Help save the life of a GS. Carb-related?

[wkmpt]

I'm getting really discouraged, frustrated. Need help before I roll it into the street and set it ablaze, or get out the 5-lb. sledgehamm--uh, wrench, and get 'wrenching'...

Here's what I know/have done to this point:

[Following Paul Musser's VM-rebuild write-up.] The carbs have been stripped, dipped, cleaned, new cycleorings.com o-rings all around. All stock internals (jets, needles, etc.) Pilot fuel jets 1 turn out. Pilot air jets 1-1/4 turns out. Floats set to 25mm. Bench synced as per the write up.

Dyna S installed, timed correctly to the F marks. Bandit 600 coils installed, getting spark on all four plugs. Freshly-charged battery.

Got the carbs on the bike, spanking new intake boot o-rings installed. Vacuum lines for #2 and #4 installed. Vacuum line for #3 attached to petcock vacuum port. Petcock appears to be functioning properly and flowing well.

In starting the bike (box fan in front moving air past bike):

Primed float bowls, no apparent leaks to indicate stuck floats.
Starts immediately on full choke. Plenty of white smoke coming from 1-2 exhaust side. (Suspect is from cyl. 1, when bike was only running on 2-3-4, no smoke.) Wisps of white smoke coming from behind the exhaust flange on #1.

Bike running until engine warmed up. Good and warm, rpm's begin to surge. When turning off the choke, had to gradually reduce choke or engine would stall.

Finally got engine to run without choke, around 1.1k rpm.
Began adjusting the pilot air screws per the write-up. Richening mixture, no change in rpm's. Leaning mixture, very slight increase in rpm's.

Adjusted #1 through #3, bike begins intermittent "chuff" sound from carb #3. At this point the bike is beginning to stall out.

Stalls out. Won't start without starter fluid, won't stay running. No, the gas hasn't run out...

Help? Places to start looking?

 

[Guest]

Did you do a valve adjustment?

 

[wkmpt]

Not yet. It's on the list, though.

 

[rustybronco]

check the valve clearance as suggested.

I would suggest you check the float levels externally with clear tubing.

I got bit by a 1982 xv920j that's in my garage. when I set the float levels to the recommended height of 23mm, it was almost impossible to get it running correctly. I set the fuel levels externally to 0 -/+ 1mm from the gasket surface, with clear tubing attached to the bowl drains and arrived at a 20.5mm float height. after setting the fuel levels that way, it would start with one touch of the starter button and I could then properly adjust the pilots as I should have been able to when they were set at the factory recommended 23mm.

I had almost the same problem on a 1973 cb350f, but the carbs flooded when set at the factory specs. I had to drop them 2-3mm to get the fuel level correct.

I will never set fuel levels any other way from now on.
twice bitten, shame on me...

 

[smagnusen]

Good advice above. Valve stems, like any metal, expand when they get hot. The reason there needs to be space between the tappets and the cams is to allow for this expansion. If there is not enough expansion clearance, the valves will not close fully, your compression will drop and you won't get proper combustion. Have you checked compression with the engine warmed?

 

[wkmpt]

Check the valve clearance as suggested.

I would suggest you check the float levels externally with clear tubing...

In regards to the clear-tubing method, that's where I attach a tube to the float bowl drain and make sure the fluid level is even with the top of the float bowl, right? Can I manufacture a tool to do this myself with hardware store fittings, or is this something I'd be better off buying?

...Have you checked compression with the engine warmed?

I have not. I will get cracking on a valve adjustment and then grab a compression testing kit and jump on that next.

 

[rustybronco]

In regards to the clear-tubing method, that's where I attach a tube to the float bowl drain and make sure the fluid level is even with the top of the float bowl, right?

Yes
the spec I found in the '750 shop manual is 2.5-3.5 mm below the bowl mating surface.
http://www.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf

Can I manufacture a tool to do this myself with hardware store fittings, or is this something I'd be better off buying?

make the tool yourself.

 

[TheCafeKid]

DAMNIT MAN! You CANNOT start tuning carburetors with valves that are out of adjustment! If you want the bike to run right, you need a level playing field and right now you dont have that. Those valves should be at LEAST checked every 5K miles or less. As they wear, the valve receed into the head, thus the clearance between the cam lobe and the bucket becomes less and less and then the valve never seals. If the valve doesnt seal, you're sucking air, or fuel or both. Compression will suck, the cylinder wont fire properly, if at all, and then you're blaming the bike because it wont run even though you spent ten dozen hours cleaning the carbs and checking the electrical connections etc etc etc when adjusting the valves SHOULD have been the FIRST thing you did. I bought a 750 motor on Ebay and had it shipped from Seattle. The thing only had "21,000" on the odo, but the first thing i did was check the valves and they were ALL out of spec, some of them 3 shim sizes. (the thing got stripped at that point because of i feared the valves had burned, ANOTHER thing that will happen if you dont adjust them) Stop what you are doing, stop running in circles and chasing your tail, and do this. You will find the bike much MUCH more likely to respond to your tuning..

 

[Guest]

DAMNIT MAN! You CANNOT start tuning carburetors with valves that are out of adjustment!

Like he said... valve adjustment first.

Regarding the fuel height gauge - easy enough to make. Use an old float bowl drain screw & drill a hole through it, then epoxy (or braze/solder) in a small piece of hard tubing (maye an inch long). Simply "push on" a length of clear tubing (maybe a foot long) to your "new" tool and hold it against the side of the float bowl - the fuel in the tube should be 5mm (.200") below the mating surface of the bowl to the carb body.

