Jetting time

[rd400canuck]

Hmmm...  cylinder head temp gauge.. thats a great idea. It would certainly put my mind at ease. I'm going to start looking for a pair. Would be nice if I could find ones with a settable limit that flashes or something when that temp is reached.

[Alain2]

I got these, they were on sale at the time, you may find them cheaper somewhere else:

https://www.treatland.tv/trail-tech-digital-temperature-gauge-in-ORANGE-p/trail-tech-743-et3.htm

Works good so far.

[1976RD400C]

For the price they sure help to let you know how warm up is going and how hot it gets when being frisky.

[sav0r]

Cylinder head temp is a factor of ambient temp. So you might say you want 350 degrees plus ambient. But in my experience it's hard to run a street bike hard enough to really learn much from cylinder head temp. Also, once cylinder head temp is too hot, the only thing that will get it back in check is turning the motor off. For example, with the Yamaha Kt100 karting engine, you would run it in race conditions but with an adjustable Walbro carb. You might regularly see 500 CHT, but if conditions are bad even 580 could be achieved relatively safely, you could however richen the carb until the needles fall out and that CHT will never fall. There's just too much mass and once it's warm you can't provide enough fuel to overcome that. So for a street bike, something that's run at 20% a lot of the time, maybe 100% for short bursts, what does CHT actually provide? In my opinion, it's a false sense of security and not much else. If it's too lean it's more likely to run cooler actually, as there's less fuel combusting, but since you arn't at full song it's never going to run warm relatively anyways. If it's too rich, it will again run too cool. EGT is likely the best, but trying to do that by watching a gauge I think it s recipe for disaster, especially on the street where attention needs to be directed towards road conditions and drivers.

[rd400canuck]

Thanks for all the tips on CHT displays...

I wasnt planning on using it to tune.... I was just hoping that once tuned, it would be a sign that one of the cylinders is running differently than the other. If I say that happening Id know it was time to take a look for air leaks.

What you guys think?

[1976RD400C]

Here's what my CHTs read on my stage II 400 with B9 spark plugs
       start up and go putt putt for 1.5 miles        160
       back road cruising                                     275
       hooligan                                                   335
       took it to a few track days                          310   maybe because it has more air rushing past the cylinders
       max I ever saw                                         340

     Noticed there can be up to 15 degree variance between the 2 cylinders and can't figure out why. I think because the sensors are touching the actual spark plug there may be a slight difference in way the plugs shed heat??? Maybe I'll try switching the plugs and see if the symptom follows???
       

[rd400canuck]

i ordered a pair....  I'll jet by plug colour and set of the pants though.  Once Im comfy with jetting I'll just have them to see of one side starts to get hotter than the other as a warning something is up.

Today is needle position and main jet day. Finally got some decent weather here. April was crap.

[Alain2]

Cylinder head temp is a factor of ambient temp. So you might say you want 350 degrees plus ambient. But in my experience it's hard to run a street bike hard enough to really learn much from cylinder head temp. Also, once cylinder head temp is too hot, the only thing that will get it back in check is turning the motor off. For example, with the Yamaha Kt100 karting engine, you would run it in race conditions but with an adjustable Walbro carb. You might regularly see 500 CHT, but if conditions are bad even 580 could be achieved relatively safely, you could however richen the carb until the needles fall out and that CHT will never fall. There's just too much mass and once it's warm you can't provide enough fuel to overcome that. So for a street bike, something that's run at 20% a lot of the time, maybe 100% for short bursts, what does CHT actually provide? In my opinion, it's a false sense of security and not much else. If it's too lean it's more likely to run cooler actually, as there's less fuel combusting, but since you arn't at full song it's never going to run warm relatively anyways. If it's too rich, it will again run too cool. EGT is likely the best, but trying to do that by watching a gauge I think it s recipe for disaster, especially on the street where attention needs to be directed towards road conditions and drivers.

No doubt EGT is a better tool, but CHT is a wonderful and cheap tool to keep an eye on the engine once it is timed and tuned.

I know what temperature my street bikes are running at (considering outside temp and riding style) and if I see x temperature I'll know something may be wrong.

Might not be useful on a race kart, but you find them in airplanes for a reason and I suggest air cooled bikes sit somewhere in between.

[rd400canuck]

I ordered some CHT stuff from amazon. I wanted to avoid brokerage fees and the border. They rob me there.

https://www.amazon.ca/gp/product/B00YY1EFOS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

and

https://www.amazon.ca/gp/product/B00V2A9JN6/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I wanted these so I can power them with 12v and will be visible at night and dont have to worry about a battery dying. Hopefully they work as intended.

