Idles for 30 seconds strongly then just dies out

[Noidea]

Hot dam well I'e been working on this beast for a while now I've done a bunch of stuff related to the carbs and leaks that I fixed. I cleaned carbs out once again then bought a chemical dip for them left em in there for about 15 hours took them out and they looked crispy also did this too all the mini parts jets and stuff of course everything looks clear to me no clogs or anything. Then I fixed the oil leak I was having (one bolt is missing because when i removed the bolts they all broke off into the engine and the very last one i used the extractor on it broke off into the bolt so i fixed that leak) and my petcock leak i was having all i( did for those was switch out the gaskets and get a new bolt to put into the gas tank with with thicker threads and walaah no more leaking.) I then changed the spark plugs put new ones in. After I got the oil back into the bike and everything set up did a cold compression test just to double check they were both at 145 so i figured all good to go. when I start her up and she idles for a good 30 seconds strongly then just dies out of nowhere as usual same problem I was having before. Sometimes if i hold the throttle down for another 30 seconds or so and have the rpm at 1500 it'll stay on for 2-3 minutes and then die out once again. I don't believe my problem is in my carbs or my engine anymore Im convinced its something else. I check the spark plugs cause before they were both fouled and now to my attention the left side is clean but the right side is fouled with carbon. WHatt givess? Also i noticed two things the Rpms sort of stay a little bit up even when the engine is off then after about 20-25 seconds they go all the way back to zero and when it is running its sort of changes noises at times sometimes it more intense and misfires or its just normal and sounds as it should. Also out of the left carb going into the air filter when the bike turns off there was a some smoke not sure if this matters or not just the more the merrier in regards to information i suppose. i would put a video if i could but it doesn't let me You guys always pull through and offer great advice anything will do. Was thinking a possible electrical issue? Maybe an ignition coil fouled up or something. I Know i wrote a lot here probably a pain to read through but yeaa thats what im up to at the moment not sure where else to go stilll researching just curious thanks guys!

 

[Bob Kelly III]

ok.... it starts and runs for 30 seconds then dies....
that is just about long enough to use up all the fuel in the choke curcuit..... it sounds like the problem is in the passage way in the float bowl
.... are you positive that passageway is clear ? can you blow air through it and get it out the other end ?
on the BS34CV carbs the passage way I am talking about is in the bowl itself , a hole that the tube goes into from the carb.
that hole in the bowl has to go through to the bottom of the float bowl .... mine were both plugged so badly that no cleaning fluid would clear it out... I had to use a sharp wire and twist it back and forth till it finally penetrated and went in another 1/4" then I could squirt carb cleaner in it and it finally came out in the hole in the bottom of the bowl.( inside the bowl)
sounds like your getting it.... however I do hope you removed all the rubber seals before you gave it the 14 hr soak treatment....
there are rubber seals around the float needles and in the choke plungers and the throttle shaft butterfly's those seals are critical
too..... and I believe there is a tiny seal under the idle-air screw with it's tiny washer.
..... one thing at a time !
if you tear into the bike fairly soon you'll be at a point you don't know where the trouble is because it's all over the place...
refresh our memory and tell us what bike it is and perhaps the others will dive in and help again !
...hang in there ! You can do it !
....
Bob..........

 

[Noidea]

Hey bob thanks for the response I before when I checked I sprayed everyhole and made sure there was a clearing for all of them last time one of the air bleed holes were clogged and I cleared it with an air gun. I have bs38's I believe my bike is a 73tx650. Yesyes I removed all the gaskets and rubber from the carbs made sure didn't have the choke mechanism in their either. However I didn't know there was a tiny washer for the mixture screw I never saw any should probably check on that. At the moment I don't plan on going into the engine or anything like that seeing as thought its in good condition thanks for the kind words I'm trying and just taking it slowly and trying to be patient despite the great weather and wanting to go out and ride I'll get it soon enough

 

[gggGary]

Throttle shafts have rubber seals (or they did before the 15 hour chemical soak)
could be fuel, ignition, oil fouling. Pull the plugs right after it quits, wet or dry? wet fuel or oil? Have you set valves and cam chain?
If they are dry it points at fuel, wet with gas, points at ignition. Wet with oil well you can guess that one.

