'82 Seca 750 Refresh Project: Now Scooby's Bike

Remove and repair that petcock - they are troblesome beasts at best, so make sure it's 100% good. Pull the plugs and clean them, put the mixture screws back where they were for now. Don't pull the carbs, just drain the fuel from each seperately into clean containers and have a good look at it - is it dirty?
Once the carbs are refilled, nothing leaking, you can restart it. Get it good and hot before adjusting anything. Your white smoke will dissappear, to be replaced by a wide smile
If you get popping then try opening the mixture screws, then balance the carbs, and re-adjust the mixture screws for fastest idle (takes a bit of practice), you might want a fan blowing across the engine.

 

Check your rebuild. When I did mine I reassembled it wrong and gas always flowed like on prime (good thing my float needles did their job). I then noticed it dripping gas which alerted me to take it apart to discover the boo boo.

 

Fixed the petcock. The wavy washer wasn't set correctly. No leakage and the knob turns nice and tight. I have yet to pull any plugs or drain fuel from the carbs.

Started her up again today, ran for a few seconds then stalled out. I'm using the bike tank at the moment but it's not filled with much gas. I set it to on then to reserve in case it wasn't pulling enough fuel. Sometimes it blips on like a cylinder or two fired once or twice then shuts off. Turned the screws in fully then backed them out 2 1/2 turns.

Cranking the motor so much is draining the battery so I haven't tried to start her up on 2 1/2 turns until I charge the battery up nice and good.

 

Wavy washer was my problem too. Jump your battery with an extra car battery if you have one or know someone who does. If enough gas flows out the petcock it must be stopped at the carbs. Float needles stuck closed? Seems like the starting circuit would still provide fuel for starting it up as long if the needles are working and the bowls are full.

 

The mixture screw settings are not really relevant if the enricher (choke) is open. Until the engine warms you need the enrichner.
So its not even starting? Pull the plugs...

 

Alright, here are the mixtures screws I pulled. Sorry if quality isn't too good. My phone camera isn't the best.

Question: How do the carbs work on these bikes? I have a single carb motorcycle which is quite new, only had it for a year. It's a DRZ400 2020. I've only really re-jet it. But since it has one float, I just prime for a few seconds and it's good to go. However, for these carbs with four floats, how does priming work? How long do I prime for? How does the fuel reach each carb. First carb fills until needle plugs hole then it runs to the next carb and so on. Because how do I know each float is nice and full for a cold start?

I pulled the carbs despite protest because I honestly have not touched the carbs since I bought the bike. I know PO worked on carbs so I assumed he set them up right. Carb looks rebuilt, fresh gaskets and all. I fixed the floats, they were kind of low around 14mm. I set to around 17.5mm +-

 

You have to bench sync the carburettors then wet set the floats and finally vacuum gauges for setting them to your engine. With the fuel tap in the prime position gravity fills the float bowls. As you have done your valve clearances carburettor work is next.

https://www.xjbikes.com/forums/threads/how-to-bench-synch-your-carbs.6366/

Owners strip the carburettors and replace the throttle shaft seals etc. I have not done mine yet because my bike was running well.

 

Please don't strip the carbs down to replace the throttle shaft seals - not yet anyway, its an intricate and easily messed up job, and your bike will run at 95% performance without seals - the 5% being at idle.
Just check all the galleries are clear, enricher jets and idle jets especially. And that the PO hasn't put the jets in the wrong place.
Then carefully balance the throttles on the bench by lining the edge of the discs up with the first hole - you need good eysight. If the fuel levels are near right your bike should start and run well enough to ride, with only adustments to mixture screws and idle speed.
We're still waiting for that first smile...

 

If the throttle shaft seals are bad then the bike will have a climbing idle (potentially all the way to redline).
It doesn't have that.
The prior owner already had replaced them when he tore the rack down, so they won't be a problem.

When replying to this thread please keep in mind that this is the same bike that Nuch started the thread with. We have several years of maintenance history to look back at when giving advice for this project.

 

Yes to a climbing idle, but if it goes anywhere near the red line the problem will not be throttle seals alone...
These carbs are so well machined and wear very little, so any leakage is tiny. However, running is one thing, running perfectly another. Right now you need running.

