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Free flowing mufflers, stock intake, (rejetting)
- djturnz
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I had a float cause some overflowing into my airbox earlier this year, so I need to get into them anyway to settle that. I was figuring on buying rebuild kits for all 4, and figuring out the jetting while I'm in there.
I wanted to read up on this and get as much info as I can. I read through some of the longer threads last night and this morning and now I want to light my bike on fire and say never mind. I've had them off only once before to clean them up when I first got the bike and it was a horrible act of contortionism to get them in place between the airbox and the motor. After reading about all the trial and error and minor changes to get it right, the thought of pulling the carb rack a dozen times to tweak them and reinstalling has me going insane.
So I've got some questions to hopefully get me started off right.
1. First thing, am I shooting myself in the foot trying to tune when it's 40 degrees or colder like it is in PA right now? I'm thinking I'll get it real good when it's 40, then it will run horribly when it's 95+.
2. I've seen charts or lists for various carbs (usually single carb units) that say something to the tune of: For each of the following increase one jet size, then back down one. Then it lists like 5 different mods that you would need to jet for. The idea being if you did 3 mods, you'd only increase by two sizes. 4 mods is 3 sizes. 1 mod is no change but tweak the needle or something. It was for a single carb v-twin, so I don't put much stock in those exact numbers for a 4 carb, inline 4. But I was hoping at least for a starting point and maybe some pointers on fine tuning. I guess I basically have an almost free flowing exhaust and more or less stock air box. I do have the air box hole exposed (KZ COP seat, set back a bit), so it's no longer pulling air under the seat. When I first did that, I noticed a roar from the intake, similar to when I put a cone filter on my car back in the day. So I don't know if that makes it flow better on the intake side or not.
3. I'd rather not buy a kit with every jet under the sun. I don't ever plan to go to pods. Breadbox MAYBE someday, but not pods. I was hoping to buy what I think I need, and maybe a size or two around thoses sizes for fine tuning.
4. Not the original owner, so I don't know that whats in there is stock. The mufflers I am replacing aren't KZ originals, but they are the JCWitney OEM replacements and just as restrictive and quiet as factory.
2" diameter, 8" body length, 12" OAL. By my calculations, the 1/2" all thread blocks 1 sq. in. of the 3.14 sq. in. area of the pipe, leaving 2.14 sq.in. Which is still much more area for the exhaust to move than the previous mufflers. I don't know how this is releavent, but I had my 10 year old figure it out as an example of a practical use of the math he has to learn.
1982 KZ750 (4) LTD
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- Stazi
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82 KZ1000-K2 LTD
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- sbc1320
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1980 KZ1000 LTD-B4(MK II engine) - Progressive suspension, MTC pistons, Dynojet Stage III, all wear items replaced, WFO paint scheme(1978), etc..
Past bikes- 2 1976 Kz900's, 5 1975-76 Honda CB750's, Honda 500 -4, Honda 250, Honda 125, Honda 100, Suzuki RM 250, Honda XL350, Kawasaki KLR 650, etc..
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- djturnz
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I plan to get the motor nice and hot Friday and see how it runs. I'm assuming the fact that it ran like crap was the 30 seconds of choke I gave it before riding the 3 or 4 blocks home. But since everybody always talks jetting, I wanted to get some background on it ahead of time so I could look at it some on Friday when I try not to freeze my tail off riding it. I'll also see if I can get my son to take some video for an audio comparison. I did take a before video.
1982 KZ750 (4) LTD
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- sbc1320
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1980 KZ1000 LTD-B4(MK II engine) - Progressive suspension, MTC pistons, Dynojet Stage III, all wear items replaced, WFO paint scheme(1978), etc..
Past bikes- 2 1976 Kz900's, 5 1975-76 Honda CB750's, Honda 500 -4, Honda 250, Honda 125, Honda 100, Suzuki RM 250, Honda XL350, Kawasaki KLR 650, etc..
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- bountyhunter
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Because the jets, needles and needle taper are all designed to exactly match and track the airflow as the RPM's rise and the carb slide raises. Changing the backpressure on the exhaust changes the flow characteristics of the whole system. I have no idea what, if any, changes will be caused by the new mufflers but you will probably be able to know if you ride it. A lean condition will make the plugs turn white and make it balky at throttle opening, it will feel weak on acceleration.djturnz wrote: I completely understand why pods or similar intake mods need jet changes. In theory, the exhaust pipes are isoalted from the carbs by the valves, which is why I have no clue why changing pipes requires carb changes, but everything I've ever read online says it does.
1979 KZ-750 Twin
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- guitargeek
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- Elitist, arrogant, intolerant, self absorbed.
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I'm looking at turndowns on the ends, and I might lollipop it like yours.
1980 KZ750-H1 (slightly altered)
1987 KZ1000-P6 "Ponch"
1979 GS1000 "Dadzuki"
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- djturnz
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1982 KZ750 (4) LTD
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- Stazi
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82 KZ1000-K2 LTD
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- sbc1320
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Stazi wrote: The air is denser in winter so by summer, when the air gets warmer and thins out, it'll make the bike run richer than how it was tuned in the winter.
Yeap low humidity is thinner air and not so heavy or soupy. More air in and more fuel needed. Just tune it for the winter and let it eat all year round if you want to.
1980 KZ1000 LTD-B4(MK II engine) - Progressive suspension, MTC pistons, Dynojet Stage III, all wear items replaced, WFO paint scheme(1978), etc..
Past bikes- 2 1976 Kz900's, 5 1975-76 Honda CB750's, Honda 500 -4, Honda 250, Honda 125, Honda 100, Suzuki RM 250, Honda XL350, Kawasaki KLR 650, etc..
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- sbc1320
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djturnz wrote: How much will the cold air now effect my "testing"? That's a big concern for me. I'd like to get this dialed over winter so when the riding season is back,I can just ride.
Bike will make better power with the cold air also. Mine is loving it.
1980 KZ1000 LTD-B4(MK II engine) - Progressive suspension, MTC pistons, Dynojet Stage III, all wear items replaced, WFO paint scheme(1978), etc..
Past bikes- 2 1976 Kz900's, 5 1975-76 Honda CB750's, Honda 500 -4, Honda 250, Honda 125, Honda 100, Suzuki RM 250, Honda XL350, Kawasaki KLR 650, etc..
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- djturnz
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I was going to use 2" copper 45° elbows as turn outs and polish them up like brass. I decided not to, but feel free if you think it would look right on yours.guitargeek wrote:
I'm looking at turndowns on the ends, and I might lollipop it like yours.
1982 KZ750 (4) LTD
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