5 horse Tecumseh surge, governor or carb? - Snowblower Forum : Snow Blower Forums
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post #1 of 12 Old 01-21-2014, 03:49 PM Thread Starter
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5 horse Tecumseh surge, governor or carb?

Maybe someone can offer some help here.

#1 Since working on bugs in my 521, nothing has baffled me like the RPM surging on the Tecumseh engine. It only does it when it's not under load. As soon as it's loaded up, and, I assume, the governor is wide open, it stops surging.

So, I thought it might be oscillation of the governor rod was the culprit. This is one of those engines with the, uh, questionable spring setup between the throttle and the governor. The rod that the spring connects to has about 30 holes in it spaced about 1/8" apart, so I'm thinking there's a bit of "fine tuning" here. However, that means that spring tension and even slight differences in spring connection through the holes could cause trouble. What we have here is a "balancing act." Something I find a little too refined on a single cylinder engine.

I have found that putting the spring in the highest hole on the rod seems to help. This gives the most tension, but it's still not enough to balance the thing out.

#2 I have heard that carburetors can contribute to this problem through vacuum leaks, either around the intake manifold or elsewhere.

There is a vacuum hose on my carb that goes from a little nipple on the carb, near the idle adjustment screw, around the carb and under the cowling of the motor. Where it ends up, I do not know.

I found, and I think, repaired a weak spot on the vacuum hose that might have been leaking. The hose is bound to wear as it wraps around fuel fittings and the edges of the carb. Another ingenious made-to-fail part.

It was too cold out to rig a splice in the vacuum line. It looks like replacement would be a big job, as it would require pulling the cowl which requires pulling at least one head bolt.

Has anyone ever just plugged this vacuum hole? I can't imagine its use. Maybe it isn't vacuum, maybe it's a fuel return hose, however I couldn't see a connection to the tank.

This whole process of setting up the governor and carb seem needlessly complex.

Right now, the engine seems to run lean, and the power adjustment screw is of little help. What has worked best is to run on the first notch of the choke, which is, at the very least, not optimal.

I'd like to feel more confident in how the engine is set up, what with the unbelievably cold and snowy winter we're having.

BTW, I think I've located a carb adjustment hole blocked from the factory. I'm not sure, so I don't want to mess with it. It appears to be just below the intake on the same side as the idle adjustment.
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post #2 of 12 Old 01-21-2014, 03:53 PM
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you shouldn't have a vacuum line just a primer line

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post #3 of 12 Old 01-21-2014, 03:54 PM
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Definatley clean our your carb first. It sounds like it is blocked (running on partial choke). From there I would play with the tuning if you are still having problems but I bet the cleaned carb will do it.

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post #4 of 12 Old 01-21-2014, 04:27 PM
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Most likely a carburetor issue. It can something is gummed up on the inside, a particle of some sort can cause a blockage of the jets, or an air leak. Start with pulling off the carburetor bowl to get an idea of its condition, because it may be as simple as cleaning that. From there you may want to take off the entire carb and give it a good cleaning, and while you're at it replace the gaskets (might be cause of air leak if there is one).

After replacing the carb and properly adjusting it, you'll probably figure out if that was, in fact, the culprit of the surging. If it wasn't then you can turn your attention to tinkering with the governor. At that point, at least you'll have a clean carburetor

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post #5 of 12 Old 01-21-2014, 05:00 PM
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unless something blew up or screws for the governor were messed with, its the carb. to address some of your post:

Generally the spring goes in the third hole from the top (all general)

Vacuum leaks are at the carb to manifold or manifold to block gaskets usually

The vacuum hose is your primer line. there is no gas in it. it goes from the rubber primer on the cowling to the carb. the primer bulb has a hole in the center. when you put your finger on the bulb it blocks the hole and when you push it sends the air in the bulb into the carb to pressurize the fuel bowl to push a little gas up into the carb to aid in starting. when you let go the little hole sucks air in to fill the primer bulb for the next push. It will run fine without any rubber line hooked up. just wont start as easy

If by power valve screw you mean in the center of the fuel bowl nut, that is your high speed/high load adjustment jet it will help but not always cure it.

The blocked hole is not blocked. That is your low speed jet. it may look blocked as it is covered by a plastic black press on cap. get a fine pointy tool and pry the little cap off and you will see a slot screw. That is the low speed jet, prob not adjustable. take it out. there are a few tiny hole in the brass screw that if clogged will also caused surging.

1 thing, You will generally have an adjustable main jet and adjustable low jet, or both non adjustable. they arent 1 of each.

