Off idle dying... HELP!?

Hi, My xs400 has some kind of carb issue. For some reason, if I give it abrupt throttle response from idle it will bog down and sometimes die. It only seems to do it when its warmed up and its really started to annoy me. It never used to do it, obviously. I tried richening it up a bit but I don't think that is the problem. My dad offered that it might be the accelerator pump but I'm not sure all bikes have one. Could this be the problem?

Any help would be appreciated!

Mines doing the same shit right now.out of first it sputters kinda throwing me around and either takes off or dies.I re-routed vacuum lines making sure it wasn't pinched.replaced filters and replaced bot coils.first guess was petcock,but once I'm passed 1st off the line it's fine.next step carbs?

Keep this post updated when u figure out the problem

http://www.xs400.com/forum/showthread.php?t=6479

Hi guys, I found this one, key words was bog down. I believe something that we don't know is 'when did the bike ran good last?' Were you on it yesterday? It ran great? or you ran it last month, and didn't put any fuel stabilizer in the tank? (Seaform, stabil) Seaform was stating that it never got off the ground as a "fuel stabilizer" which is what it was created for. be interesting to hear if an appropriate amount of seafoam would fix your issues? ((X amount times the amount of fuel in tank) 3 gallon tank) just my thoughts meandering. otherwise, double check that previous thread, I am sure it.
here is another one. http://www.xs400.com/forum/showthread.php?t=10051
and a another one, This one atleast the thread starter came back and admitted what happen, or how it got fixed. Drewpy thought some crap got up into the carbs,and I know I did have a bug in the diapham area. I found it prior to getting it on the road, so I dont know what symptoms it would have gave me. It was some sort of beattle. Okay, well there is three spots, based on the bog down keywords. Okay this seems to be indepth, http://www.xs400.com/forum/showthread.php?t=6112

You know I had used the term Italian tune up, thinking of just getting it on the road, and WOT, wide open thottle. Early in the season, I don't remember what caused the issues, I think it was still chilly, the bike sat for a week, to 10 days, and then my wife drove it, it sucked, then I drove it to work, it sucked all the way to the interstate. then I hit it hard, there was some sort of garbage that worked it way out, cause unlike that previous guy in one of the threads stating he is back to 50 mpg, I was back to my normal 40 mpg. Early in the season, I was using the non-corn sryup gas. now I dont' worry about it unless I need to leave it alone for more than a few days.
Good luck guys.

very true, sometimes you need to beat the cobwebs out of the system by riding it like you stole it, get it at maximum operating temperature and burn away all the gunk. But I'd start looking at those carbs first!

I ride it very often. And it just started doing it about a week and a half ago. I noticed the rubber cap on one the other carburator boot had rattled off, I'm not sure if it is the problem but it did the same thing, but worse earlier this year when I found that it had fallen off on some ride. I'm going to ziptie it on there and give it a whirl. If it is the problem I'll post a picture of what I am referring to in case my mechanical lingo is all wrong! Wish me luck.

ah the intake boot vacuum port cap Yes if that's off it'll make your bike run lean as hell.

Just letting you all know I figured out the problem. I'm not sure why I didn't try this first but it was the intake boot vacuum port cap. I simply put on a new one and ziptied it on so it would not fall off. The old one had multiple cracks and holes which made it run lean. If you don't know what the cap is that I'm referring to, it is simply the rubber cap that fits over the vacuum port on the black connector (boot) between the engine and the carburator. There are two boots, one of them has a hose connected to the gas tank and the other is covered by that small rubber cap. Thanks for all the input, I'm just glad it runs right again

congrats nice it was an easy fix

Any chance someone could post a pic or diagram showing where the vaccuum port intake cap is? I MAY have this issue and I am not what this is lol

I have checked my lines and they are both on tight, but not sure what this cap is.

Thanks!

Recreateme said:

Any chance someone could post a pic or diagram showing where the vaccuum port intake cap is? I MAY have this issue and I am not what this is lol

I have checked my lines and they are both on tight, but not sure what this cap is.

Thanks!

