Help Fixing some issues with SX400R Seca 1983

[12lanj01]

This is my first ever motorcycle that I bought yesterday for a good price. It has some issues, and since I am not familiar with motorcycles, perhaps some of you could help me. There are links for 2 videos where I describe my problems. Thank you!

First Video:

Second Video:

 

[Wolfe_11B]

1. Petcock. Turns fuel on and off to the carbs. Have it on 'Off' when not running, otherwise engine may fill with fuel if the carb needles/seats don't seal well. 'On' when cruising around, 'Reserve' will give you a little bit extra to get to the gas station if you run out.

2. Bulb burnt out. Replace it and the rear one will blink. The relay won't flash without a certain load, so with the front bulb out it simply doesn't flash.

3. I do believe that with the enrichment lever to the right, that is normal position (choke off). When you move it to the left you are making it rich (choke on). I had this issue before, confused me since the high revving is a sign of being lean, which shouldn't happen with the choke on(should start to run poor with more fuel). Was simply the carbs being out of sync. When you have the choke on it is probably getting more fuel to one carb than the other. Since the bike is new to you, I would go through the carbs about 5 times. Clean them out well, never know what is lurking in there. Then do a good carb sync, you can do a search on here or on google to find the proper procedure. There are some DIY things you can do, or buy a proper gauge setup.

4. Can't help with the seat. Sorry!

Enjoy the bike, welcome to the 2 wheel brotherhood!

 

[Wolfe_11B]

Also, this may be of help for you-
http://www.xs400.com/forum/showpost.php?p=46729&postcount=3

 

[12lanj01]

Thanks for all the information! I appreciate it.

In regards to the choke- I think you are right when you said that when the lever is to the right, the choke is off. So does that mean it is fine? Because it idles well when the choke is pushed to the right. If so, should the choke only be pushed to the left side when starting it up (if it needs it)? Thanks again!

 

[12lanj01]

Also, this first picture is a picture of the petcock. This is the setting at which it has been in for the last 48 hours and it has been starting and running fine. It has three settings (I think) which are prime, on, and reserve. Is there an off setting? And should it be in the off setting right now in the garage?

http://imgur.com/a/TX1fB

Further, I was looking at the petcock and I noticed a tube that is not attached to where it is supposed to be behind the petcock. You can see in the second picture that it is not attached. What is it? And should that be attached?

 

[Wolfe_11B]

You have a vacuum petcock, so things are slightly different. They are supposed to be 'idiot' proof by letting you leave it in the on (or reserve) position. It is only supposed to flow fuel when the motor is running. Use the 'prime' position only when starting, it bypasses the diaphragm in the petcock for instant fuel flow during startup. In order to use the 'on' or 'prime' positions though, that line needs to be hooked up. It goes to the barb on the carb holder (manifold).

If it's unhooked from the original owner, the petcock might be bad. I'd look into hooking the line back up and testing it out. If it works fine then so be it. If it's broke, you can buy a rebuild kit for it or just use a different petcock. Many people ditch the vacuum one and go with a standard on/off/reserve. They are pretty cheap, and tend to be less of a hassle. People have rebuilt the vacuum style with a kit and they still are bad after lol.

I just wouldn't trust leaving it in prime all the time, fuel in the crankcase is a bummer.

 

[Wolfe_11B]

Oh and that line being off like that might be enough of an air leak to be the cause of your high rev problems.

And make sure the barb on the other carb manifold has a cap on it and not sucking in air.

 

[12lanj01]

Thanks for the response. I just want to clear a few things up-

So obviously that tube is supposed to be on the petcock. My question is- how was the motorcycle running fine without that line connected? Even with it unhooked, the previous owner drove it to my house. Basically, what does that tube do exactly? Could the petcock be bad even if the guy drove it to my house?

Also, as shown in the video, the bike revved very high when the choke was in the left position. We both think that the choke is in the 'normal' position when it is pushed to the right. When it is in the right position, the bike revs at a normal rpm; is there anything wrong with the choke? Meaning, is it working correctly? Should it rev high when the choke is pushed to the left position normally? Or is it because of the carbs and/or that dis-attached tube?

 

[Wolfe_11B]

When it is set to the prime position, it's just an open valve, flowing fuel freely to the carbs. So it will work with the line off. When the line is hooked up, it pulls a vacuum, which pulls on a diaphragm in the petcock opening the valve when set to 'on' or 'reserve'.

There could be a number of things causing the crazyness with the high idle with the enrichment circuit on. Even though it works fine in the normal position, you should still sort out that run away rev issue, because it's not supposed to do that.

Basically the choke is only need on a cold motor. You can look up the specifics if you care too on google, but in short the cylinder walls are cold so you have issues with fuel and condensation. The choke will add a bit more fuel to compensate. It will run fine, then as it starts to warm up after a minute it will start to want to bog/die since its getting too rich. When you turn off the choke at that point, the mixture will go leaner to a proper air/fuel ratio.

