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1978 model rototiller, and snowblower of probably the same vintage or not far from it. Both engines have done the following and I'd like to know what's going on.
The engine will start and run at a low speed if operated at near-full choke. If the choke is opened gradually, the engine will speed up, until about half choke - at which point, if the choke is opened up further, the engine stalls out. This is what happens on the snowblower. It happens similarly on the rototiller except that the rototiller has a throttle control. (Opening the choke doesn't change its engine speed all that much, but it will still make the engine stall. It runs best at no more than half choke.) The engine will only start and run at about 1/3 throttle. Raise the throttle any further and the engine eventually stalls out.
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
44,585 posts, read 81,206,701 times
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Too much air (open choke) usually means not enough gas. It needs a full flow of gas and air to run at full speed. You might try putting a fuel system cleaner in it, such as Gumout or Seafoam.
Too much air (open choke) usually means not enough gas. It needs a full flow of gas and air to run at full speed. You might try putting a fuel system cleaner in it, such as Gumout or Seafoam.
I figured that might be the issue - but I did clean the carb on the rototiller engine before I ran it. Is it possible that I didn't do a good job? Maybe. Does that Gumout / Seafoam stuff go in the gasoline or does the engine have to be partially disassembled and sprayed?
the carburetors from those vintage small engines were pretty crude devices, but they still have some very tiny passageways for airflow and fuel delivery.
It doesn't take much to plug those up so that the carbs aren't delivering enough fuel through the main fuel circuit. Hence the engines run on the choke which enrichens the fuel circuits that are delivering, but when you open the choke up the airflow cannot pick up the fuel anymore.
A thorough cleaning of the carbs; ie, tear-down, soak in carb cleaner (or ultrasonic cleaner tank, my favorite for these carbs), blowing out the passageways, and installing a "carb kit" may restore them to proper working order. It is unlikely that a fuel system cleaner will be able to clear the obstructed passageways. It is entirely possible that your work to "clean" the carb simply didn't get all the junk out of the passageways, or that the carb is so worn/distorted that is cannot function properly anymore.
Given the cost of a carb kit and the labor involved, you may be dollars ahead to replace the carbs with new ones. I do that more frequently than not anymore on old equipment .. when a carb kit is $18 and a new replacement carb is only in the $30 range, it's not worth cleaning out the old carb.
Too much air (open choke) usually means not enough gas. It needs a full flow of gas and air to run at full speed. You might try putting a fuel system cleaner in it, such as Gumout or Seafoam.
Quote:
Originally Posted by sunsprit
the carburetors from those vintage small engines were pretty crude devices, but they still have some very tiny passageways for airflow and fuel delivery.
It doesn't take much to plug those up so that the carbs aren't delivering enough fuel through the main fuel circuit. Hence the engines run on the choke which enrichens the fuel circuits that are delivering, but when you open the choke up the airflow cannot pick up the fuel anymore.
A thorough cleaning of the carbs; ie, tear-down, soak in carb cleaner (or ultrasonic cleaner tank, my favorite for these carbs), blowing out the passageways, and installing a "carb kit" may restore them to proper working order. It is unlikely that a fuel system cleaner will be able to clear the obstructed passageways. It is entirely possible that your work to "clean" the carb simply didn't get all the junk out of the passageways, or that the carb is so worn/distorted that is cannot function properly anymore.
Given the cost of a carb kit and the labor involved, you may be dollars ahead to replace the carbs with new ones. I do that more frequently than not anymore on old equipment .. when a carb kit is $18 and a new replacement carb is only in the $30 range, it's not worth cleaning out the old carb.
these guys are right, small engine carbs, especially ones of the vintage you are talking about, are finicky pieces of equipment. back in the day when i worked on them, we made sure they were squeaky clean before we put them together.
a long soak in a good carb cleaner, anywhere from 2 to 24 hours, should get the job done for you.
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
44,585 posts, read 81,206,701 times
Reputation: 57822
I have taken apart and cleaned the carbs this summer on my mower, chains saw, and tiller. All were having similar issues, and spraying gum out into various openings and passages did the trick. If you are not comfortable with doing that, putting it into the gas tank, according to the recommended amount can help. I would add it, run a minute or two, then let it sit a few hours and run again. Sometimes it can help to simply remove the art cleaner and spray into the carb through the air inlet alongside the choke plate.
another question, are these two stroke or four stroke engines? if two stroke do they use a reid valve in the intake system? if so then the reid valve might be failing, i have seen that before.
I was also going to suggest completely purging the engines of whatever fuel you're using, and run only ethanol-free fuel in them. Ethanol isn't good for any engine, but it seems to be even worse for the smaller ones like you describe.
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