OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Tecumseh / Kirby Engines carby adjustment

hi i have a cox Orion ride on with a 12.5hp B&s motor model 2030400 dom 9340(R)
and my question is it has a adjustment screw under the carby bowl can anyone tell me how many turns out it needs to be to start tuning. as when i got it it was screwed in and he said it wouldn't run properly and he didn't know why.now i own it.

Hi blackriverfish, welcome to Outdoorking.

Please post the full Model, Type and Code numbers for your engine so we can check its Illustrated Parts List and see what kind of carburetor it has. The numbers you have quoted are not correct - the Model has too many digits, the Code is just plain wrong, and you didn't give us the Type at all.

hi thanks
the motor is a Tecumseh 12.5hp and on the ID plate it has model OHV125 203040D (E)
then underneath it has D.O.M.9340 (R)
i assume this is a replacement engine???
thanks in advance for all the help just found this site and it is very helpful.

I can't find any reference to a model called Orion in the manuals section, if you have a model number I might be more successful.

The screw projecting vertically downward from the center of the float bowl is the main mixture adjustment. According to the Tecumseh 4 Cycle Overhead Valve Engines Manual, the preset adjustment for all models having that type of carburetor, is 1.5 turns from fully screwed in. Incidentally, with the screw fully in there should have been no fuel flow through the main jet.

This is the carby tp left is the id plate

The screw projecting downward from the center of the float bowl (circled in red) is the main mixture adjustment. The horizontal screw just above the top edge of the float bowl (circled in green) is the idle mixture. Preset adjustments (that is, the starting point for tuning the carburetor) are 1.5 turns from fully screwed in for the main mixture, and 1 turn for the idle mixture:

thanks for the quick reply
now all i have to do is replace start solenoid clicks but doesn't make contact

That is seldom a defective solenoid, about 8 times out of 10 it is a flat battery or poor high current terminal connection at battery or solenoid. Second most common is a poor low current connection at solenoid or key switch. Defective solenoid is (in general) a distant third most common. On used ride-on mowers, messed up wiring is a very common problem, so if the battery is OK and so are the connections, check the voltage at the low current terminal (from the key switch) of the solenoid when you turn the key to start. If voltage is low there but high at the high current solenoid terminal, trace the wiring, and find out how much damage the previous tenant did.

did all that put a multimeter across low side and it was open circuit put on a new one and away she want woohoo all is good next tune up as it is hunting.

You probably know that hunting is usually caused by lean mixture, but occasionally it is due to a misaligned/bent linkage causing friction in the mechanism. Sounds like the first step might be to increase the main mixture adjustment setting to a bit more than the starting pre-set of 1.5 turns.

yes i tried to adjust and it maid no difference so pulled out and it looks like someone has filed of the tip as it is short with a flat tip so will get a new one.

That sounds odd. It is obviously possible that someone mangled the needle, but the result should be that you can make it either rich or lean, with no transition in between. If the needle was simply cut off very short to make the mixture non-adjustable, it should be extremely rich. Since it was hunting, it is most likely lean, and it sounds as if something else sinister has been done, such as soldering up the bore of the main jet then drilling a smaller hole than it had originally, so it acts as a fixed jet instead of an adjustable one. I think you are going to need to remove and strip that carburetor, cleaning and inspecting the parts as you go.

i think so to.i just ordered a carby kit so will replace all when it arrives (632347). will take photo so u can see,when i cleaned the carby it was full of gunk and varnish so a good strip and soak with new parts will do it the world of good.

blackriverfish, I suggest you take advantage of a free download of the full service manual for your engine, which includes detailed carburetor overhaul information:

http://th.manualwebsite.com/pdf/4-cycle_ohv.pdf

Your carburetor is described as Series 3 or 4, so do not be distracted by instructions for the other types, up through Series 10 and the Walbro LMK used on the last of the OHV Tecumsehs.

