1979 GS1000E Jetting for stock intake and Delkevic megaphone 4-1

[Bob Koenig]

Hello I’ve searched the forums but was unable to come up with a definite answer. I have a 1979 GS1000 that I am placing a delkevic megaphone on. I am going to have the carbs out for a clean up and rebuild so I figured I may as well make my initial jetting changes while they are on the bench. The bike is a 1979 GS1000E with VM26s, stock air box, and stock internals. I will likely end up taking the DB killer out of the pipe but would like the ability to pop it back in for longer days, and leaving for work at 4am without bothering the neighbors. Delkevic says no jetting change is needed, but I have seen some on this forum that say that isn’t the case. I am planning on going to a 97.5 main and shimming the needle very slightly (0.030’’). Does anyone have any experience with this setup? Any advice is greatly appreciated.

I’d like to add that the bike currently runs well with the stock exhaust.

[storm 64]

Hi Bob, I think you'd be good going up one size maybe two main jet sizes. Since you're keeping your stock air box, you won't be needing to change your jetting to drastically. It's when you remove the air box and use the K&N style individual air cleaners is when you have to fiddle with the jetting more.

Cleveland, I'm here in Youngstown. Let me know if you need anything or want to meet up sometime. 👍

[rphillips]

Yep, just bolting on a 4 into 1 doesn't take much jetting, completely changing, or even modifying, the air intake system is a much larger concern. Just my opinion.

[GregT]

Try it stock first. The 26VM's are not very sensitive to changes in the exhaust.

Any major changes are usually dictated by local conditions - altitude etc.

[Grimly]

You'll want to keep the DB killer in, the megaphone is a noisy brute.
Not sold as road legal in the UK, rated as >104db on the website (with the baffle in place).
Having said that, I enjoyed using it for the first few days I had it on, but finally had to do something with it, as it was too bloody loud and really attracting too much attention, eventually of the wrong type.

[Bob Koenig]

Thanks for the advice so far gentlemen. I may leave the jetting stock, and see how it runs. Whatever I decide to do I will report back in this thread.

[salty_monk]

I had one on the 1100G. No Jetting changes needed other than winding the screws out a bit... I would be very surprised if you need anything more than a 5 bigger main jet and move the needle up a notch.