Idle, take off issues after rebuild

[james750tz]

Hey guys, I recently had a friend of mine that is a certified Harley mechanic that built my carbs for me on my 82 gs750t. Please, no "he's a Harley mechanic, not a rice mechanic" comments....he owns a yamaha sport bike and he's damn good at what he does. I had done them myself a while back, and I couldn't seem to get them just right. Had a very bad spot in the acceleration, and it even quit on me a couple of times which really sucked. He had the bike about a month and half, and tore them down about 3 times because he kept experiencing a high idle situation that was intermittent. He said finally he raised the floats up a bit which helped the problem. However, the bike just seems unbelievably cold natured for about 30 minutes when I first ride it, and it cuts out a bit when taking off...almost like it's starving for fuel? Going down the road it never sputters once warm with say at least 3000 rpm and up and runs fantastic otherwise. I can choke it up a hair on take off which helps the sputtering tremendously which makes me think lean? Anything worn I should be looking for besides this? Or maybe should I be looking at ignition? Carbs were built with new kits. I didn't reuse the old parts. I will say that this bike has ALWAYS had some idling issues like loading when sitting, but it's always been that way since I got it in 95. Any suggestions are appreciated.

[chuck hahn]

Stock airbox and stock pipes? Modded exhaust and pods?? These will determine the nature of any answers.... Of which I will not comment on until more specifics are known.

[chuck hahn]

Although we cant comment on such issues as jetting at this time, heres some questions i have.

1...Did he backlight the diaphrams with a flashlight in a dark room to inspect for pinholes?

2..Did he check to be sure the slides rise andfall freely, smoothly and not with scratchy dragging sounds?

3..If these are the stock CV carbs, then where are the mixture screws set at?

4..Is thee the possibility that he just may have tightened a mixture screw in and the tips broke off in there?

5..What position are the clips on the needles?

6..What are the current main and pilot jets sizes?

7..Have you also inspected the intake manifolds for leaks and are the intake manifold Orings new and installed so they are not pinched?

8..Do the clamps tighten up BEFORE youve used all the available screw threads? If not, then they may be stretched and not sealing right..may need them all replaced.

9..by "new kits" does that also include all new orings on the relevent screws or just the hard parts?

Give as much of a full description and all the info you actually KNOW was done and used and this will greatly help in the answering of your questions.

[AndrewDoesHair]

My 1980 GS750L is doing exactly this, after new jets, O rings, and a good cleaning and rebuilding by a mechanic with 40 years of experience. In his defense, he works almost exclusively on Triumphs, and was reluctant to take on this job. HE says he doesn't even know where to begin to figure this out. I'll be watching this thread, hopefully it can help us both...

[BassCliff]

Hi,

Everything starts with properly cleaned carbs. Then the other systems must be properly addressed. You will find proper procedures in the garage section of the GSR website and also on my little BikeCliff website. Did you get your S.W.A.G.?

If you are here you probably have a 30 year old motorcycle that needs about 20 years worth of maintenance. You'll find all kinds of helpful tips, procedures, manuals, etc, in the links below. Let's get started.

Let me dump a TON of information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



Please Click Here For Your Mega-Welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[james750tz]

Hey, thanks for the help. The bike is 100% stock running wise.


1...Did he backlight the diaphrams with a flashlight in a dark room to inspect for pinholes? Unknown

2..Did he check to be sure the slides rise andfall freely, smoothly and not with scratchy dragging sounds? I know they were free and smooth when I did them last

3..If these are the stock CV carbs, then where are the mixture screws set at? Completely stock

4..Is there the possibility that he just may have tightened a mixture screw in and the tips broke off in there? No, all that is good. He would have never left it like that knowing this guy.

5..What position are the clips on the needles? Clarify? Clips on needles?

6..What are the current main and pilot jets sizes? Stock

7..Have you also inspected the intake manifolds for leaks and are the intake manifold Orings new and installed so they are not pinched?

Yes, there are no leaks. Did a spray test all over the engine.

8..Do the clamps tighten up BEFORE youve used all the available screw threads? If not, then they may be stretched and not sealing right..may need them all replaced.

Now this? The I don't know. The boots are the same ones that were on the bike when I got it, and I have had it 15 years. They're suprisingly soft though. I did consider replacing them.

9..by "new kits" does that also include all new orings on the relevent screws or just the hard parts? Yes, all new o-rings...everything

Give as much of a full description and all the info you actually KNOW was done and used and this will greatly help in the answering of your questions

[james750tz]

Hey guys, thanks for the info. The guy did a fantastic job on the carbs as far as I am concerned. He knows what he is doing, and it frustrated him that it wasn't perfect. I did the teardown just like the how to on the site and had similar results. I am thinking maybe diaphrams, or boots. I'm going to do my own spray test to see as well. Other than this? Runs perfect. Reliable and smooth. Exceptional for a 30 year old motorcycle no doubt.

[tom203]

Since you're adamant about your guy's carb work, I'd suspect he would check the diaphragms,so this leads to the boots and/or clamps as suspect- especially considering a random high idle. Probably best to replace, no matter how they look.

[james750tz]

Okay, any recommendations on the replacement ones? Stock, or are there some good aftermarket alternatives? Thanks.

