Quick question: 1978 GS1000 Carbs

[mattfeet]

Hey there -

So, I'm installing my Dynojet Stage III kit on my 1978 GS1000 with K&N pods and Motogpwerks 4-1 and no internal modifications. I have already 100% disassembled my carbs, ultrasonically cleaned them multiple times, blew compressed air through all passages, and replaced all gaskets and O-rings.

Few questions:

1) Do I reuse any of the stock needle washers or only the metal one that comes with the DJ kit?

2) There was a supplied drill bit. Do I use that to drill out the metal slide lift disc in each carb? If so, which hole(s)?
3) Im starting at the base settings as shown on the DJ spec sheet (138 main, clip 2nd from top, washer above, 2.5 turns out). Is this a good place to start or should my first setup be slightly different?

Thanks,
Matt

 

[tom203]

Me confused - don't you have VM style carbs?

 

[Steve]

I am confused, too. :-k

A '78 1000 should have VM carbs which don't have a "metal slide lift disk".

Unless your terminology is off a bit.

Let's start at square one: are the tops of your carbs a bit domed and held on with three screws, or are they flat and round, held on with four screws? Compare with the pictures:

VM carbs (typical on a '78):

BS carbs (CV-type, typical on '80 and newer bikes):

.

 

[Sandy]

Hey there -

So, I'm installing my Dynojet Stage III kit on my 1978 GS1000 with K&N pods and Motogpwerks 4-1 and no internal modifications. I have already 100% disassembled my carbs, ultrasonically cleaned them multiple times, blew compressed air through all passages, and replaced all gaskets and O-rings.

Few questions:

1) Do I reuse any of the stock needle washers or only the metal one that comes with the DJ kit?

2) There was a supplied drill bit. Do I use that to drill out the metal slide lift disc in each carb? If so, which hole(s)?
3) Im starting at the base settings as shown on the DJ spec sheet (138 main, clip 2nd from top, washer above, 2.5 turns out). Is this a good place to start or should my first setup be slightly different?

Thanks,
Matt

Sounds like you have a kit and instructions for the CV carbs, not the VMs that should be on the '78 - '79. ' 80 had the CV carbs.

 

[rudeman]

There really is no need for a jet kit if you have VM carbs (78-79 GS1000). All the necessary parts to get her dialed in are available through SUDCO. It's a lot of work but it's well worth the time spent getting it right.

 

[Guest]

The supplied washers are shims if you need them in addition to the stock nylon washers. I ended up using the 142 main jets, jet needles third clip from top starting the pilot fuel screws at 1/2 turn out and air screws near 2 turns when adjusted. The pilot fuel screws had to be tweaked out slightly but very little to get rid of a low speed stumble. I never used the drill that I can remember. The Dynojet needles are better than stock for transition, the kit is definitely worth it.

 

[mattfeet]

Got everything back together and on the bike. Even at baseline settings she runs worlds better than before. My goodness. I have VM carbs, as shown in top picture.

I think my terminology was a bit off. I was describing the thin metal disc (approx. 3/4" dia) that covers the needle assembly. There are 3 holes that form a triangle. The lift return hole then 2 screw holes. I read somewhere that people drill out the lift return hole to improve throttle response. I ended up not drilling it out and felt that the response is more than adequate as-is.

 

[Steve]

Your "throttle response" is dictated by the speed of your right wrist. The drilling that is suggested is in the VACUUM slides on the CV-type carbs on the newer bikes, not your mechanically-operated slides.

On your carbs, the throttle cable pulls on a rod that goes to all four carbs. Each of the carbs has a bellcrank that bolts to that rod, so that when the cable is pulled, the rod is twisted and all the bellcranks lift on all the slides. Very simple, but needs to be done smoothly to prevent fuel starvation.

