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Old 08-03-2011, 10:48 AM   #1
leakypetcock OP
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Seca 750 brake issues

My front brakes like to grab, just not release. PO said he rebuilt the calipers and I have no reason to doubt him. Now, when I squeeze the lever they grab nice and tight but won't release. The lever remains firm but the pads won't back off enough to let the wheel spin, they're not locked up, just won't release enough to easily spin the tire. I know a little bit of drag is normal but this is a lot of drag, like you're lightly holding the front brake lever. Is this a caliper problem, master cylinder issue or something to do with Yamaha's awesome anti-dive mechanism that adds 23 pounds of unsprung weight to the front end?
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Old 08-03-2011, 11:30 AM   #2
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I have a Cb 550 but I would assume that they are the same basic system.
Your system is probably all full of brown gook from 30 years of not being cleaned/flushed regularly.

1. In hindsight, BEFORE you begin the process, soak the bleeder valve threads on the top of the caliper to loosen up the bleeder valve threads. I think from the two being dissimilar metals it tends to bind.
2. Pull the two bolts off to separate the caliper.
3. Pull the brake lever until the piston pops out. Don't lose the pads, also the cotter pin may need to be replaced, it can rub the disc (I think, I need a new one) Grease the washer between the piston and the pad when you reassemble. DO NOT GREASE the pads.
4. Remove the brake line. Be careful not to bend it. Thread some bolts back in to avoid breaking it.
4. Pull the washer out that is on the side of the caliper wall. It should be a black ring that sits inside a groove. It's pretty difficult to damage, but be careful and pull it out with needle pliers. Set it aside for later, they're $9 for a new one.
5. I had tried cleaning out the walls with steel wool and rubbing compound, this isn't good enough. Go buy a small dremel attachment, the brass brush I used worked great.
6. Clean out the gook under the washer groove, this is likely what's causing the piston to hang up.
Put the washer back in.
7. I may be in the red here but I greased the washer/walls with a fingertip of silicone lube.
8. I pressed the piston back in by re-tightening the caliper bolts to reassemble the caliper. Of course this is after I put the pads and washer (lube w/ grease) back in. Don't forget to line the pads up.

Now it's all back together.

Now the hard part happens (for me at least).
If soaking the bleeder valve, which looks like a bike zert valve, doesn't work, you might have to do some hillbilly shit to get your brakes to grab.
Hillbilly shit: just loosen the brake line, put some brake fluid into a clean oil shot can, and shot it into the master cylinder intake, until it shot out the brake line. And then came back the next day. Whatever air is in the line will work itself out eventually, just don't rely on the front brake working. I stopped riding it for about 3 days while I was working on it.
If the bleeder valve does work, I think you make a closed loop by attaching a tube to the bleeder valve, filling a can with brake fluid, and feeding another hose to the master? I don't remember, because I didn't soak my valve.
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Old 08-03-2011, 12:09 PM   #3
Tosh Togo
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Originally Posted by scottybm1 View Post
My front brakes like to grab, just not release. PO said he rebuilt the calipers and I have no reason to doubt him. Now, when I squeeze the lever they grab nice and tight but won't release. The lever remains firm but the pads won't back off enough to let the wheel spin, they're not locked up, just won't release enough to easily spin the tire. I know a little bit of drag is normal but this is a lot of drag, like you're lightly holding the front brake lever. Is this a caliper problem, master cylinder issue or something to do with Yamaha's awesome anti-dive mechanism that adds 23 pounds of unsprung weight to the front end?

Pull the tank off, remove the hidden M/C, cable, and the lever assembly from the left bar. Drain the fluid and dispose it properly, then throw all the 30 year-old brake parts in the trash...

750 Seca front brakes were usually ignored more than other bikes, due to the funkified OEM cable & hidden M/C setup. I've known of a few whose owners never even knew there was anything other than the cable. Many of them never had new brake fluid, those that did weren't very often, and after a few decades the only real cure is new parts upstairs...so why not upgrade while you're at it?.

If the PO did indeed rebuild the calipers, that's great...but the symptoms you describe sound more like a clogged bleed port or collapsing brake lines.

Replace it with a newer bar-mounted M/C that has the same bore size; I've been told that an early CBR600 M/C will work, but we should wait for someone who's done it to chime in with the details. The new M/C will require different brake lines, but if the brake lines were the original set, you need new ones anyway, even if they're not the cause of the current issue.

A little brake drag is normal, but if it's enough to get your attention, there's something wrong.
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Old 08-03-2011, 12:28 PM   #4
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I think I'm going to have to re-do the whole braking system, probably disable the anti-dive as well. Next up Carbs!
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Old 08-03-2011, 12:29 PM   #5
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Brakes figured out, now Carbs!

