Jetting Database? - Suzuki GSX-R Motorcycle Forums Gixxer.com
 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 21 (permalink) Old 01-03-2017, 09:45 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Jetting Database?

I've spent a lot of time looking around for information on tuning flatslides. I was hoping there might be some kind of jetting database on this site, but have been unable to find one in a sticky or searching otherwise.

I've seen jetting and suspension databases on other sites. Do we have any?
molochnik is offline  
Sponsored Links
Advertisement
 
post #2 of 21 (permalink) Old 01-03-2017, 09:57 PM
Amateur
 
Gixxerider86's Avatar
 
Join Date: Jul 2014
Location: San Antonio
Motorcycle: 1986 GSXR 815, 2002 Bandit 1200N
Posts: 607
Re: Jetting Database?

Quote:
Originally Posted by molochnik View Post
I've spent a lot of time looking around for information on tuning flatslides. I was hoping there might be some kind of jetting database on this site, but have been unable to find one in a sticky or searching otherwise.

I've seen jetting and suspension databases on other sites. Do we have any?
I haven't seen any. the closest thing would be a member here having a similar setup as you and they give their jetting specs, but even then you can't expect to have it spot on just from that since every bike will be different.

lots of trial and error, plug readings, dyno runs with AFR readings, and just sound / smell / feel
Gixxerider86 is offline  
post #3 of 21 (permalink) Old 01-04-2017, 04:38 AM
Track Day Winner
 
Slabby1100's Avatar
 
Join Date: Feb 2016
Location: Johannesburg, South Africa
Motorcycle: 1988 Slabside 1100
Posts: 69
Re: Jetting Database?

Quote:
Originally Posted by molochnik View Post
I've spent a lot of time looking around for information on tuning flatslides. I was hoping there might be some kind of jetting database on this site, but have been unable to find one in a sticky or searching otherwise.

I've seen jetting and suspension databases on other sites. Do we have any?
What carb model is it that you have?
Slabby1100 is offline  
 
post #4 of 21 (permalink) Old 01-04-2017, 04:45 AM
Track Day Winner
 
Slabby1100's Avatar
 
Join Date: Feb 2016
Location: Johannesburg, South Africa
Motorcycle: 1988 Slabside 1100
Posts: 69
Re: Jetting Database?

Some basic info on standard setup here for Mikuni RS series Flat slides

http://www.mikuni.com/pdf/rs_app_parts_lists.pdf
Slabby1100 is offline  
post #5 of 21 (permalink) Old 01-04-2017, 04:55 AM
Track Day Winner
 
Slabby1100's Avatar
 
Join Date: Feb 2016
Location: Johannesburg, South Africa
Motorcycle: 1988 Slabside 1100
Posts: 69
Re: Jetting Database?

Also a thread for 2006 here that seems rather insightful.

Tuning mikuni flatslides vs reg carbs
Slabby1100 is offline  
post #6 of 21 (permalink) Old 01-04-2017, 10:56 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Thanks for the reply, guys.

Here's what I have:
1987 750; 1mm over; 1990 (L model) intake cam; Yosh Duplex; Mikuni RS 36 flatslides

Carb specs-
125 mains
P-4 needle jets
Jet Needles - whatever was stock from Mikuni
15 pilots
Pilot Screws - 1/8, 1/4, 1/2, 1 turn out all present issues below; 1/4 & 1/8 turns work better than 1/2 or 1

The tip of my Duplex is sooty and up to 1/4 throttle it sounds fat, blubbery, stumbles.

However, it takes a while to get it warmed up to where it won't die coming off of idle. Once it does come off of idle, it won't hang nor dip below idle when I blip the throttle.
But it does sound fat at low throttle setting as one might use cruising through neighborhoods keeping a low profile.

Also, I pulled a plug to see what's going on plugwise. If I hadn't ridden the bike and someone showed me the plug, I'd tell them it was spot on. No soot, nor any white deposits or other lean indicators. actually very clean. This was after riding for about 5 miles at low throttle settings through town.

Above 1/4 throttle it is as clean as it can be. Pulls smooth to redline - no hesitation, no stumbles.

