New engine starts, revs high but wont keep running

[russa]

Hi All,

I'm new to XS650's most of my bikes are single Brits, so I'm a bit lost at what I might have done wrong, or do next, so looking for some tips, things I can try before I pull the motor back out.. it was running when it holed a piston about 20 years ago so should go again..!.

I have rebuilt a XS1B from bottom to top, new bearings throughout, new rods, pistons, seals etc, and referencing great material on this site. And it starts but it wont keep running.

I have static timed the points, Auto advance does stick a little rubbing on the inside of the cover, but would that stop the motor? I have cleaned the carbs 3 times now, the last with 2 pairs of glasses and found some extra small holes to clean.

The bike now starts (without the use of Aerostart) but just revs for a few seconds, when I release the choke its like I'm turning off the ignition, it just wont go despite the throttle twisting. If I re-apply the choke it might keep going but wants to rev like hell again...

I'm pretty confident (although that is slipping a bit now) that I have the cam timing right, I have static gapped and timed the points and they are close enough not to stop it running, I have added 2 new condensers.

I think my next move is to give the valves some more clearance but I did follow instructions as per Yamaha Shop guru on Youtube?? Was that a mistake?

Anyway, any suggestions very welcome, I have rebuilt for a mate and I'd rather give t back to him running.

thanks,
Russell
Sunny Melbourne
Oz.

 

[TwoManyXS1Bs]

Welcome to the forum, russel. '71 XS1B? Could be that it's just cold-natured.

Fire it up with the enrichener (choke) on, leave it on for at least 30 seconds. The engine should rev higher during this, but start rich-stumbling when it warms up. If it revs way too high, without that rich-stumbling, it could be too lean, like from an air leak., or fuel delivery problem.

Otherwise, after that 30-second warm-up, turn off the enrichener while simultaneously working the throttle to keep it running. If it wants to die, re-engage the enrichener momentarily, continuing to keep it running with the throttle. Listen to the exhaust to see if both cylinders are firing. This is a real dance.

As it continues to warm-up, it should settle into an easier-to-keep-running state. Have a screwdriver handy to adjust the throttle stops.

If it fails to keep running, then there's more work to do...

 

[chizler62]

Does your throttle cable have any free play or too much? Run the idle screw in a bit further than you'd think it should be. Watch it lift the slide if you can. When you get a ton of throttle free play. Start it with the choke and let it warm then back off choke. Then you can back off idle adj till its in range to tune.

Another issue after rebuilding carbs is the needle sticks in the seat. Did you put a bit of grease on the needle?

 

[NONclow]

Another issue after rebuilding carbs is the needle sticks in the seat.

....that usually happens before they are serviced. I'd double check fit, function, range of motion, and interference issues with all moving bits, carb sync also ([cough] pilot circuit..), but what do I know

Good luck russa, and welcome! Pics???

 

[russa]

Hi Chaps, many thanks for the replies, but I now have to admit I'm an idiot.

Today I backed the bike out of the shed cos it blows a little smoke (hopefully that will settle down) to try the warm up idea etc...But also last night I continued read tips and idea's on this forum and noticed someone had drilled and taped holes under the inlet ports to help with balancing the carbs, what a great idea .... you might get where I'm going...

Anyway, started the bike a couple of times, didn't start easily but again only ran on the choke and then only for a short time. It back fired a couple of times so I thought I have look at the advance jigger to make sure it wasn't sticking... When down there.. bugger me.!! I already have a couple of pipes on the underside of the inlet ports... and there's nothing on them..!!!!

Straight in the box of sh1t that came with the bike and bugger me there's a short piece of rubber hose. Fitted perfectly, kinda... and away she went first kick running quite nice on one Cylinder...! I remembered I'd been looking at the auto advance thingy.. and forgotten to put the other plug back on.....

So after all that and about to burn the rotten thing... It starts first kick and runs... I feel like a real goose...

It does however run too fast and wont go back to idle very often, touch the throttle and it revs, but at least it now runs... and the smoke is lessening..

And again,

Many thanks for your welcomes and advice, this forum is a wealth of info that without I would never have tackled this bike...

regards,
Russell
Sunny Melbourne
Oz.

 

[TwoManyXS1Bs]

Hey, Russell, glad you found it. Thanx for the follow-up...

 

[peanut]

good news Russell

If its keen to rev but the revs stay high and come down slowly its usually a sign of a weak mixture. The fact that it runs better with the choke out confirms that .

Mine had the same issue due to the PO fitting pod filters which supply more air , which leans the mixture .

It could be that you still have an air leak somewhere on the inlet stubs . Test by spraying WD40 or carb cleaner round the inlets

You could also try winding a bit of duct tape around 1/4 of each pod to restrict the air supply and see if that improves the idle .

If it does you may need to go up one or two sizes on the pilot jets

 

[russa]

Thanks Peanut, some good suggestions there, will give them a try on weekend, thank you.

Russell.