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Kawasaki FD750D-AS04 running poorly

#1

ILENGINE

ILENGINE

I have this engine on a Scag that is runnng poorly. New NGK BPR2ES plugs. Been through the carb. Adjusted valves to factory spec. Compression on both cylnders is around 110. Will not start hot or cold without choke. Popping back through the intake intermittent on both carb barrels. Throttle shaft and linkage holes are worn and the carb and some of the intake gaskets are either hard to find or NLA.

If you apply almost full choke will smooth out and the rpm's increase greatly. But if you spray brake cleaner or dribble gas into the intake immediately goes rich. And engine will not idle and engine doesn't surge. Check spark on both cylinders using 2 different spark checkers, and spark doesn't appear to be dropping out.

And the engine has 1800 hours according to the hour meter on the Scag.


#2

T

txmowman

First of all, it is normal to have to choke an engine, even hot, with a carburetor that has a fuel solenoid. Has this engine ever had any valve maintenance? Meaning, cleaning the valves, reaming the guides, decarboning, etc.


#3

ILENGINE

ILENGINE

txmowman said:
First of all, it is normal to have to choke an engine, even hot, with a carburetor that has a fuel solenoid. Has this engine ever had any valve maintenance? Meaning, cleaning the valves, reaming the guides, decarboning, etc.
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I am going to say NO, but truely unknown. I am thinking in the back of my mind this a valve issue also, but without pulling the exhaust and the intake and draining the cooling system to pull the heads to examine the valves won't be able to prove it.


#4

StarTech

StarTech

Hmmm, No problem getting the gaskets from RBI. The 11060-2468 and 11060-2469 both are in stock as is the carb side gasket.

As the throttle holes if you referring to the carb body, resize and add bushings. Bushings will have to be made custom but they are no problem to make. Now the throttle shaft would have to replaced due to wear. I have done several Nikki twin barrel JD ZTRs and save those $600+ carbs.

As to which linkage holes you didn't say which but those items has to be replaced, or welded up and re-drilled. Usually the linkage rods would be worn too.


#5

T

txmowman

The carburetor shaft being worn would likely cause enough of an air leak for the need to apply full choke to enrichen the air/fuel mixture.


#6

Scrubcadet10

Scrubcadet10

Have you sprayed carb cleaner directly on the throttle shaft to verify it is or isnt pulling air in from there?


#7

A

Auto Doc's

ILENGINE said:
I have this engine on a Scag that is runnng poorly. New NGK BPR2ES plugs. Been through the carb. Adjusted valves to factory spec. Compression on both cylnders is around 110. Will not start hot or cold without choke. Popping back through the intake intermittent on both carb barrels. Throttle shaft and linkage holes are worn and the carb and some of the intake gaskets are either hard to find or NLA.

If you apply almost full choke will smooth out and the rpm's increase greatly. But if you spray brake cleaner or dribble gas into the intake immediately goes rich. And engine will not idle and engine doesn't surge. Check spark on both cylinders using 2 different spark checkers, and spark doesn't appear to be dropping out.

And the engine has 1800 hours according to the hour meter on the Scag.
Click to expand...
Your description favors a very worn cam.

Gummed up main jets are also a real issue if it only runs with choke,

The fuel anti backfire valve will also produce similar results when it is not working. Full choke will pull fuel past the shutoff and allow it to run as a "get it in the shop" measure. Shutoff solenoids do gum up and get sticky or quit working.


#8

ILENGINE

ILENGINE

Scrubcadet10 said:
Have you sprayed carb cleaner directly on the throttle shaft to verify it is or isnt pulling air in from there?
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I have and with no change. So I don't think leaking that much air around the shaft. Leakdown testing shows less than 15% bypass at TDC so at least top of stroke the rings, head gasket and valves are sealed.


#9

ILENGINE

ILENGINE

Auto Doc's said:
Your description favors a very worn cam.
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It is in the back of my mind. I don't remember any of the valves short stroking like the lobe is worn but I need to pull the valve covers back off and make sure they are not short duration. Meaning the lift is normal but the valve open time could be shortened if the lobe has narrowed due to wear.

At full throttle it sounds almost normal. But below 1/2 throttle is gets uneven and almost sounds like one cylinder is dropping out but I don't think it is just one cylinder I think both are dropping out.


#10

A

Auto Doc's

ILENGINE said:
It is in the back of my mind. I don't remember any of the valves short stroking like the lobe is worn but I need to pull the valve covers back off and make sure they are not short duration. Meaning the lift is normal but the valve open time could be shortened if the lobe has narrowed due to wear.

At full throttle it sounds almost normal. But below 1/2 throttle is gets uneven and almost sounds like one cylinder is dropping out but I don't think it is just one cylinder I think both are dropping out.
Click to expand...
read my upadate


#11

ILENGINE

ILENGINE

Auto Doc's said:
Your description favors a very worn cam.

Gummed up main jets are also a real issue if it only runs with choke,

The fuel anti backfire valve will also produce similar results when it is not working. Full choke will pull fuel past the shutoff and allow it to run as a "get it in the shop" measure. Shutoff solenoids do gum up and get sticky or quit working.
Click to expand...
I have removed the main jets and have both sprayed them out and also cleaned any old residue out with a wooden toothpick. And the fuel solenoid has been both operated by hand to make sure it wasn't sticking and also bench tested to make sure it is retracting. It seems to run relatively good at fuel throttle without choke. The choke in only needed when starting and also trying to get it to idle.