These have always been problematic at low end since I bought them 21 years ago. I fiddled with them, had very accomplished tuners fiddle with them, and back when they were on my LTD I paid a guy to spend a day on the dyno with it.

It has always been a choice between crappy bottom end running or crappy everywhere else regardless of who tunes it.

I can't imagine I have a reversion problem due to the larger intake cam; it's not THAT radical. I even used these carbs on a 90 motor and they gave me the same fits, so I don't suspect it's a head/cam issue/low port speed/reversion, etc.

I've looked over the Mikuni manual - it looks a lot like the one that came with the carbs except the old had a picture of Schwantz ripping a wheelie on the cover.

I did look at the thread you linked, Slabby1100, and all I can say is that the dudes who have seamless carburetion on their RSs should buy lottery tickets...or mine have been hosed from the get-go.
Also, my pilot screws are fine, everything is perfectly clean, etc. These have been a problem since the day I bought em.
molochnik is offline  
post #7 of 21 (permalink) Old 01-04-2017, 11:02 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

I was hoping perhaps I could look at similar set-ups and see if I'm way off anywhere. What I gather is that many who are pleased with their RSs, are 1100 riders, and those engines should show a much stronger signal to the carbs. Despite what I said above, I'm sure there is a port speed issue at low throttle, but I'm curious to know if this is a typical 750 problem, or I am some sort of outlier.
molochnik is offline  
post #8 of 21 (permalink) Old 01-04-2017, 12:27 PM
Amateur
 
Gixxerider86's Avatar
 
Join Date: Jul 2014
Location: San Antonio
Motorcycle: 1986 GSXR 815, 2002 Bandit 1200N
Posts: 607
Re: Jetting Database?

Ive tried running 1100 carbs on my 750, it didn't work. you gotta start looking at the AIR jets and not just fuel jets in that case. larger air jet = more air "pumping" the fuel through the system, jet leaner. and vise versa
Gixxerider86 is offline  
post #9 of 21 (permalink) Old 01-07-2017, 09:48 AM
Lifetime Premium
 
Join Date: Jan 2007
Location: Tulsa, OK
Motorcycle: I don't ride anything. Who has the time? Plus, everything I own is in pieces.
Posts: 5,152
Re: Jetting Database?

You will have reversion, I don't know of an engine that won't Shouldn't be an issue until 4-5k, or so, thus irrelevant to your off-idle issue.

What needle clip position?
javadog is offline  
post #10 of 21 (permalink) Old 01-09-2017, 08:53 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by javadog View Post
You will have reversion, I don't know of an engine that won't Shouldn't be an issue until 4-5k, or so, thus irrelevant to your off-idle issue.

What needle clip position?
Good question. I'll take a look once I open up the tops of the carbs to do a synch...not sure when I'll get to it.

I had these completely apart 7 years ago and replaced every rubber bit I could order for them from Sudco. Put 'em all back together and synched them. It was right after I did that I thought I'd do a compression and leakdown check which prompted what ended up being a full overhaul from the babbits up...all for a leaking o-ring on an oil return pipe.

To my knowledge, I set everything back up the way they were...which produced good running. Of course, with larger slugs things will change, but they are acceptable except for the off idle to 1/4 throttle running. This is a lot like my LTD ran after the dyno tuning.

Just wanted to explain why I haven't fully investigated the needles.

FWIW, I opened up the float bowls, before posting, to see what I had in there and everything was still sparkly - I was sure to drain everything before I put it in the shed 7 years ago.

I'll get the needle info out within the week. Thanks
molochnik is offline  
post #11 of 21 (permalink) Old 01-09-2017, 09:24 AM
Lifetime Premium
 
Join Date: Jan 2007
Location: Tulsa, OK
Motorcycle: I don't ride anything. Who has the time? Plus, everything I own is in pieces.
Posts: 5,152
Re: Jetting Database?

7 years is a long time. If I were having trouble with these, I'd pull them apart again and clean them. It's one thing for the float bowls to be clean, it's another for all of the very small passages to be clean.

