GT550 - Surging off throttle - educate me on carb removal

[TRC]

Yeah, I'll stick to the 8s. It's my lucky number anyway.

New pads, brake caliper rebuild kit, Motul RBF600 DOT4 fluid, Suzuki caliper shaft grease, and CRC Disc Quiet has been ordered.

[TRC]

The brake caliper rebuilt kit arrived so I went ahead and removed the caliper, pulled it apart and pushed out the piston by leaving the piston side attached so I could just squeeze the brake lever until it popped out. All of that went off without a hitch but boy is it dirty. And by dirty I mean the old fluid partially left a brown sludge in the bottom and I'm surprised it worked at all! I wonder how many decades old the fluid was... The old piston is in great shape however but I'll go ahead and install the new one and clean up the old one to keep it as a spare.

So how should I go about cleaning up the caliper piston sleeve and the casings? I was thinking acetone but that would strip the black paint off the caliper. As brake fluid is essentially a paint stripper, why they chose to paint these is beyond me. What do you guys think I should clean this with?

BTW, the pads were both fine with lots of life left on them and didn't have uneven wear - just couldn't see one of the wear indicators on one side when it was together. I'll go ahead and mount the new pads of course and toss the old ones but was glad to see there wasn't something screwy with that going on.

[yeadon_m]

IMO if the calliper paint is old and tatty, just clean it with the most powerful degreaser you have and mask/repaint when you're done.
On the cleaning, other than making sure it looks spotless inside, there's a part which is easy to miss. Thats the groove that the piston seal fits in, inside the calliper half.
That is an essential part of how the calliper works. The groove has a raised line and either side of it you will often see crud. If that is not completely cleaned out, the seal will not flex properly as intended and the brake may release poorly. I use a 25mm diameter brass brush which fits a dremel and go around that groove several times until you get a dull gleam. Don't use sharp, steel tools, or it might no longer seal brake fluid!
Cheers,
Mike

[TRC]

Great tip for cleaning up the piston seal channel and I'll certainly do that. Thanks!

UPDATE: Cleaned up with wire brass Dremel tool and now I see what you mean. I would never have known those little grooves were there. Again, a big thank you.

[yeadon_m]

Pleasure, I have had so many good tips myself here so I'm happy to pass one on when I can!
Mike

[TRC]

Ok, the brake caliper is almost back together except I'm missing the Suzuki Brake Pad PBC Grease part number 99000-25110. The stuff is expensive and will take a while to get so looking for an alternative. I've found plenty of brake parts lubricants but nothing that's specifically for brake PADS as called for on the pad held in the caliper holder (the edges of the pad, not the friction surface of course). Anyone have any ideas? Hoping for something I can pickup quickly on Amazon or locally.

[Alan H]

Copaslip or any copper based anti seize compound. Apply sparingly.

[TRC]

Perfect, thanks.

[TRC]

She's all back together - pipes back on with new gaskets and re-sealed, complete brake caliper rebuild is finished and went off without a hitch. Well, one hitch... I figured out what caused the brown sludge I found in the caliper when I popped the old piston out. The master cylinder appears to be rusting so will rebuild it too and replace the rusting bits as needed in the not-too-distant future. Unfortunately it looks like rain tomorrow and then I'm out of town on Saturday into Sunday so likely a few days before I can get her out of the garage and see how she's doing.

Just wanted to say thanks again for the pointers. And they say you can't teach an old dog new tricks!

[TRC]

Had a chance to get the bike out a couple of times now for some hour-long rides and I'm happy to report it's running perfectly now - no hanging RPMs whatsoever, no increasing idle after warming up, etc. Relieved that after replacing the carb boots, pipe gaskets and resealing them with high-temp silicone, all signs of an air leak are now gone. There were times I was convinced the crank seals were bad but glad I was persistent in fixing the other issues before making that conclusion. I was very close to thinking it was a basket case until the motor was pulled, split, and the crank seals replaced. Now that it's running like new, on to sealing the tank (has wee bit of light rust starting), replacing the fork oil, etc. BTW, the rebuilt brake caliper is working perfectly with no leaks and no more "injured eagle" squawks!

[TRC]

Still getting some surging when off throttle so I pulled the carbs, set the float levels to be spot on for all three carbs, pulled the pilot jets and soaked them in carb cleaner for a while and blew them out with compressed air, ensured the pilot jet channels were clear with a thin wire and carb cleaner shooting through, removed the air screws and did the same there as well.

Discovered that the left and right pilot jets are Mukini #25. The middle one however appears to be after market of some sort, also stamped with a 25. More interesting is that one of the holes in the side had been made to be a bit larger in that middle carb pilot jet.

The main jets are Mukini 110. Before you scratch your head as I did for a moment, the bike has Jemco pipes and pods so going up from stock makes perfect sense.

Reassembled everything and took it for a test ride this morning and...it runs exactly the same. Pulled the plugs and they show the same behavior as before which is that the left wants to be rich, middle wants to be lean, and the right is what you would expect at 1 1/4 out on the air screw. Knowing this from before, on the test ride I made the middle cylinder air screw richer a couple of times which made it better on the off-throttle surging. Ok, so the pilot jets weren't clogged and causing the surging as everything is just as it was. Other than some surging when I'm riding along and then throttle off, the bike runs well. Well, it surges too if I'm going say 40 and just want to maintain a constant speed - like the throttle isn't on and isn't off - it's in between acceleration and deceleration, if that makes sense.

At this point I'm running out of ideas to fix the surging completely. Yes, I could put a stock 25 Mukini pilot jet in the middle carb and see if that helps but I'm thinking whoever made one of the holes bigger did so in an attempt to richen that middle carb pilot jet. In other words, I think it may make it worse as the air screw on that carb is at 3/4 out and it's definitely not too rich. Bump up the middle carb pilot jet to Mukini one size larger?

Any thoughts and ideas appreciated. Thanks!

[GTandcbr]

To get a smooth running motor all the carbs and cylinders have to work together producing the same power. First thing i would do is change that bodged carb as you will never be able to set it up because its an unknown entity. The trouble with fitting pods and expansion pipes is that the pods are there to increase the airflow and the pipes increase the mixture size. So now the carbs have to be set up to suit those mods with jets and settings. The only way to do this is by trial and error until the right setup is found. Here is a link that may help you
http://www.klemmvintage.com/mikuni-tuning.htm" onclick="window.open(this.href);return false;

[TRC]

Thanks and I'll check that out. The middle carb is fine, just a funky pilot jet in it.