Tecumseh 8hp surge...

I got the carb buttoned up on my snowblower (missing needle seat) and it no longer leaks but the engine has developed a surge when under small load (auger drive engaged). When I let go of the auger drive, the surge goes away. I've tried to tune the carb (high speed needle) with the auger engaged but the surge (very slight) still persists. The carburetor was soaked overnight in Gunk Carb cleaner, rinsed and blown with compressed air. The float has no holes, needle, seat, both welch plugs, high and idle needles, and bowl nut are all brand new. The engine ran fine beforehand - I soaked it because the primer circuit was plugged. The primer now works fine and the engine runs but I just can't be rid of the minor surge. Any ideas or am I just to deal with it? The engine is 20+ years old but is still very mechanically sound. HM80-155283K Serial: 5203D

 

Hey Legal,
I know from your answers post here that you know what you are doing. But I am going to ask/suggest anyway.
Intial adjustment on carb setting is 1-1/2 turns out on both screws. Let the engine warm up for about 3-5 mins then make small(1/8 turn) adjustments to your high speed.
What carb kit did you use? OEM or aftermarket? I have found that aftermarket kits don't seem to work that well and I now use ONLY OEM carb parts. Many aftermarket kits are 1 size fits all & say they fit 5-12 hp carbs. OEM fits 5-7, 8-10, 12& bigger. The adjusting screws are VERY different.

 

I agree with Indypower, You seem to know your stuff & have helped me on this site many times. The aftermarket kits are not very good & I've been burned by them in the past. Try to open the low speed mixture screw a bit & see if that helps. I find a lot of these engines won't use the high speed circuit till you make them work hard & really get the throttle into them. Let us know what you find, & good luck, Roger

 

The 8 hp engine needs to have the lower screw out about two turns and has to be on the rich side. I seems that the long intake manifold allows the fuel to drop out some untill the heater box is on and really warmed up. The real test on this engine is under a load in a good snow fall like the wet 6+ inches we got on Friday. You can set the bottom screw to where the engine starts to load up when the choke is on the first notch and will smooth out when the choke is off. Most run this lower jet too lean.

 

I only use OEM carb kits on all engines I service. Most aftermarket kits are made in china and I'm not a fan. I set the low speed screw to 1 3/4 turns out as this was what it was before I tore it apart and from this I actually had to richen just a teeny bit as it was backfiring on decell. When I was adjusting the carb I was actually blowing about 4" of wet snow and it wasnt surging when blowing snow; It was only when the machine was idle with the auger engaged. I am getting more snow today so I am going to get it out and fiddle with the high speed a bit more. This engine does like to be on the rich side anyway but it just seems to be a little more finicky since the carb is actually clean now. Thanks for your replies and thanks for the good words... I like to think I know what I'm talking about

 

(This one is off-topic, sorry..)

You're lucky.. We only got about 3-4" of really wet stuff the other day.. I know the band of storms coming through Iowa lately has been staying pretty far south so we haven't gotten as much as you have.. Where is Southern Wisc. are you at?

 

I have the same engine with a similar problem.

Toro snowblower bought new in 96.

I let it warm up on low idle. When I advance the throttle it hesitates, shoots out a little black smoke then takes off. I've tried adjusting both screws on the carb but it doesn't seem to help much.

Once it is up to speed it runs and blows great. More of an annoyance than anything and it has done it since day one.

Could it be a governor problem?


Thanks

Baldwin

 

Black smoke on acceleration mean the high speed mixture screw is too rich. (screw in bottom of float bowl) Lean this screw about 1/16-1/8 turn and you should be in good shape. If it really hesitates you might have to go a little over 1/8 turn. Does your engine backfire at all when bringing it back to idle?

