Hard to start when hot

If I stop for I few minutes to fill with gas or check a map, just a couple of minutes the bike is hard to start. It will always start but as I turn the throttle the rpm's do not increase. If I hold the throttle open for a few seconds the rpm's will increase and everything is fine. The valves are in spec. float levels are good,carbs are cleaned and synced yearly. Plugs are a nice tan color and color tuned good. It's almost like the gas in the bowls boil to a vapor till cool gas enters the carbs. I have never been stranded by this. Is this any thing to worry about?

 

I hate to tell you this, but your float levels may need attending to.

(I've experienced that symptom.)

What about THIS thing? http://xjbikes.com/Forums/viewtopic/t=31872.html If it's wide open, it wouldn't help.

Try putting the petcock on PRI about 15~30 sec before you start the bike, then switch back to ON after it fires. See if that helps.

 

A hard starting warm engine is also a sign of a lean idle mixture. Recheck with your colortune and adjust if needed.

 

I did do the filter in the air box. I used vacuum cleaner filter. I will try putting the petcock on PRI the next time.

 

Sorry the revive this thread ...but I have the same problem with an XJ550 Seca. After running several minutes, the engine won't start, or is very hard to start. I need advice and I am very curious how lostboy solved the problem. Thanks!

 

Your symptoms could have the same cause, or NOT.

In his original post he said "The valves are in spec. float levels are good, carbs are cleaned and synced yearly. Plugs are a nice tan color and color tuned good."

Are your valves in spec? That's the most common cause of "starts fine cold, won't start once warm."

Float levels in spec? Carbs cleaned and vac sync'ed?

If you're not sure if your valves are in spec, START THERE. Then float levels, carb service, vac sync, etc.

 

I will try to find someone to help me with "checking the valves". I do not have the necessary tools at the moment.

 

Here's how: http://xjbikes.com/Forums/viewtopic/t=14827.html

part Deux, doing it without "the tool" http://xjbikes.com/Forums/viewtopic/t=29209.html

Doesn't take anything special other than a feeler gauge to check them.

Start there.

 

I solved my problem : it was the electric starter brushes.
After changing them ...the bike starts very easy when the motor is warm.
Thank you very much for the help!

 

Would the starter still roll the motor fairly fast?? Sometimes my bike refuses to start when hot until it sits for a bit. I think my problem is electrical also. I even tried dropping some gas down the cylinders and it won't even kick or sputter until it sits for a while. Its just like turning on a light switch when you try it a little later, all of a sudden it fires right up.
Thanks

 

Would the starter still roll the motor fairly fast?? Sometimes my bike refuses to start when hot until it sits for a bit. I think my problem is electrical also. I even tried dropping some gas down the cylinders and it won't even kick or sputter until it sits for a while. Its just like turning on a light switch when you try it a little later, all of a sudden it fires right up.
Thanks

 

Sounds like YOU TOO need to check your valve clearances. Those are classic symptoms of tight valve(s.)

 

Hi there, just had valves done thinking it was the starting problem which I read on here.
The carbs were removed, disassembled and cleaned.
Carbs were bench synced.
Returned mixture screws to factory spec.
Checked for vacuum leaks.
New air filter.
The bike runs great, lots of power. No smoke.
Yesterday she refused to start after a long drive in hot weather. I rolled it in the shade and 10mins later she fired up while I had one plug out checking for spark. The motor was still very warm.
Next thing I'm going to try is to see what its putting out for charge and check the brushes in the alternator. I'm also going to get new plugs.
I'm running out of money!! lol

 

OK, cool.

Here're a couple of "out of left field" ideas:

Make sure the vacuum line to the petcock is a real vacuum line and not just a hose. Hoses not made for vacuum can often collapse in on themselves under vacuum when hot.

I see where you're going with charging output and alternator brushes; and while checking them is a good thing, I don't think that's it. The alternator has nothing to do with firing the bike up, that's all on the battery. And I can't see the battery "recharging" itself just enough after sitting for 10 minutes.

What're the exact "no start" symptoms? Does it spin nice and fast but just no fire?

Do you still have the original fusebox?