Carbs popping off when starting, not running well

[TwoFitty]

To start off, I have a 1977 xs650 that just hit 120,000 miles. I was riding the other day and I went to kickstart it (electric start is so-so) and the carbs popped out of the boots/holders (I have pod filters). This happened twice more before I finally got it started and got it home. Now it does it every time I try to start it. It sounds like it could be backfiring (does that sound right?). The bike sat for around 20 years and my guess is that the boots (original) have an air leak. Could this be the cause? Also if I rev the engine in neutral or with the clutch pulled in the revs do not always come back down unless I put in gear/release clutch. I have read this could be a sign of leaky boots as well.

I purchased new boots and plan to put them on this weekend. I plan to adjust the cam chain, valves, and timing, sync the carbs, and adjust the fuel mixture. Anything else I should do? Any advice?

Two more questions. I am running some cheap pod air filters I bought on amazon with the stock jetting, I know the bs38's on a '77 aren't as lean as the bs34's but should I re-jet? And I am also running the stock ignition. Does that mean it's a points ignition?

Thanks for the help!

 

[gggGary]

First thing to check is a sticking advance or weak or broken advance springs.
Yes 77 is points. Running with a sticky or weak springs advance can hole a piston or break your foot too. Do NOT run those cheap pod filters, you can throw a cat through them without hitting any filtration. Buy a set of UNI filters
Really 120,000 miles? That's a bunch!

What boots did you buy? There are bad boots, cough... mikes.... And there are fleabay sellers that don't know their ass from a hole in the ground and sell the wrong size manifolds.

 

[scabber]

I would check the advance mech points and timing .Sounds like back fire blowing them off. The advance rod sticking they need reguler service. Looks like gggary got here first

 

[TwoFitty]

Thanks gggGary!. No experience with the advance or advance springs. If it were a sticking advance, is there a way to grease or lube it?

Yeah, it's a lot of miles, my dad bought it brand new in 1976.

 

[TwoFitty]

I bought these boots

http://www.ebay.com/itm/360609825526?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

[jetmechmarty]

georgefix is a reputable seller. I buy a lot of parts from them, but I choose to use their website. http://www.georgefixs.com

 

[gggGary]

Plus one on George fix on the dealings I had with him. Yes it is easy to remove polish regrease and reinstall the advance rod. You can also shorten a stretched advance spring. I just did it on a 79 and got the spark right back into specs.

 

[burns]

120K !!!! Golly!

the hanging idle is usually caused by weak springs in the ATU. If the springs don't return the bobweights to their seated position the timing remains a bit advanced and the idle hangs. I don't think that will cause an over-advance condition in itself, but if the locater pin slot in the ATU has wallowed out that could. I'm thinkin' its time for a new ATU.

The stuck on advance situation is also what is blowing your carbs off.

 

[gggGary]

To remove the advance rod.
Mark it's position on both ends with paint or a marker.
Undo the nut on the RH end.
Tap the shaft in a bit by putting a drift on the end of the threaded stud that will release the inner notched advance disk from the cam.
Push the cam back in to remove the small pin that located the inner advance disk.
Use a long bolt or other suitable drift and push the cam out the points side.
Clean, buff, lightly grease with a light weight grease like high temp brake grease.
Reassemble, you will have to push the points blocks open to get the points cam past them.
Re-install in the same position it came out. Put the locating pin,advance disk, washer and nut back on.
Now work those advance springs. Hint the mikes springs are often called weak and not up to the task. The e-clips that hold the bob weights like to head to the far corners of your shop never to be seen again.
An old Yamaha service bulletin calls for bending the two metal ears, that stop the weights, in to reduce "excessive" advance.

You may hold the record for highest miles on your XS on this board.

 

[thelowlife]

I just went through this last weekend..

I have a 72' fresh cleaned carbs, fresh rebuild with new rings. Started it and was chasing down some idle issues. I had the carbs pop off and a 'cough' through the carbs with no start. I have some shitty boots on my bike as well.. You probably wont be able to tune the carbs without those new boots.

I determined that I had lost a locating pin on the Auto Advance Unit side. Not saying thats your exactly problem but I'm willing to bet that timing in some form or another is your problem. Auto advance weights, springs, locating pin.

If you think about it.. the ignition system is likely firing at the wrong time and creating pressure enough to pop the carbs off the boots. Just a thought having dealt with a similar issue recently. Check the engie timing related stuff including cam chain tension, valve lash, Advance Unit stuff and make sure your locating pins are there.!