 

Seems like Tecumseh has issues with their carbs. I too have the same surge problem, but I have had my snowthrower for 10 months and I stored it with fresh gas and stabil per recommendations. I have NEVER had any problems with any of my Briggs powered equipment when stored in the same manner. I'm in Kalifornia thus the carb has no external adjustments. I did find that the fixed idle mixture screw was slightly plugged and after cleaning it the surge has improved 98%. I do have a couple of questions though. When I had the float bowl off I could see a welch plug on the body and since I don't have a manual I thought I would ask what is beneath that plug? And would it maybe be a better option to replace the carb with one that has available adjustments for idle and hi-speed operation? I am aware of why the CA. models have no provisions for adjustments and I really don't want to get into a discussion about that issue. Thanks

 

First off, IMO, any carb with a fixed jet setup is junk. Though they are trying to save the planet from smog, they do gunk up easier. Hondas are FAR worse than Tecumseh when it comes to lean surges. The welch plug in the bowl area doesnt do anything except leaves a tiny hole for a bowl vent. If the surge bothers you enough, I'd replace the carburetor with a adjustable jet carburetor. I know if you reference your engine number at an *online* parts house like this one: http://www.partstree.com/parts
You should be able to find an adjustable jet carb for your engine. I doubt you'll be able to get an adj. carb from any service center locally because of the smog law mumbo jumbo.. hope this helps.

** edit ** Not to be biased, but I am a die-hard Briggs & Stratton fan myself. The only briggs stuff I dont care for are the newer engines with the plastic carbs and fixed jets.

 

No it didn't. Leaned it out last night and it did backfire so I backed it out a hair, runs great now.

What messed me up is the book says:

Engine should accelerate without hesitation or sputtering. If engine does not accelerate properly, adjust carburetor to a slightly richer mixture.

Whatever, purrs like a kitten now. Thank you very much.


Baldwin

 

Good to hear! Have a great new year!

 

I gotta revive this thread again. Engine still surges. It has been soaked as has a new oem kit installed in it. The engine only has a slight surge at high speed w/ no load. I made small adjustments on the high speed mixture which cures the surge but then it sounds rich and not running cleanly at high speed. there is no black smoke at any time from the muffler and there is no backfire on deceleration. I don't believe the carb is the problem anymore as it has been totally cleaned and rebuild and float height is good and no leaks. Any ideas as to what may cause this condition? I just don't get it.. I'm sorta baffled now.

 

Did you replace intake to carb and intake to engine gaskets and clean up surfaces well? Small amount of air can cause a surge.

 

I did replace the gaskets.

 

You may be fighting a losing battle trying to repair your carburetor. A replacement may be the only answer, about $85.00 retail.

Your carburetor is an earlier fully adjustable carburetor that utilized a metering rod/pin in the drilled idle passage to "take up space". Instead of drilling the required small diameter hole Tecumseh drilled a larger hole and made it smaller by installing a metal pin to reduce hole diameter. This was a cheap way to do it with the consumer paying for their cheapness later . I have cut open carburetors and found the pin rusted and closing off the passage. These type carburetors can be shaken and if the passage and metering pin are in good condition, you can hear a rattle. The rattle is the pin moving. Also, if the metering pin is right inside the idle adjustment screw hole when the screw is replaced, damage to the adjustment screw tip is what usually results, or it can wedge the pin to where it will "stick" in that position. The condition I described above will cause surging.

Give you carburetor a shake and verify if this is your problem.

If you will look in the Tecumseh Technician’s Handbook for 3 - 11 HP 4-Cycle L-Head Engines Chapter 3 page 10 you will find an illustration showing a cross section view of the style carburetor you have. The illustration shows the “idle and intermediate fuel transfer passage” and the “metering rod or pin” in the passage.

You can download the manual at this link:
http://www.cpdonline.com/692509.pdf

 

See, the weird thing is the engine ran perfectly true before I soaked the carburetor. It was only after soaking it that it got a little finicky. When I get some time, I'll take it apart again and look it over. It runs pretty well despite the little quirks, so If it doesn't come out perfect I'm not out much since the machine was free and it does blow snow well. Thanks for your information.

