New set of carbs. New set of problems.

[norrie]

I know! Not another bloody carb issues thread!
Yes, unfortunately.

I was having idling issues with my 1977 XS250 which I figured were coming from my intake boots which were held together with the previous owner's boogers and chewing gum. And since I couldn't find a new set of rubbers anywhere that fitted my carbs (38mm at the engine side), I bought a set of carbs off an 80 XS250 that would fit the rubbers which were readily available (40mm at the engine side).

I cleaned the carbs three times over and blew everything out with air and checked holes were clean, put it back together. I replaced some fuel line to accommodate the change in fuel line position from centre of carbs to fuel tap side, popped on an inline filter, connected vac line from the petcock to left boot and a cap to right boot and dropped some seafoam in the fuel for good measure. Fired it up…

Still got idling issues. So, as a beginner, once I found the damn mixture screws under a sneaky plastic faux screw on the side, I thought I'd give adjusting them a try. Turned them right in but not too hard, screwed them out 3 full rotations, adjusted the idle screw back and idle seemed OK. But now she was blowing some smoke, which it never did before.

Not knowing but guessing it was too rich I thought maybe I've f#%ked up and I'll move the choke lever. The bike cut out immediately. So I figure I'd just adjusted to suit "choke on" and I turned the idle way up moved the choke and tried adjusting again. Now it's hard to kick over (usually starts first kick when it's warm), it's still blowing smoke, the revs start skyrocketing and I switch it off thinking WTF! Then I notice it's started to drop some oil on the ground which it never usually does. So time to stop playing and head to the forum.

The second question I have is, can someone please throw some advice at me but first question is should the "choke on" position be up or down? I don't know. That brass pin you can see in the last photo, does this tell us the choke is on or off?

77 XS250 with pods, non-stock exhaust and 117.5 jets. New intake manifold rubbers screwed down firmly, pods are a month old, carb gaskets seemed fine. Didn't bench sync but they looked fine. Should probably do it anyway I guess.

 

[norrie]

Also, should I turn the mixture screws out 3 turns or 1.5?

 

[16VGTIDave]

In your last pic, you see how the brass rod is extended? That is the choke in the on position.

Pods, yeah, well... They sure look stylish.

When you say "blowing smoke" what color is the smoke? What does it smell like? Does it linger?

 

[norrie]

In your last pic, you see how the brass rod is extended? That is the choke in the on position.

Pods, yeah, well... They sure look stylish.

When you say "blowing smoke" what color is the smoke? What does it smell like? Does it linger?

Thanks for the reply mate. I'll have another crack at it this morning and see how I go. From memory, grey with a little blue? I was thinking last night it might have been the seafoam. I ordered some 120 jets so should have those in a few days. Then I'll bench sync while I have them off too. I'll check the mixture screws still have their ends too.

 

[norrie]

OK, I've adjusted for the choke off. Mixture screws were pointy thank goodness. Started the mixture at 2 turns and settled on 2 5/8 (I turned the mixture screws until I stopped hearing the idle changing when the screws were turned, is this correct?). I adjusted the idle as best a beginners ears could as I don't have a tacho. But here's the thing that confused me about the choke in the first place – once I got the bike to idle, I pushed the choke lever down and the bike died immediately. I expected it to rev high. What could be causing this? And I've had to hill start it. Seems that when the choke in on, the first kick sounds like the second will work and the second kick I get nothing.

I'll let the motor cool and see how it fires from cold.

 

[norrie]

Yep! So I've let the motor cool down and as expected, it doesn't want to start cold. I get nothing with the choke on and sounds a little closer to starting with it off but still not starting. Thankfully I live on a hill but I can't always rely on that! The bike now idles, runs and starts like a champ when warm but cold, it's a lump of metal with a headlight. I tried mixing it richer by half a turn, but no change. Tap set to prime makes no difference either. I'll keep searching the forum but if anyone has any ideas, I'd love to hear them.

