Excessive backfiring?

[HackSawPyro]

Thanks fore the replies once again. Ive checked the carbs.. well.. actually, ive had them apart 6 times now. I really dont think its the carbs. Ive got an inline filter on each petcock, they are flowing good, and not collecting any rust or dirt any more. Checked all the flot levels, needle clip positions main jet sizes and what have you. It now runs fine at idle (with the choke off) but the back firing is still there (although it doesnt do it untill about 4k rpms now) The plugs when i pull hem are black (all 4 of them). I put brand new plugs in it 2 times now, and the same result (black plugs).

The bike sat for I dont know how many years (upwards of 5-7 im guessing) The only thing thats rotted are the insides of the master cylinders (Which i need new ones of if anyone has any laying around)

Is it possible to set the timing by turning the stator plate? I knwo the advance is working (You can see it move when you rev the bike) How do I check the timing, Thats what it sounds like to me, sounds like the timing is retarded to much. Doesnt make sense though, because the timing plate doesnt look like it has moved at all....

I just wanna get out on the road again!!

Thanks again, Chris.

[Shuriken]

Okay, it sounds like the bike is getting fuel. What do those diaphragm assemblies look like? Does the rubber have small holes in it anywhere?

When I wanted to check the timing on mine I went down to Autozone and bought a $20 dollar ignition timing light. You use them rarely, so they theoretically can last a very long time. They are a good investment because you can use them on whatever you want.

To check the timing, you simply remove the timing cover on the left hand lower side of the motor. You connect your timing light to the battery and spark plug lead. With the bike idling, you can pull the trigger and watch the marks line up. When you rev the bike you should see the timing plate advance. The timing light shows you how the advancer is working.

Connect the timing light and let the bike idle between 950 and 1050 rpms. Pull the trigger; the stationary pointer should line up with the "F" timing mark on the timing plate. If it does not align, loosen the base plate screws and adjust as necessary.

The manual states to "disconnect and plug the hose to the vacuum advance unit and rev the engine to at least 5,200 rpms. The timing should be 36 degrees before top dead center. If the timing does not meet this specification, the governor assembly should be removed and inspected and/or replaced."

So if you rev the motor and you're not getting 36 degrees of ignition advance, you know your timing is not going to be correct.

You need to make sure the cam chain has not skipped any teeth along with doing the strobe test. To check the cam chain situation, simply remove the gas tank and seat. Then get your bicycle allen wrench set and remove the cylinder head cover allen screws in the appropriate crisscross pattern. It takes about 15 minutes. You can then see if the dots on the cams are aligned with the raised arrows on the cam caps beside them.

On another note, when you remove the spark plugs and ground them against the cylinder head and turn the engine over, do you have fat blue spark on each?

Ben

[uk1.1s]

HackSawPyro - wrote

I eliminated the fuel octopus, got the timing advance hooked up, plugged the lines on the intakes for vaccumm (Where do theese go besides to the fuel octopus? there are 2 that are open, where does the other one go?

Bit worried that you have '2 open' vacuum pipes - tho' I'm not 100% sure what you mean.

3 of your carb inlet rubbers - between carb and the motor - should be blanked off with rubber plugs - or the famous rubber pipe with a tight fitting screw approach (who say's I'm a bodger ).

Carb 2 has a connection from the Carb Rubber to the octopus AND a connection from the Aluminium Carb Body to the vacuum advance mechanism. I've highlighted the coloured parts as I got that very wrong and it makes quite a difference.

If you have the inlet rubbers open then try covering with your fingers and see if theres a difference. In any case if you are running with them open - block 'em up. If it's not the main reason for the back-fire, it's got to be a contributing factor.

[Shuriken]

Indeed. If you are trying to run the bike without covering the carb intake rubber vacuum nipples it will run like crap. I have an '80g without an 'octopus' - thank heaven. To synch my carbs I have to attach the guage to all 4 vacuum nipples. I quickly learned the bike will sputter, pop, and run like garbage if they are not covered. Any vacuum leak on this bike, as with engines in general, causes real problems.

If the hose feeding the vacuum advancer unit is leaking the advancer won't work and your spark will be screwy too.

Also, how do the rubber intake boots between the head and the carbs look? Are they cracked and/or badly worn?

Ben

[HackSawPyro]

Ive got all of the vaccumm lines plugged on the intakes themselves, and the line from the carb going to the advance, the lines not leaking for that (new line w/ hoseclamps). The carb boots aren't leaking either (sprayed either when the motor was running, and it didnt rev up or die or change at all.) I still think it's in the coils, or something in the timing, long day at work today so i didn't really get to dink with it at all
The diapragms don't have any holes or cracks with them (checked them in the dark with a small high intesity pen light).

