Idling Problem

heckienawjoe · Posted: July 20, 2009, 10:52 am Post subject: Idling Problem

Hey guys, I am a noob so if this is answered somewhere else (I didnt see anything similar when I looked around) please direct me to it.

So I am having this issue with my 81 where it will start but idles really low (a little below 1000) and will die without some throttle (sometimes the throttle will actually just kill it, i dunno why the discrepancy) with no choke, but with half choke it idles at around 3000-4000rpm. I have to ride it with half choke all the time (even after it has warmed up a lot) or else it will stall at stop signs if I dont keep the throttle open a little.

I am also sometimes getting exhaust popping noises, but I don't know if it is related to this problem. Could this be because the fuel mix is too lean? And, if I richen the fuel mixture and need to choke at all, won't the rpms be outrageously high? Thanks for your help!

xsjohn · Posted: July 20, 2009, 10:55 am Post subject: Re: Idling Problem

Would think the Carbs need cleaning.......especially the pilot circuit.....then adjusting the mix screws maybe....xsjohn

pamcopete · Posted: July 20, 2009, 11:07 am Post subject: Re: Idling Problem

hekienawjoe,

Well, forgive me for asking this question, but did you try to just increase the idle speed with the idle screw on the left side carb?

heckienawjoe · Posted: July 20, 2009, 1:05 pm Post subject: Re: Idling Problem

okay, no i havent tried to adjust the idle screw. i will try that when i get home today and see if it makes a difference.

Xumi · Posted: July 20, 2009, 1:08 pm Post subject: Re: Idling Problem

I agree with John - sounds like the carbs need cleaning, and then adjust the mix screws and sync... should fix it right up.

heckienawjoe · Posted: July 20, 2009, 9:19 pm Post subject: Re: Idling Problem

well, i adjusted the idle screw on the left carb to result in higher idle speed, but the problem remains only this time, there are no high rpms on choke. in fact, choking results in killing the engine (when running) or inability to start (when not running). I can get the engine going with really weak idling (around 1000) but when i shift to first it dies (when giving normal amounts of throttle -- will engage and run with excessive throttle but is really jerky and u can tell the engine just wants to die).

just wondering if this new evidence changes the verdict at all. i dont mean to seem like i am ignoring your advice xsjohn and xumi, i am grateful for it and i will attempt to clean and sync the carbs next (armed with Haynes manual and instructions from the other threads). thanks again for dealing with my noobiness

Xumi · Posted: July 21, 2009, 11:32 am Post subject: Re: Idling Problem

Just confirms the need to clean the carbs, especially the pilot circuit (the smallest passageways that handle fuel and air flow at idle up to 1/4 throttle, also called the idle circuit, pilot jets or idle jets in other writeups)

Just make sure of a few things for your first time through carbs...

Take pictures before you disassemble anything, and take more along the way.

Take your time and don't rush.

Get a couple cans of spray carb cleaner and be generous with it. Let dry thoroughly, or blow it out with Mildly compressed air (about 20 psi).

If it is brass (yellow or light brown depending on the condition), it is SOFT - be careful removing, cleaning and inserting, as it can be an ex-part very easily. The jets (little tubes with screwdriver slots in them and holes through the length) are made of Brass.

Be gentle. If it doesn't come out, soak it for a little while in carb cleaner and try again. If it is a Jet that is truly stuck, then make sure your screwdriver is fat and the blade fits the whole width of the slot, so you don't disfigure the brass by torquing it.

If a gasket or o-ring is torn.. replace. I tried to make my own gaskets for carbs once.. many many hours later I wished I'd just purchased a set.

The funny rubber things under the top lids are called Diaphragms. They are VERY sensitive to tear, being a very thin rubber. Very small tears can be repaired, large damage cannot. They don't handle carb cleaner very well either. Be very careful taking them out and inserting them. When installing, make sure the lip fits the groove all the way around.. be patient, and it will usually go in fine.

DO NOT SOAK YOUR CARBS!

Let me repeat that...

DO NOT SOAK YOUR CARBS!

I'm sure that your neighborfriendunclebrotherbosscoworker has repaired at least 50 carburators in his life and swears by supergunkcleaneverything carb dip at your local chucksnapautozonemomnpopshop store, and swears that you should soak your carbs overnight.

