Backfire ?

[Mr.Sinister]

I have had a few backfires while starting . I recently put in a K&N . But this has happened before that . The other day it happend while downshifting with the clutch pulled in going down hill . Whats up ? Could I be a little lean ?

[M@Man]

Possibly, let me know when you find out for sure, cuz mine does the same thing when I decelreate.

M@

[Mr.Sinister]

I will have the carbs off this week or next week for rejetting . I will let you know . I am kinda waiting for some riding weather to do it . I will be on vacation starting the 16th for about 9days . That will give me some time to do it . I have always had a little popping on decele that is normal . The backfire is alot louder . It is not a pop pop pop it is a bang .

[M@Man]

I get the pop pop pop on decel but there is atleast one or two really loud pops.
Hey, if ya get the chance post a welcom to C@Woman under "Introduce yourself here..."

It's a nice day here, I'm gonna try and get some ridin' in.

M@

[fegs]

I had the same issue but went away once I rejetted the carbs.

[Mr.Sinister]

Any idea on why ? Am I to lean ?

[fegs]

I would think so. Mine had a backfire from new. This topic has been around for a while and agreement was that a lean condition will cause a backfire (it does on cars)

[Mr.Sinister]

Thanks .

[Machinehead]

Where's carb-boy?

I'll agree that it's prolly running lean, but a sure way to tell would be to run it hard for a few miles and examine the plugs.

Usually when a less restrictive filter is installed the mix is either richened via the A/F mixture screw or a larger pilot/slow jet is installed.

[Mr.Sinister]

I may check those pluds tomarrow . I ran her hard on Sat . What do I look for ?

[M@Man]

Is this the machine that's givin' you the backfire prob?

M@

[Mr.Sinister]

Once or twice . :wink_2:

[Machinehead]

Usually white-ish type of deposits indicate a lean condition.

You can google "spark plugs" and find a gazillion charts indicating what's what.

[Mr.Sinister]

Thanks , I will check it out !

[Machinehead]

Here's one link...

http://www.dansmc.com/sparkplugs1.htm

[Ghost_Rider]

Usually white-ish type of deposits indicate a lean condition.

You can google "spark plugs" and find a gazillion charts indicating what's what.

Machinehead,

My friend gave me these info about spark plug test, and wondering if this is the cortrect way to read the plug. Reading frm the tip can lead to a false result:

To do a proper plug test you will first need to buy at least 6 new spark plugs.

First using the old plugs ride the bike out to an open stretch of road. The engine must be HOT so you need to run it at least 10 minutes or more.

Once you get to an open spot where you can test the jetting change 2 of the plugs (1 in each cylinder) with NEW ones. It is important you use NEW plugs for each test

Now start the bike and as quickly as possible, not letting the engine idle ...get it up to top gear WOT (wide open throttle) at a high speed and hold it there as long as possible (at least 30 seconds or more) To keep the speeds at a safe level you may need to stab the brakes every few seconds but keep the throttle open. I usually test the main jets WOT and keep a 75- 80 mph or so speed by riding the rear brake a bit. While holding the throttle open, hit the kill switch and pull in the clutch at the same time. Make sure you do not let the engine idle or slow down or let off the throttle until it the engine comes to a complete stop.

Pull the bike to the side of the road.

Pull the plugs and put the old ones back in

If you want you can do all your testing in one outing.

Pull the new plugs and replace them with new ones again. Put the plugs you just tested in you pocket. Now do the same thing but this time test the jetting at 1/2 throttle, pull the plugs and replace them with new ones again and test it at 1/4. Make sure you do not mix the spark plugs up. Keep the pair of each tested plugs separate.

Now go home and check the plug color/condition.

Grayish/ light tan/coffee color = perfect

White =too lean

Dark brown or black =too rich

This test WOT is for the main jet. To test the rest of the throttle ranges you need to mark out the throttle grip for 1/4, 1/2 throttle so you can keep a steady throttle and test these ranges as well.

To properly read the plug it's best to cut away the threads of the spark plug so you can check the plug color. This is why they call plug testing a PLUG CHOP. I use a cut off wheel on a dremal tool to remove the threads down to the base of the insulator. If you don't cut away the threads you will need a good light and magnifying glass to see way down at the base of the insulator

What do you guys think?

[navillustoo]

Where's carb-boy?

MH,
It seems I lost my classification when the site was suspended last time, now I can't remember anything about carbs! Just kidding!

If the engine is popping out the exhaust, it most likely is from a lean condition. If anything has been done to either the intake side or the exhaust, the engine will most definitely be running lean. Normally, the popping can be alleviated by adjusting the idle mixture screws out a turn or so, but if the popping persists, there's one other adjustment that can be made before having to spring for larger pilot jets. Try raising the float level slightly. This will richen up the idle circuit enough to allow you to fine tune the idle mixture with the screws.

As far as reading plugs goes, a WOT test is not your best indicator of where the bike's A/F mixture is. Unless of course you ride at WOT all the time. Taking a WOT reading ONLY tells you about the main jets, 'cause that's all you're running off of then, the main jets. Taking a cruising speed reading tells you how your needles are doing, and that's what you need to be concerned with.
The best way to check your plugs is to install new ones, then ride the bike at your normal operating speed for a few miles. Then, without letting the engine idle, shut it down and pull the plugs. This will require that you find a safe place to coast off to the side of the road after you shut off the engine. I find the best way to shut her down is with the kill switch. Just roll your thumb up there and hit it while holding the throttle steady.
If the plugs are white or a very light tan, you're too lean. The plugs should have a light brown coloring on the ceramic insulator, down inside the threads. Too dark or black and sooty tells you you're too rich.

I hope this helps!

Brian

[Mr.Sinister]

I adjusted the idle screw you mentioned about a 1/4 turn and the popping went away . No back fires . This next week I will be rejetting and am sure to have more questions . Thank you everyone .

[M@Man]

So much for this thread, he fixed his problem. :disappoin

Way to go, Sinister, now all we have to talk about is Shadow's Ga--er uh Convention. LOL

M@

[Machinehead]

Glad to hear it is resolved, but if the idle speed is not within specs the carbs may need to be sync'ed. Balance them before, during and after any modifications to the exhaust/intake systems.

Way to go carb-boy :cheers:

[Mr.Sinister]

I will be in the carbs and pulling plugs and screwing with the pipes and intake soon . Thanks again with all the help .

[cryin'wolf]

you only state that this happens while decelerating while down shifting.... does it happen also while between gears upshifting? Over all my guess is yes you are running a little lean, but if your not getting a back fire on an up shift you can probably tune it out. (mixture screws) If it is happening on an up shift also look over your air box/ manifolds really good for leakage, propane is a good vacuum leak detector if you really want to test it all. You'll know where the leak is because the engine will accelerate. If there is no vacuum leaks, rejetting is probably your only fix.