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Rick
Rick, Factory Authorized Trainer
Category: Small Engine
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Experience:  Outdoor Power Equipment technical trainer since 1990, covering eight states.
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7hp tecumseh snowblower wont rev up. Starts and runs medium

Customer Question

7hp tecumseh snowblower won't rev up. Starts and runs medium idle, just will not get up to full RPM's? I disconnected the governer, opened up the carb adjustments.
Submitted: 3 years ago.
Category: Small Engine
Expert:  Rick replied 3 years ago.

Are you getting a good flow of fuel out of the fuel line leading to the carburetor? How did you clean the carb? Was it fully disassembled? What did you set the float at?

 

What model, spec, and code number is XXXXX engine?

Customer: replied 3 years ago.
Hi Rick. Yes, good flow to the carb. I removed the carb completely from the engine. The bowl was full. The little square and pointed valve with a little wire spring fell of the float, so I put the spring back onto the tabs and made sure the valve dropped in and out of the seat (not sticking) before reassembling it. There is only one screw adjustment valve which was clean but no matter how many turns out, doesn't make any difference in the performance.
I noted that the little arm to the governer was rigid, actually putting pressure on the throttle and bending the spring. So I took that arm off to operate the g independently, to no avail. Not sure how that retards the timing or if that's a problem or not.
It's a 7hp Tecumsah, elec start, Ariens snow blower. Where's the code number you are talkng about?
Expert:  Rick replied 3 years ago.

Which screw are you referring to? Was it on top of on the bottom of the carburetor?

 

The governor doesn't affect timing at all, it affect only the position of the throttle in response to changing loads.

 

The numbers I'm referring to will be on a tag on the engine shroud. There will be something like H70-35782A followed by a code or serial number. That will tell me which of many versions of 7hp you have.

 

Did you clean the small holes in the bowl nut really well? Including the one by the threads that's really hard to see? Did you probe them with soft tag wire or compressed air? It really sounds like a plugged main jet.

Customer: replied 3 years ago.
The screw I talked about is the spring loaded one which should be backed out about 1 1/2 turns or so. The one at the bottom of the bowl looked pretty clean too. However, I did not use a "soft tag wire" or compressed air. I will take it apart again and try compressed air on it. But can't do immediately - probably in an hour.
The engine shroud is rusted but these are the only stamped numbers I could read: 30210D SER - 8229. There appears to be a 0 or six following the nine, but can't tell.
Expert:  Rick replied 3 years ago.

My bet is that's an H70-130210D. If that's the one, there will be a main (high speed) adjustment screw on the bottom, an idle mixture screw on the side, and an idle crack screw on top that prevents the throttle plate from fully closing.

 

Let's go through an adjustment procedure as well after you verify the jet.

 

graphic

 

Start with the main screw underneath the carburetor set at 1-1/2 turns from gently seated. Do not overtighten. Start with the idle screw on the side at 1 turn.

Start the engine and let it warm up to operating temperature, usually about 3-5 minutes.

Move the throttle to full speed. Start with the main screw and turn it in 1/8 turn at a time, give the engine a few moments to adjust to the new mixture at each stop, and note the position of the screw when the engine starts to sputter.

Now turn it out in 1/8 turns just like before and fine the other point at which the engine starts to sputter.

Set it halfway between the two points.

Now bring the throttle down to idle and do the same thing with the idle screw.

If further adjustment is required, the main adjustment should be made with a load on the engine. Engage the auger. If the engine stops or hesitates, turn the main mixture adjusting screw out 1/8 turn at a time, testing each setting, until it engages properly.

If the engine smokes excessively, turn the main adjusting screw in 1/8 turn at a time, testing each setting under load, until this condition is corrected.

After the main mixture is set, move the throttle to the idle position. If the engine does not idle smoothly, turn the idle mixture screw 1/8 turn either in or out until it engine idles smoothly.

 

Did you clean off the carbon in the head and inspect the valves for proper seating? Do you have a compression gauge to take a cylinder reading by any chance?

 

Let me know and we'll continue.



Edited by Rick on 12/2/2010 at 10:05 PM EST
Customer: replied 3 years ago.
I've got some good news and some not so good. First, the gas line broke so I spilled about one gallon (no shutoff). Second, I wired and compressed air after removing the screws. The good news is that for about one minute the engine did run at full speed.
The bad news is that I think the float valve sticks up when the bowl drops down, as there is only a bit of gas drips out if I back out the bottom screw entirely. Consequently, no matter what adjustments I make to the mixing screws or the throttle, I can't get it to go full rpms.
I wonder if that float valve is the problem and if so how do I remedy it from sticking up, if that's what it is truly doing?
Customer: replied 3 years ago.
I tried all of your adjustments to no avail. I still cannot get the engine to run full speed. It won't even run faster than idle. It does start right up at idle, no choke and keeps on running. But as soon as I advance the throttle it dies. Fuel supply? From the bowl?
Now, when it did run full out for that minute earlier, it really spit out some sparks and flames out of the muffler, then it just cranked up while I held the throttle wide open.
So I'm thinking that tomorrow I need to take the carb apart again and blow it out. How does one clean the carbon from the valves?
I left it with the mixture screw at 1 1/4 turns and the bottom screw about the same. Idle is just above stopping or dying out.
Customer: replied 3 years ago.
Now (Dec 3rd) I'm a bit confused. Thought we were working on the problem. Can't say I'm satisfied yet, still have the same problem. But I will have to wait for a response before I can go any further. We started out good but now what?
Just to recap; should I try the cleaning again?

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