1983 GS750 Stuck Throttle Issue

[SneakySqueak]

Hi all-

I bought a 1983 GS750e (the monoshock model) in January, and have been riding it daily since then. Today, I went to start it with no choke (it was already warm) and as soon as the engine caught, it rev'd to about 8k. I shut it off immediately and tried again, same thing. On the third try it rev'd only to about 4k, so I tried riding, and the problem disappeared completely-- 25 minutes of center city traffic, no problem. As soon as I got home, right as I was reaching for the key to switch the bike off, the revs jumped to 8k again, and continued to do so on subsequent attempts to start it. Needless to say, even if the problem mysteriously vanishes again, I am not going to be comfortable riding until this issue is resolved.

As for relevant information, I had the bike in the shop for electrical work a few weeks after I bought it, and paid the guy to clean the carbs. While I have not checked the quality of his cleaning job, it has been running and idling smoothly since then. The throttle still responds normally- in fact, it snaps back into place very crisply. I just changed the petcock and saw no signs of rust in the tank, and the foam air filter looks okay to me (I'll clean it anyhow).

If any of the throttle slides were stuck in the carbs from dirt or whatever, wouldn't I be able to feel it at the handle? The bike has a single cable throttle setup (no 'push' cable), so I'm not sure. Having tentatively ruled this out, my service manual has led me to suspect that the problem lies in the 'starter system' in the carbs- particularly, the 'starting plunger'. The choke lever feels normal.

I wanted to get a second opinion before I take the carbs off, so please let me know what you think. I have uploaded the passage from the service manual that refers to the 'starter system'. Thanks!

[Steel Toed Tank]

I'm going to say that you should check for air leaks in your air intake system.

You should make an intro in the GS Owners thread, where you will receive the most valuable gift a GS owner could ever get, you're welcome package.

Welcome to GSR!

[gsrick]

Welcome to the forum, when you can go back to your control panel and give us some info on the bikes you have.
The starting plunger is just a part of the choke. On my FJ1100 the choke cable is called the starting cable. In each of the carbs there is a spring that pushes the choke back open and if it is clean there should be no binding there. I would suspect the cable. Check to make sure your cables are routed correctly and are not being pulled inadvertantly. I had a bike that had the throttle cable routed wrong and turning the handle bars a certain way would pull it taught in effect pulling the throttle. Same thing happened with a clutch cable on another bike. Worth taking a look and there should be a section that shows where the cables and wires are suppose to go. Having had electrical work reiently done I'd also check those.

[BassCliff]

Greetings and Salutations!!

Hi Mr. SneakySqueak,

In addition to servicing (lubricating) the throttle cable, making sure it is routed properly and not pinched, also check the carb balance. A vacuum balancing "how to" can be found HERE and HERE. Make sure the air intake system is as air tight as you can make it. Air should enter the system only through the snorkel on the airbox. See the air intake repair guide on my little website. OK, now it's time for your "mega-welcome".

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, diagrams, "how-to" guides, 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!

More links to helpful threads in the forum:
Help! Your Bike Won't Start
DON'T DO THESE THINGS
Help! Your Bike Won't Run Well
Oh God! Pods!


Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[SneakySqueak]

Thank you all for the warm welcome and quick responses. Those resources are more than comprehensive, and I'm sure I will be referencing them for as long as I have this bike.

After much reading, I agree that the air intake system is the most likely source of my troubles. I have ordered a set of carb and intake o-rings, hardware, and boots/clamps for both sides of the carbs. In the meantime, I will clean my carbs and adjust the float levels as per the supplied guide, and I will be sure to sync them after the boots arrive and I am able to put the bike back together. I am going to replace the air filter this time instead of cleaning it, and the airbox weatherstripping mod seems worthwhile in my case, as well.

I also have a new throttle cable on hand that I will install while the gas tank is off- I am confident this is not the issue, but it certainly can't hurt, and I have been wrong before. Hopefully I will find an obvious source of the problem along the way... I'll be sure to update this thread with the results.

Thanks again for the help. While I am not happy about spending another $200 on parts, this issue seems too serious to half-ass. Hopefully I will be on the road again next weekend.

[SneakySqueak]

Hello again-

Sorry for the delay in reply, it's been a busy week! Last Wednesday, I tore down the fuel system and found that the boots on both sides of the carbs were in pretty good shape (no dry rot, plenty of flex) so I decided to re-use them. The engine side boot o-rings were completely flattened and brittle as stale bread, and crumbled as I removed them for replacement- I am fairly certain this was my issue, although there were no cracks or other visual clues. I also replaced the throttle cable with a new, lubricated one, and weatherstripped the snorkel of my airbox. I opened a few random compartments of the carbs but they were clearly very, very clean (cleanest carbs I've ever seen) and so I just closed them back up without modification.

Anyhow, the bike ran better than ever once I got it back together, and I have logged a couple hundred trouble-free miles since. I want to say thank you for the help (especially the tip on the o-ring supplier!), its funny how far off my initial diagnosis was!

Perhaps I should make another thread, but I think this is related: sometimes when I come off the throttle when the bike is fully warm, I see a slight drop in revs- for example, if I were cruising at 3500 and pull in the clutch to slow for a red light, the revs dip to 1100 for a couple seconds before returning to 1500, which is where the bike normally idles. Does this indicate a small air leak? Is there a diagnostic test to locate a leak such as this? I still have yet to sync my carbs and time my valves, but I wanted to do thise things after I am sure my fuel system is as good as it can be.

Thanks again for the assistance!