Kawasaki FD750D-AS04 running poorly

[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.

 

[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.

 

[ILENGINE]

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.

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.

 

[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.

 

[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.

 

[Scrubcadet10]

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

 

[Auto Doc's]

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.

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.

 

[ILENGINE]

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

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.

 

[ILENGINE]

Your description favors a very worn cam.

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.

 

[Auto Doc's]

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.

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