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Engine surges up and down

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Guest

Guest
Hey guys I have a problem that I've been searching through the threads for something similar, but with no results. I have an '81 gs1000g, that has stock exhaust and pods. I got the engine running, and it idles fine, but it would start to bogg down when I tried to go over 3000 rpm. I took off the carbs and cleaned them per instructions on this site. Bench synced throttle plates useing a straight pin ( I couldn't find a small paper clip) and set the air screws at 1 1/2 turns out. Set the floats at 22.4mm per spects and instr. found on this site. My engine will go past 3000rpm now, up to around 7000rpm, but it won't hold it. It drops back down to around 1000rpm, then back up to 5500 and back down. This is with full throttle applied. After doing this for about a minute, every other surge will go from 5500 to around 6800, then back down to 1000. I've messed with the air screw adjustment with minimal difference. I've adjusted them out to about 4 full turns. If I pull the choke, all the way out or full on, it will rev up to 5100 and hold. When I say bogg I mean bogg, it is a loud hollow sound. Please help.
 
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Did you re-jet while you had the carbs out? Pods will make it very lean if not. Could be part of the trouble. Also did you replace the O-rings where the intake manifolds meet the head?

Sounds like air leaks to me. Yo-yo idle is a clear symptom of air leaks. Same for the bogging... Check all of your Carb boots and clamps. Everything needs to be sealed up.

Those o-rings at the head are often the culprit. The screws well give you hell, but they need to be replaced anyway. To check, get her running and spray some Carb cleaner around the manifolds. If she revs, you have a leak.
 
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Once you fix the air leaks, get a real vac sync done. Its like night and day for how your bike runs.
 
The pods, were on the bike when I bought it, so I don't know if it has been rejetted or not. Is there a way to tell what jets I have? I replaced two of the o-rings on intakes 1&2. They were flattend, I would have replaced 3&4, but the guy at Ace gave me two of them that were to small. Before you scold me for going to Ace, that is where a local bike shop (Cycle One) directed me to. 3&4 looked rounded and ok, not flattend like 1&2. I'll try the WD40 idea and see what happens. The intake screws came out OK with a manual impact driver, so I reused them. I did replace the vent tube o-rings and fuel tube o-rings, from a box of o-rings that a mechanic friend gave me a few years back. They were green and not black, like the old ones, but I didn't see any other difference. One other thing I'm not sure is right is the vent tubes themselves, they are onty about 5 inches in length., unlike the ones on my 78gs1000, they go all the way back past the trans. While I'm on the subject of vent tubes, I saw the thread on the vortex problem, and have noticed a similar problem on my '78 1000. Would removing them help the seamingly loss of power when I'm hit by gusts of wind, or am I just imagining it?
 
keman said:
Did you re-jet while you had the carbs out? Pods will make it very lean if not. Could be part of the trouble. Also did you replace the O-rings where the intake manifolds meet the head?

Sounds like air leaks to me. Yo-yo idle is a clear symptom of air leaks. Same for the bogging... Check all of your Carb boots and clamps. Everything needs to be sealed up.

Those o-rings at the head are often the culprit. The screws well give you hell, but they need to be replaced anyway. To check, get her running and spray some Carb cleaner around the manifolds. If she revs, you have a leak.
Click to expand...

If you have no luck finding an air leak and it has been re-jetted (properly) as Keman suggested I would start to look at your petcock. You may be starving for fuel.

-Dave
 
Still sound like an air leak.

To check the jets, you need to pull the carbs, open them up and look at the jets. They will be marked.

The vent tubes can be a problem if you have slides that have been drilled to enlarge the air lift hole, but otherwise I have not heard about them being an issue with stock carbs.

You can get a full set of the correct o-rings from cycleorings.com cheap. He also has the correct manifold o-rings.

At this point, I would be inclined to order the correct o-rings, pull the carbs, do a complete soak and clean again to make sure I did not miss anything. Then I would put it all back together double checking float levels and see how it runs.

The ace o-rings may look right, but still not work right. Cycleorings.com has the right ones, cheap.
 
Most definitely an air leak. Especially if ya removed the intakes and re-installed em with the old orings.
Ya need to re-do it. When ya have the carbs off pull a bowl to check main jet. If it's not been rejeted you'll need to do so if you're gonna run pods.
Go to www.cycleorings.com to order a brand spanking new set of orings. The kind that are made for your bike. Ya might as well go ahead and order the carb orings as well cause you most likely will need to do a proper cleaning to the carbs.
 
Hi,

What you are calling an 'air screw' is actually an "idle mixture screw" and should be adjusted according to the "highest idle method". Normally they are around 2.5 turns out.

The jets have numbers on them. Remove them, look at them. If you have not removed them and replaced all of the internal O-rings, you have not done a proper carb cleaning. If you have pod filters, larger jetting is needed. Most recommended is a Dynojet kit (probably stage 3).

All of the intake boot O-rings should be replaced. Perhaps the intake boots themselves should be replaced too.

Much more information can be found on my little website.


