Back in the day, anyone accused of tuning a two stroke had their head held under water for a lengthy period of time. If they survived that, it was deemed that they were indeed a two stroke tuner and were summarily burned at the stake. That was, of course, if their accusers were able to light said fire and find the perfect balance between air and fuel while not starving the fire pit of oil. These were anything but halcyon, civil days. You might be interested in studying up on the DKW, MZ, Suzuki and Yamaha witch trials. But be warned: Don't do so alone. And lock your doors. Thanks for the content and good luck with your endeavours.
I have the same bike and currently running it in after rebuild. When new Yamaha specified 300 miles at 4000 rpm then 300 miles at 5000 rpm. Oils have got better but revving that to six plus is a bit too much I think given the limited miles on it. Max power on these is at 7500. It is of course up to you but just the way I've always run these bikes after rebuild and not had an issue so far. I think you are right in thinking its rich. As stock they ran a 115 main jet so 160 with just pipes is a big step. My old Proddy racing 400 ran 160s and that was ported and the back of the airbox cut away. Good idea to mark the throttle👍. I would keep an eye on that whiter plug. Maybe give it a few more miles to get a bit more colour on it. One of my plugs is a lighter shade than the other but not than much. Are they genuine mikuni needles in that? Aftermarket ones are variable in quality. Enjoying the videos. Hope it goes OK.
@@RepairandRideoutYou live somewhere in France I'm guessing? Is there no weather manipulation going on over there? I'm sick of the UK, many have noticed the lines in the sky and the constant greyness and rain, it's pretty obvious now.
Just a personal thing but I call it a 'bog' when the engine is not misfiring, its just lost power it goes into a 'hole', I'd call what you have a 'stutter', you can hear the engine misfiring. A bog is caused by a lean mixture, a stutter is caused by a rich mixture. once you have the mains sorted out I'd tweak the needles up and down again, test how the engine feels at around 1/2 to 3/4 throttle, that's where the needles are having the most effect. The mains will also have an effect at 3/4 throttle which is why the needles might need adjusting once you have adjusted the mains. There does appear to be quite a difference in the mixture strength between the two carbs, look for a leak and check the float height very carefully. Even better than checking the float height is checking the actual fuel height but it is not always easy to do this, it depends on the carbs.
Thanks for you comment. There is certainly more work to do on the jetting and needle positions. I'm going to leave it for a moment while I put more miles on the engine and work on it again when I'm able to really rev it out.
@@RepairandRideouti totally agree with @sidecarbod1441's comment. Check the mixture using the 'plug chop' method. This will give a better indication of mixture setting, under load. Also, check for any potential air leak around the reed blocks, which might be unexpectedly weakening the mixture slightly, on one cylinder. This can be done with a quick squirt of 'easy start' on any joints, while the engine is idling. The revs will pickup slightly, if any 'easy start' is drawn in anywhere.
@@teej710 Cracking suggestion to use easy start. I did perform a leakdown test when the engine was on the bench, but a few heat cycles and some running could throw up a leak
From memory, I was running 138 main jets on my 250 with allspeed's, so you're probably not far off with 140's. You could try a Gunson Colortune kit to get a visual illustration of a lean or rich mixture on each cylinder.
Thanks for your comments. I have a Colourtune kit as it happens. I'm not sure how the airmixture screw effects the the running of the engine once it's off the idle circuit? I may leave that one for the next video, once I've done a few more miles
Your left hand slide is moving before the right hand one. Only slightly, just a small tweak required on the cable adjuster to get them in sync. You can use a drill bit of the appropriate size to make sure they both start at the same initial opening gap (by adjusting the tick over screws)
After backing off to 40 mains & going back to stock needle clip position it sounder & performed great. As for being a bit rich on lft cyl & bit lean on rt here’s how to handle that. 1try adjusting the pilot jet air screw a 1/4 turn out on left cyl to lean out the idle mix a bit & close the pilot screw a 1/4 turn on rt cyl to richen it up a tad & test ride. If that does the trick on both cyls hood,but if not back out the left cyl pilot screw another 1/4 turn & rt cyl another 1/4 turn in & test ride. If that gets plug’s looking good great,but if not then put the pilot screws back to where you started by screwing lft pilot screw 1/2 turn in & rt cyl pilot screw 1/2 turn out. The motor sounds happy & plugs look good with only real concern being the rt cyl is still showing a tad lean so I’d try this. Even though they sat pilot jets only affect 0-1/4 throttle it’s true but the fact is the pilot circuit is still supplying fuel to the mix all the time so what I do in a case like yours is try going up 1 size larger on pilot for rt cyl & go for a test run to see if that slight enrichment makes rt cyl plug look a med to light tan. Could also go down one size on pilot for lft cyl that’s running a tad rich to see if that get both cyls/plugs looking med to light tan. If yes great but if not & motors still running well with the pilot jet change then you could try this. I forget if your Yami has Mikuni carbs & jets,you said you went from 60 to 40 mains,well maybe you could try leaving needle clip setting as they are going up next jet size from the 40’s currently in the carbs to what ever the next size up richer main jet is (42.5,45?) for you Yami. Yes mains have most affect from 3/4 to WOT but that do also add a small amount of fuel to mix when cruising down the road at smaller throttle position below 3/4 throttle because even cruising at for example 1/3-1/2 throttle