Just got my carbs cleaned up after an 8 year hibernation with old fuel in the bowls. The bike runs but I know she needs a sync. Pipes 1-2 are at about 146 degrees after a short ride, 3-4 are at 97 degrees. I'm guessing 3-4 are richer? I'm going to make my own carb sync tool but is there a way to ball park it until then? Do I need to lean out 3-4 or richen up 1-2? Which way do I turn the screws?
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Old 08-03-2011, 09:07 PM   #6
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Carb synching is to fine tune the balance between the fuel systems so everything runs smooth and even with no surging or extra NVH.

You're right, the difference you are describing is 1 and 2 running too lean (hot) because they are still varnished or gunked. Completely soak, clean, and rebuild parts of the carbs if necessary. Synch the carbs when everything is running well and you are adding finishing touches. It doesn't change the fuel mixture, just how much the butterfly valve is open at idle. When all of the butterfly valves are set such that each cylinder is pulling the same level of vacuum, based on how well the head and cylinder are sealed, the same theoretical fuel charge will be drawn into each one on each cycle.

With respect to fuel ratio you didn't mention if you had any problem with the rubber bits. Boots, vac lines, etc that were cracked or dry rotted and letting unmetered air into the system.
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Old 08-04-2011, 03:04 AM   #7
concours
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Originally Posted by scottybm1 View Post
Just got my carbs cleaned up after an 8 year hibernation with old fuel in the bowls. The bike runs but I know she needs a sync. Pipes 1-2 are at about 146 degrees after a short ride, 3-4 are at 97 degrees. I'm guessing 3-4 are richer? I'm going to make my own carb sync tool but is there a way to ball park it until then? Do I need to lean out 3-4 or richen up 1-2? Which way do I turn the screws?

Carb synching involves adjusting the linkage between multiple carbs... adjusting the idle mixture is a different part of the equation. set them all at 1.5 turns out to start. (have you drilled/removed the plugs to access them?) As for ball parking the synch, don't touch any linkage adjustment screws, you'll be WAAAAAAAAY off with a 1/8 turn of the screw. Wait until you get a manometer hooked up. My experience shows that, unless it's been dicked with, the synch should be quite close, other probs proilly cause the problem
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Old 08-04-2011, 12:44 PM   #8
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I thought I had them really clean but I'm doubting myself now. I have removed every jet, cleaned every orifice and the things are spotless. Now when I pull the plug wire from cylinder #4 it doesn't change a thing (except it shocks the hell out of me) I did a vacuum-leak check, am using fresh gas but the thing doesn't want to run very well at all. The mixture screws are uncovered so I don't know if they've been messed with. Is there anyone in the Pacific Northwest who wants to help me?
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Old 08-04-2011, 01:39 PM   #9
Tosh Togo
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Originally Posted by scottybm1 View Post
I thought I had them really clean but I'm doubting myself now. I have removed every jet, cleaned every orifice and the things are spotless. Now when I pull the plug wire from cylinder #4 it doesn't change a thing (except it shocks the hell out of me) I did a vacuum-leak check, am using fresh gas but the thing doesn't want to run very well at all.
It always takes more than one trip in there to get goobered carbs healthy. DAMHIK.

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IThe mixture screws are uncovered so I don't know if they've been messed with. Is there anyone in the Pacific Northwest who wants to help me?
If that means that you didn't R&R the idle mixture screws last time, we've found a significant part of the problem. When you take them out (again?), be sure that you don't lose either the teeny little o-ring or the little itty-bitty washer that goes between each o-ring and the spring above it.

Once things go back together, 2.5 turns out is a good starting point for the idle mixture. Note that it's only a starting point, not a set position.

See "Pilot screw" for the little parts-


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Old 08-05-2011, 09:31 AM   #10
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I did not pull the mixture screws when I did the carb clean. I was so paranoid to change the settings that I didn't want to move them. I guess I'll be pulling the carbs again and taking screws and related hardware out, cleaning and hoping for the best. I actually hope I find a bunch of crud in there so I can clean them up. Seafoam in the spray can and PJ1 cleaner have been my friends. I think dedicated carb cleaner is too harsh and the stuff I've been using works just fine.

Wish me luck!
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Old 08-05-2011, 10:09 AM   #11
Tosh Togo
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I did not pull the mixture screws when I did the carb clean. I was so paranoid to change the settings that I didn't want to move them.
No worries...SOP for carb screw removal is to first run each one all the way in until it gently bottoms, then write down how many turns it took for each mixture screw. Repeat on reassembly, and you're back to your initial starting point.

You'll probably need to make a tool to carefully pick each idle screw's o-ring out; I use a short piece of safety wire bent 90+ degrees at the business end, the sideways part only extending out about a mm so it fits down the screw hole and can get under the o-ring without nicking it.

Quote:
Originally Posted by scottybm1 View Post
I guess I'll be pulling the carbs again and taking screws and related hardware out, cleaning and hoping for the best. I actually hope I find a bunch of crud in there so I can clean them up. Seafoam in the spray can and PJ1 cleaner have been my friends. I think dedicated carb cleaner is too harsh and the stuff I've been using works just fine.

