1986 gsxr 750 with 1986 gsxr 1100 carbs-help! - Suzuki GSX-R Motorcycle Forums Gixxer.com
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post #1 of 9 (permalink) Old 06-28-2018, 04:24 PM Thread Starter
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1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

Ok, so I’m new to this whole forum thing. I’m not really sure how to navigate this scene so I apologize if I’m asking something that has been asked or if I’m breaking any kind of etiquette or rules by making this post. I paid the $40.00, so hopefully that’ll count for something lol.
Right, so I’ll just jump in. I have a 1986 GSXR750. It came with what I believe to be 30mm milkuni carbs with dyno jet stage three kit on it. It never really ran right I bought the air box. Connected it and took out the dyno jet 160 main jet, replaced it with 136 mains but it would only run if the filter wasn’t installed in the box. So, now we have an empty air box, 136 main jets, and it ran decent for a couple weeks. The bike fell over and never ran right after that, hardly ran at all. I think something happened to the outside right carb because there’s no change when I adjust the air/fuel mix screw..but I was told if I get these 34mm stock mikuni carbs off an 86 gsxr 1100,(I have a 750) I could delete the air box and use the k&n filters that were on them and that they were already set up and rejetted and they would “line right up and run”...well...$425 later, it doesn’t. It’s gotta sporadic idle, acts like its hitting the rev limiter at 5k, bogs down and shuts off at red lights, which is pretty much the same spot I was in before... I almost want to throw this thing away, and I’m kinda mad/frustrated at myself for taking the word of someone trying to sell me something instead of doing a bit of research first. So this is my thing, I want to keep these carbs on(34mm OEM1100 gsxr carbs) and I don’t want to put the air box back on. Can I do that and still ride around town to and from work? Is there a baseline I can start at to get them set up, as far as needle position, air/fuel mix screw turns, and float height go? If I have to put the air box back on, can I keep the 34mm carbs? Are they even beneficial for performance or anything? If I have to put the air box back on, can anyone find me new boots for it? Or will the radiator hose I bought work? As long as they are sealed right? lol...I also heard the only way to really set these things up is with a dyno. I saved up for three weeks to buy these carbs and I only paid 425..so you know...money is tight right nowĮ\_(ツ)_/Į
I appreciate any and all help provided and again, I apologize if I’m asking questions that have already been answered...technology(or carbs for that matter) aren’t really my forte.

Thanks in advance,
-Jeremy
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post #2 of 9 (permalink) Old 06-28-2018, 05:10 PM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

First off you should have posted this question here https://www.gixxer.com/forums/15-oil-cooled-gixxers/ . These guys know there shit .

Now that I got that out of the way .... i'm actually surprised the bike runs at all . There is a lot more done to the carbs besides just the larger main jets. If the carbs are anything like my Interceptors were , then you probably have adjustable needles ,the slides have been drilled so that they rise at a different rate than stock . You leaned the piss out of the carbs by going to the 136's. I think I also had to adjust my floats so that they feed more fuel for the larger jets.

You may want to go to the Dynojet website and see if they have the instructions for the Stage 3 jet kit archived so you could download them . This way you could check all the adjustments and make sure that they were set up correctly. You could also call Dynojet to see if they have the info.

I'm making the assumption that it was a Dynojet kit that was used .

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Last edited by coopgt1; 06-28-2018 at 05:12 PM.
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post #3 of 9 (permalink) Old 06-28-2018, 05:19 PM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

*thread moved to oil-cooled section...
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post #4 of 9 (permalink) Old 06-28-2018, 05:41 PM Thread Starter
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Cool guys. Thanks for the info, I’ll post in this thread from now on. I’m not sure what jet size or needle position the new 34mm carbs have. I just took them off and am about to investigate as well as synchronized them to the bike. I’ll reply in a bit with all the info if the synch doesn’t fix it. Sorry for the ramble post earlier, I was frustrated. My main questions at this point are, can I run the 34mm mikuni flat slides on my gsxr 750, is there any potential gain or advantage going to the 34’s from the 30’s, please Dear God tell me I can run these (or any carbs) without that dumb ass air box? To help better answer these, I’ll get the info on what’s In the 34’s now.
Thanks,
Jeremy.
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post #5 of 9 (permalink) Old 06-28-2018, 07:04 PM Thread Starter
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Ok so it looks like one of the diaphragms has a tiny hole in it. I’ll buy I new one, for now I’ve sealed it up. The needle position is at the 3rd slot down from the top. There are six slots and the needles look like they have all the stock spacers and clips...the needles themselves looked to be oem but then again, the only other carbs I’ve ever opened up were the 30mm mikunis. It looks like the jets under the diaphragms say 730 on them...I thought maybe it was 130 but they all look an awful lot like a 7. The air fuel mix screw was set about 1 3/4 turns out. When I opened up the float bowls all the floats were set at 14mm. The main jets are 142.5 and the other jets(pilot jet?) is 32.5(the little one in front of the main) I was told these carbs came off of a running 1100 and they should be close to set up to run on my 750...”maybe some minor air/fuel mix adjustments” but that’s not the case. it idles crazy high all on its own no matter how low I set the idle, and it seems to rev up as I go thru the gears down the road. All carbs are synched.
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post #6 of 9 (permalink) Old 07-03-2018, 08:53 AM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

You need to start from scratch and quit looking for the one band-aid solution that will fix everything. Ain't going to happen and you do have some work ahead of you, if you want to fix this. I assume you are in the US and are dealing with a US spec bike. If not, let us know where you are and what you have.

