Newby seeks intermittent engine hesitation diagnostic advice

[LanarkXS]

OK, here goes, first post......

Early in the summer I picked up a stock 1980 XS650 Special with 24,000 kms on it. It looks to be in very good condition.

It was running fine when I acquired it. The second day after it was licensed I took it for an "inaugural"ride. It ran fine for 60 kms. I came to a stop at an intersection and when I went to pull away the motor bogged badly and I thought it was going to quit altogether. However it kept running and got me home.

Since then I have done a number of test rides in the neighbourhood to try to observe how it behaves. It starts easily hot and cold. In a "steady state"constant throttle the motor runs fine under load at any speed. The problem arises when starting off from a stop. Some of the time it runs normally and pulls away cleanly. However, more often than not the motor will bog and go back and forth between wanting to accelerate and wanting to die – it rides like a bucking bronco. If one is persistent it will get past this behaviour and run strongly until the next time one gears down to a stop and then start over again as one pulls away.

I was wondering if the vacuum actuated petcock might be the culprit but it does the same thing if the petcock is put in the prime position. Gas flows freely on prime as I drained the tank on prime.

I checked the compression and got 150+ pounds using the kickstarter. The spark plugs look fine.

I am thinking that this is a carburation problem of some sort and now that I have time I want to get it sorted. I was wondering if it might be diaphragm problems. I removed the tank and airbox thinking I would tear down the carbs. The slides move freely. I tried the "quick check"of the diaphragms by lifting the slides, blocking the top port and watching the descent. Both slides move down slowly and drop quickly once the port is unblocked. This would suggest that the diaphragms are ok.

So before I go any further with a carb tear-down I thought I would ask here for diagnostic advice on what to look for carburation-wise or otherwise.

I have the XS650 Garage Carburetor Guide and the CV Carburetor Rebuild Tutorial.

I welcome your thoughts and suggestions and thank you in advance.

mike

 

[XSLeo]

I would eliminate any mechanical or electrical issues first.
A tune up goes in this order.
Adjust cam chain tension.
Valve clearance.
On a points model gap and time the points. On the TCI just check timing.
This is the basic tune up. This will eliminate the mechanical.
Now on to electrical.
Check all the grounds between the battery and frame, engine to frame. Check all the wiring between the battery and ignition. Any loss of voltage anywhere along can cause trouble.
Check the plus for good spark. Should be a nice blue color.
Once you get these things checked and all are good then start with carbs.
If you have the carb guide read it, read it several times. It has a "Tuning for Mods section, these tuning steps apply to stock also. The tuning section has you test, use the results of the test to determine the next step. Do this test one thing at a time, changing two things at once you can't tell which thing caused the change.
Ok, it may be an air leak. There are several ways to test for this. I use most anything in a spray. Even window cleaner can work. Spray around where you suspect a leak. The idle will change as the liquid seals the leak. Flammable sprays work better because the leak will draw in the flammable substance and the change in idle is easier to notice.
If you find no air leaks, then it's time to go inside the carbs. This is where having the carb guide printed out is handy. You take it too the shop and follow it step by step to tear down, clean, inspect the carb.
Write down any numbers you find on the parts. Like jets, needles and such.
I might do this before I try any carb tuning. This way you know just where your at for a baseline.
Once you get the3 carbs clean the testing will be easier, you will know more about what's inside.
Leo

 

[retiredgentleman]

First thing to do, is to replace the stock fuse panel with automotive blade type fuse holders. You can use 4 individual fuse holders or a single block type that has 4 fuse positions.

The old original fuse panel is worn out and causes intermittant electrical problems, such as low voltage to the ignition.

Getting rid of the stock fuse panel is always a "must do" on these bikes.

 

[rahndo]

How long was it sitting without running before you bought it? Clean the carbs, put a filter on the gas line and go from there.

 

[LanarkXS]

First thing to do, is to replace the stock fuse panel with automotive blade type fuse holders. You can use 4 individual fuse holders or a single block type that has 4 fuse positions.

The old original fuse panel is worn out and causes intermittant electrical problems, such as low voltage to the ignition.

Getting rid of the stock fuse panel is always a "must do" on these bikes.

I neglected to mention that I have replaced the fuse panel. You are quite correct about the old stock one. I was looking at it and one of the fuse clips crumbled when I prodded it a bit.

Thanks.
mike

 

[LanarkXS]

How long was it sitting without running before you bought it? Clean the carbs, put a filter on the gas line and go from there.

I believe the previous owner started it regularly but didn't ride it any distance as he didn't have a legit plate on it. I did add an in-line filter as is my practice on any engine without one.

Doing a tear-down and carb cleaning is where I was headed - thought I would seek other thoughts before launching into it given the quirky nature of the problem.

Thanks
mike

 

[retiredgentleman]

Well, since your fuses are in good shape, the next most common problem to cause bogging/poor acceleration would be a plugged up pilot jet. Very tiny orifice, so they get blocked rather easily.

 

[weekendrider]

The problem arises when starting off from a stop. Some of the time it runs normally and pulls away cleanly. However, more often than not the motor will bog and go back and forth between wanting to accelerate and wanting to die – it rides like a bucking bronco. If one is persistent it will get past this behaviour and run strongly until the next time one gears down to a stop and then start over again as one pulls away.

mike

Welcome to the site LanarkXS.

