Won't start after carb rebuild.

[UncleMike]

Ok, if you are not getting too much air, and you are getting enough gas, you can narrow it down to a mixture of the two. Are the jets known originals, and the pipe is stock? Has the bike run well on these jets and exhaust before this problem? A true vacuum synch can help these problems, but you need to get it to idle first. Even if you can only get it to idle at 2500rpms and it sounds like poo, you can at least get the synch started and things will improve. A bench synch usually gets it started, but rarely running well. It's not even funny how little a turn on the butterfly adjusters makes a huge difference.

How did you set your float heights? If you still have problems, I'd be attaching a clear tube to the float drain and making sure it is perfect (but maybe you did?). I usually leave mine on there while I am synching the carbs to see how the bowls recover fuel as you throttle up.

If that doesn't at least get it running somewhat well, I'd be concerened about other issues. Is you battery charged and charging? 12V at the coils? Timing? Cam chain? Valves? Bad gas? Plug wires?

I don't know about the jets, but the everything else is stock as far as I know. The bike had the same sort of problem before I cleaned everything, but actually ran a bit better before the clean if you can believe that.

Floats were all set to 22mm. I just used a ruler.

My battery tested well earlier this year as well as the charging system. I can't tell you about the coils, timing, cam chain, valves or plug wires. The gas is only about three weeks old.

Mike

 

[UncleMike]

At Earl's suggestion, I slacked the throttle completely off, and then started her with full-choke. After MANY adjustments to the throttle, I got her to idle with no choke finally.

Her idle still isn't rock-solid. Varies a bit. Pat (Gravity-Tester) dropped by and took a look too. He verified that if I have an intake leak, it's not from the boots. They look brand new.

Now it's steady enough that I can do a vacuum synch on her, at least. Although not until tomorrow night, since I've got meetings all day tomorrow.

On to the next nightmare.

Thanks guys!
Mike

 

[Jethro]

Well, I think you may need to check those things if you are confident that the carbs are clean as a whistle, you dipped them correctly and all the o-rings and rubbers aren't leaking fuel or air. Something is not right. Have you tried to vacumm synch yet? Can it idle at all? Won't stay running no matter how much you mess with the main idle screw? A vacumm synch can really make the difference, it can run real sluggish and have a hard time starting unless the carbs are synched, and maybe your bench synch sucked- just kidding, trying to lighten you up:-D

Honestly, sometimes a bench synch doesn't really do the trick. Do you have a synchronizer? If that doesn't help, you gotta check everything else- timing, compression, valve clearances, voltage at the coils and voltage drop between circuts- any problems there and you will have little to no luck with the carbs. I have spent many hours blaming the carbs for something that wasn't thier fault.

When is the last time the bike ran well?

 

[Jethro]

How did you and Pat check the boots? I only ask becasue I could show you an example of brand new looking boots that only when removed from the bike and squeezed showed major cracking just at the inside flange. Even fully removed you would swear they were perfect until you squished the boot. Under pressure they amazingly sucked in air (ever seen those boots pulsate? they are under great vacumm pressure). Also, a water mist test proved nothing. Even carb spray didn't change idle- but replacing them did the trick.

 

[UncleMike]

Well, I think you may need to check those things if you are confident that the carbs are clean as a whistle, you dipped them correctly and all the o-rings and rubbers aren't leaking fuel or air. Something is not right. Have you tried to vacumm synch yet? Can it idle at all? Won't stay running no matter how much you mess with the main idle screw? A vacumm synch can really make the difference, it can run real sluggish and have a hard time starting unless the carbs are synched, and maybe your bench synch sucked- just kidding, trying to lighten you up:-D

Honestly, sometimes a bench synch doesn't really do the trick. Do you have a synchronizer? If that doesn't help, you gotta check everything else- timing, compression, valve clearances, voltage at the coils and voltage drop between circuts- any problems there and you will have little to no luck with the carbs. I have spent many hours blaming the carbs for something that wasn't thier fault.

When is the last time the bike ran well?

I have no doubt that my bench synch may have sucked,...

I got her to idle finally, see the above post. Tomorrow I'll vacuum synch with the mercury sticks I got. Hopefully that'll solve things, otherwise I'll move onto the rest.

Valve adjustment is scheduled for sometime soon after I get these carbs sorted. Compression as well. Timing, voltage at coils, voltage drop, plug wires are all a mystery to me. Wouldn't know how to check them.

The bike never ran well. When I got it, it would need starter fluid to get her going, unless ridden everyday. I put Berryman's in the gas, and it got better, as I no longer needed the starter fluid, but it would still need choke & throttle to keep her going until she warmed up.

You heard that right, choke & throttle. When I started her, she needed full choke, and then would rev immediately to 5Krpms or so for about 10 or 15 seconds, and then start to die, at which point, I'd have to give her a little throttle to keep her from stalling out.

Have to do that for about a minute or so and then could take off the choke.

 

[UncleMike]

How did you and Pat check the boots? I only ask becasue I could show you an example of brand new looking boots that only when removed from the bike and squeezed showed major cracking just at the inside flange. Even fully removed you would swear they were perfect until you squished the boot. Under pressure they amazingly sucked in air (ever seen those boots pulsate? they are under great vacumm pressure). Also, a water mist test proved nothing. Even carb spray didn't change idle- but replacing them did the trick.

Just by looking at them, sadly. I didn't take them fully off when the carbs were off, no one told me too. I just bent them around and felt how soft they were. Didn't see any cracks or anything. Didn't think they could hide like that.

I just mentioned how they pulsate to Pat tonight.

If the v-synch doesn't do the trick, it'll be the first thing I check.

