Suzuki GSX-R Motorcycle Forums Gixxer.com banner

1 - 20 of 24 Posts

·
Registered
Joined
·
63 Posts
Discussion Starter #1
Hey all,

I'm at a loss with this bike, and could REALLY use your help. I have no clue where to go from here, and am so tired of giving shops my money.

SO, the journey I have been through with the bike is:
  1. Bike was running well, but sputtered if I pinned it (unless I eased my way up to it), and wouldn't idle
  2. Took carbs off and took into mechanic. Full clean, ultrasonic, new o-rings, etc. This resolved the idle issue, but not the sudden WOT issue
  3. Took carbs off and jetted up (142.5 to 150), this seemed to SOMEWHAT help the WOT issue
  4. Took carbs off and jetted up AGAIN, and buggered up the carbs in the process. Ran like crap and were suddenly way out of sync
  5. Took them into a DIFFERENT shop. Shop resolved(?) the issue with the buggered up carbs - discovered that the nylon washers on top at least one of the slides was missing (possibly from me rejetting, possibly from the first shop). They also disassembled the carbs again, cleaned them (ultrasonic for the small parts, soak for bodies). They also synched the carbs on the bike (vacuum)
    1. They also tried to resolve the WOT issue, and checked the following:
      1) Compression test - all results were above 160 and all about 160
      2) leakdown test - less than 10% loss
      3) checked all electronics
      4) completely checked through carbs
      4) jetted up and ran on dyno
      5) jetted down and ran on dyno
  6. None of the above resolved the issue, and they gave me back the bike and suggested I adjust the valves once riding season was over - possible cause was valve float
  7. After a few weeks issues started cropping back up - it would sputter and wouldn't have much power, and would die at stop lights
  8. I took the bike off the road, disassembled, adjusted valves, and found they were all VERY tight, so honestly there's a good chance that was my WOT issue.
HOWEVER, I still haven't been able to get it just running right REGULARLY again. SO, I am here asking for what you feel the next steps are. I will do anything you instruct. Carbs are off and apart, with the following info:
  • Needle appears to be unmarked, with the clip 1 notch up from bottom
  • Main jet is 160
  • Pilot air jet looks like 760? https://photos.app.goo.gl/cEUZCqQyyv29jriF7
  • Pilot jet was suuuper hard to read - something like 735 or 7B5?
Here's a video of it running:

Here's 2 videos of me taking temps at the headers. I honestly can't tell if they're accurate, because the numbers vary so much - I should have taken another reading from the other side of the bike, because I feel like the nearest header is always reading warmer than the others:

Here's a video of it running about 5 minutes later, with me lowering the idle speed slightly and it dying:

Seems to die on idle. Also seems to run worse the warmer it gets?


Seriously, I'm at my wit's end. I've had the carbs off about 7 times now, and can't figure it out. Valves have been adjusted to spec, but if needed I can go do it again. Any advice at all would be so appreciated.
 

·
Registered
Joined
·
102 Posts
Valve float isn't going to effect idle. It really seams like its a carbueration issue to me. What was the AFR are idle and at WOT? Any decent dyno operater will be able to determine if its a carbueration issue or not, and knowing this would be a major help to diagnosis. You're located in Seattle right? what shop did you take it to? I grew up north of the city in Kenmore.
 

·
Registered
Joined
·
63 Posts
Discussion Starter #3
Everett powersports! No afr values, they must have just done the run with no sniffer. I'd honestly MUCH rather not take it back to a shop as is. If it comes to that I'd probably snag the rs36 carbs and get those tuned. I've already put $600 into getting these carbs working with no luck
 

·
Registered
Joined
·
63 Posts
Discussion Starter #4
Thoughts on next steps? Clean the carbs again? Re jet? They seem in sync, but something is definitely not running right. Clean idle jets and pilot air circuit? Does it sound like 1 is off or all of them?
 

·
Registered
Joined
·
63 Posts
Discussion Starter #5
Is it time to just give up? I'm considering just getting the RS36 carbs and eliminating one potential problem
 

·
Registered
Joined
·
102 Posts
Everett powersports! No afr values, they must have just done the run with no sniffer. I'd honestly MUCH rather not take it back to a shop as is. If it comes to that I'd probably snag the rs36 carbs and get those tuned. I've already put $600 into getting these carbs working with no luck
My buddy worked at Everett Powersports for years. They are one of the more competent shops in the area, but if they weren't logging the AFR then the dyno work was a waste of time since your concern is not power numbers and using power numbers alone in tuning is only helpful in selecting the main jet.