 

I'm repainting the fuel tank so it'll be a bit until I try to start her up again. I am, however, working on the brake system. I rebuilt the master cylinder, calipers etc and I'm trying to refill the reservoir. Since this bike has the master cylinder behind the light, I've been using an eye dropper to put brake fluid into the filler screw hole. I didn't put a whole lot but the filler hole is full already. Which is weird because the master cylinder was completely empty. There's no way three squirts filled it up and yet there's no brake resistance. The fluid in the filler screw hole doesn't seem to be pulled down into the reservoir either.

 

What is a filler hole? Pic? Are you adding fluid above the rubber diaphragm?

 

Huntchuks......on the 750r, the mc is separate from the lever. It is cable-operated and is tucked down behind the headlight....... and is a different shape than what you’re familiar with.

 

So there is some kind of screw that is removed for a filler hole?

 

There is this small hole that this plastic hex screw fits into. Because the MC is behind the aux light. Taking the light off every time to fill it up would be a pain when you need to bleed brakes. So essentially you can fill her up through this hole. There's no real way of knowing how filled up the reservoir is since there's no sight glass and I can't view the inside of it.

 

Thanks for the pic. Seems stupid to not make the reservoir translucent white plastic so you can see the fluid level.

 

When the brakes don’t work, you know the fluid is low.......lol

 

Yea of course. The fluid is low since I'm trying to fill it up from empty. But I think the brake fluid I'm putting into the filler hole isn't reaching the reservoir for some reason. I should've checked how it connects to the reservoir. I figured it was just a small hole connecting the filler hole to the main reservoir. It might be clogged. I really don't want to take off the headlight and pull out the MC to fill it up through the cap. Is the filler screw hole really the only way to refill the MC on the XJ750? I was hoping I would be able to somehow get the cap off and syphon some fluid in but there's no room to unscrew the top since it's so close to the handlebars... what a pain.

 

Figured out my brake issue. Stuck piston. Any way I can get this loose? I'm thinking about blowing some air into it to push it loose. Not sure if best approach since it could send the piston flying.

 

Can you put it on a piece of 4 x 2 timber and then pump in the air.

 

USE A GREASE GUN

 

Popped it out with a hand air pump so I wasn't blasting air in there. Grease gun also works great. Not sure why it got stuck. I just rebuilt it, new parts and sanded the bore. Though it the piston was sitting in there for a few weeks until I finally put some brake fluid in the reservoir to test it. Whatever the case, gonna re-sand the bore and use some of that rubber to metal grease.

 

How do I bench pressurize the master cylinder? The one I rebuilt doesn't really seem to pressurize too well. When it's empty and I put a finger over the output hole, I can hear air being sucked in through the reservoir. When I fill up the res I never get any pressure on the pivot. If there is any pressure build up, it's miniscule.

I have a second master cylinder I bought off ebay for cheap. It hasn't been cleaned or rebuilt and is quite dirty, yet the pressure builds MUCH better than the one I rebuilt.

 

Did you fit the seals the right way round on your rebuilt master cylinder?

 

"Sand the bore"
Why? Do you think yamaha made it too small?

 

Here's a side by side with OEM (Bottom in pic) and Aftermarket (Top in pic). My MC has little to no pressure after I installed Aftermarket seals. I bought a used MC for the bike from ebay to make learn more how the MC works and to swap parts. At first I thought it was an MC problem but I swapped the OEM seals with the Aftermarket seals in my MC and it builds pressure great. So it's a seal problem. Gonna swap some parts to see if it's the spring seal or the piston seal.

 

I watched a video on a thread here by Moto Stuff and he sanded the bore a bit with a 1500. Honing would be best but I don't have one.

 

You should drop the piston into the bore without the seals in to test the fit. Unless you have corrosion no need to "sand" anything.
Did you run your engine until the smoke cleared yet?

 

So I ran a few pressure tests swapping out parts. Seems like the Aftermarket spring seal is the issue. Aftermarket piston and seal are good. MC is good. Bore is clean. Everything fits. Gonna see if I can get a new one.

