Cold Enginengine = runs fine Warm Engine = sputters and dies

I've got an 81 maxim 650 in great condition. The problem is it dies after its been running for a few minutes or once the engine warms up( not sure which one as they both occur about the same time). After that, I've pretty much gotta let it sit for 20 minutes or so before I can start it again. 2 weeks ago it was running fine.

Here's what I've done in the past few weeks:

Cleaned carbs - twice!
Replaced vacuum lines
Replaced gas line and filter
Changed oil and oil filter
taken off headers to repaint (back on now)

I started noticing the problem after I took off the headers and exhaust to repaint. After I put them back is when I started noticing the bike wanting to die after only a few minutes of riding (could just be a coincidence). This mainly happens when it's idling, or when I'm slowing down to downshift with the clutch in. It sputters and quickly dies.

Based on Internet research I figured I needed to clean the carb so I took it apart, cleaned everything including all jets and reinstalled. Unfortunately that didn't solve the problem and it has me stumped.

What other scenarios could be causing the bike to die? I'm not sure if it dies because it warms up or if it takes that long to burn through the gas that's already in the carb. I'm guessing it's either not getting enough gas, or maybe a vacuum leak that is accelerated once everything warms up???

By the way, if I notice it starting to sputter, I can open the choke or rev it to prevent it from dying momentarily, but that only works for about a minute before the inevitable.

Any advice you guys can give me to get me back on the road is greatly appreciated.

 

Have you checked valve clearances? A no start condition when warm, points directly to tight exhaust valves being the culprit.

http://xjbikes.com/forums/index.php?threads/airhead-valve-adjustment-with-pics.14827/

 

Wow, that looks like major surgery! What does something like that cost to hire a mechanic to fix? Lol.

Also, sometimes when it starts to warm up and I rev it a bit, the ram's hang and take several seconds to come back to normal idle speed. Does that help with diagnosing?

Thanks k-moe!

 

It's not that hard at all. You all ready can see how to do it. That's how I learned. And that's not all the work that's gonna need to be done to the bike. Are the fuel levels in spec?

 

Valve clearance checks are pretty easy, and manditory every 5,000 miles. Yours have likely never been done. Your '81 is doubly easy as valve adjustment can be done without removing the cams (unlike most modern motorcycles).

This weeks reading list: http://www.xjbikes.com/forums/index.php?threads/the-information-overload-hour.27544/

The best mechanic you will ever have is you.

 

Valves do need to be checked but I don't think that's your only problem. Most of you issues are in the carbs. Cleaning is the first step, float level setting and bench sync need to be done before reinstalling the carb rack. Running sync and idle mixture comes next. The engine revs hanging is symptom of out of sync carbs and/or vacuum leaks. Vacuum leaks can be on the intake boots or throttle shaft seals. Shaft seals are commonly overlooked.

 

You say you cleaned the carbs.....give is a DETAILED, EXACT description of EVERYTHING you did. When you were done, did you:
bench sync the carbs
set the mixture screws to what settings?
what height did you set the floats at
running sync
colortune
etc......

But also, a bike that runs cold, but give problems when warmed up can also be a tci issue.

Lets keep on the carbs/fuel thoughts first though.........

Can you do a plug-chop when it stalls? Lets see if we can determine if it's running too rich or too lean at that point.

Too rich may mean you're flooding
Too lean may mean you're starving

Little steps and we'll get there......

 

its rich, is the choke off. All the way?

 

I'm a newbie so probably didn't clean the carbs to the extent I should have. I basically took off all the floats and the 3 jets/screws. None were clogged and barely any gunk was present anywhere. However, I soaked everything and used and entire large bottle of carburetor cleaner. Then I basically put everything back where it was and reattached to the bike.

I did not: take the diaphragm lids off or do anything with that entire section. I did check that each valve lifted and slid down easily, which all 4 did. I could tell the diaphragms seemed to be working based on that. I also did not know that the jets needed to be put back in with a certain amount of turns. I basically put all of them back in until they bottomed out, with light pressure.

No colortune
No sync
Didn't mess with mixture screws (not sure where those are located)

Keep in mind, the bike ran perfect only days before I took off the headers and exhaust. The problem occurred immediately after I put the headers and exhaust back on. If one of the header tubes that connects to the engine isn't perfect will that cause any problems? They feel and look tight, just trying to figure out why all of this happened immediately after I messed with headers/exhaust. It could just be coincidence.

It's also worth mentioning that I am getting some of the popping sound when it's running which makes me think vacuum leak. I also have to start it with the choke all the way open. I then have to continuously open the choke slightly to keep it from bogging out during get idle.

Please don't tell me my first bike is a lemon!

I'm curious about the mixture screws and if messing with them will make my problem go away. Where are they located exactly?

 

Uh... Yeah-- what do you mean by you " open the choke"? Are you running the whole time with it on? If so, you're carbs aren't clean and you're running only on the idle circuits.

Go back to the very beginning, start your explanations again with much more detail..... Need to know EXACTLY what you do, how it reacts, what you've done to carbs, settings, etc.....

 

Don't worry, your bike is not a lemon.

 

You did not clean the carbs correctly, not set them up correctly.

You probably dislodged some dirt somewhere to get the ball rolling.

 

you need to follow this article to a tee, or you are just mucking things up more.

http://www.xjbikes.com/forums/index.php?threads/in-the-church-of-clean.14692/

don't forget to make sure your valves are in spec first.

FU

 

You need to read " in the church of clean" To understand what must be done with the carburetors. Don't panic, if that seems daunting I do offer carb cleaning services so you can contact me on that. Just spraying several jets is not cleaning. If you haven't pulled the mixture screws, you haven't cleaned the carbs. You probably have floats out of whack, clogged passages, and dry shaft seals and fuel O rings

 

I'll send a message to your inbox.... Call me and I can talk w/ you. Best thing is while the carbs are off the bike, you get the valve clearances adjusted. YOU can do that..... It's not rocket science and we are here to help learn how to do it. Either learn to do it yourself, or pay a shop a few hundred bucks to do a job you could have done yourself.....we have NO secrets here ( as far as Xj's are concerned.... Lol) and will teach you how to do it. You only need to ask, listen, then do. Geez, im turning into Yoda......

Dave fox

 

I agree with all that's been mentioned. I too was scared I would mess something up and let a shop clean my carbs--I think it was $210 and replace the fork seals--$110. While the carbs were actually pretty clean they were way out of adjustment and running very rich. I finally took the plunge and tackled the carbs myself. I have my bike running beautifully now, but without adding to what has already been said, I do want to add that you need to follow the carb cleaning instructions exactly, no short cuts and no assumptions, or you will end up doing it again, and again, which many of us have done. We all want to get the bike running quickly, but that usually results in short cuts that end up costing more time. If you have any mechanical ability it's not hard, but the first time is a learning experience and will take time. Plan on having the bike down for several days, go slow, and ask questions. While you have the bike down you might as well get the valves checked.

 

We talked on the phone and I think he realizes all of that now.... He'll get his bike straightened out, it's a decent bike. And the engine is quite nice!