[rd400canuck]

So now that I'm ok the 27.5 pilot I decided to mess with the needle height today. If anything... the bike is close I think but my concern is it's lean from the plug colours I see. So I raised the needle to #4 for a little more fuel and went for a ride. It was subtle but the bike definitely felt better in some ways.  I 'think' it pulled a little harder while opening the throttle.  I did feel that it ran smoother in a way. Like it accelerated smoother and more consistently. Also any surging at various throttle openings and engine speeds has lessened as well. Checked the plugs and they are a nicer caramel brown colour now too.

I'm going to leave it like that... I'm much happier with them on #4. Next is to get some new plugs and do some main jet plug chops. I'm enjoying the bike more and more the more sorted and fine tuned I get it.

[rd400canuck]

Guys... this is going to sound like I'm neurotic but going premix and taking the oil pump spring out of the throttle cable tension has transformed the bike.

Ive been complaining about the amount of effort I have to put into twisting the throttle. Going up through the gears every time I leave a light or exit a corner that throttle made it feel arduous and laboured.  Made it feel like I was the one working to get the bike going. So I disconnected the oil pump and added some pre-mix. In the garage alone the ease at which I could twist the throttle was so freaking noticeable. That pump mechanism took a huge amount of force to twist it around... seemingly double of what the two carb springs combined.

Took it for a ride and holy shit what a difference. The bike feels effortless to me now without me having to force that throttle around and hold it in place. The bike has become so much more of a joy to ride it's crazy what a smooth easy throttle did. The bike even feels smooth and less vibraty.. i guess unconsciously I have loosened my grip on the bars maybe. I dunno... the bike feels so effortless to get going and smooth now.

Thats it... I can never go back to oil injection again on this bike. Which sucks because it's so much easier than having to worry about premix and carrying oil on rides... but the bike is a dream to ride more than before. I'm in love with this bike more and more with each change and fine tuning i do. Best thing Ive done was buy this thing and rebuild it to stock spec. Next is the main jet plug chops then I'll be done.

[rd400canuck]

Alright... I finally got around to plug chopping the main jets and I was a little surprised.

I could feel the power delivery change as I opened the throttle past 3/4.. kind of tailed off then picked back up as I rolled it back. I assumed it was because it was rich. The 120's I put in (115's stock) came out bone white. The ceramic was clean clean white and the electrode had white deposit on it as seen in he first pic. BTW I am at 45:1 now.

I put in the biggest ones I have, 130's, and did it again with new plugs and they came out almost as white... maybe... MAYBE a tinge of tan. I must say the bike's power delivery was so much better with the 130's.. no dips or changes... the bike just pulled pulled pulled no matter where I had the throttle while I was on the hwy testing. I'm so pleased with how this bike is at hwy speeds... it's just so eager to go-go-go and wants to rev. I'm losing my fear of taking old two-strokes on steady hwy speeds. If you ask me, this bike could stand some higher gearing... dropping the rpm's by 500 is something I will look into next year.

Ive ordered some 135, 140, 145 and 150's.

Considering I have a 27.5 pilots and needle on 4th.... is anyone surprised I need such bigger jets than the stock 115's? Given the 130 plug chop it really seems I'm going to end up with at least 140's.

[SUPERTUNE]

No, not surprised... as I told you to go way bigger on main jets for pump fuels today!
Chuck

[rd400canuck]

OK as long as I'm not crazy      I also have that uni-filter in there.

It's crazy how sensitive these motors are.. I can see why people end up never getting it right and chasing their tails.  I run 4th clip on needle and 1/2 out on air screw. I wanted to try 5th clip and aside from chuffing and steady 1/4 throttle 4000 rpm  blues... the bike pulled harder at 1/2 to 3/4. It really seemed, power wise, the bike wants 5th position. Once on the hwy at a steady speed I thought the bike was seizing on me because I could feel the power coming in and out but it was the needle causing it to kind of do this fast stuttering that only went away if I opened the throttle more or the bike was under a load.

Anyway! I went back to 4th position and the well mannered bike returned until I was on the hwy again and noticed some of the same stuttering at steady speeds. I remember I had messed with the air jet... it was at 1/4 out and I usually run it 1/2 so I put it back and the stuttering went away.  Learned something new with that one! 1/4 turn on air jet affected hwy speed steady throttle mannerisms.

I'm now wondering if I can keep the 5th clip for the extra power and solve the chuffing and surging with pilot and air screw?

[SUPERTUNE]

Are the needle jets new?
I always preach...never reuse any of the old brass, only the needle unless bent or the anodizing worn off.
The needle jets are a high wear item...
Chuck