Methinks she's running lean off-idle

[Anonymous]

Hello all,

Having probs w/ my '77 GS750. I managed to get the idle air settings down right, and she idles nicely at about 1000 rpm. Now, when riding around, I get popping out the exhaust and every now and then poofs coming back through the carbs. Sounds like leanness to me. Earlier this winter I pulled the carbs down and cleaned them all out, so they're physically ok. The bike has EMGO pod filters, and a 4-1 exhaust w/ a Yoshi muffler of some sort. When I bought it it had the exhaust on it, and no filters. I assume the previous owner was running pods. I pulled the carbs back off, and found out the mains are marked 117.5 (they also have an R and a square with a line half through...I don't know if that means anything). The aluminum needles have the little e-clip set in the middle position. As far as I know the air screw on the side of the carbs should only affect idle. I have not yet adjusted the fuel screw on the underside of the carbs. The Clymer's says hands off, so they don't give a reference point for how many turns out to start with, and if those mains are stock, then from what I have gathered on the board just adjusting those screws won't be enough. Alas, I don't know what the stock sizes would be on a '77 GS750. If 117.5's flow more fuel than stock then I would reason that adjusting those screws might do the trick. But I don't know. Need more info. So if anyone has a reference that tells the stock jet sizes, that would be cool, and any and all advice on improving the situation would be greatly appreciated. Thanks,

Ryan
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mueller@xta.com

[Anonymous]

Clymer says hands off the fuel meter screws only because tampering with them is an EPA no no, and Clymer is published in the USA. If your model was available in Britain, Haynes often has UK published manuals that give the screw settings. I obtained one off e-bay for my 850. On the other hand, you could just back them out a half turn, and if you don't like the result, it's easy enough to return them to the original settings. It does sound like it's lean in the slow-idle circuit. And those screws can make a big difference.

[earlfor]

Re: Methinks she's running lean off-idle

For a 77 to 79 8 valve 750 with the 26 mm VS carbs, the baseline setting for the idle air screw is 1 3/4 to 2 turns out. For the fuel pilot screw (which is underneath the carbs and protruding at the front edge), the basic setting is 1 12 to 1 3/4 turns out. You definitely are running lean. However, as you say "she idles nicely" That is because your lean problem has nothing to do with the idle air and pilot fuel screws and your idle setting. Those two screws in combination do contribute to the overall mixture throughout the rpm range, however, as rpm increases, the percentage of the overall mixture they contribute becomes less and less. At mid range to high rpm operation, their effect is minimal on mixture. Adjusting those screws will not cure your problem. Stock main jet size for your bike ia 102.5, so it has been rejetted for the aftermarket 4 into 1 pipe as your main jet size is what is normally recommended for a 4 into 1 V&H. There are three possibilities causing your problem. 1. Have you replaced the induction "O" rings on the intake boots that are between the rubber intake boot and the cylinder head? It is almost a given that they will need replacing with a bike of this age, and most people dont know they are even there. :-)
You dont say what rpm range or speed you are going when you let off the throttle and the problem occurs, I suspect that it would be in midrange somewhere around normal highway speeds. You can try raising the needles to allow more mid range fuel through. If this doesnt help, you can do one of two things. Increase the jet size of the midrange jet, or decrease the intake air. To decrease the intake air, (as a check to see if it will solve the problem) You could wrap the pod filters with masking tape to block off some air and test ride the bike. I suspect that if you do nothing more than block off some of the intake airflow through the pod filters, your problem will be solved.

