21" Craftsman Mulching Mower

peabodyn

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Mower is hard to start:

I rebuilt the carb, new air filter, new spark plug, the coil checks out fine with a spark tester and with my multi meter.

I have cleaned out the gas tank and the fuel line.

After it does start and runs for a while, it re starts without issue.

The primer bulb looks fine and I smell gas when priming.

I also made sure the kill switch from the coil to the engine brake is fine.

It starts on one pull when I squirt in starting fluid

What could be the cause of the hard start?

Thanks.
 

Rivets

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When you rebuilt the carb, did you replace the float needle and seat, plus check to see the the float level has been set properly? When you post back make sure you include the model and spec numbers for the engine.
 

peabodyn

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Rivets - thanks for the response.

The model # is 917 38851.

I replaced the needle valve seat but not the needle itself, and as far as adjusting the float level - I never knew that these were adjustable.

I did blow into the fuel inlet when the carb is upside down to make sure the needle closes the flow of gas against the seat.

Am thinking - maybe the fly wheel needs to be gently sanded (as well as the coil contact points) as maybe the mower was stored outside and it's only when the engine is running does it achieve enough speed to fire the coil.
 

slomo

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Rivets - thanks for the response.

The model # is 917 38851.

I replaced the needle valve seat but not the needle itself, and as far as adjusting the float level - I never knew that these were adjustable.

I did blow into the fuel inlet when the carb is upside down to make sure the needle closes the flow of gas against the seat.

Am thinking - maybe the fly wheel needs to be gently sanded (as well as the coil contact points) as maybe the mower was stored outside and it's only when the engine is running does it achieve enough speed to fire the coil.
That rust on the flywheel/coil has ZERO magnetic impact on the coil. Don't waste your time sanding and polishing.

slomo
 

Rivets

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Forget sanding the flywheel, waste of time, will not help. With the numbers I now know you have a Briggs engine, which for a DYI is not adjustable. That means if you just replaced the needle the seat probably swelled up and now the needle is closing to soon, which will result in hard starting and a lean running condition. I suggest you purchase Briggs part number 398188 which is a needle and seat. This procedure which I use and recommend on this forum. You will not be able to adjust the float level on your engine, so you must mak sure that the seat is installed as deep as possible.

Needle and seat replacement.

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. Next check to make sure that the float does not have any liquid in it. If it does, replace. If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: On the side of some Tecumseh carbs you will find a plastic cover. Under this cover will be an idle jet. Remove it and check to see that the jet is open both horizontally and vertically. You should be able to push the old float needle wire through the vertical opening.
 

seattlepioneer

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Jun 20, 2020
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Mower is hard to start:

I rebuilt the carb, new air filter, new spark plug, the coil checks out fine with a spark tester and with my multi meter.

I have cleaned out the gas tank and the fuel line.

After it does start and runs for a while, it re starts without issue.

The primer bulb looks fine and I smell gas when priming.

I also made sure the kill switch from the coil to the engine brake is fine.

It starts on one pull when I squirt in starting fluid

What could be the cause of the hard start?

Thanks.

I went through all these exertions with a Briggs Quantum engine. It too would start if fuel was squirted in the carburetor and quit after that was consumed.

I eventually found that the plastic fuel manifold was cracked, which prevented the fuel/air mixture from being sucked in from the carburetor. Just air was sucked in from the crack.

This defect was AFTER the carburetor.

It looks like you have a similar Quantum engine. When you pull off the carburetor, an O ring is visible on the plastic manifold that was cracked. You might want to examine that carefully for defects. I had to take off the coil to be able to view the manifold crack and replace the broken manifold.
 

peabodyn

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I went through all these exertions with a Briggs Quantum engine. It too would start if fuel was squirted in the carburetor and quit after that was consumed.

I eventually found that the plastic fuel manifold was cracked, which prevented the fuel/air mixture from being sucked in from the carburetor. Just air was sucked in from the crack.

This defect was AFTER the carburetor.

It looks like you have a similar Quantum engine. When you pull off the carburetor, an O ring is visible on the plastic manifold that was cracked. You might want to examine that carefully for defects. I had to take off the coil to be able to view the manifold crack and replace the broken manifold.

Wow - never though about a cracked manifold. I'll check that out. Thanks
 

peabodyn

Member
Joined
May 4, 2013
Threads
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Messages
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I went through all these exertions with a Briggs Quantum engine. It too would start if fuel was squirted in the carburetor and quit after that was consumed.

I eventually found that the plastic fuel manifold was cracked, which prevented the fuel/air mixture from being sucked in from the carburetor. Just air was sucked in from the crack.

This defect was AFTER the carburetor.

It looks like you have a similar Quantum engine. When you pull off the carburetor, an O ring is visible on the plastic manifold that was cracked. You might want to examine that carefully for defects. I had to take off the coil to be able to view the manifold crack and replace the broken manifold.
I took it all apart last night. The plastic manifold was not cracked - tested it with air pressure. Put it back together and used gasket cement to seal it to the engine (just in case). Reset the coil using a business card as a spacer. Examined the spark plug - it was a CJ-8. Went to the computer and saw that the manual calls for a RJ19LM. Found an old one in my tool box, cleaned it, reset the gap, installed it and today tried to start it. It took several pulls, but it did start and then started easily throughout the day.
Lesson: - always check the basics when you get a mower from someone else......

Thanks for all the help.
 

seattlepioneer

Active Member
Joined
Jun 20, 2020
Threads
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Messages
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I took it all apart last night. The plastic manifold was not cracked - tested it with air pressure. Put it back together and used gasket cement to seal it to the engine (just in case). Reset the coil using a business card as a spacer. Examined the spark plug - it was a CJ-8. Went to the computer and saw that the manual calls for a RJ19LM. Found an old one in my tool box, cleaned it, reset the gap, installed it and today tried to start it. It took several pulls, but it did start and then started easily throughout the day.
Lesson: - always check the basics when you get a mower from someone else......

Thanks for all the help.
Congratulations!

Apparently just replacing the spark plug as a matter of routine would have solved the issue right off the bat. Unless you replaced the old spark plug with a new one of the same model!

Do our pro repairmen either reliably know the correct spark plug model to install or look up the one specified by the manufacturer? Or might you be caught out by simply replacing the spark plug you find with another of the same kind?

I've noted that B&S recommends routine replacement of the spark plug after a set number of hours. It sounds like the one you installed might be worth replacing with a new one as routine maintenance. It would be interesting to know if that gives you better than the marginal performance you describe.
 
Last edited:

slomo

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Jul 14, 2019
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I took it all apart last night. The plastic manifold was not cracked - tested it with air pressure. Put it back together and used gasket cement to seal it to the engine (just in case). Reset the coil using a business card as a spacer. Examined the spark plug - it was a CJ-8. Went to the computer and saw that the manual calls for a RJ19LM. Found an old one in my tool box, cleaned it, reset the gap, installed it and today tried to start it. It took several pulls, but it did start and then started easily throughout the day.
Lesson: - always check the basics when you get a mower from someone else......

Thanks for all the help.
You mean it was the spark plug this whole time? That is the #1 thing people change first. Then the air filter and totally forget about the cylinder block cooling fin cleaning ritual. Glad to hear it is running.

slomo
 
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