Well, as many great carb guys here will tell you.. don't do it. You'll end up needing new carbs instead of just clean carbs. There are exceptions of people soaking their carbs in things like Simple Green and a few other mild cleaners.. which is probably ok, but I've never found it necessary, including cleaning out the bug and mud infested carbs that were on my barn find.

99% of the time, a thorough cleaning of the bowls (the bottom containers of the carbs), the jets (funny looking brass screws with holes in them), the little air holes that go everywhere, and the float assmebly and valve(looks like a Siamese twin version of an old-school toilet bowl float) will fix the problem.

Don't try to disassemble the butterfly assembly the choke assembly or separate the carbs unless things are REALLY nasty... because it makes the job of reassembly harder, and as I said above, 99% of the time isn't necessary.

What happens during that 90% is that the bike sat with fuel in the carbs.. the fuel evaporated, and left behind something very similar to what's left when coke evaporates. It clogs up the fuel passageways and jets, and sometimes even the small air passageways in the bowls. It gums up the float valve, which leads to carbs leaking when the valve can't shut off the fuel flow.. Get this varnish/crap/whatever out of the way of the fuel and air, and you have working carbs.

The other 9% is typically bad gas, old gas, rust or some type of contaminant that has gotten into the bowls and fuel passageways and prevents the smooth delivery of fuel. Same solution - clean thoroughly, but now you at the least need to drain your tank and replace the fuel (and buy a good fuel filter)... and at the worst have rust in your tank to deal with. If you find a brown/red powder at the bottom of your bowls.. you have rust, and if you don't deal with it before trying to ride again, you'll be taking those carbs apart again soon.

Last piece of advice... Read every write up you can get your hands on.. Twice. Ask questions if you don't understand. Take apart your carbs, cleaning everything as you go, and then read those write ups again, because (for me anyway) until I had seen the things apart, I didn't understand the writeups very well. Put things back together... and of course adjust and sync according to manual (or there are great writeups here on the subjects), and enjoy.

heckienawjoe · Posted: July 27, 2009, 10:32 am Post subject: Re: Idling Problem

The bike is back in action and it's running well!

I pulled the plugs - they were pretty black and a little oily - and I tried diagnosing the problem with an article I found on 650central, but with no conclusive results. So I decided it was def the carbs and I cleaned them this weekend - there was a good amount of gunk in there and I'm sure cleaning the pilot circuit helped with the idling problem I was experiencing. I'm thinking that putting in a fuel filter would be a good thing to have to keep the carbs cleaner.

I also did the dead cylinder method to tune the bike. I was hesitant to do it because the throttle valves seemed to be exactly aligned when I looked at them, but the right exhaust was still making a "fuff fuff fuff" sound as opposed to the beefy sound i got from the other side. So I ended up turning the sync screw a turn or so toward the right and then I got equal sound and pressure from both exhausts. Runs and idles great now, I just feel kind of weird knowing that the throttles for each cylinder are not opening equally. Is it okay to run like this? Also redid the soldering of some wires under the seat connected to the ignition.

Havent ridden it for any long period yet, but if it clunks out again I will know it is the engine heat getting to the coil (original) and I'll get a new one. Thanks for your help everyone, and I really appreciate the detailed advice xumi! You guys have made my first carb job much easier than it would have been!

I also found this video, which helped me to visualize some of the stuff I needed to do. Just thought I'd pass along.
www.youtube.com/watch?v=MSn1ca5KEfo

Xumi · Posted: July 27, 2009, 11:49 am Post subject: Re: Idling Problem

Congratulations on your repair! Glad we were able to help.

Retiredgentleman · Posted: July 27, 2009, 2:16 pm Post subject: Re: Idling Problem

heckienawjoe;
Use the "dead cylinder" method to adjust the air/fuel mixture screws (idle mixture screw).

To sych the carbs, you can use some plastic tubing to make a manometer. Its very cheap and very accurate. If you need details, just ask.

heckienawjoe · Posted: July 27, 2009, 3:45 pm Post subject: Re: Idling Problem

RG, could you plz direct me to instructions on how to make and use one of those manometers? I cant find details anywhere.

so as far as the dead cyl method goes, I guess I am pretty confused. this seems to be the way i understand it and the way i did it this weekend (credit to pamcopete with added clarifications):

Bring the idle up to 1700 to 2000 RPM.