I haven't started the bike yet because I brought the fuel tank to be glass bead blasted so I can repaint it myself. There's only two motorcycle shops by me. Because I do all my own work except for some things that I don't have the tools for, I bring in small parts to work on at the shop and I think they put my parts LAST on their big list of repairs.... why do a 50 buck job when you can do the 1000 dollar jobs first? So I'm waiting until they call me or I bug them that it's been three weeks now...

 

I fixed the brakes. So I'm back to working on getting the bike to run. Unfortunately, the owner of the bike shop I was going to have the fuel tank glass beaded had died this weekend so I have to find another location to make the tank have a nice bare metal look so I can repaint it.

I have, however, got a nice aux tank setup so I could work synching carbs. About 20 seconds later and the starter motor is no longer turning. There's no clicking sound. Hitting the "start" button doesn't do anything. I didn't completely rebuild the starter. Any ideas? Otherwise I'm going to pull it, test it. Could it be pulled without draining the engine oil?

 

Yes you can remove the starter motor without draining the oil. Try jumping the solenoid contacts first to see if starter operates before removing the starter motor. You could try a car battery too and jump leads in case your bike battery has a low charge. Your bike looks great.

 

I guess no then, poo, looking forward to a big YEESSS from you after all this hard work...

 

I just fixed the starter motor today. So another attempt at synching carbs. Tomorrow I'll try to get the engine started again and take a quick video.

 

Had a small break from work so I decided to start up the engine. See how it is. Cylinder 3 doesn't seem to be firing. Stalls out when I pull off choke. Stalls out when I blip the throttle. No more white smoke so it must've been when I added oil into the cylinders. I was working quick so I think I turned off choke too early or I tried adjusting the mixture screws while on choke. Mixture screws turned out three turns. Any ideas? Gonna try more this weekend.

 

The video doesn't tell me much, other than you are trying to run a cold engine without enrichner - you can't, well not if the idle jets are correct and mixture screws set close to right.
Warm it up on choke and throttle before adjusting anything. And the white smoke gone? - I told you so.

 

Been adjusting the mixture screws. Turned them out to around 3 1/4. Starts up on fully open choke. Revs up to maybe 2k. I let it sit around there for about 30 seconds. Occasionally I hear some pops but not a whole lot compared to when I first got the bike. The RPMs also don't fluctuate wildly. I tried to ween off choke but it slowly dies out and will stall if no choke is pulled.

I gave a little tiny blip of the throttle and it shot up to 7k RPM and had a bit of an issue coming back down at a steady rate.

Cylinder 3 seems to firing.. but only occasionally? I'm not sure. The pipe isn't cold. But it definitely isn't hot like the other pipes. You can put your hand on the 3 cylinder exhaust and hold it there with no issue. I plugged the vacuum line with a plug from autozone. It could be that it's not plugged up fully or the spark plug is fouled. I'm gonna check those. I think before I do anything. I should make sure cylinder 3 is firing alongside the others.

If choke has to be fully open, even after the bike is warmed up then it should mean the current mixture with choke off is too lean right? I don't know if I can turn the screws out more than 3 1/2

 

Got the bike to run without choke. One of the spark plugs wasn't firing so I just replaced all of them. It holds an idle around 1400-1600 rpm. Sometimes the rpms randomly shoot up to 2 or 3k when I start up the bike. Blipping the throttle makes the rpms hang high around 2k and slowly come down. Not really sure what's going on there. But I don't know which screw I should adjust. The idle screw sitting in the middle of the carbs or the mixture screws to fix these random rpm spikes or the hanging rpm when throttle is blipped.

 

The idle screw in the middle is the idle speed screw. The ones on the carbs are mixture, and if you don't have any other way to set them adust each one for fastest idle - the idle speed screw is tweeked in between. But, it sounds like you need a vacuum synch first - this sets all the butterflies to the same position, and is vital to get it right.

 

I got the idle to sit around 1050 with the idle screw. Getting ready to check vacuum synch and color tune the carbs. With that whole blanking tool for YICS engines. I read mixed thoughts on it but I guess I'll just follow the book.

I was looking at a thread about clutch adjustment and saw I might have set my clutch lever arm wrong. The two lines were lined up before I got rid of free play. So without free play, the line on the lever passed the clutch cover line. So I moved the lever arm so that the two lines match up without any free play left until you need the mechanical advantage of the cable to disengage the clutch.

