Very weak idle on cold start. Could be carbs or engine?

I noticed this issue the second time I went to start my bike. I went to start it and it barely kept from stalling. It was sitting at about 500rpms. Putting the choke on even a bit would immediately kill the engine(it still does this warm as well). I thought it could be the air filter because it smelled like it was running rich. I checked and the air filter was relatively clean. There is some very quiet ticking in the engine, so now I am onto suspecting it to be caused by valve clearances perhaps? I am using the best of my google-fu to diagnose the issue, but I am not a very seasoned mechanic, even though I can turn a wrench.

Symptom list:

Low rpms on cold start
slight ticking
relatively clean air filter
exhaust smells somewhat rich
low air intake vacuum(one or more even feels like it is blowing)


I am going to do valves this weekend and probably change sparkplugs just because I have them. With it smelling rich and the previous owner saying they never needed to change the sparkplugs that could mean dirty plugs which would only add to issues. I have been running seafoam through the tank for the carbs and I will probably put some in the crankcase this week as well, since I have an oil mod due in the mail this weekend. Other than that are there any other suggestions on what I can do to get my new baby up and running solid on a cold start? I got it for a good deal but I would like to keep it around a while.


Thanks in advance everyone!

 

First of all, drain the float bowls and pour some FRESH fuel into the tank.

Most likely the low starting speed indicates that one or more cylinders aren't firing. Check for cold headers after it's been running for a minute, then pull plugs and check spark on the cold-pipe cylinders, also checking for wet plugs, which would indicate leaky float needles. If you find good sparks and dry plugs, your carbs may need cleaning, for which seafoam seldom works. If you're not interested in getting deep into your carbs, you can send them to me for cleaning, adjustments, and testing. eaceful:

 

Thanks for the tips. I will add carb cleaning to the list of stuff I gotta do, lol. Can't get a bike this clean for $850 without a little diy, I guess. I'll check the pipes on my way home from work today(I stubbornly rode to work despite her ill health) and update later this evening. Valves are still on the table anyways since I want to check the cams and its good practice to do them.

On an unrelated note, I just realized my bike has a '88 cbr600 rear shock instead of the stock one. It's got the red coil and the lower dampening ring on it which looks quite a bit different from the stock shock, lol. Anyone know how common this swap was? And anyone know how to adjust the preload offhand? I don't know if I'll probably need a special tool for it which probably won't be in my kit.

 

I've been working on my ST1100 carbs lately so have a little first hand knowledge here. I'd suggest the enrichener circuits might be clogged, on my ST these are the long plain brass tubes that hang into the float bowl. The other likely culprit would be the slow speed jet which is really tiny.

If you want to see what you are in for, this thread has fantastic pictures.

http://www.st-riders.net/index.php?topic=10249.0

 

Right-o, chocolate boy !! The long brass tubes must be clear enough to pass air through and a .010" steel wire or ye get no enrichment on starting. A very common problem.

 

Here's an update to the issue, albeit a bit later than promised. All four cylinders are definitely firing on startup, pipes all warm up quickly and evenly. I got a half a tank of gas after work as well. It may just be my imagination, but after my bike was parked at home for a while, I went for a ride and it seems to have started a lot easier. I'll be kicking myself into next week if my seafoam mixture caused the issue. I've been using this stuff since I started riding with good results. Doesn't fix the need for a valve adjustment, though. I'll have to wait a little more and see.

I would lean against this assumption only because it idles fine after some time has passed and it happens consistently on cold starts. Wouldn't a jet clog show constant issues? Enricher circuit could be a culprit. The only carbs I've worked on used butterfly chokes so they didn't have one if I understand correctly. They just closed off the intake valves. The fact that the choke still kills it on cold is what leads me to believe it.


EDIT AGAIN:

I decided to take a peek at my plugs on lunch (or at least one of them) to help narrow down the issue. I pulled one out and it looked alright to me. I'll look at the others after work; hopefully it could aid in some diagnosis of which carburetor it could be causing me grief since that is what I am kinda leaning towards now. I started it before I pulled the plug and it was doing the typical low rpm chugging so I don't think it was my fault with the sea foam.

 

Plug looks OK, a Cadbury light milk chocolate.

