1981 RD350LC running lean, need help.

Hello,

I purchased a 1981 RD350LC that had been sitting for 6 years. Cleaned up the carbs, put new throttle cable / oil pump cable. The jetting is all stock and idles and runs great through the gears but I never seem to hit the power band in any gear. I checked the plugs and they are completely dry. There is a bit of oil but its by no means black, they practically look new. I lowered the needle clip 2 positions down to make it rich and had no changes. Plugs still look the same. I tried to following the manual on how to adjust the oil pump but it is difficult to stop the engine at the right point that the pump is fully out. My thought is that there might be too much oil which is causing it to run lean if that is even possible. At this point I am thinking of just removing the oil pump or blocking it off and running some premix to see if that is any better. Anyone have some recommendations for me on how I can properly set the oil pump injector? Or what else I should test.

Thank you,

Miguel

Hi!

on my aircooled RD there is a standard setting on the oil pump, even though its now heavily tuned i never changed anything on it.

When you twist the throttle the mark on the pump should align with another mark on the oil pump disc...check your workshop manual for that.

Set youre carbs standard and make sure they are super clean, run carb cleaner trough EVERY tiny bore in the carbs.There are tiny drillings on the intake side which are overseen easily.
When youre done with this start with new plugs and see what she does.

Setting up the oil pump:
On the aircooled RD´s one just simply adjust the "slack" of the bowden that activates the oil pump.There are two nuts that adjust the bowden.When you fully twist the throttle the marks should line up.

Concerning using premix:
When the pump is set up right: put some premix in the tank and pull off the oil pump lines from the carbs...then pull the cable on the pump and see if the pump is delivering oil to both of the lines...if yes reconnect and run the bike with fresh gas.

to me it sounds more like a fueling issue...
could also be dirty exhaust baffles blocking the air flow...

do you already have the yvps valve?

Thank you for the detailed reply. I have cleaned the carbs numerous times. The one thing I did replace was the air filter, which I had to create from a custom piece from K&N Foam pad. I am not sure if that might have any issues with it running lean since it was slightly thicker than the stock filter. The bike is running the original air box. Would the oil injection have anything to do with the bike running lean?

Too much oil mainly makes your plugs foul.
Had the bowden 1 or 2 times stuck on my oil pump on full stroke and the bike would stutter and die after a few meters...it simply kills your plugs.
There is a plastic 'hat' at the engine case which can keep the oil pump bowden from fully seating...then the plugs foul.
Does the bike revv trough the full range?

I have a KN on my RD and just bigged up the mains for about 2-3 sizes.
Start rich and work your down down.
What are your stock mains?

Did you bench synchronise your carbs?
On the aircooled rd's there are screws which can be removed to see if the slides match up.

I did bench synchronize the carbs as it is a bit difficult to do it on the bike with the airbox situation. I wish I had more history on the bike but I don't so I am not sure how it ran 6 years ago. The big goes through all the gears and revs fine. The main problem is that the plugs are completely dry and I never can get the bike to hit the power band.

From memory

350LC oil pump is adjusted with the motor stopped, open the throttle fully and the line on the oil pump lines up with the little arm.
Carb balancing is done with motor stopped, open the throttle fully and the dimples on the slides should be in the middle of the little Windows on the carbs.
I think standard mains on an 81 350LC are 220s but I could be wrong, 1980 350LCs jetting varies as Yamaha had a fair bit of trouble getting the first 350s to run well, 81s have torque arms under the engine, 80s don't.
If it isn't holing pistons then it isn't running lean, a standard 350LC isn't that quick, 110mph flat out is about right, they're also pretty smooth standard, they're not difficult to get 130+ out of.
Join the LC club in the UK

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julian.allard66 said:

From memory

350LC oil pump is adjusted with the motor stopped, open the throttle fully and the line on the oil pump lines up with the little arm.
Carb balancing is done with motor stopped, open the throttle fully and the dimples on the slides should be in the middle of the little Windows on the carbs.
I think standard mains on an 81 350LC are 220s but I could be wrong, 1980 350LCs jetting varies as Yamaha had a fair bit of trouble getting the first 350s to run well, 81s have torque arms under the engine, 80s don't.
If it isn't holing pistons then it isn't running lean, a standard 350LC isn't that quick, 110mph flat out is about right, they're also pretty smooth standard, they're not difficult to get 130+ out of.
Join the LC club in the UK

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Click to expand...

