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Discussion Starter #1
Hoping for knowledgeable input from folks with experience.

Running a 1978 Bob-Cat 5 HP-20" Type T5-1-20-19549 (mfd. by now long-gone Wisconsin Marine, Inc., Lake Mills, WI) with a Briggs Model Series 130252.

Put in fresh gas; starts and runs, but requires partial choke to remain running smoothly even after warmed-up. Will very much appreciate input from anyone with expertise. Naturally, would like to start with the most simple stuff that's likely to be helpful.

A big thank you in advance for your interest and for sharing your expertise.
 

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Remove and clean the carburetor. Easiest but doesn't always work, put some Seafoam in the tank. Next, remove the carb, disassemble, spray carb cleaner in every hole. No? Then buy Berryman's carb dunk solution. Lastly, buy another carb.
 

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Most likely varnish in the main jet, or the main running orifice. As suggested, clean out the carb. but you probably have both low- speed and high- speed adjustments on an engine of that vintage- it is running lean so backing the main jet out (opening it) will enrich the mixture.


Hoping for knowledgeable input from folks with experience.

Running a 1978 Bob-Cat 5 HP-20" Type T5-1-20-19549 (mfd. by now long-gone Wisconsin Marine, Inc., Lake Mills, WI) with a Briggs Model Series 130252.

Put in fresh gas; starts and runs, but requires partial choke to remain running smoothly even after warmed-up. Will very much appreciate input from anyone with expertise. Naturally, would like to start with the most simple stuff that's likely to be helpful.

A big thank you in advance for your interest and for sharing your expertise.
 

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Due to the age, the throttle shaft may be worn allowing an air leak. Check for play in the carburetor body.
 
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Discussion Starter #6
sea foam,
does anyone really know what it is? or it's composition?

Hydrocarbon blend* Blend < 95%
Isopropanol 67-63-0 < 25%
or mix your own
Homebrew Sea Foam (SeaFoam) Motor Treatment Recipe
4 parts diesel, 2 parts naphtha 1 part IPA better known as isopropyl alcohol
Thank you all for your prompt responses. Carb is hidden under sheet metal, etc., but parts info seems to show just one needle valve. Nor can I readily get to throttle shaft to check for play. Parts sheet shows a felt washer on the shaft, another possible culprit I suspect.

I have, but have not yet used, a can of Techron. Is it worth a try? In interest of starting simple first, would you start with Techron (or other cleaner) or with adjusting needle valve, if I can easily get to it? (It's too darn cold now to spend much quality time out there.) Logic suggests to me that adjusting valve might compensate for a varnish issue. Agree?
 

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Thank you all for your prompt responses. Carb is hidden under sheet metal, etc., but parts info seems to show just one needle valve. Nor can I readily get to throttle shaft to check for play. Parts sheet shows a felt washer on the shaft, another possible culprit I suspect.

I have, but have not yet used, a can of Techron. Is it worth a try? In interest of starting simple first, would you start with Techron (or other cleaner) or with adjusting needle valve, if I can easily get to it? (It's too darn cold now to spend much quality time out there.) Logic suggests to me that adjusting valve might compensate for a varnish issue. Agree?
YES!!! on the techron just don't overdo it
 

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Using Chevron Techron or Lucas FI cleaner might do some good but use a measured amount. Whatever they are telling you to use is already more than enough.

Have you tried to take a 1/2 turn or two counter clockwise on that screw under the carb to richen up the mixture ??

.
 

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For difficult cleaning jobs I think the strongest fuel cleaners are Berryman's fuel cleaner, Liqui Moly Jectron, Gumout Regane, Seafoam. I never thought highly of Techron. Lucas I use in every gas can for maintenance. I buy Lucas by the gallon, $25, and give some with Stabil enough for 2 gallons to every customer whose mower or blower I've serviced. I also sell a small bottle to some people when I do servicing on their cars.
 

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sea foam,
does anyone really know what it is? or it's composition?

Hydrocarbon blend* Blend < 95%
Isopropanol 67-63-0 < 25%
or mix your own
Homebrew Sea Foam (SeaFoam) Motor Treatment Recipe
4 parts diesel, 2 parts naphtha 1 part IPA better known as isopropyl alcohol

I think it's over rated. I buy it if it's cheap, and on sale. Other than that it's Lucas or Chevron for me. Marvel if it's going in the crankcase.
 

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Discussion Starter #11
More thanks to all. Next time I wind 'er up, will plan to try the needle valve adjustment (readily accessible), which seems like the quickest/easiest shot.

Then, will post result.
 

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Have you tried to take a 1/2 turn or two counter clockwise on that screw under the carb to richen up the mixture ??

.
THis is job #1

if it doesnt work, got to take it up a notch by going FULL STRENGTH on the Sea Foam

Warning: prepare yourself for the magic powers that it gives

 

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Discussion Starter #13
Finally was able to spend a few minutes on the beast. Removed needle valve and seat; no significant buildup. Someone had apparently overtightened needle valve and put a very slight groove in it; nothing I deem significant. Put 'er back together, lightly closed needle valve and backed 'er out 1 1/2 turns. No start!
 

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Any damage on the needle is generally regarded as catastrophic, since the clearances are so minimal to begin with. Also, did you check the small ports on the side of the man needle body? They are in the threads, and very hard to notice, but if plugged, block all fuel flow, since that is the inlet path of fuel to the needle. Since the needle is damaged, you might try opening further, since it was clearly driven in too far at least once.
 
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