I'd also replace all of the rubber parts, including all of the o-rings. These things don't like to be used, then stored, then put back into service. Float bowl gaskets that old will be flat and hard-pressed to seal again.

Your pilot jet is already one size smaller than stock, so I'm surprised you feel like you have a too rich mixture down low. One thing I'll caution you on is reading the mixture by looking at the tail pipe...

Have you synched these things?

JR
javadog is offline  
post #12 of 21 (permalink) Old 01-09-2017, 10:25 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by javadog View Post
7 years is a long time. If I were having trouble with these, I'd pull them apart again and clean them. It's one thing for the float bowls to be clean, it's another for all of the very small passages to be clean.

I'd also replace all of the rubber parts, including all of the o-rings. These things don't like to be used, then stored, then put back into service. Float bowl gaskets that old will be flat and hard-pressed to seal again.

Your pilot jet is already one size smaller than stock, so I'm surprised you feel like you have a too rich mixture down low. One thing I'll caution you on is reading the mixture by looking at the tail pipe...

Have you synched these things?

JR
I appreciate your admonishment regarding the age of the rubber. I did clean out all the passages after noticing this issue then opening up the float bowls to verify my jetting.

Everything checked fine.

I, in fact, wanted to run them a bit in hopes of possibly letting the O-rings get wet before opening up the dry carbs. I guess we'll see about new leaks when I put them back on.

I mention the tail pipe because it appears to diametrically oppose the plug reading. And of course, crappy California pump gas won't be the best indicator anyway.

I synched them 7 years ago and have yet to synch them since I put it back together. I wanted to get a little of time of the engine before it spent time idling and heating up with fresh bores, et al.

Granted, I may be premature in asking about the jetting without a recent synch, but these characteristics are nothing new with or without a synch; however, I do expect a synch will clean things up a bit.

I guess the crux of my original post was a hope of finding others with flatslides on a 750 and comparing what they have and where they live with what I have and where I live.

I'm at least as surprised as you are by the stumbles with the small pilots. I'm happy for any advice, though.

Like I said, I'll let you know what my needle is at and report any improvement with a synch.
Thanks again, I appreciate your interest!
molochnik is offline  
post #13 of 21 (permalink) Old 01-09-2017, 10:38 AM
Lifetime Premium
 
Join Date: Jan 2007
Location: Tulsa, OK
Motorcycle: I don't ride anything. Who has the time? Plus, everything I own is in pieces.
Posts: 5,152
Re: Jetting Database?

My observations from life:

I've never been happy with a set of carbs that sat for that long between runs.
I've never had a problem with a set of carbs that was freshly rebuilt.
Reading anything from plugs or any other visual cue is a waste of time.
Synching is the first thing you should do.
Tuning these on a dyno and measuring the CO is the way to tune them.
No idea where you live but temperature might be an issue. Where I live, what works in the middle of summer won't run worth a crap today. It's cold outside...

JR
javadog is offline  
post #14 of 21 (permalink) Old 01-09-2017, 12:28 PM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by javadog View Post
My observations from life:

I've never been happy with a set of carbs that sat for that long between runs.
I've never had a problem with a set of carbs that was freshly rebuilt.
Reading anything from plugs or any other visual cue is a waste of time.
Synching is the first thing you should do.
Tuning these on a dyno and measuring the CO is the way to tune them.
No idea where you live but temperature might be an issue. Where I live, what works in the middle of summer won't run worth a crap today. It's cold outside...

JR
Ha! Well said.

I'm in the high desert of southern California; our weather has been....abnormal (in comparison to the rest of the year)
molochnik is offline  
post #15 of 21 (permalink) Old 01-10-2017, 05:56 AM
Track Day Winner
 
Slabby1100's Avatar
 
Join Date: Feb 2016
Location: Johannesburg, South Africa
Motorcycle: 1988 Slabside 1100
Posts: 69
Re: Jetting Database?

Quote:
Originally Posted by molochnik View Post
Thanks for the reply, guys.



