74 Harley backfiring and popping

purplecatty

purplecatty

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Hey those who know about Haley Davidsion motorcycle especially V-Twin 883 (bored to .30 inch). Since last Febuary, It ran great and responsive. It was ridden approximedly 10th to 12th times mostly around the block on normal speed. Then suddenly, my friend informed me that his harley just acting up and it backfiring and popping. So to find out what's wrong. I decide to ride his Harley and it won't start on open choke during hot weather (It normally fires up happily on warm day with open choke). I switched to closed choke and it fired up. I opened it and it died. So I decide to close the choke and fired up and open 1/4 way and it stayed running but backfiring and popping. I drove on the street, it was lurching and popping. I bumped the choke to 1/2 and it was going so I throttle up and it was stalling but kept running, won't let me throttle up. Then on end of the street (the engine should already warmed up). I hit open choke and it died. So I can't figure out what's heck is wrong with his Harley.

I removed the air filter and it showed black film inside around the carb. I swabbed it with my finger and smelled it. It smell fuel. So anyone can give me a hint what's wrong? Is it a carb on lean or rich. His Carb is a Molsen type. Made in Japan and stamped above it is AMF-Harley Davidson.

I'm just Noob on Harley engine sorry!!

So Can anyone give us a suggestion?? If you had any similiar experience and solution, tell us!

Thanks
Catty
 
Yup, thought so. I had a gut feeling that timing was off. In my mind how did it happened cuz last Thursday, it ran like charm. Today, my friend took it and it faltered. I'm going to interrogate him what he did with it. Even Harley isn't mine but been "babysitting" his motorcycle for 5 months, fixing and ride around block every now and then to keep engine primed. I treated Harley like a baby and rode it easy and gentle. So I will find out what he did to it. He's a Harley noob too even he have own and ridden kawaski.

I do not have special tools to remove certain parts of V-twin. So I am going to have him to take it to his friends who fixes the Harley.

Catty
 
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Are the exhaust valves opening correctly? I once had one that was shut due to fuel/ash hardening into it. Got it cleaned and ran on perfect timing. The fuel leakage was also taken care of! LOL
 
SCBassist said:
Are the exhaust valves opening correctly? I once had one that was shut due to fuel/ash hardening into it. Got it cleaned and ran on perfect timing. The fuel leakage was also taken care of! LOL
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Ok I just looked into Harley Mechanic book and It showed it's all gear timed, no belt or chain.... So I figure that it's impossible for gear to jump one notche to get it out of timing. The oil reservior smelled like fuel. What you said is probably the correct one. I will let my friend know that Exhaust valve may be stuck closed. I may not be working on his Harley because I will be going on vacation. So He will have it towed over to his friend to have it fixed.

Thanks for the info!!! :lol:
Catty
 
I called my friend and told him about the exhaust valve may be sticking. He disagree with me and he ramble on blaming carbeurator, throttle cable, fuel filter, air filter and choke. I told him none of those cause those problem!! I told him cable been fixed and lubricated, Carbeurator is working fine and it's been rebuilt by previous owner But the throttle part of carb may need new spring cuz it's weak and can't pull back throttle cable, Fuel filter hose may be a little crimped on one side and maybe need longer hose to loop to carbeurator. Air filter have nothing to do with it cuz it's brand new. The choke is perfectly fine. He complained that choke "butterfly" was vibrating wildly while it's closed (Choke have spring on it's side to flex to allow some air in). I told him it's perfectly normal cuz it's two stroker! He disagree with me with everything else!! It was a heated argument. I pointed out it's the exhaust valve!! cuz if the exhaust valve is stuck, The fuel is being compressed thru the piston ring and into the crankcase and mixed with oil. The oil reservior is smelling fuel!!! The carb was backfiring and exhaust pipe was popping. He said then maybe it's the timing on distrubutor. I told him DON"T TOUCH IT!!! Hands off!!

Shush!! I told him to ask someone else who are more expert with harley engine!! Ask any HD guys in bars who are willing to check out his engine. I'm sure the guy will point the engine same way what I did told him. So I told him to tow his motorcycle out of my garage and park it at his friend's place because I'm going to go on vacation and locking down my house.

So It'll be his problem trying to blow his buck on carb, cable, spring, fuel filter, ect to try to fix the problem then I guarantee he'll ended up tearing apart engine. He think the motorcycle is a curse. I told him no it's not a curse, it's the valve!! simple as is.

Catty
 
When I cranked the engine. I covered the carb hole. I can feel strong "suck-suck-suck-suck" while the exhaust "blow/suck- blow/suck-blow/suck-blow/suck" on both exhaust pipes. It seem the exaust can fully blow brief suck. I am guessing the exhaust valves are either burned or dirty and it's not seating to valve seating well enough. Is that correct?

Catty
 
purplecatty said:
When I cranked the engine. I covered the carb hole. I can feel strong "suck-suck-suck-suck" while the exhaust "blow/suck- blow/suck-blow/suck-blow/suck" on both exhaust pipes. It seem the exaust can fully blow brief suck. I am guessing the exhaust valves are either burned or dirty and it's not seating to valve seating well enough. Is that correct?

Catty
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Okay, let me think about this a little bit. If the exhaust is fully seated, it shouldn't suck at all, it should always blow. Therefore if you can feel it suck at times, it would seem that it is not seating fully like it's supposed to. I would have to agree with you that it is correct.
 
purplecatty said:
When I cranked the engine. I covered the carb hole. I can feel strong "suck-suck-suck-suck" while the exhaust "blow/suck- blow/suck-blow/suck-blow/suck" on both exhaust pipes. It seem the exaust can fully blow brief suck. I am guessing the exhaust valves are either burned or dirty and it's not seating to valve seating well enough. Is that correct?

