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Discussion Starter #1
Hi,

I am new to the forum and i need some help on my bike.

The bike seems fuel starved. I am saying this because it starts fine, revvs fine even rides fine for a few km, and then suddenly it boggs and dies on me.
I have cleaned my carbs, pump, petcock, which are all sparkling and i replaced the fuel filter to no avail.
At first i thought it could be flooding, which is why i checked the carbs and the plugs. My rear plug is slightly carbonated on the insulatorm the front seems perfect according to a chart i consulted.
Any help will be appreciated.
Thanks in advance.
 

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Fuel tank vacuum, fuel pump filter,...internal one, fuel supply line kinked/damaged, fuel valve blocked/insufficient vacuum, blocked/sticking float valve/needle. The tank may have water/gunk in it that eventually blocks the fuel supply. There may be water in the carb bowls. That's about all I've got atm. When it happens pop the fuel cap...if it clears then the tank vent is not working. Run some good quality cleaner through...leave it overnight...you may have a blockage in the system somewhere.

Good luck....Oh how is the air cleaner?...and check for any air leaks at the carb boots, although that would show up at any rpms. Also are you sure it isn't electrical, showing up due to heat...plug caps/cables/coils in that order. Also some bikes show weird problems if the reg/rec or battery is on its way out

Just read your other post...I wonder if the float level on the rear is too high also are they working in sync?
 

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Discussion Starter #3
Not so sure about the synch. Since i bought it i havent touched it. Removed them cable and all each time as the manual suggested.
I have checked for vacuum leaks on the boots as well as on the fuel line intakes. I have also checked the diaphragms on both carbs.
I checked the plugs, lines and coils. Resistance is on spec and very little difference between the two.
What irks me is that both cylinders seem to idle and rev near perfection.
I have held it at 6-7k to see if the bowls empty. 5mins and no problem. Somehow its only when i ride.
I had to take the day off to check this.
 

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Discussion Starter #4 (Edited)
Also i must add i checked both float levels. Perfectly on spec.
Reg was tested and is fine
Also the air filter is brand new. It was one of the first things i replaced when i got it along with oil oil filters etc. I also checked that its theexact same filter as the old one.
I also checked fuel supply at the intervals
- from the tank there is a very strong flow
-After extra ball valve there is still strong flow
-There is a slight flow after the pump very slight which is why i installed the extra ball valve.
- when i turn then engine it pumps moderately.
 

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Discussion Starter #6 (Edited)
Alright, so i discovered my fuel looks like coke and i drained my tank, ran acid through it and put some very good chemical resistant rust coating in the tank for the bit i couldn't chemically burn off. Guess its time to check the carbs and the fuel pump.I should afd that when i checked the pump yesterday and cleaned it, the fuel ran through it clean as it would be from a good gas pump.

Alright, update.

I pulled the rusty tank
I gave it a nice inside acid bath. You won't believe the amount of rust flakes that came out..
I cleaned the petcock and put it back like it was.
I cleaned the pump again.
I cleaned botg carbs again and like clock work my friend arrived from work. Time to get fresh fuel and try again.
Checked all fuel lines for kinks and blockages. None were found.
 

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Discussion Starter #7
AAAAAAAAND a big nothing. Will rip the carbs again tomorrow. have feeling there is a piece of debris that escaped me. This has to be a fuel problem.
 

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STOP please. PLEASE.

What modifications from stock have been made to the the engine "system" ?

It sounds to me very much like one of two things is happening, neither of which you have mentioned in any of your posts.
1) The engine is running too lean ONLY WHEN HOT from opened up pipes, high flow air intake or an intake vacuum leak that only happens when hot.
OR
2) A vacuum is developing in the tank after some fuel is drawn out, stopping the fuel flow.

Make that 3: The vacuum operated petcock is failing after it runs for a while.

What happens AFTER it dies ? Will it immediately restart ?

