Stall under acceleration

[simplewell]

Hoping that someone with more experience can help me out of this jam. I picked up a 1980 XS1100G that run, but had a hard time getting fuel (so I thought). I got it home and did the usual, new plugs, cleaned/replaced filters, oil and cleaned carbs (adjusted float levels also). The issue I'm having has not changed
1)Start her up...fine
2)warm um...fine
3)choke in...fine
4)turn throttle...dies

It doesn't matter whether I really lean on it, am in gear or neutral, or ease on the throttle, the engine immediately stumbles and dies.

Since then I've checked for vaccuum leaks and gone through the above items again, but to no avail.

A mechanic friend of mine told me it had to be my pilot jets, that there is a small tube inside the pilot jets that I can remove with an M1 screw and make sure they are flushed out. I've found no such tube. The Clymer's manual says that the float adjustment should be measured from gasket height, not flange height, but for the illustration of the 1980 Mikuni's it shows from flange, maybe I picked the wrong point to measure from? (Carbs are currently on my bench and I'm re-adjusting the floats)

I also noticed that I'm missing a piece from the carb diagram, the pilot jet plug, I'm not sure if this is a functional piece, but I'm missing all 4.

Any suggestions, relevant input, friendly advice or help would be greatly appreciated. As an amatuer mechanic I feel like I'm spinning my wheels with this issue which is probably a very simple fix that I'm missing.

[tw1980]

My guess is your not getting enough fuel to carbs.You might have an octopus problem or have the hoses switched.Make sure the tank is at leased half full and turn petcocks to prime.Also you might want to check the filters inside the tank.If one of the carb diaphragms has a hole you need to repair that.As for the pilot jet plug,someone probably removed it.That was installed to keep people from tampering with fuel mixture and keep the EPA off Yamahas back I think.Good luck Terry

[DGXSER]

It doesn't matter whether I really lean on it, am in gear or neutral, or ease on the throttle, the engine immediately stumbles and dies.

Have you tried this with the choke pulled half out? Sounds like your running very lean. When you open the throttle on these bikes your adding air and then the velocity of the air pulls the fuel in.

A mechanic friend of mine told me it had to be my pilot jets, that there is a small tube inside the pilot jets that I can remove with an M1 screw and make sure they are flushed out. I've found no such tube.

Well the pilot jet is one item and the mixture "jet" screw is another. On the 80-81 model the mixture screw is in a tunnel on the engine side of the carbs. This may also be an issue of bad aftermarket pilot jets. Were they recently changed out? The pilot jet is down in the small tube you see in this picture.



The mixture screw is shown here. The factory put a small metal plug over the mixture screws which sometimes is still there after all these years. This picture shows it removed.

The Clymer's manual says that the float adjustment should be measured from gasket height, not flange height, but for the illustration of the 1980 Mikuni's it shows from flange, maybe I picked the wrong point to measure from? (Carbs are currently on my bench and I'm re-adjusting the floats)

Float height is measured from the gasket flange WITHOUT the gasket in place. Float to low = higher float height measurement, could cause your lean problem.

I also noticed that I'm missing a piece from the carb diagram, the pilot jet plug, I'm not sure if this is a functional piece, but I'm missing all 4.

If you mean the plug over the pilot jet as shown above and not the mixture screw, that diagram is for the earlier model carbs. The later (80-81) do not use that plug. If your mixture screw is in the tower/tunnel as shown above, you do not use the plug.

There is much talk about the "triple clean" here on Channel 11. The reason being, most people will try to get away with a less than thorough cleaning, and go back in again, then do half what is still needed, and go back in again. Since you have them on the bench, take some time and break them down completely, pull the floats off, remove the main and pilot jets, remove the top of the carb and pull out the slide and needle valve, push out the emulsion tube, and then look at the inlet bell and remove the pilot air jet in the lower left corner. When you get to removing the mixture screw, first, turn it in slowly counting the turns until it seats lightly, no torque needed, you'll feel it seat and stop. Then take it out recording the number of turns in for each individual carb. Often times folks work one carb at a time so you have three others as reference for how things go back in. Then, soak all the metal parts in carb cleaner, I took the cap from my spray carb cleaner and sprayed a puddle into there, put the parts in, and put a cover on it and let them soak. Mena time spray every opening and passage you see with the carb cleaner, especially that pilot jet circuit. Also, try to post a picture of your pilot jet. It will help us see if you got bad ones.