 

Surging is an indication of a blocked idle or intermediate passage. This could have happened during the immersion cleaning. A foreign object is blocking or restricting a passage. Possibly a piece of trash got left in a passage and has probably hardened. It is just a matter of getting it out and may be impossible to do so.

Here is what I would do if I were working on it:
I came across an aerosol carburetor cleaner that changed my opinion of spray cleaners. This is a cleaner sold by at Auto Zone parts stores. It is an Auto Zone brand “Valucraft Carb Cleaner” Part Number: AZ-4, 13 ounces in a yellow and black aerosol can with a red plastic cap. It for around $2.50 per can. I have been very successful in cleaning carburetors often without removing them from the engine. I have not had many carburetors I could not clean. Sometimes I use the entire can. At the price it sells for, so what.

WARNING - Do not get “Valucraft Carb Cleaner” in your eyes or on your skin. Use a full-face shield for eye and face protection. Wear protective gloves. The cleaner will damage rubber so remove rubber carburetor parts to prevent damage.

Valucraft Carb Cleaner will melt and wash away varnish. Spray as much cleaner as possible into the idle and intermediate passage. Follow by blowing out with compressed air. If this doesn’t work you may try disassembly and immersion cleaning again. Be sure to blow passages and everything else out after cleaning.

 

I always use compressed air after rinsing to get the remaining stuff out. Thanks for the info.. I'll try that and see what happens.

 

I had a factory rep (Tecumseh) in my shop last week just stopping by while he was in the area. I ran by him a strange problem my customer has with his Ariens lawnmower with a Tecumseh engine. Problem is it starts & dies on him. I had it running for 15 mins here at the shop. I did not take the carb off as it was only in here for an oil change & new blade. I asked the rep. His response is that he is hearing more & more like this.
The problem is with the gas. Pump gas can contain up to 10% ethonal without stating it. This is causing more & more problems in our small engines, especially engines older than 2001. The smaller the engine, the more problems it has. Over 10 hp seems to be affected less. 3 hp lawnmower engines up to 7 hp lawnmower/snowblower engines are affected much more. Seems like the more gas it burns, the less the affect ethonal has on the way it runs.
Just like ya don't even notice any different performance on your big V-8 truck engine.
Small engines have BIG problems coming their way with ethonal.

 

I live in on the MN/WI border and in both states the pumps say it contains 10% ethanol in regular and mid grades of gas. Most of the premium 91/92/93 octane fuel has no ethanol so perhaps that may be worth a shot.. Its $ .20 more per gallon but if it makes that big of a difference maybe its worth it. I never thought about that as being a problem...

 

If the ethanol gas doesn't make the difference, take a close look at the governor spring. You might even make an adjustment to compensate for the ethanol fuel by increasing/reducing the tension on the spring. There should be a set of holes in the governor arm for the spring. Note which one it's in now, and then try one up or one down and see if it improves or not.

 

All good ideas. I will find out what works and post back. Thanks guys/gals! (do we have any gals around here? )

 

Its getting to be that time of year again.. I'm trying to get this ancient snowblower running right once and for all.. I took the side cover off of the engine to look at the governor spool and related parts.. What should I be looking for in the governor parts if its failing or broken and not working the right way?

After replacing the carburetor with a brand new one, I still had a surge. I readjusted the gov. linkage as per the manual and still had a slight surge. mixture screws would not remedy the problem thus taking the engine apart. Everything looks good inside - counterweights on gov. spool gear move freely as does the spool.

 

Anyone..? I want to get this thing working right so I aint gotta mess with it this winter when its 30* colder...

 

Legal, I went back to the start of your posts. You said the snowblower is 20+ years old. 1985 or so is when they di away with points. Does your have points? If so, you may want to replace them as worn points can cause surging. Just a thought.

 

This question came up before - the engine was made in 1987. Solid State Ignition. (My Parts guy ran the engine code and confirmed this) The only thing thats left to figure out is the governor, I believe. I tried readjusting the governor arm (according to the book) and this did nothing. It doesnt surge like a Honda, but it is there and when under load it gets kinda boggy.