Author Topic: simple diagnosis? (Read 4285 times)

HonderCB · « **on:** August 06, 2012, 09:32:12 PM »

Should start off by saying im a relative newb as far as motorcycle mechanics...

On my way home from a vintage bike night tonight, had put approximately 65 miles on the bike there and back (almost home) when all of a sudden it starts sputtering and popping.

My first thought is fuel is low, so i reach down and flip it to reserve on the fly. Doesnt fix it. I keep it pegged cause it acts like it will die if i dont. I limp in to town and as i come down off the throttle taking a turn and it seems to come back to life, until i get the rpms up then its back to sputtering. I try slowing back down and it doesnt help, its sputtering all across the full rpm range. I get all the way through town popping and sputtering and as i slow down pulling up to my friends garage it dies and wont start.

Spark? I pull out plug number 1, it looks ok. I put it back in the cap and hold it to the block as i hit the starter. I have spark. I put it back in, and for sihts and gigs i hit the starter... it fires up. It seems fine idling there, so i take it around the block, but it does the same thing again after i get down the street. I limp it back, dies in the driveway, wont start again.

Bad fuel? I pull the tank off and drain the gas out, walk a block to the gas station and buy some fresh fuel (not the same gas station i had bought previous fuel from). Pour it in, hit the button, starts up, but doesnt sound right, i dont even get out of the driveway this time.

Only thing i guess it could be now is fuel delivery in the carbs. i got tired of messing with it for the night and got a ride home. I'll go back tomorrow with a fresh mind. I guess i'll start by pulling the bowls off the carbs and cleaning the jets, anything after that and i will be lost.

Anybody else have any ideas or similar experiences to share so i know anything else i might check? I really was having a pretty good night until this, bike was running great and saw a lot of neat bikes. Oh the joys of riding a 35 yr old bike lol.

Thanks in advance for any input

scottly · « **Reply #1 on:** August 06, 2012, 09:45:11 PM »

How much gas did you drain out? How much did you put back in? Did you switch from reserve back to the on position? Please post pictures of all 4 spark-plugs before tearing into your carbs.

HonderCB · « **Reply #2 on:** August 06, 2012, 09:47:08 PM »

couple gallons, couple gallons, yes, and i will definately look at them all before i do anything else

scottly · « **Reply #3 on:** August 06, 2012, 09:52:09 PM »

Stock ignition?

HonderCB · « **Reply #4 on:** August 06, 2012, 09:53:07 PM »

yes, as far as i know

scottly · « **Reply #5 on:** August 06, 2012, 10:00:05 PM »

And the electric starter works fine all the time?

HonderCB · « **Reply #6 on:** August 06, 2012, 10:03:27 PM »

it seems to, i kinda wore the battery down though while attempting to start it to the point it wouldnt crank. 5 mins on the battery tender and it had enough juice to crank though, it will be on the tender all night. I always start with the electric started and havent had a prob in the year i have owned the bike

scottly · « **Reply #7 on:** August 06, 2012, 10:08:57 PM »

Post a pic of the plugs, and we'll go from there. Your problem sounds like it's a bit intermittent, which makes me suspect ignition?

HonderCB · « **Reply #8 on:** August 06, 2012, 10:14:53 PM »

i wondered about that too. the fact that it started back up after cooling down and nothing else changing made me suspicous of the electronics, but the way it ran had me thinking fuel. The more i think about it, ignition makes more sense. I'm glad i came on here instead of messing with it tonight. Hopefully i have some time to mess with it tomorrow, definately some time this week though. Thanks for the help scottly. Have a good evening.

CB750F2 · « **Reply #9 on:** August 06, 2012, 10:39:58 PM »

I have had similar trouble. I was able to trace the trouble to the "new" Daichi points that I had recently fitted. There was a loose rivit on one set which caused a high resistance and so acted like a very dirty set of points. The result was I was intermittently running on two cylinders. I suggest that you check your points for this condition. Disconnect the blue and yellow wires from the points and check the resistance across the points when they are closed. You should measure close to zero ohms. You will need a digital multimeter to do this. Pat

dave500 · « **Reply #10 on:** August 07, 2012, 12:12:39 AM »

if you think it has stock ignition as far as you kinow and youve had this bike for a year i think its about time you removed the points cover and find out?

phil71 · « **Reply #11 on:** August 07, 2012, 12:56:25 AM »

undervolt from weak charging can cause this too.. sitting will help the battery recover a little, but before long, you'll be back in the same boat.

HonderCB · « **Reply #12 on:** August 09, 2012, 06:09:11 PM »

Quote from: dave500 on August 07, 2012, 12:12:39 AM

if you think it has stock ignition as far as you kinow and youve had this bike for a year i think its about time you removed the points cover and find out?

Thanks for smart-a$$ comment, but it isnt needed here, try another thread, maybe someone else will like being treated like an idiot while trying to get help and learn something, i dont. I know what kind of ignition my bike has, i just dont know if the points are stock or aftermarket, now for those who are actually trying to help, heres whats happened so far....

First i drained and flushed the tank. There was some debris/ rust flakes in there, but the filter was clean. The flakes most likely came from the underside of the gas cap, as the tank has been sealed with caswell kit. (putting cleaning underside of lid on my to do list.)

I pulled the plugs, i didnt get a pic, but they looked like the bike was running a bit rich, but they werent too bad, cleaned them and put them back... didnt help

Pulled off points cover and checked gaps, they were off, but not much. reset them to .014 plus or minus a thousandth... didnt help

Re-timed ignition using timing strobe... didnt help

Replaced both coils with spares... didnt help

Replaced all 4 spark plugs... didnt help

Pulled the carbs (twice actually). Jets were dirty, and turns out were oversized (110 instead of 105). Must be because PO had pods on when i bought the bike, but i switched to stock box. This also explains why the bike was running rich i suppose. Cleaned the carbs, put in 105 mains, set screws to 1.75 turns out per the manual as a starting point. Cant get the things tuned because the bike still wont idle steady or long enough.