You could solve it with your wallet. Having a fresh set of carbs to swap would be very useful for diagnosis, however there is the chance that it will not solve your problem. That being said flat-slides are a nice upgrade, and they are easy to tune, I have RS-34s on my my KZ1000 and KZ750 twin and they have run great other than leaking fuel a little overnight. The sound of them rattling when you roll on the throttle sounds so mean! If it were me I'd probably would have bought the carbs along time ago as I personally have limited time for my projects and wasting months of my time troubleshooting carbs is worth more to me now than $700 for carbs, but YMMV.

IIRC you already replaced the carb boots, correct? i still think its a carbueration issue but if you're searching for an answer with no results its always good to cross of things that it can not be to eliminate it as a possibility. Here is a list of things I would check in no particular order:

triple check the carb diaphragms, and I mean really inspect them, pull them tight and hold them over a light source to check for holes, particularly where they meet the slide. I chased this for a year in a bike once.
Its possible the PO put in the wrong jets, or even drilled them out, replace jets with OEM jets.
make sure carb clamps are tight
Quadruple check the pilot circuit in the carbs, using your fingers to block ports and switch them around as you spray cleaner so you can guarantee the passages are clear. make sure you don't spray carb cleaner on the diaphragms this will break them down.
is it smoking out of the breather?
is your petcock flowing? - check with an external fuel source to eliminate
are the carb breathers free and clear?
float levels set correctly
have you checked your coils? if a bike runs worse when hot this can be the coils breaking out once they get hot. Its possible for coils to test fine when they are cold but fail once they heat up. Check them while they're hot.
Bypass the switch gear and run power to the coils straight from the battery via a relay to the kill switch - its common in old bikes for the terminals in the switches to degrade and not pass full voltage to the coils. I bypass them on every vintage bike I touch and it usually makes them run better and start easier.
what do the plugs look like?
 

·
Registered
Joined
·
63 Posts
Discussion Starter #7
Honestly I'm completely with you at this point - particularly considering that I've already spent $600 on these carbs. Coils are new Dyna coils, here are the plugs:


Sent from my Pixel 2 using Tapatalk
 

·
Registered
Joined
·
63 Posts
Discussion Starter #8
triple check the carb diaphragms, and I mean really inspect them, pull them tight and hold them over a light source to check for holes, particularly where they meet the slide. I chased this for a year in a bike once.:
THIS RIGHT HERE. This is why I'm getting RS carbs.
Its possible the PO put in the wrong jets, or even drilled them out, replace jets with OEM jets.
Did that - Everett Powersports changed out the jets to 160s
make sure carb clamps are tight
Clamps are tight as they'll go - might just be that they're not tight enough for the carbs any more, but doubtful
Quadruple check the pilot circuit in the carbs, using your fingers to block ports and switch them around as you spray cleaner so you can guarantee the passages are clear. make sure you don't spray carb cleaner on the diaphragms this will break them down.
I'll check those again - though RS carbs sound way nicer than chasing this any further
is it smoking out of the breather?
No smoke out of breather
is your petcock flowing? - check with an external fuel source to eliminate
Using an external fuel source right now, definitely flowing
are the carb breathers free and clear?
Yep - accidentally tipped the carbs upside down and gas went everywhere
float levels set correctly
I'll check that - I haven't yet and honestly am not sure if any shop has
have you checked your coils? if a bike runs worse when hot this can be the coils breaking out once they get hot. Its possible for coils to test fine when they are cold but fail once they heat up. Check them while they're hot.
New Dyna coils
Bypass the switch gear and run power to the coils straight from the battery via a relay to the kill switch - its common in old bikes for the terminals in the switches to degrade and not pass full voltage to the coils. I bypass them on every vintage bike I touch and it usually makes them run better and start easier.
That's a great idea!
 

