BST36SS carb issues - Suzuki GSX-R Motorcycle Forums Gixxer.com
 
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post #1 of 9 (permalink) Old 07-10-2018, 12:39 AM Thread Starter
Squid
 
Join Date: May 2018
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BST36SS carb issues

Hi,

I'm from Sweden and I just bought an 1988 GSX-R 750 Slingshot and I have now found this great forum!
I'm pleased with the bikes behavior, however I have a small anoying problem with the carbs and I thought I'd ask you guys for advice.

When I'm out riding it and if I give it full throttle it will bog down/hesitate/jerk at 8000-9000 RPM and it really struggles to get over 9000 rpm.

Also, if I stop and let the bike sit for a while (carbs fills up with fuel?) and if I then start it up and give it full throttle it will pull all the way up to 13000 rpm no problem for one run.
And after that it will start to bog down/hesitate/jerk at 8000-9000 RPM again...

This is what I've done so far:
Valves are set.
Carbs are cleaned.
Floats are set at 14,6 mm.
Jet needle is at second from top.
Carbs are synchronized.
Fuel/air mixture screw is 2 1/2 turns out.
Idles perfectly.


Here's my thoughts:
The carbs are setup right and there shouldn't be any problem with them since it will run properly at first and also if I just cruise at slow speed for a while and give it full throttle it will the again pull hard all the way to rev limit.
I suspect something with the fuel pet cock or am I missing something?

English is not my native language so bare with me for any wrong spelling...
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post #2 of 9 (permalink) Old 07-10-2018, 12:04 PM
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Location: San Antonio and Houston
Motorcycle: 1986 GSXR 815, 2002 Bandit 1200N
Posts: 855
Re: BST36SS carb issues

yeah sounds like the fuel petcock is faulty, I've never had any luck with them on any Suzuki street bike I've owned. Go with a Pingel valve, they are much better and dont rely on a vacuum source (depending on which model you get) just be sure to turn the fuel off whenever you park the bike
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post #3 of 9 (permalink) Old 07-11-2018, 12:35 AM Thread Starter
Squid
 
Join Date: May 2018
Posts: 4
Re: BST36SS carb issues

Thx!
When I firts suspected the fuel petcock I looked at the Pingle valve but wanted to wait before I got some input...
I just got a Petcock repair kit and I'll try that one first and see if it helps. If not, I'll buy the Pingel.

Thanks again!
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post #4 of 9 (permalink) Old 07-11-2018, 12:02 PM
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Motorcycle: 1986 GSXR 815, 2002 Bandit 1200N
Posts: 855
Re: BST36SS carb issues

Quote:
Originally Posted by Wild Swede View Post
Thx!
When I firts suspected the fuel petcock I looked at the Pingle valve but wanted to wait before I got some input...
I just got a Petcock repair kit and I'll try that one first and see if it helps. If not, I'll buy the Pingel.

Thanks again!
I rebuilt the petcock on my Bandit and my GSXR, The GSXR's still did not supply enough fuel and the bandit's still leaked. If I were you I'd just return the kit and use the refunded money towards a Pingel unit. Good luck
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post #5 of 9 (permalink) Old 07-11-2018, 02:46 PM
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Re: BST36SS carb issues

+1. Don't bother with the OE unit, it is marginal at best.

Pingel all the way, the double outlet is easier to fit, but more expensive. I fitted a single outlet to mine, with a T then 2 additional fuel filters nestled between each carb pair, above the fuel inlets.

Also, test the tank vent, do you get the same problem if the cap is left just open? Do not do this with a full tank!
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post #6 of 9 (permalink) Old 07-23-2018, 01:16 PM Thread Starter
Squid
 
Join Date: May 2018
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Re: BST36SS carb issues

I have now installed the repair kit and still got the same problem.
So I removed the tank to check everything over once again...

On the pet cock there are two outlets.
I sucked on the vacuum hose to see if there was coming any fuel or not and if it was an even flow of fuel.
From one of the outlets thers was barely coming any fuel but from the other I had a good flow.
So I mounted a T-pipe on the good outlet and plugged the bad one on the pet coock.
Out for a test run and now verything works as it should, so now we have an oil cooler back out on the road where they should be :-)

Much cheaper than a Pingel...

Thanks for all ideas and good advices.
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post #7 of 9 (permalink) Old 07-23-2018, 02:23 PM
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Re: BST36SS carb issues

going from memory; the second gens had stock dual fuel outlets. if one outlet isn't working, but the other outlet is, then it could be clogged. if the bike runs fine at high speeds/high rpm's, then i wouldn't worry about it and just ride.

the stock petcock has 3 positions:

1. On; normal vacuum
2. Reserve; low fuel with vacuum
3. Prime; constant flow, no vacuum necessary

for what it's worth; the stock first gens had a single fuel outlet, and i run the stock suzuki fuel petcocks on all of my first gens without issue. even my trackbikes with mikuni RS 36mm carbs, the petcock supplies enough fuel.

either way, good to hear you figured out your problem.
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post #8 of 9 (permalink) Old 08-04-2018, 09:57 PM
Squid
 
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Re: BST36SS carb issues

Hey All,

I noticed the OP stated his air/fuel screws are set to 2 1/2 turns out. That said, I set my carbs to 1 1/2 turns out because just about everything I could find said 1 1/2 turns out.

Bike is on the bench and idles OK, carbs are freshly cleaned and sync'd. Not had a chance to get it on the road yet so can't comment how it rides or pulls on the road, but will do shortly.

QUESTION - Should I set the AF screws to 2 1/2 turns or leave it at the 1 1/2 turns as set today?

(I've read the manuals and various threads and the AF screws on the USA bikes all say "preset", but don't say what the actual preset is.

Thanks in advance...

Matt.
post #9 of 9 (permalink) Old 08-11-2018, 12:21 AM
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Join Date: Dec 2016
Location: Adelaide, Australia
Motorcycle: 1991 GSX-R 750
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Re: BST36SS carb issues

Quote:
Originally Posted by [email protected] View Post
Hey All,

I noticed the OP stated his air/fuel screws are set to 2 1/2 turns out. That said, I set my carbs to 1 1/2 turns out because just about everything I could find said 1 1/2 turns out.

Bike is on the bench and idles OK, carbs are freshly cleaned and sync'd. Not had a chance to get it on the road yet so can't comment how it rides or pulls on the road, but will do shortly.

QUESTION - Should I set the AF screws to 2 1/2 turns or leave it at the 1 1/2 turns as set today?

(I've read the manuals and various threads and the AF screws on the USA bikes all say "preset", but don't say what the actual preset is.

Thanks in advance...

Matt.
1 1/2 turns out is a good starting point, it wont take you long to work out if its wrong - you will have a rough idle.
Make sure you adjust after bike has properly warmed up.
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