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Message started by Chris911 on 09/19/20 at 10:39:39

Title: Backfiring - All the time - Wide open Throttle
Post by Chris911 on 09/19/20 at 10:39:39

Hello:

My name is Chris and a friend of mine just bought a 1996 LS650, and I am tasked with making it run for him.

The motorcycle had sat for many years, so I began by cleaning the carb in my ultrasonic tank, and then rebuilding it. I also replaced the floats.

The petcock was bad, so I replaced it with a K and L that looks like the factory piece.

But now it is hard to start. And when it does start, it backfires like crazy. I get it that these are jetted lean, but there is more going on here. If I hold it wide open, the backfiring is awful, and the pipe is really heating up.

Does anyone have any suggestions? I have searched this forum for weeks and have seen no similar issues.

Thanks so much. I am sure that as caretaker of this motorcycle, I will be on this forum a lot, LOL.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by zevenenergie on 09/19/20 at 12:18:41

Clymer handbook states:

leaking spark plug cap and or cables.
Ignition timing incorect,
Leaking in and / or outlet valve. :-X
Or the springs broken.
I would measure the compression first.
Must be at least 114psi (service limit). Normal is 142-200 psi.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/19/20 at 13:50:53

The petcock was bad, so I replaced it with a K and L that looks like the factory piece.

A link to that petcock might help.

KNowing the tubing inside diameter of the petcock outlet, not the rubber gas line, could be good to know.
If you added an inline filter, remove it.

Check the float height by putting piece of clear(ish) tubing on the bowl drain nipple. Hold the tubing up next to the junction of the bowl with the carb body. Thats where the fuel level should be.
Did ya clean out the tank? Was it rusty? Is it possible the petcock filters are clogged with junk?

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Chris911 on 09/19/20 at 14:15:24

Justin, no. The petcock filter is clean. I like your method of checking the float height. I just installed the new float as-is. I hope that is OK.

I will do some more checking and report back.

Z, the motorcycle only has about 2000 miles, it should be OK.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by IslandRoad on 09/19/20 at 18:16:37

Has it got the stock muffler or open pipes?

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Chris911 on 09/19/20 at 18:19:45

Stock muffler. It is completely blued. All of it. And it was so hot, it actually shot "soot" on the case in front of the oil check window.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Dennisgb on 09/19/20 at 18:22:03

My guess is super lean or you have bad valves or they are out of adjustment and staying open. Rare to have them popping like crazy with the throttle open.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/19/20 at 20:47:09

If anyone adjusted valves
Which way did they turn the crankshaft to get tdc?
What other mistakes could create this?

Don't remember seeing model and miles, don't wanna go back from here.

Okay, 96 model

Miles?
Any other work that has been done
And when,

But now it is hard to start.

When did that start?
The more details about
How long it sat
Why was it parked
When did trouble start
What was it doing
Give up the 411, duuude.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Chris911 on 09/20/20 at 04:37:32

You are killing me! LOL

Sat for about seven or eight years.

I'll be back on it today. Can't do the compression check, as the plug hole is too small for my tester.

I took off the tank and used my "IV Bag" for gas, and the carb promptly overflowed all over the left side of the cylinder. Now I have to remove it once again! I put in the floats with the carb in situ, as I always use allen head bolts for the float bowl, but now I think I need to explore further.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/20/20 at 04:55:19

I put in the floats with the carb in situ..

Yeah,, standing on yer head,, probably not the most advantageous position for such work.
Removing and reinstalling the same float, of known proper adjustment would be a different thing..
Dont sweat the compression,, probably not an issue,, Unless after sitting the rings werent at all oiled, which is a real possibility.. But now that its been run, the walls are oiled,, hopefully no damage was done. OIling prior to starting would have been an ace idea..

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Dave on 09/20/20 at 05:12:58

I assume the battery is new - have you checked the battery voltage? The ignition system requires full voltage for correct spark....even a new battery can be defective and not provide the correct voltage. The weird part about a Savage is the battery can have enough voltage to run the starter - but not enough to provide good spark.

Did you replace the spark plug?

Do you know why the bike was parked? Was it running well when it was last ridden?

Why would you run a popping/backfiring engine long enough to blue the pipe? If the engine is not running properly and is not able to start and respond to throttle - there really is no need to run it for more than a few seconds before you shut it off and start looking for the problem.

If the next carb cleaning doesn't resolve the issue - I suggest you at least try adjusting the valves to confirm the timing is correct on the cam and that the valves have proper clearance. If the valves are not within a few thousands of having the proper clearance....I would suspect the engine has worn cam lobes and rockers - this is a common problem on engines that were run with oil having a low ZDDP content (modern car or motorcycle oil). I worked on a bike with 3,500 miles that had worn rockers and camshaft.......the owner used "regular" oil and would start the bike and let it idle often to charge the battery in the winter months, and this wore the camshaft and rockers out as a result of the low ZDDP level and the low oil pressure/flow that occurs at idle speeds (it also blues the exhaust pipe as there is no air flow to keep it cool).