Tecumseh carburetors have a fairly evil reputation, but most of them can be serviced very successfully by following the instructions and having a kit of service parts close to hand. Note the warning not to remove any "cup or ball plugs", but this does not apply to ordinary Welch plugs provided replacements are included in the overhaul kit. (However, I personally don't remove Welch plugs unless every other approach fails, which it seldom does.) I think you will need to use a spray can of proper carburetor cleaner to actually get the gum out, but do not put it on plastic or elastomer parts, and blow it out immediately after spraying it on or squirting it into passages. In my experience, lesser solvents do not remove hardened gum (and emulsifiers, in particular, often require multiple blasts to get the small radial holes clear. On Honda carburetors I often have to use jet drills on the radial holes of less than 0.5 mm).

Here is a diagram showing the working parts of your carburetor:


As I said previously, I currently suspect that there has been foul play in that carburetor, and you need to be on the lookout for "tenant's improvements" made before you got this machine. Look especially for signs that the "main nozzle" (a combined main jet and emulsion tube) is either fouled or modified. If you are lucky, it is badly fouled and the previous tenant amputated the working part of the main adjustment screw to compensate for this, rather than clean it out, then when the fouling progressed even further and it became lean despite the amputated adjuster, he/she disposed of the machine.

We are here to help at any time. Please don't become one of the people who conclude that Tecumseh carburetors are unfixable garbage: they are not unfixable unless made so by previous attempts to repair them.

wow thanks for all that information this a photo of the mixture screw and float after first clean it was ugly

You have to get the emulsifier/main jet out of the carburetor body before you will get anywhere. If it doesn't come out easily, it is probably stuck in by hard gum. That happens a lot to Honda emulsifiers, and is something of a hassle with them, because they are only held in by the main jet screwing up from below and pressing hard against the bottom of the emulsifier. With those, you mustn't push down hard from the top or you'll damage the top of the brass emulsifier, which is the discharge area. In the case of your Tecumseh though, I suggest that the emulsifier probably screws in with a thread near the bottom, and there is currently lots of hard gum gluing it in place along the length of that thread. Just check whether there is a screwdriver slot in the bottom of it, right above where the mixture screw goes in. (Most likely the slot will have been completely trashed by the yahoo who had it before you.) You have to remove the gum so you can unscrew it, and this whole exercise will be quite a trial if there is no slot left. Regardless of that, removing all of the gum is the first step. I rather suspect that in the end the emulsifier will be a total loss by the time you get it out, and you'll have to source another one somehow. I don't think it will be possible to clean out the lateral/radial holes in the emulsifier without removing it from the carburetor. Please keep us posted as you go with this, before you trash it the rest of the way, just in case we can find a non-destructive solution.

thanks well there no adjustment at all it ether surges or dies. and it looks like there is no slot to screw out emulsifier so i would say its a press fit hopefully the repair kit has one if not it will be softly softly till i get it out.in the old days we used to soak rusty tools in malases i wonder if that would work with this wont hurt but may help.

o no there is none in the carby kit.

I don't think molasses will help with hardened petrol gum, and I don't think it will penetrate a tight thread. The stuff that works is a spray can of carburetor cleaner, and it is almost miraculous if you haven't used it before. However it can't dissolve what it can't reach, and that may be a problem in this case.

Can you post a picture of the carburetor from underneath, as close as possible, so we can have a look at the "main nozzle" (that is, the emulsifier) and try to work out how it is retained in the body casting? I'm used to them being screwed in. I just can't see it being pressed in because you then wouldn't be able to get it out for cleaning.

photos of carby

Thanks blackriverfish. I agree, it does not look as if that used to have a screwdriver slot. It still has an entry radius and I can't imagine the previous tenant having reproduced one of those, and polished the thing, if he/she had just finished ripping the screwdriver slot off it due to overenthusiasm.

You seem to now have a couple of options. The one I'd consider first, is trying to pull the whole main nozzle out of the carburetor. I'd try cleaning it up thoroughly to get the gum off, then use a short piece of steel tubing, with a longitudinal split down the outside, pushed over the outside of the bottom end of the main nozzle. Use a clamp around the outside of the tube to tighten it onto the main nozzle, then pull and/or twist the tube.