Do this test with the bike on the centerstand & idleing.

mike

 

[rustybronco]

Like he said... valve adjustment first.

the fuel in the tube should be 5mm (.200") below the mating surface of the bowl to the carb body.

That's what I would have guessed, but...

the spec I found in the '750 shop manual is 2.5-3.5 mm below the bowl mating surface.

 

[Guest]

That's what I would have guessed, but...

My bad... thanks for the correction. I should have read the previous responses a little closer .

Forgot the '77's used VM carbs. The 5mm level is for CV carbs.

 

[wkmpt]

Did you do a valve adjustment?

check the valve clearance as suggested...

Good advice above...

DAMNIT MAN! You CANNOT start tuning carburetors with valves that are out of adjustment!...

Like he said... valve adjustment first...

So hold on...I'm confused...what am I supposed to do first?...

I'll make sure I do that before I go any further.

Anyone have an extra vm carb float bowl screw sitting around they don't want?

 

[ryonker]

check the valve clearance as suggested.

I would suggest you check the float levels externally with clear tubing.

I got bit by a 1982 xv920j that's in my garage. when I set the float levels to the recommended height of 23mm, it was almost impossible to get it running correctly. I set the fuel levels externally to 0 -/+ 1mm from the gasket surface, with clear tubing attached to the bowl drains and arrived at a 20.5mm float height. after setting the fuel levels that way, it would start with one touch of the starter button and I could then properly adjust the pilots as I should have been able to when they were set at the factory recommended 23mm.

I had almost the same problem on a 1973 cb350f, but the carbs flooded when set at the factory specs. I had to drop them 2-3mm to get the fuel level correct.

I will never set fuel levels any other way from now on.
twice bitten, shame on me...

Thanks Rusty Bronco! I never knew about this method.

 

[ryonker]

So hold on...I'm confused...what am I supposed to do first?...

I'll make sure I do that before I go any further.

Anyone have an extra vm carb float bowl screw sitting around they don't want?

Second on the extra vm float bowl screw. I suppose you can just order it like any other oem part.

Rick

 

[wkmpt]

I quite literally just found one. Seems in the box of (mostly garbage, some parts) parts that came along with my bike, there was a float bowl with the screw in place!

So score one for odd boxes of shyte!

If anyone needs the orange lenses from one of those long trapezoidal-shaped turn signals, or the internals from the same, let me know, I have about eight of them. The signal bodies are dried out and cracked to shi*, or broken to pieces, but the lenses and internals appear to be okay.

 

[TheCafeKid]

HEY! I might take those off your hands. Are they the kinda triangular shapped lights? Like on an ES? I might be interested in the lot, boddies and all. Let me know!

 

[Guest]

Anyone have an extra vm carb float bowl screw sitting around they don't want?

Might want to consider these - all allen heads...

http://cgi.ebay.com/ebaymotors/GS55...da&_trksid=p4506.c0.m245&_trkparms=65:10|39:1

 

[wkmpt]

Might want to consider these - all allen heads...

http://cgi.ebay.com/ebaymotors/GS55...da&_trksid=p4506.c0.m245&_trkparms=65:10|39:1

Ordered a set today. The Philips heads on mine were getting a bit sketchy.

 

[wkmpt]

Update on valves. It's my understanding that the appropriate tolerances for my 77 750 are between 0.03mm-0.08mm, so that's the standard I attempted to measure to.

My smallest feeler gauge is a 0.051mm/0.002in. I think I'm going to order this set http://www.sourcingmap.com/steel-metric-thickness-feeler-gage-gauge-002100mm-p-21339.html, so I can have some thinner sizes as well.

But at any rate, that 0.051 feeler is too thick to pass on all of my valves. At this point, I should see if I could get my hands on a very thin shim, to get a clearance I can pass, so I can figure out which shims I'll need to get to match spec, right?

I pulled all of my shims (one at a time) so I'd know what's currently on the bike.

#1 in-2.80 ex-2.75
#2 in-2.85 ex-2.75
#3 in-2.85 ex-2.80
#4 in-2.70 ex-2.85

I've thought about grabbing one of the 2.70's and dropping it in place of one of the 2.85's or 2.80's, to try and get a ballpark of how much thinner I might need to go. Would that be a good use or a waste of my time?

 

[TheCafeKid]

Update on valves. It's my understanding that the appropriate tolerances for my 77 750 are between 0.03mm-0.08mm, so that's the standard I attempted to measure to.

My smallest feeler gauge is a 0.051mm/0.002in. I think I'm going to order this set http://www.sourcingmap.com/steel-metric-thickness-feeler-gage-gauge-002100mm-p-21339.html, so I can have some thinner sizes as well.

But at any rate, that 0.051 feeler is too thick to pass on all of my valves. At this point, I should see if I could get my hands on a very thin shim, to get a clearance I can pass, so I can figure out which shims I'll need to get to match spec, right?

I pulled all of my shims (one at a time) so I'd know what's currently on the bike.

#1 in-2.80 ex-2.75
#2 in-2.85 ex-2.75
#3 in-2.85 ex-2.80
#4 in-2.70 ex-2.85

I've thought about grabbing one of the 2.70's and dropping it in place of one of the 2.85's or 2.80's, to try and get a ballpark of how much thinner I might need to go. Would that be a good use or a waste of my time?

Good use, but if you're .05mm is too large to fit, I would simply change to the next smaller shim. The shims range in thickness by .05mm, so even IF your .05 passed, jumping to the next shim would make it .10..acceptable. Loose, but acceptable.