Earl

Hello all,

Having probs w/ my '77 GS750. I managed to get the idle air settings down right, and she idles nicely at about 1000 rpm. Now, when riding around, I get popping out the exhaust and every now and then poofs coming back through the carbs. Sounds like leanness to me. Earlier this winter I pulled the carbs down and cleaned them all out, so they're physically ok. The bike has EMGO pod filters, and a 4-1 exhaust w/ a Yoshi muffler of some sort. When I bought it it had the exhaust on it, and no filters. I assume the previous owner was running pods. I pulled the carbs back off, and found out the mains are marked 117.5 (they also have an R and a square with a line half through...I don't know if that means anything). The aluminum needles have the little e-clip set in the middle position. As far as I know the air screw on the side of the carbs should only affect idle. I have not yet adjusted the fuel screw on the underside of the carbs. The Clymer's says hands off, so they don't give a reference point for how many turns out to start with, and if those mains are stock, then from what I have gathered on the board just adjusting those screws won't be enough. Alas, I don't know what the stock sizes would be on a '77 GS750. If 117.5's flow more fuel than stock then I would reason that adjusting those screws might do the trick. But I don't know. Need more info. So if anyone has a reference that tells the stock jet sizes, that would be cool, and any and all advice on improving the situation would be greatly appreciated. Thanks,

Ryan
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mueller@xta.com

[Anonymous]

Popping on decelleration is almost always a result of a lean condition in the slow-idle circuit, regardless of the cause. Restricting the air intake will richen it up, but it doesn't solve the problem. Stock fuel screw settings would obviously be too lean with pod filters and no air box.

[Anonymous]

Earlfor and co......first off, thanks for the replies. Good info....

To address a few of the things I should have specified...I'm not really getting up to much speed when I encounter these probs. The bike is not licensed yet, so I'm just primarily running laps around a few blocks in town. Probably looking at no more than 30-40 mph. I'm guessing from my poor memory that it starts around 4000 rpm, *maybe*, and continues from there on up, although I believe it wouldn't even come close to approaching redline. Just ran out of, well, gas, so to speak.

One other item I thought of; the EMGO pod filters that are on the bike are dry. I vaguely recall hearing that when you install the filters they should be dipped in clean motor oil, and allowed to drip drain for a bit, and then be put on. In my mind this would restrict airflow somewhat, although I don't know if it would be enough of a difference between a wet and dry set of filters to cause my problems.

So, I have a set of the o-rings on order from my friendly local Suzuki dealer (yes I knew they were they, and yes, they were pretty funky when I pulled the tubes off a few days back) . The induction tubes themselves have a little cracking....a spot or two on each tube, but it is external in nature from what I can tell; doesn't look like it goes through to the inside at all, so I believe they are still quite useable.

I know I ought to make one change at a time, but I'm almost tempted to raise the needles one notch when I replace the o-rings, as I will have the carbs off, and really don't want to pull them again if just the o-rings don't solve the problem. Ah well, we shall see.

Thanks for the help, it is much appreciated, and I will update with my progress early next week sometime (out of town this weekend).

Ryan

[earlfor]

I would replace only the "O" rings as I feel there is a very good chance that is all that is needed to solve your problem.

Earl

[quote="aeronca7"]
So, I have a set of the o-rings on order from my friendly local Suzuki dealer (yes I knew they were they, and yes, they were pretty funky when I pulled the tubes off a few days back) . The induction tubes themselves have a little cracking....a spot or two on each tube, but it is external in nature from what I can tell; doesn't look like it goes through to the inside at all, so I believe they are still quite useable.

[Anonymous]

update on situation

Hello all,

My o-rings finally came in from the Suzuki Mothership, but, of course, they were not the correct size. Every time I order parts they apparently look it up in the computer, and not in the old microfiche, and it ends up ordering parts for later model GS's. It took 3 tries to get float bowl gaskets, 2 for an oil filter/o-ring, and the induction o-rings that I ordered this time around are a slightly smaller diameter, and not as thick. Argh!

Anyhow, I took the old o-rings, which although funky and crusty, were still pliable and intact, and threw them in some soapy dish water and played w/ them for a while, and they came out looking and feeling almost new, and certainly serviceable, I feel. I wire-wheeled the induction tube faces and scotch-brited the cyl. port faces, and reinstalled everything. Ran into a bit of a problem w/ a sticking float on number 1, as it was pouring fuel out the overflow tube as I was riding, but I popped the bowl off that carb and played w/ the float a bit, and for whatever reason that stopped.

