tecumseh 7 hp carb question

mikefealk · 12-06-2008, 08:20 PM

one more question. Vintage yardman snow bird snowblower early 70s I believe. h70 tecumseh motor. the carberuator has no high speed adjustment screw on the bottom of the float bowl, as most old tec's have. also, there is one hole for an adjustment screw on the side of it opposite the fuel line. is this the main jet? Now heres the real question. When I recieved this antique there was a screw in this hole with a tiny hole in the end, and not a sharp cone shaped adjustment screw. There also was no spring, or rubber/metal washer in it. I believe this is the incorrect screw to be in this hole. I took the idle speed adjustment screw out of another tec 7 hp I have, and put it in the carb, and it seemed to run better. Im not sure which one is correct.

MrChooks · 12-07-2008, 11:57 AM

Mike - have a look at the attached "LHead" Tec manual that was brilliantly located by my TSF colleague SABL

http://www.smallenginesuppliers.com/...nformation.pdf

Chapter 3 covers Tec's carbs and hopefully you can locate which one is yours and see if the jet adjustments you need are covered there.

k2skier · 12-07-2008, 03:30 PM

What must have been done is someone replaced it with a new style carb, maybe the only thing available, or someone just stuck on any newer carb ( I would guess the later to be true as most replacement carbs that were adjustable, the replacements were also). The idle air bleed screw that you removed is the correct style of screw (fixed air bleed jet) for the newer emission compliant carbs, do not put any thing else in the hole other than what came out of it. When you removed the idle air bleed orifice it will allow more fuel to enter the system, and by installing a standard screw in it you may have caused damage to the carb. With Tecumseh going bankrupt, parts will be hard to find after 2009.

Ad; all Tecumseh carbs have the same body and bolt pattern, most will interchange, be careful someone didn't put a vertical shaft lawn mower carb on it, the venturi is too small and the jets are way too small for an H70.

mikefealk · 12-07-2008, 03:52 PM

thanks for the info. so should the idle air bleed screw be adjustable in and out (w/ a spring) and washer, or should it just seat all the way in?

MrChooks · 12-07-2008, 04:16 PM

Not sure about your specific carb - but my experience with carb adjustment screws has been that they have a spring and resistance washer to stop vibration from "shaking them out of adjustment".

I have seen some (on cheap and nasties) without a spring and washer - but these were "cheapies" and they used a deformed thread arrangement to make the screw thread tightish all the way along its length - The idea works - but quickly wares out and then it's a PiA

.

Anyway, the spring & washer are there to create interference to the screw turning - so, so long as your's is a little tight to move (along its entire length) you might get away without needing one.

A more important issue is that raised by k2skier - make sure you have the correct screw / jet in place - and you may need some inputs from a good Tec repair shop 'cause these parts are very similar and very often inter changeable (fit wise) to one another and even though a Tec carb part may fit - it can still be hopelessly wrong

hence a skilled and experienced eye is needed to select the correct jets and adjusters

k2skier · 12-08-2008, 10:10 AM

Quote:

Originally Posted by mikefealk

thanks for the info. so should the idle air bleed screw be adjustable in and out (w/ a spring) and washer, or should it just seat all the way in?

It needs to be seated all the way in.

mikefealk · 12-10-2008, 06:46 PM

thanks, so if it needs to be seated all the way in, whats to keep it from loosening if it doesnt have a spring?

k2skier · 12-11-2008, 11:37 AM

It's a tapered seat, just being snug is enough to hold a tapered seat.

jroberts · 12-19-2008, 12:34 PM

I have a eatons viking snowblower.The engine is a 2 stroke it starts and runs but dies after a few minutes.Maybe someone mite no whats wrong

MrChooks · 12-19-2008, 03:39 PM

Hi & welcome to TSF

It's better if you start a new thread for a new issue / problem

OK - on to your problem - as your engine starts and runs OK at first, we can discount ignition and initial fuel flow issues - so that leaves fuel starvation.

One problem that manifests itself in your symptoms is a blocked fuel cap vent. The fuel tank has a tiny breather hole in it - usually in the fuel cap to stop a vacuum forming in the tank as fuel is burnt - which, if blocked, then starves the engine of fuel.

Try this, start the engine and loosen the fuel cap so it isn't sealing perfectly, if the problem goes away, strip the fuel cap and see if you can locate a small (about a needle thickness in diameter) hole and see if you can clear it.