 

You leave me out of this, Squirrel!

 

I went ahead and pulled the carbs today because rain was scheduled in the forecast for tonight. Got them out, would be lying if I said it wasn't a pain in the ass. I haven't ever worked on a v rack so it was kinda new to me and I did make some mistakes along the way(Didn't help that I was racing rain clouds). I lost one of the throttle springs, the ones that go opposite to the screw which adjusts the valve. That should be an easy replacement. I also cracked the plastic fuel tee foolishly trying to pull the carbs out one by one to avoid cracking the boots(in hindsight the boots aren't even that hard, so I guess I've found a reason to be kicking myself). Had to bite the bullet on a $45 replacement for that. Rain is scheduled up until friday so I suppose I'm not hurting time wise.

Past my tedious ranting, I cracked the bowls open and they were all pretty nasty. Sprayed em out and checked the jets. The pilot jet was pretty clogged on at least one of the carbs. The enricher circuit that you guys were talking about, that would be the tube sticking up next to the jets without the slot, yes?



The other one looks like it runs into the needle valve and that isn't really cleanable. I sprayed the hole good but I am not sure how I can see if I've knocked out any blockages. I topped it off and am letting it sit like that with the bowls on now. Just waiting for my next clear day and I will stick em back on to see how it runs.

Thanks for the help so far; I will be keeping you all updated.

 

Yes in your photo the enrichener is the plain brass tube upper most in the cluster of the three jets. On my ST1100 there is a narrow restriction about 10mm up that pipe, a fine piece of wire opened it for me and I followed that with a jet of carb cleaner. You might need to open the enrichener lever to get it to flow through.

You should be able to unscrew the main jet (the biggest one in your pic) and then the emulsion tube under that can be unscrewed. While the emulsion tube is a big bore (has the needle sliding into it), it has a number of fine small holes drilled into the sides which should be cleared.

The pilot jet needle circuit leads through the adjustment needle and into some really tiny passages in the floor of the carb downstream of the butterfly, and for best low speed running you should make sure these are open.

 

Went ahead and tried that wire method as suggested. It felt empty up to the point where I hit a stop at about 1cm as described, but I could not get my piece of wire in. It may perhaps have been too thick, but I wasn't sure what to expect. I didn't have a lot of time yesterday either(uni crunch time plus full time job equals agony), so I will probably give it a go again before the weekend.
View attachment 35941

 

Figured I would give a final update to the resolution of this issue. It was indeed the enricher circuit. Now that the carbs have been reassembled and installed, there is definitely a tactile difference in the action of the lever. It feels much smoother like the valves are actually opening and the bike stays on with a cold start. It still idles low on cold but that is more expected now, as long as it stays on.

 

bOOST THE COLD IDLE SPEED WITH THE ADJUSTING SCREW.

 

I did that at first but then it was idling at 2k fully warmed lol. I could try finding a happy medium or just adjust every time. It is not sitting quite as low with the enricher but it still registers at just under 1k.
Once I get around to doing a valve adjust(soon, promise) then I will sync the carbs as well which should aid. It has been raining on and off here and working between storms with the carbs was already a pain in the butt.

 

tHE ADJUSTMENT KNOB IS EASILY REachable, and may need to be turned UP for cold starts and then turned DOWN later when the engine reaches operating temp. THAT'S normal. :smile:

 

Sorry, maybe I'm just too used to my old fuel injected baby . Gotta remember I'm not driving a 2008 anymore. That, I can get used to.

HOWEVER,

Started it up today. 50F outside. Start her up, coax it to stay into an idle, and then with the enricher on, tease it up to the point where it won't die with me having it held at ~1500. The clutch makes a clunky dry sound in neutral unless the lever is depressed. Should I look at putting some lighter oil in? None of my bikes in the past made noises like that when cold, and I used to drive my nighthawk in sub-zero temperatures. I do not know what the previous owner has put into the engine, but it doesn't have a lot of miles on it. I put in a tiny bit of 10w-40 to replace what came out after installing my oil mod. I feel like 50F isn't that cold for it to behave the way it is. I might just be overly worried because I don't want my new baby suddenly exploding on me but still. I know y'all know what the hell you're talking about so I figured I'd consult at the risk of being over-worrisome.