 

[Tomterrific]

It could be as simple as the heel of the points wearing and retarding the timing. Adjust the points. Check the timing.

Tom

 

[burns]

It could be as simple as the heel of the points wearing and retarding the timing. Adjust the points. Check the timing.

Tom

but retarded timing wouldn't raise the idle would it?

 

[5twins]

No, it would probably drop it a little, make it "lumpy" (rough) too.

 

[TwoFitty]

Thanks everyone. I won't even be able to look at it until Saturday. It sounds like the advance unit is the problem, and makes a lot of sense with my symptoms. Once it starts it runs fine at higher rpms, but dies at lower. I really hope I don't have to replace the whole unit; I am on a tight budget. If I do need new springs or parts, where can I find them (if mikes are too weak)?

gggGary - you really think so, I knew it was a lot of miles but I did not know it was that outrageous. I plan to put a lot more on it!

 

[deadchef]

..... Do NOT run those cheap pod filters, you can throw a cat through them without hitting any filtration. .....

funniest shit i've heard all week!

 

[5twins]

As mentioned, you can shorten your existing springs if they're too weak. Cut the hook loop off one end and bend the next coil out to act as a new hook. Only do one and test, it may be enough. But before any cutting, lube everything up. That may be all it needs.

Besides lightly greasing the advance rod, you should grease the bushings in the ends of the cam. Once the rod is removed, you'll see the cam end bushings have grooves cut into their I.D.s. Those are for grease retention .....

Clean any old grease out and fill with fresh stuff. The factory recommends a grease with a high moly content. I use VW CV joint grease .....

Be sure to assemble the advance rod so the locating pin for the little advance disc you removed points in the same direction as the locating pin for the points cam. If you don't, your timing will be 180° off .....

 

[TwoFitty]

Ok, so finally got to work on it today. First I adjusted the cam chain, then the valves. Then I got to the ATU. I could push the weights out and they would not come back in on their own. So I removed the advance rod and cleaned and lubed it with CV joint grease. They still did not come back so I cut a coil off of the weaker of the two springs and after refitting it the unit seemed to be working just fine. I

So I put it all back together, tried the electric start, no go. Tried the kick start and got a sort of cough and smoke out of the left air filter. This made me realize I had forgotten to put the new boots on so I did that and kicked it again and it fired right up. Sounded better and no throttle hover at all. A few hours later (petcocks left on) I came back out, kicked it, and the same cough/smoke in the left side again. Kicked it again and it started right up and ran great. I did not get to ride it at all as I put it in gear and started down the driveway and the clutch cable broke, but I can fix that.

Any ideas what may be causing the smoke issue? It also seems that my carbs are leaking a little bit of gas somewhere, not sure if that could be related. Thanks. I had to leave the bike at my father in laws and probably will not see it again until Easter. But any help would be appreciated. Thanks!

 

[XSLeo]

With that many miles it may need a good carb cleaning and a bit of carb tuning.
Have you read the carb guide? www.amckayltd.com/carbguide.pdf
It has a section on tuning. Download it, print it out. Read it, several times if necessary. With the pod filters you need to at least adjust the idle mix, probably rejet. Depending on the pods you have it can be hard to tune them. Poor air flow as well as possible blocking of air ports in the carb bell.
Leo

 

[TwoFitty]

Leo, Thanks. I have read the carb manual. I plan on doing some carb work over easter weekend. But I was worried about the smoke because wouldn't that mean that there is either bad compression (I need to get a tester, but don't have one), an open valve, or bad timing. I really hope it is just the carbs as that shouldn't be a hard fix, could a lean/rich mixture or engine flooding cause the smoke I described? If so I would guess it was a rich mixture as both times it happened with the choke on, then started with the choke off, sorry I forgot to mention that in my post.

If it were a rich mixture, I would guess that it is float height or a sticking needle, could possibly account for the gas leaking as well. I guess it could be the pods blocking an air vent; I wish I had the bike here so I could go look at it now...

 

[5twins]

If you flooded it, it may smoke afterwards for a little bit. You've just dumped excess fuel into the cylinders which is going to wash some of the oil out of there, hence the smoke. Honestly, with as many miles as you've got, I think you'll be doing some work on more than just the carbs, lol.