Dear MOby,

I dragged home an ’82 Suzuki GS1100E from a friend of a friend’s basement a couple months ago. At first, it appeared way dusty and sad and I thought I was being taken. But after not all that much cleaning and polishing, it’s a really terrific looking old motorcycle nobody else has, and I’m really liking it.

I don’t know how long it had been sitting. There was no gas in the tank, but some terrible ex-petroleum semi-liquid did dribble out of the float bowl drains. I took the carbs apart and the jets were all actually totally plugged with dried-up residue. I took them to a local shop and had them cleaned in one of those ultrasonic tanks. Put in new spark plugs and air filter, and inspected all the intake area for leaks. Everything seems to be good, gas is flowing through the petcock, spark is good to all four cylinders. It’ll start up, idle, and run pretty okay up to 5,000 or so rpm – but past there, it spits back and runs rough and refuses to rev any farther. What’s the problem?

Revless in Seattle

Dear Revless,

Mickey Cohen of Mickey Cohen Motorsports and right-hand man Cyle Winkler tell us what’s often the malady in situations like this is that your main jets have actually been etched by the nasty old brew that sat in there, a sort of PTSD for carburetor brass parts. In the old days, it was a no-no to drill jets out because they’re much more than just brass plugs with holes in them; those holes are actually carefully shaped for smooth fluid flow.

Carburetor jets

Shiny and new…

The scars left behind by the old gas in those soft brass nozzles, especially if ethanol was the last fuel in there and especially if they were plugged solid, actually disrupts the smooth flow of gas through the carburetors and into the engine. MC suggests ordering up new jets, both main and pilot, and replacing the float valve needles and seats while you’re at it, since they’re also brass. Good luck!

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  • Old MOron

    Revless, if that’s your bike in the lead photo, you did a great job polishing it up. Congrats! I hope you get many happy miles from it.

  • Jon Jones

    And check the primary leads at the coils. This model has spade connectors. It’ll run fine at low revs, then cut out at higher revs.

    • John A. Stockman

      I found a very neglected KZ440, only 700 miles on it, original owner. After I rebuilt the entire bike (it was laying completely on its side under a pile of furniture, 7 year old gas, battery acid leaked all over, ruined the electrics under the seat, you name it…), I had that issue of cutting out at higher revs. I did find some minuscule pin holes in the CV diaphragms, which couldn’t be easily seen. A super-bright light behind them showed the holes, but holding them up to the window didn’t reveal them. The usual new jets, float valves, gasket kit, still started, idled great but when it got to about 6000, crapped out. It was those spade connectors on the coil! Just enough vibration at those revs to disrupt the integrity of the connector. I found it because one day while test riding and still not being able to get past 6000rpm, the positive lead vibrated off and the engine quit, like I’d hit the kill switch. I squeezed the spade a little, fit tighter, and it started right up. I turned around to go home and it revved right to redline with no issues. I got some new spades, soldered, heat shrink, ran great, never anymore not revving past 6000rpm. If it hadn’t vibrated all the way off that day, I might’ve been chasing it longer.

      • Jon Jones

        Good one! I check the primary leads any time I service a bike now, when applicable. They’re almost always a bit loose.

  • Johnny Blue

    Congrats on your purchase. It looks really cool. I really like the shape of the tank. And the colour.
    About your problem. Does it happen at any time when you try to rev it from idle, or when you’re riding it? If it’s happening while riding it and not right away after idling it, before spending on new jets I’d check the level of gas in the float bowls when it sputters. If the debit through the petcock is not sufficient it might get enough gas for low revs, but when the demand increases it might starve for fuel. I’ve seen it happening with an old car I once had. Someone before me had bent the fuel line and the carburetor wasn’t getting enough fuel at higher speeds.

  • Johnny Blue

    I’d also check the vacuum. If there’s no vacuum to lift the needles from the main jets… there’s no going fast.

  • Gruf Rude

    As noted in an earlier article, carb diaphragms that are cracked or pin-holed can kill the ability to rev. Some years ago I bought a BMW R100RS that the previous owner sold because “I just can’t keep up with my friends any more.” Started, idled and ran OK up to about 4500 and then wouldn’t go any faster. Turned out both diaphragms had a one-inch split from old-age. New diaphragms and ZOOM!

    • DickRuble

      You’ve ruined the myth of evil alcohol etching brass. Who do you think you are to come up with a sensible and far more plausible explanation?

