Okay...at my wits end here. Debated putting this in Tech or here in Vintage where you guys might've encountered these issues before. 1992 zx7 Two issues I'm running in circles with. 1. Front brake is building pressure on its own. Rebuilt calipers...all new seals. Brand new steel lines. 5/8" Nissin radial master cylinder. Bled system multiple times in order to get decent feel at the lever. Brake fluid level at midway between min and max. Rolled the bike on the trailer to take to a buddy's place...15 minute trip. Both of us could barely pull the bike off the trailer. Had to crack open the master cylinder to free up the system. Took the bike home...bled the system. Sat for a month with me randomly squeezing the lever checking the pressure...felt normal. Today had hardly any lever movement available and brakes were dragging while rolling the bike around the garage. Cracked open one caliper and the system returned to "normal". What the heck am I missing? 2. 38mm CV carbs cleaned and jetted based on "custom" jet kit (provided model, modifications, altitude etc.) Bike will run and I have to adjust the idle a lot while it is warming up. Throttle will either be crisp and responsive or it will seem sluggish. Sometimes the rpm will hang up and not drop even when I see the throttle cables are not bound up and return freely. It will eventually idle while warming but then abruptly shut off. Needle height and air jets set based on jet kit recommendations. Does the hang up of rpm mean its sucking air somewhere? I have another set of carbs that have junk needles in them so I'll probably rob the current set of jets and needles and try the second set to see if some magic happens. Any suggestions would be appreciated. Regards, Chad
On the caliper rebuild? I didn't lube them...all I did was take a finger of brake fluid and moisten them when I inserted them. Would a lack of lube result in pressure build up without actuating the brake lever? What lube is typically used...red tacky axle grease? Regards, Chad
Actually...after looking at the rebuild kit I had ordered...I now remember that I did use the lube that came with the seals. As far as possibly putting some in backward...I honestly can't guarantee that didn't happen. Regards, Chad
1-wrong brake lever that's holding the master slightly engaged? take the lever off and let it sit. 2-air leak in the bodies or intake (spray em while running w/something like brake/carb clean)
I'd vote for 1, the master cylinder is not returning fully to allow the bleed back, either sticking or as was stated the lever is preventing full return of the master cylinder piston.
re. Problem #2: check for tight exhaust valve clearances, set them to loose end of tolerance. For mysterious reasons I don't understand this slightly increases intake vacuum which can make CV carbs, uh, carburet better.
Thank you all for the inputs, I really appreciate them. #1. The lever is correct for the master cylinder and the "plunger/post" seems to function in the lever pocket normally. The lever appears to return fully...but I will remove the lever as suggested. The abnormal pressure hasn't built up again... yet. I will break the whole system apart this weekend and see if any of the seals are in backward as suggested. #2. I just went thru a second set of carbs. I verified the balancing caps were sealed off on the intake boot area like suggested. I verified the needles and jets were all installed as recommended and the slides all move and return freely along with the choke mechanism. While apart I sprayed cleaner thru the jets to verify the flow. The bike seems to run stable while warming up without as much fluctuation in idle. The throttle response seemed a little lazy and hung up slightly. It maintained idle around 1700 rpm for about 30 seconds without additional throttle input and then just stalled. Like it was shut off...it didn't gurgle to death. A hit of the starter button and it fired back up. ?????? Regards, Chad
https://www.amazon.com/GENUINE-Corrosion-Oxidation-Resistant-TS-2-34-04/dp/B01L63SXSU So an older race wrench turned me onto this stuff. Holds up to moisture better than brake fluid. The pressure thing sounds like a.plugged port.
As I recalled...I actually used the red lube from the rebuild kit. I don't know if it compares to the lube you suggested. I'll do a tear down of the brake system and see if I can identify anything stupid that I might've done. Regards, Chad
I had a similar problem with a vintage master cylinder not allowing bleed back. Turned out the bleedback hole (very tiny) in the MC was blocked from solidified brake fluid. I used a guitar string to clear it and that fixed the problem.
1. Brake system = I swapped out the radial master for the old stock master and cracked open the calipers, checked the seals, lubed the pistons and reassembled. Lever feel is there but not as strong as I'd like. Oh well. 2. After some advice from others at the track on Monday...it was noticed that although the slides all seamed free, one returned faster than the others...so I polished some of the slides and swapped out springs across the 8 carbs I have available to try to maximize the return rate of the slides across all of the carbs. Another piece of advice is to check the small O-rings in the on the bottom rail that connect the carbs. They are not part of a standard rebuild kit. If they are bad, they might allow air to suck in and create the rpm hang up that I'm experiencing when the engine warms up. I haven't tried that yet. Not looking good for this weekend... Anyone have a line on a set of 39mm FCR's that are set up foe a 91-92 zx7? Regards, Chad
Well after a last ditch effort on the carbs tonight...it's just acting a little too unpredictable to take it on track. It's got me mental. It still looks good though...lol. I bought a race license again this year and didn't get to use it...that doesn't bother me because I look at it as supporting WERA even though I didn't get to race. I'll probably head up to Grattan with my son to watch everyone and feel sorry for myself...lol Regards, Chad
#1 Almost certainly is either the lever holding the piston forward or the tiny, tiny balance hole got plugged. Not the big one, the tiny one next to it. The crusty can be hard, best bet is a Amazon Jewelers drill bit set, or a stainless wire yanked from a brush can work too. #2 Probably a cracked intake boot. Good on ya, keep 'em running!
Okay...I've given up on the CV carbs and was able to get a line on some 39mm FCR flatslides. I had them spaced for the 92 zx7 and I need help with my stupidity. The CV carbs had one line coming from the fuel pump into the middle rail of the bank of carbs. The FCR carbs have two ports on the rail...one in the center and one between the number one and two carbs. What is that second port for and what do I do with it? See pics. Regards, Chad
Those are both fuel inlets to the common fuel rail. If you can flow enough gas through one to keep up with demand, just cap the other one.