The dots on the cam line up (just as they would in a car)

I borrowed a spark tester (PLugs into the boot, and has another boot that you put on the plug itself, its sort of like a test light) to check to see if the motor's missing spark every once in a while or something. Im going to give that a shot tommorow on my lunch break probably.

I really don't think its a fuel problem, It's gotta be in the ignition somewhere!

ON another note, if anyone has any used (but working!) brake assemblies around that they are looking to get rid of, or have no need for, PLEASE let me know. Mine sat with no fluid in them, they are JUNK. (this is a really needed item, Can't GO, if ya can't STOP.)

Thanks again guys, you guys have been great, especially to this newb.
Chris

[skids]

Re: Pulling my hair out!!!

Backfiring out the carb is from running too lean or from a crapped-out exhaust system.

[i]Its backfiring out of the carb, and theres a loud pop from the exhaust.. this thing is REALLY starting to get to me!!!

Please help! [/B]

[newmaac]

Chris, What you are describing is a classic "lean pop".
Do you have access to a Color Tune kit? I would be willing to bet a substancial amount that if you tested the mixture, you would find it to be way off.

I don't recall anywhere in your posts where you mentioned your location. There are enough guys in this group, that there might be someone close to take a look. Sometimes a fresh set of eyes can be an amazing help.

For the brake components, what parts are you looking for? I have a Midnight Special that I am about to part out.

Mike

[Redbaron]

Carb Synch

Carb sync here is very important, i've found that after adjusting all else, a small backfire begins when i get the synch just a little off. I'd suggest using a meter or vaccum gauge to do this. One of the tips on the site is how to make a vaccum synchronizer. Worked well for me, and as always start simple and work to the harder things. HTH

[HackSawPyro]

Im located in michigan, near alpena. I dont have acess to what you called a color tuner or what have you. I dont see how the adjustments for the jetting could be off, 4 or so years ago i remember the bike crusiing around, and it ran like a raped ape. It was never adjusted or anything (jet sizes), If the motor is running lean, the plugs would come out white, right? Well, they doint they come out just as black as the night time.

Im looking for pretty much everything that has to do with the brakes, minus the rotors and the mouting assembly (mine is trashed the calipers and master cyls, and if your lines are good, i may as well put thoose on too)
I am going to be testing the coils tonight, and i will let you guys know, well... lunch times over.. back to the grind.
Thanks again guys
Chris

[Shuriken]

Inconsistent spark will cause a lot of problems. In my experience on my '80g it manifested itself in a terrible throttle response - sputtering and soft and mushy. What did I do to fix that? The good ol' pickup wire fix as mentioned in the maintenance section on this site. I found the pickup coil wires under the left hand side cover were trashed - I had an intermittent short as had been predicted by the XSives here online. After I fixed that the bike ran a lot better. When I fixed that and bought some better carb diaphragms from a generous XSive, my spark plugs started getting lighter and more predictable.

If you are getting backfiring after going through all of the stuff in the last 10 or 15 replies, start considering things you haven't already. Skids mentioned the exhaust. Carb synch and idle mixture could be way off if you don't have access to a colortune and/or a carb synch tool.

The reason I think its possible your plugs can be black even with a lean condition is because the carb has multiple fuel delivery circuits. If you are idling it there, you need to see if, when idling with a new set of plugs, they still become black. Then you need to put the bike under load and test the 2.5k range, 5k range, and wide open throttle range. Exactly when the bike is backfiring could be exactly when the lean condition results, on a particular circuit. Then when you back the bike back down to idle and kill it and examine the plugs they are black. Perhaps your idle circuit is causing the black plugs and the midrange or mains are lean. They don't recommend riding while the colortune is installed. However you may be able to get away with doing it just up the block and watch what color the combustion is (if there is any) when the backfiring occurs.

In my experience with the color tune: I can watch the color while turning the mix screws - the RPMs drop, exhaust begins to smell rich, and the bike begins to sound different - softer. Put them back and cause a blue combustion flame and idle picks up and the cycles sound better. When I set some to blue and some to orange or white (orange=rich, white=lean), the bike starts popping, at least at idle.

In my experience with the carb synch: If one cyl is drawing 5cm's of vacuum and the others are at 2.5 (for example), my bike runs like crap through anything above idle.

Both the synch and mix have to be exact on the 4-carb setup. If you have a bad valve or rings on any one cylinder, it will mess up your synch and mix.

About exhaust: I just asked a question about my Honda thumper XL500 on another list. Symptoms are when the bike gets hot, it begins to run really rich, and I can start having rich, mushy, but powerful backfires through the carb and airbox. Another lister on that board said he had the same thing until he fixed his crappy exhaust.

Food for thought.

Ben