Engine loses power on hills/ long straights

[davidcumbria]

Struggling to understand the behaviour of my bike. It starts up fine, idles and pulls sweetly and then powerfully as the revs rise over the first few miles. Then i go on a dual carriageway and it blasts up to 80 mph but when I try and maintain this speed after a minute or less the engine seems to lose power like its running out of fuel. problem occurs sooner if there is an incline. I have to slow down and pullover since although i change down it simply wont pick up and goes slower and slower, cant achieve much over 30 mph eventually. when I can find a place to stop its obvious 2 or 3 pipes are hotter than the others and it sounds very flat and unresponsive on the throttle. But then after a bit of idling and revving the problem clears and it starts to rev smoothly from idle. The engine temperature gauge does climb fairly quickly towards red during these 'rests' ( couple of minutes) but goes back to normal as soon as as I start riding again which I am inclined to do asap to get the temp down.The hot pipes do seem very hot with exhaust gas scalding my hand. If i then just ride on A roads at 40 - 70 mph changing gear and speed and keeping the bike revving well pretty soon everything seems generally fine with no loss of power. I have changed the plugs which i thought were fouling. I reset float levels some time back and the jetting is as i got it. For 750 miles it has not had this problem but then it started. Dont understand how the bike seems to 'heal' itself after a short period idling and always runs fine during the warm up phase but simply cant maintain a moderately high cruising speed or go up hills when it was fine before. It has to be oil or fuel related because the ignition system is capable of sweet running at high revs and repeated smooth acceleration through the revs both when cold,after a good run and after these layby pauses. Anyone recognise these symptoms - I am thinking fuel starvation, possibly sticking float valve again or some kind of air leak. Coolant tank is full so no gasket problems I hope. Not much experience of two strokes so I am looking for guidance. the problem can occur on A/ back roads but it is now a regular as clockwork happening when I try maintain a constant higher speed, especially up a hill and happens very quickly within the first mile.

[silverstrom]

Several possibilities, one being a leaking crank seal. Any crank seal leak will result in uneven running and a marked drop-off in performance in higher gears or under load. You don't say which pipes are cooler, but if you're sucking in gearbox oil, that would be a contributing factor.

Look for other air leaks, such as manifolds, reeds, base gaskets, etc.

Could also be a partially blocked fuel tank vent. Ride with the gas cap open to test that theory. Could also be partially blocked carb bowl vent(s). If air can't get out, fuel can't get in. Insects love to crawl into vents. I've had that problem.

Could also be partially plugged main nozzles (emulsion tubes). Time to fully strip the carbs and have a look. Carbs should be where you start any troubleshooting. Once you rule them out you can focus on the few other possibilities. Sticking float valves are a definite possibility.

Don't rule out ignition issues. If the high speed coils are bad on the stator you'll have symptoms as you describe. A failing ignition coil will have the same effect. Under load you'll have weak spark. Also check HT leads and plug caps. a bad contact where the HT lead joins the plug cap will cause issues under load. Cut 5 mm from the end of the HT leads and screw the caps back on. Replacing the caps is a better option and you'll never have to worry about it again.

There aren't a lot of possibilities for your problem. You just need to be patient and thorough as you work your way though the list. Don't do anything half way. Pressure and vacuum test the cases if required. Replace wear items like spark plugs and caps. Meter the stator as per the manual. Meter the ignition coils as per the manual. And remember, the engine must be cold when you meter electrical components. If it's hot your readings will be inaccurate.

[davidcumbria]

Many thanks silverstrom. will get to work stripping the carbs. What i dont get is that if there was an airleak or failed seals wouldn't this be a permanent ongoing problem once warmed up so that when the engine is really sucking at max acceleration in second or third gear wouldnt I notice a significant performance drop off? the problem only manifests after a time running at higher constant speeds in 5th gear and it still pulls my arms off most of the time before and not very long after that occurrence with a little clearing period inbetween. similarly Whilst i will check out the ignition with my multimeter again I dont see how it could be the cause if loading the engine by max acceleration in second and third gears revs out smoothly and as powerfully as ever when the valves cut in. I really hope I find something in the carbs but annoyingly due to travel its going to take me a week to get to it !

[silverstrom]

Unfortunately there is no easy answer. CDIs will cut out and come back again. So will the PV controller. A bad ground will cause headaches. That's what makes this sort of thing frustrating. I do think it sounds more like a fueling issue, but unfortunately, electrical issues will come across with the same symptoms.

Higher gears = higher loads and not necessarily speed related, so any seal leaks will be more evident in higher gears.

You're not using a fuel filter are you?

Your fuel line routing is correct? http://www.rzrd500.com/500phpBB3/viewto ... 432#p71432" onclick="window.open(this.href);return false;

[davidcumbria]

Thanks for all your input Siverstrom really appreciated. Couple of quick checks this morning. Gearbox oil is full. there is a slight oil smudge next to the pointer on the outside of the fuel cap which I haven't seen before. Must check out tank breathing as suggested. Back in a week but will be on line if anyone has any further thoughts.

[MK]

Some good points already made, but I'll put my eggs in only two of the baskets.

1) venting (tank and carb)
2) carb or other mechanical issue on the failing cylinder (dirt clogging something, leaks, piston or seal failure)


And I'll add why the other things seem unlikely to me:
If the source coil fails (which can be temperature dependent) ALL cylinders will be affected.
If the CDI fails (which can be temperature dependent, too) at least one bank will fail. Remember it has only two outputs for two HT coils.
For the same reason I'd plead not guilty for the HT coils - a single lead/cap/plug issue may be likely.
Note that all is based upon what you wrote (I understood that it's the same cylinder all the time ?)

[WVWRZ500N]

Please provide jetting info also. At first glance it sounds electrical like mentioned already but also like plugs fouling.

[davidcumbria]

Thanks for the replies www and mk.

Tank venting also suggested by dealer I bought from. Can't find anything in service manual. Does tank vent through filler cap? Anyone had problems or experience of solving issues with this ?

[MK]

As you didn't state which part combo you have:
The RD500 has different tanks and different caps - one sort with a vent and one sort without.

If you use the unvented cap with the unvented tank ....

[silverstrom]

The cap is vented, not the tank, unless you happen to have a German spec tank which has a vent valve on the bottom. I believe the Denmark tank is also vented.

If you have an unvented cap, or a dirty cap, you could have problems. As I said, the easiest way to test is to ride with the cap loose or off. Remove the cap, put tape over the opening and put a small hole in the middle and go for a ride. If the symptoms persist it isn't a venting problem.

You can see the tank vent difference in this pic of some of my tanks

[davidcumbria]

Thanks again. Mine is an rzv jap import (derestricted) with the original cap as far as I know. Definitely no third pipe underneath like the lh tank would have. Can these filler caps be stripped down ? Is there a pin hole that gets blocked? Will certainly do the run with cap removed /taped aperture as soon as I get back.

[Speed Freak]

Tank cap can`t be stripped down.
The tank ventilation system is mounted with caps which are pressed into the aluminum body.

[silverstrom]

The tank vent is just one possibility, and as I said. quite easy to test. Test it as described and move on to the next phase.

[Twinsport]

I'm sorry to add to the confusion, but:

... I believe the Denmark tank is also vented...

May not be correct. My two bikes (one for Denmark and one from Germany) Does not have the vented tanks.

/Steen

[silverstrom]

We've had this conversation before Steen

http://www.rzrd500.com/500phpBB3/viewto ... 14&t=12989" onclick="window.open(this.href);return false;