You are right about how the oil is adjusted and I set it exactly like you stated. I tried to set the carbs the way you mentioned but I don't see enough of the dimples through the glass, at full throttle the dipples don't show up all the way through the glass. Not sure what you mean by " if it isn't holing pistons then it isn't running lean". I will post some pics tonight of the spark plugs for folks to take a look.

Too much oil from the pump will not cause the engine to run rich or lean. That is determined by the carburetor jetting. Two seperate things. Now if you were on premix too much oil will make your jetting lean. I don't know much about 350LC specifics other than I wish I had one.

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clem said:

Too much oil from the pump will not cause the engine to run rich or lean. That is determined by the carburetor jetting. Two seperate things. Now if you were on premix too much oil will make your jetting lean. I don't know much about 350LC specifics other than I wish I had one.

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Thanks Clem. Just wanted to make sure the oil injection wouldn't have anything to do with it running lean. I am going to try and make it as rich as possible on the needle jet and see if there is any change on the plugs. If not I am not sure what else to really try. Just so strange that I can't really feel the power band kick in at all in any throttle position. Someone mentioned in a forum on another post that it might be the crank seal but not sure how to really diagnose something like that to see if there is a leak.

Did you check the timing?

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clem said:

Did you check the timing?

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Going to check that next, just need a dial.
Here is a pic of the spark plug.



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One thing I noticed is with open throttle fully, the dimple on of the slides is visible through the window but the other carb I can barely see it and am not able to adjust it any further. The throttle cable is brand new and I checked to make sure there was no routing issue. At this point not sure I can make any further adjustments on the carb that needs to be synced. Wonder if I need to order another cable or look at having the one side shortened a little.

This is def wrong.
When the throttle cable is the correct one,the only way that this can happen is when you put the slide in the wrong way.
Carefully unscrew the top of the carbs,pull out the slide and have a look.
There should be also springs and a gasket on the inside.
The cutaway of the slide should face on the intake (airfilter) side (!!!!) if its facing the slide is stuck in full throttle!

Adjusting the slide position is easy,there is a nut on each carb top...have a look.

Would be nice if you would post more pics to support your thread.

The LC has electronic ignition?so if it starts properly it should be in the ballpark,i would rule that one out.

Ryan Stecken said:

This is def wrong.
When the throttle cable is the correct one,the only way that this can happen is when you put the slide in the wrong way.
Carefully unscrew the top of the carbs,pull out the slide and have a look.
There should be also springs and a gasket on the inside.
The cutaway of the slide should face on the intake (airfilter) side (!!!!) if its facing the slide is stuck in full throttle!

Adjusting the slide position is easy,there is a nut on each carb top...have a look.

Would be nice if you would post more pics to support your thread.

The LC has electronic ignition?so if it starts properly it should be in the ballpark,i would rule that one out.

Click to expand...

I believe this cable is wrong cause the slides are correct. I already adjusted the nut as far as it can go on the carb top. I went ahead and ordered a new cable.


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If the carbs are not synced would that have a huge effect on the bike running lean and not reaching power band?

I would like to richen up the bike so I can at least see it from the spark plugs but not sure where to start, pilot jet, needle or mains?

Did the bike idle properly with the gas cable installed?
I cannot imagine that the bike would even start or idle properly with the needles not seating correctly...even the slightest change in needle height can have huge effects.

If one of the slides couldnt move "trough the whole range" its no wonder that the bike couldnt hit band,youre basically running on one cylinder.

Many people make the mistake to install the slides in the wrong direction (as I previously stated).

Stop messing with any of your carbs setttings,set your carbs factory,factory mains,factory needle height,float height etc....
Or you will run into more problems!