 

[Bob Kelly III]

Hay Gary ! are there tiny O-rings on the BS38CV carbs ? I know there are on the 34's but not sure about the 38's might save him the worry !
.... Noidea.... Does the bike run ? can you Keep it going or does it flat out and die and not want to go ever again type thing ?
if it just quits the only thing that can change is the fuel so you wait a long while and it starts up again..... that points to fuel starvation !
....I bet you'll need to replace throttle shaft seals now buddy that 14hr soak will have destroyed them for sure !
....
73' has points ,so we don't have to worry about intermittent TCI stuff ! LOL
.... here's a check you can do to try and determan what's up.....
start the bike ( choke on) run it till it dies but try to keep it going..... after it quits turn off the gas, the key and pull the spark plugs like Gary said... check the plug electrode for dry or wet conditions. sense you have the plugs out put them back on the spark plug lead and ground them on the head turn the key on and check for spark....
.....
I have seen coils that will spark for a few minutes then quit.... after a bit they will spark for a few minutes again then quit.... those are bears to find but it is possible that is what we're looking for ..... to discover IF the coil is doing that ... it's doubtful but possible.
if you still have spark at the plugs after it dies on you then it MUST BE FUEL.... it's either not getting enough or perhaps it's getting way too much....
Spark ,Compression,Fuel all in the right order and it will run....
....
if your points are not adjusted properly it can cause the engine to not take throttle , it won't rev up at all....
I think you already went through the points and timing so I think we can eliminate that. please confirm if you did the points and timing or not !
.....
I think you have a fuel issue..... are the floats set to the proper height ?
..... Bob...........

 

[meanEG]

I would make sure the bowls aren't going dry. After 30 seconds maybe it ran out of gas. The petcock could be clogged or fuel line. Just an idea.

 

[peanut]

well Bob seems to have got it all sorted so good luck

 

[Bob Kelly III]

my bike will run for a good 2 minutes without the fuel turned ON ! so I don't think it's an issue of running out'a fuel ....from the petcock
and I don't think a 72' has the vacuum petcock ....monstrosity on it ! LOL..... ( leave it to engineers to come up with something needless but functional ! )....HA !
I'll wait for his report of Spark Afterward ( after it dies) and plug condition before I venture a further guess ! LOL
.....peanut ...glad your here ! I value your input !
Bob..........

 

[Noidea]

Yea in reponse to the spark plugs they are dry after the bike runs just the right one is fouled with soot. The bike does run and i can keep it running if i hold the throttle down once i let go it might stay on a little longer or straight up die out usually if its warm itll stay on and die if coldf after letting go of the throttle. Yea guessing im gonna tear through the carbs again now and see whats up with the seals Is there a diagram I can see or anything like that regarding the seals cause i wont know whats missing if its not there.(

) i tried watching this video as reference but I feel as though there are probably certain different pieces in this one that i may not have like washer and etc. I should make sure I have the seals or order them if i don't before I keep trying to start it. and yep my floats are set to the proper height as well 2.5mm or a tiny bit less than 1inch is what i have them set to. I checked the spark by just grouding them and pushing electric start see if there was spark thats all i knew how to do it for testing they're both giving me spark. Hope that was what you wanted me to do . But yea if you guys could tell me where the seals are located that would be neat all i have are the 2 cups on the side of the carb I don't have any other seals within the throttle shaft besides that.

 

[Bob Kelly III]

Noidea: Have you done the dead cylinder test yet ? the one where you adjust the idle air screws for the highest idle ?
on both cylinders ?
....
Bob..........

 

[Noidea]

No I have not I'm assuming i should probably get that done

 

[Noidea]

Both of the exhaust are hOTHOT though so im assuming they are both firing.

