Dazed & a bit confused

[Crashedkiwi]

Well I have to ask for the great wisdom of the group again. I rebuilt my xs650 xs650B (actually was a box of messy bits, but that is another story) into a "cafe racer" for want of a better description.
The engine shows reasonable compressions at 150/ side, the head and valves were professionally cut and seated and a new timing chain fitted. I've fitted VM34 carbies ex Mikes XS and they are jetted as they came. I've also fitted Tri spark ignition and a MIkes XS stator/rotor kit. Tank is clean, sealed and fuel is good.

When I first finished it, the bike started and ran and I rode it around this city satisfactorily for a number of weeks and then it just went temperamental on me and then would not start.

I've now gone slightly mad trying to figure out why. I've checked and reset the cam chain tension, valve clearances and reset the ignition timing. I've de-mounted and checked the carbies for blockages etc & checked the float levels. Spark is fine and plugs are new Iridium ones - I've even taken the complete ignition system off and installed it on my other XS and it runs perfectly.

The bike turns over sometimes part fires, but does not start. When I first assembled it , it started first turn and ran smoothly.
any suggestions as to why I cannot get it to run gratefully received.

 

[Signal]

My first thought is the charging system with the battery slowly losing charge as you ride the bike.
Try testing the battery and charging system to make sure that is ok.

 

[WideAWAKE]

I’ll throw you a random one…

Do you have inline fuel filters?

Some of the nice metal ones that you can clean come with a seal that breaks down with ethanol, turns into goo and clogs it up.

Clean, replace with proper oring and good to go.

…

Does kinda sound like a low battery though.

 

[motormike]

We have " Harbor Freight ".... they sell tools.. trailers.. trailer bits... small engines... lifts... etc etc ....one item is a small 12 volt gauge... cheap... I make a U bolt clamp for the bars... mount the gauge... long wires to battery..... ride in the real world for a few minutes... at idle... battery voltage... above idle... 13 plus voltage.... Mike's sells a digital (colored bar) for a permanent mount.... (photo on my Brit)... The cheap set up I use for a easy.. quick check on my bikes and client's bikes..... the system can be checked while on the center stand... but I like to see what's going on in real time. I believe every bike should have a voltage gauge... have one on my 82' Xs... out on the boonies of Iowa with the wife and I noticed the gauge was in the yellow..... stopped and it dropped to the red... I turned around and beat feet back to camp... 2o miles... parked... went to start.... " click click click..."...

 

[YamadudeXS650C]

The bike turns over sometimes part fires, but does not start.

So, the motor is turning over.
This means that the battery is at least adequate. Charge the battery if it gets drained trying to start the bike.
Try kicking it over, anyway.

However, I'm thinking gas; make sure it is getting plenty of gas. The vent in the gas filler can clog; clean it out.


.

 

[gggGary]

Well I have to ask for the great wisdom of the group again. I rebuilt my xs650 xs650B (actually was a box of messy bits, but that is another story) into a "cafe racer" for want of a better description.
The engine shows reasonable compressions at 150/ side, the head and valves were professionally cut and seated and a new timing chain fitted. I've fitted VM34 carbies ex Mikes XS and they are jetted as they came. I've also fitted Tri spark ignition and a MIkes XS stator/rotor kit. Tank is clean, sealed and fuel is good.

When I first finished it, the bike started and ran and I rode it around this city satisfactorily for a number of weeks and then it just went temperamental on me and then would not start.

I've now gone slightly mad trying to figure out why. I've checked and reset the cam chain tension, valve clearances and reset the ignition timing. I've de-mounted and checked the carbies for blockages etc & checked the float levels. Spark is fine and plugs are new Iridium ones - I've even taken the complete ignition system off and installed it on my other XS and it runs perfectly.

The bike turns over sometimes part fires, but does not start. When I first assembled it , it started first turn and ran smoothly.
any suggestions as to why I cannot get it to run gratefully received.

Recent compression test?

 

[Crashedkiwi]

Recent compression test?

Yes recent compression test - compressions seem fine at 150psi per side

 

[gggGary]

That rotor from mikes have a keyway in it? check that TDC is still correct.

 

[JOHNDADDY]

Possible loose electric connector - connections?

 

[Crashedkiwi]

That rotor from mikes have a keyway in it? check that TDC is still correct.

Cheers Gary - yep TDC still OK - I set TDC off the Shaft (keyway to bottom) & scribed TDC onto the rotor from Mikes as it does not come with TDC or timing marks; kinda frustrating !

 

[jpdevol]

I've fitted VM34 carbies ex Mikes XS and they are jetted as they came.

Slide: 2.5. PJ: 22.5 to 25. NJ: Series 159, P-5 or P-6. Needle: 6F9. MJ: 180 to 190. Main Air Jet: Remove.

 

[Kevin Werner]

I feel your frustration. Pics? Oh, and did you post pics? What air filters are you running?

