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1978 gs 1000 e sputters at 3/4 to full throttle

  • Thread starter Thread starter lrgguy
  • Start date Start date
L

lrgguy

Guest
Ok I have had these carbs out 3 times now in the last couple month , carbs were taken appart completely and soaked for 30 hrs , blew out poked at every hole crevis crack etc stock original exhaust and air box , fuel screws turned out 7/8 turn . Air mixture screw turned out 2 turns . Bike has always ran good until you crack the throttle ...
I find in every gear from 3/4 to full throttle the bike stutters oh so lightly .. to me I feel it sounds as though it wants more fuel .. intake orings have been replaced and air box is air tight .. no leaks in the stock original exhaust !!
Any suggestions would be appreciated ...
 
Try turning the air screws in 1/2- 3/4 of a turn a little at a time until it runs correctly.
 
I have been told by a few senior members here . For the fuel screw to be 7/8 to 1 turn out and double that on the air screw ..and thats worked for them on the exact same yr and model
 
And doing that made mine run like crap. At least TRY what I am suggesting or live with it running like crap. It is your bike, do as you wish.
 
lrgguy said:
Any suggestions would be appreciated ...
Click to expand...

Can you get to the choke lever while in that 3/4-full throttle zone? If you can, try pulling a bit of choke as it is stuttering and see what happens. If it gets worse you are rich, if it gets better you are lean. What main jets are you running? At 3/4+ throttle you should be solidly on the main jet and may need to go up (or down, depending on the choke test) one size.

You could also try GSX1000E's suggestion because it is quick and easy. I would hesitate to mess with the bottom end jetting in a quest to solve a top end problem, but it is easy enough to try it out and go back if it doesn't improve things.


Mark
 
Ill give both a try tonite when home .. thx guys
As for the main jet size , my eyes are shot even teied using a magnifier . Couldnt make out the size .. but was told by the original owner he never messed with any of the jets , he was the only owner of the bike so im trusting him that its all stock ..
 
lrgguy said:
Ill give both a try tonite when home .. thx guys
As for the main jet size , my eyes are shot even teied using a magnifier . Couldnt make out the size .. but was told by the original owner he never messed with any of the jets , he was the only owner of the bike so im trusting him that its all stock ..
Click to expand...

That does sounds reasonable, but one of standard rules is to never believe the PO and check for yourself

Ed sums that up as "to measure is to know"
 
Like I said .. I even used a magnify glass and I couldnt make out the size on the jet ... even asked my daughter and she couldnt make out what was stamped on the jet either ..tried adjusting air mix screw tonite on all four carbs . First tried going down to 1 3/4 turns on all and it was no improvement , then turned them all back to 1 1/2 . & it went a little worse !! . Turned them all back to 2 1/8 turns out & it pretty much is back to how it was to begin with !! Gunna yank the carbs tomorrow after work and check all jets again .. I had the tank and petcock off not to long ago and the tank looked clean .. the only other thing I can think of is crap has been sucked through and is plugging up a main jet ...
 
Did you count and record the number of turns your various adjustment screws were set at prior to destructing your carbs for cleaning? Did you set your float level and fuel level for each carb?
 
I sure did !! Fuel screw was 2 1/2 turns out and air screw was 2 turns out .. didnt understand why the fuel screw was out so much .. should only be 1 turn .. thats what its at now !!
 
Pulled my carbs again tonite pulled every jet , cleaned again .. 4 th time set fuel screw to 1 turn out , put air / fuel screw to 1 1/2 turns out .. bike fired right up idled fine ....
Took it for a ride and same thing 6000 rpm 3/4 throttle every gear , bike stumbles , parked bike and adjusted all air fuel mixture screws to 1 3/4 turns out and same thing ..... frustrated !!!!!
Pilot jet size 15 .. main jet 102.5 in all 4 carbs .. I do believe they are stock??
 
Last edited:
Stock jetting is:

Main Jets 95
Pilot Jets 15
Jet needle clip 3rd groove

Your mains are 3 full steps above stock. Your fuel mixture screws are for the low speed circuit. I think you might be too fat on top. How high above sea level do you live? That would play into it as well, especially if you're elevation is above 2000ft.

Also, how healthy is your ignition system? Have you checked the voltage to your coils? How are your plugs? Etc....
 
Last edited:
lrgguy said:
Took it for a ride and same thing 6000 rpm 3/4 throttle every gear , bike stumbles , parked bike and adjusted all air fuel mixture screws to 1 3/4 turns out and same thing ..... frustrated !!!!!
Click to expand...

Did you try the choke test?


Mark
 
Yes I did in 2 nd 3 rd and 4 th gear ... no change still sputters at that rpm and 3/4 to full throttle ..
My boss use to have a couple suzuki's back in the day , he suggested checking the points ? I dunno if that would cause this ??
To me it feels like its wanting gas and the right amount is just not being fed to the engine ... lets just say after yanking these carbs 4 or 5 times now , I know them inside and out !!
 
New plugs ... bought 2 weeks ago .. as for altitudes im on ontario canada , its pretty flat here !
When I purchased the bike there was no cover for the air box and I fabricated one een before running the bike , looks original !! Could the previous owner had that air box cover off for a reason ?
 
The previous owner did have the fuel screws ( below flaot bowl bottom of carbs ) 2 turns out which I thought was just crazy !!! I guess for the heck of it , ill remove the air box cover and take it for. ride and see how it behaves , if that doesnt do anything ill try backing those fuel screws out to 2 turns and see hiw that effects things ... im sure my fuel consumption will change dramatically ....
 
No I didnt !! As I have a 83 gs 650 and it wouldnt run if I removed the air box cove . So I just fabricated one for this 78 gs 1000 before I even started running it .. I think ill give it a shot ! Nothing to lose ...
 
Well, now you know

Somebody changed the jets
The PO lied to you

Your low speed circuits are rich, fuel 3/4, air 1 1/2 to start, 95 mains as noted above

Sputtering most likely due to overly rich jetting

But, you should check your points. Clean, new? New condensors? Properly gapped and timed? Pull the timing cover, and check for arcing in the dark
 
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