Has anyone actually tried to optimize the carb tuning on an RX1?

[NLP_SLED_GUY]

I'm assuming that at some point over the last 20 years someone has actually taken a wideband and attempted to optimize the carb tuning of an RX1.

I recently bought mine used with a whole pile of modifications, including an ECP. After playing with it for a while I determined that the silver CV springs are not the right springs for a carb filter application. But I needed the sled to be at least close to right for an upcoming trip. So I bought all new Mikuni jets and installed them with the original airbox and a new foam filter. Synced the carbs and it now runs great.

The trip is now completed and the sled was fine. Now I used to do a lot of automotive tuning. I still have my portable wideband. So into the tailpipe it went. Stock idle fuel screw settings at 2 turns out. 12.0:1 mixture. 1.5 turns yields 14.6:1 mixture. Perfect right where I want it. But once the carb transitions into the pilot jet and needles the mixture ramped right back to 12.0:1. 12.0:1 pretty much all of the way up. Now 12.0:1 is okay for WOT, actually a touch rich but leaves room for safe atmospheric and temperature variations. So I dropped the needles one notch. Now it's about 12.3:1. I can drop them some more but it won't move it enough to make me happy. I'd guess maybe 12.5-12.6:1.

Does anyone know any reason these engines cannot be run at 14.0-14.6:1 mixture? This mixture shouldn't require any special octane or timing changes. In fact, when i looked this up for the R1 motorcycle they run the bikes at 14.6:1 until it's fully into the main jets.

This would be a noticeable increase in economy as well as throttle response IF the engine reacts in the sled like it does on a bike.

And BTW, the carb tuning parts are all stock except for the green Holtzman CV springs. This is when I realized that (as well as Chris Schmidt telling me!) that the red springs are the best springs for filters on carbs. So I have ordered a set of those. I also ordered a set of one step smaller primary jets and new 165s to start filter on carb tuning. I had a set but they were kind beat up and not Mikuni jets.

I realize this is 20 years too late. But I'm really just attempting to the the sled to run the way I want it to. But if anybody knows of anyone or any data please let me know.

 

[74Nitro]

What are the miles on the machine?
On many two strokes over the years I've changed the needle jets as the hole wears bigger at the top where the needle slides into it.
Not saying this is your problem for sure, but it's worth looking into.
It would explain the mid range rich condition if they are in fact wore slightly.
The part number is 8FA-14141-44-00

 

[NLP_SLED_GUY]

What are the miles on the machine?
On many two strokes over the years I've changed the needle jets as the hole wears bigger at the top where the needle slides into it.
Not saying this is your problem for sure, but it's worth looking into.
It would explain the mid range rich condition if they are in fact wore slightly.
The part number is 8FA-14141-44-00

5600 miles. Carbs have been ultrasonic cleaned and rebuilt with all new parts. The only parts that were not replaced were the needle jets. I even replaced one of the CV diaphragms because I didn’t like the way it looked. .

One question: if the seat worn a bit wouldn’t dropping the needle essentially compensate for that?

I’ll look to see the availability of these just in case.

Thank you,

 

[74Nitro]

5600 miles. Carbs have been ultrasonic cleaned and rebuilt with all new parts. The only parts that were not replaced were the needle jets. I even replaced one of the CV diaphragms because I didn’t like the way it looked. .

One question: if the seat worn a bit wouldn’t dropping the needle essentially compensate for that?

I’ll look to see the availability of these just in case.

Thank you,

No, dropping the needle won't help if the hole has worn bigger.
You could buy one and visually compare it to an old one, or use a digital vernier to measure.

 

[STAIN]

No, dropping the needle won't help if the hole has worn bigger.

This was a problem on the Mikuni's in the 1980's.
I put a set of 1989 GSX-R carbs on my 79 GS 1080
The needle jet was worn from the needle and it took me quite a while to figure out what the heck was going on. Main jet changes made no difference in how it ran.
I ran into an article on Factory Pro that steered me in the right direction.
If you remove the needle jet and hold it up to the light, you might be able to see the oval wear pattern if it worn.

 

[NLP_SLED_GUY]

Thanks for the responses.

I took the carbs off again last night for a closer look. Specifically the needle seats. i didn’t see anything on them that would indicate a tapering or excessive wear. So I double checked everything and gave it all a quick shot of carb cleaner to make sure. Reassembled and reinstalled. It’s amazing how fast you can get at doing this.

I also dropped the needles one more setting by moving the clip to the top ring. I also reset the idle screws from 1.5 turns to 1.75 turns. checked sync and TPS. Still spot on.

This lowered hot idle mixture an average of 14.0. The richer mixture did smoothen the idle out a touch. This was also to help smoothen out transitioning from idle to pilot jets.

The mixture at cruise appeared to be 13.0-13.2. Leaned up a bit more than I expected. But the sled is considerably smoother and even sounds completely different and stronger. Snappier.

Now I’ve got the sled sitting with a bit of seafoam in the cylinders, fuel and oil. Just to ensure the rings aren’t carboned up. Rich mixtures will certainly increase that potential. But a bad case of ring carbon often shows up in leakdown and compression tests. just last week it showed 195 psi (1000 ft) and 1.5% evenly on all 4 cylinders.

Doesn’t look like what little snow we have will hold out very long. Worst season ever here. So I think I’ll put some more miles on it and see.