Let us know how you get on

12-06-2008, 08:20 PM	#1 (permalink)
mikefealk Registered User Join Date: Dec 2008 Posts: 7 OS: xp	tecumseh 7 hp carb question one more question. Vintage yardman snow bird snowblower early 70s I believe. h70 tecumseh motor. the carberuator has no high speed adjustment screw on the bottom of the float bowl, as most old tec's have. also, there is one hole for an adjustment screw on the side of it opposite the fuel line. is this the main jet? Now heres the real question. When I recieved this antique there was a screw in this hole with a tiny hole in the end, and not a sharp cone shaped adjustment screw. There also was no spring, or rubber/metal washer in it. I believe this is the incorrect screw to be in this hole. I took the idle speed adjustment screw out of another tec 7 hp I have, and put it in the carb, and it seemed to run better. Im not sure which one is correct.

12-07-2008, 11:57 AM	#2 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: tecumseh 7 hp carb question Mike - have a look at the attached "LHead" Tec manual that was brilliantly located by my TSF colleague SABL http://www.smallenginesuppliers.com/...nformation.pdf Chapter 3 covers Tec's carbs and hopefully you can locate which one is yours and see if the jet adjustments you need are covered there.

12-07-2008, 03:30 PM	#3 (permalink)
k2skier Registered User Join Date: Sep 2008 Location: Oregon Posts: 313 OS: XP Home-SP3 My System	Re: tecumseh 7 hp carb question What must have been done is someone replaced it with a new style carb, maybe the only thing available, or someone just stuck on any newer carb ( I would guess the later to be true as most replacement carbs that were adjustable, the replacements were also). The idle air bleed screw that you removed is the correct style of screw (fixed air bleed jet) for the newer emission compliant carbs, do not put any thing else in the hole other than what came out of it. When you removed the idle air bleed orifice it will allow more fuel to enter the system, and by installing a standard screw in it you may have caused damage to the carb. With Tecumseh going bankrupt, parts will be hard to find after 2009. Ad; all Tecumseh carbs have the same body and bolt pattern, most will interchange, be careful someone didn't put a vertical shaft lawn mower carb on it, the venturi is too small and the jets are way too small for an H70.

12-07-2008, 03:52 PM	#4 (permalink)
mikefealk Registered User Join Date: Dec 2008 Posts: 7 OS: xp	Re: tecumseh 7 hp carb question thanks for the info. so should the idle air bleed screw be adjustable in and out (w/ a spring) and washer, or should it just seat all the way in?

12-07-2008, 04:16 PM	#5 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: tecumseh 7 hp carb question Not sure about your specific carb - but my experience with carb adjustment screws has been that they have a spring and resistance washer to stop vibration from "shaking them out of adjustment". I have seen some (on cheap and nasties) without a spring and washer - but these were "cheapies" and they used a deformed thread arrangement to make the screw thread tightish all the way along its length - The idea works - but quickly wares out and then it's a PiA. Anyway, the spring & washer are there to create interference to the screw turning - so, so long as your's is a little tight to move (along its entire length) you might get away without needing one. A more important issue is that raised by k2skier - make sure you have the correct screw / jet in place - and you may need some inputs from a good Tec repair shop 'cause these parts are very similar and very often inter changeable (fit wise) to one another and even though a Tec carb part may fit - it can still be hopelessly wrong hence a skilled and experienced eye is needed to select the correct jets and adjusters

12-10-2008, 06:46 PM	#7 (permalink)
mikefealk Registered User Join Date: Dec 2008 Posts: 7 OS: xp	Re: tecumseh 7 hp carb question thanks, so if it needs to be seated all the way in, whats to keep it from loosening if it doesnt have a spring?

12-11-2008, 11:37 AM	#8 (permalink)
k2skier Registered User Join Date: Sep 2008 Location: Oregon Posts: 313 OS: XP Home-SP3 My System	Re: tecumseh 7 hp carb question It's a tapered seat, just being snug is enough to hold a tapered seat.

12-19-2008, 12:34 PM	#9 (permalink)
jroberts Registered User Join Date: Dec 2008 Posts: 1 OS: Vista	Re: tecumseh 7 hp carb question I have a eatons viking snowblower.The engine is a 2 stroke it starts and runs but dies after a few minutes.Maybe someone mite no whats wrong

12-19-2008, 03:39 PM	#10 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: tecumseh 7 hp carb question Hi & welcome to TSF It's better if you start a new thread for a new issue / problem OK - on to your problem - as your engine starts and runs OK at first, we can discount ignition and initial fuel flow issues - so that leaves fuel starvation. One problem that manifests itself in your symptoms is a blocked fuel cap vent. The fuel tank has a tiny breather hole in it - usually in the fuel cap to stop a vacuum forming in the tank as fuel is burnt - which, if blocked, then starves the engine of fuel. Try this, start the engine and loosen the fuel cap so it isn't sealing perfectly, if the problem goes away, strip the fuel cap and see if you can locate a small (about a needle thickness in diameter) hole and see if you can clear it. Let us know how you get on