left exhaust running hot

[jonny]

I noticed when warming up the left exhaust heats up a lot quicker than the right. You can also tell by the discoloration on the exhaust pipe, left side is darker. I'm thinking the mixture is lean, but for the 1981 XS650 the fuel/air mixture was factory set and there is no adjustment screw. Anyone have recommendations or experience with this?

 

[Detroit650]

Same exact thing happened on my bike. The right pipe is bright chrome but the left is straw colored. I started by spraying all around the carb mounts with ether to see if it had a vacuum leak on the left side (it didn't rev when sprayed so it didn't have a vac leak). But while I was messing with it I noticed it was puffing black smoke out the right pipe. Knowing it was running rich, the carbs were taken off and torn apart. All of the jets are the correct size, but the little rubber plug at the bottom of the pilot just was half rotten and obviously leaking. When this plug leaks, unmetered fuel is getting past the main jet, and makes it run rich which can be seen in the cooler EGT's.

 

[XSLeo]

www.amckayltd.com/carbguide.pdf explains how to clean and adjust your carbs. There is an idle mix screw, but it is hidden under a plug. You need to remove the plug to access the mix screw.
It's all in the carb guide.
Leo

 

[XSLeo]

The rubber plug is under the pilot jet and lets unmetered fuel bypass the pilot jet, not the main jet.
Leo

 

[Detroit650]

Doesn't a leaky plug overfuel the main circuit? When looking in the hole the rubber plug goes in (bottom of the pilot jet), you can see a drilling between top of the main jet and the bottom of the pilot jet. This would be the metered side of the main jet but the basically unmetered side of the pilot jet. So if the plug is leaking, unmetered fuel will enter the area of the main circuit that is supposed to be metered. The pilot jet is above the area plugged by the rubber plug so the pilot circuit should still be restricted and therefore metered.

The area I am trying to explain is the area "Note that the passage..." points to. You can see the plug goes below the pilot jet. Between the main jet and the pilot jet you can see the drilling that I'm talking about. If the plug is missing, fuel can bypass the main jet.

 

[jonny]

Thanks for all the tips The left diaphragm had not been seated all the way around, no tears so I just placed it in correctly. Also readjusted the mixture screws and synchronized the carbs. I'll have to check the EGT's again when the engine starts from cold. If the problem persists I guess it would be a good time to rebuild the carbs. Thanks again for the help!

 

[XSLeo]

I misspoke earlier, A leaky plug doesn't bypass any jets.
With the plug inplace the pilot jet draws fuel through the main jet. That's what the passage is for. This small passage and the main jet to a certain extent restrict the fuel flow to the pilot.
With a leaky plug there is less restricition of the fuel the pilot draws, this makes it run way rich.
Leo

 

[birdog4549]

My '81 is exactly the same with the left pipe blue and the right just a little "goldish". If you all find a "final answer" I would appreciate the insight. I haven't gotten into the carbs yet. All my older bikes had slides with cables and not diaphragms. I planned on rebuilding after riding this season. I won't be putting on a lot of miles as I just enjoy a short cruise now and then. I am as interested in doing a little customizing as riding so it's double the fun!

So, is this a potential BIG DEAL? Or can it wait till the end of summer?

 

[5twins]

It could be. You have one cylinder running leaner than the other. If it's way leaner, it could cause some damage over time. It could be as simple as out of sync carbs or an air leak. Or maybe you have a partially plugged jet or circuit and the carbs need to be cleaned. Or float levels may be off.

 

[birdog4549]

It could be. You have one cylinder running leaner than the other. If it's way leaner, it could cause some damage over time. It could be as simple as out of sync carbs or an air leak. Or maybe you have a partially plugged jet or circuit and the carbs need to be cleaned. Or float levels may be off.

Would I be able to "read" each plug to see if any variance is serious enough to warrant carb removal now? I'll have to read up on it to see exactly when to remove the plugs and look at them. That should confirm suspicions right?

 

[5twins]

If it's off enough, it'll show on the plugs. Don't take a reading right after starting with the choke. The plugs will be black from using the choke. Ride it for a few miles, maybe 5 to 10, to burn that choke richness off, then take a reading. Don't let it idle for a long time when you come to a stop for the plug check. That will allow the idle circuit to color the plug. The reading you're going to get from a normal ride will be midrange mostly. If that looks OK, start the bike back up not using the choke and do let it sit and idle for a couple minutes. This will let the idle circuit color the plugs. This should help you pinpoint what area of the carb is off.

 

[birdog4549]

I also have ordered the basic "rebuild" kit from Mike's. I might just as well go through the carbs now to look for obvious stuff, do a cleaning and checkout and then do the plugs for confirming info. Nothing fancy or change jets or needles just a cleanup and checkout. I did notice when I put in new air filters that one of them had a split foam allowing extra air to come in. That might have "leaned"one side (can't remember which side had the open filter. It should have been on the "blue" side.) It's probably smart to do the carb check now before I put on miles this summer. I just got it a few weeks ago. Thanks for all the info.

