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

[lrgguy]

Ill take a look at the points tonight and try wrapping my head around checking the timing and points ... I read the hole thing on bikecliff about setting points and hooking up timing light , just cant wrap my heaf around it .. will take the cover off tonite and take another look tonite !! Thx

 

[lrgguy]

So what would you suggest the fuel screw and air fuel screws to be set at with the 102.5 main jets ? Perhaps this was why the PO was allowing more air into box , by having the cover removed ...

 

[Guest]

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 ..

Then you are certainly on the rich side on your mains.

New plugs ... bought 2 weeks ago .. as for altitudes im on ontario canada , its pretty flat here !

According to the interwebs Mississauga's average elevation is 450ft, so you certainly aren't very far above sea level. Not enough to affect jetting, anyway.

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

So what would you suggest the fuel screw and air fuel screws to be set at with the 102.5 main jets ? Perhaps this was why the PO was allowing more air into box , by having the cover removed ...

You are confused regarding the carbs and what circuit does what. There is nothing you can do with the air and fuel screws to compensate for overly rich mains. The screws mostly affect the pilot circuit and small throttle openings. If the mains are too big, and it looks like they are, you should be changing back to stock jet sizes and then sorting it out.


Mark

 

[lrgguy]

And if I wanted to eliminate the air box and go with pods ? Wouldnt my main jets need to be bigger ?

 

[Guest]

And if I wanted to eliminate the air box and go with pods ? Wouldnt my main jets need to be bigger ?

Yes, usually 4-5 steps bigger than stock along with bigger pilots jets and possibly a new needle.


Mark

 

[Guest]

I had the same problem with my '78GS1000E while tuning for 4-1 pipes and pods (Dynajet stage-3 jet kit). It was definitely too rich. The stutter from 3/4 throttle to red line was a plug fouling. It took an extremely humid day to show itself, one plug completely fouled and I was running on three cylinders. When you lightly seat the pilot fuel needle screws in front of the float bowls you can you see the tips of the needles in the throat of the carburetor? If They stick up into the throat of the carburetor at all, the seats are damaged and that changes the tuning game a lot. Normal seat, the tips of the needles are just visible below the little hole and it takes a flashlight to see them. If they come above this point, they have been jammed in too tight and made the seat larger requiring the adjustment to be further in to emulate proper adjustment. Mine were real bad, I ended up putting the carburetor bodies in the recycle bin. Luckily I had a virgin set that was in perfect shape, paint still on the screws from the factory. I could never get that old set of carburetors to tune right. The new set dialed right in. I did discover that the pilot fuel screw setting moves the air screw setting for highest idle back and forth depending on the setting and that when properly set, the air adjust for highest idle is real close to two turns out. My initial setting for the pilot fuel screws for my large main jet size started at 1/2 turn out. they were spot on tweaked out the width of my screwdriver blade from 1/2 half turn. All the air adjusts for highest idle were real close to 2 turns out. I believe with smaller main jets the pilot fuel screws are going to need to be further out, but that might give you a method for determining the proper setting. When you adjust the pilot fuel screw, don't move it more than the width of your screwdriver blade for each adjustment (each adjustment will require an air adjust for highest idle until you hit the sweet spot). That screwdriver blade width was the difference from my new carburetors stuttering at low speed barely opened throttle (too lean at 1/2 turn) to being spot on and smooth.

 

[lrgguy]

Thx so much . I messed with it a little more tonite and its running ALOT better . Still does a little stuttering but just for a few seconds then it stops .. still at 6000 rpm . Removed the air box cover for a little test .and the bike runs really good from 1/2 to full throttle that way . But anything below half throttle the bike loses its balls ... . Going to try it now with air box cover on but not 100% sealed ! But definetly with everyonea suggestions so far shes running much better ..
Thx all : )

 

[Big T]

Just one more person who asks for advice, then ignores it

I'm out

 

[lrgguy]

Just one more person who asks for advice, then ignores it

I'm out

What r u talking about ? Been off here for a few weeks .. working like crazy .... picked up 4 new size 95 main jets .. just have to put them in ...

 

[rudeman]

That's a good move. Also make sure the pilots are #15 (STOCK) and the jet needles clips are set on the middle groove.

That's how your carbs were set when the bike was new. As far as setting the pilot and mixture screws is concerned, refer to the outstanding VM carb rebuild instructions here. If you haven't already, make sure the valve clearances are right prior to attempting to sync your carbs.

