'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.