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jomama

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OK lads am the newest of the newbes here and I have a couple of questions. I cant find the model#s on the barbs on my 80 XS400 .I know they should be BS34 and cant find a very descriptive pic anywhere. Secondly There is mentioned that some manuals are wrong on the float settings . Mine were 27MM and the proper is 32MM . Just how much of a difference would that 5mm cause ? Thanks much for any help.
 
Experimentation and experience have led to the conclusion that 26mm (with the round brass floats) is about right. Leave yours at 27m and you should be fine. 5mm makes a huge difference and in the case of going to 32mm, a difference for the worse. As for whether yours are BS34s, post a pic if you have any doubt or look at any number of the pics posted on this site.
 
Well sir, I am pretty sure mine are the BS 34 and I just reset the floats back from 32 to 27. BIG difference. HOWEVER i am still plagued by the same problem I have had with this bike for years. Warms up and it will slowly decrease in idle and die. If you give it gas before it dies, it will stall. I swear it is running out of gas. I know this problem has been addressed before and the suggestions were change timing. This 1980 has elect ign.check tank cap for venting . It will do it even with the cap open. Petcock. I run it on prime and still the same results. Pilot jet screws out between 3&1/2 and 4 turns. I installed new diaphrams and I swear it actually ran better before. Pilot jet screws re out 3 I am about to give up and stash it in the shed and ride my electra glide.
 
What's your compression like? If it's around 120 or so or under, try advancing the timing just a bit. After making sure the valves are in spec and the carbs balanced and cleaner than you think they should be, advance it while running and the idle should increase and when it starts to slow on advancing, back it off a few degrees and try that setting. No timing light necessary- just your ear. I had a similar issue and this worked for me.

If your compression is well over 130, that's not it. If the compression is up there (again, assuming surgically clean carbs), I would wonder how well the battery is charging or whether the battery is good. Believe it or not, the electronic ignition models seem to have a few more charging issues.
 
Funny thing, after reading so many posts on this or very similar problems there was one where the poster said he set the floats at 22 which I did . It runs like a scalded dog down the road. Better than ever. Set the pilot ccrews to about 4 turns . HOWEVER as soor as it heats up and you stop say for a light, it wants to stall just like its running out of fuel. Even with the gas cap open and I have plenty of flow to the carbs. It will sometimes spit back through the carb when i try to catch it before it does stall. This sounds like a lean thing to me but no matter where the pilot jets are set, it still does it. I have checked the valves and all are in spec. I have had the battery oh a charger and its up to snuff. I think its getting time to send it down the road. I have tried to fix this problem for years and cant . One more argument for single carb setup. I could never understand why the european and japanese opted for a carb per cylinder .Lets face it they made cars for many yrs with as many as 16 cylinders and only 1 carb .
 
Is your bike stock or do you have aftermarket exhaust and pod filters on, if you have aftermarket exhaust and or pods on you need to rejet if you haven't already, this could cause it to run lean like you are saying, just adjusting the fuel mix screws won't fix the problem alone if you need bigger jets. Not sure if you have aftermarket exhaust or pods so not sure if this is the problem. Just thought I'd throw it out there.:shrug:
 
after all these years of messing with cars and dirt bikes, i learned on this site that..... the fuel that is metered by your idle screws is actually a mixture of air and fuel that is mixed bye your air jet and your pilot jet. a lean condition at idle cannot be overcome by backing the screws out. a larger pilot jet may be needed just to ovrcome the crappy fuel that we are forced to use nowadays.

does this sound like a solid theory???
 
OK Lads, after walking away from this problem for several times and reviewing all the helpful comments I now am looking at the fact that this bike does in fact have some type of Tony NoName mufflers and the fact that although the air boxes are original, I recall that yrs ago when I first came on to this machine that the foam air filter elements were shot. None avaibable at the time or the only option was complete new metal inserts covered with the proper foam. Money being tight at the time plus the fact that like most of us here I figured why not try something like removing the old foam pieces and re wraping w/a textured foam fabric which i believe may have been from a ac filter. When i think back that this stuff was nowhere as dense as the orig stuff. Sooooooo both factors (mufflers & filters ) surely could contribute to a lean situation. All that being said, what has helped the greatest is setting the floats at 22m and setting the pilot screw out to 4 and a half . Even though it runs down the road like a scalded dog, there still is the idling issue which when below 1500 it wants to stall and sometimes will when moving from a stop. So now I need to up the ante on the pilot jets. Any suggestions as to where i can find them?. Once again thanks much for all the help.
 
OK Lads, here is a question i have. If a pilot jet is replaced with a larger one, does the pilot air jet also need to be replaced and if so is it done in the same incriments as the pilot. My schematic shows both . Also the manual lists various stock jet sizes and lists a "starter jet" but nowhere in the schematic is it pictured. Is there another name for this jet?
 
i have not heard of anyone changing an air jet thus far. the most common course of action is to order the next two sizes up and try them out! mike's xs seems to be the best place!
 
I ordered 2 sets of jets from Mikes . 45 & 47.5 and will change them out with the smallest first of course and see what happens. I will keep you informed.
 
I replaced the jets with #45s and no change. Set pilots at 4 turns, new diaphrams, set the floats 40 ways from sunday, checked the coils,wires and plugs.
starts well when cold but dosent want to return to an idle for say 15 seconds after throttle is closed. Once warmed up it will sit nd idle and gradually slow down and stop. Trying to restart with kicker or elect only prosuces a few putts then it quits. I am about to get the cutting torch out. Nothing but frustration. After decades of this it may be time to give it up.
 
Today i pulled the carbs for like the 6th time .Made absolutely positively cartain all passages were clear. Replaced them started it up and once it runs like a scalded cat down the road UNTIL it heats up and you try to get to idle . It gradually slows down and quits. I even rechecked and reset the valves. Coils are in speck and fire even when it quits . Its elect ign and never been opened up so i doubt its off. It acts like it is eventually running out of fuel but the bowls are full. So i think ign but there is still spark even when it quits. I also know its not the valves. I just dont know .If it were cdi related then there would be a spark issue.
 
I havent checked the comp in yrs but will do so today. As for the timing advance, is it possible with this cdi system?. I remember when HD went to elect. ign inthe late 70s. Many guys pulled them out and replaced them with the old points setup. I doubt its even possible with this system. MY 77 xs400 had points and no trouble. As i always say, " I'll take old and reliable as opposed to new and improved any time ".
 
Checked the comp and it was 120-125 and i know its not in the upper numbers listed in my manual, its at least within 5lbs of one another. I finally got the ign cover off and i can tell its never been touched . When the temp dips down a little i will hook up a light and see for sure. I just hate the thought of taking an oil shower . Since replacing the diaphrams the throttle takes forever to return to neutral . I was very careful when i did it as to make sure the were in the exact position as the originals. Between diaphrams ,jets, rubber plugs etc I am into the carbs for 90 some bucks and i should have left well enough alone. Sometimes the only way to fix a suspected problem is by replacing the suspect part and as we all know it gets expensive when it disent cure the problem.
 
Just for kicks, start it up and let it idle, then advance the timing. The idle speed should speed up. When you have advanced it far enough that it starts to slow again, back it off a few degrees, close it up, then adjust the idle speed with the idle air screw. See how it runs then. Doubt it would hurt.

Once the engine has some wear, and your compression shows where, but is still OK (mine's about the same and runs fine), the stock timing setting needs a little advance.
 

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