Wish me luck!
After being parked that long, your carbs need carb-cleaner, and the only way to hurt the carbs with it would be to leave them immersed for a long time....like a few days or more. Soak, then use shop air to blow through every passage in every possible direction. Repeat a few times. Do NOT use hard objects to poke jets out...anything harder than the soft brass jets can result in weird jetting results later on.

-There's also a little orifice/jet in the float bowl itself: It's on the engine side, at the bottom of a hole in that odd slot in the bowl's gasket surface. It's usually plugged, and takes a bit of persuasion to clear.

If it's not too late, keep each carb's internal parts segregated: the two jets that unscrew from the carb are OK to move around, but each needle/needle jet pair and the float needle sets wear together in a manner similar to bearings, and if you play musical idle screws your notes about how many turns for each one will be changed. Playing mix & match float bowls/gaskets usually leads to more oozage. Mark the parts, put them back as original = fewer problems.


PS- ammo cans are the perfect size and shape to immerse the complete stripped carb assembly.

It ain't luck- it's persistence, and a willingness to ask questions before breaking out the BFH.
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Old 08-06-2011, 07:35 AM   #12
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Originally Posted by Tosh Togo View Post
After being parked that long, your carbs need carb-cleaner, and the only way to hurt the carbs with it would be to leave them immersed for a long time....like a few days or more. Soak, then use shop air to blow through every passage in every possible direction. Repeat a few times. Do NOT use hard objects to poke jets out...anything harder than the soft brass jets can result in weird jetting results later on.

-There's also a little orifice/jet in the float bowl itself: It's on the engine side, at the bottom of a hole in that odd slot in the bowl's gasket surface. It's usually plugged, and takes a bit of persuasion to clear.
Do NOT soak the entire carb rack for any lenght of time as each carb's throttle plates has a unique (and vastly undocumented) "Q"-ring on each side which will be degraded/destroyed. Two very good cleaners (which do not adversly affect rubber) are the Yamaha carb cleaner and Pinesol. Definitely remove ALL bits from each carb body prior to cleaning; soaking the brass jets in strong carb cleaner (or the other mentioned cleaners) is fine. Be VERY careful running any cleaning tools through the jets/emulsion tubes (steel guitar strings seem to work well). The OEM mixture setting is 1.5-2.5 turns out from lightly seated (most find 2 turns out to be real good). You can "bench sync" the carbs prior to reinstallation and you definitely need to check the float bowl fuel level prior to reinstallation. All this and much, much more can be found at the motherlode of Yamaha XJ info - xjbikes.com. There is also a list member (Chacal) who can supply just about any part you will ever need. This site also has vast info about repairing/cleaning/replacing the odd 750 Seca master cylinder and front brake system.
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Old 08-06-2011, 09:18 AM   #13
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I pulled the pilot screw from #1, the tip was gunked up and I can see goo down the hole it came from. That's about the only place I didn't clean, guess I'll be pulling the carbs again and doing a once over on the pilot screw passages.
Thanks for all the great advice.
Scotty
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Old 08-06-2011, 09:26 AM   #14
Tosh Togo
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Do NOT soak the entire carb rack for any lenght of time as each carb's throttle plates has a unique (and vastly undocumented) "Q"-ring on each side which will be degraded/destroyed. Two very good cleaners (which do not adversly affect rubber) are the Yamaha carb cleaner and Pinesol. Definitely remove ALL bits from each carb body prior to cleaning; soaking the brass jets in strong carb cleaner (or the other mentioned cleaners) is fine. Be VERY careful running any cleaning tools through the jets/emulsion tubes (steel guitar strings seem to work well). The OEM mixture setting is 1.5-2.5 turns out from lightly seated (most find 2 turns out to be real good). You can "bench sync" the carbs prior to reinstallation and you definitely need to check the float bowl fuel level prior to reinstallation. All this and much, much more can be found at the motherlode of Yamaha XJ info - xjbikes.com. There is also a list member (Chacal) who can supply just about any part you will ever need. This site also has vast info about repairing/cleaning/replacing the odd 750 Seca master cylinder and front brake system.

(Sigh)... Apparently I should've been more specific. The carb cleaner that I suggest using is what Yamaha sells at their stores. Silly me... I thought you girls could figure that out for yourselves.

The traditional old-school automotive carb-cleaners that contain cresol (white/milky/sweet-smelling in a metal bucket) will quickly make any and all rubber/neoprene/buna components in the carbs swell and turn into junk. Given enough time it'll also erode brass and aluminium parts.

I've used the Yamaha stuff for a long time with good results...never have tried Pine-Sol, but others say it's also a good choice.

Unless the carb synch is way off, bench-synching won't do a lot of good. The carb-synch will be the last thing to do, after everything else in the carbs is OK and the valve clearances have been set.

Don't just eyeball the floats to verify the level... Yamaha specifies checking the float levels wet- there's a procedure in the manual to walk you through it, and it does make a difference.
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Old 08-06-2011, 11:10 AM   #15
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Did the float level as per the manual, clear tubing with digital calipers to measure the level. Good to go.
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