Wrong carbs on new bike - Screwed??

[Bustedknuckles]

SWEET!! :dancing:

So after some magical advice and parts from GSX1000E, and a whole heck of a lot of coaxing into position, I finally got the carbs mounted nice and tight. Turns out all I needed was some 80' Intake boots, some ingenuity from a fellow GS'er and BOOM! adapters...

So I have my 79 VM's on my 1980 GS550, Pod filters, Stock exhaust...
A fresh tear down, cleaning, and rebuild, O-rings and all...
New intake boots and O-rings...

I bumped up my Jet Sizes...

Main
92.5 > 100 (3 sizes)
Pilot
40 > 42.5 (1 size)

I followed the VM rebuild guide and set the fuel/air screws by its recommendation for a good starting point.
Fuel - 1 turn
Air - 1.25 turns

I was able to set up a "test gas tank" and was able to get the bike started pretty darn easily:dancing:. BUT I am having a heck of a time getting it to idle correctly, I have been exclusively playing with the air screws, (haven't touched the fuel screws yet) But cant seem to get the bike running without leaving the choke all the way on. Any attempts to give it even a little throttle have resulted in a quick choke of the motor and dying.

I have looked around quite a few different threads but everyone's problems are so different than mine, and my carb/jet/intake/engine setup is so unique that I'm not sure if any of my calibrations are even close to correct...

At this point I just want to reach out for some more advice to see if I am even on the right track. Thanks again everyone!

Sincerely,
~Nate

 

[Bustedknuckles]

SO... I have done almost everything I can think of and the bike still doesn't want to run right.

The carburetors are 100% rebuilt and bone stock. New intake boots and new o-rings. re-sealed airbox, filter box, and brand new factory air filter. so, the intake/carbs are 100% brand new, factory settings, and rebuilt.

Valves have been adjusted and all 8 are within spec. no fluid leaks anywhere, brand new spark plugs with good spark on all 4, fresh oil and filter, plenty of gas with good flow.

The bike always starts no problem with choke. It will warm up, and soon run without having the choke on. But it has an erratic idle that can sometimes be steadied out through mixture screw adjustments sometimes not... but regardless of getting the idle to steady. It will ALWAYS slowly die down in RPM's until it stalls out. even adjusting the idle screw outside of normal parameters will only work temporarily. It will slowly lower in RPM's until its just chugging along, then it craps out...

I'm not sure what to try next, any suggestions?

Thanks in advance!
~Nate

 

[Crankthat]

I run one of those inline filters on my 750 without problems, would be worth a try taking it out of the system on your bike setup just to make sure that is not the problem.
I have read different results with them on and it would be easy enough to take off just to rule it out.

 

[Crankthat]

The erratic idle sounds like a air problem and the stall out after running for a bit sounds like the symptoms of fuel not filling the bowls fast enough.

 

[Bustedknuckles]

just tried running it without the filter in the line and am having the same result. The fuel flows very freely, I've cracked open all 4 bowls one at a time and they have constant flow drawing from the funnel... not it

 

[cowboyup3371]

How many turns out are your mixture screws?

I wonder if that airbox is allowing TOO much air in as it doesn't look like a factory top on it.

 

[chuck hahn]

I would be looking at carb syncing issues first. Take the carbs off and rebench synch them very carefully. I always set the butterflies so that a small paperclip is about the gap. Then set the mixture screws a full 3 out...may be a bit rich but it should be enough to keep it running. And recheck you dont have a broke off tip on any screws.

Eratic idling and or engine "chugging" is a good indicator of a bad sync and the engine fighting itself between cylinders. Once it will actually stay running get a timing light on it.

 

[chuck hahn]

Got any pinched diaphram edges under the top caps?? Have you backlit them to see if you detect any pinholes in the diaphrams??? What position is the clip on the needles???

 

[Bustedknuckles]

*sigh* It looks like its off with the carburetors AGAIN.

I would be looking at carb syncing issues first. Take the carbs off and rebench synch them very carefully. I always set the butterflies so that a small paperclip is about the gap. Then set the mixture screws a full 3 out...may be a bit rich but it should be enough to keep it running. And recheck you dont have a broke off tip on any screws.

Eratic idling and or engine "chugging" is a good indicator of a bad sync and the engine fighting itself between cylinders. Once it will actually stay running get a timing light on it.

How many turns out are your mixture screws?

I wonder if that airbox is allowing TOO much air in as it doesn't look like a factory top on it.

I have the mixture screws set to between 2 and 2.5 turns out and they are all in perfect shape with new o-rungs. No broken tips. The floats will have to be re-checked. When I was adjusting them with my caliper (following a walk through on GSR) I was very careful as to where i was measuring from and to. I checked and double checked but I DID have to move all 4 floats a significant amount. It seemed incorrect to me but I thought "the numbers don't lie" Maybe I screwed something up...