the needles will be pulled partially up out of the main jet emulsion tubes adding a bit of fuel to the mix & see how that does. Again,I’m most voncerned with ensuring rt cyl is rich enough to get better richer looking med to light tan color vs current ver light tan to yellow lean looking. But the lft cyl plug doesn’t look horribly rich and just as long as lft cyl plug stays dark brown without eventually turning black & fouling I’d leave it alone. Could dbl chk carb slide sync 1 more time to ensure the lft & rt cyl carb slides are both lifting at the same exact moment you twist the throttle off idle position. I find it better to stick 2 fingers from my left hand in both carb throats (positioning fingers in upper portion of the carbs against the slide & carbs throat/body at the same time) & then use my right hand to twist the throttle to feel exactly when racy slide starts to move. Let us know how it go’s. Btw,I know the 2stroke drill,I’ve been wrenching & restoring (for myself & others too) Kawi triple 2strokes & big fours since the early 70’s so I’ve been there done that more times then I can remember. At 68yrs young I still own 2 74 h1 500 triples,2 78 kz1000 LTD’s & 1 a 79 kz1000 LTD with 3,900 original miles on it. All my classic Kawi’s are in very good to excellent cond being well sorted bikes that are all registered & insured that I ride in good weather here in the north east. But I have to thin the fleet so will be selling 1 of the 74 H1’s & 1 of the 78 kz1000 LTD’s too. I will be listing them on eBay in Kate May or early June 2024. Happy motoring from the USA! Scott
You need to do a proper plug chop! use say 3 rd gear run full throttle for half a mile then kill switch the engine and coast to stop, take the plugs out immediatly and check the colours for an acurate mixture check thats a main jet full throttle check
Lots of good comments here. You do have to be a little nutty to work on two strokes and carbs. But, if you have the patience and discipline to work your way through it, the payoff is the wild ride of a two stroke howling its angry song, full throat.😊 You will get there. Remember your fundamentals. Clean main, pilot, and needle Jets. Clean float bowls. Correct float height. Synch'ed carb slides. Above is a good starting point. You are off to a good start, adjusting the main jet size and reading the plugs. That should get you close. Aim to be be just a tiny bit too rich. Slightly rich is better than too lean. She sounds good, you are getting close. Ride safe.
For stock airfilter you should use 120 main jet and needle 2nd clip from top. It works really good (iam using this setup also) but use genuine mikuni parts. I reccoment to check inlet rubbers for air leak. This can cause leaner looking spark on one cylinder.
I had an rd250e, back in 1979, with allspeeds and no air filter, it had 130 main jets, it went very well, so if you're running an air filter, you could probably drop down to 130 or less from the 140's you have fitted
Howya Bud , I noticed air bubbles in the oil delivery pipe. I'd check that out , could be air leaks on the lines or a sticking check valve in the pump. Better to use the proper oil line clips than jubilee clips or cable ties. Don't want to wreck that lovely build due to oil starvation .
I had a similar issue with my 350, it was bogging down, almost felt like just one cylinder was losing power. It turned out that the float heights of each carb were at different heights, so the right hand cylinder was starved of fuel!
Have you checked the condition. Of your reed valves! These can cause similar symptoms to carb issues . Inspect them carefully even if they were replaced!
Having owned (still do have a RD400, watercooled, dry clutch, cr trans, etc) and raced a few, I’d say you’ve not come to grips with the tuning, jetting with the chambers and I’d even pull the heads and check the cylinders and pistons for signs of seizure. I’ve also had the bullet electrical plugs to the coils arcing- simply squeezing the female connectors a bit tighter solved that.
great job lad its not a million miles off as someone mentioned earlier looks like air bubbles in oil feed lines try bleeding pump again next video please
Cheers, will do. Forecast is for rain for the next week so not much chance of riding. I have a few bits arriving for the Harley which I can film in the garage
If everything is standard ie air filters, pipes porting etc then should the carbs not be set at factory settings first? A quick scan of Google suggests standard mains to be 120. With pilot 25 to 27.5. Needle clip is usually centre groove. The factory knew what they were doing to make a clean running and reliable bike. Just my opinion
Thank for you comments. I'm trying to avoid lean running by increasing the jet sizes and getting the carbs to match the pipes. Mains at 160 were too much as was the center position on the needle clips, so I'm coming down seeking improved performance. I hope that I've found a good balance at the moment, that gives me confidence in running the engine for a few hundred miles, before seeking the best possible performance at high revs
i have heard its tricky to read the plugs with fuel that has ethonol in it ,i use to have a 250 e and a 400 c super bikes but they went a few years ago good luck
Nice video and good progress. Have you checked that the float heights are the same and any air mixture screws are set the same on both carbs? Failing that, switch the HT leads / coils to make sure you have a strong spark on both cylinders.
The float heights were set during the engine rebuild, but no harm in double checking if I change the main jets again. The sir mixture screw is set at 1.5 turns out. I'm hoping the ignition system is producing a strong spark, it's a new Vape set up, but a good idea to swap the HT leads
Hi first of all nice bike a classic. The bit of advice I will say is try and contact Allan milliyard. He has a channel on you tube. What he doesn't know about engines is unbelievable...
I dunno how critical it is for tuning, but it seemed to me that the left carb opened up a fraction sooner than the right one. No idea if that minute amount matters, but it's what I noticed.
