poor running after carb rebiuld

[Guest]

Hi Guys
I need any help available, I have a GS1000EN 1979, I have just built a set of carbs from a box of bits, utrasonic cleaned, all holes cleared, needles in good condition. I have a set of bellmouths on them and a 4-1 performance pipe. I fired the engine up and it was only running on choke on the outside cylinders, occational firing in the middle ones. If I take the choke off it doesn't run....unless I put my hand over the air intakes and it fires up OK on all 4 with some throttle..only for a short time. I did put 125 jets in with the circlip on the middle slot on the needle..I know the jets may be to big (VM28's)...any help welcome...not a problem taking them off again but will need guidance on set forward, I have some smaller jets on the way.

cheers

Guys

[78550GS]

O-rings good on the intake boots? Inside carbs?

[greenbraes]

all new and tight, I have just taken a good set of carbs off, these ones were built for a bit of a change

RB

[78550GS]

And the bell mouths would be velocity stacks? I'm lost after that if that's the case. Never tried to tune with stacks, the airbox works better.

[greenbraes]

yea bellmouths are same as velocity stacks, thanks for reading and your input, all help welcome , I can always put the other ones back on, these ones are for a bit of fun and be good to get them working too

Cheers

RB

[greenbraes]

Here they are

https://www.bikepics.com/pics/2015/03/26/bikepics-2732821-800.jpg

They were in such a state I had to paint them, the colour was a bit of fun and a trial to see if you can copy red anodising, to be honest it looks OK

RB

[Rob S.]

This is what I had to do after installing APE pods to get her to run good, before I had her jetted on a dyno:

image.jpg

(Pic is upside down.)

[greenbraes]

that makes sence to what I had to do to get her to fire on all 4. To much air, does that mean the jets are to big or to small????

[Rob S.]

that makes sence to what I had to do to get her to fire on all 4. To much air, does that mean the jets are to big or to small????

Wish I could answer. BlowerBike, RapidRay or some of our other racers will chime in soon enough. Racers always know best.

Maybe one day I will be able to snatch the pebble from Master Kan:

https://m.youtube.com/watch?v=j1wjvP-raOI

[Steve]

What are you air and fuel screw settings?

With pods, I would suggest 1 full turn or just a bit more on the fuel screws (the ones on the bottoms). With your stacks, maybe 1 1/8 to 1 1/4 turns out. Start with the air screws (the ones on the sides) about double that, or 2 1/2 turns, then adjust them for best running when the bike is warm.

As a 'rule of thumb', I have heard that you add 3 to 5 sizes on the mains for a pipe and another 4 to 6 for pods. Your 125s are 12 sizes bigger, which might be OK for the stacks, but that won't really affect how it runs at idle.

.

[greenbraes]

right, my settings are miles away, I started with 3/4 turn on fuel and 1 1/2 turns on air srews, needles have circlip on middle slot (2 up from bottom). When you talk about jet sizes is that 2 1/2 per size. To be honest I would not know what the original jet size was when bike was stock.
thanks for this, I will try this start point tomorrow

RB

[greenbraes]

set the carbs up as mention below and engine would not run, I think I have to take stock and see what I have done wrong in the build. Took them off and put the old ones on (also rebuilt but with 122.5 jets) and engine fired up perfect. I think I will strip them down and see what is a miss. Can anyone help me find the part number for the pilot fuel screw (VM28 GS1000EN 1979), the one under the carb that is a nightmare to adjust in situ. I know it must be on the fiche diagram but I can't find it.

cheers

RB

[Steve]

right, my settings are miles away, I started with 3/4 turn on fuel and 1 1/2 turns on air srews, needles have circlip on middle slot (2 up from bottom). When you talk about jet sizes is that 2 1/2 per size. To be honest I would not know what the original jet size was when bike was stock.
thanks for this, I will try this start point tomorrow

RB

3/4 turn on the fuel screw is even leaner than the factory setting.

Yes, Mikuni jet sizes go up by 2.5. Other manufacturers use different numbering systems, they do NOT cross-reference directly.

Stock main jets in your bike were 95.

You mentioned you "set up the carbs as mention[ed] below". That tells me that you still have the default display settings. That makes it VERY hard to read, with newer posts on top. It is much better if you go into the "User CP" section and change your preferences to change your display format to "Linear, Oldest first". While you are in that area, change it to show 40 posts per page, it will cut down on page-flipping when reading longer threads.

EDIT: Well, it used to be called "User CP". Now, you have to click the "Settings" button in the upper-right corner, then scroll down the left side, look for "My Accout" and "General Settings". In the General Settings section, scroll down to the "Thread Display Options" area and do your thing.

.

[hampshirehog]

Have you got the vacuum nipple plugged off?

[greenbraes]

Have you got the vacuum nipple plugged off?

The vaccum line to the petcock was on, I don't know if I have the right fuel pilot screws, they came off another set of bits I have, the orginal ones were broken, and yes I did clear the broken tips. The only difference I can think of are the jets are 125's unlike the set that work, they have 122.5's. Gojng to have a look later, I must have missed something daft. Cheers for the help

RB