Hard to Start and will not Rev

[Oleschool]

My bike was running great a few days ago and then started to sputter and lose power.It eventually stalled and would not start.I had to do the walk of shame and push it home...

When I got home I pulled the plugs and cranked it over and there was spark.There was fuel in the bowls but when I put the plugs back in and cranked it,the bike wouldn't start.I squirted some fuel into the cylinders and it still wouldn't go.

The next day I was able to crank it and with the throttle wide open the bike would only hit 6k.It will only start with the throttle wide open but does not blow black when I let off.

Could this be ignition related? I'm leaning away from a carb issue because it ran so smoothly and then suddenly developed this problem during a ride.

I've read about problems with the TCI. Could this be the problem?

 

[Oleschool]

Anybody?

 

[Herd]

Sounds like ignition. I just had ghe same scenario unfold with my cb750. I am not sure if there is a way to test TCI or not. I think you basically trouble shoot everything else and if that all passes, replace TCI. May be able to open it up and look it over. There are blog posts of people repairing them around the net. They said it was just a couple diodes to replace that cost them pennies.

 

[Oleschool]

Thanks,I pulled the tank off and will begin testing.This comes at a bad time for me as I'm leaving for an extended trip nest week. The old XS may not see the road until next year...bummer.

 

[arfstrom]

Check for flooding, (air filter, and oil) . (test by smell)

guessing at this point. make sure you are using a in-line filter from fuel tank to carb. (I like paper filters, others work too.)

If your trouble shooting comes to ignition, trim .5 inches from both plug wires, on both sides. (shortening the line by an inch, and putting fresh copper against the appropriate device(coil and plug cap)

 

[Oleschool]

Well I'm back from my trip and I pulled out the old XS.I pulled the air filters and one was missing foam and both were dry and falling apart.I pulled both carbs and both the main and pilot jets were clear.I had to order new filters which will only be here in a week or two.Will it run (for testing purposes) without the air filters? I'll trim the 1/2" from the wires tomorrow.

What else can I check out?

 

[Sesty]

will run with out filters... probably not well since its tuned to run with filters.

would make sure the whole pilot circuit is clean.. hit every hole with cleaner and compressed air. (make sure diaphragms are out before using any carb cleaner)

 

[Oleschool]

I found a couple of things wrong with the carb yesterday.When I removed the two pilot needles,only one had a spring in it,yet they were both out about 1-3/4 turns.IMO the spring when bottomed out would add a dimension that would not be there for the pilot without the spring.Basically the two carbs would be set differently as the screws were both turned out the same amount from bottom.The needles I am referring to are on the downstream side of the carb in the throat.Sorry if I've mislabeled them.
Also I set up my carbs on the bench and checked the float level.One carb was right on and the other was about 1-1.5 cm below the float bowl mating surface.

I'm also going to look at the vent in the gas cap.I'm really hoping this problem is fuel related and not ignition related.

 

[arfstrom]

Sounds like your close. The spring is suppose to keep the vibration from adjusting your screw while driving. Since its sitting still, I agree with you, its doing its job regardless of lack of spring. Most of us for initial post refurb of carb, will put the pilot screws to 3 turns out. from factory, it was set to 1.5 turns out for US emissions purposes. Once you have a manometer, you can fine tune where you want your pilots settings to be.

Ignition might be easier, New plugs, caps, wires should be good since you have/ or soon will trim .5 in off. A local auto shop will have a spark plug testor, that will plug into your plug, and then in to your cap, and will show spark, while everything is plugged in. That will tell you if coils are fine or not. (TCI as well)

My story with the carbs include a hole in one of my carbs, i would get it to work, then It would be late, I would go to bed, then in AM, float is flooded. So it would not run the next day. eventually I would take one out, and hear the fuel in the float as I shoke it next to my ear.

remember, don't dig deeper, than you need to. you will find more things that don't make sense. so it doesn't make sense to dig in the stator housing, until you have ruled out the TCI, VR/REC, Coils, Carbs, Floats. I hope that makes sense. If the stuff under the stator housing hasn't been changed,then there is no reason to suspect it.

Have you checked the fuses? Have you downloaded the manual? someone reposted a manual, when its permanently "sticky-ed" to the top of the garage forum. That will have all the appropriate test for what I just mentioned. I have one more suggestion, I just can't think of it. Make sure your intake boots don't have severe dry rot, or the hose to the fuel petcock isn't off, (hole-y, melted or just not connected, either side) I use the rescue tape, available everywhere, "self fusing silicone Tape" See this website. Seems perfect for sealing potentially leaky dry rotted intakes, it can handle temps to 500f, seems perfect for many issues with our bikes. either electrical or closeness to heads... http://www.rescuetape.com/. (similar products available at various stores near you, (for me Menards, Walmart...)

 

[arfstrom]

I remember what I could not remember, from last night, now. Valves, have they checked out ok?

 

[Oleschool]

I found a hole in the intake boot so I replaced it along with the air filters.The bike fired up nicely and then started to sputter after about 15 minutes of idling in the yard.I checked the fuel levels while it ran and as soon as it stalled and they were good.There was no spark at either plug.I checked the resistance at the plug which powers each coil and they read 3.1/3.4 ohms.I checked the voltage across the leads which power the coils while cranking and the voltage was about 5.0 volts.

I have not checked the valves yet.

Any idea what it could be?

 

[NewHavenMike]

My bike would only run at 4000 rpm and above one time.. wouldnt idle at all. Turned out to be the timing was wayyyyy too far retarded past TDC

 

[BBS360]

I checked the voltage across the leads which power the coils while cranking and the voltage was about 5.0 volts

I wouldn't worry too much about the voltage while cranking. What's the available voltage at the coils when you turn on the ignition but before you try cranking?

The bikes aren't really supposed to idle that long. Someone with more experience may be able to clarify but you may have just fouled the plugs.

 

[Oleschool]

I did not check the resistance on the secondary side of the coils and should have.I'll do that tomorrow.

 

[Jeff0133]

15 minutes of idling?...yep... fouled plugs

 

[Oleschool]

I'll check the plugs,but the bike will start again after sitting for a while.I chose to idle it rather than taking it for a cruise and having it die on me.

 

[Oleschool]

I edited this post because I realized I had used info from a newer model bike which may have been wrong.I will double check the resistance of the pick up coils and post results.

 

[Oleschool]

The resistance of my pulse coils checked out ok.It is supposed to be 700ohms and mine are both around 720ohms. I figured this would point to the TCI.I ordered one from EBay and installed it last night only to find the same thing happens.What can it be?