It also could be due to something electronic failing when hot and then working again after it cools off.
Crud in the carb usually is NOT temperature sensitive.
 

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Discussion Starter #9
Easyrider Thank you for your input on this.Yes, I have somehow neglected to mention that i have tried what steve has suggested with opening the tank when it happens to rule out a lock in the tank.As for the rest when the bike sits for a while and i mean quite a while (2-3+ hours) She starts up like a dream, idles like it is brand new and revs up with no delay. Which is how i have been able to do vacuum leak tests and so forth at operating temperature.Yesterday i took her for a spin down the road after having warmed her up to the point where the fan came on.It went the same distance as it did the other days it very nearly died but somehow she stayed alive enough for me to turn back up against the mountain.With the extended periods of standimg and the fan working i have been thinking it seems like fuel filtering through somewhere on that time.So to address you.1) It has a two to one system on. The muffler that is on is a tad bit smaller than that of the two original tips.Albeit i have been riding the bike for about four to five months after it came back.2) i tried opening the tank to rule out vacuum lock in the tank. Nothing.3) the petcock isn't hooked up to a vacuum line. It never has been i gor the bike like thisand i have looked everywhere to see where that vacuum part of the petcock hooks up to. Nada. Not even the full manual adresses that in its hozing, carb nor tank sections.Based on my one perfectly burnt plug and my one blackened plug which i consulted an sgk chart on to tge letter. Rear is running a tad rich and front burns to perfection.This just suddenly upped and happened after she ran dry (no fuel gauge ) right in front of a gas stop. Filler her up. She worked okay for two days then nothing.Ps. No, she doesnt start up again.Plugs lines and the rest were also tested at temp.
 

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Discussion Starter #10
I spoke with the previous owner to get some more background on the bike. Well, at least what i don't already have.He says the rear cylinder flooded a few times due to an incorrectly set float. Which was replaced and set correct by what i have checked.So as soon as the rain stops i will be checking the oil first and foremost to see if it smells like fuel. I hope not.
 

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No, she doesnt start up again.Plugs lines and the rest were also tested at temp.
OK, well you need to test EVERYTHING while it is actually failing.

First, test for spark when it dies and won't start. It really sounds like you have a heat sensitive electrical component.

If the spark is good, then test your fuel theory by spraying a LITTLE starting fluid or propane into the intake to see if it fires that way.

Do the carbs have drain screws on the bottom (almost all do) ? When it is failing, does fuel come out.........and continue to flow if you leave the screw open for a while ?

I am assuming that this model does NOT have a fuel pump ??
 

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Discussion Starter #12
Hi again.
It does havea fuel pump. Works on vacuum from the front carb.
Pumps like a boss.
I tested spark right after fail. Spark was really great on both plugs.
I have actually drained the bowls after failure (quite close to failure) and they were full actually.
Yes it also continues to flow. Moreso if i turn the engine as its supposed to.
Also, it does fire up with some quickstart directly after fail.

For some reason both my friend and i thought about oil shortage last night each on our own.
I filled it three weeks ago so when i checked this morning it seemed empty as my head is sometimes.
I read somewhere that oil shortage can actually greatly affect vacuum on your carbs and possibly starving your engine itself.
This fits with your diagnosis of an air problem vacuum problem and/or lean running eventhough neither my plugs nor my vacuum tests are affected seeing as there isn't actually a leak.
The plugs won't show seeing as it's not ridden long enough to foul.
Question is where the oil went seeing as its been three weeks only and i only ride it 30km a day and it stands on weekends
So i got the appropriate oil and i just filled her up with some.
Going to go get more fresh fuel and try her as soon as the rain stops again.

Does it make any sense though?
 

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Hi again.
It does have a fuel pump. Works on vacuum from the front carb.

Does it make any sense though?
NO. Especially the line above.

I've been doing this for about 50 years now and have NEVER seen a fuel pump that is vacuum driven.

Your most recent description indicates...............that everything is working perfectly, when it obviously is NOT.

