1977 GS400 Running Lean

[gorillafan208]

Hi, everyone, I purchased a 1977 GS400 back in May and have been slowly working to get it back to tip top shape. I cleaned the carbs but had to drill out the pilot jets and could only find size 20 jets instead of the stock 22.5 for the BS34 carb. Because of this (and the pods on it, thanks PO) its running pretty lean, won't run without choke and likes to idle high. I ordered O-rings to replace on the intake boots, but when I took those off, I couldn't see any O-rings to replace, could anyone confirm that these 400s don't have intakeboot O-rings? I am just looking for advice on what I should do to fix this lean condition considering that the jets I do need are unavailble and the next size up is 30. I have checked the throttle cable, replaced fuel line and fuel filter, cleaned the tank, and messed with the idle adjustment which helped a bit but it still dies without choke. The gasket connecting the intake boot to the engine does look a bit beat up so I ordered a new one which could help making it lean. Can anyone think of anything else that I could do to make it run richer? Or if anyone has a pair of 22.5 N151.067 jets that they would be willing to sell let me know.

[Gorminrider]

Can anyone think of anything else that I could do to make it run richer?

You have to know your valves and pistons are providing suction and that carbs are sealed at the engine-side first. Taking the pods off and putting your hand over the carb mouth or measuring manifold vacuum might inform as to leaks..

I ordered O-rings to replace on the intake boots, but when I took those off, I couldn't see any O-rings to replace,

Did you know the seals were leaking in the first place?and if O-rings don't exist for this bike, how were you able to order them?

This isn't a real solution but it might "inform"...Try covering parts of the pods to restrict air. You will probably need to cover a lot of their area to see any effect...air is compressible so it'll just go faster through the uncovered part to make up the demand of the pistons but at some point the pod material should restrict it...

[gorillafan208]

You have to know your valves and pistons are providing suction and that carbs are sealed at the engine-side first. Taking the pods off and putting your hand over the carb mouth or measuring manifold vacuum might inform as to leaks.. Did you know the seals were leaking in the first place?and if O-rings don't exist for this bike, how were you able to order them?

This isn't a real solution but it might "inform"...Try covering parts of the pods to restrict air. You will probably need to cover a lot of their area to see any effect...air is compressible so it'll just go faster through the uncovered part to make up the demand of the pistons but at some point the pod material should restrict it...

I did not know they were leaking, but looking at the "carb and fuel" part of the forum it said to replace the o-rings on the boots because they are usually crapped out. I just ordered Suzuki intake boot O-rings as I assumed that they would be interchangeable. I took off the boots and there was no O-ring or a place for an O-ring, but I can post a photo of them too. I will try taking the pods off and putting my hand over the carb mouth, thank you.

[Nessism]

Please check the Newbie Mistakes thread linked in my signature to see if anything hits close to home.

Realize that the bike won't run for crap with pods and standard jetting. Pods drastically change the bikes jetting needs.

The early GS bikes like yours don't have intake boot O-rings. Check Partzilla (or similar) if you haven't already, since the parts fishe shows what parts are involved. One way or another, you are going to have to figure out how to get the boots to seal properly, otherwise, the idle will never be stable.

[Rich82GS750TZ]

Unlike the 4 cylinder models w/ intake boots that bolt onto the head, the 400 appears to not have on o-ring against the head but has:

boot /PIPE, INTAKE B,XB - # 22,

an INSULATOR B,XB - # 21,

and a GASKET, CARBURETOR B,XB - # 20

-- All NLA.

[rphillips]

Dang, those pictures look like 2 CV carbs. Did the GS 400's get CV's that far before the bigger bikes?

[Rich82GS750TZ]

All I know is what's on the fiche at partshark.com. Can't/won't know until/unless the OP posts pics.

[gorillafan208]

Dang, those pictures look like 2 CV carbs. Did the GS 400's get CV's that far before the bigger bikes?

They are CV BS34 carbs, pretty neat except for the fact that mine apparently has unique jetting and is impossible to find the pilot jet...

[gorillafan208]

Please check the Newbie Mistakes thread linked in my signature to see if anything hits close to home.

Realize that the bike won't run for crap with pods and standard jetting. Pods drastically change the bikes jetting needs.

The early GS bikes like yours don't have intake boot O-rings. Check Partzilla (or similar) if you haven't already, since the parts fishe shows what parts are involved. One way or another, you are going to have to figure out how to get the boots to seal properly, otherwise, the idle will never be stable.

Oh I know, I ordered the replacement gaskets for the intake boots, not even sure if they are broken, but I am just trying to replace everything that might be messing this up. I know with pods it won't run well with stock jetting, but for the pilot jet I only have the choice between size 30 and size 20. I am using 20 right now and it runs like crap, and I am going to see how it runs with size 30. Let me know if you have any other advice, I am trying my best not to be one of those clueless people who misses every obvious problem.

[rphillips]

Just looking at pictures of Mikuni pilot jets. The pilots for CV and VM carbs sure look a lot the same, Wondering if VM pilots would work in CV's, Plenty of 22.5's for the VM's... Also just looking found the "77" GS750, with VM carbs use 22.5 pilots, not that it means anything, just interesting.

[gorillafan208]

I accidentally did buy 22.5 VM jets cause I saw the 22.5 and the same dimensions and thought they were the CV ones so i definitely could try them out

[rphillips]

No doubt a 22.5 hole in a VM jet is the same size as a 22.5 hole in a CV jet, You'd think "IF" all else fits, it got to work.

[gorillafan208]

I will try it out tonight!

[gorillafan208]

Put in the VM jets and they did indeed work. I can start it without the choke now but I have to hold the throttle a bit open or it will die. Messed with the idle air adjustment screws but couldn't seem to get it. I'm hoping when I replace the intake gaskets it might help. Should I do a valve adjustment as well just to try and cover all my bases?

[Rich82GS750TZ]

…….. Should I do a valve adjustment as well just to try and cover all my bases?

Yes, should always verify valve clearance is in spec before attempting to tune carbs.