 

[16VGTIDave]

Make sure you are using the correct starting procedure. Plenty of threads with instructions.

 

[norrie]

Make sure you are using the correct starting procedure. Plenty of threads with instructions.

Yes, I have been.

 

[16VGTIDave]

When you adjusted the idle mixture, was the engine at operating temp? Oil above 80C (176F) is my definition of operating temperature. This typically requires 20 minutes or more of spirited riding, depending on the ambient temp.

When trying to start with the choke (cold start enricher) on, can you smell fuel? Are the plugs wet or dry? Are you opening the throttle?

 

[norrie]

When you adjusted the idle mixture, was the engine at operating temp? Oil above 80C (176F) is my definition of operating temperature. This typically requires 20 minutes or more of spirited riding, depending on the ambient temp.

When trying to start with the choke (cold start enricher) on, can you smell fuel? Are the plugs wet or dry? Are you opening the throttle?

I can't remember. Possibly not.
I've not noticed a fuel smell. I never open the throttle when starting. I'll check the plugs.
I have some 120 jets incoming so on the weekend I'll pull them again, do another clean, sync, put them back in and adjust the mix again. Then report back. Anything special I need to do with these to make sure the choke is clear? I don't recall seeing a little hole in the bottom of the float bowl as I've seen mentioned in other threads.

 

[16VGTIDave]

When you remove the float bowl, was there a brass tube that extended into the wall of the float bowl (sorry, I've only worked on DOHC carbs and don't know if the SOHC are exactly the same)? If so, that is the fuel supply for the cold start enrichment circuit. At the bottom of the float bowl, there is a small orifice for fuel to enter and get to the brass tube. If this is plugged, there won't be any additional fuel delivered and the mixture will actually be leaner than if the enricher (aka choke) is off.

I'd suggest you don't change jets until you have everything else sorted. The main jets are mainly for wide open throttle above 7000 RPM. Make one change at a time to preserve your sanity. DAMHIK.

 

[norrie]

From this pic I took last weekend… Looks like that's a yes. Thanks again mate. I'll make sure that's clear

 

[norrie]

When you remove the float bowl, was there a brass tube that extended into the wall of the float bowl (sorry, I've only worked on DOHC carbs and don't know if the SOHC are exactly the same)? If so, that is the fuel supply for the cold start enrichment circuit. At the bottom of the float bowl, there is a small orifice for fuel to enter and get to the brass tube. If this is plugged, there won't be any additional fuel delivered and the mixture will actually be leaner than if the enricher (aka choke) is off.

I'd suggest you don't change jets until you have everything else sorted. The main jets are mainly for wide open throttle above 7000 RPM. Make one change at a time to preserve your sanity. DAMHIK.

While I have you, any thoughts on where this new oil leak that's popped up under the bike is coming from? It started a couple of days ago when I was fiddling with the idle and mixture. Bike was revving off it's head and blowing smoke. As soon as I noticed the smoke I switched it off and this oil leak appeared.

 

[16VGTIDave]

My first thought is excess chain lube. Could also be the clutch push rod seal, counter shaft seal, or neutral switch. Pull the side cover off to find out.

 

[norrie]

My first thought is excess chain lube. Could also be the clutch push rod seal, counter shaft seal, or neutral switch. Pull the side cover off to find out.

Will do. I know it's not lube. I put lube on yesterday and it started a day or two before that. As a newbie, I'm cautious to remove anything without asking for fear of dumping oil everywhere. A quick youtube tells me it's fine Thanks!

 

[norrie]

When you remove the float bowl, was there a brass tube that extended into the wall of the float bowl (sorry, I've only worked on DOHC carbs and don't know if the SOHC are exactly the same)? If so, that is the fuel supply for the cold start enrichment circuit. At the bottom of the float bowl, there is a small orifice for fuel to enter and get to the brass tube. If this is plugged, there won't be any additional fuel delivered and the mixture will actually be leaner than if the enricher (aka choke) is off.

