Small Engines (Lawn Mowers, etc.)/Carburetor


QUESTION: hello, have a snowblower carburetor adjustment question. Have a 23 year old MTD/Tecumseh 3hp/21 in.   Last winter did a carb rebuild(Your suggestion). Runs good-after warm up. But when I engage the auger it loses some power. Cleaned carb. Trying to find some sort of adjustment . It is a 632410B Tec Carb.  Do I adjust at the main bowl nut(Too tight) or their is a screw and spring(Idle screw?)on top.  Or is it a fixed idle. Which means after season consider buying a new carb. Have rebuild most of it except motor.
Thanks, Jules

ANSWER: On the bottom of the carb, is there just a nut or is there a spring and a needle adjustment on the bottom of the carburetor.

FYI, some have a fixed nut, which is just a flat nut, and some have an adjustable high speed with a needle/spring in the bottom of the carburetor.

Can you attach a picture of the carburetor?

If you have an adjustment in the bottom of the carburetor then try backing it out a little.


---------- FOLLOW-UP ----------

QUESTION: It has a fixed flat nut. Can it be adjusted? It's tight. Can it be backed out a little?My 80 year old neighbor who likes to tinker with lawn equipment says it might be the belt. I've owned it ten years. Don't know if the belt has been changed. May go ahead and just replace it. It's a 632410B Tec carb but is now 640098A. After season may(?) swap that out. Thanks.

ANSWER: The flat nut is a fixed speed jet, no adjustment is possible.

When you cleaned the carb did you dis-assemble it, removing the float bowl nut, float, needle and clean with compressed air from an air compressor?

The parts diagram for a Tecumseh 632410B carburetor shows an adjustable high speed nut, part number 632385.

Did you dis-assemble the carb when you cleaned it?


---------- FOLLOW-UP ----------

QUESTION: To answer your question previously I totally took the carb apart and used a carb kit. After even more research found out my blower was manufactured before 1990 most likely 1985-1986 not 1993. ( I also have a 178cc 2012 MTD) Tmo 35272A & B model.  Been using a MTD parts reference from 1990-93.  THey  are relatively same set up.  I'm wondering if the original carb 632410b was swapped out for a fixed nut. But today's  MTD Replacement reference is 640098A which is a fix nut. Will swap out after season. Also the belt is a 754(954)-0367.  Some are 34",  34.4", and 34 1/2".  Why the discrepancy? Does it really matter. Thanks again . You are the best.  And will say so. This blower is an oldy but goody. Wont take anymore of your time.

If you live near a local small engine repair shop call them and see if they have part number 632385, the adjustable needle.  Many carbs will accept the adjustable needle.  You could even take you carb with you and verify you carb will accept the adjustable needle...the shop should be able to tell you for sure.

As far as the belt, I've found similar discrepancies with other belts...not too sure why...may be a supplier thing where a different length is cheaper as most parts are tied to money...if it is cheaper and it works that is the one the equipment manufacturer will long as it works and there are no safety issues.

If you have an adjustable idler I would use the shorter belt as it will stretch during use.  A 1/2 inch on a belt it quite a bit.  If the 34 inch will not fit then try the next 1/2 size up.

Have you checked the head bolt torque on the engine?  I have had older Tecumseh engines with loose head bolts cause weird problems that seemed to be carburetor related...they were, sort of, as some of the air/fuel mix was leaking past a slightly loose head bolt...actually saw tiny bubbles.  My rule for older Tecumseh engines on every tune-up is to re-torque the head bolts as it only takes a few seconds to do.

Let me know if you carb can accept the adjustable needle.

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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