I did look at the thread you linked, Slabby1100, and all I can say is that the dudes who have seamless carburetion on their RSs should buy lottery tickets...or mine have been hosed from the get-go.
Also, my pilot screws are fine, everything is perfectly clean, etc. These have been a problem since the day I bought em.
Mine on the 1100 run just like you describe. Crappy down low, but pull clean from 4000 rpm. I agree with your statement above
Slabby1100 is offline  
post #16 of 21 (permalink) Old 01-10-2017, 09:26 AM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by Slabby1100 View Post
Mine on the 1100 run just like you describe. Crappy down low, but pull clean from 4000 rpm. I agree with your statement above
It gives me great comfort to know that there at least two of us on the planet.

I'm bummed that my last set of CVs left with my LTD 11 years ago. An ex-boss had these things working pretty well (albeit on the aforementioned LTD), I wish I had documented what he had done, but I was dumb kid and just wanted to rip around more than take notes.
Slabby1100 likes this.
molochnik is offline  
post #17 of 21 (permalink) Old 01-10-2017, 10:33 AM
Lifetime Premium
 
Join Date: May 2016
Location: Moscow, Idaho
Motorcycle: 1991 GSXR 1100, 2004 H/D Roadking, 2011 BMW GS 1200, 1975HondaCL360 Cafe, 1975 Honda VFR 750
Posts: 10
Re: Jetting Database?

I'm new to these old bikes and this info will be appreciated
roadster1 is offline  
post #18 of 21 (permalink) Old 01-20-2017, 01:04 PM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by javadog View Post
7 years is a long time. If I were having trouble with these, I'd pull them apart again and clean them. It's one thing for the float bowls to be clean, it's another for all of the very small passages to be clean.

I'd also replace all of the rubber parts, including all of the o-rings. These things don't like to be used, then stored, then put back into service. Float bowl gaskets that old will be flat and hard-pressed to seal again.

Your pilot jet is already one size smaller than stock, so I'm surprised you feel like you have a too rich mixture down low. One thing I'll caution you on is reading the mixture by looking at the tail pipe...

Have you synched these things?

JR
Hey Javadog, an update for what it's worth...Last weekend I synched them and took a look at the needle clip position.
The clip is moved down one from center. I decided to leave them there since the midrange and top end seem so clean.
While warming it up to do the synch I tried having the pilot screws backed out a full turn. I didn't need the choke as long as before and it still idled...about the same.
I took it for a spin after the synch and the low throttle operation is still pretty much the same.
The carbs were a little out of synch and the idle has smoothed out, but it's still not great at low openings. Tolerable, but not great.
I sorta hoped there was some new wisdom out there on these carbs; most of my experience with them was pre-internet.
Thanks again for the advice!
molochnik is offline  
post #19 of 21 (permalink) Old 01-21-2017, 11:30 AM
Lifetime Premium
 
Join Date: Jan 2007
Location: Tulsa, OK
Motorcycle: I don't ride anything. Who has the time? Plus, everything I own is in pieces.
Posts: 5,152
Re: Jetting Database?

Quote:
Originally Posted by molochnik View Post
I sorta hoped there was some new wisdom out there on these carbs; most of my experience with them was pre-internet.
Okay, there's plenty of wisdom, you just have to accept it.

Start by making sure that you have the original tuning guide that Mikuni included with your carbs.

Then, recognize that your right wrist, as directed by your brain, is the most important thing, especially at small throttle openings and low revs. This is why God invented the CV carb, because most people send the wrong instructions to their right wrist. You can get away with this at 9,000 rpm; not so much at 900 rpm.

Then, remember I told you to clean the damn things and replace ALL of the rubber bits. Sometimes the path to success in not the shortest path chosen.

In the same vain, I'm hoping that you've verified that the float heights are correct and you measured them correctly.

Now, understand that you can't think of things in terms of engine rpm. That's CV carb thinking. You must think only of throttle position. When you say the mid-range is clean, thus the needle position must be correct, you are thinking like a CV carb tuner.

When tuning an RS carb, the first thing you do is disable the accelerator pump. There is a right way and a wrong way to do this. Do it the Mikuni way, as illustrated in your tuning instructions. Hopefully it hasn't been screwed with and is only starting to operate at 1/4 throttle. When you get done with the basic tuning, you'll want to start with the accelerator pump working in the range that Mikuni suggests. It's all laid out in the guide. For now, no pump for you.

if I recall correctly, your needles have 5 clip positions. Put the clip in the middle position. I have no idea why it was raised one clip; put it back where it belongs.

