Wouldn't start, then trouble idling

[UncleMike]

Air filter came from Dennis Kirk today, so I slapper her right in which completed my impromtu tune up, including fresh oil and filters, and new sparkplugs, freshly gapped for the first time in my life thanks to you guys!

Now, she wouldn't start so I sprayed some starter fluid on the air filter and she roared to life after a couple of cranks and a little twist of the throttle and full choke. But she'd try and stall if I didn't keep the RPM's up by keeping the throttle constantly twisted a little bit.

Now here's the interesting part: Got the bike in Oct. of last year, and this was pretty typical of the starting procedure, excepting that last year, I had to keep that throttle twisted for a long time, even after riding for a while, I'd have to keep twisting the throttle at stoplights and such or she'd stall.

Today, after doing this for only a few minutes, I was able to take the choke completely off, and she'd idle right around 1100-1200 rpm's, but after a minute or so, she'd slowly start to go down to 1000, 900, and start to sputter a bit, but this is still a tremendous improvement from last fall. I've put Berryman's and Lucas in the tank along with some MMO, so perhaps that's helping? I'm gonna let her sit for a day and then run her again, hoping that the cleaners will dissolve some more gunk.

Another interesting note: Up on the centerstand, when in neutral, and even with the clutch in, the chain and tire would spin when she was idling. Not very forcefully, though, as I could easily stop it from spinning with a toe. After she was warmed up, it stopped doing that.

So what does this all mean? What shall I do next? What didn't I tell you that you'd need to know?

Thanks,
Mike

 

[flyingace]

First of all, which of your 3 bikes are you talking about?

 

[UncleMike]

First of all, which of your 3 bikes are you talking about?

My bad. '83 750T.

450 was given to my buddy for a wedding gift, and the 750L is being parted out after a head gasket leak.

 

[flyingace]

Does the bike idle cleanly when fully warmed up (as in after 15 minutes of running)? I have to keep some choke on my bike for at least 5-6 minutes before it will idle steadily.

 

[UncleMike]

Does the bike idle cleanly when fully warmed up (as in after 15 minutes of running)? I have to keep some choke on my bike for at least 5-6 minutes before it will idle steadily.

Actually, I didn't want the choke on for too long, so I took it off after about a minute or two, and just kept blipping the throttle. After a couple of minutes, no more than four or five, it would idle with no choke and me not touching the throttle around 1100 rpms. After about a minute or so of idling there, it would steadily and very slowly start creeping down,...1000rpms, 900rpms, where it would start threatening to stall out. A slight blip of the throttle would bring it back up to 11 or 1200, where it would stay for a minute or so before starting to crawl back down again.

 

[flyingace]

Actually, I didn't want the choke on for too long, so I took it off after about a minute or two, and just kept blipping the throttle. After a couple of minutes, no more than four or five, it would idle with no choke and me not touching the throttle around 1100 rpms. After about a minute or so of idling there, it would steadily and very slowly start creeping down,...1000rpms, 900rpms, where it would start threatening to stall out. A slight blip of the throttle would bring it back up to 11 or 1200, where it would stay for a minute or so before starting to crawl back down again.

You can have the choke on as long as it's needed - no harm is done. But you didn't answer my question - does it idle OK after being fully warmed up?

 

[UncleMike]

You can have the choke on as long as it's needed - no harm is done. But you didn't answer my question - does it idle OK after being fully warmed up?

Well, this is the first time I've had it started since December,...

...but like I said, once it was on and would stay on without the choke, it would hang around 1100 rpms for a minute or so, and then creep down a little over the next minute until it would try and stall out. I only had her running for five minutes or so.

 

[mark]

Its hard to say, but you could just be running out of gas. You could check your fuel flow to see if that is normal. I don't know if you have a "prime" on your petcock but turn it to that and see if your situation improves.

 

[Billy Ricks]

Drain the float bowls and start off with a new tank of fuel. It may or may not help but it's worth a shot.

 

[duaneage]

Check the boots between the head and carbs and the carbs and airbox for leaks. Sounds like it could be the o rings on the intake boots too.

 

[UncleMike]

Its hard to say, but you could just be running out of gas. You could check your fuel flow to see if that is normal. I don't know if you have a "prime" on your petcock but turn it to that and see if your situation improves.

Meaning just run it on Prime while warming up? I drained the float bowls and let it run out on Prime for a while last night, and I got what looked like good flow,...