It is definitely running better, as I can get to redline, but it still sounds "off". It will pop through the carbs once at approx 4000 to 4500 rpm the first time, and maybe once more after that, and it still sounds, for lack of a better term, ever so faintly "congested". I think it's really close to being correct, but it's just barely not there.

So, now I'm soliciting suggestions as to what to do next. Should I tweak the fuel screws on the underside of the carb a little bit; would taking my EMGO individual filters and dipping them in a K&N type oil provide enough restriction to bring it to where I need to be? Do I need to try and find an airbox to put back on this thing?

Thanks for the help,

Ryan

[earlfor]

Re: update on situation

I suspect that although the refurbished/soaked "O" rings look good, they probably are not sealing 100%. I would still install the new ones when they come in. The foam airfilter elements are supposed to be soaked in oil and patted damp dry. That will also help, but is not a long term solution as they will eventually dry out. I would go ahead and raise the needles one notch when I replaced the "O" rings. What color are your spark plugs center ceramic?

Note: Adjusting the pilot fuel and air screws will not help your problem as they are idle range adjustments.

Earl

So, now I'm soliciting suggestions as to what to do next. Should I tweak the fuel screws on the underside of the carb a little bit; would taking my EMGO individual filters and dipping them in a K&N type oil provide enough restriction to bring it to where I need to be? Do I need to try and find an airbox to put back on this thing?

Thanks for the help,

Ryan

[Anonymous]

Update

Soo....while I had the carbs on w/ the old "cleaned up" o-rings installed I went ahead and popped the tops and lowered the e-clip on the needles, thereby raising them one notch. This did get it to stop popping for the most part, but made it impossible to get the bike to idle. I had the idle speed screw turned all the way in, and no amount of adjustment to the idle air screws would get her to idle. The best I could get was a stumbling 500 rpm, which doesn't hold for too long before she dies. Choke would kill it. Tells me it's running too rich. So off the tops of the carbs will come, and the needles will go back to the base setting.

I went down to Suzuki today and verified that the part number of the o-rings they ordered for me off their computer matched the numbers from the microfiche. Sam, the owner of the dealership, espoused the theory that after a mere 26 years the o-rings would have swelled, and possibly stretched, and recommended I try the slightly "thinner" and slightly smaller o-rings that were what Suzuki called for, so that is what I shall do. Between installing the new o-rings and treating the EMGO pod filters w/ some K&N filter oil hopefully this will take care of the prob. Either way it should get me close enough to just take it out and ride. Can't expect perfection from a old girl that hasn't been run regularly in a long time, I guess. Thanks for the continued advice,

Ryan

[Don Lobacz]

When you changed the needle settings, did you remove the 8mm bolt that holds the arms to the rod? Anytime you loosen this bolt the synchronization has to be reset. This may have caused your idling problem.

[Anonymous]

The fun never ends, but at least it's getting better...

Don: No, I did not remove those nuts. I removed the bolts that secure the arms to the rod that moves the slides up and down, pulled the slides and pivoting arm assy out completely, and went from there.

I went ahead and tried the o-rings that Suzuki got me, and dipped the pod filters in 5W-30 and let them drain out, and apart from being initially a little rich and smoking while it sucked some oil through (should've drained it a tick longer!), it settled down within moments and runs nicely now. I was able to back the idle set screw off all the way, and she ticks over at about 1100 rpm. A little choke at startup for a bit, and she's quite happy.

Now, all that is left is to license her, sort out some problems w/ the front brakes not holding pressure....have to pump a few times to get full brakes......and she will be on the road again.

THe only complaint is that she stumbles a little at about 5000 rpm on the way through the gears, but if I give it more throttle it will push through and keep on going smoothly to redline. Have to sort that out, but at least it won't keep me from riding. Thanks for all the help,

Ryan