Carbs - Carburetors

I think the carbs were tuned right, thanks for the info. the bike had a nice idle to it when I ran it this morning. but it was leaking gas everywhere. it was leaking where the petcock attaches to the gas tank, upon inspection I put two washers on one screw and none on the other. woops.

then it was leaking at the float bowls. I tightened the screws as best I could but it still leaked, although less. during the idle I saw gas slowly leaking from where the gasket should be. then I remembered that I replaced the old black plastic gaskets with cardboard mikesxs ones that didn't properly fit my float bowl so I cut them down to fit. I think this is probably the reason it,s leaking. I will put the old plastic ones back in to see if anything changes.

Good morning guys, i'm new to these bikes, I just picked up two from a guy who had a lot of money but could not change a spark plug. The bikes set in an air-conditioned shop for about a year and a half with fuel spill in the tank and carbs. I have drain the tanks and acid washed them to remove the rust. I have corn down the stock dual carbs on one bike and needless to say they were a gummed up mess inside. I did a very thorough job of cleaning and blowing everything out with air and carb cleaner. I have never done any work on carbs with vacuum slides. I have the bike cranking up in idling ok but as soon as I tried to give it just a small amount of throttle it starts to break up and stalls out. The battery on the bike is also dead but I did not think that would matter. Can anybody offer any advice on what my problem might be. The bike ran fine and he was riding it before you parked it. He stopped writing because he had a fall on another bike.

Thanks a lot

2 rats said:

Good morning guys, i'm new to these bikes, I just picked up two from a guy who had a lot of money but could not change a spark plug. The bikes set in an air-conditioned shop for about a year and a half with fuel spill in the tank and carbs. I have drain the tanks and acid washed them to remove the rust. I have corn down the stock dual carbs on one bike and needless to say they were a gummed up mess inside. I did a very thorough job of cleaning and blowing everything out with air and carb cleaner. I have never done any work on carbs with vacuum slides. I have the bike cranking up in idling ok but as soon as I tried to give it just a small amount of throttle it starts to break up and stalls out. The battery on the bike is also dead but I did not think that would matter. Can anybody offer any advice on what my problem might be. The bike ran fine and he was riding it before you parked it. He stopped writing because he had a fall on another bike.

Thanks a lot

Click to expand...

A little more about your bike would help: year, exhaust/air filter modifications or stock?, etc.

These bikes NEED a solid working battery/charging system or you will have these types of issues. Also, did you sync your carbs? And did you set the air/mix screws to spec?

check for air leaks around the diaphrams and check the rubbers for tiny holes or splits.
Throttle response is largely governed by the slides ,diaphrams, pilot jets , air mixture screw settings and general air leaks around the inlets or on the carbs themselves.

When the engine is warmed up enough to not need the choke on.. try putting on a tiny bit of choke and blipping the throttle. Is there any improvement in the pickup response ? (too much air ,weak mixture etc )or is it worse

Good one Peanut !
....
Bob.......

good to hear that my post was useful Bob .
How did it help you specifically with your throttle response issues .?

well it didn't.... but that is a clever way of seeing if the jetting is correct just put on the choke /enricher a little !
if it's too lean it will speed up bit.... good thinking !
what cleared up 90% of my problems was finding those pilot screws under the frigging caps ! I finally found them after someone told me they were hidden under those plugs.... mine were at 3/4 of a turn ! both of them !!!! now they are at 3 1/2 turns and its at least idling now on BOTH cylinders
so that is a major breakthrough.... the dead at idle on the right then left then right again was because of those silly caps over the screws !
I know enough about engines to know that the silly things needed adjusted but could not find them but following I think it was 5Twins photos
i finally saw where they were at and went out and rilled a 1/8" hole and used a drywall screw and a flat crow bar to pull them out.... they were stubarn! but the flat crow bar with it's nail puller about 4" from the front was perfect I slipped the drywall screw 's head in the nail puller and pried against the valve cover and out they came ....
..... had it running this morning at 2 turns out but it was still too lean so I pulled the tank and set each pilot screw to 3.5 tirns out from the seat.....
( no i havn't done the dead cylinder "tune yet.... ... and it runs much better now..... in the proccess of removing the tank for the 50th time I ade a hole in the gas line so now I have a gasleak ! if it's not one thing it's another so I will go get some proper gas line 3/16" and 1/4 nd replace the ones that have been gving me trouble all along !
..... I think I am going to have to re jet it too as the plugs are looning mighty black... I am at 3500 ft here and I poked holes in the exhaust plates in the back to releave some back pressure ... only a tiny mod but combined with the altitude I think it's enough to warrent the re-jetting of the mains !
.......
Bob............

