Rebuilt carbs, bike won't start now.

[NewestOnTheBlock]

I've got a 1980 xs650. I just rebuilt the carbs yesterday, made sure everything was clean and all passages were clear. I also replaced the floats, float valve, float needles, diaphragms and butterfly throttle seals.

I got them on the bike today. It ran good for the first few minutes, then after that it wouldn't start at all. I've tried starting it and I can't get the bike going. The battery is now dead from how much I have tried it. I'm taking a break from the bike and its recharging now.

Prior to rebuilding the carbs, I had no problem starting the bike. I had random idling problems, which is why I rebuilt the carbs. But now the bike won't even start.

When I try starting it, the bike backfires + pops so hard sometimes the carbs actually pop out of the carb boots.

What could be causing all of this?

 

[retiredgentleman]

I suspect your charging system is not fully charging the battery when the engine is running. The battery keeps getting weaker until the low voltage causes the ignition to stop functioning properly. TCI does not like low voltage.

If your battery is old, it may be on its last legs.

Bench charge the battery until its fully charged. If you can get the engine started, wait a few minutes, then rev the engine to 3000 to 3500 rpm. You should see at least 14 volts as measured at the battery. If you don't, then charging system needs repairs.

 

[NewestOnTheBlock]

I suspect your charging system is not fully charging the battery when the engine is running. The battery keeps getting weaker until the low voltage causes the ignition to stop functioning properly. TCI does not like low voltage.

If your battery is old, it may be on its last legs.

Bench charge the battery until its fully charged. If you can get the engine started, wait a few minutes, then rev the engine to 3000 to 3500 rpm. You should see at least 14 volts as measured at the battery. If you don't, then charging system needs repairs.

Yes. I think that my charging system sucks. My battery is a Shorai, and is less than 6 months old. I have it hooked up to a maintainer, so nearly always the bike is started on a full battery.

I will check on the voltage...

But how does the backfire work? carbs popping out of the carb boots......doesn't make any sense to me

 

[weekendrider]

But how does the backfire work? carbs popping out of the carb boots......doesn't make any sense to me

Out of time or valves not closing when they should because of blockage of what ever nature. Bent? Carboned up? Burnt?

 

[NewestOnTheBlock]

Damn really? i've never had issues with the timing or valves. I took the carbs off last week to rebuild them. but didn't touch the engine or wiring at all.....

 

[retiredgentleman]

Yes. I think that my charging system sucks. My battery is a Shorai, and is less than 6 months old. I have it hooked up to a maintainer, so nearly always the bike is started on a full battery.

I will check on the voltage...

But how does the backfire work? carbs popping out of the carb boots......doesn't make any sense to me

You can't run these bikes with a charging system that does not fully charge the battery. Connecting a "maintainer" everytime you park the bike, is a band-aid approach and does not solve the root problem.

Diagnose the charging system and repair it. You seem to be focusing on the carbs; forget about the carbs until you have the charging system working 100%.

The TCI is not working well with the low voltage, which could be causing timing problems and back firing results.

You may have several problem areas, but repair the charging system first.

 

[NewestOnTheBlock]

Let me rephase my original statement. I "believe" my charging system sucks. Right now and the last few months I haven't really been able to use the charging system because i've been so focused on the random high idle issue.

My general process has been to tune the bike, and then go out for a test ride. Usually i get less than a mile away before the bike dies. With help from the forum i've come to the conclusion it is either a lean issue or the throttle seals. With that i've been focusing on the carbs.

Though I wouldn't be surprised if my charging system was bad. The battery that the previous owner had was from walmart. I've replaced it with a shorai.

 

[79xs]

It takes about 2 minutes to test the charging system...

Start the bike, and put a volt meter on the battery at idle. What is the reading? It should be ~12v.

Rev the bike up to 3,500 RPM. What is the reading? If its not 13.5-14v you have a problem.

Like previously mentioned, your bike has the TCI ignition. They are weak at best, and do weird things when they experience low or fluctuating voltage.

Test and fix your charging system first. Also, after taking carbs apart for cleaning you need to synch them. Even if you 'put them back the way they were', they are probably off. Having your newly cleaned carbs out of synch will make it run poorly too... but this is not your only problem.

 

[NONclow]

How well are the regulator and rectifier grounded? I'd check for bad/broken connections on the whole charging circiut.................AFTER testing the system as stated.

"Some carb issues should be checked with a voltmeter"

 

[NewestOnTheBlock]

UPDATE

Tested the charging system, everything comes out good (13.8v).

The battery has fully recharged.

I've taken the carbs off and disassembled everything looking for stuff that I might have missed before or messed up on.

First thing I noticed was the tips of the float needles, one was fine, other looked slightly swollen and looked to be coming off. Since I ordered the float seat + needles, I put in the stock float needles but kept the mikesxs float seat. Rechecked the float height and found that it was a few mm below the needed setting. So I changed that up to 22mm.

Everything else carb related looks fine to me.

I then took out the spark plugs and brushed them off for good measure.

Got everything on the bike and used the electric starter. It fired up on the very first try

I let it run for 5 minutes to warm up, then I was going to perform the dead cylinder method. But then I noticed that the left carb seemed to be puffing/spitting, and I could actually see it move the entire carb body whenever it made that sound....really odd.

So I tried the dead cylinder method, but started on the right side just to see. No problem, right side fired right up and ran like a champ. Rev'd it a few times to make sure.

The left side however, would not start on its own. It would actually backfire so loud that the pods would come off the carbs, and the carbs would come out of the carb boots. This would happen everytime I tried to start it on the left carb only.