 

[Crashedkiwi]

Hello all and Happy New Year to all; It shall be a good one.
Now back to the saga of the bike:….
I’ve now eliminated I believe many if not most vaiables that could cause the erratic running of the bike. I am satisfied that the fuel, plugs, ignition and charging system are not causing the issues I am experiencing.
The bike now starts and runs well, idles beautifully and revs smoothly through the rev range.
Until it gets hot - after say 5 or so minutes of running, it starts to miss stutter and ultimately stops running. It then will not start. Leave it to cool down, come back and it starts and runs. Until it gets hot and then starts to stutter etc..
So I’m now thinking mechanical things; head gasket or cracked head or barrel or piston perhaps?
I’d love your opinion here - I will run it up and check compressions when it is hot - but I’m kinda thinking that it’s pointing to a mechanical issue as opposed to a fuel/ ignition matter.

 

[WideAWAKE]

Coils

 

[gggGary]

When it happens pull the plugs;
wet=iggy problem,
dry=fuel issue.
You've cut your search in half.
in line spark testers show up missing spark quickly.

 

[Melnic]

I had something similar on a 4 cyl carb bike and it was a fuel issue. In my case it was not the "warming up" but the depletion of the fuel in the bowls.
That bike had a drain tube so when it was having the problem, I could get off bike, hook up clear tubes to the drain and route it upwards then open drain and check the fuel level compared to before riding the bike. It was evident that bowls were not filling back up. In that case, it was the float needle both sticking plus an after market filter screen that was so fine that the fine gunk in the tank I did not get out after de-rusting got in there. I had a rock filter on after that which clogged in 300 miles. Solution was to filter my fuel thru the tank several times then ditch the rock filter. This is not applicable I don't think to these carbs but what I'm pointing out is the carbs may have some issue to resolve.

I know my BS38 carbs don't have a drain and I had to buy a special tube to check float levels but its not adequate for checking quickly like the Hitachi carbs in my above case.

Can you get the bike to be "hot" but take short pauses to see if that extends how long before it stutters?
That could isolate a fuel flow vs heat issue.
Taking short pauses would allow the bowls to fill back up if there was a flow issue.

 

[Jan_P]

Hello all and Happy New Year to all; It shall be a good one.
Now back to the saga of the bike:….
I’ve now eliminated I believe many if not most vaiables that could cause the erratic running of the bike. I am satisfied that the fuel, plugs, ignition and charging system are not causing the issues I am experiencing.
The bike now starts and runs well, idles beautifully and revs smoothly through the rev range.
Until it gets hot - after say 5 or so minutes of running, it starts to miss stutter and ultimately stops running. It then will not start. Leave it to cool down, come back and it starts and runs. Until it gets hot and then starts to stutter etc..
So I’m now thinking mechanical things; head gasket or cracked head or barrel or piston perhaps?
I’d love your opinion here - I will run it up and check compressions when it is hot - but I’m kinda thinking that it’s pointing to a mechanical issue as opposed to a fuel/ ignition matter.

Typical symptoms of a non Charging with perhaps old battery ..
It can be overcharging also if Old Mechanical regulator And electronic ignition. ,,Is a Voltmeter installed on the Motorcycle if not install One can be a way Forward.

Almost always is electrical.

Checking the light when it stutters and perhaps go to HI beam se what happens if it dies the spark is weak for the mixture

Alternator shorting Hot ?

Dont think it is Mechanical and dont think it is Carbs It should typically be one side only unless the delivery is clogged in tank or no opening for air into tank.

Can of course be shorting anywhere if it is heat related and electrical .But my guess in the Charging Circuit
Serviced Connectors ??

 

[Raymond]

I can relate to dazed and confused. Problem as first reported was bike would not start properly. Problem now is runs but gives up after 5 mins. Coil breaking down when warm has already been suggested and sounds like a candidate. All the things @Jan_P says. Another is fuel starvation - are you using both fuel taps, one to each carb?

My Bullet was driving me insane with similar symptoms, would start readily, idle fine, run fine, take throttle at first but then give up. Long story - swapped the plug, re-jetted the carb, set the timing, even swapped the points for BB system, all to no avail. Experimented with the fuel flow and found OE fuel tap only gave a dribble so swapped it for one with better flow and at last that solved it.

 

[Crashedkiwi]

Thanks all. I’ll get an inline spark tester and see what that tells me. The charge system is a new Mikes XS stator, rotor and regulator - I’ll get a voltmeter into the system and check this also. The coil is a new one that came with the ignition system and I believe both to be OK - I swapped them across to my other xs and they worked fine.
Fuel is good - clean sealed tank with two new taps both giving good flow rates. Carbies are I believe fine also - float levels at 22-24,, as per the VM manual. I’ll have one long play around the electrics see what I can find.

 

[Kevin Werner]

I am new here but you are newer. Good luck with your sorting out. Be sure to grace us with pics of your rides. Many of us have not had the pleasure of visiting your riding grounds.