1981 RD350LC running lean, need help.

I had a question about the the slides and how the orientation should go for the top piece that screws in to hold the needle. Is the third hole suppose to be visible or covered by the screwed plate? Images provided of both ways it could go.


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plyzo said:

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

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Click to expand...

The plug is black, that usually indicates rich mixture, why do you thinknit's running lean?
One jet size lean on an LC main jet is enough to make it hole a piston.
What symptoms are you having?
How fast does bit go?
Have you removed the carbon from the exhausts?

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I don't know if there is a difference in how the plugs should look from 4 stroke to 2 stroke but they just looked to me like it is lean but maybe you are right since the ceramic is black. The bike just never gets into the powerband but maybe cause it's too rich?


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I don't know much about the rd350lc, but what exhaust is on the bike?
I had a two stroke trail bike from the early 70s and it really had no powerband either. I think the pipe plays a big role in how the power comes on. My TRX250R, quad had a big expansion chamber on it and you could definitely feel when it came on the pipe.
I could be way off, but the pipe may be making the bike more tame for the street.


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Let's back up a little shall we. The symptoms you describe were it isn't hitting the powerband and you think that may be because it's lean.

Let's start with the lean thing. Unless you did a plug chop at WOT on a run, the plugs don't tell us much of anything because they are not hot enough. The plug picture shows a relatively new plug with zero indication of being hot enough on the electrodes. That could be because it's too rich or the timing is retarded or because the engine is not high enough in the rev range.

How much throttle are you giving it? what does it rev to in any gear above first? In say second or third as you get the throttle wide open, how does it respond and what revs does it reach - does it reach the Red zone or not? Do not rev it until it breaks.

Changing needle position will potentially change 1/4 to 1/2 throttle response but has no real impact on WOT. That is down to Main Jet, air intake resistance, and exhaust. Also mechanical condition and ignition timing.

I would start by cleaning the carbs again paying particular attention to the tiny passageways. When you have both bare bodies clean, get a can of carb cleaner or WD40 and blow it through one drilling on one carb and then repeat on the other carb to ensure that they are the same. Then repeat on the next drilling. While the crabs are apart, I would recommend fitting new genuine Mikuni pilot jets and main jets. Also check needles and needle jets for wear where the needles rub and rattle in the jets.

Then check ignition timing and with it running, use a timing light to see if it changes with engine speed as per the FSM.

Then I would clean out the exhaust baffles and after all that road test it. If it still feels weak, get another LC jockey to ride it and comment or get it dyno tested. Stock LC is the same as a stock air cooled RD and doesn't have a huge kick. An RZ or RD350 YPVS hits 7,000 and the exhaust valve rises changing it from mild mannered Clark Kent into Superman as the exhaust timing changes from street RD to Race TZ and that kick is noticeable, but keep it below 7,000 and iy doesn't hit that powerband point.

New cable arrived and still having problems getting the dimple to show through the glass. Checked routing of throttle cable and there is no problems with that. The only way I can get the dimple to show up is if I don't have carb fully threaded to the body at the top. I already have the adjustments as far as they can go on both. Slide cutouts are facing intake side (airbox). I am at a loss here.


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STOP. Did you say that the dimple can't really be seem? If that's right, try to grab the cable and pull the outer up away from the carb and see if the slide now lifts further.

If so the issue is that teh slides are not lifting enough. The problem could be at thr throttle housing or the splitter of the two carb cables. You could try also to wind the throttle wide open and grab the outer sheath near the throttle and see how far it comes away from the throttle.

Yes I am able to see the dimples if I don't screw the top cap in all the way. Once I screw it all the way into the carb body I never see the dimples again and I can't adjust any further the individual cables at the carbs or at the throttle. I removed from the throttle body and from the original routing just to see if there was any issue with how it was routed and I have the same results. It's even really stiff to pull and even turn from the throttle. I've never had this issue with my other VM30 carbs on my CB350 so at this point I am stumped.

If you take the carbs off can you push the slide up so you can see the dimple in the window?
Also how do you know you have a problem, have you ridden another standard LC that was loads quicker than yours?
They aren't that quick standard or that power bandy, I really wonder if you're expecting it to be quicker than it is.

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plyzo said:

Yes I am able to see the dimples if I don't screw the top cap in all the way. Once I screw it all the way into the carb body I never see the dimples again and I can't adjust any further the individual cables at the carbs or at the throttle. I removed from the throttle body and from the original routing just to see if there was any issue with how it was routed and I have the same results. It's even really stiff to pull and even turn from the throttle. I've never had this issue with my other VM30 carbs on my CB350 so at this point I am stumped.

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Have you got the wrong carb tops or slides?

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Stupid me. It was the retaining clip that goes in the slides for the spring that were upside down therefore not letting the springs reach all the way to the bottom. I've never ridden and LC350 and just figured since it was a two stroke you would at least feel some of the power band.

Julian is spot on. Have you tried another LC as a comparison to yours.

Stiff throttle sounds odd though. The cable is a three into 1 with two carbs and oil pump and should be quite light. Check cable routing - take off the fuel tank and see if setting the cables free makes it easier. You can check the throttle itself with and without a cable.

With a carb off the bike and cable attached, how far open is the slide when you open the throttle "fully"?

plyzo said:

Stupid me. It was the retaining clip that goes in the slides for the spring that were upside down therefore not letting the springs reach all the way to the bottom. I've never ridden and LC350 and just figured since it was a two stroke you would at least feel some of the power band.

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Are the springs in the carbs the right springs?
Are the springs correctly installed?
In my video you see that the springs are under tension when the 'dimple' reaches the hole....
On the aircooled RD I have (last aircooles one) the rope attaches to a springloaded thing that attaches to the slide (sorry not my mother language)...

Is the dimple OVER or UNDER the hole?
Carefully use a soft plastic piece or finger and push trough the intakeside (remove boot) push the slide up and see if the dimple can be seen.

For me it sounds like your needles are not seated fully.
Very interesting that your bikes idles and runs (could you post a video of the bike idling?at which rpm is it idling?).

The only reason for this can be:
- a mistake in the assembly (wrong rope for example)

Or

-wrong needle wrong slide etc.

Is this the stock carb of your bike?





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So throttle works great now. The reason it I didn't see dimple through glass was cause I had the clip that goes before the spring in the slide on backwards which made it have more tension and no ability for the slides to go higher when given full throttle. I set everything back to factory and runs great. There still doesn't seem to be a big powerband but since I've never ridden one before I cannot compare.


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I am posting a video to YouTube of the bike idling. I also notice a lot of smoke which not sure how much is typical on these bikes. I removed the baffles and didn't notice any blockage.



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https://youtu.be/3H2mrl72x9I


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Good to hear that thing.
Too much smoke.

Are you running premix or oil pump?
Or both?
Has the oil settings been changed?

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Running the oil pump. I adjusted cable with full throttle to the second marking.


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Checked the timing and it is spot on to the F Mark when at 2k RPM.


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