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Carb Main Jet Tuning

  • Thread starter Thread starter codonne81
  • Start date Start date
C

codonne81

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Hey guys. Trying to figure out a carb tuning issue. I have a 1980 gl 1000. Fully cleaned carbs, valve clearance good, none leaky air box, new intake orings, intake boots ect. I have recently installed a new 4 into 1 yoshi style exhaust system and opened up the back of airbox and dropped in a k&n, rejetted the carbs with a dynojet stage 3. Bike runs really well through all of the rpm range in 1st and 2nd gear. once i get into 3,4&5 she stumbles and bogs at 6k. assuming im still rich, just curious if the richness is load dependent and why its not noticed in the first 2 gears. Mains are DJ165.
Any help would be greatly appreciated
Thanks,
Casey
 
Did you sync the carbs? Typically a stage 3 jet kit is for pods and a pipe. Seems to me that the mains are probably a bit large for what you have installed.
Where did you set the needles when you installed the jet kit. How do the spark plugs look? Need some more information.
 
The needles are set to 3 from the top. Did the sync after the jet change. My airbox is pretty much wide open on the backside of the box, i left the side covers and bottom to protect the filter from rain. Ill grab a pic of my airbox tomorrow. I was told by a local mechanic with a pretty long history with suzukis that running a stage 3 kit with the new set up would be fine. I haven't done a plug chop yet. I was hoping to gather some info on the situation first. Im pretty sure she is rich on the main circuit. The way i learned to tune carbs was you need to establish your mains before you can tune the midrange, low end and idle/low rpm. Suggestions? Drop the main down? Am i stuck with the stage 3 since i have the main air corrector in?
Thanks for the quick response!
Casey
 
almarconi said:
Did you sync the carbs? Typically a stage 3 jet kit is for pods and a pipe. Seems to me that the mains are probably a bit large for what you have installed.
Where did you set the needles when you installed the jet kit. How do the spark plugs look? Need some more information.
Click to expand...

synching the carbs will have no effect whatsoever at 6k rpm
 
codonne81 said:
The needles are set to 3 from the top. Did the sync after the jet change. My airbox is pretty much wide open on the backside of the box, i left the side covers and bottom to protect the filter from rain. Ill grab a pic of my airbox tomorrow. I was told by a local mechanic with a pretty long history with suzukis that running a stage 3 kit with the new set up would be fine. I haven't done a plug chop yet. I was hoping to gather some info on the situation first. Im pretty sure she is rich on the main circuit. The way i learned to tune carbs was you need to establish your mains before you can tune the midrange, low end and idle/low rpm. Suggestions? Drop the main down? Am i stuck with the stage 3 since i have the main air corrector in?
Thanks for the quick response!
Casey
Click to expand...

did you get 2 sets of main jets with the DJ kit? most kits (i think) come with 2 different size jets. if so have you fitted the larger set of the 2 sizes?
 
stock main jets are 115 i believe on your bike, DJ 165 mains are equivalent to Mikuni 155 mains. that sounds far to high for the mods you have done. i would say you need to drop them to at least 135(Mikuni size)
 
synching the carbs will have no effect whatsoever at 6k rpm
Click to expand...

I was trying to get an idea of what maintenance had been done or not done to the bike.
 
To answer the original question, yes, it is load dependent. It might not be noticed (as much) in the first two gears because there is not enough load on the engine. I use a wideband (sniffer) when I tune my carbs and I generally ignore the first two gears and concentrate on the readings from the upper gears (with the assumption that the jetting is close enough for fine tuning the mains, of course).
From my personal experience the main jets supplied in the Stage III kits are too large.
 
the bike was bought from a retired military vet! He said he took good care of it. Once i bought the bike i checked compression. (120-115 across) Oil change, full carb strip dip and clean up. Adjusted the valves, replaced the plug caps and plugs, several wire mods, including the coil mod. the bike has 17.5k on it.
Initially i put the DJ 170's in and that was to rich dropped down to the DJ165's and still presented with the same symptoms of stumbles and bogs above 6k.
If i drop to smaller jets do i need to remove the main air jet corrector?
 
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