Running for X amount of time and then failing to deliver enough fuel is a sign of fuel pump failure......if there really is one.

A vacuum line from a carb to the fuel delivery system almost always is a safety shut off at a petcock or similar device.

You are overlooking something obvious here.
Wish I could tell you what.
 

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Discussion Starter #14 (Edited)
I consulted the manual again. I am struggling a bit to upload pictures but ill be trying again soosoon.

There seems to be something i am overlooking yes. I think i might have discovered it.
It has mikuni carbs ( BS36SS and BDS36SS). If you would like to refer to something.
Now, after many agonizing attempts to look at this, I discovered that they have internal filters inside where the needle of the float goes just deeper. I haven't personally seen them yet. Ill have a look when i am home. They apparently also clog up. Which explains why it starts after the bike sits.
A work colleague suggested it might also be my battery. So ill take my work tester home and test it with a different much better tester.
Also, manual shows the vacuum going from the front boot (only) to the pump and how the pump works. It also describes it as a vacuum pump.
Also, there is a breather pupe on my rear head that goes doen to my airbox, could it be the culprit? It is a very soft pipe. The tank goes over it and it goes over another much harder air pipe. It could be kinking with the tank on. Ots the factory routing. That i checked aswell.
 

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Filters don't become clogged and un-clogged as a result of temperature.

I STILL think you are relying too much on thinking and making guesses and too little on actual test results.

I'm out of suggestions. Good luck.
 

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Discussion Starter #16
Well i did straight up tell you that i did perform tests. I may not have given you the numerical values of say testing the coils and leads. Doesn't mean i didnt test things to spec.However i did find the actual solution to the problem.Two very small sift filters past the needle and seat of my floatThey were clog which supports my initial thesis of a fuel starvation.So instead of heat building up causing some electrical fault in a short while, it was the bowls not filling fast enough due to the crud in the filter. Whfn it stood, petrol would seep by, filling is enough for the carb to restart its process.Regardless, thank you for the help. It was appreciated.
 

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it was the bowls not filling fast enough due to the crud in the filter.
Yep it's tough to gauge the fuel flowing out of the carb drain if you don't first know what it should be.
And doubly tough if it really has a vacuum operated fuel pump.....which only works with the engine running.

Glad you got it fixed !!! :bluethum:
 

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Discussion Starter #18
Comes with not having owned the bike for so long. Interesting build this vx though.
Thanks for all the tips and dedication.
Ill be contributing where i can.
 

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Discussion Starter #19
acceleration issue

Hi guys its me... again..

I have a new problem today i can use some ideas on.
Note: i haven't done anything yet. I simply cant think what the problem could be.

Alright. So as we know i have a suzuki vx800. Splendid bike if it runs fine.
I decided to take her for a spin since i have sorted the starvation issue just to realize i have a new issue.
Problem is that usually in first gear i need to be very careful on the throttle as this thing has some really good power and tends to spin easily. Suddenly there is no power. I have to ride it a while at about 10km an hour to gain momentum and then she starts accelerating like a boss. Though on my throttle control there is a much bigger delay than usual before i slowly start getting what i asked for.normal stops and pull aways after that is fine when there is very little traffic. But the momenr she stands a while idling i have ro restart though it doesn't take as long..

Another strange new thing is when i switch off the bike, there are two deep pops that come grom my exhaust after i killed the engine.
I dont even know where to start looking.
So i come to those who might know.
 

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Hi guys its me... again..
If you had posted here before about problems with the engine on this bike.......it would be REALLY helpful if you just continued THAT THREAD so that we don't have to go back and search for it to see what was suggested and done before.

I don't have time to do that now; maybe later.

It sounds like it's running too lean when cold. Most common causes: mods to the pipes or intake, vacuum leak or carb problems.

You DO know that a "normal" carb'ed bike needs to have partial choke for the first 10 minutes or so until it warms up ??
 
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