Engine misses and loses power above 3-4000 rpm

[scharny61]

Hi all, Iv'e rebuilt my engine (1979 sf/f non CDI) and put it back together. Have replaced the points with a Pamco ignition. The valve clearances are OK. The Cam chain is set OK.
The Carbie has been cleaned out 100 times (and Iv'e read the Carbie info 101 times) so think the Carbies OK. Fuel level is set at 22 mm (CV34 carb)Pilot jet set at 3 turns out.

I've checked the timing with a light and it's OK. I have good spark.The bike starts easily (without choke?) and idles beautifully. Problem is, when i rev it ,it pops and loses power.
Can anybody give me a direction to look?
Could the fact that the alternator is not charging the battery cause this?
It seems to me like a fuel problem, too rich? I'm on the verge of getting new carbs but don'r want to waste $$$$.
Thanks for any help offerred.

 

[pamcopete]

Did you check the timing goes to full advance at 3,000 RPM? Is the advance rod binding? It should snap back, like in this video if the springs are OK and there is no binding in the bushings.

 

[5twins]

These bikes won't run right once the battery starts to get low. If you're not charging, that could be happening. Also, you say you have BS34s with the floats set to 22mm. Are they the plastic or brass floats? The plastic get set to 22mm but the brass are different. Their setting is 27mm.

 

[scharny61]

Thanks guys, I have plastic floats, so I set them to 22mm as suggested.
I keep the battery charged and it's new so I'm reasonably sure the voltage is OK. I'll check the advance timing tonight to make sure it's working ok. I have noticed some metal filings in the advance mechanism side. I wonder if it's rubbing on something?
cheers

 

[scharny61]

Did you check the timing goes to full advance at 3,000 RPM? Is the advance rod binding? It should snap back, like in this video if the springs are OK and there is no binding in the bushings.

Hi Pete
I checked the advance mechanism and it appears to be working as it should. When i checked the timing, I can get pretty close to it but there is not quite enough adjustment. Also, when I increase the throttle the timing mark moves towards the advance and when it gets to a certain RPM the strobe light stops working. When I back off the revs, the strobe light starts working again. I'm beginning to doubt my power source. I checked the resistance between the white wires in the alternator side of the plug and there was no resistance. There is also no resistance between the green and brown. Would this suggest both alternator and stator are kaput? The bike sat around in the tropics for many years in the humidity.
Would you suggest replacing them with a PMA?
thanks for your time
Mark

 

[retiredgentleman]

Try connecting the timing light to the opposite cylinder that you are now using.

You need to tell us what voltage you measure at the battery:
1....before starting
2....a couple of minutes after starting, @ 1200 rpm
3......@ 3000 rpm

 

[5twins]

If you run out of adjustment on your points plate, that can be an indication that your timing chain is all stretched out and in need of replacement.

 

[scharny61]

Thanks guys
My timing chain is new and adjusted OK. It was tight to fit on , so I reckon it was the correct size. The voltage is as follows;
1. 12.7 volts
2. 10.9
3.10.9, the draw would be from the headlight I reckon.
For some reason, the strobe doesn't work on the other side even though i have spark there. (Don't tell pete but I did accidently run the bike with no plug in) Coil still works OK. Hope I haven't f...cked it up.

 

[retiredgentleman]

Thanks guys
My timing chain is new and adjusted OK. It was tight to fit on , so I reckon it was the correct size. The voltage is as follows;
1. 12.7 volts
2. 10.9
3.10.9, the draw would be from the headlight I reckon.
For some reason, the strobe doesn't work on the other side even though i have spark there. (Don't tell pete but I did accidently run the bike with no plug in) Coil still works OK. Hope I haven't f...cked it up.

OK, your charging system is not working at all. Don't look at anything else until you repair the charging system.
http://xs650temp.proboards.com/index.cgi?board=Charging&action=display&thread=3461

 

[XSLeo]

And when you get it chrging you might wnat to go throuigh your ignition wiring. If your timing light flashes at idle and quits about the same place as your engine starts cutting out then you likely have a loose connection, ground most likely.
Leo

 

[scharny61]

Thanks for the info. That seems logical to me. I'll get the charging working first and take it from there.
cheers