Not sure if anyone will answer me, but i'll givver a shot.
The Bike:
late 1980 (Hast 4T6 vin so I believe it is treated as an 81).
Bike was 100 percent stock (to my knowledge) when I got it and since I have added foam pod filters and Mikes XS 2 to 1 exhaust.
I live in Calgary AB (approx 1000m above sea level)
The bike has been running great until lately where it has seemed to run rich. I have been lurking the carb advice and read the carb guide and just want to make sure my next moves are correct before pulling the carbs off for cleaning/closer inspection. I also completed a cam chain adjustment and valve adjustment this morning and it seems to run the same. The bike will start and idle fine for a minute or two before eventually running rough and then dying. I use the choke upon startup for a minute and then push it in.

With this being said, and I am trying to keep this short, would my next move to take a look at the idle mixture screws and ensure they are 3 to 3-1/2 turns out? I have never adjusted anything on my carbs and have been riding as is and it has been totally fine. I have owned the bike since 2015

Once I check the idle mixture screws and if that does not seem to help should I then check the float heights? And if that doesn't work, then give the carbs a clean?

Please be nice if I have missed some vital information that I have not read Picture below of my bike.

I would not spend too much time trying to adjust the idle screws. If you have not ever touched them and it just started running rich then you probably have some particle in your pilot jet. That means you get to take the carbs off. The pilot jet has very tiny holes that are easily plugged, but not so easy to unplug. I used a .015 guitar string (high b) to clean mine. You will have to remove the pilot jets from the carbs. Be careful you don't lose any parts or forget the order of removal/installation. If you get those cleaned out and re-installed you might as well clean your main jets, too. I would check the float levels if I was doing it since your already there. I do not know if the gaskets and various o rings are the originals, but you might want to be prepared to replace them as well. I always do one at a time. That way you can compare if you get confused.
I know this is not the ideal time of year to have a bike that won't run.

personally I would check to see that the choke is going off all the way when you turn it off....
float height is critical,....... and preform a dead cylinder test and get those air screws adjusted properly !
synchronize the carburetors too!
good luck !
Bob......

Did you do the swap to pod filters and new exhaust and then it started running bad? Or did you do the swap and it ran great...but now all of a sudden it's not running well?

From my experience, changing the exhaust and air filters would typically lean out your carbs...not make it richer....however, it could be that the pods filters you have are blocking the air inlets on the carb, and thereby making it richer. Or it could be that the two into one is more restrictive than stock...or the same. If that's the case then I would focus on dirty jets, etc. But personally, my suspicion leans toward the pods/exhaust changes you made as that should have made a noticeable impact to your carb settings...and if you've never touched them...then it would make me wonder a bit.

I would pull the carbs, clean them, but also check you're not blocking air passages, etc. and I wouldn't be surprised if you find other issues with them (once clean) with the changes you made.

Thanks for all the reply's everyone. I appreciate the input. I changed to the pod filters two years ago now and the bike ran good with a smooth idle and nice acceleration. They are the Unifilter foam pod filters that I have read about others having success with. Last year I switched to the Mikes XS 2 to 1 exhaust and the bike still ran the exact same. When I replaced the plugs at the start of this season I actually noticed that the bike was running rich (black soot buildup) which I did not expect with the less restrictive air flow and a more free flowing exhaust, but thought maybe since I live at the altitude I do (1000m/3300ft), that it was not getting the the air it needed to begin with? I will be taking the carbs off tomorrow to give them a clean and see if that helps.

I am starting to think that maybe with the foam pods I may have picked up some dirt that found it's way into the carbs...
This forum has been a staple to my bike troubleshooting, along with the maintenance manual so thanks again for the experienced advice.

David

So I cleaned my carbs today, reassembled and the bike kicked over no problem. It idles what I think to be nicely. But upon giving it gas it doesn't want to rev much higher than 3k RPM and is slow to come down and when trying to ride down the street a few feet upon giving it gas it is not responsive at all. Where did I go wrong?

When I removed the bowls there was very little sediment sitting in the bottom. I readjusted the floats to 22mm with no gasket, bench synced the carbs and set the mix screws to 3 turns.

For cleaning I sprayed carb cleaner everywhere followed by using compressed air to blow everything I could, wiped everything down and reassembled. I never removed the jets and just blew air through them after spraying.

