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Discussion Starter · #1 ·
hi everybody, i’m new to this forum, and also new to motorcycles. so please help me!

bought my first bike a few weeks ago, a 1971 cb350 with 722a carbs. it has aftermarket air pods + short mufflers. bike ran fine the first week i had it. then it started to have throttle issues. i would give it throttle, and the bike would struggle. the acceleration would go in and out, like a jerking feeling, and i couldn’t even get it to go 45 mph.

so i bought a carb rebuild kit from ‘4 into 1’ that also included new floats. bought a new petcock, clear fuel lines, and gas cap seal from ‘common motor collective’.

i cleaned out the rust in my gas tank, installed the new petcock and fuel lines, and cleaned the carbs and put in all the new parts (the parts were not of high quality as the emulsifier tubes wouldn’t seat and would slip right out, o-rings wouldn’t retain there shape, and the floats didn’t float as well as the ones previously in the carbs. i followed the youtube videos from ‘common motor collective’ and put the carbs back together.

all the prior carb parts i replaced were original keihin parts with the ‘k’ logo imprinted, besides the main jet. the main jet that was in the bike when i bought it was 115, secondary was 68. the kit i bought came with 100,105, and 110. i started out with 105 since i found online that 722a:

main primary jet: 105
main secondary jet: 68
slow jet: 35
pilot screw: 1 1/8 turn out
float: 26mm

so i installed all the parts to factory specs. fired her up, and noticed both float bowls were leaking out the sides. forgot to mention that before cleaning the carbs, the original floats were set to 23mm, but the floats had no spring action on the needles. but the original setup didn’t have fuel leaking out the sides of the float bowl.

rode around the neighborhood and still was struggling. same symptoms, but now the bike seamed to run lean. had a harder time setting the idle, and when i’d shut the bike off, i could hear pings inside the cylinders. engine was also noticeably hotter.

so i changed the main jet to 110. bike seemed to run better, not as much stuttering/cutting-in-and-out acceleration. the throttle ran smoother, but wasn’t getting enough speed, felt under powered.

so i thought maybe i should try the original 115s. so i replaced the old o-rings on the 115 with the 100s that came with the rebuild kit and reinstalled the 115s. back to stuttering/cutting-in-and-out acceleration.

so i checked the spark plugs, and both were black telling me the bike was running rich. so i bought new spark plugs and noticed the difference in power instantly. also,upon reinstalling the right side spark plug boot, the wire came off with ease. dunno if that had anything to do with it, but i cut the wire, and screwed it back on till it was tight.

rode around the neighborhood a bit, with the acceleration still stuttering, and checked the new plugs. the attached pic shows the spark plug on the left and the one one the right.

can someone tell me if these plugs are lean or rich?

can someone suggest how to fix this throttle stuttering problem?

i’ve been tinkering with this problem for almost 2 weeks now, and only have 2 hrs to work on it each day, since a neighbor complained and i have to be quiet in the neighborhood by 8. i’m so frustrated. i’ve probably taken off and put back on both carbs 20 times by now. i’d take it to a shop, but with the current problem, i’d struggle to make it there. towing will cost me an arm and a leg.

i just want to ride the damn thing!!! please help!
 

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Discussion Starter · #3 ·
i checked with a multimeter to see how many volts the battery was putting out with the engine off. it was reading 13.1v. it's an antigravity 8 cell lithium ion battery, and i believe a fully charged one puts out 14.8v.

i took out the battery to charge it over night, and will put it back in the bike when i get home from work. do you think maybe because the battery wasn't fully charged that was giving me the issue?
 

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The one cyclinder is obviously running richer than the other. Im assuming those plug colors are after running it once. Idk anything about the jets on that bike but once you know you have the right ones, make absolutely sure that you cleaned the carb parts well. How far open did you have the throttle on your test runs? You might need to adjust the turns on the pilot screw if running bad at idle and throttle slightly open, but that doesnt affect the throttle when its open too far. The stuttering could be a bunch of things (dirty carb, bad gas, accelerator pump, igniton related issue, electrical wires loose ,etc. ).First of all, get good quality parts and the right ones. I would clean the plugs (or install new ones) , then change the plug wires to the other cylinder and see if it causes the same color. Do a compression test to make sure you dont have an internal issue if you can. Doesnt sound like the battery voltage is the problem but check to make sure the cables are tight. Then go from there
 

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Discussion Starter · #5 ·
yes, i only rode the bike around for 5-10 mins before checking the new spark plugs. the bike idles great at 1200 rpm, with no needle bouncing around, and no stalling. for the first 30 secs to a minute, the bike will run fine, no struggling. then it will begin to struggle when i give it any kind of throttle, from barely giving it any throttle to near WOT. i haven't tried WOT because i'm afraid the throttle will catch, and the bike will go launching forward.

i've taken apart the carbs and cleaned them each time i changed the main jet, and floats. made sure all the rubber o-rings are good on the jets and float needle seat, and that they fit snug. i fill up with 91 from Chevron.

side note: the acceleration struggling problem started one day when i went to brunch, came back to put my key in the ignition, and noticed it was already in the on/ignition position. (something's wrong with my ignition key switch since you're not suppose to be able to remove the key when it's turn to the on/ignition position) so the bike was sitting in the parking lot with the ignition in the on position for about 45 min- 1 hour.

first thing i did when i got home that day, was check the volts with the mulitmeter, and it read around 13v, so i figured the battery was okay right? bikes run somewhere around 12v right? that's when i thought it might be a fuel problem and went thru all those steps to try to fix it.
 

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Discussion Starter · #7 ·
so i got home and the battery was fully charged at 14.3v. i put it back on the bike and hooked up the terminals, and did another reading, and it drop down to 13.4v. started the bike up and rev’d to around 3k rpm while reading it and it slowly climb up to 13.6v.

am i suppose to keep reving it until it climbs higher?

as i’m reving it in neutral, the bike is doing it again. cutting in-and-out of acceleration. i don’t even need to ride it around the block to know it’s hesitating.
 

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I hope you still have the old emulsifier tubes. In fact, you need to use all the OEM brass parts that you can. Rubber bits in these kits are usually not as good as they should be. For example, there is a guy called Randakk who sells very high quality repair kits for gold Wings and other bikes. He recommends using the old brass parts and replacing the O-rings and such things with his high quality Viton O-Rings.

That is as much as I can say without violating forum rules
 

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Discussion Starter · #10 ·
the video i posted is with all the original parts reinstalled. the only things i used from the rebuild kit is the main primary #110 and secondary #68 jets.

i was thinking about buying a rebuild kit from ‘common motor collective’ as their kit is priced a little higher at $25/kit, but doesn’t include floats.

most of the original parts are okay except for the #68 jet which is a bit corroded, and the floats don’t have any bounce on the float needles.
 

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I would check two items, One the petcock if not a original HOnda model, I had this as same issue on a CB 450 and it was the petcock while on reserve could not provide enought fuel flow under any load, Second as you left the key on did you do any harm to the coil if you had current flowing from the battery and one set of points was conducting current thru the primary coil side to ground, Coil issues and insulator break down can cause irregular running under any load as it is harder to produce a spark gap jump with more cylinder pressure, IE under load. I had a coil issue that was causing sputtering under any type of load.

Good luck
 
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