pin in carb keeps bending

[mxwannabe]

Ok I have 1979 rm100 and i have been trying to fix it up. It ran fine until the crank bearing shot. so it sat around for about six month until my friend gave it to me to fix up. so I got a new carb and it ran fine for awhile. all of a sudden it stop running so I looked it over and the pin in the carb was bent horablly. so i bought a new carb on **** and installed it. but after starting it once it it died and the pin was bent again. The only thing i could think of that was bending it was backfires. Eversince the crank went it has been backfiring. would that be enough to bend the needle. anyhelp is greatly apprecciated.

 

[originaldirt]

I presume that the "pin" you are asking about is the carb "needle" . I have never seen one bend except from mis-handling, or vandallism. I can't imagine that the force of any backfire from a mx 100 would bend the "needle". Sumpthin ain't makin sense here. There has to be more of the story. Is there an air box and filter on this bike?


Why keep buying whole carbs when the crank is shot????????????????? Carb parts are available in the aftermarket, and no amount of carb repair will fix the crank/seal/bearing problems. Fix it or forget it. Don't buy more carbs.
OD

 

[mxwannabe]

the crank is not shot anymore i repaired it. after the repair it would start up fine but no idle, also when i started going it would run for awile and then start bogging and backfireing. then it wont start until it cools down.

 

[originaldirt]

If the rebuild was done correctly with new crank seals, and piston assy. the timing must be out. Probably too advanced. Could also need new reeds. Did you check them? 2-strokes don't easily backfire with the timing set correctly. Also bad reeds would make it hard to start and it would not idle or run very good either.
OD

 

[mxwannabe]

well i couldn't replace the gaskets cause, well lets face it 1979 gaskets aren't easy to find. and i am not exactly rolling in cash being 15 and all. would bad timing bend the needle?? what could do that. two different carbs have bent two different needles. the only thing i could think of was the backfiring. there are no where marks in the carb so i dont thinks its rubbing. i have no chance of buying a new bike so any help is greatly apriceated.

 

[2stroke]

Hmmm. thats weird. We had an old RM 80 that developed a taste for air filters once, you see we put some dumb velocity stack from a KZ1000 on it and stuck a piece of foam in it, and Ill be damned if the thing didnt suck the foam in, chew it up and spit it out.
(And kept running) the needle didnt even get tweaked then, so I cant imagine what could be bending the needle on your bike!
I know where your at with this thing, Ive been there. Hell Im still there, as far as being on a tight ass budget, and Ive done some weird stuff with bikes in my youth and even today, but Ive never heard of this one!
IVe re used gaskets plenty of times.
I can see if the needle got bent, and you bent it back that it would not run quite right...if it was not perfectly straight you know....
Hmmmmm.....

 

[YZ165]

When you put the top back on the carb, was it hard to compress the spring far enough to get it to screw back on? If so, there's you're problem. Make sure that the neddle is going into the hole at the bottom of the carb. There should be little if any resistance to the slide going down. Sorry if that's harsh, there's just not much else that could be happening. YZ165

 

[handywork]

Sounds like you have a timing issue first,and I have had backfires caused by hotspots from carbon build up.But do timing first.As for the slide needle,I think it wasn`t seated properly when assembled.Put slide in and guide needle with fingers helping from rear of choke,before even screwing down cap.It`s a Mikuni and I`m guessin one that has a screw down plate over needle clip and under spring,as in other ones the plate isn`t secured to piston slide or they use a "W" shaped clip and if the needle dont go in it just pushes up and pops the clip or the plate compresses spring.Also check your adjustment on cable as it should be adjusted so the needle don`t come out of jet,bottom of slide not dissapear from sight when looking up rear of the choke.

 

[handywork]

Sorry,just looking back I missed the bit in the thread about overheating and being able to start it when it cools.Heat will cause joints to seperate,and a weak link could be a gasket failure due to reusing and imperfections brought about by bits sticking to either surface when you pulled surfaces apart.But check timing before you pull it down.And if it`s a seal/gasket failure you understand that you will have to pull it down either before or after the bike leans out enough to get really hot and do major catastrophy.And if I can rebuild a 80 model yz50 and a 78 model yz80 and find gaskets in rural Australia,why can`t you in U.S. Base gaskets can be made with minimum fuss and even if you can`t get the right part number for head gaskets,The capacity is the same on how many air cooled RM or same bore diameter of how many air cooled 2 stroke machines,improvise.No such thing as "I can`t".The crank seals should have a number on them,Suzuki ain`t got none,well go to CBC Bearings,SKS Bearings or such,big multinational companies like them have got heaps,who do you think supplies motor corporations,they will even be cheaper as no overheads because they aren`t put in a box marked SUZUKI,hell why your there get all the bearings for your bike too,and your dads car.

 

[mxwannabe]

thanks for all the replies. i havent had time to work on it latley cause of school. but when i do i will see if these suggestions work