·
Registered
Joined
·
870 Posts
first off, you have the hose that operates the diaphragm on the petcock open in these videos, thus creating a huge vacuum leak. also the fuel line is not in a constant downward slope, remember that this fuel system is gravity-fed, so the carb banks are probably starving for fuel. what kind of mods do you have on the bike? what kind of carbs are on the bike? was the bike at some point in time during your ownership running perfectly fine and pulled to redline cleanly? if not and if you don't know the bike's history, next time you have the carbs off the bike, or if they're off already, look VERY carefully at the set you've got, look at everything. in particular, your AIR JETS, you have a main and a pilot, just like you have a main fuel jet and a pilot fuel jet that you can switch out. 1st and 2nd gen GSXR carbs are identical, but these air jets are different, and no matter how you tune those carbs you'll never get the bike running properly unless you redo everything. that is, if you have 1100 carbs on a 750, or vise versa. however, if it was ran on a dyno then they should've checked AFR readings and that would immediately tell you if its a jetting problem. if you have just pods and exhaust then your jetting to get it running decently shouldn't be too far off from stock settings. if your compression is good on all cylinders and leak down test proved good, then your valve lash shouldn't be affecting the way its running. make sure you have the correct spark plugs, I believe its D9EA
 

·
Registered
Joined
·
63 Posts
Discussion Starter #10
OOHHHH! Good call! OK, I'll plug that line. Fuel line shouldn't be an issue - you can route a gravity fed line back upwards as long as the source is above the terminus and there isn't pressure lock.

Carbs are BST31ss.

  • Needle appears to be unmarked, with the clip 1 notch up from bottom
  • Main jet is 160
  • Pilot air jet looks like 760? https://photos.app.goo.gl/cEUZCqQyyv29jriF7
  • Pilot jet was suuuper hard to read - something like 735 or 7B5?
I'll reach out to Everett Powersports to see if they took AFR readings while it was on the Dyno!

Mods are: Pods, Yosh pipe

Bike was never running without the redline issue, however it WAS running completely fine in every other way. Thoughts were that the redline issue may be because of valve float, which would still read correct on a compression test.

Current goal is to get it idling correctly - it DID idle correctly with the current setup at one point. It doesn't appear that the mixture is off, but that may be it. I did recalibrate the mixture screws (to one of them) to verify that they were all open equally.

As I mentioned, even after I got it back from the shop, it ran well, but still seemed to have SOMEWHAT wonky idle, which progressively worse. I feel like the issue has to be carbs at this point, as I agree it can't be valves that cause the idle issue. I'm wondering if I'm chasing a lot of stuff due to the unplugged vacuum port as you mentioned. I did also find a vacuum leak at boot #4 (prior to the videos posted), but resolved it with some RTV.

Carbs are currently off - I'll spot and identify the other air jet for you guys. Thanks for the help!

Tomorrow's plan is:
  1. clean out all pilot passages again
  2. examine diaphragms
  3. identify air jets
Anything else I should do while the carbs are off?
 

·
Registered
Joined
·
870 Posts
OOHHHH! Good call! OK, I'll plug that line. Fuel line shouldn't be an issue - you can route a gravity fed line back upwards as long as the source is above the terminus and there isn't pressure lock.

Carbs are BST31ss.

  • Needle appears to be unmarked, with the clip 1 notch up from bottom
  • Main jet is 160
  • Pilot air jet looks like 760? https://photos.app.goo.gl/cEUZCqQyyv29jriF7
  • Pilot jet was suuuper hard to read - something like 735 or 7B5?
I'll reach out to Everett Powersports to see if they took AFR readings while it was on the Dyno!

Mods are: Pods, Yosh pipe

Bike was never running without the redline issue, however it WAS running completely fine in every other way. Thoughts were that the redline issue may be because of valve float, which would still read correct on a compression test.

Current goal is to get it idling correctly - it DID idle correctly with the current setup at one point. It doesn't appear that the mixture is off, but that may be it. I did recalibrate the mixture screws (to one of them) to verify that they were all open equally.

As I mentioned, even after I got it back from the shop, it ran well, but still seemed to have SOMEWHAT wonky idle, which progressively worse. I feel like the issue has to be carbs at this point, as I agree it can't be valves that cause the idle issue. I'm wondering if I'm chasing a lot of stuff due to the unplugged vacuum port as you mentioned. I did also find a vacuum leak at boot #4 (prior to the videos posted), but resolved it with some RTV.

Carbs are currently off - I'll spot and identify the other air jet for you guys. Thanks for the help!