Catty
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The exhaust valves probably has worn out springs that should keep the valves closed during the combustion process.
 
That's what I thought! Oh well it's his problem. I will just let him know and leave it up to him to listen me or listen to himself. I just sent AIM to him that it's cheaper to rip head off and clean it or repair it then put it back on than buying carb, cable, and rest of the parts on right side of Harley.

Catty
 
Sounds like the fuel air mixture is not correct. Since tweaking the choke seems to have an affect it could be one a couple different things. Lets start with the eaisest first.

1. Change the Air filter.
2. Overhaul the carb.
3. Buy a Kawasaki :lol:
 
rockdrummer said:
Sounds like the fuel air mixture is not correct. Since tweaking the choke seems to have an affect it could be one a couple different things. Lets start with the eaisest first.

1. Change the Air filter.
2. Overhaul the carb.
3. Buy a Kawasaki :lol:
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He got a new air filter fairly recently

Carb been overhauled by former owner, It looks clean and squeaky.

He have Kawasaki, It's pieces of junk right now. I told him to throw it to Motorcycle scrapyard. Piston in engine is seized and rest of other been parted out and some stolen and vandalized.

It's the problem with exhaust valve, there are air leak and been backfiring and hard to start. I personally feel that former owner put together using old springs ect after cylinder been bored to .30 inches. So That why it's popping and backfiring. carb recently just had black film inside the hole. Oil in it's reservior is smelling gasoline too. Not too good..

Catty
 
****NEWS FLASH!!***

MY friend just cooled off and he went to bar and met with the Auto Dealer guy. He asked about his Shovelhead engine on 74 Harley. The guy told him the Shovelhead engine have bad reputation for fix fix fix fix fix. He was :eek2: about it and realized that his motorcycle is "cursed". The guy gave him the mechanic's ph number and his name that he fixes Harley cheap. He sent me AIM notifying me about the situation on engine. I sent him email cuz he logged off AIM, telling him to send it to mechanic and have it fix and sell it to sucker fast and hard (to college kids). :rofl:

I suggest him to ask the guy which Harley engines are "trouble free" or lest problems. or Go for Japanese V-Twin :rofl:

No wonder why it's problemic. It ran fine till I handed it over to him to take it to inspection and it faltered cuz of exhaust valve.

Catty
 
I checked sparkplugs on each cylinders. Left side sparkplug look "ashed" but look good(Normal and usable). Right sparkplug, oily look. I checked the gearcase, I smelled fuel mix with oil. I wonder does harley share engine crankcase oil w/ gear? Also Exhaust pipe from Right side is filmed w/ fuel.

What ya think :lol:

Catty
 
purplecatty said:
I checked sparkplugs on each cylinders. Left side sparkplug look "ashed" but look good(Normal and usable). Right sparkplug, oily look. I checked the gearcase, I smelled fuel mix with oil. I wonder does harley share engine crankcase oil w/ gear? Also Exhaust pipe from Right side is filmed w/ fuel.

What ya think :lol:

Catty
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It does sound like exhuast problem. Looks like the head will need to be pulled and the valve looked at. Might also need to look at piston and rings to make sure it's not damaged. I wouldn't be surprised if the rings at least needs to be replaced.
 
Secretblend said:
It does sound like exhuast problem. Looks like the head will need to be pulled and the valve looked at. Might also need to look at piston and rings to make sure it's not damaged. I wouldn't be surprised if the rings at least needs to be replaced.
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I agree with you. It need valve work and may need check piston rings.

Catty
 
purplecatty said:
He got a new air filter fairly recently

Carb been overhauled by former owner, It looks clean and squeaky.

He have Kawasaki, It's pieces of junk right now. I told him to throw it to Motorcycle scrapyard. Piston in engine is seized and rest of other been parted out and some stolen and vandalized.

It's the problem with exhaust valve, there are air leak and been backfiring and hard to start. I personally feel that former owner put together using old springs ect after cylinder been bored to .30 inches. So That why it's popping and backfiring. carb recently just had black film inside the hole. Oil in it's reservior is smelling gasoline too. Not too good..

Catty
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have a 74 sportster...if i leave the fuel petcock open,then fuel drains into crank case......check fuel level in tank before retiring at night....if the level is lower in the morning, try turning the fuel petcock to the off position....and obviousley change the oil
 
charliedone said:
have a 74 sportster...if i leave the fuel petcock open,then fuel drains into crank case......check fuel level in tank before retiring at night....if the level is lower in the morning, try turning the fuel petcock to the off position....and obviousley change the oil
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It's exactly what I have on his 74' Harley. I told him get a new petcock 4 months before Summer came. He didn't want to change it cuz he want a "classic look" !! It's an old fashioned petcock is a two valve on both sides and when you turn one or both (doesn't matter as long as one side is open and fuel will go thru.), it have bumps on sides that when you twist the valve, it "pulls" the needle inside to let fuel go thru. He have flaky rusts inside the tank and a pieces of rust flakes got stuck inside petcock needle, preventing it to close. That's what it cause fuel to drain from tank to crankcase overnight. I told him get a new one preferly a shut off valve type! He realized his mistake and gave up fixing his Harley. He's gonna replace petcock and change oil, remove rusts from gas tank by using BB pellets or handful of ball bearings and shake the tank. Then sell it to next owner.

Sheesh!

Now he bought Chopper to replace 74 Harley Sportster. He even offer me if I want to buy his 74', I told him no thanks cuz I knew too well about problems.

Catty
 
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