Hope all of this is some help.

[tarzan]

Like DGXSER said,
The floats are measuerd from the flange not the gasket.So your floats are low in the bowl.However that should not affect off idle much.
So yea,your going into the carbs again.Dont feel bad that seems to be the most common path for most guys picking up a neglected XS or XJ.We go through the carbs with enthusiasm and expextations of hearing her purr and getting to ride it for the first time.Then put it together thinking it is squeaky clean in the carbs only to be let down.So we mumble a few favorite colorful words then settle down and thoroughly do the job one more time.Sure that this time it is done right.And the funny thing is ,time after time,there ends up being a third tour of the carbs.And sometimes there ends up being a thread for days or weeks with everyone trying to help a guy get it running right.
But I digress.....
Welcome to the forum,
Check out the search function, there is literally days worth of reading here for useful info and you will prevail.
The pilot circuits are probably your problem.But one thing you could check before you start.Let the bike idle a little bit ,then spray a little water on each exhaust pie to see if one is cold.You may be able to narrow it down fairly quickly.
Sorry about the long post,I'm bored right now.LOL
Rick

[Bigfoot]

When you cleaned the carbs, did you get the emulsion tubes out and clean them? That may be the tube that your friend is referring to. It has small holes in it that need to be cleaned out. Someone correct me if I am wrong but if the bike idles fine, then the problem most likely is not the idle mixture screws.

[bikerphil]

Not sure if it's been mentioned, but it not necessary to seperate the carbs from each other to give them a proper cleaning. When removing the pilot jets, soak 'em with PB blaster first, then either obtain or make a good screwdriver that will fit exactly. They are soft brass and can strip very easily.

[TopCatGr58]

Hey there, well simple sometimes it's not!

Just to add fuel to the fire so to speak, in 80 Yamaha was in a transition with their carbs, and some folks have come across the bastardized type, where the carb body still has the small tunnel between the Main Jet tower and the Pilot jet tower, and the pilot jet shares/gets its fuel supply from the MAIN JET and tube, not directly from the float bowl, and so they require a screw or rubber cap over the pilot jet tower, and the MAIN JETs are of a much larger size ie. 137.5 vs. what's listed in the manual of 110 to 120.

If it doesn't have the sharing tunnel, then the Pilot jet gets its fuel directly from the float bowl, and it's tower is NOT capped, and the Main jet is then the smaller 110-120 size since it doesn't have to share with the pilot jet.

And has been mentioned, the pilot SCREW on the front top engine side of the carb body needs to have the brass cap removed to access the screw for both removal, cleaning the circuit...there are small rubber and metal washers and spring down inside that recessed tunnel.

The Main Jet's emulsion tube can be removed once you remove the top diaphragm vac slide, and the Main Jet and washer, the emulsion tube slides UP thru the carb body out the top. There's a small notch on the Main Jet end, be careful when pushing it out, easily damaged!
T.C.

DO NOT SOAK THE ENTIRE CARB BODIES IN CARB CLEANER or you can suffer damage to butterfly shaft seals, big vacuum leaks!!

[DGXSER]

Still learning I suppose. I thought that the 80's models that had the crossover from the mains to pilots, also had the older style mixture screws. Basically, I thought they threw some of the older model carbs on the first run or so of the 80 model bikes. Then changed over to the new style. I am mistaken? Again?

[bikerphil]

The early 80 odd carbs are the series III bodies with rubber plugs in the pilot jet towers to block off the cross drilled fuel port. They have the late type mixture screws with the towers, but large size mains that were used in the series II carbs, IIRC

[DGXSER]

And again, I learn something new. Thanks Phil!!