Now, go ride the bike and don't use the throttle like you would a CV carb.

When you get back, dial the pilot screws back to the 1/4 turn-1/2 turn range and ride it again. If you have any access to a CO meter, use that (properly) to set your idle mixture.

You might also want to check for air leaks, everywhere between the cylinder head and carb throttle plates. If you have ANY, fix those before going any further.

Make sure it's not so cold out that all of this is a waste of time at the moment.

JR
javadog is offline  
post #20 of 21 (permalink) Old 01-23-2017, 03:27 PM Thread Starter
Track Day Winner
 
Join Date: Mar 2016
Motorcycle: 1987 GSXR750
Posts: 80
Re: Jetting Database?

Quote:
Originally Posted by javadog View Post
Okay, there's plenty of wisdom, you just have to accept it.

Start by making sure that you have the original tuning guide that Mikuni included with your carbs.

Then, recognize that your right wrist, as directed by your brain, is the most important thing, especially at small throttle openings and low revs. This is why God invented the CV carb, because most people send the wrong instructions to their right wrist. You can get away with this at 9,000 rpm; not so much at 900 rpm.

Then, remember I told you to clean the damn things and replace ALL of the rubber bits. Sometimes the path to success in not the shortest path chosen.

In the same vain, I'm hoping that you've verified that the float heights are correct and you measured them correctly.

Now, understand that you can't think of things in terms of engine rpm. That's CV carb thinking. You must think only of throttle position. When you say the mid-range is clean, thus the needle position must be correct, you are thinking like a CV carb tuner.

When tuning an RS carb, the first thing you do is disable the accelerator pump. There is a right way and a wrong way to do this. Do it the Mikuni way, as illustrated in your tuning instructions. Hopefully it hasn't been screwed with and is only starting to operate at 1/4 throttle. When you get done with the basic tuning, you'll want to start with the accelerator pump working in the range that Mikuni suggests. It's all laid out in the guide. For now, no pump for you.

if I recall correctly, your needles have 5 clip positions. Put the clip in the middle position. I have no idea why it was raised one clip; put it back where it belongs.

Now, go ride the bike and don't use the throttle like you would a CV carb.

When you get back, dial the pilot screws back to the 1/4 turn-1/2 turn range and ride it again. If you have any access to a CO meter, use that (properly) to set your idle mixture.

You might also want to check for air leaks, everywhere between the cylinder head and carb throttle plates. If you have ANY, fix those before going any further.

Make sure it's not so cold out that all of this is a waste of time at the moment.

JR

I dunno where my tuning guide has gotten to. I've looked at the ones available on this site and elsewhere, and they seem as vague as the one I originally had.

I understand your suspicions about the carbs not being clean. I've worked on many carbs the owners claimed were clean - and weren't. Mine are clean. The floats are all in spec. This is far from my first rodeo.

I appreciate the advice to replace all of the rubber, but I'm not going to do that again. There are no fuel leaks on any of the static seals, nor the pilot screws.

I think I've been pretty clear in referring to throttle settings vs. RPMs, so I'm not sure why you believe I think I have CVs. I understand the differences between effectively operating both types of carbs.

I know why the needle has been raised; I did it. I've tried a number of different configurations with needle jets, needles, mains, et al. I can see if I was all the way at one end or the other-an indication of something amiss with needle jet or main size, but I would be shocked if everyone's needles were on the middle slot.

In regard to the accelerator pump; I took most of the operation out of mine. It doesn't activate until 1/3 throttle and shuts off just above half.

It's important to understand that the low throttle issues are nothing new...regardless of tuner, regardless of age. I bought these brand new and it has *always* been an issue across 3 engines and two chassis.

I don't have access to a CO meter.

I assure you that I am not attempting to frustrate you.
molochnik is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Suzuki GSX-R Motorcycle Forums Gixxer.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome