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4 to 1 exhaust jetting
- Prairie rider 29
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13 Oct 2015 01:40 #694366
by Prairie rider 29
4 to 1 exhaust jetting was created by Prairie rider 29
Hey guys. I just put a Mac 4 to one exhaust on a 81 csr 650. It's running a bit lean over 2000 rpms. I was wondering if anyone else has already done this and if so where to start when rejetting.
Thank you!
Thank you!
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- GPzMOD750
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13 Oct 2015 02:31 #694367
by GPzMOD750
Replied by GPzMOD750 on topic 4 to 1 exhaust jetting
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- redhawk4
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13 Oct 2015 05:24 - 13 Oct 2015 05:28 #694396
by redhawk4
1978 KZ1000A2 Wiseco 1075 kit
1977 KZ650B1
1973 Triumph Tiger TR7V
1968 BSA Victor Special 441
2015 Triumph Thunderbird LT
1980 Suzuki SP400
Old enough to know better, still too young to care
Replied by redhawk4 on topic 4 to 1 exhaust jetting
Usually a 4-1 exhaust will make it run leaner so you'd expect to change jets. It's virtually impossible to advise anyone else as to what jets they need exactly with all the variables in bike setup and altitude On my KZ650 stock jets work with my V&H because I'm at 5.000 feet. Just an exhaust doesn't make a huge difference, I'd try going up one size on the main jets and then checking you plugs. What was you mixture like before the changes to the exhaust, if it was ok then, one size bigger is likely all you need. Some bikes come weak from the factory so even at stock you could probably use on size bigger, in which case you might try 2 sizes bigger.
You say you are weak at 2,000 rpm what are the symptoms and how much throttle are you applying, it could be your pilot jets are too small too.
You say you are weak at 2,000 rpm what are the symptoms and how much throttle are you applying, it could be your pilot jets are too small too.
1978 KZ1000A2 Wiseco 1075 kit
1977 KZ650B1
1973 Triumph Tiger TR7V
1968 BSA Victor Special 441
2015 Triumph Thunderbird LT
1980 Suzuki SP400
Old enough to know better, still too young to care
Last edit: 13 Oct 2015 05:28 by redhawk4.
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- Tyrell Corp
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13 Oct 2015 06:30 #694407
by Tyrell Corp
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
Replied by Tyrell Corp on topic 4 to 1 exhaust jetting
weak at 2,000 rpm what are the symptoms and how much throttle are you applying
Yes, it is load and speed.
Try lifting the needles a notch.
Yes, it is load and speed.
Try lifting the needles a notch.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
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- Nessism
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13 Oct 2015 07:02 #694412
by Nessism
Replied by Nessism on topic 4 to 1 exhaust jetting
Is the stock airbox still in place? Typically, only minor jetting changes are needed when a header is installed by itself. Pods on the other hand, whether by themselves and/or in conjunction with exhaust system changes, require more extensive jetting correction. Best bet is to purchase a jetting kit from either Sigma or Dynojet, particularly if you are using pods.
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- Prairie rider 29
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14 Oct 2015 13:21 #694568
by Prairie rider 29
Replied by Prairie rider 29 on topic 4 to 1 exhaust jetting
Thank you all for the info. I will give one of the jet kits a try. Yes, it still has the original air box. It was always a tad bit lean running.
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- redhawk4
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14 Oct 2015 19:37 - 14 Oct 2015 19:43 #694612
by redhawk4
1978 KZ1000A2 Wiseco 1075 kit
1977 KZ650B1
1973 Triumph Tiger TR7V
1968 BSA Victor Special 441
2015 Triumph Thunderbird LT
1980 Suzuki SP400
Old enough to know better, still too young to care
Replied by redhawk4 on topic 4 to 1 exhaust jetting
If you are running the original air box then I would suggest you would only need to go up one size on the mains, the pilot should be fine. I have a V&H 4-1 on my 77 KZ650B1 and run stock jets and it works fine, but I am at altitude so normally would be jetted down one size. I have the VM24 carbs, i expect yours are the later CV carbs. Is everything clean in your carbs if it was running a bit lean any way? although a lot of the later bikes were set up pretty lean because of the emissions standards of the day, which were not an issue in 1977.
I'm personally a little wary of some of the jet kits, because they are rather one size fits all. I tend to double check what's in there and then just buy the individual jets one size up, or whatever I guess will work and go from there, sometimes there's some trial and error, but most times if it's running pretty good already only small changes are needed.
I'm personally a little wary of some of the jet kits, because they are rather one size fits all. I tend to double check what's in there and then just buy the individual jets one size up, or whatever I guess will work and go from there, sometimes there's some trial and error, but most times if it's running pretty good already only small changes are needed.
1978 KZ1000A2 Wiseco 1075 kit
1977 KZ650B1
1973 Triumph Tiger TR7V
1968 BSA Victor Special 441
2015 Triumph Thunderbird LT
1980 Suzuki SP400
Old enough to know better, still too young to care
Last edit: 14 Oct 2015 19:43 by redhawk4.
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