'77 shovel backfiring

[Joeytats]

Have a 1977 flh 1200 ,, bendix zenith carb , running points. Just got the bike not too long ago and im currently going through it to right some issues . The bike is set up with an electric starter and kick starter . Both work fine . 2 kicks with the kick starter. Recentlythe bike was getting harder to start ,and on a ride the bike started sputtering when throttled and eventually started to backfire . Next time i started it , it ran for a good 15 second count and died . Would not start back up. Pulled the plugs and they were black and wet. Ok , so the weather is getting cooler so im probably running rich. The carb i have has the adjustable main jet . Not a whole lot out there on tuning these. Clockwise all the way in on the main jet and run it back 4 full turns , ok. 2nd mixture screw closer to the motor turn all the way clockwise and back off 1 full turn. Did this and replaced the plugs. took it out and got it up to temp and a quarter turn here and there and this thing was running great ! and then 10min down the road im sputtering and backfiring like crazy. Tried to dial it back in on the side of the road and it just would not dial in ... not far from home , got it there , tried dialing it in there and it just doesnt want to cooperate .Will start but still back firing ... Where to go from here ???
Appreciate any help , thanks !

[JBinNC]

You are fouling plugs, buy a box full. You have some tuning to do. You may need to check the float level and needle and seat sealing as well, but tune the jets for now.

The four turns out on the adjustable main jet is just a starting point. (As an aside, my Bendix ran best with the main jet adjustment only 3/4 turn out, at 4400 ft. elevation.) You need to fully warm up the motor, 15 or 20 minutes of riding time. Then set the idle mix and stop screws for best idle. Then start adjusting the main jet. Accelerate the bike hard in second gear and see if it "breaks up " at higher rpm. It should, with the main jet turned out 4 turns. Turn the jet in 1/2 turn, and test again. Keep doing that until the bike will pull in second gear to whatever you consider your red line. At the MOST, this exercise should result in the main jet 2 1/2 turns out, and maybe a lot less. (This adjustment is very crude on these carbs.)

Once you have established that, install fresh plugs and ride the bike in a normal manner. It should NOT foul plugs. From that setting, experiment and check your plugs until you get the exact main jet setting that works. An eighth of a turn will make a difference.

The above presumes that your ignition system is spot on: good points & condenser, properly adjusted, timing right on, advance unit good, plug wires, good coil. If you question any of that, start with the ignition first, and get right with God. Then do the carb adjustments.

Jim

[Joeytats]

Thanks Jim , did the timing yesterday and I feel it’s good ... actually great ! I dialed that zenith down to 2 full turns and before I could get around the block I had some slight backfiring ... dialed down one more full turn and still a bit of backfiring ... pulled the plugs and they were black ... I’m convinced there’s something wrong with the carb , jetting or its fucked up somewhere ... maybe I should pull it and rebuild.... maybe I should commander an S&S Super E ... decisions .....

[JBinNC]

Don't stop now. Dial it down another half turn and put in new plugs. (You did buy a box full didn't you?) At some point the bike will accelerate clean in second gear through the rpm range. Then you have a baseline to start tuning the carb.

Keep in mind that a weak coil or sketchy plug wires will cause missing and sooty plugs, irrespective of the carb adjustments.

The Bendix is dead simple, and has a venturi size well suited for a 74 cu.in. motor. If you decide to rebuild it, get the Bendix/Zenith factory kit ($$$). The import kits are a TOTAL waste of time and money.

Jim

[farmall]

Just got the bike not too long ago

Heed JB. I go through every carb when I buy an older bike even if it runs well since I want to know internal condition. I won't use the import kits either because the accelerator pump boots disintegrate, the pump leather isn't durable and the Viton tip on the needles doesn't last like real Viton so it's probably mystery rubber.

I also replace intake manifold seals when I do a carb so I'm starting fresh and I take care to ensure the manifold is aligned and a proper carb brace fitted. James seals work well for me. Avoid mystery cheap seals.

If you question any of that, start with the ignition first, and get right with God.