Bike is still running rough and fluctuating RPMS at idle, but it does start and run now, so i guess i am getting somewhere cause it would hardly do that before, it just doesnt want to run well. plus i am getting pretty good at pulling and re-installing my carbs (push-pull cables are a pain to get on) quickly.

The only thing i am still weary about is the points. How much spark am i supposed to be seeing between the contack points when they are open? 1-4 is sparking quite a bit, whereas 2-3 is sparking hardly at all. I still have spark at the plugs, but it seems wrong for them to not be sparking equally. Do i need to replace and start again from there?

Total cost so far... $11 bux for 4 D8EA plugs, and a crap load of frustration burning my hands tring to adjust the carbs... seriously... who put the adjusters on the bottom?! Not to mention the PO had a serious over-tightening problem, thank god for impact drivers.

HonderCB · « **Reply #13 on:** August 09, 2012, 06:16:33 PM »

oh yea, all the things i did werent necessarily in that order, thats just the order i remembered them in lol.

NewOldSchool · « **Reply #14 on:** August 09, 2012, 06:19:22 PM »

Sparking between the points?

I'm willing to bet everything that you sir have a bad condenser or two.

Had the exact same symptoms and replaced my condensers and BOOM perfect. Replace/adjust the points as well while you're at it.

HonderCB · « **Reply #15 on:** August 09, 2012, 06:26:06 PM »

yea, i knew one or the other had to be wrong, i just didnt know which was correct, i will replace the condenser on the sparking set of points tomorrow and see what happens, i have a garage full of parts bikes to rob from at my father-in-law's guess i picked a good wife, her dad likes the same kind of bikes i do

CB750F2 · « **Reply #16 on:** August 09, 2012, 06:30:42 PM »

Yes check your conensors and spark plug caps and do the check that I suggested in my first post. The spark plug caps should have either a 5k or 10k ohm resistor in them. Remove them and check with a multimeter on the ohms scale, While you have the caps off check the ends of the ignition wires for corrosion. You may need to trim back the cables to get rid of the corrosion. You may need the help of a friend if you don't have a multimeter or don't know how to use one. Pat

NewOldSchool · « **Reply #17 on:** August 09, 2012, 06:43:19 PM »

Quote from: HonderCB on August 09, 2012, 06:26:06 PM

yea, i knew one or the other had to be wrong, i just didnt know which was correct, i will replace the condenser on the sparking set of points tomorrow and see what happens, i have a garage full of parts bikes to rob from at my father-in-law's guess i picked a good wife, her dad likes the same kind of bikes i do

Awesome!

Good luck brotha, report back, I'm curious.

scottly · « **Reply #18 on:** August 09, 2012, 08:33:49 PM »

What do the new plugs look like?

HonderCB · « **Reply #19 on:** August 09, 2012, 10:08:08 PM »

still clean, havent run the engine enough yet to get any sort of color on them, i just put them in today. They did help the bike run better though, but i wasnt able to run it much.

dave500 · « **Reply #20 on:** August 10, 2012, 12:17:10 AM »

Thanks for smart-a$$ comment, but it isnt needed here, try another thread, maybe someone else will like being treated like an idiot while trying to get help and learn something, i dont. I know what kind of ignition my bike has, i just dont know if the points are stock or aftermarket, now for those who are actually trying to help, heres whats happened so far....

no sweat,at least we know it has points now,heaps of these bikes have had conversions of some sort over the years and will need different types of advice depending on what type or brand it has,like itll have different ohm coils and the way its wired etc,i wasnt being smart HonderCB.

Retro Rocket · « **Reply #21 on:** August 10, 2012, 01:11:14 AM »

Quote

Thanks for smart-a$$ comment, but it isnt needed here, try another thread, maybe someone else will like being treated like an idiot while trying to get help and learn something, i dont. I know what kind of ignition my bike has, i just dont know if the points are stock or aftermarket, now for those who are actually trying to help, heres whats happened so far....

What an ass of an answer from someone that was asking for help... The answer was common sense, maybe you should look at that as well...

HonderCB · « **Reply #22 on:** August 10, 2012, 12:13:42 PM »

haha RR, if your not here to help then you have no business. kindly stay away.

As for dave, i'm sorry. the way your post was worded it seemed like a smart aleck comment. i appologize and hopefully no hard feelings.

dave500 · « **Reply #23 on:** August 10, 2012, 02:07:13 PM »

no sweat.

HonderCB · « **Reply #24 on:** August 10, 2012, 02:50:20 PM »

just got back from workin on the bike at my in-laws.

when i got there my father-in-law had swapped out the points for a set off a donor bike, and it was running better, but still not good... still rough. I noticed it was still sparking pretty good on the 1-4 points, so i pulled the condenser off and swapped it for another and viola! the bike ran smoothly. I got the strobe out and re-checked the timing... still good. I did some tuning of the carbs, ran the bike a bit, pulled the plugs and they looked nice and light greyish-tan. Plug 1 had just a tad oil on it, the valves probably need adjusted... but as i mentioned previously, the PO had a SERIOUS over-tightning problem and i cant get all of the tappet covers off. guess i will have to try a chisel and hammer, otherwise cut them out, but its good enough to last the rest of this season, i'm just happy it runs now. I'm planning to pull the head this winter anyway.

Final verdict... mostly the condenser, but i think there was a big chain reaction of little things, because everything i cleaned/adjusted/replaced helped the bike to run just a little better every time. Thanks all for the help.

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Author Topic: simple diagnosis? (Read 4285 times)