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

[lrgguy]

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 ?

[rudeman]

Did you run it w/o the cover?

[lrgguy]

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 ....

[lrgguy]

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 ...

[Big T]

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

[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 ...

[mmattockx]

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 ?

[mmattockx]

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

[OldVet66]

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.