#12

StarTech

StarTech

ILENGINE said:
I have and with no change. So I don't think leaking that much air around the shaft. Leakdown testing shows less than 15% bypass at TDC so at least top of stroke the rings, head gasket and valves are sealed.
Click to expand...
This why you to the modified leak down test on OHV engines so you can all of the stroke. Can't be done on L-heads but quite easily done on OHV engine. Taper and oval is more pronounce at the middle and bottom of the stroke.

I had several years ago a Tecumseh horizontal that was giving running problems when I cam with the modified test and found the lower part of the stroke badly worn out.


#13

A

Auto Doc's

ILENGINE said:
I have removed the main jets and have both sprayed them out and also cleaned any old residue out with a wooden toothpick. And the fuel solenoid has been both operated by hand to make sure it wasn't sticking and also bench tested to make sure it is retracting. It seems to run relatively good at fuel throttle without choke. The choke in only needed when starting and also trying to get it to idle.
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Hello ILENGINE,

Does this carburetor have the top plate on it with 3 screws? If so....

The carburetor can usually stay mounted, perform the following:

Remove the top plate and gasket carefully. You will see the right and left channels and some very tiny holes. Use a very fine strand of wire such as an instrument tenor string or a single wire pulled from a wire hand brush to clean the small holes out. Do not try to jamb anything soft into the holes. Clean out with carb spray lightly.

Then put the gasket and plate back in place and snug the screws down. Don't overtighten the screws.

Those very tiny holes are the idle bleed air passages.

Hope this helps you.


#14

ILENGINE

ILENGINE

Auto Doc's said:
Hello ILENGINE,

Does this carburetor have the top plate on it with 3 screws? If so....

The carburetor can usually stay mounted, perform the following:

Remove the top plate and gasket carefully. You will see the right and left channels and some very tiny holes. Use a very fine strand of wire such as an instrument tenor string or a single wire pulled from a wire hand brush to clean the small holes out. Do not try to jamb anything soft into the holes. Clean out with carb spray lightly.but may

Then put the gasket and plate back in place and snug the screws down. Don't overtighten the screws.

Those very tiny holes are the idle bleed air passages.

Hope this helps you.
Click to expand...
This carb has a 2 screw cover that covers a cavity that basically acts like the fuel bowl vent. It has separate air bleed screws that can be accessed from outside the carb. I have blown carb cleaner through the air bleed but may go back and recheck with running wire through the air bleed holes.

Also when I get a chance may pull the rockers to do another leakdown test.


#15

ILENGINE

ILENGINE

Update. It appears that there are sources that have the compression for this engine incorrect. The source I came across say compression was supposed to be 107. But that is a misprint and is actually supposed to be 170. Gentleman we have a compression problem.


#16

S

slomo

ILENGINE said:
New NGK BPR2ES plugs.
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Hope that is the OEM plug number. That number 2 in the part number is a rather hot plug.


#17

ILENGINE

ILENGINE

slomo said:
Hope that is the OEM plug number. That number 2 in the part number is a rather hot plug.
Click to expand...
It is.


#18

A

Auto Doc's

ILENGINE said:
It is.
Click to expand...
lawnmowerpartstore.com

Spark Plug for Kawasaki FD501V FD671D FD711D FD750D 920702110 BPR2ES 92070-2110

Spark Plug for Kawasaki FD501V FD671D FD711D FD750D 920702110 BPR2ES 92070-2110
lawnmowerpartstore.com lawnmowerpartstore.com


#19

A

Auto Doc's

ILENGINE said:
Update. It appears that there are sources that have the compression for this engine incorrect. The source I came across say compression was supposed to be 107. But that is a misprint and is actually supposed to be 170. Gentleman we have a compression problem.
Click to expand...
Hello ILENGINE,

I looked on Parts tree and it shows the cam along with a small return spring, so my assessment is that this cam has a compression release. 107 PSI cranking compression is actually decent compared to others I have seen.

Not sure how or if 170 PSI can be achieved with a compression relief camshaft design.


#20

ILENGINE

ILENGINE

Auto Doc's said:
Hello ILENGINE,

I looked on Parts tree and it shows the cam along with a small return spring, so my assessment is that this cam has a compression release. 107 PSI cranking compression is actually decent compared to others I have seen.

Not sure how or if 170 PSI can be achieved with a compression relief camshaft design.
Click to expand...
Straight from the FD750D service manual

Compression Measurement
• Before measuring compression, do the following.
􀀀 Be sure the battery is fully charged.
􀀀 Thoroughly warm up the engine so that engine oil between the piston
and cylinder wall will help seal compression as it does during normal
running.
􀀀 Stop the engine.
• Disconnect the spark plug caps of each cylinder and remove the spark
plugs.
• Attach the compression gauge assembly firmly into one plug hole.
Special Tool - Compression Gauge: 57001–221 [A]
Compression Gauge Adapter: 57001–1159
• Ground the spark plugs to the engine.
To avoid fire, do not ground the spark plugs in closed positions
to the plug holes. Keep the plugs as far away as possible from
the plug holes.
• Using the starter motor, turn the engine over with the throttle fully open
until the compression gauge stops rising; the compression reading
obtainable.
• Repeat the measurement to the other cylinder.
Cylinder Compression (MIN): 1171 kPa (170 psi)


#21

A

Auto Doc's

Maybe they did not have the throttle wide open (high) and choke fully open? Need to retest to verify. For both cylinders to be low would be unusual.


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