Thanks,
Mike

 

[KEITH KRAUSE]

Sounds like you've been busy but it still idles badly?
If you think it will run well enough to try a vacuum synch, then do that. But if the idle is very choppy it may be difficult.
After the bike is warmed up (if you can warm it up) I would then hook up the vacuum tool, start it, and carefully (don't suck up any mercury, always return throttle slowly) run it at about 3,500 rpm's just to see the initial vacuum levels. Don't bother with a choppy normal idle rpm that may be hard to keep running anyway. Unless you have other problems, any uneven levels will be similar at 1,100 or 3,500 rpm's. This is just to see the initial levels and if they're uneven enough to be your problem. If you see very uneven levels at this rpm, there's a good chance the synch is your problem. I would then set the levels correctly at about 3,000 rpm's and test. If the initial levels were fairly close, your problem isn't the vacuum synch but you can set them at this time if you want.
If the bike still won't idle well at about 1,100 rpm's and the rpm's still hang before returning to the set idle, I'd focus on the pilot circuit passages and tiny bypass ports near the throttle plates. It's very easy to think these ports are clean and they aren't, or forget them completely.
If the ENTIRE pilot circuit is clean, including pilot/primary air jets and you verify the pilot jet size as stock, and you still have the problem, then an intake leak may be present. An intake leak will usually show itself by simply riding the bike until fully hot. Even if the bike idles poorly when colder and you can't set it to hold 1,100 rpm's, most intake leaks increase the "closed throttle" rpm's so much that you'll have to hear the difference between cold and hot. If it rises significantly, you have a leak somewhere. In your case, a poorly installed carb to manifold or manifold itself. If the rpm's don't rise very much, you most likely don't have a leak, but do have a mixture problem. Plug reads would be helpful.

 

[UncleMike]

Okay,...


Got the bike to idle and did the vacuum synch. Carb one was WAY off, almost double the others, which were actually kind of close, but still off. I synched her up.

Is there something I should be doing with the air screws? I set them all at 1-1/4 turns, but they vacuum synch procedure didn't mention anything about them, so I didn't touch them.

When I was finished with the synch, I was tightening down one of the screws and the bike died on me. Wouldn't start again. The starter was initially going like normal, turning over quickly, and then it suddenly got VERY sluggish, and would turn VERY slowly, almost threatening not to at all. The headlight and guages were still bright.

I put everything back together, and pop-started her and went for a ride. She seems to have a lot more power now, but actually seems more "buzzy" than before the carb clean and synch.

AND!

She still died at a light, and wouldn't start again. Had to pop-start her.

A bit frustrating,...

 

[Steve]

Is there something I should be doing with the air screws? ...

What I usually do is to sync them, readjust the idle, then slowly adjust each of the idle mixture screws, looking for fastest idle. Go through all four of them, will probably have to do it more than once.

By the way, the 1-1/4 to 1-1/2 turns out is a good STARTING point. I found that on my carbs, they ended up about 2-1/2 to 3 turns out. Bike ('82 850L) starts instantly on about 1/2 choke, idles about 1500 while putting on the helmet, then hit the road. While accellerating in second gear, turn the choke off. Total time on choke, less than a minute. When warmed up, idle is back down in the 1000-1100 range. Can't ask for much better than that.


.

 

[KEITH KRAUSE]

Is there something I should be doing with the air screws? I set them all at 1-1/4 turns, but they vacuum synch procedure didn't mention anything about them, so I didn't touch them.

When I was finished with the synch, I was tightening down one of the screws and the bike died on me. Wouldn't start again.

They're called mixture screws. They should be set using the highest rpm method. This should be done on a completely warmed up motor and on the centerstand. This should be done before the vacuum synch.
Generally, setting them to about 1 1/2 is a good starting point.
Set idle to 1,000/1,100 rpm. Start at any carb. Slowly turn a screw in either dirction until you hear the highest idle. Fine tune. Reset idle to base with the idle adjuster knob. Repeat to the others.
What screw ("one of the screws") are you talking about that you tightened down and the bike died and wouldn't start again??

 

[UncleMike]

They're called mixture screws. They should be set using the highest rpm method. This should be done on a completely warmed up motor and on the centerstand. This should be done before the vacuum synch.
Generally, setting them to about 1 1/2 is a good starting point.
Set idle to 1,000/1,100 rpm. Start at any carb. Slowly turn a screw in either dirction until you hear the highest idle. Fine tune. Reset idle to base with the idle adjuster knob. Repeat to the others.
What screw ("one of the screws") are you talking about that you tightened down and the bike died and wouldn't start again??

Sorry, yes. Mixture screws.

For the other, I'm talking about the three throttle screws I was adjusting for synch.

 

[Hoomgar]

Mike, I'll let the carb gurus walk you through the fine tuning. I wanted to comment on this though:

The starter was initially going like normal, turning over quickly, and then it suddenly got VERY sluggish, and would turn VERY slowly, almost threatening not to at all. The headlight and guages were still bright.

If the lights were still bright you should verify with a meter but it sounds like the battery is still charged. If so this is your starter motor. Check to make sure all it's connections and ground are solid and if this continues to happen then it needs rebuilt. Especially if it works better cold and gets worse when it is warm/hot. The brushes most likely need replaced. There are usually a lot of these going across eBay. Sometimes it is easier to just pick up another one but rebuilding is always better.

 

[UncleMike]

Mike, I'll let the carb gurus walk you through the fine tuning. I wanted to comment on this though:


If the lights were still bright you should verify with a meter but it sounds like the battery is still charged. If so this is your starter motor. Check to make sure all it's connections and ground are solid and if this continues to happen then it needs rebuilt. Especially if it works better cold and gets worse when it is warm/hot. The brushes most likely need replaced. There are usually a lot of these going across eBay. Sometimes it is easier to just pick up another one but rebuilding is always better.

I noticed a while back that it's a replacement from a 550, too.