Engine loses power on hills/ long straights

[Twinsport]

I know

I wonder if we would all be bored if Yamaha had a plan when they made these machines, instead of just tearing down parts from the shelves and put them together to get a 500 V4 ?

/Steen

[Luther]

David, Are you running stock motor carbs airbox pipes? It sounds like your saying if you ride going up and down the revs, shifting gears it runs good but if you hold a steady speed for a long distance it goes bad. If so I would ride till its going bad, kill the motor coast to a stop and check all plugs. First thing you want to know is are all 4 pots doing the same thing or do you have one ringer. Even used plugs will change color pretty quick on one of these bikes, i'll swap the darkeset and lighteset and check further down the road. Worst case is one cylinder goes lean gets hot goes pop and the other 3 drag the dead one into oblivion. Please don't go there.

Its a good idea to park your 500 on a paddock stand when you get home as left and right banks of carbs tilt opposite on the floats and for whatever reason rz500's are hard on float needles.

[davidcumbria]

So finally had time to go for another test run. Problem showed up as usual after accelerating up to 85mph , holding 75 mph and riding for 1 mile. Stopped and took off fuel cap and all good for a few miles but then it started again ( so definitely not tank air lock ). when i stopped it was the top left hand exhaust running colder stuttery as opposed to lower right previously. Will have a look at carbs but not sure what I will find since problem seems to move around between cylinders and related ignition coils. I may have had this problem for longer than i think because I generally ride 40 -70 through the rev range in second to 4th gears on twisties where the problem doesnt show up as opposed to constant throttle 70 mph plus on straight fast roads. perhaps it has been incorrectly jetted all along. Anyway at least I can still enjoy my bike most of the time and maybe the problem has to get worse before I can pinpoint it.

[davidcumbria]

David, Are you running stock motor carbs airbox pipes? It sounds like your saying if you ride going up and down the revs, shifting gears it runs good but if you hold a steady speed for a long distance it goes bad. If so I would ride till its going bad, kill the motor coast to a stop and check all plugs. First thing you want to know is are all 4 pots doing the same thing or do you have one ringer. Even used plugs will change color pretty quick on one of these bikes, i'll swap the darkeset and lighteset and check further down the road. Worst case is one cylinder goes lean gets hot goes pop and the other 3 drag the dead one into oblivion. Please don't go there.

Its a good idea to park your 500 on a paddock stand when you get home as left and right banks of carbs tilt opposite on the floats and for whatever reason rz500's are hard on float needles.

Thanks Luther these are good ideas that I will try out

[muttsnuts]

check your float heights, they will come into play at higher fuel demand, so mainly higher load on the engine for a prolonged period, which is what yours sounds like, so as your riding along if the float heights are too low, e.g. not holding enough fuel in the bowls then you will get fuel starvation slowly, have you tried letting it drop back to say 50mph for a 1 mile and then seeing if you can accerlate up to 75/80mph and see if it does it again (which I am sure it will ) if that's tjhe case, then I'd be looking at float heights

Hope that helps

[PilotMarky]

Ugh! This sounds like what is happening to mine. It's my front left cylinder that is having issues. Seems fine for a bit, then it looses power and sounds and feels flat. Spark looks weak to me, but only one cylinder with issue. I have metered everything and seems fine. Waiting on a new battery to see if that helps. In the meantime, will check the suggestions here also.

[Luther]

I have metered everything and seems fine.

I remember when I was in the same boat. Reground coils and look for the cracked lower bracket. Run wire from the battery to that coil to verify good power. NGK 5 ohm caps if you haven't yet. Man I had measures good but cant carry a load in several places, good luck

[V4 Heaven]

I had a similar issue with my RD.

After winter, it went on its first run out - I changed nothing at all through the winter. For the first 10 miles, it went really well. Then it would start to struggle then not pull through the rev range cleanly at all.

Changed all 4 plugs, same issue.

I suspected it was my new inline fuel filter maybe restricting the fuel, so I took it off and the problem was still there, so I put it back on!

Stripped and cleaned the carbs, same issue.

The next run out made me suspect the top coil. Put a spare coil on and now the bike goes like stink. I've been out on it twice in the last couple of weeks and it's fine, even on 12 month old petrol.

So, as mentioned, I wouldn't discount the coils and just stick a couple of known working spares on - if it's still playing up then you can discount the coils.

Good luck!

[pstamper]

Have you pulled the plugs out when this happen and at that immediate time? Does it do it if you pull the choke open? Mine did that when I ran a tank bag. I had to put a small rag over the cap so it could get air. Need to check plugs. Do not keep riding it because you do not want to cause major damage to the engine. How long have you had the bike and do you know and history or service that has been done. What fuel are you using and how old is it?

[Speed Freak]

Didn't read everything... I know this behaviour from 2 4-stroke bikes.
Both had a leaking vacuum line to the fuel tap.
Also a hole in the membrane can cause the same issues.

Result was that it still opens with closed carbs (high negative pressure) and no issues when opening them for a short time as the bowls are filled with fuel.

As soon as you drive up a mountain with a lot and long full throttle passages the engine runs lean.

Common problem of the Honda VTR1000F as the hose is routed around a sharp edge...

I don't have it in my mind where the RD500 takes the vacuum, lower or upper left carb? If there is a leak it draws some air in. This cylinder will run lean earlier than the others.

[pstamper]

Good diagnosis. Love these bikes but when they get a glitch, not so nice.

[vma500]

Yep I second speedfreak on this , vacuumlines leaking fuel inside , choke cables not seated well,faulty coils cause cylinders to fail

[PilotMarky]

Good stuff, lots to go on here... will try some coils first! Thanks!