1982 xs400 seca dohc problems starting and stuff

[Jataylor]

Hey guys,
My name is Josh and I've got some problems getting my motorcycle fixed up. It's been quite frustrating and I'm not really sure what I should do next. Here's the situation:

The bike will only start if I use starting fluid. When it is running it seems to idle fine, no surges and it settles down nicely at around 1200 rpms. However, the bike will not run at all with the choke off, which is I believe when the carburetor opens some holes to let in more air. While the bike is idling, the right side exhaust is poofing much stronger than the left side is, and the left side exhaust smells of gas. When the throttle is opened, there is a significant delay before the engine responds and revs up. If I rev the engine, it will stay revving and hang around 4000 rpms for probably 5-8 seconds or so before slowly settling back down to idle. I have recently cleaned the carbs a couple times but I have not synchronized or done any of that. Any help would be greatly appreciated.

 

[chkm8]

First thing I would do is clean the carbs again, every part, inside and out. Then clean them again. Then sync, adjust the fuel mixture and set the idle. Have you done any modification to the bike or is it stock?

 

[Jataylor]

Thanks for replying so quickly. The bike is stock. I soaked the carbs overnight in a cleaning solution last time i cleaned them, and I cleaned them twice thoroughly before that, so that should be good? How do i go about syncing the carbs?

 

[Militant_Buddhist]

my money is on vacuum leak.
any takers?

"cleaning solution"... the stuff in the spray can or the stuff in the bucket?

 

[DCopp]

hopefully not pinesol

 

[Jataylor]

The solution was a bucket of carb cleaner. The first two times I cleaned it with regular carb cleaner from the can. I thought it was probably a vacuum leak as well, and I read elsewhere on the site to try propane to find a leak. So I did that, and as far as I could tell the propane didn't make any difference in the rpms.

Yesterday when I got it running it was acting different than the situation i described above: it was still doing the revving up to 4000 rpms, but it was not settling back down into idle. From the moment it turned on, it shot up to 4000 and just stayed there until i started messing with the choke, which seemed to get it under control. With the choke slightly out i could get it to about 1500 rpms. I checked the compression when it was warm and the left cylinder is 130 psi and the right read 135 psi.

 

[chkm8]

I'd check for a vacuum leak, especially around the intake from the engine to the carbs. The old boots tend to crack. A can of propane can diagnose that. Also, check the o ring under the mixture screws. Those can go bad after 30 years or so. Once you know those are good, then sync, adjust mix if needed and reset the idle. Houghmade has a good thread on making a home made tool for carb sync using a ladder, 10 ft. of rubber tubing and some ATF. Not a lot of work for those steps and it should improve. Also, you didn't mention if the bike is still stock or not. Different exhaust and/or intake with screw with your carbs if they aren't rejetted.

 

[Jataylor]

The bike is stock. When I checked for leaks with the propane, I couldn't find any, I checked very carefully around the boots. I'll go ahead and sync the carbs and update after I've done that. Thanks a bunch guys.

 

[chkm8]

I'd also check out OliverB's threads about leaky mixture screw o-rings, usually a cause of hanging rpms. It details how to change those out.

 

[Jataylor]

Ok I'm about to sync the carbs, now what is the procedure for adjusting the idle mixture screws?

 

[Jataylor]

So I just used the manometer that I made to test and sync the carbs and... they were perfectly on. I turned the bike on and the liquid stayed put. I even turned the screw and the liquid moved, so I know it was working. I was kind of hoping it would be way off so there would be something to fix. I guess the next step is adjusting the idle mixture screws? It is still running like crap and the rpms hang for extended periods of time around 4000.

 

[chkm8]

The good news is that you know what's going right. From what I gather here, hanging rpms typically mean a leak somewhere. Check out OliverB's posts, since a common spot is the o-ring seal under the mixture screw. Since you've said the carbs are clean, this is all I can think of offhand.

 

[thlillyr]

My bike wouldn't idle without the choke. The problem was one of my idle jets was plugged even though my carbs were sparkling clean. Somthing from the gas tank go in there. Need to shove a paperclip in to disloge it. Now my bike Idles without the choke. Even starts without choke too. Oh and when you open the choke your not letting more air in your letting more fuel in. To adjust the ilde mix screws pull the tank or at least lift it up. and you'll see 2 screws on top of the carbs. 1 per carb. Trun them all the way to the right until they stop. Then turn the back until the desired effect happens. 2.5 turns is stock. Most old bikes need. 3.5 turns. My bike is 4 turns. This fixed my throttle response issue but not hanging RPMS and the exhaust poof uneveniss you mentioned. I have that too love to hear what fixs that for you.