[Nessism]

Even experienced mechanics often do not understand the specific needs of the GS carbs. There is a carb rebuild tutorial linked in my signature that you might want to review to be sure everything if fully addressed. For example: aftermarket carb kits often come with jets that are a compromise across various models for various countries. They are also often of inferior quality to the OEM Mikuni jets the bike was build with. Standard recommendation here, learned by input from many members, is to reuse all the original brass parts in your carbs. Jets don't normally wear out, so all you need to do is clean them to assure they are ready to go back into service. If you follow the procedure fully, there is no need to tear down the carbs more than one time. Anyone doing this three times obviously didn't know what they were doing. Also, aftermarket carb kits do not come with all the critical O-rings in the carbs. For example: the O-rings on the interconnection pieces between the carbs. These are some of the O-rings most prone to failure too. Cycleorings.com sells a full O-ring kit which should be considered mandatory for a proper rebuild.

Regarding your bike in general, please check the Newbie Mistakes thread also linked in my signature. You may not be a newbie, but the suggestions contained within are universal. For example: running issues can often be traced back to lack of maintenance. A vacuum sync and valve adjustment for example. You can't trouble shoot until all the maintenance is up to date.

Good luck

[Steve]

Hate to say it, but this could be part of your problem:

Carbs were built with new kits. I didn't reuse the old parts.

Many of the "rebuild kits" are filled with inferior parts that may not be quite the right size.
You are usually better off with the original parts, after they are properly cleaned.

However, the bike just seems unbelievably cold natured for about 30 minutes when I first ride it, ...

Sorry, I have a bit of difficulty comprehending a bike that is "cold-blooded" for 30 MINUTES.

I don't think that ANY of my bikes require "choke" for more than 30 SECONDS aftter start-up.

Whenever we see comments about "cold-blooded", we automatically know that the carbs are not properly set. "Stock" settings are not necessarily correct, as they were set up to comply with EPA regulations, not for proper running. Now that the bikes are out of warranty and the dealer does not have to worry about compliance, set it up to run RIGHT, and it will be fine.

Where are you? Maybe one of us is close enough to stop by and help.

.

[tom203]

So, to recap
bike very coldblooded
once warm, stumbles below 3k, otherwise ok
erratic idle at times.
You followed tutorial on carb cleaning , but poor results
Carb rebuild kits- aftermarket or suzuki? did you save old parts?

[james750tz]

Thanks Ed. I probably need to adjust the valves for certain since I have been running it 17 years (parked for 8 years though). When I built my carbs I used the tutorial that was on the site at the time. Yours is a bit more thorough. I may invest in a second set of carbs and try to build them to see if there is a difference in how it runs with them.

Any recommendations on the boots? Stock or good aftermarket? What brands of kits do you consider inferior?

Thanks again.

[james750tz]

So, to recap
bike very coldblooded
once warm, stumbles below 3k, otherwise ok
erratic idle at times.
You followed tutorial on carb cleaning , but poor results
Carb rebuild kits- aftermarket or suzuki? did you save old parts?

Mostly. Idles okay, but sometimes at 1500, sometimes 1000? Just on takeoff mostly is where I get some stumbling.

2008 November....Followed the site tutuorial when I did it the first time. Ran great!! About 3 weeks in it started backfiring some. I tore them back down only to find there was water somehow in the bowls? Tore them down and cleaned anyway following the same process I did the first time since the tank isn't really rusty, but there was some trash in it (now filtered). Ran like crap. HUGE dead spot from middle throttle to wide open. Tried everything I knew. Replaced petcock too. NO difference. Suzuki genuine part too.

Strangely, I could do an odd warm up proceedure and it would run better. Start it, let it run 90 seconds with the choke closed. Shut it off let it sit for 5 minutes, no choke...instantly idles...and good too...and it would run pretty decent with less dead spots...sometimes almost none. Had it quit on me a couple of times and decided to let someone else take a stab at it because I obviously wasn't doing something right (September 2012). Other than the stumbling, it runs pretty doggone good.

I think I have some of the old parts. They looked identical in every way to the new ones. I always check stuff like that. Aftermarket kits used both times. I reused the kit when I personally built them the second time. It was a K&L I think? The other...can't remember exactly.

[chuck hahn]

if the intake boots are supple and not torn or any other damage, then just replace the clamps so they will tighten properly against the carb bodies and not have any leaks.

And as for riding it for 17 years ( 8 of which it was parked )...and in all this time you never checked the valve adjustments?? I can understand that if you only oput maybe 1000 miles a year on, but certainly not if it was like a daily rider!! The valves for sure need some attention!!

And as you said "stock" to where the mixture screws are at...how was this determined? The basic default setting is 2 turns out from lightly seated.

To clarify " what psoition is the clip on the needles"...when you pull the slides to check the diaphrams for pinholes, you remove the jet needle from the center of the slide. You will see that the top of the needle has a little E clip and there are some grooves. The clip goes in the CENTER groove.

I know he knows his stuff..but just for your piece of mind, open the bowls and at a minimum do this..PLEASE..

1..are there rubber plugs in the holes the pilot jets go in? If not there are supposed to be.
2..remove the pilot jets and be sure all the holes are poked out and be sure to look at the rounded end as well...theres a tiny hole in there too.
3..remove the needle jet and also be sure all the holes are poked out and run a pipe cleaner down the big hole in the center.
4..recheck where the mixture screws are at... there should only be 1 external adjustment screw..which is the mixture screw on the top back part of the carb throats.