Sudden Loss of Power - Part II

[Guest]

Hey all,

A new thread for an old problem. Sorry about a long first post, but here's the summary...

Pulling onto the street while riding away from work I heard the engine tone change. When I pulled away from the next stoplight the bike was bogging down and continued to feel like it was running out of gas. After some checking I determined that I had black fouling (of uncertain origin) on plug #1, but good spark (from a fresh plug) and good compression. I also had thin, whitish smoke from my left-hand exhaust pipe while the bike was warming up on choke. At that point the field split between leaking valve seals and something wrong with the carbs.

Even if I didn't already have a set of carb o-rings, for this newb rebuilding the carbs seemed more manageable that rebuilding the head, so I made plans to do that. In the meantime, I ran a couple of cans of Seafoam through (4oz per tank) and that actually helped a lot in the power department, but the extra "roar" the exhaust note stayed.

My petcock is new, my valves were adjusted 4000 miles ago (wow, 4000 already!?), I sealed up and re-booted my airbox and replaced my carb boot o-rings already.

So the stars have finally aligned and I've got the carbs 1/3 through the rebuild (everything's apart and/or soaking).

Everything looks good so far, except that my float heights were off. The spec is 22.4 +/- 1mm.

1. 18.77mm
2. 21.11mm
3. 20.81mm
4. 20.86mm

They're so off (esp #1) I thought maybe I was measuring wrong, thus the pic. Did I? If not, could this be the source of my power loss or at least cause the fouling?

The upside-down measurement totally breaks my brain :?, but I think a lower measurement means more fuel in the bowl.

[waterman]

According to the picture, you are reading the float correctly. There is one small detail that makes it much harder, measure this distance while the little tang of the float is just making contact with the float needle valve pin. This is the critical detail that makes it difficult for me, I have a difficult time telling when the tang is just touching the pin and then simultaneously reading the calipers.

If this is how you are measuring float height, then bend tang to bring floats to specifications, I believe this should lower actually float in bowl and ultimately lower gas level in bowls. If you want to get real fine, measure fuel level in bowls. I do a static level using a piece of tubing stuck in bowl drain hole while I have carbs mounted in vice. May not be on running bike as manual suggests but a whole lot easier.:-D

[Roostabunny]

There is one small detail that makes it much harder, measure this distance while the little tang of the float is just making contact with the float needle valve pin. This is the critical detail that makes it difficult for me, I have a difficult time telling when the tang is just touching the pin and then simultaneously reading the calipers.

When you say "just touching" do you mean resting on but not compressing the needle valve pin? Like, make sure you don't compress the floats with the caliper? If so, then I think I've got it.

Carb 1 reassembled and float height set to 22.57mm. \\/

Bending that tang is a mother - needle nose pliers on the main metal part and prying from underneath with a tiny screwdriver did the trick to raise the floats, but it feels like I'm going to slip and break something.

Side question - can anyone confirm that only the mixture screw gets seated and then backed off and that the idle jet gets fully seated?

[Roostabunny]

Another side question - do any of these mechanisms need to be lubed? And if so, with what? Maybe I'm looking in the wrong place in the shop manual.

I'm thinking...

• sync screws
• choke plungers
• choke rail
• Throttle levers

Thanks!

[waterman]

All of the jets (brass pieces with hole or holes) are seated fully. This includes Main jet on bottom, pilot jet under rubber plug, air jet on mouth of carb. Pilot mixture screw (whatever people call this) on top near intake is adjustable (somewhere around 1.5 to 2.5 turns out).

No lubrication on parts except throttle cable. It might not be too bad on choke rail, maybe?

[Roostabunny]

Success! Well, partly. :-D

Went through the whole carb rebuild process and thanks to constant flipping back and forth between the shop manual and the GSR Carb series and Robert Barr's nicely organized o-rings, I bolted the rack on, primed her, and she started right up! Chalk up another successful newbie carb rebuild thanks to the GSR!

She sounds better, for sure - like I remember - less rumbly and more chirpy overtone like I think it's supposed to be. Feels smoother, too - maybe due to my float heights being in spec? Power's not at 100% but I have yet to fine-tune the mixture and vacuum sync. That's this afternoon.

And then the sort of part...

When I started her up on choke this morning I still got thin whitish smoke from the left pipe only. I'll see what happens after fine-tuning the carbs, but if it doesn't go away (and I continue to get fouling on plug #1) I guess I'll have to put valve seal replacement on the calendar.

[Roostabunny]

Wahoo!

This thing hauls! And smooth? Uh-huh.

My wrench buddy with the sync gauge was helping me adjust the mixtures and we couldn't get any effect from moving the mixture screw on #1. He fiddled with some carb cleaner and blew some compressed air in there and viola! When we put the screw back the idle jumped right up. We checked across again and it was all set. Hopefully that ends my plug fouling, but I'm still going to watch it.

Meanwhile, took it around the block and had to remind myself to hold on a little tighter to the bars. The Grin is back. \\/

Thanks again fellas!

[catbed]

the whitish "smoke" could be condensation from being cold, if it WAS cold.

[Roostabunny]

the whitish "smoke" could be condensation from being cold, if it WAS cold.

:-D And it most certainly is not. We broke triple digits today.

Glad I picked up that mesh jacket from NewEnough.

[Roostabunny]

Bonus! No smoke this morning! \\/

Looks like whatever was keeping the mixture screw from doing its thing was also the cause of the smoke. I'll take a gander at the #1 spark plug tonight.