What could be happening with your bike might be related to the line being off, might have one carb with a clogged up enrichment circuit, might just be out of sync with each other real bad, carbs could be all dirty/gunked up inside.

Bottom line is, when you get a new bike the first thing you want to do, and I think everyone that's owned more than one machine will agree, is to pull the carbs off no matter what. Take them apart, toss a rebuild kit on them, give all the internals a good look, clean them a few times, even if you think they are clean they are not, check float heights, check that the jets are correct sizes, check the slide diaphragms for holes/cracks, check the gaskets and o rings and seals(looks like you have a leaky shaft seal from the pictures you posted), replace fuel lines, add a fuel filter, make sure airfilters are clean, check carb boots for cracks, check plugs and plug wires.

That's some general fuel/air system basics that I do every time I buy a carbed vehicle. You'd be surprised what you will find, no matter what the original owner has said they have done.

So pull them carbs, crack open a beer, and get learning! We can walk you through any part of the process.

 

[12lanj01]

Great, thanks for all the information! I guess I'll do two things.

1) Set the petcock in the 'on' position and see what happens when I start the bike.

2) Take off the carbs and give them a really nice cleaning.

In regards to taking off the carbs, and advice on the procedure of actually taking it off the bike without spilling gas or just the general process? I have seen threads on here about the cleaning process, but not about actually taking them off the bike. Thanks again!

 

[16VGTIDave]

You are about to experience the joy of a DOHC XS400. Removing the carbs can be challenging. It is advised to have the bike warm so the rubber parts are soft and easier to work with. The airbox should be loosened and moved as far to rear as possible to give you some room to move.

Now may also be a good time to tell you that you have the wrong screwdrivers. No, seriously, those "cross" screws are NOT Phillips screws. Look closely at the heads and you will notice a dot stamped in the screw, in one of the V of the cross. These are Japanese Industrial Screws, or JIS for short. Do not think that the cross screwdrivers that you have are good enough. They aren't and you will strip the heads of the screws, causing yourself lots of frustration. Search online and buy a set of JIS screwdrivers. #1, 2, and 3 sizes. Vessel is one popular brand name, but I've read that they no longer make a true JIS screwdriver anymore.

Welcome to the world of vintage Japanese bikes!

 

[12lanj01]

Good call with the screwdrivers- I had no idea JIS even existed! If I take the carbs off, will it leak gas all over? What are the steps to taking off the carb?

Also, I want to give the bike a good cleaning. How do you take off the fairings? Thanks again!!

 

[16VGTIDave]

Most people, including experienced bike mechanics, don't know that JIS screws existed.

If your petcock is in decent shape, you can drain the float bowls before removing the carbs.

The 2 side panels are held on with molded pins into rubber grommets. Spray some lube like WD40 onto the pins before trying to remove the covers or you might brake the pins off. You don't want to do that as it is very difficult to find good plastics for old bikes.

Be sure to download and read the service manuals for your bike. They can be found in one of the sticky posts at the top of the garage. Your Seca is a DOHC XS400. Most parts that fit the SOHC bikes won't work for you. Though many of the Maxim parts will.

 

[12lanj01]

Okay, so I can turn my petcock on the 'on' position, drain the float bowls and hope the petcock doesn't have any leaks?

Also, where are the molded pins into rubber grommets that you mentioned? I can't find them anywhere!

Lastly, do you know how to lift the seat? Here is a video of my attempting to open the seat:

Thanks!

 

[Wolfe_11B]

Okay, so I can turn my petcock on the 'on' position, drain the float bowls and hope the petcock doesn't have any leaks?

Yep. I would recommend clamping the feed line, just in case it does leak. Don't clamp it too tight or you'll just destroy the old rubber line. Shouldn't really matter though, those lines look beyond saving and should be replaced.

 

[16VGTIDave]

You are missing the right trim cover. The left one is installed. I believe that there are 3 pins on it. Grab a mirror and a light and you will find them. Once lubricated, the cover should pull straight away from the bike and come off.

I haven't worked on a Seca, so I can't offer any suggestions about the seat other than to mention that you have demonstrated the correct operation of the helmet lock. Yeah, that pivoting hook thing that is released by the key lock on the side there is where you lock your helmet to the bike. If your helmet has D-rings on the chin strap. The hook goes through the D-rings and is then locked, securing your helmet to your bike. Be aware that drunks think it is funny to piss in bike helmets, so don't park near bars, soup kitchens, or homeless shelters.

All that doesn't help you get the seat open though, does it? Have you tried turning the key the other direction? Just a thought...

 

[12lanj01]

Hey, thanks for all the info guys. I found that the seat has an additional lock on it that must be opened with your hand before using the key to unlock it.

I put that hose back onto the petcock and it idles fine now. Do you think I need to take off the carbs, or can I just run seafoam through the system?

Lastly, I changed the directional and it works now! But for some reason the left side blinks twice as fast as the right side blinkers. Any explanation for that? Thanks!