Hard Starting - Looking for Ideas.

1980 - XJ650 Maxim. Work done to date: Rebuilt carburetors (including wet setting floats, new O-rings on transfer tubes, pilot jets two and one-half turns out, bench synch, new intake throats and good cleaning inside and out), adjusted valves, new clutch, new starter relay, rebuilt front and rear brakes, new control cables, etc.

Problem - It is hard to cold start. Once started it runs great and will start right back up when warm. When trying to cold start it sputters like its going to start but dies when the starter button is released. It may even turn a couple of revolutions before conking out. Giving it more throttle makes it worse, it won't even sputter. First thought it was flooding but plugs are dry. Then though it was being starved for gas but choking and more throttle didn't help. Inspection of plugs after running indicates correct fuel mixture, no oil and right color.
Could it possibly be the electrical? Voltage at battery terminals when running is as follows: 3000 RPM = 13.5V, 2000 RPM = 12.8V, 1000 RPM = 12.2 Volts seems kinda low. Could enough juice not be getting to the plugs to provide a hot enough spark when cold? Any ideas?

 

do a running synch

 

Yes, do a running sync; the bench sync only provides a starting point. However:

those alternator output readings are indeed low. You should be at 14.5 ~ 14.7 at 3000prm; output should hit that point at around 2200 or just above.

Check wiring, connections especially the big white connector coming off the regulator/rectifier, battery cables, etc., and it may be due for alternator brush replacement.

Give it a quick schpritz of starting fluid in the airbox the next time it exhibits the issue. If it lights right off, then you have a fuel delivery issue and the problem is most likely still-plugged enrichment wells in the carb bowls if you've got the "choke" full on and it still needs fuel.

But you do have a charging issue as well.

 

Thanks for advice. Cleaned copper rings on rotor, brushes looked good so left as is, cleaned connectors from alternator, rectifier, etc. Started bike and it ran great. Measured voltage output at battery terminals at 14.4 volts at 2k rpm. Resistance between white wires 0.5 ohms and 5.6 ohms between green and brwn. Next day hard to start again. Finally got started and voltage at battery terminals measured at 13.3 v at 2k rpm. Resistance between white wires still 0.5 ohms but resistance between green and brown measured 8.6 ohms. Have decided to replace brushes as they may be old and contaminated. Is there anything else that could be breaking down and causing low voltage? This seems to be main reason for starting difficulty.

 

Thanks for advice. Cleaned copper rings on rotor, brushes looked good so left as is, cleaned connectors from alternator, rectifier, etc. Started bike and it ran great. Measured voltage output at battery terminals at 14.4 volts at 2k rpm. Resistance between white wires 0.5 ohms and 5.6 ohms between green and brwn. Next day hard to start again. Finally got started and voltage at battery terminals measured at 13.3 v at 2k rpm. Resistance between white wires still 0.5 ohms but resistance between green and brown measured 8.6 ohms. Have decided to replace brushes as they may be old and contaminated. Is there anything else that could be breaking down and causing low voltage? This seems to be main reason for starting difficulty.

 

The low voltage you had could have been due to running the battery down cranking over if you measured soon after starting

Try the starter fluid trick Fitz mentioned, the enrichment jets (the ones hidden down a well in the float bowl itself) are a pain to get cleaned & could be your issue IMO

Also, silly question. What is your battery voltage when it's been fully charged and left to settle overnight, before trying to start the bike?

 

For starters, run it up above 2K RPM to take your readings. More like 2500 RPM.

The alternator brushes have to be a certain length to work properly. They have "wear limit" lines in them; if you don't see the little lines cut into the brushes then they're worn beyond the limit.

And I read back through the thread, I see no mention of the age of the battery itself. If you don't know how old the battery is, check the date code. Fully charge it and take it to an auto parts store and have it load tested.

 

Didn't see a wear line on the brushes but the part that sticks outta the holder is 17mm. I'll check again.
Battery is fairly new, several months old. Its holding about 12.5 volts
Much as I hate to I'm gonna take the carbs off again and take another look at the starter jet and the brass siphon tubes. Those suckers were real cruddy and full of crap when I got the bike. It sat for a long time. I thought I'd cleaned them real well. One of the siphon tubes was broken off, I made a new one, drilled out what was left of the old one out and silver soldered the new one in its place. I know its clean but the others were full of gunk that I did a quick clean on, I may have not have completely cleaned them out, especially the jets. Anyone out there know what size (dia)the starter jet is? I've got some really small drill bits but don't want to screw them up and as ya'll know its next to impossible to see down in that well.

 

About 12.5 volts could be either good or bad IMO, a fully charged battery that's stood overnight should show 12.6v, where a battery at only 75% would be 12.4v. As Fitz suggested, I'd advise a load test to eliminate the battery. I've had cheap batteries fail dead cell in under a month!

On the starter jets, I can't recall the size off hand but I know chacal sells the special long drill bit to clean them out. When they're clean you should be able to see the reflection of a penlight shone down their well, or they should shoot carb cleaner clear across the room (mind your eyes!) Also, the siphon tubes have a *TINY* hole in the side close to their junction with the carb body that if blocked (or not drilled into your new one) will stop them drawing fuel up.

 

I'd suggest two things:

1. make sure that the well in the carb bowl is very clean, and that when you shine a bright LED light right into the hole at the bottom of the bowl, you can see the hole at the bottom of the well when you look down into it. If you can't see the light, it ain't clear. If it ain't clear, your not going to have enough fuel to start up. As others said, make sure the pick-up tube is also clear

2. the other thing that I find, more often than not, is that hard starting when cold, is due to a weak battery. I don't care if you just brought it home from the store.......it IS possible to to have a weak battery right out of the box. Had that happen enough, and seen it here enough...........

Dave F

 

Aw man! wish you hadn't told me about that small hole in the side of the siphon tubes. You're right, its there and three are clean. Now to drill one in the side of the tube I made. Thats going to be a real challenge.
Used a 1mm bit to get as far down inside the wells as possible without drilling, its still too large to get down inside the jet but brought out a bunch of gunk. May have to spring for that special bit to actually get it clean all the way through.

 

Sorry! but at least when you get her running you won't have one lean cylinder till she's warmed up... They do say everything happens for a reason, if she'd run perfect fiirst time you might never have known

You might be able to clear the starter jets with a piece of stiff wire (I've used a single strand of an old clutch cable before) provided the gunk isn't set too hard, but Id bet chacal's drill bit makes the job a hundred times more pleasant to do...