1. Start with the left cylinder. That is, disconnect the plug on the right.
2. Start the engine.The idle will go down when operating on just one cylinder.
3. Adjust the working cylinder (left) to 1,000 RPM (using the throttle stop screw/idle screw on the left side of the left carb). Stop the engine
4. Reconnect the right plug.
5. Disconnect the left plug.
6. Start the engine.
7. Adjust the sync screw in between the carbs to set the right cylinder RPM's to 1,000.
8. Reconnect the spark plug. Start the engine.
9. The idle will go up to 1,500 or more because both cylinders are working.
10. Adjust the idle speed to 1,500 using the idle screw on the left (aka the throttle stop screw mentioned in step 3).

now i assume the mix screws on top of each carb "mouth" are set to factory recommendation (for my 34s that is 3 to 3-1/2 turns out) and were set before starting the procedure.

So would someone plz correct me if I am wrong? I get very confused reading everyone's writeups with different names for all the screws. Thanks for your help!

Retiredgentleman · Posted: July 27, 2009, 10:37 pm Post subject: Re: Idling Problem

heckienawjoe;
As you may know, there are quite often severals ways to accomplish the same task. Pamcopete has considerable experience with these XS650s, and you can't go wrong following his advice.

I have been following the carb tuning as layed out by Grizld1 and 5twins over at the 650garage site. Their methods have worked well for me. Here is what they say about adjusting the air/fuel mixture screw ( also called idle mixture screw and pilot screw)

2. Adjustment
Before attempting to adjust fuel screw settings, ensure that you are not compensating
for incorrect settings elsewhere. Inspect and if necessary adjust cam chain tension,
valve lash, and ignition timing, in that order.
Turning the fuel screw clockwise (in) leans the mixture, turning counterclockwise (out)
richens. Adjustment of fuel screws is best performed using the "dead cylinder" method.
Turn the fuel screws in until they bottom lightly (overtightening will damage the screw
and/or seat), and turn them out to one of the following settings.
XS1, XS1B: 1 turn
XS2, TX650, TX650A: 0.75 turns
XS650A, B, C, D: 1.5 turns
XS650E, F: 2.25 turns
BS34, all: 3 turns
Warm the engine to operating temperature, then raise the idle to around 1500 rpm. On
bikes with breaker point ignitions, pull off a sparkplug cap. Electronic ignitions can be
damaged by operation with an ungrounded ignition wire. To prevent that, shut down the
engine, attach a spare sparkplug to a cap, ground the plug solidly on the engine, and
restart. Adjust the throttle stop to hold lowest steady idle, then move the fuel screw 1/4
turn each way, seeking highest idle. When you find the direction of improvement, set the
screw 1/8 turn in that direction from your starting point and again move it 1/4 turn each
way. As idle rises, lower it with the throttle stop, as changes are easiest to detect at low
engine speeds. Set the screw at the inmost (leanest) position that yields highest idle
speed. (And yes, I know; some owners advocate finding the point where idle drops due
to leanness, then the point where it drops due to richness, and setting the screw at the
center point. I do not concur.) Repeat for the other cylinder.
Note: this process will go very quickly after practice but can take awhile the first few
times through. A big fan and some cooling breaks will do your engine (and maybe
yourself) a lot of good.
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Its important to lower the RPM as low as possible (with the idle speed screw) when running on one cylinder; this will make the adjusting of the mixture screw more sensitive.

This is what I use to sych my carbs:
Buy 22 feet of 3/16" ID, 5/16 OD clear plastic tubing. I then folded the tubing in half forming a "U". Fasten the "U" to any 4.5 feet long board with plastic clamps. This will leave you with 2 open free ends thart are each about 6.5 feet long. Get yourself a small amount of coloured liquid such as ATF or stabil. Any liquid can be used but if its coloured its easy to see. Draw some of the liquid into the bottom of the "U" such that the liquid is half way up the board. Connect the 2 free ends to the barbs that are on your intake manifolds. Some guys like to put a restriction into each end of the plastic tubing, but I have not found that necessary. When you run the engine, one side will be higher than the other, so simply turn the sync screw that is between the carbs to make the 2 sides of liquid match.
I find I can leave the gas tank in place, and still reach the sych screw with a long bladed screwdriver.

heckienawjoe · Posted: July 28, 2009, 8:21 am Post subject: Re: Idling Problem

cool thanks for the details RG!

nj1639 · Posted: July 28, 2009, 12:24 pm Post subject: Re: Idling Problem

Excellent post.

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