Carb Questions

Sup guys... i have a 74 kz900 z1-a ... and i have converted to a Sportster tank w/ the single petcock... i have the fuel line comming from the petcock and then T's off and runs to both carb fuel inlets.... i had the bike where it would start and kinda stay running w/ the choke on but as soon as you turned it off it would die... so i had the carbs cleaned at a shop and put them on and now it wont start... i spray starter fluid in them and it runs for about 3 seconds then dies... i dont know if the single petcock w/ the T is supporting enought fuel... i thought people on this forum were using it as well... any suggestions?

is there fuel coming out of petcock?how big is the outlet?is the gas cap vented?try running with the cap open while it is sitting,does it help?

Yea fuel is comming out... i dont kno what size it is but alot of fuel comes out.... I also tried it w/ the cap off and still nothing

Here's some random thoughts.

Is there possibly a clogged in-line fuel filter or kinked fuel line preventing fuel from reaching the carb after leaving the petcock?

May assure fuel is getting into each carb by removing its float bowl drain screw and checking for continuous flow of fuel out the drain screw hole while the petcock is open. Best done outside instead of inside a closed garage because of the gas odor and cleanup needed afterward.

If a good supply of gas is getting into the float bowls, maybe the vacuum caps or intake manifolds are leaking (old and cracked) and allowing outside air to be sucked in causing a too lean fuel mixture. Try keeping it running long enough to spray WD40 (or propane or starter fluid) around the intake manifolds. If ingested, the spray will cause the rpm to pick up. If no change, the vacuum caps and intake manifolds are probably sealing okay.

If the above things check out okay, something is probably wrong inside the carbs. Because choke action seems to help keep it running, maybe the float levels are set too low or the pilot jet circuits are clogged or the float needles are stuck in their seats or the float needle seats are clogged.

What do the spark plug firing terminals look like? Are they dry or wet with gas? Being dry would be more consistent with a diagnosis of too lean fuel mixture from whatever cause. While the plugs are removed, they should be checked to assure having a good fat spark.

Hoping it's one of the more simple things.

Re-read the original post and noticed the choke helped keep it running before the carb work was done. Nevertheless, spraying around the vac caps and intake manifolds while trying to crank might still have some effect.

Petcock seems to be okay and passing sufficient fuel.

Be sure the carbs are fully inserted into the intake manifolds and that the clamps around the intake manifolds holding them onto the carbs have been tightened.

tried it again tonight and it started for some reason... but now it only runs on the two right cylinders... but when the choke is fully up the other two start to fire ( placing hand over exhaust tips, feeling the heat difference)the carbs are overflowing like crazy out of the overflow hose... im thinkin the two left carbs arnt getting enough fuel for some reason... and that the floats need adjusted what do you think?

DemonSpeed wrote:

tried it again tonight and it started for some reason... but now it only runs on the two right cylinders... but when the choke is fully up the other two start to fire ( placing hand over exhaust tips, feeling the heat difference)the carbs are overflowing like crazy out of the overflow hose... im thinkin the two left carbs arnt getting enough fuel for some reason... and that the floats need adjusted what do you think?

Suggest re-reading above posts for several of many reasons carbs may "overflow like crazy" notwithstanding perfect float level settings. IMO chances are remote that tweaking the float level adjustment will cure the overflowing. Would think that whoever did the carb cleaning work already checked the float levels and had them somewhat close.

Which carbs are overflowing?

Have you done the above suggested spraying around the intake manifolds test for ingestion of outside air? What was the result? Even a negative result from this test may help with further diagnosis.


Seems the overflow system is working as designed and hopefully keeping excess fuel from passing into the air filter area and/or into the cylinders and on into the crankcase.

yeah you would think but... the guy was a dumbass and will never take anything to him again!! i sprayed starter fluid around all the seals after the carb and nothing they seal up fine.... it seams like both outter carbs are leaking

thanks patton!!

Kyle

Thanks for the report. Good to eliminate leaks in manifold or vacuum caps as possible problem areas.

If need to verify which cylinders are firing, may spray water onto exhaust pipes while engine running and watch for sizzle. Will assume you're correct about #1 and #2 cylinders not firing unless "choked".

So it seems that float bowl overflow on #4 carb is not preventing firing on #4 cylinder, and #3 seems to be firing okay and without any carb overflow. But even with the overflow situation on #1 carb, the #1 cylinder is receiving insufficient fuel mixture unless choked, and same for #2 but without the overflow condition.

From current symptoms, #3 and #4 are running okay (except for the pesky #4 carb overflow).

#1 and #2 seem to suffer most from "too lean" fuel mixture symptoms (and #1 carb overflow).


Will hazzard a preliminary diagnosis
Blockage in primary fuel supply circuits carbs #1 and #2 (failure of fuel passing from the float bowl through the pilot jet and on through the passageway to where it meets the pilot air screw tip at the small orifice in the carb throat (located just before entering the intake manifold) where fuel mixture is provided during idle and low rpm running (before the throttle slide and needle are raised). Cleaning and clearing the pilot fuel circuit requires carb removal and disassembly. Was hoping for something more simple.

And another guess as to the overflowing. Grit or crud in the float needle/seat area preventing closure and thereby allowing entry of excess fuel which escapes through the overflow spigots.

But the overflow might just be from a "sticking" float or float needle sticking in the seat. Sometimes the time honored method of tapping on the float bowl will free a stuck float or float needle and stop the overflow. (Okay to tap "pretty hard" but not Godzilla style).

And a final guess regarding float level. They could very well be perfectly okay. But the service fuel level should be checked (use the clear plastic tube method) before removing the carbs from the engine. However, the overflow must be first corrected in order to perform a valid service fuel level test.

Were the carbs "rebuilt" recently or have they been sitting for months. Is it possible one or more float valve is stuck open. Are you positive the linkage is back exactly correctly, such that all four carb slides are lifting?
Just some thoughts; I am novice at diagnosing problems, but I _DO_ understand what has to happen in order for engine to run correctly.

Hi Demon, sorry if this sounds like a really obvious question but are you sure you have the fuel line going to the carb fuel intake and not the vacume. Your overflow problem sounds suspiciously like a problem I had w/my twin while trying to get it together. I had mine together once w/the fuel going to the carb vacume t-line. The bike started and ran until it died and started peeing gas all over the bike and floor. I think mine was running and peeing, at the same time, for a short while before it died.
Good luck
Ron