Thank you for your indulgence,

BassCliff
 
Well WD40 didn't work, still same problem. Question, I read in another thread the other day, where someone made paper gaskets and it worked even though it was only temporary, untill there o-rings came in. I have gasket material, thin paper, green paper thicker, and cork. If I used one of these shouldn't that at least eliminate the intake o-ring possibility? Which jet do I need to check, to see if its been rejetted, and what number should it be? Last question, I used Gunk brand carb. cleaner, the kind that comes in a gallon can with the dipping basket. Is this OK, because thats the only kind I've seen at the local parts store. I soaked each carb for about 6 hours, rinsed out with water, used air compressure to blow out passages, then used spray carb cleaner in same passages and blew out again with compressed air. I also made the matchstick wire brush tool and cleared all of the tiny wholes, like in the instructional. Am I missing anything?

Thanks.
 
Sorry, Basscliff I didn't see your post before I reposted. I'm a slow typer.
 
Rick

Just do it correctly - if you ordered from cycle O rings, you'll have your stuff before the weekend

So, what jets did you find in your carbs?
 
Hi,

gsrick said:
Sorry, Basscliff I didn't see your post before I reposted. I'm a slow typer.
Click to expand...

Not to worry. It sounds like you are pretty well up on the carb cleaning. Sometimes it can take 24 hours to soak a carb body. Have you seen these?

Mikuni BS(CV) Carburetor Rebuild Tutorial
(Mr. Nessism)

CV Carburetor Rebuild Guide
(Courtesy of GSR and John Bloemer)
(Click here to see the CV Carb Notes)

Also have a look at the maintenance lists in your "mega-welcome".

A lot of the maintenance tasks are documented on my website and on Mr. bwringer's website.

There can be several issues going on at the same time. That's why you must address each system individually, one at a time. Clean carbs, air intake system with no leaks, properly functioning petcock, properly venting gas cap, etc. Once you have eliminated any fuel or air issue and you are still having a problem (unlikely) then we'll move on to ignition, etc.

Thank you for your indulgence,

BassCliff
 
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I'll order some as soon as I get paid again, poor boy at work here. I clicked the link from octain, for cycleorings, but I couldn't get the web site. I'm going to pull the carbs before the night is over, but I'm not sure which jet I'm looking for. This is not my main bike, its a project, my '78 gs1000 is working ok, but it pops and spits a little. I have a church member, that is going to give me his old sync tool, his bike is fuel injected and he doesn't need it anymore. Its the mercury type not vacume, but I've been told they'll get the job done. Any tips would be appreciated.
 
I followed the CV Carburetor Rebuild Guide and looked over the Mikuni BS(CV) Carburetor Rebuild Tutorial and the only thing I didn't do was lube the o-rings.(origional ones). The carbs looked pretty good before dipping and the passages flowed the cleaner from the spray can right in to my eyes pretty fast. Learned a leason on that pretty quick. The intakes looked like they are in good shape, but I'm new to working on bike engines. Can I try the gasket idea, just to eliminate the intake O-ring possibility? The intakes look better than the ones on my '78, they look like a previous owner used some silicone to seal it. I'll pull the carbs to check th jets, which one am I checking, the main jet? And how do I know if it is still stock? I'll check back in a little bit, to see what yall think. And thanks again for the help. Yall and this web site are a God send. Its easier to win the lottery than get ahold of my soon to be ex-mechanic. But thats another story for another time and thread. Oh yea, I origionally drained my tank using the prime setting on the petcock and it flowed pretty good. I also switched it during my test while it was surgeing, but had no effect. Be back later.
 
The photos in the Carb tutorial show what jet is what. Main jet is right in the center once you remove the bowl . If you followed the tutorial, you have already taken it out once.
 
When you are looking for air leaks yo might want to pull the cover off one of the end carbs and check the butterfly shaft seal. That is if you have pulled the carb rack apart since yo can't get it out otherwise. They should be supple and not split, there is also assembly grease on the shaft that you should not clean off. It helps the seal seal. I had this problem on a xj maxim and once I replaced those seals it idled nice.
 
Keman is the main jet, the jet that you change, if you ad pods? And is there a number that I need to look for? I'll pull the carbs off in a few to see what I'm working with. Any thoughts about the gasket idea, on the intakes, if its a go, which material would you suggest I try? I'm trying to cure this problem as quickley and as cheaply as possible. If this is the problem, I will replace the o-rings, but I wont be able to get them for at least a couple of days. I have someone coming over tomorrow night, as a possible buyer, to look at it. I need to sell one of my bikes, so I can get a pick-up, and this the closest bike, I have to being completed. I wont sell my '78, shes my first love. Check back in a little, I think its going to be a long night.
 
You can make gaskets but they won't seal for long. Long enough to sell the bike, but then you will be one of those "previous owners (PO)" we love to cuss.

As for the running problem, my guess is the jets are wrong in addition to the leaking intake pipe boot O-rings. Please check my signature for the "newbie mistake" thread.
 
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