Some basics: The '86 750 came with 31mm CV Mikunis. The '87 750 came with 34mm CV Mikunis, as did the '86-'88 1100. There are differences in the jetting and other details between the 750 and 1100. You should probably start by getting copies of the Suzuki servoce manuals for both the 750 and 1100, so you can learn which carbs you have and which jets and other components they started with. There are several version of these carbs and you'll find a series of letters and numbers lightly stamped on the carb bodies. Use this to look up (in the service manual) which carbs you have.

Rebuild the carbs. Take them off, disassemble and clean them and replace ALL of the rubber o-rings with original parts from Suzuki or Mikuni. Do NOT use aftermarket o-rings.

Set the float heights correctly. 90% of people do this incorrectly, it's been discussed here a bunch. Not going to type it again, just do a search.

Identify which jet kit you have, for sure. I prefer Factory Pro over DynoJet. If you use DynoJet, I'd suggest a stage 1, not a stage 3.

Use K&N pod filters, clean and properly oiled. There's too much oil, and too little oil, Follow the directions.

You should be able to pick a reasonably close jetting solution by talking to the people that made the kit you use, or by using their instructions. When first tuning them, You'll want to check for air leaks, set a base idle speed and base fuel setting with the slow speed screws and a synchronization using a set of good gauges. It should run well enough to make incremental tuning changes with the main jet and needle settings. If it runs as poorly as you describe above, you've screwed something up.

Factory Pro has a CV tuning guide on their web site which is worth a read.
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post #7 of 9 (permalink) Old 07-06-2018, 12:52 PM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

i completely agree with java. you must first identify the type of carb you have, since there is a jetting difference between the 31mm and 34mm. there should be an identification number on the side of the carb body, or you can just measure the intake ID.

no need to run the stock airbox. all of my first gens have the airboxes removed; stage 3, individual filters, and they run excellent.

factory pro has baseline settings that should get you in the ballpark; they did all of the R&D.

going from memory, my first gen 750 engine with 34mm stock carbs run either 135, 140, or 145 mikuni main jets. don't remember the needle clip, but check with factory pro for baseline settings. the 31mm carbs run different main jets.

oh, and make sure you thoroughly clean all orifices, otherwise, you will have running issues.
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post #8 of 9 (permalink) Old 07-07-2018, 02:48 AM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

Quote:
Originally Posted by StevOC80 View Post
Ok so it looks like one of the diaphragms has a tiny hole in it. Iíll buy I new one, for now Iíve sealed it up. The needle position is at the 3rd slot down from the top. There are six slots and the needles look like they have all the stock spacers and clips...the needles themselves looked to be oem but then again, the only other carbs Iíve ever opened up were the 30mm mikunis. It looks like the jets under the diaphragms say 730 on them...I thought maybe it was 130 but they all look an awful lot like a 7. The air fuel mix screw was set about 1 3/4 turns out. When I opened up the float bowls all the floats were set at 14mm. The main jets are 142.5 and the other jets(pilot jet?) is 32.5(the little one in front of the main) I was told these carbs came off of a running 1100 and they should be close to set up to run on my 750...Ēmaybe some minor air/fuel mix adjustmentsĒ but thatís not the case. it idles crazy high all on its own no matter how low I set the idle, and it seems to rev up as I go thru the gears down the road. All carbs are synched.
Hi Dude, youíre crazy idle would possibly be caused by cracks in your inlet boots (rubber between carbie and engine) and this is what happens when they suck air. If they have never been replaced they go hard and crack. You will probably have to order genuine ones from Suzuki as they are getting hard to get now.
Stuttering and bogs down and shuts off at the lights tell me itís too rich.

Buy a float level tool and set all to the same factory spec as supplied below by Flying Scotsman on another thread, I know you say they are set at 14mm but if you dont get this correct and you set to low they will always run rich:
Depending on what stock carbs you have, the float heights are as follows.

29mm mikuni slide carbs VM29SS=14.2mm +/-1mm

31mm mikuni cv carbs BST31SS=14.6mm+/-1mm

34mm mikuni cv carbs BST34SS=same as 31mm carbs

Looking at above specs just go 15mm its better to be higher than lower and find out what the standard jets are, but you will need to know which carbie you have first ??

Note: say you set floats at 12mm this puts more fuel in the bowl and it floods / setting at 15mm gives less fuel in they bowl and doesn't drown your jets.

Good luck
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post #9 of 9 (permalink) Old 07-07-2018, 09:54 PM
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Re: 1986 gsxr 750 with 1986 gsxr 1100 carbs-help!

Just noticed Old Skool_R has done a fantastic write up on these carbs suggest you it. The thread is called:

Understanding Carbs, Rebuilding Forks and 1100 Shocks!
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