 

[XSLeo]

Have you read www.amckayltd.com/carbguide.pdf ?
Usually you can tear the carbsd down and do a good cleaning without a rebuild kit. Many of the kits use generic parts, These parts may work. Not often on the XS650. Gaskets are ok, the needles and jets are usually wrong.
If you are careful and a po hasn't used a sealer on the bowl gasket it can be reused.
Leo

 

[Detroit650]

I also have ordered the basic "rebuild" kit from Mike's. I might just as well go through the carbs now to look for obvious stuff, do a cleaning and checkout and then do the plugs for confirming info. Nothing fancy or change jets or needles just a cleanup and checkout. I did notice when I put in new air filters that one of them had a split foam allowing extra air to come in. That might have "leaned"one side (can't remember which side had the open filter. It should have been on the "blue" side.) It's probably smart to do the carb check now before I put on miles this summer. I just got it a few weeks ago. Thanks for all the info.

How long did it take you to get the kits? I need to order them too.

 

[birdog4549]

How long did it take you to get the kits? I need to order them too.

I just got done taking my carbs apart and flushing everything I could with Valvoline carb and throttle body cleaner (good stuff IMO) and blowing out with compressed air right away. I was too timid to separate them from the joining frame. I had the diaphragms out and when I put the carbs together I did the test by lifting the slide and plugging the top oval hole with my thumb and the right diaphragm has leaks. This makes my left cylinder do more work. I think I have fixed my problem. I got the replacement diaphragms from JBM Industries for far less than replacement slides/diaphragms. They also have a good reputation here.

Sorry to put you through all the reading but I was thinking maybe it would be helpful. Mike's ships quickly and does a great online job with email notes etc.

Just a suggestion, but I would consider replacing the intake manifolds as well. Stock OEM or better (will work with ethanol) can be found at 650 Central under the "Carburation OEM" tag. He also sells a carb kit with needle assy and gasket. He has a good rep around the forum I have found and although you actually have to call "Mike" he is nice and ships fast and can give you any tips you might ask about.

I researched all of this including the vendors both here and in experience. Hope it is helpful. Read the carb guide as well before anything if you haven't yet.

 

[5twins]

I like to follow flushing with carb cleaner by flushing with something mild like WD40 or kerosene. Carb cleaner and rubber parts don't get along. Install rubber items in areas you just had filled with carb cleaner and you could be asking for trouble.

 

[birdog4549]

I like to follow flushing with carb cleaner by flushing with something mild like WD40 or kerosene. Carb cleaner and rubber parts don't get along. Install rubber items in areas you just had filled with carb cleaner and you could be asking for trouble.

I may have to wait and see now. the only rubber items I can think of were in the pilot jet screw (the little flat one under the tiny washer) the rubber boots around the choke linkage (the big ones on the outside) and I hear there is a rubber o-ring on the drain screw (I did not remove the drain screw). the diaphragms are being replaced as they leak and were not exposed to the cleaner so that was not what hurt them. That little flat guy might be hard to get if I need it. Do you know a source for these items as they do not come in "kits". Thanks for the head's up.

 

[5twins]

That "little flat one" was originally a normal looking o-ring. They get hard and flattened out with age. I source my o-rings from McMaster Carr but there are other on-line sources. Mix screw is 1mm thick X 3mm I.D. Float bowl drain screw is 1.6mm thick X 4.1mm I.D. A new float needle seat w/ o-ring should be included in your rebuild kit but if you just need the o-ring, it's a 1.5mm thick X 7.5mm I.D. size. Sometimes the float needle assemblies in these kits are crap and you're better off just using your original if it only needs a new o-ring.

 

[birdog4549]

That "little flat one" was originally a normal looking o-ring. They get hard and flattened out with age. I source my o-rings from McMaster Carr but there are other on-line sources. Mix screw is 1mm thick X 3mm I.D. Float bowl drain screw is 1.6mm thick X 4.1mm I.D. A new float needle seat w/ o-ring should be included in your rebuild kit but if you just need the o-ring, it's a 1.5mm thick X 7.5mm I.D. size. Sometimes the float needle assemblies in these kits are crap and you're better off just using your original if it only needs a new o-ring.

Thanks, I like Mcmaster Carr. Lots of stuff!

 

[5twins]

If you place an order, it's best to get several items. Order just one thing and the shipping kills the deal. Something else you might consider are o-rings for the cam chain adjuster cap nut. Mike's gets a few dollars for one, for not much more you can have a whole bagful. For some reason, this o-ring seems to wear quickly. Probably because it doesn't protrude much from the cap nut. It doesn't take long for it to flatten out a little and start leaking. There happens to be an American size that fits perfectly - 13/16" I.D. X 1" O.D. X 3/32" thick. I change mine pretty much every season.