I'm going to assume by persistent you mean you get the rpms up? Then have to slip the clutch some to have a controllable (non-wheelie) start?

While the other advice is valid and good maintenance I think you have diagnosed the problem correctly. The carbs need cleaned.
It could be you have a build-up of gummy varnish affecting the pilot circuit.
Namely the mixture screw orifice. It is at this point the opportunity for clogging from varnish build-up would happen first in my mind. Without going into the carbs you could try Sea Foam in a heavy dose. I've use it to soak varnished jets with success.
Or you could go ahead and take things apart to clean them with aerosol carb cleaner to soften and compressed air to force the blockage out.
Another thing a tear down might show are black flakes like ground pepper. This would be the original gas line disintegration. Sea foam and or carb cleaner won't help in this case but compressed air will clean the pilot jet and fuel path.
I'm thinking you really want to go ahead and take them apart anyways? If for nothing else but to have a look see bout what is what. Go ahead and do it, never hurt to learn about something. I would suggest being the first time to do one at a time in case you need a reference.

 

[pamcopete]

I believe the previous owner started it regularly but didn't ride it any distance as he didn't have a legit plate on it. I did add an in-line filter as is my practice on any engine without one.

Doing a tear-down and carb cleaning is where I was headed - thought I would seek other thoughts before launching into it given the quirky nature of the problem.

Thanks
mike

1. When you added the filter, you disturbed the fuel lines which have an accumulation of crud in them, so that disturbance has allowed that crud to beak free and get into the carbs where it is causing the problem you have.

2. Try unplugging the regulator to disable the alternator as a test. Sometimes the TCI gets a little cranky with the magnetism from the rotor affecting the TCI sensors, assuming that a 1980 XS650 in Canada would have a TCI ignition.

 

[LanarkXS]

1. When you added the filter, you disturbed the fuel lines which have an accumulation of crud in them, so that disturbance has allowed that crud to beak free and get into the carbs where it is causing the problem you have.

2. Try unplugging the regulator to disable the alternator as a test. Sometimes the TCI gets a little cranky with the magnetism from the rotor affecting the TCI sensors, assuming that a 1980 XS650 in Canada would have a TCI ignition.

Were the OEM fuel lines of the black rubber variety? I notice that the lines are of the clear plastic type. I suspect that someone has been through these carbs before.

I now see some threads describing intermittent TCI problems and the associated tests. Thanks for that.

mike

 

[jagg]

Hello gentlemen , as you can see from my post count I am more of a reader than a contributor . I have a 1984 XS650 that I have had for 3yrs. It has been a joy to ride and maintain . Ever since I got my bike it has never been able to go over 5000rpm without surging and bucking. I could never get above 100km [60mph] . I did all the usual , rebuilt carbs, timing ,valve adj., Then one day this past summer I got on the bike for a ride , when all of a sudden gas started pouring out from around the carbs. The problem was the carb fuel line T .This is the part that the fuel line attaches to then goes into each carb. I could not find a replacement part , so I found the appropriate size O rings and pushed 1 into each inlet. This created a seal that had developed due to a aging part . Long story short, fuel leak has stopped and I found my problem by accident . I can now WOT to max revs and have hit 140km so far. Hope this helps . Jeff

 

[LanarkXS]

Always a good idea to close out a thread one has started.....

So through the winter I went through the bike but didn't find anything that I thought would account for the problem. As the result of Pamcopete's post I also read up on the TCI-related problems and in particular the problem of the weak magnet not energizing the pickup coil sufficiently. I had to wait until Spring to try out the suggestion about disconnecting the R/R and sure enough the bike ran fine sans alternator. I attached a 4mm x 1mm rare earth magnet to the existing magnet using JBWeld and the bike is running very happily.

Thanks to all those that responded.

mike

 

[uebe]

Thanks for the update........

Always good form to let us "students" know the outcome to help us learn

 

[LanarkXS]

Well I put several hundred kilometers on during which the bike was running very well and suddenly the bike started running poorly again with exactly the same symptoms. First check was to see if the small magnet was still in place and it was. Then I disconnected the R/R and the bike ran fine. This suggests that I again have an issue with the alternator's magnetic field interfering with the triggering of the TCI. Not sure what the next step should be.

I did learn from the previous owner that the rotor had been replaced by him. Apparently the original owner parked the bike due to charging problems. The previous owner solved the charging problem with the rotor replacement. I read somewhere that the replacement rotors can have problems with the magnet and/or a greater gap to the pickup coil.

Wonder if I can stack another magnet on top?

P.S.
So to answer my own question no, there is insufficient clearance for a second magnet - and the second magnet is only 0.8mm thick.

There is another thread on here where someone had a similar experience (added magnet, ran fine for a while, ran poorly but ran fine with R/R disconnected) and he ended up replacing diodes in the TCI so my next step is to remove the TCI and have a look. It will probably be a while before I get to this but I'll report back eventually.

mike

 

[LanarkXS]

After removing the TCI from the bike and having a look at the board I decided that I wasn't going to mess around trying to replace diodes or whatever on a 35 year old circuit board and I installed a PAMCO e-advancer. Bike starts on the first kick and runs great.

Mike