The vacuum-operated slides on the CV-type carbs are not the throttle assembly, they are actually more of a variable venturi. The throttle is actually the butterflies just downstream of the slides. As the throttle is opened, more air passes below the slides. The quickly-moving air goes past a hole in the bottom of the slide, that is what creates the vacuum. The vacuum is passed through the hole, up the middle of the slide to the chamber above the diaphragm. That is what lifts the slide. The vacuum is NOT related to manifold vacuum, it responds to the amount of air passing under the slide. That is a direct relation to throttle opening and engine speed.

.

 

[mattfeet]

Understood. Thanks for the information. It's odd that they include the drill bit/screw in the kit for the VM carbs. I checked with a friend of mine who has the same bike/ST3 and he also received the drill bit/screw in his kit as well.

 

[chuck hahn]

And the slides drop instantly on VM carbs as they are pulled down by the return spring. CV carbs each have an individual spring in the tops that pushes the slides down and its not an all that strong spring. By drilling the holes in the CV carb slides the air passess from side to side quicker making acceleration and decell that much easier and quicker.

 

[mattfeet]

My #3 carb bowl is leaking after the bike starts running. Tonight I took the carbs off the bike, replaced the needle, needle seat, adjusted the floats, and reinstalled everything. Still leaks. A somewhat-steady drip out of the drain tube on the bowl. Thoughts?

 

[Guest]

Could check the bowl gasket? Make sure it's not impeding the float. If the float doesn't rise to where you levelled it at, fuel could continue to flow.

 

[mattfeet]

Will do. Thanks.

 

[chuck hahn]

Check the overflow tube for any cracks too. Ive seen some that cracked and drip.

 

[Guest]

Mine did that. Tapping the bowl with a screwdriver handle would stop it temporarily. Kept coming back until I just started riding it a lot and keeping an eye on it. It stopped on it's own after a while and a lot of tapping.

 

[trippivot]

ask before you drill.

ask before you drill.

the drain tube is tricky - good tip there! no really,, there is good info on this thread - at the beginning post#1 ,#2,#3 had me a little nervous about this self repair.. mechanical slide - drill!!??! jet kit!?! Nooooo ..stooopp! lol - ok I'm in a good mood. the drill bits ? some are in the kit to remove the EPA mixture cap - some are for the CV vacuum slide . not really clear unless you have done a half dozen or more...

non removable float needle seats - with new float needles installed -- will still drip sometimes - probably the toughest leak to cure - my solution is to polish inside the seats - make them mirror shine way down inside there with simichrome or flitz on a q-tip cut in half and put it in a cordless drill. The porosity of dull brass is really a rough surface so smoothing it out to a mirror surface will help it will seal better. hope that is a tip that helps.

this guy needed to post before he went to work on his bike... ever seen something like this? epic failure!!

http://,

 

[mattfeet]

Overflow tube was cracked. Grabbed a spare bowl from another set of carbs and no more drips.

 

[hannibal]

Where was it cracked, at the base?

 

[mattfeet]

Yessir. Tube was sitting at a 5-10? angle and was slightly cracked. Took it off and put gas in the bowl and she immediately started dripping.

 

[mattfeet]

Next question:

- Last night I took her on her maiden legit voyage (whopping 20 miles) in stop-and-go interstate traffic and through 35-45mph side roads. The bike never really pulled hard. I came home and measured my header temps (instant read laser) and cylinder 2 was ~102* whereas all the others were between 240-260*. The idle was set dead nuts even across all cylinders and mixture screws are all set to 7/8 turn out from lightly seated.

(Pic is upside down, but I wanted to show cylinders in same order of 1,2,3,4)

I pulled the plugs this morning and #2 (shown in order of 1,2,3,4) was black and wet. All others were coffee-with-cream tan.

I just changed the plugs to NGK 8BES and let it idle for awhile and giving it gas. After the change, headers temps were as follows:

CYL 1: ~180*
CYL 2: ~185*
CYL 3: ~230*
CYL 4: ~230*

Im going to go out on a quick ride to see how she feels. Thoughts?