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Both carbs "plug into" the Carb mounts/boots/spigots (call them whatever makes you happy). These are the rubber things that bolt to the head, have a clamp around them to hold the carbs in. Both of these rubber things have what looks like brass nozzles sticking out. The left side one has a vacuum hose to the petcock. The right side has a rubber blank-off plug on it. They are both used when syncing the carbs, that's why there is one on the right side as well. The rubber cover on the right side rots off and causes vacuum leaks. The vacuum line and the petcock diaphragm on the left rot and cause vacuum leaks. The spigots/boots/carb mounts themselves rot and crack, and cause vacuum leaks. The price you pay for rubber/polymer. The carb mounts are rubber/polymer for several reasons: ease of mounting, some vibration insulation, and some heat insulation. The heat, UV from the sun and ozone kill them off. Ethanol helps this along, so all of the rubber fuel system parts need endless attention when using ethanol. If you need to let the bike sit for more than a few days, I'd drain the carbs first. Drastically easier than pulling and cleaning them. This is a problem with carbs, and is a problem with my FI bikes as well. The only advantage FI has is the fuel is under pressure and forces the goo out the injector(s) where atmospheric pressure pushes the fuel towards the vacuum in a carburetor.

I never thought I'd miss MBTE....(ethanol needs to go back to solvent use)

Gotcha, I have two hoses on my bike, I always assumed they both were in use. So if I remove the right side I need to plug their brass nozzle and plug the hose ? Or can I leave the hose unplugged?

You have to plug it. If you switch from vacuum petcock to a new petcock with out the vacuum, you will need 2 plugs. With out a plug, the bike will run Lean, as too much air is getting in there.

Mike is just stock in that respect, how do you plug the hose normally?

Typically a rubber vacuum cap. You can find they at most auto parts stores. Or just take a short piece of vacuum hose and plug one end with something like a ball bearing, golf tee, screw, bolt, silicone sealant, or whatever you have that will make it airtight.

Just stick a screw or bolt in there and tighten it down with a zip tie, that'll do.

Just for the record, I wouldn't recommend using ethanol in any motorcycle...ever. Premium is the way to go. Ethanol wreaks all kinds of havoc on carbs and isn't that great for the engine either. If you still want, I could post a picture of my vacuum cap but it really doesn't warrent it. It is a pretty easy fix.

karatekid1194 said:

Just for the record, I wouldn't recommend using ethanol in any motorcycle...ever. Premium is the way to go. Ethanol wreaks all kinds of havoc on carbs and isn't that great for the engine either. If you still want, I could post a picture of my vacuum cap but it really doesn't warrent it. It is a pretty easy fix.

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I can't speak for your area, but all of our gas has ethanol, premium as well. Just an aside here: all of these bikes should be running premium. I wouldn't run any motorcycle on 87 octane fuel.

It doesn't realy matter what octain you run mostly all grades of gasoline at the pump has ethanol these days.I mentioned this in another thread but our wonderful gov is pushing for even higher amounts of eth in our fuel.The only way around it is to go to a local marina if theres one near you and but efree premium.Luckily Im in the great lakes region so we have marinas all over the place.I ran a tank full this summer what it difference it made.

Scorpio1963 said:

It doesn't realy matter what octain you run mostly all grades of gasoline at the pump has ethanol these days.I mentioned this in another thread but our wonderful gov is pushing for even higher amounts of eth in our fuel.The only way around it is to go to a local marina if theres one near you and but efree premium.Luckily Im in the great lakes region so we have marinas all over the place.I ran a tank full this summer what it difference it made.

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Yeah: I never thought I'd miss MBTE, but I do. Lucky for me most of the things I have are FI, but even FI engines don't fare well with ethanol.

If you're an off road type as well, putting some of the VP race fuel sold for the MX/Enduro guys makes a huge difference. They now make non-ethanol fuel that is emission compliant as well, so you can run it in newer catalyst equipped bikes. Certainly not for daily drivers at that price, but something to think about during storage: VP can sit in your tank/carbs all winter and won't gum up. Just like going back in time to the days of fuel being fuel, not solvents.

The primary difference made by running premium grade gasoline is the octane rating. To keep it simple, the higher the octane, the lower the flash point of the fuel which results in slightly cooler operating temperatures. Due to principles of vapour pressure - I'll spare you the thermodynamics there - if you're in high elevation e.g. 4,000ft above MSL or more, a higher octane rating isn't as crucial, your fuel will flash at a lower temp simply due to lower atmospheric pressure allowing it to enter the gaseous phase more readily - this is why when I was living around 4500 last year, they didn't have 93 as they do back here in Chicago, only 91. Sorry for getting nerdy, I'm a chemistry Ph.D. student with a M.S. and B.A. and can't really help myself.