[red bandit]

I've never seen anything bigger than 120 mains in any of the 80's carbs, including the one's w/ the cross over hole. But that's just me I guess!

[simplewell]

No luck so far

First let me say wow...the amount of responses this post received and the time in which those were received stuns me...thank you all.

Same problem, starts fine, idles fine, I even got to give it gas a few times, but then it went back to stumbling and dying. It sounds like backfiring when it stumbles.

When cleaning the carbs both times I removed and soaked the main jet, pilot jet, starter jet, main screw (emulsion tube), adjusted float height (23mm +/- .5mm), checked for holes in diaphragms (using compressed air, found none), checked needle jet adjustment (only one location, c-clip cannot be moved) and air cleaned fuel filters.

There is a test for the octopus in the Clymer's manual that my octopus seems to fail, or it means my petcocks are failing. My petcocks have (4) positions, on, off, prime, res. The Clymers says that if I set the petcocks to res or on (vaccuum activated right?), remove the two gasoline tubes (front of each petcock) and I still have gasoline flowing that the octopus needs to be replaced, this happens with mine, but when I was draining the tank I noticed that the fuel flows with the petcocks in all positions except off. This says to me that there doesn't need to be vaccuum to flow and that there is something wrong with my petcocks, what does it say to you? Maybe the petcocks need to be replaced because they are flooding the carbs instead of running lean (haven't gotten any gas from an overflow tube or vent)?

I'm not really sure what to think at this point.

[TopCatGr58]

Okay Simple,

The Special Petcocks are GRAVITY feed style, and fuel will flow directly from them in ON/RESERVE out of the rear spigots, and PRIME from the front spigot. The OCTY "is" the vacuum control valve, it should NOT flow fuel with the engine turned off(no engine vacuum) with petcocks in the On/Reserve position. IF it's flowing, then the vacuum valve isn't moving/closing off the petcock fuel flow.

However, IF the carb float needle valves are working properly, the constant fuel flow will NOT flood the carbs, the fuel will be stopped/controlled by the normal action of the float and needle valve. The octy is a safety device to protect the engine from a Float Needle Valve failure that could then flood the carb, and flow into the intake, into the cylinder, down past the rings and into the oil, severely thinning the oil and leading the bearing lubrication failure and engine death! Many Special owners have removed the Octy, and just remember to turn off the petcocks when they park!

Sounds like you've cleaned the carbs well, have the later model style, but you didn't state whether you could verify the presence of the shared Main/Pilot jet sharing tunnel? ALso what size are you jets.

Also, not sure how you checked the vacuum slide diaphragms for holes with compressed air?? You either hold them up to a bright light and slightly stretch them looking for pinholes, as well as having them in the carbs, pushing them up compressing the slide spring, holding your thumb over the arced port on the top of the inlet bell, and releasing the slide, if it dropped quickly=holes, if it dropped very slowly or almost not at all=no holes!

Okay, once you get it started, idling and warmed up a bit, advancing the throttle and it dies with backfires thru the carbs...this is usually a sign of lean! Try pulling the choke/enrichener out to 1 click and see if you can advance the throttle any??
T.C.

[red bandit]

I type to slow.

[simplewell]

From what I gather

Again, thank you all, here's what I can answer thus far (to the best of my knowledge) and another question for you all...

From what I can tell I do not have a tunnel, so the pilot and main do not share, both get their pick up directly from the float bowl (answering my previous question of "Why don't I have a pilot plug?") and I believe the main is a 120

The pilot jets are marked as #42.5 (to my knowledge that is the correct size)

Attempted 1-click on choke/enricher, same problem persists.

When playing with the diaphragms previously they did drop to position very slowly while re-assembling the carbs. I'd like to try the octy bypass before I open the carbs up for the fourth time (I've learned to try only one thing at a time so your clear on which "solution" worked), which leads me to my question...

Is the "diagram" below accurate for the octy bypass?