JohnnyL's Cafe Carb Problems Please Help!

[JohnnyL]

Hey ya'all. My bike has been sitting in my barn and not ridden for quite some time. A few weeks ago, I decided to get it out to prepare for the upcoming Distinguished Gentleman's ride that I am doing with my son this Sunday. The bike didn't want to start so I decided to tear the motor down one more time. With the help of Bwringer, we discovered that one of the cylinders had a sort of divot taken out of it. Possibly something I didn't catch on the first rebuild. The bike always blew a lot of smoke from the oil catch can. I found a nice cylinder off of ebay and quickly ordered it. Received the cylinder, painted it and honed the cylinders. Reassembled the motor again, checked valve clearances and started the bike. The bike started right up but would hang at 3000 RPM. The slightest touch of the idle screw would drop the idle down and then below idle and die.

Brian took the carbs(VM22SS) and disassembled them and looked at them very carefully. He found a few things that were suspect. Grooved mixture screw, some bad o-rings, tiny specs of dirt in the bowls and clogged choke passages. He cleaned them thoroughly, we replaced the four mixture screws and new o-rings. Thinking this would resolve the issue, I slapped the carbs on and the bike started right up but still hanging at 3000 RPM.

I am running an open exhaust and velocity stacks. I have upped the main jet from 80 to 90. I have also upped the pilot from 15 to 17.5.

I just pulled the plugs this morning and they are black. Obviously running very rich. Carbs tend to burp now and then.

I pulled the brand new carb boots this morning to see if there were any obvious signs of leaks but didn't see anything. They are new factory boots and o-rings.

I have yet to check the bikes timing dynamically. It has a Dyna S ignition. Could the timing be off enough to cause this issue? The bike revs out nicely.

I am desperate. I need to get this bike running by Sunday so I can do this ride with my son. I could ride my MT-09 but would much rather be on the cafe bike along with my son on his cafe bike. Any input or ideas are much appreciated. Thanks.

John

 

[bwringer]

I think that just about covers it -- I'm at a loss for what we might be missing here. This saga has stretched to over a year and a half, and I think the engine is finally healthy.

But something is WAY WAY off in the carbs. I'm pretty much out of ideas, too.

- Float levels set to 26mm. We have not yet verified the actual fuel level with that setting, although I have verified that it's very close.

- Fuel screw (the bottom screw) setting from manual is 2 turns out (different than VM26 carbs).

- Not sure what the air screws on the side are supposed to be set at.

 

[Gorminrider]

Never had these carbs but :
I get that removing the airbox wants "upping the jets"

I have upped the main jet from 80 to 90. I have also upped the pilot from 15 to 17.5.

but It All sounds like too much gas. Not lean-rather, not enough air... You MIGHT try, as a quick experiment, turning OFF the gas altogether and see if "momentarily" the bike gets normal. It's not a great test. It's short-lived and even less useful if the adjustments you've made at screws are "out of spec" per synching etc...but-it's quick!

Could the timing be off enough to cause this issue? The bike revs out nicely.

probably not. "Advanced" pings, and is hard to start blah blah. Plenty on the web about symptoms slow and fast...

 

[JohnnyL]

I went to Napa and purchased a timing light. I checked the timing and all seemed good except #3. The spark was sporadic on #3. I removed the boot, cut off about a 1/4" of ignition wire and re-threaded the boot on. Spark much better now. However, still doing the same damn thing.

1. Start bike
2. It idles at around 1400 RPM perfectly
3. Crack the throttle up to about 6000 RPM
4. Idles back down to 3000 and stays
5. Adjust idle screw to get it to idle at 1400 and then it eventually lower than 1400 and dies
6. If I catch it before it dies with the idle screw, I can get it to idle again at 1400 perfectly
7. Crack the throttle to 6000 and the whole process starts over again idling at 3000.

I tried shutting off the gas entirely and it made no difference. Ran it for about 2 to 3 minutes like this.

 

[grcamna2]

Never had these carbs but :
I get that removing the airbox wants "upping the jets"


but It All sounds like too much gas. Not lean-rather, not enough air... You MIGHT try, as a quick experiment, turning OFF the gas altogether and see if "momentarily" the bike gets normal. It's not a great test. It's short-lived and even less useful if the adjustments you've made at screws are "out of spec" per synching etc...but-it's quick!

probably not. "Advanced" pings, and is hard to start blah blah. Plenty on the web about symptoms slow and fast...

Have you checked your mechanical advance mechanism(which bike is this:the 81' GS550L?)yet ? Sometimes they stick or the springs may be stretched enough to keep the advance from dropping back down.There probably is something 'carb. related'.. have you looked at your intake rubber manifold o-rings? could be leaking vacuum from that.

 

[roeme]

VM's, hmm...

I guess you have the obvious stuff covered already, so...

- Floats can move freely? (Might be scraping the bowl gasket).
- Slides can move freely and are connected properly to the trottle shaft?
- Also, just to be sure, you've verified that the needle valve closes off properly? No overflow, yes?

