742 exhaust manifold getting hot!

[apfisch]

Good morning I got a bobcat 742 with a KSG 416. Been having some issues for a while started using a lot of fuel and then I noticed the exhaust manifold would get pretty red within 20 minutes of running machine under normal use conditions, figured head gasket had failed because had also found a broken head bolt so long story short replace the head gasket went through the cylinder head At Machine Shop reassembled everything start it up runs great but after about 20 minutes of running at the exhaust is still getting red and it's really weird because the exhaust is only getting red in the center of the manifold and then following up the pipe about 4 inches. I'm getting good airflow out of the exhaust tip, the carburetor has been rebuilt and replace the distributor with one that has electronic ignition pulled the timing cover make sure didn't skip the keyway. The timing marks lineup exactly where they're supposed to be chain was nice and tight. I'm running out of ideas. Thank you.
Sent from my iPhone

 

[Dave1234]

running lean?

 

[apfisch]

Plugs look pretty good

 

[Dave1234]

Plugs look pretty good

That was quick. Do look very white, not tan. And brand new. Be sure to shut down after running full power immediately. Best engine torque slightly rich; these look pretty lean to me--would make for exhaust smelling pretty good, but maybe a hot manifold.

Lean Spark Plug Reading Chart: Color & Meanings

Spark plugs are a critical element in every engine's performance. However, few people can differentiate lean vs. rich spark plugs. Click for more info.

www.lazerhelmets.net

 

[apfisch]

Okay, what do you recommend, this just kinda started happening

 

[Dave1234]

I would be suspicious of a vacuum leak first--PCV valve, vacuum line, loose carb to manifold nuts, bad carb to manifold gasket, bad manifold to head gasket or loose bolts there. If the intake is somewhat far away, try spraying brief squirts of brake cleaner near/on any potential leak area and listen for change in RPM. If the intake is too close, it will be very hard to tell if it is sucking in the fumes there vs through a leak. Other than the PCV valve, other leaks should have shown up worst at low RPMs/high vacuums requiring idle mixture adjustment or increased idle speed screw. Possibly a problem with the carb rebuild--low fuel level/incorrect float level.

 

[dfb]

I would also suspect vacuum leak or problem with carb. Very simple method of checking for lean running condition is to remove air cleaner and lightly cover top of carb with your hand or a rag slowly restricting airflow. If it is lean the rpm will increase. I would first check it at idle. Another method is to add supplemental fuel, like small quick shots of carb cleaner to check for rpm increase. I also use propane.

 

[foton]

might want to check your timing also,just to take it off the list of possible causes.

 

[Grandpa Chuckie]

Prior comments are good to start. Timing too far advanced will cause overheating. Incorrect spark plugs, too. (Dave 1234---great spark plug diagram!!!)

I would also check two other conditions, air and coolant flow. First, check for radiator coolant flow by removing radiator cap when is cold. (Assuming it has a radiator as opposed to air cooled). Start engine, watch and should see coolant flowing when thermostat opens when temp rises. Also check upper and lower radiator hoses for noticeable temperature difference. (Stuck thermostat, scale buildup in radiator or engine could cause overheating). Second, make sure air cleaner and muffler have good air flow. I had and old 4 cylinder Wisconsin air cooled heat up like yours, and the muffler had rust build up inside that was restricting the exhaust, even though the exhaust gases seemed to be plenty. I removed muffler and heard stuff rolling around in it. Shook it and rusty particles kept falling out. Kept shaking/rattling till no more. About a cup+ came out. Reinstalled and no more overheating manifold.

All comments are easy checks!!

 

[Dave1234]

Reading spark plugs got me wondering if there was more than I knew--WOW Check this out. Several other similar youtubes if you search. .

 

[Grandpa Chuckie]

Not sure if Dave1234's YT video helps apfisch or not, but it sure helps me!!! That spark plug video has info I have never heard!! Thanks, Dave1234, for digging that video out. See, you can teach an old dog new tricks!