Kawasaki FH721V (25hp mower).. carb issue?

[KE4AVB]

Good idea about the fuel pump issue under full load.. but what do you think would happen if the diaphragm was just stiff.. lost its elasticity or something like that? I had an old briggs 5hp on a leaf and grass catcher where the fuel pump diaphragm was built into the carb.. taking it apart it looked perfectly good.. but when I got a hold of the rebuild kit and felt the new one, it was obvious the original was much stiffer and less flexible.. The leaf vacuum engine was experiencing almost the same behavior..

Well.. in any case.. the new fuel pump is a $10 waste of money if I'm wrong. We've covered almost everything else so whatever is left must be the solution yes? Or at least I hope so..

If you learn something from the trial then it not a total waste, you will at least gain some valuable experience.

Not every repair job as clean cut as most would like either. I currently have string trimmer in the shop that has the new to me air scavenging setup. It runs perfectly fine until it starts opening the air port. It will take me some time and extra expense on parts to figure out exactly what is driving it crazy but I usually chalk this up to the learning curve and write-off the expenses as training costs. Personally the experience I get from even making mistakes make me a better tech in the long run.

[HondaG100]

If you send me an audio file of the Morse, I'll tell you what it's trying to tell you. I'm good up to ~30 WPM.

di dah di dit ----- dah dah dah ---- di dah di dit

Good luck.

Funniest thing ever posted on this forum! Are you sure you don't have a plugged filter or fuel inlet instead of a bad pump? Also is this carb one of the twin high speed jet types that has a specific jet for each side that may have been reinstalled incorrectly? You have an idle circuit problem. I know from experience that the big twins can be very hard to get right since you have almost twice the possibilities for trouble.

[Murphy625]

Funniest thing ever posted on this forum! Are you sure you don't have a plugged filter or fuel inlet instead of a bad pump? Also is this carb one of the twin high speed jet types that has a specific jet for each side that may have been reinstalled incorrectly? You have an idle circuit problem. I know from experience that the big twins can be very hard to get right since you have almost twice the possibilities for trouble.

Plugged fuel filter.... we do plan to replace it.. could be but somehow seems to simple.. It will be checked.

Yes, this carb has twin pilot jets.. the exploded parts diagram shows only one part number for the needles.. (only actually shows one needle).. The number of turns they are set however is different.

When you comment about "reinstalled incorrectly",, are you referring to a left and right? I don't believe there is a left or right.

[KE4AVB]

Yes, this carb has twin pilot jets.. the exploded parts diagram shows only one part number for the needles.. (only actually shows one needle).. The number of turns they are set however is different.

If look closely at the ipl it shows branched line leading to location of both screws. One screw is shown for ipl clarity since both are the same.

When you comment about "reinstalled incorrectly",, are you referring to a left and right? I don't believe there is a left or right.

If you didn't removed the jets you should be fine but if you did then you need verify that they are installed correctly.

There is actually two different slow jets and two different main jets. In order verify which should one should be where you need the full engine's model number; otherwords, the alphanumeric after the dash too. These jets maybe same for all versions but not necessarily. My vendor has over 40 versions of this engine listed.

[bgsengine]

Water in the gas will cause that popping , so will valve clearance issues (which would also cause you a hard start) have you checked valve clearances, do a leakdown test and check for any air leaks after throttle - did you replace the throttle shaft seal? did you replace the intake gaskets? water in the gas does not have to be a visible presence - small droplets can be suspended in the fuel and cause problems.

[Murphy625]

Water in the gas will cause that popping , so will valve clearance issues (which would also cause you a hard start) have you checked valve clearances, do a leakdown test and check for any air leaks after throttle - did you replace the throttle shaft seal? did you replace the intake gaskets? water in the gas does not have to be a visible presence - small droplets can be suspended in the fuel and cause problems.

We tried a fresh tank of gas (unit has two gas tanks) and no change. We also checked valve clearances and adjusted to the middle of the allowable range.. None of the was out of spec but we adjusted anyhow.

We did compression check.. 85 PSI.. Did not replace throttle shaft seal. Intake gaskets? On the manifold or the carb? We never disassembled the intake manifold, just took the carb off it. Gaskets are in good shape.

[bgsengine]

Gaskets may be in good shape but re-using them can cause problems - gaskets are designed to have a certain amount of "crush" to them when you torque things down - helps fill in imperfections and once crushed , no longer re-usable - we always replace gaskets if they are removed - you could have a .0002" (thinner than human hair) gap between a gasket and the carb allowing air to leak past and you'd never see it or really be able to affect it spraying carb cleaner (Use an unlit propane torch to find leaks while engine runs) - you either have an air leak somewhere or you have a plugged or restricted carburetor. Throttle shaft seal - some of them are small rubber-like mini-seals (like a miniature oil seal) and they can harden and break apart over time as well allowing air leaks past throttle shaft. Also, compression tells you nothing about condition of valves - only a leak down test or visual inspection can tell the tale, and that is nothing like a compression test..

Have you tried new spark plugs? - even if the ones you have already are "new" - New is not the same thing as "good".

But based on the fact that you have to adjust needles so rich to get it to even run semi-right, you have either got a fuel restriction, or an air leak. Also does it have an anti-afterfire kit on it? (solenoid - some people mistake them as fuel shutoff)

[Murphy625]

Gaskets may be in good shape but re-using them can cause problems - gaskets are designed to have a certain amount of "crush" to them when you torque things down - helps fill in imperfections and once crushed , no longer re-usable - we always replace gaskets if they are removed - you could have a .0002" (thinner than human hair) gap between a gasket and the carb allowing air to leak past and you'd never see it or really be able to affect it spraying carb cleaner (Use an unlit propane torch to find leaks while engine runs) - you either have an air leak somewhere or you have a plugged or restricted carburetor. Throttle shaft seal - some of them are small rubber-like mini-seals (like a miniature oil seal) and they can harden and break apart over time as well allowing air leaks past throttle shaft. Also, compression tells you nothing about condition of valves - only a leak down test or visual inspection can tell the tale, and that is nothing like a compression test..

Have you tried new spark plugs? - even if the ones you have already are "new" - New is not the same thing as "good".

But based on the fact that you have to adjust needles so rich to get it to even run semi-right, you have either got a fuel restriction, or an air leak. Also does it have an anti-afterfire kit on it? (solenoid - some people mistake them as fuel shutoff)

I don't think a leaky gasket could cause this much trouble.. that, and the fact that it started right after I ran out of gas.. It would have to be a pretty big air leak that just suddenly appeared.. Plugs have a good strong spark to them.. it ran like new after I replaced the port side coil.. it wasn't until I ran it out of gas for the first time ever that this happened.

I think its either fuel pump or filter. Waiting for fuel pump and changing them out to find out.

[Luffydog]

just something to try and its simple. get some carb clean crank your engine and spray around to check for vaccum leaks. when your spraying around and it tries to kill the engine you know you have a vaccum leak. quick and simple to find out if any. but best way is like bg stated back in his post. maybe this will kinda help out a bit not a good way but its away to get just check in a simple step.

[Murphy625]

just something to try and its simple. get some carb clean crank your engine and spray around to check for vaccum leaks. when your spraying around and it tries to kill the engine you know you have a vaccum leak. quick and simple to find out if any. but best way is like bg stated back in his post. maybe this will kinda help out a bit not a good way but its away to get just check in a simple step.

Thanks for the suggestion but its one of the first things we tried.