But now I can't get the knurled part of the clutch cable to reach that little clutch hook so I'm not able to adjust the clutch. Am I doing something wrong?

 

Fooling around with the clutch again and I lined up the marks as best as I could. It's about one spline off. I'm not sure if this is OK or not because the cable simply cannot reach or the lever needs to be pulled in more. Right now it's completely stopped with just using fingers. Pliers would be needed to pull it over more But then the lever would always be under tension.

With some adjustments I'm able to get 3mm freeplay at the handle bar lever. Starting up the bike and shifting into first, the back wheel rotates even when the lever is pulled completely in. So it must not be fully disengaged.

 

Normal for a wet clutch on the center stand. If it's on the ground and lurches forward then you have a problem.

 

So long as it doesn't creep when your in gear at a standstill, or slip when giving it the beans you're fine. Springy, rubbish outers can cause this.

 

I was able to align the splines. Gave a 3mm free play at the lever. This should allow more range to pull the clutch. Yet, the rear wheel still spins. It's fully engaged despite having clutch lever pulled in fully . This is Not a spin that can be stopped by hand, if it was then it would just due to oil. I've made sure to align the dots on the basket when installing new clutch plates. The only thing I can think of is maybe the clutch cable is stretched. But the knurled adjust nut is all the way at the top. It's as tight as can be. Last resort is taking a look at the internals...

When one problem is solved... another arises...

 

Tighten up on that free play a little, and put some miles on the clutch before stripping (assuming you can get it to release by the aforementioned tightening free play). My experience with these is that there is very little margin for error - too much free play and it doesn't release, too tight on the adjustment and it will slip. Worn lever pivot, spongy outer cable, bad routing can exacerbate this, so don't rush into taking things apart (again).

 

zero free play gives more travel to the clutch arm.

can you stop it with the brake? my clutch is adjusted and maybe i could stop it with my hand but my hand would never be the same.
if the brake can stop it without killing the engine, i would sit on it and start it in gear.
point it out the door first, just in case

 

So, I've tightened up the free play on the lever. It's basically zero now. And put some miles on the clutch means I should ride the bike? Isn't it a bit spooky to shift into first and the wheel immediately shoot the bike forward? I'm going to attempt it eventually... the bike is heavy. Maybe the weight will stop the wheel somewhat. I am able to stop the wheel with the footbrake and the engine doesn't stall out. I dont get what's making it spin. I oiled the plates before installation... the only explanation I have is the plates are sticking together?

 

Put the bike outside, warm it up. Sit on it, hold the brake (choice of two), pull clutch, bang it into 1st.
If it stalls you have a clutch problem. If not, go forth....
You 're overthinking stuff.

 

So just ride it, no danger there.

 

That amount of wheel spin while sitting on the center stand doesn't seem outrageous to me.

Remember that those clutch plates are still spinning in very close proximity to each other, with oil in between, so it shouldn't be surprising that the rear wheel would spin a little bit without any resistance.

I would test it by doing the same thing, but sit on the bike and have the rear brake engaged when you shift into first. As @Minimutly said, if it stalls you have a clutch problem.

 

Ran the bike before I left for a bike trip to the Midwest and you guys were right. The spinning was no issue once the bike was on the ground. I took her for a spin but only made it about two blocks until she stalled out and I had to push a 500 lb bike back home. The bike has poor throttle response when blipped. It takes half a second or so for the cylinders to respond when the throttle is opened. So getting the bike rolling can be difficult unless I apply a large amount of throttle. Releasing the clutch slowly doesn't move the bike forward but will stall it out. Even with a tiny bit of throttle applied, the bike stalls. Opening the throttle at least half will get it going.

I've vacuum synced the carbs using the YICS tool. I also took a look at color tuning. Which is kind of a pain. Should all mixture screws be the same screwed in or out? Or can carb 1 be 2 1/2 turns while carb 4 is 3 turns. As long as they hit that blue color? Or must they all be 3 turns out etc. Because I've turned all the mixture screws out completely to hit an orange color but no matter how far I have them turned out, the color doesn't seem to change.

Edit: I tried starting the bike this morning and... it's seized. I was gone for two weeks and I guess the rings got stuck or something. If the starter motor can't free up the crank with it's torque, how could I with a wrench?