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Won't start after carb rebuild.

  • Thread starter Thread starter UncleMike
  • Start date Start date
U

UncleMike

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Cleaned carbs and replaced all o-rings. Did the full dip with the bodies soaking for 12 hours. Blew them out. Dipped and manually cleaned out the jets. Set the float levels all to 22mm.

Fresh oil and filter today, along with four new and gapped plugs. Even replaced the seal on the air-filter lid, as it was toast.

Slapped everything on and it just won't start, with or without choke.

Attempted to pop-start her in second and on the fourth or fifth try with full-choke, she started. If I attempt to take her off choke, she dies.

I pop-started her again, and quickly attempted to catch her with the throttle when taking off the choke. Throttle is very slow. Lags quite a bit, as there's a delay between twisting and engine response.

Probably worth mentioning that I replaced the throttle cable during the carb rebuild. The sleeve near the handlebar broke on the old one. I replaced mine with a new OEM one from an '83 E as I have much lower bars than stock.

Help?

Thanks,
Mike
 
I might have answered my own question:

I disconnected the choke and she started right up. I'm gonna go do some more investigating and I'll tell you guys more. I just wanted to make sure you didn't do more thinkin' than necessary because of my dumb a$$.

I'll be back.

Thanks,
Mike
 
Choke cable was at least part of the problem. Throttle cable was also too tight. I also noticed that some of the airbox-to-carb boots had slipped partially off. I fixed those as well.

So she started, but the throttle response is still very sluggish, and to add to a wonderful afternoon, the third exhaust pipe isn't as warm as the others. My spit bounces right off the 1st, 2nd and 4th pipes, but sticks to the third. It is warm, however.

And the bike will still die after idling for a while. It idles at around 3500rpms, and when I attempt to bring that down with the adjustment knob, it stalls out. If I rev it up, the rpms "hang" for a bit.

Man, I just want to RIDE!

Suggestions?

Thanks,
Mike
 
*It seems I only get responses when I bring up religion or politics,...*
 
Quick reply 'cause I gotta watch the NBA finals.
Intake leak. If it idles COLD/WARMING UP close to normal, about 1,100rpm's, then idles significantly higher once fully warmed up, that's an intake leak 98% of the time. Only takes one carb/cylinder to cause your problems/symptoms.
You need to pay attention to the bench and vacuum synchs too, AFTER fixing the intake leak(s).
 
Couldn't tell you, as I can't keep it idling long enough to warm up.

Perhaps I'll order new carb-to-airbox boots anyway. They were pretty pliable, but a little stiff in this colder weather we've been having.
 
UncleMike said:
Couldn't tell you, as I can't keep it idling long enough to warm up.

Perhaps I'll order new carb-to-airbox boots anyway. They were pretty pliable, but a little stiff in this colder weather we've been having.
Click to expand...

OK. An idle of 3,500 rpm's suggests a mechanical problem or intake leak.
"Hanging" or slow to return to idle suggests a lean condition or intake leak or mechanical problem.
One cylinder running cooler but still firing could be either a mixture/vacuum problem or poor spark. In your case, I'm guessing it's a mixture/vacuum problem.
I'd try a good bench synch first and test. If you already tried a bench synch, it sounds like you didn't do it right or you may have a mechanical problem with the throttle plate(s). I'd check that first since it's basic tuning stuff. If you're sure the synch and throttle plates are correct and operating right, then I'd focus on an intake leak.
As for buying new carb to filter rubbers, that's fine, but that's not the cause of an intake leak. Only a leak on the engine side of a carb creates an intake leak. Filter side of carbs creates a leaner mixture.
 
KEITH KRAUSE said:
OK. An idle of 3,500 rpm's suggests a mechanical problem or intake leak.
"Hanging" or slow to return to idle suggests a lean condition or intake leak or mechanical problem.
One cylinder running cooler but still firing could be either a mixture/vacuum problem or poor spark. In your case, I'm guessing it's a mixture/vacuum problem.
I'd try a good bench synch first and test. If you already tried a bench synch, it sounds like you didn't do it right or you may have a mechanical problem with the throttle plate(s). I'd check that first since it's basic tuning stuff. If you're sure the synch and throttle plates are correct and operating right, then I'd focus on an intake leak.
As for buying new carb to filter rubbers, that's fine, but that's not the cause of an intake leak. Only a leak on the engine side of a carb creates an intake leak. Filter side of carbs creates a leaner mixture.
Click to expand...

It's gotta be a mechanical problem then. I must have royally f*cked up the bench synch, because my intake boots on the engine side were nice and soft and rubbery. They felt new! And the clamps are nice and tight, and with the 16v engine, I don't have the intake manifold o-rings either.

Thanks Keith,
Mike
 
If #3 is only "warm" Mike and not really hot it probably isn't firing at all. The heat from the other pipes will heat it up and make it warm but it will never get hot. If that cylinder is not firing all bets are off until you figure out why.

