This post is the long, long, long, drawn-out story with the details of what happened between strapping the RZ on the Dyno on Thursday night, and the final carb settings that the bike had on Sunday.
I wasn’t going to post it, because it’s really long and really dull, but it might be useful to someone, and since I already had it written, I’ll post away.
On Thurs., May 13/21, we ran the 87 RZ on the dyno.
Run #1 – 51.01HP and 29.98 ft/lb torque
DG Pipes, 26mm Power Jet carbs, 360 MJ, 27.5 PJ, needle on the 2nd clip
Bike was lean in the mid-range and on the top end.
Pulled the carbs to make changes and found that the needle was on the 2nd clip. WTF?
It should be the 4th clip, so I put it on the 4th clip, and went up 2 sizes on the MJ
Run 4 – 52.70 HP and 30.87 ft/lb torque
DG Pipes, 26mm Power Jet carbs, 380 MJ, 27.5 PJ, needle on the 4th clip
The bike made a strange/different sound in the midrange, but there was an improvement in both HP and torque, so we were going in the right direction, however, it still seemed to be a bit lean.
I didn’t have any 390 or 400 main jets, but I did have some 410 Toomey MJ’s that I got with my pipes.
We put in the 410 MJ’s and raised the needles to the 5th clip.
Run 7 – 52.54 HP and 30.88 ft/lb torque
DG Pipes, DG Pipes, 26mm Power Jet carbs, 410 MJ, 27.5 PJ, needle on the 5th clip
The HP and torque are almost identical to what I got with the 380 MJ.
However, the Air/Fuel ratio showed that the bike was running leaner with the 410 MJ’s, than it was with the 380’s.
And the motor still made a strange sound in the mid-range.
Well that’s interesting, but it was after 10 PM and we’d all had enough fun for 1 night, so we shut it down and went home.
I was the last one to leave the shop that night, and when I fired up the bike, it ran like crap.
It wouldn’t idle, and it had a huge stumble from 3000 to 5000 rpm.
At 5000 rpm the stumble changed to the normal 5k stutter.
At 5700 the bike cleared up and pulled really strong.
When I got home, I turned the pilot air screws 1/4 turn out, to see if it would increase the idle. It didn’t.
I took it to work on Friday and it ran the same way (lousy), so when I got home that night……..I took it apart.
Thursday night, while the bike was on the dyno, I took a quick glance at the dyno charts, but didn’t get a chance to really study them, because I was busy pulling carbs and changing jets.
When I got home and relaxed for a bit, I took a closer look to see if they could help explain why the bigger jets made the mixture leaner, and why the bike was running so bad.
One thing that bothered me was why the hell the needle clip was in the 2nd clip in the first place.
Did I have a brain fart when I installed the clip, and count the clip positions from the wrong end of the needle?
As I thought about it, it occurred to me that the needle clip position on the 86+ PJ carbs, was different than the non PJ carbs.
I checked the manual and sure enough, the stock clip position is #2.
I currently have the clip at #5, and the bike runs like crap at 1/8 to 1/4 throttle. Go figure.
On the dyno, with clip position #2, the bike seemed to be lean, so I decided I’d put the clip in position #3.
While the carbs were apart, I took out the 410 Toomey MJ’s and put the 380 Mikuni MJ’s back in, because they gave me the richest air/fuel mixture at 9000+ rpm.
There were a few guys hanging out watching the dyno runs, to see if the bike would blow up, and they had some theories on why the engine is running leaner with the 410’s
1 – The petcock is not flowing enough fuel, and the float bowls are running dry.
2 – The big 410 Toomey jets don’t flow as much fuel as the smaller 380 Mikuni jets.
I’m leaning towards #2, so I ordered some 390, 400, and 410 Mikuni main jets.
****Since I first wrote this story, there are 2 more theories that have come up.
1 – We found that the filter on the Air/Fuel Analyzer is plugged and not reading correctly
2 – It’s possible that I didn’t have the choke cross-over tube on all the way****
On Sat., May 15/21, after getting off work, I went for a test ride with the 380 MJ’s and the needle on the 3rd clip.
The bike fired up first kick and after warming up for a couple of minutes, it settled into a nice idle.
That was a good sign.
I find it interesting that the needle position f*cks up the idle so bad.
The engine runs better, but not great.
It easily pulls away from a stop, and is a lot smoother between 3000 and 4000 rpm.
It still has a stumble from 4000 to 5000, a stutter 5000 to 5700, and is really strong over 6000.
Hmmm. What to do next.
A – Put the clip back to the #2 position (stock).
B – Put the clip back to the #2 position with a washer under the clip to raise the needle by 1/2 a clip.
Well, the dyno chart says #2 clip position is too lean, so I should try it with the washer.
But, on the dyno, that “lean” condition at 4500 rpm, is right after the dyno guy whacked the throttle WFO.
Is the #2 position still too lean when cruising, or gently running through the gears on slow residential streets?
I’ve got 3 other RZ’s with pipes and pod filters and All of them are running the clip in the stock position.
I have tried putting a washer under the clip, but found that the bike had a bad stumble at 4500 when it was accelerating.
It would cruise at 4500 just fine, but as soon as you gave it gas, the engine coughed and sputtered.
However, none of my other bikes are using the Power Jet carbs, so is that even relevant.
On Sun, May 16/21, I went for another test ride with the 380 MJ’s and the needle on the 2nd clip, right where the Yamaha manual says it should be.
It fired right up, had a good idle, and pulled nice and smooth fro 2000 to 5000 rpm.
There might be a slight stumble at 4500, but it’s really small. Hell it might just be my imagination.
Above 5000 rpm, there was no change. A stutter to 5700 and pulls hard from 6000 to 9500.
Ok, I’m happy
Someday, if I’m really bored and have absolutely nothing better to do, I may put a washer under the clip just too fully convince myself that it would be too rich in the mid-range.
But, for now, I’m done playing with the needles.
Next on list was pilot air screw adjustment. The Stock setting is1.5 turns out.
However, on my first ride on this bike, I found that this setting made it hard to pull away from a stop.
I had to give it a lot of throttle.
I turned the air screw in ¼ turn to 1.25 and it was much better.
All of the dyno runs were made with the air screw at 1.25 turns out.
After the dyno, I set the air screw to 1.5 turns and left it there while testing the #2 and #3 clip positions.
I did a few laps around the block with the air screw at 1.5 and then 1.25 turns out, and here’s what I found.
At 1.25 turns out
- When the bike is idling and you blip the throttle, the motor is somewhat slow to respond
- It does not require very much throttle to pull away from a stop. You can almost take off at an idle if you’re good at feathering the clutch.
- It’s very smooth, when gently accelerating from 2000 to 3000 rpm, in 3rd or 4th gear.
At 1.5 turns out
- When the bike is idling and you blip the throttle, the motor is really crisp and quickly picks up rpm
- You have to give it a bit more throttle to pull away from a stop, but once you’ve got it moving, it really takes off.
- There is a very slight stumble/stutter/hesitation when gently accelerating from 2000 to 3000 rpm.
Final Carb Settings for the 87 RZ with DG Pipes.
26 mm Power Jet Carbs, 380 MJ, Needle Clip #2, 27.5 PJ, Air Screw 1.5 turns out.
I would like to put in the bigger main jets when I get them.
If I feed that motor a bit more gas, I think I can get a dyno chart that says 53 point something HP.
I also think it would be a good idea to go up 1 size on the Pilot Jets, (from 27.5 to 30).
They’re cheap, so I ordered a set from the Yami dealer, and I’ll give them a try.