      • Gruf Rude

        I’m somebody who owns an old Airhead BMW and a KLR – both notorious for diaphragm problems and (in the KLR’s case) ethanol plugged pilot jets.
        Not familiar with etching (corrosion from water attracted by ethanol, though), but the varnish deposited by bad ethanol fuel can be impossible to remove, even ultrasonically, so replacement with quality OEM brass is good advice.
        I went with diaphragms because the bike idles and runs OK up to 5000, which leads me to believe that the cleaning got the pilot jets (and thus main & needle jets) opened up.
        As an aside, StarTron has worked best for me to keep the ethanol swill we get up here in Wyoming stable over our long winters.

        • DickRuble

          I blamed ethanol for many years (about half a dozen to be precise) for my bike’s problems. It’s less than ideal as a fuel, but ethanol is not the culprit of everything gone bad. The reality is that it’s the detergents that do some of the damage, followed by ethanol absorbing water, which drops to the bottom of the tank and carburetor if left sitting for more than 28 days. Once the tank and carburetors emptied and rinsed (with fresh gasoline), if the problems persists, the cause is elsewhere. In my case it was the packing of the silencer that had completely disappeared. This made the bike run very lean. It was very rough (and loud). I first rejetted.. got mucho power and even mucho mas noise. Unbearable. Once I learned that silencers can be repacked and did it, I had to return jetting to the original state, ’cause now bike was running too rich and was choking on gas at around 4000 rpms..

          But if you want to know more about ethanol induced madness, read my post below…

  • Sentinel

    That bike is sweet! I’ve got an 83 GS450E that’s still going, but could surly use some carb work.

  • SRMark

    One of my all-time favorite bikes. Burns gives you great info. You may also want to try running some SeaFoam through those carbs. You might get lucky.

  • Gary

    I had a GS1100. Great bike … though probably not as great as I remember it. Funny how that works. But congrats on finding such a clean one. Well worth fine-tuning.

  • JohnnyS

    Suggest you check for leaky carb boots: With the engine idling, spray a little carb cleaner around the rubber boots between the carbs and the head: If the engine revs up a little, you have a leak. That will cause lean running, poor vacuum and an inability to rev. If you have a leak, replace the boots and that will help.

  • DickRuble

    I used to be a preacher leading the anti-ethanol crusade. Driven mad as a hatter by the inability (mine, and my mechanic’s) to tune up my clunker, I had come to the conclusion that ethanol was the evil source of my torment. Solution: eliminate ethanol from the gasoline. How? One way is to buy ethanol free gasoline. $10 a gallon and available only at select and rarer than dodo birds gas stations that deliver only in metal containers. Not much of an option. Another way (you can now judge the madness) was to separate the ethanol from the gasoline. To that effect you add a cup of water to your 5 gallon fresh gasoline mix, stir well, and let sit overnight. Next morning you have a two phase separation. At the bottom, 1/2 gallon + 1 cup of (ethanol-water) mix, at the top gasoline and whatever dispersants and additives did not separate. You decant, et voila, you have 4 1/2 gallons of pure(r) gasoline. Problem is the octane level is now way lower. You have to add some octane enhancer. I used that mix and the garden tools ran fine, though the engines didn’t seem to want to rev quite as fast as they used. You may say; ok, I can live with that as long as I can now store my bike without worrying about ethanol separating and etching its evil name in the plastic of my Ducati. However, that doesn’t really solve the issue. As it turns out, alcohol only absorbs half of one percent of water from the air, and it holds its water well, meaning it won’t separate just from that amount. The real issue is water condensation on the walls of the tank.Yes, yes, yes. The emptier the tank, the more air it contains. The wider the temperature and humidity swings, the more water collects on the tank walls, then slowly finds its way into your gasoline. And that quantity of water is much larger than any amount ethanol may have absorbed or contained. That amount of condensation water is enough to lead to phase separation when alcohol is present, and enough to form a water layer at the bottom of the tank on its own. To make a long story short: Storing your bike with less than a full tank is more likely to lead to your bike starting issues than the amount of ethanol. Now I’ll let you go back to taking off that tank, cleaning it thoroughly and reinstalling it. But remember, if you will not use your bike for any significant amount of time, you’re better off topping the tank than draining it (unless you can dry it inside, and fill it with nitrogen, and seal it tight).

    • Jon Jones

      A very good post.