Bogs, hiccups, stalls, only when hot, after 12 - 15 mins 1980 Special 650

Pyrobooster

Pyrobooster

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Hey boys,

I have been having a hard time chasing this problem down.

My problem:
After about 12 - 15 mins of normal riding, my bike begins to bog and cough a bit like when you are running out of gas. After another minute it gets worse, I have to give throttle at stop to keep from sputtering. Maybe another minute or two later it will sputter and cough and bog even when running at 30mph with throttle. Then if I stop or slow down it typically dies. Lights work still so the battery isn't dead I think. Then after sitting for 15 - 20 minutes I can usually restart and run for 10 mins before having the same problem. It an intermitent problem, it happens most of the time, but not every time.

I usualy keep a battery tender installed when parking overnight at home. The battery is 4 years old.

I have heard these following possible problems on other forum threads:

-Bad coil, fails when hot
-Clogged something in the carb
-Floats misadjusted in carb
-Ignition problem
-Weak charging system

Can someone please help me understand where to start?

Thanks in advance,
pyro
 
TwoManyXS1Bs,

It does have a vacuum pecock.

From what I understand there is a vent hole in the gas cap.

Is that correct? If so where is it? Is there some other venting location or just the hole in the cap somewhere?

How do I test this? My idea is ride it til it happens, then pop the gas tank open. This should remedy the problem quickly and I'll have my answer. Evidence would be cap will suck in air like when opening a vacuum sealed jar of jelly or something?

I'll try that next chance I get, also thanks much for the fast reply.

Pyro
 
Thanks, any other ideas? I plan to get this hammered out all at once so I need as many ideas as possible.
 
Anyone else care to weigh in? I am hoping to make a day of getting this figured out and need some alternatives in case the above mentioned vent problem is not the issue.

-pyro
 
Are you running fuel filters? How old are the fuel lines, Have you removed and cleaned petcocks, petcock screens. Have you checked spark when the bike quits? (carry a spare plug) Compression test cold, hot. When's the last time the cam chain and valves were set?
voltage at the hot terminal of the coils when it dies.
Have you removed and cleaned the fuel screens above the float valves? (BS34)
Have you checked, measured, changed spark plugs, caps, wires. Is this a TCI bike? Most 80's are. Checked pick up ohms? What charging rotor are you using?

Well that's it for off the top of my head for now.
 
I might first start by eliminating some of the possibilities.
Lets start with the mechanical aspects first.
Check and adjust the cam chain tension.
Check and adjust the valves.
This eliminates these things from the problem.
On your coils, yes, they can act up as heat builds up in them. Your repair manual covers how to test them. Ohms on the primary and secondary sides. Test them cold. Now run the bike till it starts acting up. Retest the coil. If it reads the same hot and cold I doubt your coil is the problem.
On your ignition you can test a few things, the coil, the pick ups and the wiring. This can be found in your repair manual. The TCI box has no testing procedure other than swapping it for a known good one.
If you do a bit of searching for TCI box fixes or igniter box fixes you can find how several people have fixed theirs.
If your bike runs ok most of the time I doubt the ignition is at fault.
Now the charging system. The simplest test is to check voltage at the battery while running. At idle it will be somewhere around 12-13 volts. Now as you rev the engine slowly the battery voltage should rise as the rpms increase. At about 2000-2500 it should be up around 14-14.5 volts. As you further raise the rpms the voltage should stay at the 14-14.5 volts, never more.
If this check shows low charging then you need to follow the charging troubleshooting guide. It can be found in the XS650 TECH Section.
These things cover the mechanical and electrical things most usually found to give you symptoms such as yours. Now on the part that most intimidates newbies. The carbs.
www.amckayltd.com/carbguide.pdf tells you how to tear down, clean, inspect, adjust and reassemble your carbs. Don't buy anything for your carbs till you do the tear down, cleaning and inspection. Most of the carb parts will be reusable. Most of the kits you can get have generic parts that you can't use. The most replaced part is the float bowl gaskets.
Read the carb guide thoroughly.
Once you get them clean and things set to factory specs there is a section on how to tune your carbs. This is the most likely culprit in your running issues.
Do all the other things first. Then do the carbs. You want as many of these other things working properly before you tackle the carbs.
Leo
 
Guys,

Thanks for this very comprehensive list. I am making a big list now based on it on how I will attack this problem. Seriously this is great, such a great resource.