 

[chuck hahn]

Use the baseline settings for the pilot and mixture screws. As you can see by my signature, I have GS 1000s and I know where mine are liking things. Here is what I have found to work on the VM carbs..which yours should have.

PILOT SCREWS ( BOTTOM ONES BY THE BOWLS ) 7/8 OUT And you LEAVE THEN ALONE after setting them!!!!!!!!!!!!!! HANDS OFF!!!!!

MIXTURE SCREWS ( ON THE SIDE OF THE CARB THROATS ) 2 OUT AS THE START POINT. Then you do ALL of the FINE TUNING from the mixture screws...period. Turning the mixture screws IN will RICHEN the mixture. OUT will LEAN the mixture. Make all adjustments NO MORE THAN 1/8 turn at a time and give the engine a few seconds to reequalise itself after making adjustments.

 

[chuck hahn]

And the sync can be affecting the response as well.

 

[rudeman]

And the sync can be affecting the response as well.

More so off idle than at 1/2 to WFO.

Good advice from Chuck re: fine tuning the mixture using ONLY the mixture screws. FYI: The pilot screws on my EN were set at 3/4 out. There is some slight variation on that setting apparently. Record your current settings before changing them, especially if the bike is running.

The process is not easy but it is rewarding when you get her dialed in. Enjoy it and learn from it.

 

[chuck hahn]

Rudeman..the 3/4 was the factory setting far as any information I have ever been able to gleen. This, however, was at the very edge of being TOO lean because of the 70s EPA bullcrap back then.

The 7/8 is just a slight slight bit richer.but not too rich from what I have been able to tell from how mine react. And my feeling is that I would rather be just a tad richer than too lean for the health of the valve train!!

 

[Spyderman]

Suzuki Service Manual: October 1979
GS1000
1979
Model: C

Idle Speed: 900 - 1100 rpm
Carb: Mikuni VM26SS
Id no: 49020
Bore size: 26mm (1.023")
Float height: 24.0mm +/- 1.0 (0.94" +/- 0.04)
Fuel level: 4.0mm +/- 1.0mm (0.16" +/- 0.04)
Air screw: PRE-SET (DO NOT DISTURB)
Cut away: 1.5
Jet needle: 5DL36-3
Pilot Screw: PRE-SET (DO NOT DISTURB)
Pilot Air Jet: 1.2
Pilot Jet: 15
Pilot Outlet: Not specified
Needle Jet: O-2
By-pass: Not specified
Main jet: 95
Main Air Jet 1.5
Throttle Cable Free Play: 1.0 - 1.5mm (0.039"-0.059)

1978 GS1000 (VM carbs)



Pilot Air Jet: 1.2
Pilot Jet : #15
Cut-a-Way: 1.5
Jet Needle: 5DL36-3
Needle Jet: O-2
Main Air Jet: 1.5
Main Jet: #95
Float Height: 23-25mm
Fuel Level: 3-5mm


here are your stock factory carb settings
for the pilot circuit follow what chuck hahn has outlined for the pilot screws and the mixture screws



these carbs have 3 circuits to then
Pilot circuit = 0 to 1/4 throttle
needle jet and jet needle = 1/4 to 3/4 throttle
main jet = 3/4 to wide open throttle

it would seem to me that perhaps you are having a problem with the main jet circuit by what you are describing
i would take the carbs apart confirm that they are clean and check all your settings and jet sizes if they are all correct

then perhaps it is a fuel starvation problem at that throttle setting.
i had this issue with my 78 1000 the petcock was suppling enough fuel but the smaller fuel line and low flow fuel filter was causing fuel starvation at above 3/4 throttle the solution was slightly larger fuel line and a high flow fuel filter
i use a 95 CBR 900 RR fuel filter on my bike emgo part # 14-34481
i had 3/8 fuel line on it and i now have 7/16 fuel line and when i made this change i had no more problem with it cutting out above 3/4 throttle

 

[lrgguy]

Thank you all !!!today I got a little free time . Installed the new front break pads and the new air filter .. due to more work in the am didnt yank the carbs to throw in my 4 new #95 main jets . All my pilot jets are 15's btw .. why the previous owner had 3 - 102.5 main jets and 1 - 95 main jet makes no sence .. oh through in 4 new spark plugs tonite too .. noticed the bike was running a little better after new plugs ... work crazy hrs again sunday through to friday so maybe next weekend will have some more free times to yank the carbs again ..