Tomorrow's plan is:
  1. clean out all pilot passages again
  2. examine diaphragms
  3. identify air jets
Anything else I should do while the carbs are off?
are you sure they are 31mm carbs? measure the venturi's just to make sure, apparently '86 GSXR 750's did in fact come with 31mm carbs however both of mine that I've owned had 34mm carbs on them. however the case, use this as a jetting guide for OEM settings: https://www.gixxer.com/threads/understanding-carbs-rebuilding-forks-and-1100-shocks.159718/
your pilot air jet is indeed a 160 and should be for BST31's. seems to me that your pilot jets are 35's, which is one step richer than stock, which is good. I think 160 on the main jets is pretty fat considering stock was 117.5 for BST31's. only AFR and plug readings will tell. on those particular carbs, the main air jets are the only holes facing the air filter at the back of the carbs. they should be 1.7mm, get some calipers and measure something that is slightly smaller in diameter and poke it thru these jets to verify that they are the correct size. I believe safety pins are pretty close.

an easy way to check if you have vacuum leaks at the intake manifolds to to spray soapy water or wd-40 or something around the bases while the bike is running and observe if the rpm's drop or the engines behavior changes. I'd rule out valve float, unless you've taken off a set of valve springs and measured their free length to find that they're worn and compressed (doubtfully). synchronizing the carbs with that big vacuum leak will absolutely affect the way the bike idles, its all off-balance!! redo it after you ensure that theres no vacuum leaks anywhere, valve lash is set correctly, and the bike is properly jetted. synchronizing the carbs should be one of the last things you do. however, you mentioned that compression across all 4 cylinders is almost identical. save yourself the trouble and just do a bench sync if thats the case: https://www.youtube.com/results?search_query=bench+sync+motorcycle+carbs+ start with your mixture screws 3 turns out. check your float heights, they should be 14.6mm +/- 1mm. measure those heights when the float is NOT compressing the little pins/springs on the float needles
 

·
Registered
Joined
·
63 Posts
Discussion Starter #12
Awesome, yeah I'm thinking float height is the one problem that I could be missing. I found one vacuum leak at a boot on the cylinder side, but rtv fixed it up. Honestly I'm gonna try one more time with float height and plugging the vacuum, but am so ready to buy the RS carbs.

I have verified that mine are BST31SS. Do I need to change out the intake boots to work with RS34?

Sent from my Pixel 2 using Tapatalk
 

·
Registered
Joined
·
102 Posts
I couldnt see the videos you posted before because i was at work and they block videos, so good catch on that. If that vacuum port was unplugged that would certainly contribute to the symptoms you are describing.
 

·
Registered
Joined
·
870 Posts
Awesome, yeah I'm thinking float height is the one problem that I could be missing. I found one vacuum leak at a boot on the cylinder side, but rtv fixed it up. Honestly I'm gonna try one more time with float height and plugging the vacuum, but am so ready to buy the RS carbs.

I have verified that mine are BST31SS. Do I need to change out the intake boots to work with RS34?

Sent from my Pixel 2 using Tapatalk
no you don't, they are indeed easier to tune and simpler, but they won't give you a huge boost in power. also the throttle pull will be much heavier and the power much more snappy
 

·
Registered
Joined
·
63 Posts
Discussion Starter #15
I'm alright with that. Really just looking for tuning simplicity. All of my vehicles have mikuni flat slide carbs, so I'm pretty familiar with tuning them - the CV stuff just confuses me

Sent from my Pixel 2 using Tapatalk
 

·
Registered
Joined
·
63 Posts
Discussion Starter #16
Alright, picking up the RS34 carbs tomorrow. What are you guys running with them? Jet size / accelerator pump position? I'm hoping to be able to tune them without taking them in to a shop, but the accelerator pump tuning will be the most challenging, I'm assuming.

I have Mikuni HSR carbs on my Volvo 140, which are pretty similar, but they tune super wonky to work for a car (accelerator pump comes on immediately and stays on the entire time).
 

·
Registered
Joined
·
63 Posts
Discussion Starter #17
Mostly just looking for a solid baseline, and I can tune further from there (based on plug readings etc)
 

·
Registered
Joined
·
63 Posts
Discussion Starter #19
can't help with flatslides as Ive never owned a set, but I believe baseline jetting is on their website, or you can give them a call
Mikuni? Awesome, that is excellent advice. Hopefully they'll have info for the accelerator pump as well. This bike has been un-rideable for about 6 months now, and I picked it up 8 months ago. I just really want it to run - I'll worry about eeking out the extra 3 HP down the road.
 

·
Registered
Joined
·
63 Posts
Discussion Starter #20
ALSO, I still haven't actually snagged the carbs - I was told that RS34 is gonna be better for the 86 GSXR 750, but wanted to verify with you guys that that is accurate.
 
1 - 20 of 24 Posts
Top