Hit the bank with a rubber mallet (don't overdo it). If the engine stops misbehaving or changes idle, you have a mechanical problem in the carbs.

...and another thing – but I'd be surprised to see somebody else having that exact same problem as me – is when the "butterfly" casting part that connects the throttle cables to the (slotted) shaft comes loose, the symptoms are quite similar.
That little screw needs some Loctite. Doubtful tho.

 

[gustovh]

Had a problem similar to yours, turned out to be the little O rings under the little washers sealing the pilot circuit.

V

 

[JohnnyL]

Have you checked your mechanical advance mechanism(which bike is this:the 81' GS550L?)yet ? Sometimes they stick or the springs may be stretched enough to keep the advance from dropping back down.There probably is something 'carb. related'.. have you looked at your intake rubber manifold o-rings? could be leaking vacuum from that.

It's actually a 1980 GS550L with a 1979 head and 1979 VM22SS carb rack.

I just got back from Cycle Re-Cycle in Indianapolis. I talked with the owner. He also rebuilds carbs for people. He wants me to bring the carbs down tomorrow. He will look them over tomorrow night and have them back to me Thursday morning. He thinks maybe one of the slides is sticking due to the arms being worn. He also mentioned looking at the advance mechanism. He did say I need to go back down to the 15 pilots.

I removed the intake boots this morning and looked them over. They are new factory boots and o-rings. No obvious signs of leaks.

I will keep you posted as to what Rob from Cycle Re-cycle says. I'm really hoping he finds that one thing that is causing all this grief.

 

[JohnnyL]

So Rob, the owner of Cycle Recycle 2 had my carbs for two days. He went through them and found a couple of minor things. For whatever reason, whether it is wrong in the Haynes manual or wherever we got our information, the carb float height was wrong. The Haynes manual states that the carb float height is supposed to be 26mm measured without the gasket. Rob stated that the carb float height is supposed to me set to 24mm +/- 1mm. He set all the floats to 23mm because I am running velocity stacks. I had set the Jet needle to the 4th position(clip on the bottom groove richest position). Rob moved the clip to the 3rd position and put in a .5mm shim. He also noted that one of the choke pads was indented on the #4 carb causing it not to seat properly. He replaced the pad. He replaced the 17.5 pilots I had in there with the stock 15s. On the vacuum line in the middle of the rack, I had a piece of tubing with a screw in it because I am not using this vacuum port. He removed the tube and sucked through it to discover that the screw was not sealing the vacuum line. He put a vacuum cap on the port.

Rob decided to deliver the carbs to me personally to make sure we resolved the issue. He showed up at 4:30 in the afternoon yesterday and we put the carbs on the bike. The bike started right up and did the same exact thing. Long story short, he narrowed it down to an air leak on the carb boot sync ports. The oem stock carb boots come with 6mm allen screws with washers on them for the sync ports. We removed the washers and re-inserted the screws and hot damn...the bike started right up, idled perfectly. Crack the throttle and the bike returns to idle. There is still a slight lag but he told me to get some aluminum washers for the carb sync ports and that will seal them even better.

I couldn't be more pleased and I can't say enough great things about Rob from Cycle Re-Cycle 2. Rob finally left my house around 9:00 last night after shooting the *@%^$*@%^$*@%^$*@%^$ and talking about bikes. Amazing guy. I also talked to him about the clutch on my bike and how it drags. He immediately noticed I had the wrong clutch cable on the bike. The cable I had purchased was a motion pro cable supposedly for my bike. I would have purchased an OEM cable but they are back ordered indefinitely. The Motion Pro cable is slightly too long and won't allow any free play. He thinks he has the one I need at his store so I will be picking that up today.

This saga is finally closed! As Brian said, "Man there are a lot of layers to this onion". Well we finally peeled them all off and I believe all issues are finally resolved! Thank you to everyone that has helped. Especially Brian Wringer and Rob from Cycle Re-Cycle. Without you two, I'd still be scratching my head.

 

[bwringer]

Woohoo! I just love a happy ending!

I never in a million years would have thought to look at the sync port screws, or that they could be in place but still leak that much air. Or that the screw in that piece of hose would leak air. Or that the spec for float height was so far wrong.

I bet this information will help someone else sort out their GS!

Rob is indeed a hell of a guy, and of course incredibly knowledgeable. It's fantastic that you were able to connect with him and save this project.

And much kudos to you for seeing this through. I think a lot of folks would have stuck the bike in a corner and tried to forget about the whole thing long before this point.

 

[Gorminrider]

Great! I can feel the joy all the way up here! There's not many things better than getting a bike you just know should run actually doing it!

 

[pdqford]

Just want to thank JohnnyL for sticking with this issue until the final solution.
AND, for taking the time to post a detailed solution to the issue.
Wish more threads ended this way.

 

[roeme]

Very informative! I sure as heck will keep that in mind. Also, cool dudes all around, I must say.