Title: Re: Backfiring - All the time - Wide open Throttl
Post by ckahleer on 09/20/20 at 08:11:15

Before you reinstall the carburetor, use the IV bag to verify it is not overflowing while the carburetor is on the work bench.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Serowbot on 09/20/20 at 08:32:05

6F445E455F614D444D2C0 wrote:

The petcock was bad, so I replaced it with a K and L that looks like the factory piece.

Is this new petcock vacuum operated?...
I ask because there is a vacuum tap on the right side of the carb... if that is not connected or blocked you will have a massive air leak/lean condition.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by ohiomoto on 09/20/20 at 18:07:11

Assuming that no one crappity smacked the bike up before it got parked, a bike with 2k miles doesn't just have their valve go out of adjustment form sitting for years.

More likely is that the carb was gooped up form sitting, which is where the OP smartly started. There is a lot right there that needs to happen.

First, the fuel tank needs to be cleaned and the petcock need to be fully functioning. Let's assume any crap that might have been in the tank was flushed with the installation of the new petcock. BUT, is this aftermarket petcock functioning properly? And are we using the stock airbox? Aftermarket pod filters can be an issue.

Next, don't replace anything inside of the carb with aftermarket parts. Put the original floats back in or replace with new OEM parts. Make sure all of the jets are clean or replace with OEM parts. Make sure the main jet and pilot jet didn't get switched the the main air jet and pilot air jet that are supposed to be installed in the top of the carb. Make sure the diaphragm and slide are functioning properly (my best guess at what's wrong).

Stick with fuel the delivery issues.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/20/20 at 18:44:01

Just soaking one isn't all.
Gotta shoot something through the little passages. I like Chemtool, B 12, not cheap, but good
Absolutely must not let any hit an eyeball.
Ventilation is important.

And yeah, unless someone decided to mess with the valves and didn't Know how,, odds are, they aren't the problem.
They might need adjusted, but they aren't the problem.
Was the whole pipe blue when you first saw it?
If no
Then it wasn't doing that before.

Good questions are waiting for answers.
Whoever rode it last could help all of us.

The petcock was bad, so I replaced it with a K and L that looks like the factory piece.

How big is the inside diameter of the outlet feeding the carb?
Did you add an inline filter?

Title: Re: Backfiring - All the time - Wide open Throttl
Post by ohiomoto on 09/21/20 at 05:22:02

I improperly installed my slide once and my bike wouldn't go 20 mph in any gear. The butterfly valve opens, but the slide stays closed. Talk about lean.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Chris911 on 09/26/20 at 10:32:37

OK. I have the carb back off the motorcycle. Does anyone know how to set the float height?

Title: Re: Backfiring - All the time - Wide open Throttl
Post by norm92de on 09/26/20 at 11:08:03

If it were me I'd put a genuine Yamaha raptor petcock on it. You will eventually put one on anyway.

With the carb on the bench "completely level" devise a way to supply fuel to it. First it should not flood i.e. no fuel on the bench out of the overflow vents. Then with apiece of plastic tubing attached to the drain hole hold it up beside the carb. And with the drain screw open you should be able to see the fuel level. It should be level with the joint between the float bowl and the main body of the carb. If not you will have to bend the tab on the float to achieve this.

This job is so easy when on the bench compared to the bike. Remember absolutely level for the carb. :)

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/26/20 at 11:24:14

687771766B6C5D6D5D65777B30020 wrote:

It will be, ‘ok’ but if you’re trying it out of, say, an AR pistol with a barrel shorter than 14.5 inches, you’re going to see significantly reduced performance.

Did ya do that already?
What did it do? Was it low?

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Chris911 on 09/27/20 at 07:26:25

Success!!!

Per a bunch of replies, I took the carb apart once again. This time, I shot 2+2 (carb cleaner) into every orifice, let it soak, and then blew it out with my air line. I also noticed that I had not replaced the secondary jet on my first go-around.

With the carb installed, it now runs fine. It backfired a bit, and then settled right down, and I was able to take a ride around the block. It runs great. But when you roll off the throttle quickly, it will backfire. And I don't care! LOL

I can't thank you all enough for the suggestions.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by Dave on 09/27/20 at 11:13:25

614A504B516F434A43220 wrote:

But when you roll off the throttle quickly, it will backfire. And I don't care! LOL

Welcome to the benefits/curse of owning a big single with a carb. You cannot jet out that malady.....when you slam the throttle closed you are shutting off all the fuel except the idle jet circuit, and it cannot supply enough fuel for the high vacuum condition that you create when you close the throttle completely.

Learn to roll the throttle ON and OFF.....and if the backfiring occurs when slowing down or going down a grade - just open the throttle a tiny bit and the noise will go away.

Title: Re: Backfiring - All the time - Wide open Throttl
Post by justin_o_guy2 on 09/27/20 at 14:20:43

Or, you can smile a little smile and enjoy the symphony of Baarhdeblappblap blaaarh,,