Slow to return to idle sounds like a typical lean mixture caused by a small air leak somewhere on the inlet rubbers or the carb bodies.

if you were to study your idle jets you would see minute the amount of air and gas is needed to supply an idle condition. The tiniest air leak anywhere can ruin your mixture .

First I would check both your slides to ensure that both your diaphrams are sealing properly..there is a simple test you can apply without removing the carbs .
Next try revving the engine and at the same time apply a small amount of choke. Your choke will supply an increased amount of gas and enrich the mixture .
if a little choke improves throttle pick up and return to idle then your mixture is too lean.

As others have said ...if you have straight through silencers and any kind of pod filters you will definitely need to fit larger idle jets . I had to go from 27.5 up to 35 ( 3x sizes ) on my 79 BS38 carbs to get my idle mixture correct and eliminate a slow return to idle.

You haven't done a proper carb cleaning. You have to remove all the jets and the mix screw too. You should also pull the needle jet out. That's the thing the main jet screws into the bottom of. It adds air to the fuel supply coming up through the main jet. It has rows of tiny holes down the sides. If those are getting (or are) plugged, you'll get mostly fuel and run rich. That could explain your black plugs.

If your bike is truly a Canadian model and not a U.S. import, you should have the adjustable Canadian needle. You could experiment with it's clip setting to see if it runs better. I can't say what the stock setting is. I don't think anyone has ever reported it. Normally, it's about in the middle of the range.

5twins said:

You haven't done a proper carb cleaning. You have to remove all the jets and the mix screw too. You should also pull the needle jet out. That's the thing the main jet screws into the bottom of. It adds air to the fuel supply coming up through the main jet. It has rows of tiny holes down the sides. If those are getting (or are) plugged, you'll get mostly fuel and run rich. That could explain your black plugs. I am sure my bike is a truly Canadian Model as the gas tank has the Yamaha Dealer from Winterpeg Manitoba markings on the gas cap. Moving the needle "lower" will increase the air, not fuel mixture correct?

If your bike is truly a Canadian model and not a U.S. import, you should have the adjustable Canadian needle. You could experiment with it's clip setting to see if it runs better. I can't say what the stock setting is. I don't think anyone has ever reported it. Normally, it's about in the middle of the range.

Click to expand...

Thanks 5twins for the advice. I pulled the carbs again (glad its been raining and ugly out the last few days) and I have a diaphragm leak that I will troubleshoot soon. I will give it a proper clean this time, although I am sure my problem was the air leak.

Peanut- Thanks for the Youtube posts! I am definitely a visual learner and this helped troubleshoot and my left side carb was good, but my right side carb slide was not to spec! This has been a very valuable learning experience for me. I am sure all my questions have been asked in some form, but sometimes learning and asking for myself in a way that makes sense to me is best I also double checked my float heights and mix screw and they all appear properly set, so I am hoping it is just the air leak that was causing the bike to idle fine, but run poorly once revved.

Thanks again. Will report back soon.

Thanks for the guidance to everyone that responded. I am happy to report back that upon reassembly of my carbs for a second time along with swapping out the plugs, checking and adjusting the valve clearance and checking the cam chain tension my bike seems to idle and accelerate nicer than before. I plan on going on a longer ride when the weather clears and will then check the spark plugs after that time.

DavidIsaak said:

Thanks for the guidance to everyone that responded. I am happy to report back that upon reassembly of my carbs for a second time along with swapping out the plugs, checking and adjusting the valve clearance and checking the cam chain tension my bike seems to idle and accelerate nicer than before. I plan on going on a longer ride when the weather clears and will then check the spark plugs after that time.

Click to expand...

Hey fellow Canadian, It appears I may have the same problems you had. I have a 82 xs650 heritage special US spec in original condition and am now experiencing similar problems ... so I will have to do likewise with my bike. I am sure it needs a good carb inspection and cleaning.. Leo

First , Thanks to Grizld1 and 5twins. For their guide to the solex carbs


The last time these carbs engine ran Ronald Reagan was still president.


Question ? Do I have to remove the floats to change the needle valve ?

Yeah, you do. Drip a little carb cleaner on the ends of the pin first and try to push it out. If it's won't move, don't beat on it, those posts can break. An automatic punch will usually move it. Another oldtime method is to drive a tack through a piece of lath, set a nut under the pin, and press in a vise or C-clamp to get the pin started. There's enough corrosion on those floats that you probably need to replace them anyway, or at least leak test them in hot water. Welcome, and good luck with the refurb work!