I'd suggest you don't change jets until you have everything else sorted. The main jets are mainly for wide open throttle above 7000 RPM. Make one change at a time to preserve your sanity. DAMHIK.

Pulled the carbs again last night and cleaned out the choke/enrichment. Didn't have any air on hand but poked some wire in there and soaked and sprayed plenty of carb cleaner through and had it squirting out the other end. Still nothing when trying to start with the choke on. Mixture seems good to me. I don't get what the problem is. Tried the choke and got no signs of starting. Then I kick started it without the choke, turned it off straight away and tried again with the choke. First kick gets half way there, each one after I get nothing.

 

[16VGTIDave]

In your video, was the engine running before you recorded that? Had you tried starting it? The reason I ask is that first start is how I'd expect a warm engine to start, not a cold one. Using the enricher on a a warm or hot engine should flood it.

I'm somewhat expecting you to say that you'd tried starting it a couple times, got it running briefly, then recorded. If this is the case, then I'd expect the mixture is set very rich. If it runs that well without the enricher and any heat in the engine, it will be much too rich when at operating temp. I'd be checking the fuel levels in the carbs when on the bike (using a clear tube connected to the drain) and then consider adjusting the pilot screws leaner (in) until such a time as you can properly tune the carbs.

 

[norrie]

In your video, was the engine running before you recorded that? Had you tried starting it? The reason I ask is that first start is how I'd expect a warm engine to start, not a cold one. Using the enricher on a a warm or hot engine should flood it.

I'm somewhat expecting you to say that you'd tried starting it a couple times, got it running briefly, then recorded. If this is the case, then I'd expect the mixture is set very rich. If it runs that well without the enricher and any heat in the engine, it will be much too rich when at operating temp. I'd be checking the fuel levels in the carbs when on the bike (using a clear tube connected to the drain) and then consider adjusting the pilot screws leaner (in) until such a time as you can properly tune the carbs.

I'd tried kicking it about 10 times with choke on and got nothing. I kicked about 6-8 times and got it started with choke off and had in on for 10 seconds, switched it off, tried again with the choke and got nothing, tried again with it off and got it started after a few kicks, switched it off and then recorded this video. The mix is 2 5/8 turns out.

 

[16VGTIDave]

The number of turns on the pilot screws is just to get the bike running. Nothing more. I'm going to stick with my earlier suggestion to lean the idle mixture. Try 1.5 turns and see that happens. After you verify the actual fuel level in the float bowls.

Anyone (everyone) who suggests there is a magic number of turns for the pilot screws is wrong. Many different factors such as manufacturing tolerances, wear, age, barometric pressure, humidity, fuel blend, air filters, exhaust system, and so on all effect the adjustment. As long as the final adjustment falls between 1 to 4.5 turns, all is fine. More or fewer turns indicate an issue with the pilot jet sizing.

 

[norrie]

The number of turns on the pilot screws is just to get the bike running. Nothing more. I'm going to stick with my earlier suggestion to lean the idle mixture. Try 1.5 turns and see that happens. After you verify the actual fuel level in the float bowls.

Anyone (everyone) who suggests there is a magic number of turns for the pilot screws is wrong. Many different factors such as manufacturing tolerances, wear, age, barometric pressure, humidity, fuel blend, air filters, exhaust system, and so on all effect the adjustment. As long as the final adjustment falls between 1 to 4.5 turns, all is fine. More or fewer turns indicate an issue with the pilot jet sizing.

The way I set the mix was to turn the screw half a turn, if it made a difference to the sound of the idle speed, I adjusted the idle and turned the mixture screw again til I found the point at which the idle made no change. Then I richened it by 1/4 turn having read that it's better to be on the rich side than too lean. Is this not the correct way of setting the mixture?
Also, the other day, I made it leaner by half a turn and still couldn't start it. Then I put the mix back where it was.