'81 gs1100ex runs LEAN, need pointers

[RipRoaringFun]

This is my 1981 GS1100ex. It runs very lean. It has a very baffled (quiet) SuperTrapp 4-into-1 and the stock air filter element is not enclosed in the stock plastic airbox surround -- the airbox surround was gone when I got the bike.

Here's what I did:
0) valve adjustment: CHECK! Starts up very easy now, more power. Still super lean though.

NEXT: checking the carbs as a possible reason for leanness and high idle:
1) main jets were already WAY bigger than stock, float levels are perfectly in spec at 22.4mm +/- 1mm.

2) the rubber intake manifolds between the carbs and head were shot, they had mega-cracks like crazy, I bought new ones, will install when I reinstall the carbs.

3) has electronic ignition, timing/spark is fine.

SO...... since the carbs are still off the bike (I was checking float height and jetting etc.) I'm inspecting them for any blatant source of unwanted air getting in -- and I found two large nipples, one is between carbs #1 and #2. The other nipple is between carbs #3 and #4. See the pictures. Could these nipples, since I found them like in the photos -- wide open -- be allowing unwanted air into the carbs?


Here are photos I took of these two nipples that I found pointing upward between carbs 1&2 and 3&4. By the way -- the hose with the bolt in the end with a tiewrap is the vacuum line to the petcock -- the prior owner put a non-stock petcock on that is not vacuum actuated:

NIPPLE BETWEEN CARBS 1 AND 2 (ignore the TV dude there)



CARBS 3 and 4 NIPPLE:



ALL 4 CARBS

[7981GS]

Those are vents.
Run some hoses from them up and out where the battery vent tube goes.
You probably had very large jets because of the manifold leaks.

Daniel

[RipRoaringFun]

Those are vents.
Run some hoses from them up and out where the battery vent tube goes.
You probably had very large jets because of the manifold leaks.

Daniel

Okay, thanks, will do. Based on that I take it to mean the nipples are supposed to be open and routed back via hoses, and that they are not causing an air leak.

I sure the heck hope the new manifolds cure this mega lean problem. I cannot find anything else to explain the erratic, sometimes very-high-idle condition and the super lean plugs.

If the prior owner missed the manifolds I don't blame him a bit. From the outside the damn things looked absolutely perfect.

In the hunt for this problem though, I took the manifolds off and found grand-canyon-sized crevices on the insides of all four manifolds. I didn't actually find any 'all-the-way-through' cracks, but man there were so many, I imagine under engine heat and suction from the motor the manifolds flexed and maybe the crevices introduced unwanted air by way of a 'membrane' leak from the very bottoms of the biggest cracks.

Will find out soon enough.

[7981GS]

Don't forget to get the new O-rings for the manifolds from www.cycleorings.com

Daniel

[RipRoaringFun]

Don't forget to get the new O-rings for the manifolds from www.cycleorings.com

Daniel

Wow thanks, I can't thank you enough for this reminder, as I completely spaced on checking them. If the intake manifolds were in such bad shape I'm sure I'm gonna find the o-rings need replacing too.

Very much thanks here and for that link, my memory is not that great at 51, I had thought to check these several times during my hunt for the intake leak, and I'm pretty dismayed I forgot about it. I was ready to reinstall the carbs tomorrow, the memory is a-goin' out on me.

Thanks. The pictures and explanation in the link are excellent.

[almarconi]

Don't forget to get the new O-rings for the manifolds from www.cycleorings.com

I believe his bike is 16 valve (80-81 1100E) so there are no manifold o-rings.

stock air filter element is not enclosed in the stock plastic airbox surround -- the airbox surround was gone when I got the bike.

Thats not good..you probably should get an air box don't cha think?

[RipRoaringFun]

You're right -- my bike is a 1981 gs1100ex. After reading your reply I checked the partslist and there are no intake o-rings. So this is one time (ONE time) my crummy memory was not a liability.

Also, see the picture of my airbox situation -- do you think this will still cause troubles/a lean condition? After all, the main jets are huge. Here's what I mean.

When I was troubleshooting the lean condition and pulled the carbs, I found that the main jets had "107.5" stamped them, which is the stock main jet, so I thought "oh, here's why the bike is lean: the prior owner (1) removed the stock airbox surround; (2) and put on a 4-into-1 less-restrictive exhaust; and then didn't rejet for those changes.

So was advised to go up to 117.5 by a board member here. Well I went to the parts counter and the 117.5 main jet hole was MUCH smaller diameter than my 107.5 mains. In fact the 127.5 mains also had a MUCH smaller diameter than my "107.5" mains and it dawned on me the prior owner drilled out the mains. The 150 or so main jets at the parts counter that day had about the same diameter hole as my 107.5 mains. The p.o. *really* drilled them out.

Have a look at the airfilter below, would be interested in advice on it.

[Dave8338]

That filter will work and should be pre oiled (not soaked) prior to fitting.

The air tubes alone, when cracked, will be enough to cause the lean condition and high idle SO...when you get them installed, with a little adjusting, you may be good to go. New clamps are also a good thing as the old one tend to get a little out of shape from several PO botch jobs. Just a thought.

[tom203]

That filter will work and should be pre oiled (not soaked) prior to fitting.

The air tubes alone, when cracked, will be enough to cause the lean condition and high idle SO...when you get them installed, with a little adjusting, you may be good to go. New clamps are also a good thing as the old one tend to get a little out of shape from several PO botch jobs. Just a thought.

Yeah, get those new boots on and you'll be on your way!

[RipRoaringFun]

Yeah, get those new boots on and you'll be on your way!

You know, the interesting thing about this is that the prior owner chose to drill 107.5 stock main jets out to about 150-155 size and never bothered removing the intake rubberboots. It took me all of 5 minutes to get them off and find the cracks and huge crevices. He went to some trouble chasing down the lean condition by the amount of drilling on the 107.5 mains that he did.

It got me wondering how many times did he pull the carbs and the main jets and open them up a bit more, and how frustrated did he feel when, after all that drilling, the bike still had the 'air leak idling' problem and super white burned plugs. He must have been beside himself. I can't wait to install the new boots, I'd wanted to get to it today but work was an all day thing.

As soon as I get them on I will post the result. I decided to leave in the 150+ sized drilled mains in the carbs and I'm hoping I'll find that the bike is now running too rich when I'm on the mains. Then I have my 115 mains I bought ready to install -- the 115s are three sizes larger than the stock 107.5 mains.

[chef1366]

Put in 47.5 pilot jets
122.5 main jets
shim the needle with two washers
Adjust the idle mixture screw out with the highest idle method one at a time