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I have an ultrasonic cleaner. Cleaning several carburetors and using them on 4 different 8hp-9hp Tecumseh engines, all with the same problem, engine surging caused by the carburetors.

To clean the carburetors, I first used the manufacturer's carb varnish buster solution and having carb surging issues I then rebuffed the carbs and again disassembled them, switched to Berryman's Carb dunk cleaner in my ultrasonic cleaner. All when assembled and installed still having carb surging issues, all with several carburetors, and the side Welch plug was removed each time, jets removed, all holes were cleaned using welding tip cleaners, then each hole was cleaned using wire pin drill bits, again with the Welch plug removed. This was done twice with two different cleaning solutions. Not one carb on one engine. I also did not replace the two needles, I just cleaned them with fine steel wool.

I'm thinking of slightly increasing the diameter of the holes that are behind the side Welch plug then trying it out. I'm not sure if I should do anything about the small side angled side hole in the brass jet.

Using that little pin drill holder seems forever to drill holes in aluminum let alone brass, so I'm thinking my Dremel might be able to hold the wire pin drill bits.

Comments other than screw it and buy a Chinese carb. I want to discover the exact cause of this problem.
 

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I had to try drilling out a Chinese carb jet recently for a Briggs engine, the carb was running lean out of the box. I used the manual pin vise and kept spinning until I got through. It took maybe a minute or so. I'd try that before using the Dremel. I think my cheap micro drill bits said they're for manual use.

I didn't have a suitable drill size as I was working my way up, so I used a torch tip cleaner file, and worked that back and forth, to open the hole just a bit more. I didn't really like that approach, since I couldn't say the hole was size XX, but it did help provide more flow.

I was only doing the main jet in mine. That seemed to help it run properly (good power, no surging), at least when under a load (and using the main jet). It was still surging with no load. In this carb, from the drawing, the idle jet looked like it was going to be very difficult to access (it was behind a pressed-in plug), so I just unscrewed the main jet and limited my modifications to that.

But it definitely made a difference. Out of the box, it was surging with no load, and with a load, and it was weak when I put it into the snow. After gradually opening the main jet a few times (baby steps), I could at least get it to smooth out with no load, by adding partial choke (originally it kept surging even with full choke). And it gained a lot of power, and ran smoothly without surging, when I was blowing snow.
 

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Discussion Starter #3
RedOctobyr - Was this a replacement engine? A specific snow engine?

Most surging is caused by the idle/low speed holes.

Good you got more power, surprising it runs better but still surges. If a replacement plug is available, they are usually cheap, $1, and easy to replace. However they need to be sealed when replaced. I use a bright color nail polish to seal it. This tells me the carb has been cleaned and the plug has been replaced.

My Dremel Chinese clone has an adjustable speed so I will use the lowest.
 

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JL: are you saying that you have 4 different used machines with surging carbs? How old? I assume they once worked. It seems to me that opening up hole sizes is not the proper fix. Something has broke / wore out over the years. Did you replace the o-rings for the idle jets, and/or the o-rings on the emulsion tubes? Did you clean out the small vent hole on the main carb body? Are the throttle shafts wore out? Any chance you are opening up any the existing holes when using drill bits?

I know you have alot of experience on these machines, so I'm sure you are cleaning them well and assembling properly. Let us know how your modification works.
 

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i have a tec 8hp carb that only runs at full choke. so i watched donyboy's 4 part video and followed it to a T. now i can't get it to run at all but about 10 seconds.

I'm about to pull the hair out of my head as I have spent several hours on this. yes. there is fuel in carb. as dony suggested the air screw is out one turn and the main jet is out a turn and a half. have tried different adjustments to get it to keep running with no success.

have cleaned out scores of Honda carbs and this tecumseh carb cleaning is easier than a Honda carb.

if i am having to run full choke when it was at least running does this suggest main jet or something else? I think all you have on this carb is the main jet and the air/fuel screw. i did not see donyboy address and idle jet in his video.

this blower was given to me and everything works great except this carb issue.
 

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I keep 3 of the small block Tec carbs and 3 of the medium block ones on the shelf at all times ( Chinese!), and if a simple bowl drop and inspection with a wipe and squirt of cleaner doesn't do it, I swap it out. I have a bucket of Tec carbs that need cleaning I I'm really bored, or run out of Chinese carbs.
 

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are the carbs non adjustable carbs? donyboy73 did a video on that said they can be finicky and it is sometime better to swap out carbs with an adjustable carb
another good one to watch
 

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JL, it's a 2-stroke snow engine, a Briggs R-Tek in a Toro SS.

I got a $10 carb on Amazon, which surged and ran lean with no load, and with a load. Seller sent a replacement, exact same behavior. No air leaks that I could find.

Opening the main jet helped it run smoothly, and gain power, with a load. I tried that drilled jet in both carbs, they both ran better with it. But would still surge without a load, presumably due to a lean idle jet.

That plug I mentioned wasn't a Welch plug. On the carb drawing from Walbro, it looked like maybe a ball bearing, or similar, pressed into the drilled hole.

In the meantime, I got the rebuild kit for the original Walbro carb. It ran nicely with a new needle, and cleaning it. No surging at "idle", after it warms up for about a minute. Good power, and no surging, under a load.

So I'm sending the Chinese carbs back. Maybe it was just a bad batch of them, maybe their drills were a little too small when making these ones, I don't know. For this model engine, I could not find any adjustable carbs, original or aftermarket, sadly.
 

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It might also be that the fixed jets were set for summer conditions. The last Tec I redid, I finished in the summer, and had it tuned perfectly. The first time in the cold, and it ran like crap and required a redo . . . the cold, denser air can really make things go lean . . . . If those were 'universal' carbs, they just may not be suitable for use in the cold . . . ? ? ?
 

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That's certainly possible, good point. They were listed as being for my Toro snowblower, and others. But that doesn't guarantee they're not actually the same as ones set up for lawn mower use.
 

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I think that for ChinFatCo products, if the fit is close, they call it good with very little consideration to application, but I could be wrong . . . and fixed jetting certainly does not help . . .
 
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