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?
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.
:twocents: I'm far from an expert but I stayed at a Holiday Inn once.
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
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.
What oil are you using?
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.
true. ive experienced that as well.
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.
You're running 54:1 which is not enough.
Sent from my SM-G973F using Tapatalk
I was under the assumption that with modern oils we can get away with running less oil.
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.
Sent from my SM-G973F using Tapatalk
All true.... I should be more concerned with longevity.. not like cylinders are a dime a dozen.
What is the recommended ratio?
i like to run 40:1
here we go.. oil thread. :dawg:
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.
Sent from my SM-G973F using Tapatalk
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.
Sent from my SM-G973F using Tapatalk
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.
There is a 12% tolerance from the factory on pumped oil amount. This is for everything though, bigger bores, pump cam wear, and I guess bigger jets.
Sent from my SM-G973F using Tapatalk
Im going to do 40:1.... its more than I do now and should provide more protection against wear.
I deleted the pump because I happened to drive it one day with it disconnected from the throttle during testing and I was so surprised with how light the throttle pull became. It felt so good I decided to run premix. It's psychological... when the throttle is resisting so much it makes me feel like the bike is struggling to do anything... a light pull makes it feel like the bike is freer revving under load and lighter in general. Try it sometime and see if you are as crazy as me.
The pulley on your pump has two possible holes for the pulley spring. It may have been on the 'tighter' one.
Interesting what you say though. Yamaha made those springs softer and softer overtime. On pumps that are still available new, the spring only just about returns the pulley, even with the plunger in the out position!
Sent from my SM-G973F using Tapatalk
Ive taken a wind out of flatslides before to lighten the throttle so I see where you are coming from, but I love the pump on a street bike:)
25-30:1 guy here with jaso or tc oil in the aircooled gear. Theres an article around somewhere with a test for maximum power from back in the day and IIRC it may have been 20 or 16 to 1. Also, iirc, i think they still ran even down to 6 or 8 to 1. Oil is easy to buy, cylinders, cranks and pistons, not always.
MX bikes run in tight woods tend to load up a bit as well, totally normal, clean em out on the hill climbs or in the fields. Seeminglu less of a problem on bikes meant for trail riding.
I've done a fair amount of experimentation on an old weedeater and a 50cc razz with injection and it seems that any oil will work, even cooking oil and used motor oil. They dont all work well and tend to junk things up but they dont sieze immediately, usually theres a noticible decrease in power and increase in heat. If it feels like its running out of gas but shouldnt be, pull in the clutch:)
More of any oil, appropriately jetted, does not seem to increase smoke, if anything, less oil seems to smoke more. Maybe less lube, more friction, more heat, more smoking oil? Someone probably knows:)
Just my .02, plenty of ppl round here that have experimented at a higher level and with real consequences