Topic: Odd timing issue, the closer to F the worse it runs.

[Deltarider]

Update, the dry plug got me thinking, so I cracked open the bowl drain on that carb, almost no gas came out, after wards, I opened the fuel petcock and would only get a drop every couple of seconds, the next carb to the side had a good fuel flow. so I'm guessing the line that joins those carbs is blocked, so I'll take them out and clean that.

Could well be it. After all this you can consider yourself an expert. It's a very long time ago (80s) I had my first look in the holes after removal of the floatvalves. I seem to remember I saw some feltlike substance in there as if there was some sort of filter. Can anyone confirm this?

[strynboen]

yes think some bikes have a small filter on the top of the flote valve..a vhite plastic..pressed dovn on the top..canrt renember if it are the cbx 400 four or the 550...

[Jore]

The only felt I found on my carbs where the felt washers on the pins from the linkage, but the float valves didn't have any.

[Jore]

I deracked the carbs, and found that the one next to the carb on the non firing cylinder doesn't have the o-ring gasket thing on the float bowl, i'm not sure but I suspect that that's causing some weird vacuum issues with the other carb and that's why it doesn't get fuel, either way I cleaned the passages and will buy the o-ring tomorrow and hope for the best.

[evinrude7]

I deracked the carbs, and found that the one next to the carb on the non firing cylinder doesn't have the o-ring gasket thing on the float bowl, i'm not sure but I suspect that that's causing some weird vacuum issues with the other carb and that's why it doesn't get fuel, either way I cleaned the passages and will buy the o-ring tomorrow and hope for the best.

i had a problem with not getting enough fuel into a carb bowl.  i had placed the float valve in upside down after some carb cleaning. 

[carnivorous chicken]

Update, the dry plug got me thinking, so I cracked open the bowl drain on that carb, almost no gas came out, after wards, I opened the fuel petcock and would only get a drop every couple of seconds, the next carb to the side had a good fuel flow. so I'm guessing the line that joins those carbs is blocked, so I'll take them out and clean that.

Could well be it. After all this you can consider yourself an expert. It's a very long time ago (80s) I had my first look in the holes after removal of the floatvalves. I seem to remember I saw some feltlike substance in there as if there was some sort of filter. Can anyone confirm this?

My '75 750F has small, white plastic filters on 3 of the 4 carbs above the float valve.

A missing float bowl o-ring shouldn't cause a vacuum issue on that carb, I'd continue to look for something prior to the float valve. And if you want to show yourself how well your bike will run once you get this pesky gremlin sorted, manually fill that float bowl with gas and stick it back on and fire it up.

[Deltarider]

manually fill that float bowl with gas and stick it back on and fire it up

Fire it up? Do you think that is wise?

[carnivorous chicken]

If he's got good compression and the bike is tuned properly and is only experiencing fuel starvation at one carb due to a clog in the float valve, it's not going to do any harm is it? It's just going to replicate what would happen if the clog was fixed. On some twins I've had weird fuel delivery problems causing a dry float bowl. Filling the bowl manually and putting it back on the carb (much easier with a twin, and with clip on float bowls) somtimes alleviates the issue and fuel flows normally after that.

[Jore]

So I think my problem is fuel starvation, I hooked up the carbs, opened the bowl drain and then the petcock and only got some drops on the non firing cylinder, I had the brilliant idea of blowing air through the fuel line and promptly made a huge mess in my garage, but when I tried hooking up the fuel line to the tank and letting the bowl drain i got a nice and steady stream of gas. Fired the bike up, let it run for a bit and tried touching the exhaust pipes with a wet rag after turning it off, no luck I still have one dead cylinder although it was hotter this time, I'm guessing fuel is getting cutoff at some point.

[flybox1]

now that we think you have a clear fuel line, clear tube test that bowl to make sure gas is filling to the proper level.
hope youre doing all of this off the bike.  so much easier 

[Jore]

I took the float drains out to perform the clear tube test, when I took the one from the dead cylinder out a piece of mangled o-ring came out, so that's one clog right there, either stuck the clear tube in the drains, opened up the fuel petcock and well I found this:

]https://www.youtube.com/watch?v=AxK3PBWRyHg[url][/url]

The dead cylinder isn't getting any fuel, I'm suspecting one of the o-rings from the crossover tube broke and that's what's blocking the line.

Oh well, i'll take the carbs off once more.

[Jore]

So I found that the clog on the carb from the cylinder is in the gas intake passage, I'll soak the carb body in berryman's chem dip for a while and see if that dislodges it after a few shots with compressed air, so far only using air hasn't been enough.

