Hi folks,
I'm a new poster here and am looking for some advice. I have an Ariens snowblower with a Tecumseh 7hp "H70 130266M". It did not run, but had great spark so I got a carb kit and rebuilt the carb. Basically, I cleaned out all ports except that I left the welch plug in. I put a new jet(adjustable type), needle/seat, new air/fuel mixture screw, and bowl gaskets. The original settings prior to rebuild were 3/4 turn out for both jet and fuel mix. I set new ones to 1.5 turns out to get it to start for purposes of fine tuning. Now it starts right up and runs so so. I tried adjusting both screws to get the happy medium, but it's surging at low and high speeds. It's not backfiring or anything like that, but I can't get it to run smooth, particularly at low speed. In fact, if I leave the jet at least one or more turns out, the thing will run with the air/fuel mixture screw turned all the way in. I think this is the main clue to what's going on. Any advice, particularly on why this engine could possibly run with the air/fuel mixture screw turned all the way in? Thanks for the help!!

 

Bowl type or diaphram carb?
Bowl type, you have blockage of some type in idle passage, Diaphram style check valve in main nozzle probably not seating. In either case blow the jets out good with carb cleaner (use little plastic blow pipe that comes with the can)and let it set for a few minutes then blow all of the passages out with both needles removed with a good shot of air. Stubborn trash may have to be pushed out of the jets with a soft tag wire follwed by another shot of air.Let us know lol

 

It appears you have not cleaned the carburetor, merely installed a new kit. The surge is a symptom of a lean condition. The fact you can turn in the air/fuel screw (which is actually a fuel adjusting screw for the idle circuit) is because you are likely running the engine above idle RPM's and this needle has very little effect on performance at anything above idle RPM's. The "jet" as you referred to is the main adjusting needle and this handles fuel delivery at anything above idle RPM's. You need to remove the carburetor again and soak it in a quality bath type cleaner (I like Napa's #6402) and then spray out with a spray cleaner and then blow out with compressed air and then install the kit. While you're there, check for any fuel in the brass float and replace such if any fuel is present. Also, be sure to replace both mounting gaskets, Tecumseh part numbers 31688A and 27915A.

 

Hi again,

thanks for the very helpful information. It is a bowl type carb. I took it apart, sprayed some more carb cleaner through the idle mix screw circuit and noted that I am getting some spray coming through the inside threaded area of the metering rod area. It looks like one very small stream of spray, but I thought I should see 2 streams of spray in that area?? (I am referring to the orfice where the main bowl screw would screw into). I put it back together with the main bowl needle out 1.5 turns and the idle air mix out 1.25 turns. It's still surging at idle but smooths out a bit if I turn the idle air mix screw in quite a bit. Of course, doing that raises the idle which to me means it's bypassing the idle circuit alltogether. It does smooth out a bit at wide open throttle though. I just took it all apart again and put it in the parts cleaner basket and will try again tomorrow (Sat). Prior to me throwing in the towel on this one, do you guys have any other suggestions if this overnight soaking doesn't work? I might add that I did blow tons of compressed air through all circuits, and I am positive that all linkages are in the right holes.

 

The idle mixture is not meant to adjust idle speed. Idle speed should be set using the screw stop that connects to the throttle plate. Adjust the screw out/CCW until the screw is not resting on the stop, then turn it in/CW until it just starts to hit the stop. The idle mixture may now need to be adjusted to get it to idle. Once adjustment is made then the idle speed can be set to correct rpm.
As Puey mentioned the idle circuit is not in use beyond throttle movement that causes the butterfly to move beyond the idle passages in the throat (Higher RPM)

 

Soaking it in a spray cleaner likely will not do the job, try the solution I mentioned above. Be sure to buy protective gloves and eyeware when handling this powerful cleaner.

 

Hello Folks,

I know this is an old thread but I just wanted to add my 2 cents.. The problem the Original poster complained about - Engine will run only with the mixture screws all the way in" can often be caused by the choke butterfly not correctly set. I have seen this exact problem on tecumseh engines where someone has swapped carbs on, and the original choke actuating linkage is not connected, Most of those old H50,60, etc. carbs had the choke plate on a spring which caused it to be fully closed by default. if you are experiencing this kind of problem, have a quick look at the actual position of the choke plate in the mouth of the carb. The mixture settings on the tecumseh adjustable carburetors is to be done with the engine fully warmed up and the choke fully open!

T. Lawrence
LMS Power Equipment Repair
Ledyard Machine, Inc. - machine shop | Small engine, Motorcycle & ATV Repair | Gunsmithing