 

[Bob Kelly III]

ok both cylinders firing is a good thing ! mine had one that didn't want to fire at all ....but that's another story !
what is the lowest RPM you can get it down to without it dieing ?
remember 1200RPM is what the idle is supposed to be set at which feels fairly high for an idle..... I think mine is at like 800rpm
YES DEFINITELY DO THE DEAD CYLINDER TEST and get those idle air screws adjusted it will probably solve all your problems !
..... it sounds like the idle air screw passageways are blocked in the carbs, but if I remember correctly you took them apart several times now and cleaned them and made sure they were clear.... so lets assume they are for a moment and go from there...
....
set the left carb idle adjustment for the lowest RPM you can get without it dieing a bit more won't hurt at all just so it don't die on you...
now with the engine warm pull the left spark plug and leave it in the sparkplug lead and use a pare of vicegrips to clamp it to the head if you can.... ( you don't want it falling off with the vibration) make sure you can turn the right carburetor idle air- screw with a short screwdriver ... then start the bike ..... it will sound horrable pushing air out the other cylinder and it will be loud .... it should idle
on just one cylinder with no problem turn the idle screw to where its the lowest RPM you can get without it dieing.... now adjust the idle air screw for the Fastest idle.... you may have to go a long way or not... it doesn't matter you want the fastest possible adjustment of the idle air screw.... lower the idle on the left side of the bike again and repeat those steps again..... getting the fastest idle you can by adjusting the idle air screw in the front of the carb.( I am doing this from memory of my BS34CV carbs they are slightly different
so where ever the idle air- screw is ! that's the thing you want to adjust ! LOL
you don't want to take an hour to do this, so have it straight in your head what you plan to do before hand....
Once you get the idle air screw adjusted to the highest speed for the slowest idle stop.... give it a rest and prepare to do the same exact thing for the other cylinder..... just put the plug back in and pull the right one out and clamp it to the head.
then do it all over again for the left cylinder ....don't let the bike get too hot.
that is the dead cylinder test in a nut shell it's purpose is to get the fuel mixture at idle just right ! now with both cylinders running at just right mixture it shouldn't die out on you .....
if you find that adjusting the idle air-screw " has no effect at all" the carbs are dirty ! and need to be cleaned better ! or the float level is way off....
I am not that up on the BS38CV Carbs ...so there will be some differences but the idea is the same adjust the idle air-screws to get the highest RPM at the lowest idle setting....
no matter the engine or the carb for that matter, setting the idle air-screw is done the same way some of the newer lawn mowers don't even have an idle air-screw so you are stuck with the factory setting !
they tried something similar with my 83'xs650 in that they put brass plugs over the screw so you couldn't adjust them !
i had to drill a hole in them and pull them out with a screw ! your 72 won't have that problem they built them right back then ! LOL
.....
another thing that could cause the bike to die at idle is the point gap being too wide but I am assuming you set the ignition correctly before all this !
.....
once that is all done NOW you need to synchronize the carbs static synchronization is only good for getting it going... you need to do it more precisely for running it and using it !
but you know that already !
....Good luck
Please let us know what you run into one way or the other !
....
Bob.........

 

[Noidea]

Hey guys just wanted to update its been a while. I would make a new thread but dont remember how to do so. I managed to get her running with idle and all due to overlooking something stupid within the carbs I didnt have the butterfly plate open at all during idle. I was watching a video on bench testing the carbs and saw that they should be set to have a sliver of space when at idle to allow air and fuel to pass through silly me glad I got it figured out I also realised that on the carbs the pilot jet was bigger than spec so I got all spec parts for them and the spark plugs are looking clean when she runs & WAHHALAA there is idle. Only problem I have now is it that when its hot it wont kick over and I looked it up and realized its due too weak spark. So I'm gonna check the coils out see what kind of spark I get when the engine is hot and follow the other threads with people that have similar problems. I couldn't really find any info on the measurement of the opening during idle if any info on that it would be helpful although it probably depends what setup your running however mine is straight stock. Lastly the decompression/starter lever, my battery is fully charged but it doesn't seem to work it did before and suddenly stopped working how can i test it or can i see a wiring diagram for it. Also any other threads on tachometers and speedometers mine don't work that well speed doesn't work and the tach doesn't register rpms correctly.

 

[gggGary]

This is a typical idle screw setting, both sides should be very close to this. If your screws are far from this position IMHO you are covering up other issues that need sorting yet.
Decompression lever contains switch at bottom that activates (grounds) starter relay, check for operation.
On speedo remove cable from gauge back check that it spins with wheel movement. Long dormant gauges sometimes respond to a nice warm hairdryer session to warm reliquify stiff grease.

.

 

[xjwmx]

i tried watching this video as reference

Fwiw I think this is a better video, emphasizing the possibility of stripping the throttle shaft threads on Mikunis and how not to do that.