High speed miss on 80 sg

[SIZZSAM]

I just cleaned my carbs on my 80 sg and after discussing the oversized jets on the forum I decided to go back with close to stock jets. The previous owner had installed 4-1 exhaust with pod filters. He had 140 main jets and 45 pilot jets. I put in 115 main and 42.5 pilot. I finally got the carbs synced and it idles fine but when I get on it hard it seems that it isn't getting enough gas. Does that mean that it is running lean, too much air from the pods and too small jets? It wouldn't be much trouble to put the older ones back. I just thought I would get the input from some of you that may have experience with that problem. As always I appreciate the help.

[John]

140 is WAY too big for your carbs. With your setup, I would go with either 117.5 or 120 main jets, and keep the stock pilot jets, and set the pilot screws to about 1 1/4 -1 1/2 turns from a light bottoming out.

[SIZZSAM]

Thanks John, I checked your pictures and it looks like you have a couple of 80 sg's. The one I saw had the stock air box. I bought this one with the 4-1 exhaust and pod filters. It has the type of carbs that requires carbs 1-4 to have 110 main jets. After asking for advice on the forum I went with 115 main and 42.5 pilots. The 42.5 are stock. I was wondering if I'm getting too much air and not enough gas since it takes a while for it to get going. I was running about 80 and opened the throttle and it hesitates some before it kicks in. I have a 79 sf and a 78 e that take all you want to give it and quick, no hesitation. I don't know the jet size on the 79 f but it has the stock air box. I may do trial and error till I get it right. I have the idle screws out 2 turns when I synched the carbs. I have a set of vacuum gauges that work pretty good. Thanks for the help.

[Crazcnuk]

I am playing with my 80G, right now. It also had the 110's all across.

I have stock head pipes with S&S slip-ons, and a K&N airfilter.

My bike has no power, to speak of, above 4500rpm. In 5th gear, at highway speeds, if I roll it on full, it accelerates like a school bus.

In a 4000rpm roll on, in 5th, the bike would top out at 5000rpm. Iwould have to shift down to 4th to get it to rev past 5000, and in 4th it would have a tough time getting past 7000.

I jumped my jets up to 115s. Now it pulls reasonably (but not spectacular) to 7000ish, then lays down.

Mid range is great, low range bogs a bit, at this point. The bike will accelerat to redline in 1-3rd with no problem.

I am still using the original pilot jet, but I have some 45's, just in case.

I have ordered a set of 120's, as MikesXS doesn't have 117's. I should have them in a few days and can let you know how they work.

[boyat68]

Crazcnuk:

My 80G came with #115s in no. 1&4 and #120s in 2&3 as per the manual. I replaced them with new jets of the same size and it seems to be running well. The carbs had rubber plugs in the pilot towers with cross drilled hole from the pilot to the main. I tried running the bike without the rubber plugs but could not dial in the pilots as the bike would rev up uncontrollably. I put the plugs back in the pilot towers and the bike synchronized beautifulyand the idle could be set without a problem.

I reasoned that the plugs forced the pilots to use the metered fuel through the main until the bike got up to 3 or 4 thousand where the lift of the vacuum piston allowed more fuel through the emulsion tube. This arrangement only allows the amount of fuel passed by the main jet. If the plug is left off, then more fuel is allowed in the combination of the main jet and the pilot jet, which drowns the engine at the higher RPMs. I think that the cross drilled arrangement was an attempt to more precisely control the fuel flow and raise the economy of the bike as well as conform to the EPA rules of tail pipe emmissions. I get 38-40 MPG with this arrangement.

[Crazcnuk]

I have the 80 Special carbs, for whatever reason, and they don't use the rubber plugs as they aren't cross drilled.

As per the manual my carbs are supposed to have the 110's across the board.

I did the calculations, from the juetting guide, and determined that I should go up 2 jet sizes, which I did, and it helped but still is not where it should be.

I guess the S&S mufflers are even more free flowing than most 4 into 2 systems. I do know they are straight through, and louder than I like.

I suspect that 117's are what I really need, but I could only get 120's from Mikes. If they are slightly too rich I will drill the airbox to compensate.

If I was REALLY switched on, I would just finish the 1200cc one I am rebuilding in my shed!

[SIZZSAM]

Hi Crazcnuk,
When you say 80 g I guess you have a standard so you have the special carbs. I have the same special carbs on my 80 sg that haven't been drilled between the pilots and mains and don't have the rubber plugs. I did have to drill out the idle mixture screws that had brass plugs in them to clean. To me your problem sounds like it could be your exhaust. If you don't have enough back pressure it will run like a dog. Sorry to say that but I like dogs. It's just an expression. I have a problem right now with my 79 sf where it isn't running well and I noticed a crack in the muffler. I have a wirefeed welder so I'm headed down to the basement to repair it. My brother has an 1100 e and it was hesitating in 2nd gear and it was an exhaust leak where the headers meet the exhaust pipe on a 4-1. Could be.

[boyat68]

SIZZSAM:

Let us know how well that welder works on that muffler as many of us may have to resort to that in the coming years.

[SIZZSAM]

Hi Norm,
I thought I could weld that exhaust but it was too thin and I had to patch it. The PO had already done it once but I hadn't noticed. He used aluminum and some pop rivets. I used some aluminum flashing material and banding clamps like big radiator clamps. I made it real tight and then I had some aluminum tape that I put over the repair job. It comes in a big roll like duct tape. I think the heating and air condition industry uses it. I rode for about 70 miles this afternoon and it didn't miss a lick. That was on my 79 sf. The exhaust was a Kerker 4-1 pipe. I have the same problem on my 80 sg. It is leaking where the headers meet the exhaust pipe. The end of the headers got mashed a little and are not round. I can tell it leaks right there. It makes it run a little rough. I'll work on that tomorrow.

[Crazcnuk]

I do suspect the exhaust system.

For one, it is straight through and likely has very little backpressure. However, I should be able to tune around that. I would lose some bottom end, but pick it up in the top.

I do have a leak, where the left side muffler joins the headpipes. I have been trying to seal it up, but so far nothing has held. I am sure that is not helping.

My system also has no x-over.

Derwat had both his mufflers crack (79SF) and it ran like crap until he welded them back together.

He recently went to Vancouver and said it ran great, at sea level. This would indicate, to me, that he is running rich? Ever hear of anyone jetting a stock XS down?

[SIZZSAM]

Hi Norm,
I don't know much about tuning around the exhaust. I think the standard xs has a crossover. If you could get some standard exhaust it probably would solve your problem. I still have a leak on my 80 sg where the 4-1 headers mate. I just bought some Permatex Exhaust repair muffler tail pipe sealer at Advanced Auto. It is high temperature sealer so it might work. My header pipes are not round as they were mashed a little so I'm going to take them off and try to make them more round and then use this sealer. I'll let you know how it works out. I had an 82 honda 650 nighthawk with four into four exhaust. My cat had sprayed up on the bottom and one pipe rusted out. I couldn't see the hole and it ran sooo bad. When I finally found the problem I was able to weld a piece of sheet metal over it and it ran like new. It looked like Frankenstein but ran great.