As far as the airbox, There is only 1/2 inch open and it is sealed up everywhere else very well. When I cover up the hole more the bike will Jump up in RPMs big time. SO, i suppose my floats could be set too low (not enough gas in the bowls) and with the combination of too much air. It could be fuel starved? Which may explain the slow drop in RPM's until it stalls? INTO THE CARBS WE GO!!!

 

[chuck hahn]

On the float hinges youll see a little tab bent at a 90 degree thats in line with one of the posts..be sure that tab is facing you when you put the floats in.

 

[cowboyup3371]

Let me see if I might have another top for the airbox. I have to swing by the garage and shed in a few minutes anyway and will look for you.

 

[Bustedknuckles]

Good news and Bad news...

Good news!
I figured out why my bike was slowly dying down in RPM's until it stalled out every single time. When I rebuilt the carbs, for whatever reason, I neglected to put the pilot jet rubber plugs back in. (I deserve your ridicule, bring it on...)

So my carbs were slowly flooding my cylinders due to WAY too much fuel getting through and stalling it out. (that problem is fixed)

Bad news!
I have everything put back together (rubber plugs included) But now, my RPM's wont drop below 3k-4k even with the idle screw backed all the way off... On a cold start, I still have to use choke but not very much. It will soon run without choke and then climb up to 3K RPM's pretty quickly. I have played around with the mixture screws quite a bit already between 2 turns - 3 turns but its the same result every time... When covering up part of the air filter box, my RPM's jump up even more... Sooooo, running too rich? Should I try opening up the air filter restriction a little bit? any advise welcome!

 

[tkent02]

When covering up part of the air filter box, my RPM's jump up even more... Sooooo, running too rich? Should I try opening up the air filter restriction a little bit? any advise welcome!

If making it richer makes it rev up, it's too lean.

Got a huge air leak? Synch adjusters way too tight lifting up the throttles? How far open are they when the throttle cable isn't being pulled? Should be just a tiny smile.

It's something big, so that means it's something easy to find.

 

[Bustedknuckles]

Annnnnnd I'm an idiot... I tightened the throttle cable too tight on the carb bracket. It was holding the throttle open just a little bit. causing the bike to get a little too excited upon startup! Got the throttle cable adjusted properly and now it runs much better... with a little fine tuning. i think im finally close to getting this problem child in order!

 

[Bustedknuckles]

ITS ALIIIIVE!!!

It runs nice and smooth now! no hanging throttle, no dancing idle, and no more wanting to set it on fire...

I have it really close to being ride-able. Only thing I'm trying to sort out now is that it boggs just a tiny bit when hammering the throttle from idle. If I go nice and easy on it it revs up fine. But slamming on it chokes it out for a split second and then it catches up. I have all of the mixture screws around 2.5 turns out.

Just wanted to make sure I was correct in thinking that more than likely its getting too much air. and turning the mixture screws out more lean's out the mixture right? so I should try turning them in a bit right? Maybe try covering up my highly sophisticated air filter box cover a little more?

 

[chuck hahn]

What are you using for filters??? CV carbs require a swift movement of air into the throats to operate the slide diaphrams..which in turn lift the slides. Stock airbox boots have built in velocity stack just for this purpose.

Take an air hose and gently blow into the kidney bean shaped thing at the top and youll see the slides go up and down. Now youll understand why it stumbles and has no throttle response without some sort of velocity stacks..either built into pods or from the stock rubber boots.

So now do this little experiment. Take toilet paper rolls and split them so they will go over the ends of the carbs. Tape them to the carbs and tape up the slits down the sides. Now you have made velocity stacks and it should have much better responses.

2 1/2 out on the top mixture screws is about just right in most peoples experiences. I am betting on not the right intake air flow to actually operate the carbs as they were designed to do.

 

[tkent02]

Just wanted to make sure I was correct in thinking that more than likely its getting too much air. and turning the mixture screws out more lean's out the mixture right? so I should try turning them in a bit right? Maybe try covering up my highly sophisticated air filter box cover a little more?

On the CV carbs, turning the screws in leans the mix, turning them out richens it.

 

[Carter Turk]

In the bottom left of this picture is an air box lid, but I think it came off a 79 550?

 

[Bustedknuckles]

Alrighty, so I've taken the bike around the block a few times and it seems to run and ride pretty well. Now I've discovered something else i'm not too sure about... The poorly designed petcock has no markings of any sort on it except for "prime. So im just guessing at where "run" and "off" are. Can anyone tell me for sure?

Right now I have it rotated CLOCKWISE so that its parallel to the ground. I'm hoping that's off...

 

[tkent02]

Horizontal, that's run and off both. Off when the engine is shut off, on when it's running and developing vacuum. Just leave it in that position until you get a Pingle.