I recently bought a wrecked 96 F3 (unknown miles,no gauges) but,anyway! Long story short... When i got the bike it wouldnt start and sounded rough while attempting. So i broke it down and pulled the fuel pump and filter(filter trash)and cleaned the contacts in the pump and put it back in(it began working)
So i sprayed the carbs with carb clearner and hooked up the fuel lines and fuel pump and left the carbs open while proping up the tank. I connected the fuel line and pump and all that so i could try to start it with the spray and see if it will continue running under its own fuel. Well,it worked and after a little adjusting and all that stuff its good to go! BUT!... It has a strong thump(like a 650) when idling it goes " thump-thump-thump-thump...you get it lol. When i twist the throttle it smooths out slightly but still has it. Twist it hard and it sounds good. I dont think it has a knock because the "thump" doesnt get louder as you rev up. The exhaust is complete crap!! It looks like someone taught themselves to weld on the pipe. While idling i removed the exhaust(down-pipe+muffler) and it didnt change it. My question is...is there anything internal that can make it sound like that? I drove it today and it drives fine.but it does somehow idle its self up during riding. When i stop i have to turn the idle back down. Smell kinda rich but it does t smoke or leak at all. Im planning to change the plugs and wires.will that help? Sorry for the extremely long post! Im new to the forum and happy to be here!!

 

by any chance do you have a vid of it? when anyone says "man, it sounds like a twin" or in your case a thumper - it always says to me that it's missing on a cylinder - which wouldn't be that out of bounds considering you bought a bike that was a little rough. and it could be intermittent with dirty carbs and what not.

i would bet that before anything internally was wrong. and if you youtube some vids of guys with knocks on cbrs - it's unmistakable as anything but an internal problem. it sounds like someone's hammering a piece of steel or tin.


have you checked the plugs yet?

if you have an infrared gun, an easy way to tell is to just shoot the gun at each header. all the headers should be running around 350-400 degrees - and a missing cylinder will be running at 120-150 or so. it's a great investment - it'll save a lot of headaches - and it pinpoints which cylinder is having an issue. so it could tell you which coils, which carb, which spark plug, etc - for anything in the future. or if you don't have an infrared gun, you could do the squirt bottle trick. water will quickly evaporate off the headers that are running - but it wont off a misfiring cylinder.

and i would definitely pull the carbs apart and thoroughly clean them up. especially with ethanol-ed gas, all the jets and float valve needles could easily get gummed up if the bike has sat for any time at all. and remember in '96 - there was no ethanol gas, so those rubber lines can't handle the extra strength of the ethanol

 

I will for sure try the "squirt trick" . Also,thank you for your reply/advice!! I will shoot a video of it in the A.M. The plugs? Yes i pulled one plug wire( when standing over the bike,Looking down on the motor,from left to right 1-2-3-4,i pulled 3) it was nasty brown and did not look like it was healthy at all! Also,the carbs... I've heard that messing with carbs can be a very annoying/sensitive ordeal! Meaning its easy to mess up. I'd love to clean them and the jets and all that.

 

Forgot to ask... Out of curiosity,what would my options be if it were a cylinder problem? I did put some fuel treatment in it.cant remember the name(blue bottle&ue liquid) i think enzym? Or similar. Also,the k&n filter ugly lol. Smells like oil and gas and hold up to the light and hardly no light gets thru and its almost all black. Bad plugs/wires.bad air filter.dirty carbs.possibly using fuel treatment too soon... And possible cylinder problems? Damn! Sounds bad...

 

no, carbs are easy imho. ya, there are a lot of parts, and ya you don't want to mix them up - but almost all carbs out there are the same basic design. once you do it once, you'll have a good understanding of how they go together. it's best to take them inside, and do your work on a towel on the table. you want to make sure you drain the gas first (obviously), but after that, it's nice and easy when you're sitting at the table or workbench.


i'd say its either carb related (a clogged jet, or a gummed up needle valve) or plugs/coils because the bike's in a little rough shape. but as for the motor, those f2/f3/f4 motors were bullet proof. so i would hesitate to say it'd be internal damage of some sort. it's not that there couldn't ever be something wrong - it's just a carb/electrical problem would be more common and much cheaper to fix - so that's where you should start in order to diagnose the problem. it should definitely sound like an i4, and not a thumper.


with the squirt bottle, make sure you wait a min or 2 so the headers get up to temp. but you'll see, the water will almost instantaneously on running cylinders - and it will sit there on the non running ones.

 

Ok i have a video of it running/idling but i cant figure out how to post it! But,thanks for the encouraging info on the carb work! This morning i tried covering the muffler with my hand to see if it helped,i think it kind of did help. Something i have not thought of is,could it be a worn out header/exhaust problem? Can an old exhaust system cause weird sounds(combined with needing a good tune-up/cleaning)? Sorry to keep asking you so many questions,and i appreciate all of your advice/help!! Thanks alot! Aside from that... How hard is it to fit F4 wheels and fairings/headlight to an F3? I noticed spicymeowmix posted about how to convert gauges from F4 onto an F3...

 

OK I've cleared you to use all the facilities. We vet all new people to keep the spammers and undesirables out. LoL
Look in the new member area for the how to on posting vids.

An exhaust with holes in it can have quite strange effects on the performance - leaks cause whistling, humming, in fact all kinds of noises.
I'd be inclined to check that you're getting good spark on all cylinders and then check your idle jets - a blockage will cause the bike to only run on three...............

 

Awesome!!! Thanks alot guys! Yeah when i come to a stop i have to idle it down a little bit,why i dont know! But i just drained the tank and filled with fresh gas(no treatment). I have not a clue of how to go about cleaning carbs and or jets or idle jets! To me that Spanish! But i need to learn the ins and outs of my own bike! So, thank you guys again for the advice/help! Plugs are for sure bad,wires also! Carbs are dirty(literally you can see it) the exhaust is garbage! Sounds like you guys gave me a great list to start with!

 

oh for sure an exhaust leak can definitely make strange sounds. if the pipe has been off and on, off and on, off an on, not torqued enough - and a dirty old copper press washer could certainly make an exhaust leak - which could really make a weird sound - and it could make the motor sound like a thumper too.


basically, you can completely disassemble the carbs with a flathead and phillips head screwdriver. take pictures of what goes where, all of the jets will have numbers on them. draw diagrams to help you remember along with the pics. its very easy. plus im sure that if you search the forum, you'll find many disassemble and reassemble threads about carbs. remember, the jets will have different numbers and what not, but it'll all basically be the same. so if you can only find an F4 thread about carbs for example - that's okay.

 

Sweet!! About the exhaust...it can be taken off and on without any effort! The bolts/clamp is rusted and striped. So its not at all secured onto the bike. When i finally get a picture/video uploaded,you'll see what i mean. Im gonna tackle the carbs on my next off day. Whats a rough estimation of time it takes to break down and clean carbs? Im above average with mechanical/electrical stuff. I.E. disassembling,fixing and re-assembling bike parts! I'd be lying if i said im not a little intimidated by the idea of digging into a major component that operates the bike! But if i follow whatcha said and prep and take my time i should be ok. New question...what wheels fit on a f3? Can i put on a f2/f4/f4i/ Yamaha,kawi,Suzuki etc etc?