RD350LC air in oil lines / low on performance

[123Flysky]

The two conditions, (air in oil lines and lagging performance) I believe are exclusive.

After installing transparent oil lines and bleeding the pump, (manually adjust pump to max oil delivery during start up), small bubbles of air continue to appear even after 15 to 20 minutes of operation.

Performance: Even before I changed the oil lines, the engine will rev clean without hesitation to over 9,000, (when parked in neutral). On the road, wack open the throttle and the engine begins to accelerate until about 6,500 rpm, (with the throttle held WFO) the engine RPM will not increase above 7,000 until the throttle is released slightly. After slightly releasing the throttle, the engine will again gain RPM. Again turn the throttle fully open and the RPM lags. Under load, on the road, the RPM seems to increase without hesitation but only when the throttle is opened slowly. The condition is worsened if the enricher circuit, (choke) is pulled on.

The bike has a new petcock and fuel flow has been confirmed. New plugs were installed and the air filter / intake examined for any obstruction. Carbs are synchronized and the float level confirmed accurate. The oil pump kit, (seals and gaskets) was installed.

The bike is pristine, (less than 5,0K miles).

Any suggestions as to the cure for the above.

[JonW]

Hav a bit of a search and a look round here, oil lines need to be OEM and i bet you need new crank seals by now...

[2smoke]

Wow that sucks because the bike only comes alive at 6000-6500rpm.
Anyways clear oil lines are hard to find that fit tight. Probably leaking at the clamps. Try Yamaha oem black line. Cheap and fit extremely tight.
Main jets are clean?
Plug caps and wires in perfect condition?
Tested stator with Yamaha manual?
Are the plugs getting fouled (wet) when this happens?
Yes, could be crank seals worst case.

[Arrow]

Hi, have you got the correct retainers on the oil pipes?
I had the same issue with my bike when opening the throttle. Going down one size in the main jet sorted it completely.

[hondaror]

Why does everyone jet "SAFE". Safe is too rich. The plugs will tell you. Too lean and they are white. Guys, you want tan plugs period. No oil, not black=too rich, which also means, runs like shit or not at all. The bike should sound crisp, responsive, and it should pull all the way.

[123Flysky]

Thanks for the tips.

The tiny bubbles are visible in the lines starting at the oil pump outlets. Since the pump and the outlets are well below the oil reservoir, (gravity rules), and the oil is pushed out through the outlets by the pump, if the clamps were not tight, wouldn't oil be leaking out from between the oil lines and the outlet nipples?

Although the charging system functions fine, I have not checked the stator. The plug caps are new, (as are the crank seals), the plugs are not fouled. I had the carbs apart several times, the main jets, (new and stock size) are clear.

I can replace the oil lines with OEM units however, the non transparent lines may not allow the air bubbles to be seen.

[Arrow]

Thanks for the tips.

The tiny bubbles are visible in the lines starting at the oil pump outlets. Since the pump and the outlets are well below the oil reservoir, (gravity rules), and the oil is pushed out through the outlets by the pump, if the clamps were not tight, wouldn't oil be leaking out from between the oil lines and the outlet nipples?

Although the charging system functions fine, I have not checked the stator. The plug caps are new, (as are the crank seals), the plugs are not fouled. I had the carbs apart several times, the main jets, (new and stock size) are clear.

I can replace the oil lines with OEM units however, the non transparent lines may not allow the air bubbles to be seen.

The oil rarely leaks from there as there is no pressure as such. The height of the oil in the tank is controlled by the check valves in the pump. Even if the valves are passing then the oil will flow very slowly into the inlet tract. Because this is open ended there is no pressure in the system. In use however the outlet pipes are under constant vacuum and if the pipes are not sealed correctly at the oil pump end this will show up as the tiny bubbles. What clamps are you using?

[evan_calgary]

As above, you have a vaccuum which can pull in air. Suspect oil will be less likely to leak than air due to density/viscosity. I have posted this a few times but see this pic. Your problem sounds like a main jet issue. Jetting issues will not appear until under load versus sitting still and revving unless extremely bad.

[RuZty]

the non transparent lines may not allow the air bubbles to be seen.

Problem solved. I have tried all kinds of clear line and the only one I use now is Tygon that I buy at our local hobby shop. The RC car guys use it for nitromethane fuel line. It stays soft, is semi transparent yellow (although I think other colours are available) and I don't use clamps. I've never had any leaks and the lines are plenty tight on the fittings. You could use a small cable tie if you wanted something there, or the stock clips might work too I've just never tried.

[Arrow]

Please don't use cable ties. They are bad news on small diameter pipe. There is always a gap under the block because its not round. Even on soft pipe there will be way less pressure in that area. That model fuel pipe I have also considered. It grips well and does not appear to need clamps.

[JonW]

I use Tygon on brakes reservoirs, but always with clamps, as its one of the few pipes thats brake fluid safe. I'll second the cable tie comment, never do that.

[RuZty]

Sorry, retract bad advice on cable ties, I don't bother with clips on Tygon and offered it as a piece of mind thing if the OP is hung on fixing the hoses in place without having actually done it. Thanks for the back check Jon and Arrow.

[123Flysky]

Excellent stuff. I will try Tygon lines and if necessary use the small OEM clamps.

Regarding the main jet size, since the engine, air intake and exhaust systems are stock, I'm wondering how the engine's operation has changed to demand less fuel at high load / rpm.

The fuel I'm currently running is the low lead aviation gas, I doubt however the AV gas is contributing to the fueling issue.

Thanks everyone for the valuable information.

[Arrow]

My bike was also stock. The 4L0 lists three main jet sizes as standard fitment; 210, 220 and 230. Mine ran best on the 210's. In the winter it may have run best on 220's, but I never ran it between early November and early March. Remember, race bikes can be rejetted 'on the day' to allow for changes in atmospheric conditions.

[123Flysky]

The current jets are 220's. I may try the 210.

I concur, atmospheric conditions can make a big difference. I had a Kaw 500 triple that would run especially great on cool fall days when the dew-point was low.