Is the bowl for that cylinder filling with fuel?
 
Hoomgar said:
If #3 is only "warm" Mike and not really hot it probably isn't firing at all. The heat from the other pipes will heat it up and make it warm but it will never get hot. If that cylinder is not firing all bets are off until you figure out why.

Is the bowl for that cylinder filling with fuel?
Click to expand...

Yup. All four had fuel. I'm re-doing the bench-synch right now.
 
Just throwing this out there, but is it possible I mixed up the carb bodies? I can't think of how I would get them back together if that was the case, however.
 
Bench-synch was off. Fixed it.

Also, I pulled the plugs and #3 was firing, it seems. I looked into the plug hole, and it's a little moist in there. Pretty "carbon'd" as well.

There's a small oil-seep that drips near that plug, just FYI.

Worried,...
 
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hey Mike, I know what your going through, Ihave a 81 750 and do to stupidity on my part I messed up #2 carb and have to locate another
one, cold on idle but hot on rev. I have to be more careful!!!!!!

Good Luck! bmac
 
UncleMike said:
Bench-synch was off. Fixed it.

Also, I pulled the plugs and #3 was firing, it seems. I looked into the plug hole, and it's a little moist in there. Pretty "carbon'd" as well.

There's a small oil-seep that drips near that plug, just FYI.

Worried,...
Click to expand...

Mike, don't worry about what the #3 hole looked like. Now that you have it firing correctly let this thing warm up really good if it is running well enough. Finish your rough setup and run it. Take it for a ride if you can. A good long one if possible (once you know your not running too lean or anything) and let it burn that stuff all out of there. The cylinder looked like that because it wasn't firing right. They get pretty bad looking pretty quick when they are not firing right. A good burn off run should fix that right up.

How is it running now?
 
Hoomgar said:
Mike, don't worry about what the #3 hole looked like. Now that you have it firing correctly let this thing warm up really good if it is running well enough. Finish your rough setup and run it. Take it for a ride if you can. A good long one if possible (once you know your not running too lean or anything) and let it burn that stuff all out of there. The cylinder looked like that because it wasn't firing right. They get pretty bad looking pretty quick when they are not firing right. A good burn off run should fix that right up.

How is it running now?
Click to expand...

Not sure yet. I didn't put the carbs back on and try to fire her before hearing the prognosis from that cylinder. Didn't want to do any damage. I did, however, make sure that #3 was sparking, and it is.

I'll throw 'em back on and let you guys know what I find.

Thanks for the patience.
Thanks for the help.
Thanks for the GSR.

Mike
 
Ok, got the carbs slapped back in, and all the boots on snug and tight. I can't imagine where there'd be an intake leak now. They are incredibly soft and pliable and no cracks. And those clamps are ON.

But the bike still won't start without a pop-start in second, and then only with choke.

If I take the choke off anymore than full or 3/4, it'll try to stall out, and I have to either put it on again full, or take it off completely and catch it with the throttle.

I have to keep giving it throttle, or it'll die.

On the bright side, #3 is firing and the pipe is nice and hot.

But that's the only bright side.

Airscrews are at 1-1/4 turns.

And I'm ready to kill someone.
 
Last edited:
On a side note...

On a side note...

Your throttle may be sluggish because of the shorter bars... try to reroute that cable so it has more tension on the sleeve over all... if there is too much give in the sleeve it will not respond to a sharp twist of the throttle..

Joe
 
Does your petcock have a vacuum line hooked up to it and the carbs? It sounds as if the carbs are running real lean, or has an air leak as Keith said. There isn't an inline fuel filter installed, is there? You are using 5/16th inch fuel line and 1/4" vacuum line? The fuel line is routed smoothly? All the float bowl screws are tight and the gaskets are air/liquid tight? You have all the jets in place (don't laugh, I troubleshooted my bike for a week before realizing the pilot air jets were sitting on the bench)? The float heights were checked during the carb rebuild? Your petcock flows nicely? I know you discussed you gas cap vent with others, so that is set... Your choke plunger seals were all replaced and the plungers are tight?

And, I'm spent....
 
Jethro said:
Does your petcock have a vacuum line hooked up to it and the carbs? It sounds as if the carbs are running real lean, or has an air leak as Keith said. There isn't an inline fuel filter installed, is there? You are using 5/16th inch fuel line and 1/4" vacuum line? The fuel line is routed smoothly? All the float bowl screws are tight and the gaskets are air/liquid tight? You have all the jets in place (don't laugh, I troubleshooted my bike for a week before realizing the pilot air jets were sitting on the bench)? The float heights were checked during the carb rebuild? Your petcock flows nicely? I know you discussed you gas cap vent with others, so that is set... Your choke plunger seals were all replaced and the plungers are tight?

And, I'm spent....
Click to expand...

Yes to all.
 
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?
 
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