 

[HoughMade]

Thanks for replying so quickly. The bike is stock. I soaked the carbs overnight in a cleaning solution last time i cleaned them, and I cleaned them twice thoroughly before that, so that should be good? How do i go about syncing the carbs?

If your bike is running the way you described, it doesn't matter that your previous cleanings "should" be good enough. The carbs are still dirty. What you describe is a classic dirty idle circuit. I had my carbs on and off and cleaned at least 5 times before they were right. If you did not visually verify that every passage was flowing freely, you can not know if they were clean.

As for your hanging idle, what are the idle mixture screws set at? The factory specs are very lean and you need to richen up the idle mixture by having the screws out further. For instance, on my bike, the stock setting is 1.25 turns out from lightly seated, but my bike runs correctly at 3 to 3.5 turns out.

Don't bother trying to sync until you have the carbs verified as cleaner than clean and the idle mixture adjusted. Syncing is more of a final- fine adjustment after all the larger adjustments are done.

Good luck!

 

[lhaolpa]

These carbs are sometimes hard to get clean.I boiled mine overnight twice,the second time,they were still dirty despite looking clean as can be. You really have to blow out all passages,and especially the emulsion tubes under the main jets,as they can hide gunk that can cause trouble later when you put it all back together and start it up. Check the slides,and make sure they move easily without binding. I cleaned mine with 1200 wet-dry sand paper gently with W-D 40,and I finally got it to slide gracefully in it's bore.You don't want to remove any metal,just dirt,burrs,etc. Good luck. lha

 

[OnePhate]

I have the same bike, same problem. These carbs are a real bitch. I've cleaned mine thoroughly so many times I can't count, boiled, dipped, sprayed, blown, everything but ultrasonic cleaning. Maybe I'm having a misadjusted float, I still haven't attempted to sync the carbs as I can't get the bike running long enough. Good luck and let me know how it all works out for you.

 

[bcware]

Hit the passages with compressed air and carb cleaner; there is nothing quite like 100 psi I'd also pull the pilot jets for this procedure making sure the tiny pin holes on the side of the jets are also clear. If they are not clear use a single strand of brass wire from a brush or wheel to clear them.

All I have is a little air compressor, but it was cheap, does jobs like these, and fills my tires.

 

[OnePhate]

you know what, come to think about it i've never taken out the pilot jets, they are pretty well sealed and factory set, so i've always been hesitant about ripping out the seals and taking them out without a clue of what the settings should be.

 

[bcware]

Are you talking about the idle mixture screws or the pilot jets? On the newer carbs the idle mixture screws have a rubber o-ring that tends to break down. Houghmade just told you the settings a few posts up by the way

We're all basically saying the same thing; the carbs are still dirty and/or have leaky o-rings (if you have them).

 

[Jataylor]

Thanks for all the input guys, this really is an awesome forum. Things have been moving slowly ever since school started back up, but I'm getting closer to where the bike is running somewhat proficiently. The problem has evolved somewhat, I just have this last real issue with it: whenever I'm riding and i pull the clutch in, the rpms will hang around 4,000. If it's revving above there and i pull the clutch in, they will settle down to 4,000. If it's above around 2,000-2,500, they will raise themselves to 4,000. Eventually they will settle down, but this typically takes 10 or more seconds, so I've taken to putting it in gear and letting out the clutch just enough to get them to bog down, at which point they'll settle down to 1,100 or so. If the bike is just idling and I rev it above the 2,000-2,500 mark, the rpms will shoot up to 4,000 rpms and hang there. Even when I'm in gear and not on the throttle, the rpms will hang around 4,000, keeping me at that speed depending on the gear. This happens at least in gears 1-4. The bike seems to do it more readily when it is warmed up, but I'm not completely sure. Another thing, when taking off in first, the bike is really finnicky and wants to die. To take off in first, I typically must rev it to 2,000 or 2,500 just to keep it from dying on me on takeoff. It also doesn't want to accelerate straight off the clutch, once I am off the clutch it takes off. I think the wanting to die on takeoff may just be a mixture screw adjustment, but what do you guys think? Any advice you guys could give would be greatly appreciated.