Take a pic of the carb and we can help more.
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post #6 of 12 Old 01-21-2014, 05:43 PM
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wrenchbender! your surging problem is not uncommon and i have found two things that can contribute to the problem. the fuel bowl nut on the bottom has some very small holes that are fuel passages. they could be plugged, or you have the needle that is in the center of that bowl nut set too lean. if you remove the nut you can use carb cleaner and a small bread tie wire stripped of the plastic to clear the holes. take note of how far out the needle is from litely seated from bottom before you remove it. once removed clean the oriffic as well as the tip of the needle. the initial setting of the needle (which is the high speed jet) is 1 1/2 turns out from litely bottomed but don't be allarmed if it needs to be turned more. the initial setting on the idle mix screw is one turn out from bottom. i like to have the high speed adjusted so that when the cold engine first fires you can within just a couple seconds ltake the choke off all the way. if the high speed jet is partially blocked,dirty , or set to lean it will surge at high rpm and not want to stay running when started from a cold start. the reason your engine runs better partially choked is because the high speed mixture is too lean. either a carb to manifold air leak,jet plugged, or jet set to lean. the idle mixture jet will be right when you can accelerate to governed rpm briskley without it coughing or wanting to die out.

Last edited by mkd; 01-26-2014 at 05:16 PM.
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post #7 of 12 Old 01-25-2014, 03:04 PM
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Not sure if 'MKD' meant that your surging problem IS common, I certainly find that it is. I've dealt with it across most of my lawn mowers, tractors, snowblowers etc. I just bought a '97 10/28 PowerShift and it surged like crazy. Cleaned the carb, and like a moron, forgot to do the air screw. Put it all back together and it still surged. Then I did the air screw, cleaned etc. and replaced.... Ran like new. My dime: Carb. Either clean thoroughly, (soak overnight in carb cleaning solution), the use carb cleaner spray, then air spray... If that don't do it, or if you can tell that the needle or other parts don't look pristine, a whole new rebuild kit is usually $7 or $8 bucks.

Good luck.

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post #8 of 12 Old 01-26-2014, 12:04 AM
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An old GM service manager showed me how to find vacuum leaks on manifold, carburator throtle bushings, cracks, bad gaskets very easily.
Have the engine doing it's surging. Then he'd spray W-40 at exact locations till the engine revved up. After two three repeats hits, it was obvious the bushings were worn out that time. I found a loose manifold bolt on a Toyota year later.
Years later I proved the Honda lawn mowers engines had terrible throttle bushings within the third year.
Any acceleration proves a vacuum leak. Before tearing things down try the easy tests.
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post #9 of 12 Old 01-26-2014, 05:05 AM
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Yeah. I use that approach as well...only with carb cleaner. I always have my ABC fire extinguisher right next to me as a precaution. MH
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post #10 of 12 Old 01-26-2014, 04:06 PM Thread Starter
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Originally Posted by motorhead64 View Post
Yeah. I use that approach as well...only with carb cleaner. I always have my ABC fire extinguisher right next to me as a precaution. MH
Thanks to all for the cleaning and tuning tips. Some I have tried, but a lot are new ideas.

motorhead: I've heard of the carb cleaner test for air leaks, but it seemed a bit riskier than I wanted. The fire extinguisher is a good idea. It would seem to me that the WD 40 that "Mr Fixit" suggested would do the same thing with maybe less of the fire/explosion risk (but what do I know about volatility?) I've thought of a couple of other sprays I could mention, but I wouldn't want to recommend anything until I tried it myself.

MKD: I have tried all kinds of settings of the hi-speed adjustment in the center of the bowl, and sprayed the needle and inside the hole generously with carb cleaner. I will double-check for those little holes in the fuel bowl nut, which I did not notice. Note: when I set the hi-speed nut where the surging stops, the engine runs very rough. I think it's too rich, and setting the needle leaner and leaving the choke on one notch gives a better overall result. (I know this sounds very rinky-dink, but when there's a foot of snow on the ground, ya gotta do what ya gotta do!)

td5771: There may well be a black press-on cap under what I called a "blocked" hole, but it is covered by what looks like a piece of aluminum foil, like from the top of a little bottle of gas additive. I imagine under that is the cap and the idle jet. I have seen video of removing and cleaning that jet, but it wasn't under an aluminum cover like that. I'm waiting a while before going there, as the jet is tiny and the garage floor is a slushy mess waiting to gobble it up.

SlowRider2: Thanks for the suggestion of first cleaning the bowl first-- I had thought of starting there but wasn't sure I could do any more good taking it off. Then I'll move on to more thorough carb-off cleaning.

For those of you who mentioned the primer line, be assured I whapped my forehead as I recalled what that line was for (my brain was frozen on "vacuum"). When it was warmer, I knew what it was. I believe it is actually made out of a piece of vacuum hose. It definitely isn't up to standards of good fuel line. Hence it does not stand up well and has a tendency to abrade. I will still have to splice it at the worn section, when I find a piece of tubing small enough to connect the two ends. It gets so cold here that I often need to prime it quite a bit.

The cold is another reason that my carb work gets done a little at a time. Also, I don't want to tear down a carb that still kind of works and not have it ready when big one hits.

Just for the carb-cleaning record, in addition to lots of spray carb cleaner, I have been putting just a little bit of Sea Foam in every tank of gas. A tablespoon or so, just to see if I luck out.

Thanks to all. As I sit here waiting for the wind to die down a bit, I recall that this is the second winter in a row here that's been way worse than all 5 preceding years put together.
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