79 550 ? starting issue after electrical work

[kulchur]

Hi all,
I am prepping my bike for the year and I'm having some carb/starting issues after working on some electrical components. Hoping someone is able to help me out.

A week ago I got the bike de-winterized and running just fine after putting on a fresh battery, new starter last fall, electrical connections cleaned and the like. As recently as a week ago, it started running and idling just fine and seemed like it was ready to ride for the year. I noticed that the headlamp and gauge cluster backlight were not working, so I replaced all the fuses in the fuse box and it fixed the problem. All seemed fine ? easy to start with either switch or kicker, idling at a good RPM, not backfiring. It needed to warm up on choke but afterward could be started with no choke and no throttle just fine.

Now, for some reason, it won't start at all unless I have the choke fully engaged, and after 5-10 seconds of normal revving (certainly "cold" to start) it slows down dramatically and dies. I've been alternating between kicking with choke engaged and without and that seems to at least result in normal compression. If I walk away for a few minutes and let it sit I can come back, turn the choke on and get a bit more normal running time before it dies ? I was trying to get it running for half an hour just now and the run time (with 5-minute rests between attempts) went up from 5 seconds to about 15 or 20. Turning the choke off and trying to control/rev with throttle doesn't seem to help at all.

The only thing that I can think of that could have changed after replacing the fuses is that I may have accidentally left the choke open for a day or two, but that shouldn't affect the bike as it sits. The only other variable is that the seat was off when I got it started perfectly last week (from putting the new battery on) and it's on now ? I tried removing it thinking my air intake may be somehow compromised but that didn't help much. I'm recharging the battery now as I pretty well drained it trying to switch-start over the weekend.

Any ideas? The carbs, idle adjust, etc. were all fine when I put it in the garage in the fall, and the fact that it was running just fine last week has me hoping I haven't fouled the carbs somehow. There is definitely gas in the tank and there's no increase in starting performance between run, prime and reserve. And here I was thinking I was ready to sell it! Any help is appreciated.

 

[tom203]

"Now, for some reason, it won't start at all unless I have the choke fully engaged, and after 5-10 seconds of normal revving (certainly "cold" to start) it slows down dramatically and dies."

sounds like it's running out of fuel...bowls aren't refilling quick enough. When you put it away last fall, did you stabilize the fuel?

 

[roeme]

a) What tom said.
b) I'm a bit confused wether you have trouble starting the bike, or trouble keeping it running.

Either way it sounds like your carbs are starved for fuel or something is clogged up. Sometime back it was recommended to you to change the petcock, no idea if your ever did this or it's condition. Right now, It could be the petcock, clogged jets, pinched fuel line, leaky vacuum line, stuck needle valves, stuck float hinges...

 

[kulchur]

When you put it away last fall, did you stabilize the fuel?

I knew I was forgetting something! I did not. That's a stupid mistake.

Sometime back it was recommended to you to change the petcock, no idea if your ever did this or it's condition. Right now, It could be the petcock, clogged jets, pinched fuel line, leaky vacuum line, stuck needle valves, stuck float hinges...

I did replace the entire petcock assembly and gasket two or three years ago. If I've been trying to run unstabilized fuel through the system, is there a chance I've clogged the petcock? If so, any way to clear it short of buying a new one?

I will start by draining and replacing the current tank of gas. After that, if things don't improve, I'll do a complete carb rebuild in hopes of solving the issue. Anything else that stands out as a to-do for this problem?

 

[tom203]

Your petcock is likely ok. Change to fresh gas. Me, I'd try a good dose of seafoam with new gas, deliberately trying to overfill bowls so seafoam can hit the float needle seats. Fill them up, let sit overnight and make sacrifices. Then try some running- you might get lucky and not have to reclean carbs.

 

[roeme]

I have no idea about the fuel quality in your area and the humidity where the bike was parked, so not sure if in your case one winter is sufficient for the fuel deteriorate enough to clog up stuff.

However, if what tom said doesn't help, I'd first check everything else before digging into the carbs again, or you risk re-clogging your freshly done carbs. For example, I'd do a test run with an external fuel tank (or a simple funnel...), if the issue persists, you'll know the problem is around the carbs, if it goes away, you'll know its your tank/petcock.

 

[kulchur]

Thanks for the advice. Things seem promising after an afternoon of work.

I drained all the gas out of the tank and carb system and put up a clean new external tank to try things out. The bogging/dying problem was still there while running for 5-10 seconds so I am thinking the petcock is clean.

I put the regular tank back on with Seafoam added and primed everything. Once the new gas worked its way through the system, it still died as usual, so I took a closer look at my fuel supply situation and noticed that it wasn't drawing gas well through the line. I took the tank off and cut off about 8" of fuel line ? I liked it longer for ease of installing/removing the tank but there was enough extra to make a loop/S-shape under the tank, which didn't seem to be filling. Now there's a direct, mostly horizontal line on the fuel line down to the carbs. Once it filled the line and started sucking gas, it fired right up and stayed running on choke for a minute or so, then even without choke for a few minutes more. It was racing a bit so I backed the idle screw out a turn and it slowed to a normal idle for a few minutes before slowing down further and dying. I can get it started again on choke but it's totally racing, and any reduction in choke (even a notch down to 7/8 engaged or so) kills it. I'll let the Seafoamed gas sit in there overnight and hope things are a little cleaner tomorrow.

I'm going to feel like a real dolt if the issues were caused by too much fuel line!

 

[kulchur]

Another update today: Things seem to be running much better with the Seafoam in the system and a shorter fuel line. It started right up today and didn't really have trouble with dying. There is an inconsistent idle at the moment ? starts normal with idle screw turned in a bit, then warms up and races, then backs down when I take the idle down, then settles, then races some more. I am hoping that this is just the carbs adjusting to a cleaner fuel source and gunk leaving the system, but if it persists, what can I do to address it? I eventually found a setting where it seems to idle happily for 10+ minutes after some warming up.

 

[steve murdoch]

You should not let your bike idle for anywhere near 10 minutes unless you have a big fan blowing on the engine.
A complete carb cleaning might be in your future.
Before you do that check for air leaks around the carb boots. An erratic idle can be a symptom.

 

[kulchur]

Thanks for the advice. I'll do a check tonight and see if I can get things tightened up at the boots. My airbox boots are pretty chewed up and could be replaced, but complete airbox assemblies are rare and usually in rough shape. Are there any replacement parts or alternative boots from other models I can use to replace them with new rubber?

 

[kulchur]

I've worked on closing up the gaps in the airbox boots and my #1 and #4 are pretty much sealed. No matter what I do I can't make much progress on the middle two as my airbox seems to cave a bit toward the middle. Any advice on snugging these up further? Any way to get inside the front of the airbox and lever outward? I have the rings cranked as tight as possible and as far forward as I can get them to make a seal with the carbs, but clearly there's still a ways to go before they're totally snugged up. I also tried levering the carb assembly backward a bit but that didn't make much difference.

 

[kulchur]

Here's a second photo. You can see that #2 in particular is not seating well.