/diy/ - Do It Yourself

>>2792305
I can help you as long as you give me the information I ask for and take pictures of what I request.
First things I need from you are:
who makes that? looks like briggs & stratton.
the model number which is a series of number stamped in to the cover. could be on the top near the spark plug, could be on the sides, could be on the side opposite the spark plug.

I think that is a pulse a jet carb.

>>2792541
i figured anyone who know their stuff could recognize it at a glance
its a briggs 94500 series, 3.5hp
i too think the carb has a diaphragm pump, but i think that part is fine. starts on half a pull and guzzles fuel.

>>2792659
Ok. so your mower appears to have been made in 79. I am researching but this model has very little information.

>>2792836
ha me and my luck again.
but following on my op post, what would be the general order of procedure of "tuning" the govener max tension and fuel mixture?
Should i follow the manual and lean it out more while running it past 4000 rpm until it finally drops, or is it only running that high cause the govener tension is too high due to the missing stop screw? like i mean these engines are simple and similar enough

also, you have any idea what that first visible butterfly valve does?

>>2792305
>The manual says adjust throttle cable (green circle) until the screw (missing, red circle) touches the casting.
the missing screw is very likely the idle adjustment screw. when the throttle is set to idle the screw should contact the stop. the way you would adjust that is to install a screw (with a spring under the head of the screw the spring holds tension on the screw to prevent it from turning and changing the idle speed.

to find the idle speed you would install a screw and start the engine then push the throttle until the screw touches the stop. then adjust the screw till the engine starts to shutdown. you want as slow of an RPM as you can get but the engine does not quit. you do not need an rpm gauge for this.

>>2792843
>the missing screw is very likely the idle adjustment screw. when the throttle is set to idle the screw should contact the stop
no the screw is called top-no-load stop and it should make contact at full throttle.
on the opposite end of the arm there is this part, the kill switch. afaik this carb does not have an idle screw, there is a similar model which does have one

>>2792846
here a pic of the two different carb types

>>2792305
>Step two would be to lean the engine (screw orange circle) until the revs drop and then turn back half a turn, but if i lean the engine with full throttle it will rev way past 4000 rpm an i know this is not safe to do

I see you have one of those inductive RPM gauges. make sure it is configured correctly. that mower will spark every 1 revolution.
press the S1 button for 4 seconds if it says 02 that should be correct.

the instructions for this mower give idle rpm as 1750 which seems high to me. I (so far) cannot find a maximum RPM.

>>2792842
>also, you have any idea what that first visible butterfly valve does?
that is the automatic choke.


I am doing more research on what would be a safe max RPM.

>>2792863
>I (so far) cannot find a maximum RPM.
guess its 3600 as printed on the cowling

>>2792847
you engine and carb are in the Briggs & stratton repairman's handbook engines 1919-1981 ce8069.pdf

your carb is the Automatic choke. "vacu-Jet carburetor.

>>2792865
>guess its 3600 as printed on the cowling
well yes. the only other way to get a max rpm is to do some calculations based on the blade diameter.

>>2792846
>no the screw is called top-no-load stop and it should make contact at full throttle.
ok my bad the diagram is not the best.

then you would just set this to a max of 3600 rpm.

>>2792846
so the adjustment would be as such:
install a screw in the top end stop. rev the mower to 3600 rpm or lower.

adjust the needle valve and throttle to get the highest rpm that runs smooth regardless of what it is. reduce the throttle to 3600 rpm.
turn the high end set screw to touch the side of the carb at that rpm.

then just follow the instructions in the manual you are referencing from the start.

>>2792878
>adjust the needle valve and throttle to get the highest rpm that runs smooth regardless of what it is.
alright, just asking since im more versed in two strokes. Is there potential for catastrophic engine failure due to running to lean?
I will set it up tomorrow like you explained, thanks my dude

>>2792883
as long as you don't run the engine for more than a minute or so above 3600 rpm it should be ok.

all >>2792878 this is doing is getting you a base line to start the adjustment from the start.

I would check the spark plug if the carb is running too rich the plug will be caked with black soot. clean it then adjust the engine. run it for a while and check the plug again. there are pictures on line of what a properly adjusted fuel to air ration should look like on the spark plug.

setting the max rpm via the needle may make it higher. then you reduce the throttle with the lever and set the screw. this should set the max RPM at or below 3600.

readjust the carburetor again and reset the screw if the engine runs too fast.

>>2792871
this is the formula for safe blade speed
19000 ft per minute is max blade tip speed. some kind of law or safety thing.

19000 divided by (blade length x 3.14 Divided by 12) = max engine rpm
19000/((21x3.14)/12)
19000/(5.495)=3457

This is the max rpm for a blade tip speed below
19000 foot per minute

so 21" max engine speed to fall under 19000 fpm is 3457 rpm

so I would set the speed to 3400 if 21" blade and 3600 for 20" blade.

ok, i did the carb adjust at lower speed and then after adjusted the throttle cable for max rpm. runs nice when warmed up, will further fine tune with the spark plug buildup
>>2793239
>so I would set the speed to 3400 if 21" blade and 3600 for 20" blade.
the manual says mow speed should be ~3000 rpm (i guess epa) , but since i will abuse this one its nice to have headroom for tall grass.
So far the limiting factor on this mower is not horse power but the rear chute clogging up, i can live with that

>>2793328
when that mower was made EPA and safety were not a major concern. the date code on that is 79. it has no kill bar or engine brake. That's a keeper and with good care will last 30 years or more.

mix some barrymans, or seafoam in the gas and it should remove some of the carbon buildup that is almost certainly inside the cylinder head and around the valves..

>>2793334
>it has no kill bar
one of the reasons i bought that one

>>2792305
Unrelated but figured I'd share anyway
am I retarded for doing this ? My other property has real fucked up tall grass and it keeps binding at the output so I wired it open with #12 copper
Disregard the toe nail jammed it rock climbing last week

>>2793360
i have wire on all my side chutes so it throws the clippings in a 2m wide stream

>>2793360
I had lawn mower that was recent made and it came with the side opened like that. not a big deal. now if it was at the back that could be dangerous.