Stock jets are 117.5. 7 sizes larger would be 135, 11 sizes would be 145, so you could be close. I have also heard that a bore increase will require a slightly smaller main jet, but I have no experience with that, so I don't know how much. Just a wild guess here, but I am thinking you might need something in the 130 to 140 range.
And, ... you don't have "air screws", those are your "pilot mixture screws". Three turns out is a good starting point and might be where your bike needs to be, with those modifications, but a little fine-tuning won't hurt anything. If you find that it runs even better when they are turned more than about 4 1/2 turns, consider upping the size of the pilot fuel jet one size, from 37.5 to 40.
What are your spark plugs telling you?
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helmutholderbenz
Originally posted by Steve View PostThe general "rule of thumb" for jetting increases will ask you to go up 3 to 5 sizes for an exhaust system and 4 to 6 sizes for pods. Since you have both, something in the range from 7 to 11 sizes larger than stock. Stock jets are 117.5. 7 sizes larger would be 135, 11 sizes would be 145, so you could be close. I have also heard that a bore increase will require a slightly smaller main jet, but I have no experience with that, so I don't know how much. Just a wild guess here, but I am thinking you might need something in the 130 to 140 range.
And, ... you don't have "air screws", those are your "pilot mixture screws". Three turns out is a good starting point and might be where your bike needs to be, with those modifications, but a little fine-tuning won't hurt anything. If you find that it runs even better when they are turned more than about 4 1/2 turns, consider upping the size of the pilot fuel jet one size, from 37.5 to 40.
What are your spark plugs telling you?
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go up 1 size in the pilots may solve this.MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550
NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.
I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.
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helmutholderbenz
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helmutholderbenz
I've got my bike running real well now but I believe I can get it even better. No more surging, rock steady idle, crisp throttle response. I have 140 main jets and want to try maybe 135s. my question is when I change main jet, do I have to change other settings on the carbs?
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GSCafe
Originally posted by helmutholderbenz View PostI've got my bike running real well now but I believe I can get it even better. No more surging, rock steady idle, crisp throttle response. I have 140 main jets and want to try maybe 135s. my question is when I change main jet, do I have to change other settings on the carbs?
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helmutholderbenz
Originally posted by GSCafe View PostI think what posplayr is saying is "yes". Let me expand on this based on my own experience. Everything setting in a carb overlaps another setting. Main jet size is supposed to be the WOT tuning, but I've noticed that changing it will affect the mix curve as it were. For larger, say, not as much effect on idle, maybe, but as the needle starts to rise, there is more fuel than there used to be the higher it gets. But then you might still need to fiddle with your A/F screws to keep your idle/off idle in the sweet spot. Before you know it, you're starting over.
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GSCafe
Originally posted by helmutholderbenz View PostThanks GSCafe! I'm not sure if I should even do anything. the bike is really running good. Any bike if you put the coals to it in a tall gear is going to have to wind up a bit right? I mean its not a bog really, kinda sounds like a quadrajet carb if you know what I mean. If I'm in the rpms the bike really gets it. the only real reason I wanted to try the 135s is because the table guidelines say with my mods I should go up in jet size 9 to 12 sizes larger than stock. stock for my bike is 117.5 + 12=130s. I'm using 140s
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helmutholderbenz
Some people will ask a question they already know the answer to to get a conversation started. I want to talk about my bike and what I'm doing to it and how I can make it better. I come to this forum to get help and answers from people I believe have similar interest but most people in this forum get mad at the new guy for asking questions. I thought thats what a live forum was for, to ask questions, give answers and just shar the love we have for these bikes. You guys got me scared to even ask a question. Think about that! Helmut
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GSCafe
Originally posted by helmutholderbenz View PostSome people will ask a question they already know the answer to to get a conversation started. I want to talk about my bike and what I'm doing to it and how I can make it better. I come to this forum to get help and answers from people I believe have similar interest but most people in this forum get mad at the new guy for asking questions. I thought thats what a live forum was for, to ask questions, give answers and just shar the love we have for these bikes. You guys got me scared to even ask a question. Think about that! Helmut
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helmutholderbenz
I appreciate you GSCafe, and everyone who has taken time to answer my questions even though you've heard them asked countless times before. Thanks, Helmut
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GSCafe
Originally posted by helmutholderbenz View PostI appreciate you GSCafe, and everyone who has taken time to answer my questions even though you've heard them asked countless times before. Thanks, Helmut
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