If you conclude that this will not work, you have a crude-fix option available. If you blast carburetor cleaner into the hole in the base of the main nozzle (using the long thin extension tube that comes with the can of cleaner), giving say three half-second bursts, you will probably clean out the whole length of the tube, and the main discharge orifice at the other end of it. What you probably won't do though, is open up the air ports near the bottom that make it an emulsifier - see red circle on diagram:



However it may be just about possible to clear them by putting your finger over the main discharge orifice (finger in the venturi of the carburetor) while you do the carb cleaner blasting, hoping that the plugs of gum in the radial holes will be pushed out and dissolved.

those 2 marks are reflected light,have given a good dose of carby cleaner and a lot gunk came out ,can u push it out from inside the venture .i looked the mixture screw under a magnification and it was very pitted.but the new one will fix that.

You may be able to push it out from the top, but that approach is fraught with difficulties. Here is a Honda (Keihin) one I tried that on:


The problem is that the top (main discharge) of emulsifiers is precisely shaped to do a job, and it will do a different one if its shape changes.

I think the key issue here is whether the main nozzle is actually held up by the float bowl retaining nut. If it is, it is now only supported by gum, and if you do a good enough job of removing the gum, it should drop out. Can you carefully inspect the top of the nut, and the bottom of the main nozzle, and tell us whether they are supposed to be in contact when the nut is screwed in fully? If they are, the nozzle is now only supported by gum, so you just need to remove nearly all the gum and soften the rest, then push the nozzle downward from the venturi end, as you proposed. I think it is safe to try this if you only push very gently on the top of the nozzle. If it won't drop out with gentle pressure, hit it again with the carb cleaner. I can tell you that we have had a couple of threads where people tried to do this with Honda carburetors and failed - presumably through not enough persistence with the carb cleaner, because on those carburetors the emulsion tube is definitely a loose fit in the carb body, and drops out readily if it is not gummed in.

On the other hand, if the top of the bowl nut does not contact and support the bottom of the main nozzle, it is probably a press fit and cannot be removed. If you look at the Carburetor Disassembly Procedure on Page 14 of the manual (Page 17 on the Acrobat page counter) it tells you to remove the "main nozzle tube" on Series 7 carburetors only. The subject is not mentioned for other series, and that makes me worry that it may not be removable.

well i have tried every thing and it wont move.i even pulled the butterfly s off and tried rotating it and it wont move and the bottom of the main nozzle doesn't touch so now i assume its a press fit.i put my finger over the outlet then filled it with cleaner 3or 4 times a lot of gunk came out so hopefully the air ways maybe just a little bit clean wont know till it assembled and tested.

If the bottom of the main nozzle doesn't touch the top of the bowl nut, it seems like the nozzle would have to be pressed in or it would not be positively located. That also lines up with the instructions only referring to it being removable on the Series 7 (yours is Series 3/4). So, the next trick is to get as much gum out as you can, then try it. Did any crud come out the last time you blasted it with the discharge nozzle blocked? When you do that, is crud coming out of the main air bleed, close to the throttle plate? If you can squirt cleaner in the bottom of the main nozzle and have it come out of the main air bleed, I think it has to be going through the radial holes to get there.

well i filled the tube with cleaner with my finger blocking it off then hit it with compressed air 6/7 times till it ran clear and that was after a soak.so not much i can do now but wait for parts to arrive then test added is a photo of tube in the venture

It would be worthwhile running the engine, and seeing how many turns of the main mixture adjustment screw gives the best results. If it is about 1.5 turns, chances are things are working reasonably well.

Remember to clean the small ports in the float bowl retaining nut - these seem to be Tecumseh's version of the main jet and idle jet:


Incidentally, there appear to be two screws holding the throttle plate to its shaft. That makes your carburetor a Series 4, not a Series 3 (which only has one screw, same as the choke).

yes it is a series 4 with 2 screws

well good news i reassembled carby with the old parts to test and it runs good no hunting bet not much adjustment but that will be fixed with the new parts,so i would like to thank you and this forum for all your help.will let you know how it goes with the new parts.