Truth, and I seal the ignition cover because humidity can get inside and quickly cause problems. I pull the points place to inspect the advance and springs. I carefully mark the points plate/cone cover interface with a Sharpie in three places, scratch a thin line down the center of the Sharpie marks and align per the scratches for easy starting afterwards. After reinstall I check with a timing light. (I finish mine by ear but I've been at it a while.)

I love points because they're cheap, very simple to troubleshoot, and easy to replace on the road.

With points I buy copper core V8 plug wire kits and any boots etc (depends on coil and kit) online then make my own solid wires. Cheaper than motorcycle parts and I always have spares though solids last many years.

[Tattooo]

Post some pics of your plugs when you get a chance...........

[TriNortchopz]

Sounds like your getting close with the carb settings.
When you checked your ignition timing, were the points in good condition?
Did you notice excessive arcing across the points while running? - small occasional sparks are normal. If so, that is a sign of a failing condenser(s), which can cause breakdown of proper ignition firing, especially under load...couple bucks to replace 'em.
Can test them if you want using your ohm-meter, ["Place the meter leads on the base and the terminal end of the condenser. The meter will go to zero end of the scale then smoothly climb to the other, infinity end of the scale (the battery inside the meter is charging the condenser). If you switch the leads the condenser will discharge then charge in the opposite direction. If the meter stays at zero the condenser is shorted. If it doesn't move it is open. If it stays in the middle of the scale, the condenser is leaky" http://www.hydra-glide.com/phpBB3/viewtopic.php?t=7208] but replacement is best option...and if no difference, you got an extra for next time...but they have a shelf life.

[brooklynbomber]

Zenith bendix carb works best when it’s off your bike and in the trash

[JBinNC]

Zenith bendix carb works best when it’s off your bike and in the trash

Bendix works best with a decent rebuild, the choke assembly removed, and an adjustable main jet.

My '72 FX would hit the ton, at will, two up, on the Western slope in CO. That's over 4000 ft. altitude.

Jim

[Tattooo]

Bendix works best with a decent rebuild, the choke assembly removed, and an adjustable main jet.

Yep ALL of those factory carbs work great if they are set up properly.............. Much better than a S$S on the street............. Way better gas mileage............

[Joeytats]

I didn't mean to abandon this thread and i have an update where im at . So i continued to dial the Zenith down until I only had a half turn left and was still running rich, plus had some gasoline dripping out of the mouth of the carb itself. I had a super E on another shovel here and decided to install it on the problem '77 FLH ... Carb came off a '78 FX that was running fine with no issues. So now the Zenith is out of the picture and sitting on my workbench. After installation the FLH fired right up and i felt was idling very smoothly . Took the bike off the lift and took it for a ride around the neighborhood without the air filter on in case i had to get to the air/fuel mixture screw for adjustments while riding . mind you the temperature here in chicago has been upper 40's low 50's . The bike ran smooth for the first 4 blocks and then had a little sputter in 2nd gear toward redline rpm. Shifted into 3rd and couldn't get more than a half throttle and the bike was coughing and sputtering bad. Came to full stop, back in 1st gear and the bike ran smooth until I got to a high rpm, Right around time to shift to 2nd , and i was getting some backfiring. Same thing in 2nd , pretty smooth up to high RPM and hesitation , backfiring, and sputtering... Brought it home and parked it... Going to replace the points and condenser with "Echlin" brand - Points (CS788) and Condensor (RR174). I hear its a good upgrade... coil maybe sketchy, also plug wires . This bike was sitting for awhile before I got it and was just filthy and covered in dirt & oil ... I'll try and post a picture

[capomorra]

main jet clogged??????

[JBinNC]

Sounds like you have an ignition problem masquerading as a carb problem.

Jim

[Joeytats]

Well, after replacing the carburetor , points and condenser, coil , spark plugs and wires we are running pretty smooth ! gonna replace the ignition switch on the dash next week ( no keys ) and start rewiring some things i found that may fail in the future . Love the old bike , it's gonna be a good one ! Thanks for your help , i'm sure i'll be posting up asking for more help in the future

[brooklynbomber]

Lovely motorcycle btw