Thanks,

 

[74Nitro]

Thanks for the responses.

I took the carbs off again last night for a closer look. Specifically the needle seats. i didn’t see anything on them that would indicate a tapering or excessive wear. So I double checked everything and gave it all a quick shot of carb cleaner to make sure. Reassembled and reinstalled. It’s amazing how fast you can get at doing this.

I also dropped the needles one more setting by moving the clip to the top ring. I also reset the idle screws from 1.5 turns to 1.75 turns. checked sync and TPS. Still spot on.

This lowered hot idle mixture an average of 14.0. The richer mixture did smoothen the idle out a touch. This was also to help smoothen out transitioning from idle to pilot jets.

The mixture at cruise appeared to be 13.0-13.2. Leaned up a bit more than I expected. But the sled is considerably smoother and even sounds completely different and stronger. Snappier.

Now I’ve got the sled sitting with a bit of seafoam in the cylinders, fuel and oil. Just to ensure the rings aren’t carboned up. Rich mixtures will certainly increase that potential. But a bad case of ring carbon often shows up in leakdown and compression tests. just last week it showed 195 psi (1000 ft) and 1.5% evenly on all 4 cylinders.

Doesn’t look like what little snow we have will hold out very long. Worst season ever here. So I think I’ll put some more miles on it and see.

Thanks,

We aren't refering to the needle seats. It's the needle jets.

 

[NLP_SLED_GUY]

One question. What is the normally targeted mixture ratios? Without knowing that I may be troubleshooting something that isn’t broken. Just not optimally tuned.
Green springs maybe altering the mixture?

Btw, I ordered 4

8FA-14141-44-00 nozzle, main​

Not stocked anywhere and not found at the normal jet houses. That I found. Partzilla says ship in 3-5 days. $117.00. Expensive little buggers. Other prices were $44 plus $37 shipping EACH from Yamaha in Japan. And $90 CDN on Amazon Canadian.

thanks,

 

[74Nitro]

You can't get them from your local Yamaha dealer?
They are about $35 CAD each here, should be less as you are in the USA

 

[NLP_SLED_GUY]

We don’t have a McDonalds local here. My driving would cost as much, if they were stocked. The ones relatively near by (an hour or so one way) haven’t been useful in the past. They get the parts but they end up waiting just as long as I do.

These were about $25 each. X4 plus shipping and tax.

No big hurry as the sled runs great and is very rideable as it is. Just the minor changes have made a difference so far.

Thanks,

 

[jumpmasterjoel]

I'm assuming that at some point over the last 20 years someone has actually taken a wideband and attempted to optimize the carb tuning of an RX1.

I recently bought mine used with a whole pile of modifications, including an ECP. After playing with it for a while I determined that the silver CV springs are not the right springs for a carb filter application. But I needed the sled to be at least close to right for an upcoming trip. So I bought all new Mikuni jets and installed them with the original airbox and a new foam filter. Synced the carbs and it now runs great.

The trip is now completed and the sled was fine. Now I used to do a lot of automotive tuning. I still have my portable wideband. So into the tailpipe it went. Stock idle fuel screw settings at 2 turns out. 12.0:1 mixture. 1.5 turns yields 14.6:1 mixture. Perfect right where I want it. But once the carb transitions into the pilot jet and needles the mixture ramped right back to 12.0:1. 12.0:1 pretty much all of the way up. Now 12.0:1 is okay for WOT, actually a touch rich but leaves room for safe atmospheric and temperature variations. So I dropped the needles one notch. Now it's about 12.3:1. I can drop them some more but it won't move it enough to make me happy. I'd guess maybe 12.5-12.6:1.

Does anyone know any reason these engines cannot be run at 14.0-14.6:1 mixture? This mixture shouldn't require any special octane or timing changes. In fact, when i looked this up for the R1 motorcycle they run the bikes at 14.6:1 until it's fully into the main jets.

This would be a noticeable increase in economy as well as throttle response IF the engine reacts in the sled like it does on a bike.

And BTW, the carb tuning parts are all stock except for the green Holtzman CV springs. This is when I realized that (as well as Chris Schmidt telling me!) that the red springs are the best springs for filters on carbs. So I have ordered a set of those. I also ordered a set of one step smaller primary jets and new 165s to start filter on carb tuning. I had a set but they were kind beat up and not Mikuni jets.

I realize this is 20 years too late. But I'm really just attempting to the the sled to run the way I want it to. But if anybody knows of anyone or any data please let me know.

This may seem the dumbest new guy question, but looking toward the engine from the front, are the carbs numbered from left to right?

 

[NLP_SLED_GUY]

This may seem the dumbest new guy question, but looking toward the engine from the front, are the carbs numbered from left to right?

Not at all. I’ve had to look this up recently. Look for the timing chain hump in the car covers. Aka, PTO side. That’s number one. That fairly normal for most inline engines.

If I’m wrong, I really got lucky syncing the carbs.

 

[jumpmasterjoel]

Not at all. I’ve had to look this up recently. Look for the timing chain hump in the car covers. Aka, PTO side. That’s number one. That fairly normal for most inline engines.

If I’m wrong, I really got lucky syncing the carbs.

So looking at the sled, #1 is on the right, the clutch side.

 

[NLP_SLED_GUY]

On an RX1 at least,it’s the cylinder right behind the primary clutch. No matter how you look at it.

 

[RobX-1]