Runs well but smokey at times

rd400canuck · May 31, 2021, 10:52:31 AM

Hi guys, long time no chat! Hope all is well with everyone.

I wanted to ask about my jetting... my 76 RD400 you all helped me rebuild from the tires up runs super well. I must have made 50 jetting changes to test everything I could and landed on my current set up. I know I ended up on the rich side but it's the only way I could get it it not surge at stead throttle at relaxed paces and also I run the bottom rich so it doesnt buck when I shut the throttle to start slowing down. If I open the air screw just a 1/2 turn from where I have it then it starts to bucks on decel.

Around town it's fine and at city cruising speeds it perfect but when I start to roll the throttle open to get up to near hwy speed is starts to noticeably smoke. Not a thick cloud, not that bad but more of a haze left behind. Same when I open it 100% to accelerate on the hwy it does this, but more so. I run premix at around 45:1 if I recall correctly. I'll have to check that little container I use when I fell after hitting reserve.. but it doesnt seem to be too much oil when just bombing around town... i dont really see any smoke at all. jusrt checked... its 8.5oz or 250ml that pour in when I fill and it takes 13.5 liters

Am I right in thinking that if I lower the main jet size I will not only lean out WOT but it was also lean out half throttle and up?

hayduke · May 31, 2021, 10:24:33 PM

My guess is puttering around town is leaving a little gas/oil in the crank case and when you really get going you clear out the reside in the motor, thus the extra smoke.

I'm far from an expert but I stayed at a Holiday Inn once.

rodneya · May 31, 2021, 10:35:59 PM

You also spit a bit of gas out the carbs when puttering about or decelerating which gets sucked in when you hammer it suddenly. Usually worse with pods sitting right behind the carbs

Jspooner · June 01, 2021, 10:27:07 AM

Stock pipes have a tendency to leave a trail of smoke too. The two stroke slime tends to collect in them over the years and the result is what you are seeing.

Alain2 · June 01, 2021, 12:13:57 PM

What oil are you using?

Striker1423 · June 01, 2021, 02:36:06 PM

Quote from: Jspooner on June 01, 2021, 10:27:07 AM
Stock pipes have a tendency to leave a trail of smoke too. The two stroke slime tends to collect in them over the years and the result is what you are seeing.

Joe's right. My bike was like smokey without the bandit before I got the chambers for it.

Was kinda fun in a way. Upshift, smash gas, and spray oil on the bumpers of tailgaters.

m in sc · June 01, 2021, 02:40:15 PM

true. ive experienced that as well.

rd400canuck · June 28, 2021, 03:54:14 PM

Thanks for feedback, guys.

The bike is running so well Im terrified to start effing with jetting again. I do have stock pipes (all stock intake as well :) Makes sense to me.. I never thought about them collecting oil residue and it burning off when I really dump the heat into them on hard acceleration.

Fingers crossed the border is open next may and I can finally come to North Carolina and meet you guys. 2 years in a row Ive wanted to come and couldnt.

Arrow · June 30, 2021, 05:24:46 AM

You're running 54:1 which is not enough.

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rd400canuck · July 01, 2021, 07:41:30 PM

I was under the assumption that with modern oils we can get away with running less oil.

Arrow · July 01, 2021, 07:44:31 PM

You could be risking a lot on an assumption.
I would never go any less that standard, prolonging the engine life is the best option IMO.
If you are happy at 54:1 then that's all that matters I guess. I wouldn't be happy at 54:1, but its your call.

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rd400canuck · July 01, 2021, 09:48:55 PM

All true.... I should be more concerned with longevity.. not like cylinders are a dime a dozen.

What is the recommended ratio?

m in sc · July 01, 2021, 11:07:03 PM

i like to run 40:1

here we go.. oil thread.

Arrow · July 02, 2021, 01:23:08 AM

There is no ideal, as the motor was designed to run different ratio's according to load and speed. 40:1 seems to work for many though.
Bare in mind that at full bore the ratio is around 20:1 from the pump.

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m in sc · July 02, 2021, 11:24:27 AM

Quote from: Arrow on July 02, 2021, 01:23:08 AM
There is no ideal, as the motor was designed to run different ratio's according to load and speed. 40:1 seems to work for many though.
Bare in mind that at full bore the ratio is around 20:1 from the pump.

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Arrow, not arguing. but.. thats on a stock bike right? reason being is that on a modified bike with much bigger jets etc this wont nec apply.

for the record, im a supporter of the pump but do have 3 premix bikes for other reasons.

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Runs well but smokey at times