One thing occurs to me that may evidence a fuel problem:
If I run it to stall and then openthe drain plugs on the carb and get little to nothing that should prove or disprove the fuel delivery system (at least gas tank to the float bowls) ) as the culprit? Am I correct in making this assumption, or will I have some fuel left over there anyways and not prove anything?

Thanks again,
Pyro
 
The bike will quit when the fuel is low, not completely gone. I like to cut a quart oil bottle to fit under a carb, remove the drain plug turn the petcock to prime, watch for a good steady fuel flow for about a cup of gas in the bottle, look for debris in the bottle.
 
Guys, I have compiled a list here based upon all of your awesome responses. Tried to give props where I could, forgive me if I failed to.

Check it out, any feedback would be most appreciated and potentially save me a ton of time:

Clogged vent hole in gas tank lid:
There should be a small vent hole in the gas cap somewhere. If this is clogged a vacuum with be created and gas will not flow into the carbs. This can be easily tested.
1. Check for the vent hole and clean if clogged
2. Run the bike until it starts to bog and die
3. Pop the gas tank open while running and listen for air to be sucked in
4. This should remedy the problem quickly
5. Alternatively the engine could be killed and the carb drain opened. If no gas leaks out immediately, it is dry and not getting fuel for some reason. This would prove no gas, so check the whole fuel delivery system.

Clogged or obstructed pet cock vent line (?) Not sure where that is:
Petcock has never been removed and cleaned and should be.
1. Removed gas tank
2. Remove and inspect petcock, screen, vent line and clean and replace for any and all obstructions
3. Now would be a good time to rebuild the petcock
4. Check vent line (?) I don’t know where this is? Possibly the second line running from petcock (the not to gas tank, and not to carb line (assuming there is one)

Clogged gas line:
Replace all available gas lines and hose clamps
Cut and inspect old lines
Replace fuel filter if needed.

No spark when bogging and stalling:
Verify all connections are tight, looking for bad connections or grounds props to scabber
Just after a stall out pull the plugs, ground out to engine and turn over motor (with ignition on) to verify spark at both cylinder
If spark is fine move on, if no or weak spark then swap plugs for new, try again.
If no or weak spark persists then the wires or ignition system (wires, caps, coil etc) is likely to blame move to next step
Bad spark plug cap or wire
Verify all connections are tight, looking for bad connections or grounds

Check resistance in both plug caps, and wires:
If there is uneven resistance between the two sides then replaces all and see if that alleviates problem. Move on to next step

Bad coil props to XSLeo:
Verify all connections are tight, looking for bad connections or grounds
1. Check resistance on primary and secondary cold
2. Check resistance on primary and secondary when hot (or just after it dies)
If they are different (between hot and cold) then you likely need a new coil

Bad ground in ignition system:
Verify all connections are tight, looking for bad connections or grounds
Check and verify ground wires in the ignition system and coil

Not charging:
Verify battery water level is correct
Charge battery to capacity
Check voltage at idle (12-13 volts) and at 3000 and up RPM (should hold steady at 14-14.5 volts) if low the battery is bad or charging system is bad props to gggGary

CARB and VALVE issues and adjustment
-wont detail here-

Thanks in advance, I am really looking forward to putting some miles on.
 
Whew! When you put it in a list like that, all in one post, it shows just how so many things can go wrong that produce the same problem/symptom. And, it could be more than one, multiple combinations. You guys should ask for a raise...
 
I know it didn't seem to itimidating until I sat down and started looking at all at once. But theoretically most of these shouldn't take terribly long. Wait scratch that.

I am really hoping its that clogged vent in the gas cap. . .
 
The vent in the gas cap is a convoluted deal with an amazing amount of holes, passages and places it can be blocked. But normally the rubber cap/neck seal is cracked in about 20 places so none of that matters. LOL
 
I swear I spent three hours getting one cap rehabbed so I knew it vented, sealed and had a lock that operated smoothly and matched the ignition.
 

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