OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Tecumseh / Kirby Engines Tecumseh HM80 8HP

Folks I picked up a MTD Chipper Shredder with a HM80 Tecumseh powering it. When I looked at the unit the fellow started it and it ran well. Started easily and ran at peak revs well. The only thing it did was that it backfired if decelerated too quick, according to the owner. He said the large flywheel/cutting disc kept the motor spinning so he decelerated it slowly.

Today I started it after bringing it home on the weekend. It fired first pull but ran with the occasional miss. After warming it up I put some clippings through it and didn't sound fine. It was missing and backfiring.

It seemed odd as I putt clippings through it when I picked it up and it didn't miss a beat.

I am thinking that the trip home on the back of the ute may have put some gunk through the fuel lines and causing the syptoms I experienced today.

I do know that the seller said the unit has done very little work but has sat for quite a while. Upon getting it ready for sale he put in a new needle and seat and float. He said the bowl was gummed up from stale fuel.

Today I pulled the bowl off and it was still fairly gummed up. I'll try and clean it during the week.

I cannot find any numbers on the carb itself. Only on the long intake port. Would this be the carb number?

Is anyone able to identify the year of manufacture of the engine with these numbers 8HP Cast Iron Sleeve HM80 155426M SER 1308D?

Thanks
Alf

Pictures would help.
People are lazy and dont like to search, but will help.





Clean it out and try it.


Or buy a new one US$40
http://www.mowers4u.com/oregon-tecumseh-carburetor-hm80-hm90-hm100-p-787.html

Heres an overhaul kit US$10.95
http://www.mfgsupply.com/m/c/22-10948.html

Bruce may be able to get you either of the above in the store if you message and ask.

Some of the mower engines have a fixed size jet others have and adjustable jet. I assume this will have one or the other. If its adjustable it might need tuning.



Theres three different carbs apparently.

Thanks for the links Rodeobob. I was typing stuff into the computer all day trying to find links and you put up two. Cheers.

I ended up buying a second hand carb which is close to mint. I cleaned the external grime, put it on and added a fuel filter this time and it fired right up. It was a quick tune due to the time of day but I'll have a better play tomorrow.

It idled beautifully and ran out to full revs without a cough. There was no backfiring on deceleration too which was good.

Once I removed the air cleaner housing and the intake manifold on the old carb I found it had quite a lot of corrosion. I didn't think that fuel would do that. Perhaps it had some water in it at some stage during it's storage??

If I can get the camera working I'll take some pics.

The only small issue I have to work out is that the new carb must have run a linkage choke lever. The choke is spring loaded. The old choke was a direct mounted lever.

The part number that you require for a new genuine carby is 632351 and cost around $160.00 but it depends on your budget if you want to go for a new one or a oregon one.

Probably ethanol fuel. Tecumseh motors hate that stuff.

Thank you Bruce. I'll be putting the chipper through it's paces this weekend with a stack of Mock Orange clippings.

If it plays up I'll be getting onto you about a replacement carburettor.

I'll also get some pictures hopefully and post them of both the damaged carb and the choke cable job I hope to rig up.

If the fuel contains ethanol and you let it stand for a long time, it absorbs moisture and becomes discoloured. The discoloured fuel will not run an engine properly and is likely to cause partial or complete blockages in the fuel system. Also, you should not leave ethanol in contact with any polymer components of the fuel system, because it attacks them chemically.

Personally I don't use fuels containing ethanol, to avoid these difficulties.

Thanks Grumpy.

I drained the old fuel from the tank and it was very yellow and smelled like old paint.

That sounds like a fairly typical description of old fuel containing ethanol, Aldo: the ethanol has become combined with water by absorption. The yellow smelly stuff seems to be prone to blocking things up. Gum formation in old fuel is a separate problem, mainly relating to fuels with a high proportion of cat-cracked constituents. Olefinic hydrocarbons of that type are not very stable in the presence of oxygen, and the oxidised products include gum.

This oil company bulletin may be helpful (note that the reference to "oxygenates" relates to ethanol, methanol, and certain octane improvers used in the US).

http://www.chevron.com/products/prodserv/fuels/technical_safety_bulletins/ltg_background.aspx

Thanks Grumpy.

I ran the unit today for 30 to 40 minutes and it ran perfectly. Once done I drained the oil and added some replaced it with some fresh 30W Briggs oil. The choke I installed works nicely. It is interesting that I found the replacement carburettor is from a 12 HP OHV Tecumseh. It bolted straight up.

I'll get some pictures in the morning.

A lot of things like that just need minor tuning between engine size some need a jet change

If the 8hp is side valve it would probably need a similar size jet to an OHV 12HP

Good point Bob. The only differences I picked up apart from the spring butterfly choke was the screw in the main jet for the old carb goes to a needle point taper. The newer carb has a taper but then a squared off top. The last 4 to 5 mm of needle is removed.

Here are some pictures of the old carb and the new one

Old carb with the direct choke control



Corrosion in the old carb, sorry for some average pics






The new carb and the choke control I dodged up. It bolted straight up and the machine runs great. I just had to make up some quick brackets and on old cable to get it running.




Cheers

Al

That choke setup looks very well done, not dodgied up at all, I have seen much worse home repair jobs before

Can you take a pic or two of the whole machine for me please.

I like boys toys and you cant get more manly than a machine like that.

Thanks Joe. It certainly does the job even though not original.

Rodeobob, I'm not sure if you are pulling my leg but here you go

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=29355#Post29355

Nah not pulling your leg.

Sounds like a stir that my wife would give me

Fellas I have a question on a problem that I have solved but curious to know the reason.

I picked up some fuel filters a while back. They were petrol filter which were an inline job that had a clear canister which housed a cylindrical pleated paper element. I use them on my push mowers as I feel they filter better.

I put one on the shredder and the trouble started. It would run fine but if it stopped, it would never restart. You had to pull the fuel line from the carb and fuel would run freely. Reconnect and it would fire right up. If you stopped it would not restart and had to repeat the process.

Why does it run in the push mower yet give problems in the ride on and shredder?