On the aircooled RD´s there is one more issue to address: Do not switch the float bowls...One bowl is matched to the choke carb, it has a tiny bore, that if its not mounted on the right carb will kill your choke function.

Could you post some pics of your carbs?

EDIT:her´s a little video of how my carbs are being synce´d

https://www.youtube.com/watch?v=lRNGr4MSjwI&feature=youtu.be

Ryan,

The bike runs fine at idle and even up through full throttle. I have a cable coming soon but in the meantime I will post some pics of the carbs. I know the slides are in the correct orientation. It's a bit difficult to see in a photo or video of the dimple through the glass cause it looks to be slightly faded from the sun but I will do my best at showing that once I get the cable and I sync carbs. I wish the carbs syncing was visible like the Carbs you have on your air cooled RD.

All good advice from Ryan - especially:

Ryan Stecken said:

Stop messing with any of your carbs setttings,set your carbs factory,factory mains,factory needle height,float height etc....
Or you will run into more problems!

https://www.youtube.com/watch?v=lRNGr4MSjwI&feature=youtu.be

Click to expand...

It is amazingly common - human nature I suppose - to make the assumption that hard to fathom problems are bigger or more difficult than they really are. A couple of observations and suggestions:

First, reconsider re-cleaning the carbs. Maybe you have them perfect, but the VAST majority of carbs that have come through my hands had remarkable similar characteristics. 1) usually "just rebuilt". 2) Usually "done by the dealer with an ultrasonic cleaner so I know the carbs aren't the trouble. 3) brand new carb "kits" so they are fine. 90% of the time, the ONLY problem is that the carbs are dirty. Otherwise, and often enough the new brass from the carb kits is the trouble and swapping them out for used OEM parts cures the problem. Only rarely is there some actual issue which is usually apparent with normal disassembly and inspection. So make sure they are clean. If you have not removed the emulsion tubes from the bodies, they are NOT clean.

Since your bike is almost completely stock, probably the jetting is ok. Put the needles back to the factory clip position. The needles have NOTHING to do with how the bike runs at wide open throttle. Synchronizing the throttles (slides) does. Place an 1/8" drill bit (or any small exact same size rod) under both slides - all the way in under the engine side of the slides - and adjust the cables so they lift off of the drill bits at exactly the same time. Make sure the cables are all properly installed, seated and routed so their operation is flawlessly repeatable first. Your throttles will be perfectly mechanically synchronized. If you believe you are lean at wide open throttle, adjust this ONLY by changing the main jets for larger. If you are trying to jet by looking at the plugs, and you are not cutting the plug apart to look at the insulator base, good luck. The hardest part to see is the only thing that shows anything about the mixture.

Ignition timing on your bike is by far the most important thing so far as engine tune and whether it lives and runs great or dies a quick and painful death. Make sure it is correct. When in doubt, use less advance. Get this sorted before worrying about anything else.

As has been mentioned, the oil pump can not impact the air fuel ratio. The volume of oil in premix does because the air mixes with the combined oil and fuel as a single fluid. In any volume of premix, some of it is oil and the rest is fuel. With more oil there is less fuel so the ratio with the air will be lean. With a pump, the A/F ratio is determined independently by the carburetion. The oil is simply added in to this mixture. Likely your pump is fine, but it is worth checking. Often pumps are rich because they are still at the factory new setting. At the first factory service, the pump volume usually is supposed to get turned down but often this didn't get done. Extra oil likely will be more of a benefit. There are two adjustments. The pump stroke, determined by shims that limit the stroke, and the cam rotation which is determined by cable adjustment.

jpmobius:

Thank you for all that info. I am going to take a part once again the carbs and do full cleaning for the 3rd time just to be safe. I did purchase a carb kit and used some of the parts but left a lot what I thought didn't need replacing - pilot jet, main jet, needle, etc. I will also go through the process of syncing the carbs and will report back once I get everything back together. I would be more than happy to post any pictures if there is something people would like to see.