 

[flyingace]

You can try all those things, but if the bike idles fine after it's warm, it's none of them. The symptoms you describe are of a bike trying to idle when it isn't fully warmed up. Seeing how it idles after it's warm is the acid test of that.

If it still falters when warm, turn up the idle set screw between the carbs and see if that stops the idle from falling.

 

[UncleMike]

You can try all those things, but if the bike idles fine after it's warm, it's none of them. The symptoms you describe are of a bike trying to idle when it isn't fully warmed up. Seeing how it idles after it's warm is the acid test of that.

If it still falters when warm, turn up the idle set screw between the carbs and see if that stops the idle from falling.

I'll let her fully warm up soon and let you know what happens.

Thanks, guys.

Mike

 

[mark]

Meaning just run it on Prime while warming up?

Yeah. Not saying that's what it is, but you'd know for sure you were getting enough gas and it wouldn't hurt anything. Flyingrace could be right too, you might just need to adjust your idle speed.

How's it go down the road?

By the way if you can stop your rear tire from rotating with your toe when its up on the center stand, you're good to go.

 

[UncleMike]

Yeah. Not saying that's what it is, but you'd know for sure you were getting enough gas and it wouldn't hurt anything. Flyingrace could be right too, you might just need to adjust your idle speed.

How's it go down the road?

By the way if you can stop your rear tire from rotating with your toe when its up on the center stand, you're good to go.

Once it's going, it seems to run great to me, although I'll admit I don't have much experience.

It occurs to me though, that none of this solves the problem of it not starting without starting fluid,...

 

[flyingace]

It occurs to me though, that none of this solves the problem of it not starting without starting fluid,...

Oh... I thought that was a one-time thing. Now I'm more inclined to go along with the fuel starvation theories.

I would still do the fully warm idle test, but needing starter fluid each time you start indicates something more sinister. I'll ask you this question: Do you crank the throttle with the choke on? If you do, stop doing that. It defeats the purpose of the choke.

 

[UncleMike]

Oh... I thought that was a one-time thing. Now I'm more inclined to go along with the fuel starvation theories.

I would still do the fully warm idle test, but needing starter fluid each time you start indicates something more sinister. I'll ask you this question: Do you crank the throttle with the choke on? If you do, stop doing that. It defeats the purpose of the choke.

I do, but only because I'm trying to get the choke off as quickly as possible. It's not really "cranking" but more like holding it at a small degree of rotation. I don't have to, however, if I kept the choke on at a reasonable level.

Now, I had the drain plugs off and the petcock at Prime last night, and all four were flowing. Doesn't that mean that the petcock isn't blocked, or could it still be blocked in On?

 

[mark]

What makes the gas flow when the petcock is on "on" is vacuum created when the motor starts. There is a smaller line that goes from your petcock to somewhere on the carb. That's your vacuum line. So its possible to get fuel flow on "Prime" but not "on". Prime just gets around all that.

The only thing I can think of that would keep your bike from starting when cold, if when its warm it runs fine is that the choke isn't fully open somehow. You could check and see if your cable fully opens the choke when you use it. Usually you can just reach in there and open the choke by hand to check it. Other than gunked up carbs I can't think of anything else.

Also, flyingrace is right about the choke throttle thing. Opening the throttle when you're using the choke makes the choke ineffective (non-effective).

 

[UncleMike]

What makes the gas flow when the petcock is on "on" is vacuum created when the motor starts. There is a smaller line that goes from your petcock to somewhere on the carb. That's your vacuum line. Prime just gets around all that.

The only thing I can think of that would keep your bike from starting when cold, if when its warm it runs fine is that the choke isn't fully open somehow. You could check and see if your cable fully opens the choke when you use it. Usually you can just reach in there and open the choke by hand to check it.

Also, flyingrace is right about the choke throttle thing. Opening the throttle when you're using the choke makes the choke ineffective (non-effective).

Well, now I'm thoroughly confused. I guess the diaphragm could be bad though and prevent gas flow while in the ON position. I've never attempted starting it when warm, since I got it in late Oct., but the PO said that he needed to use starting fluid when it had sat for a couple of days.

I'll start it tomorrow and use the choke properly and give you a full report.

Thanks guys,...I appreciate it more than you know.

Mike

 

[UncleMike]

Although,...the bike won't start initially, without giving it a little goose with the throttle at least, but once it's started, I don't need to throttle it if I have the choke on.