[strynboen]

hope to se good resultats from you.think it are the last problems before it runs good..
.mine 400 vas done last Winter ..bit i just start to ride it now..after i sold my cbx..and i have also some fuel related starvasion..it runs fine smooth vhen i start..but after some ride..it starts to be slow and not acc so fast and iden become some unstabile..so think i also have somd dirt in the fuel system..so need to start from the tank ..and go the vhole vay trough to the intakes..

[Jore]

hope to se good resultats from you.think it are the last problems before it runs good..
.mine 400 vas done last Winter ..bit i just start to ride it now..after i sold my cbx..and i have also some fuel related starvasion..it runs fine smooth vhen i start..but after some ride..it starts to be slow and not acc so fast and iden become some unstabile..so think i also have somd dirt in the fuel system..so need to start from the tank ..and go the vhole vay trough to the intakes..

I went through the whole fuel delivery system, everything had good flow except the non working cylinder, I took just that carb off, hooked up the remaining 3 and opened the fuel petcock, I got good flow from the outlet to the removed carb, cleaned everything on that carb put it back together and put them back in to the bike, tried cranking the bike and it wouldn't run, but the not firing cylinder was now the only hot one, and since that plug was almost new, I changed the  other 3, tried starting the bike again and success, she was smooth ran well, tested the exhaust temp with a wet rag all four sizzled but the non working one felt a bit colder, still hot but not as much, left it a bit to cool and  ran it again, and well the problem's back, the cylinder seems to be not firing again since I took the ht lead off while the bike was running and when i got to the non running one the revs didn't change a bit like on the others, tried the wet rag test and well this time the tube didn't sizzle.  I opened the drain screws on the carbs and all 4 have good fuel flow, and are about on the same level with the clear tube test. Afterwards i took the spark plug out and it was dry, blackish but dry, I swapped the leads on the coil to see if the problem followed the lead and nothing.

So I'm lost for the moment on what to do next.

[TwoTired]

Do the pipes get equally hot if you hold 2000 for a minute-ish?
If so you are back to pilot circuit fail or improper carb sync, I'm afraid.

The clog you cleared may have found its way the pilot jet.

[Jore]

I went to start the bike this morning, opened the petcock had some fuel coming out from the overflow tube in the non firing cylinder, started the bike, revs went up, left the bike run for about 2 minutes, within the first 10-15 seconds all 4 tubes felt about the same temp, turned of the engine, touched the tubes with a wet rag and they all sizzled, but the non firing one was cooler, went to re-wet the rag again the 3 firing ones felt really hot and sizzled, the non firing felt hot-ish but way cooler than the others and only about 30 seconds had passed between the first test and the second one. I'll try the test again in a couple of hours.

[Jore]

As of now all four run, but with idle set to around 2k i'm not entirely sure since my mechanical tach cable broke and the digital one i have reads about 2k more then what it really is. I took the bike out for a ride, felt stronger than the last time i took it out on 3 cylinders only, but not perfect, top end was kinda low on power, my top speed was around 80-85 km/h at full throttle, then when I got to my first stop light the bike died, fired her back up without issue I just had to keep the revs up so it wouldn't stumble and die again, headed back home and with the bike in first it would buck a bit got to the entrance of my garage and she dies again, try cranking it and it takes a few more efforts than last time but she starts I ride the bike in to the garage, turn it off try the rag test and all 4 seem equally hot.

I haven't resynced the carbs, probably my timing is off, as are the carb adjustments, I'm running the bleed screws 3/4 of a turn out. I'm waiting for the engine to cool a bit so I can take a look at the plugs.

[Jimray23]

You should check the plugs again

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[Jimray23]

Does the carb for the cold cylinder still have fuel coming out of the overflow. If so your float needs reset.

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[Jore]

I don't have any overflow coming from the tubes anymore, I still haven't gotten around to checking the plugs :/
I think I should get another set of plugs so I can start doing plug chops also.

[Jimray23]

That sounds like a good idea to me

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[Jore]

The plugs are out, all 4 are black sooty and dry, i'll post some pictures tomorrow since I couldn't get any good light for them just now.

[Jore]

This is the state that my plugs have:

[TwoTired]

Well they are all even, that's good.
They will soon misfire with that amount of carbon build up.  Not so good.
What's the run time/regime on those plugs?

Give us a carb jetting review/status?  I haven't looked back through the tome.

[Deltarider]

Air obstructed?