If I had them both hooked up, then I could get the bike started. But it was obvious that the right carb was taking care of most of the buisness. The left one kept spitting/puffing.

I found this thread, which sounds similar to my situation.

http://www.xs650temp.proboards.com/thread/12060

Anyone ever experience this before?

 

[angus67]

I bought some flaot valves from mikes, and with in a few months, the tips were swollen, and falling off. I bought some new tour max valves on ebay, no probs since.
when I do the dead cylinder method, It is a bit harder to start on th eleft side. Just doesn't seem to run with same cadence as the right. But I chalk it up to a fresh rebuild with rings still seating in. Only have 100 miles on it.

 

[NewestOnTheBlock]

yeah the swollen tips was what I was first suspicious of. I can't find the thread, but there is a side by side comparison with mikes and oem.

 

[barelycompetent]

I know we have been down this road before, and I was as well only my bike ran on the left side and not the right, and it wasnt backfiring hard enough to pop the carbs out. I believe you have a set of bs34 carbs, and I believe I told you to check the o ring under the mix screws. There is a spring, washer and o ring under the screw. If that o ring is bad, it will cause some of those symptoms you are describing. Its easiest to replace both the o ring and washer. Then put them back in, in the correct order, the o ring first, washer, spring then the screw. Then set your screws the same way out. Course before doing all of that, do a proper bench synch so that you can get your carbs in the ball park. That way when you do the o ring, the carbs are bench synched and the bike should fire up with both cylinders.

 

[barelycompetent]

Also that puffing and spitting and moving when it makes that sound indicates an air leak. Check to make sure you have the vacuum line from the carb boot hooked up to the petcock, and then check to make sure the other vacuum port on the other carb boot is blocked off. If either of those are not connected the bike will do what you are describing.

 

[NewestOnTheBlock]

Also that puffing and spitting and moving when it makes that sound indicates an air leak. Check to make sure you have the vacuum line from the carb boot hooked up to the petcock, and then check to make sure the other vacuum port on the other carb boot is blocked off. If either of those are not connected the bike will do what you are describing.

I'm running pods, so I just have plugs on my carb boots. I've just installed new ones.

There is a spring, washer and o ring under the screw. If that o ring is bad, it will cause some of those symptoms you are describing. Its easiest to replace both the o ring and washer. Then put them back in, in the correct order, the o ring first, washer, spring then the screw. Then set your screws the same way out. Course before doing all of that, do a proper bench synch so that you can get your carbs in the ball park. That way when you do the o ring, the carbs are bench synched and the bike should fire up with both cylinders.

First time I rebuilt the carbs (about a month ago) the o ring's in the mix screws we're the first thing I checked. That Is where I found that the previous owner had put 2 o rings in 1 side, and none in the other

Carbs we're also bench synched before I got them on the bike.

 

[5twins]

You have a single coil that fires both plugs at the same time. They usually either work or don't work. Yours seems to be working as it is firing the one side fine. What could be bad is the other plug wire and/or plug cap, on the side that's misbehaving. Try this simple test - swap the plug wires from side to side. If the misfiring and bad running moves with the switch, you found the problem.

 

[NewestOnTheBlock]

You have a single coil that fires both plugs at the same time. They usually either work or don't work. Yours seems to be working as it is firing the one side fine. What could be bad is the other plug wire and/or plug cap, on the side that's misbehaving. Try this simple test - swap the plug wires from side to side. If the misfiring and bad running moves with the switch, you found the problem.

Just gave this a try. Was hoping this might pinpoint the cause.

Unfortunately, both plug wires work fine

 

[NewestOnTheBlock]

So a interesting update.....



I found some new spark plugs that I apparently forgot I had. I wanted to test each cylinder. So since last time the right side was the only reliable one, I went for that first. It fired up right away, and I let it idle around 1500. Great. Next was the left side, it to fired up right away, and I let that side idle around 1500 as well.....

Now here's the interesting part. I plugged both sides in normally, and the started it up. Instantly both sides backfired through the carbs and popped them out of the carb boots.....followed by a small cloud of white smoke (from the engine, through the carb boots)

I put them back in, and gave it another try. This time the idle shot up to 3000, but no backfire. I killed it, and then gave that a try 2 more times. Same thing, idles at 3000. I would say its now a 50/50 chance on if the bike will start or if it will backfire through the carbs (whenever I start the bike)

Thoughts? What gives?

 

[retiredgentleman]

1980 year, so I assume you have a TCI. If the trigger magnet has weakened over the years, you can get intermittant timing issues and may cause back firing/blown out carbs, etc.

If the back firing returns, as a test (use a fully charged battery), you can unplug the rec/reg unit, so that you have no magnetic field in the alternator rotor. Start and run the engine and see if it runs smoothly with no back firing. If that solves the problem, then its possible to glue on a new magnet, over top the old trigger magnet.

If you search the site you will find threads about this same problem, and the fix for it. I think they used Radio Shack magnets.

 

[NewestOnTheBlock]

1980 year, so I assume you have a TCI. If the trigger magnet has weakened over the years, you can get intermittant timing issues and may cause back firing/blown out carbs, etc.

If the back firing returns, as a test (use a fully charged battery), you can unplug the rec/reg unit, so that you have no magnetic field in the alternator rotor. Start and run the engine and see if it runs smoothly with no back firing. If that solves the problem, then its possible to glue on a new magnet, over top the old trigger magnet.

If you search the site you will find threads about this same problem, and the fix for it. I think they used Radio Shack magnets.

Great. I will give that a try.

Also, I have a buddy who heading over to help out, he is bringing over a timing light. Do you think this issue might be timing related?