Please explain primer bulb function

[Chevboy0167]

I moded my Kawasaki X2 jet ski with a plunger primer to shoot fuel into both intake manifold runners before the reeds. Started all the time every time with 3 pumps.

 

[pioneerguy600]

I moded my Kawasaki X2 jet ski with a plunger primer to shoot fuel into both intake manifold runners before the reeds. Started all the time every time with 3 pumps.

View attachment 982065

I used that same primer on all my snowmobiles, they were a bugger starting them in the high humidity , severe cold winters here.

 

[Old2stroke]

When you are operating the primer bulb, as soon as you can feel that you are squishing fuel through the bulb rather than just air, it's time to stop pressing it. If it isn't pumping fuel, there is an air leak somewhere in the fuel supply, leaking nozzle check valve in the carb or maybe a bad primer, any suspect issue with the primer can be resolved by disabling it, just pull the primer line off the carb, plug the line and push it back onto the carb. Without the primer you will just have to rely on the choke to fill the carb with fuel, a little more pulling.

 

[Okie]

Maybe already mentioned:
Lots of info on-line about such and how to test.

 

[Syncop8r]

As others have said many "primer" bulbs are actually purge bulbs - they purge air from the system (which draws more fuel into the carburetor).
This video explains it well; understanding the concept is essential when reconnecting the fuel lines:

 

[SLV-JIM]

If purge bulbs were introduced on Pro saws before homeowner saws they would be all the rage!

 

[thenne1713]

I have worked on many auto, boat, lawn equipment and generator motors etc but I am not
familiar with exactly how or what the primer bulb does. I know what priming means.... in the old
days just squirt fuel into the system to get it ready to run when usually cold. I have one chain saw
that says five squeezes of the bulb for cold start and another that says ten squeezes of the bulb for cold start. From the side of the bulb that would be squirting a massive amount of gas into
the intake guaranteeing flooding so i think something else must be going on. Where does the bulb squirt the fuel ? I dont really know how a chain saw carb works because I dont think
it has a carb bowl and carb float on account if the saw working in all different kinds of positions.

Maybe good time to tell the story of little Poulan primer fuel line; 1-inch long between primer and carb, it had a small almost crimp that would prime fine, start first pull and die 15-seconds later. Repeatedly (Short version of long story)= CURE finally determined to be trimming 1/8" from line length to slightly straighten line, removing crimp (allowing FREE FLOW of fuel), and all cured.

 

[KASH]

The primer Chevyboy showed is the type I install even put one on a pioneer 1450.
Primers are a god sent on snowmobiles even if the temp is -40 one or two pull starts are usually the norm. I have a few older snow machines that have the Mikuni carbs with no choke just a primer I always carry a Sunlight soap bottle with mixed gas just in case.
The older machines with Tilly carbs really benefit from the primer way less pulling.
Trust me when a Tilly acts up you can go a long way just using the primer.
These primers dry up during summer storage it doesnt look like the come apart but they do and you can change the o ring and loosen the check valves I usually pull some brake fluid in the primer before storing the machines work like new when you go to start the machine in the fall.
Kash

 

[ValleyForge]

if it has a choke lever, then its just a purge bulb

Yep…on the 500i, the bulb pressurizes the high end fuel circuit …..

 

[skids-stihls]

I know this is an old thread, but I’ve already started a few in my short time as a member, so thought I’d try my luck here first.
Purge bulb on an Echo CS3400, no matter how many times I push it, I can see (with air filter removed) that the clear line from carb to the bulb is still drawing air bubbles through it.
Does this ring true as a normal scenario or does this mean that the erratic idle and lack of control on L screw is likely due to an air leak in the fuel delivery hose on the other side of the carb, or possibly from a diaphragm or jet issue?

I’ve only owned 2 primer/purge bulbs, one on a homelite for my 21st birthday (still have it, just not used for a while), and the other was on a “disposable” lawnmower with no choke, so that would be a primer as a pose to a purge? Either one never needed work in that area so I’m not sure if what I’m seeing is normal or an easy diagnosis for the neighbours saw that I got asked to have a look at.

Thanks all, will see how this goes for a day or so before starting a new thread.

And no I’ve not vac/pressure tested yet as I can’t quite decide on my best purchase option (need it for one of my work horses and will be handy for some projects that are in the post now) I do have a compressor but that could blow a fufu valve on the saw pretty easy too.

 

[Okie]

Purge bulb on an Echo CS3400, no matter how many times I push it, I can see (with air filter removed) that the clear line from carb to the bulb is still drawing air bubbles through it.
Does this ring true as a normal scenario

Air bubbles in the purge line can be normal.

erratic idle can be caused by carb and or vacuum leak (crankshaft seals

Thanks all, will see how this goes for a day or so before starting a new thread.
Yes, a new thread would be a good thing

First: Install a new spark plug of correct type, properly gapped and test.

Mityvac MV8500 that does both pressure and vacuum is a good tool for such.

Mityvac MV8500 Silverline Elite Automotive Test Kit Provides both Vacuum and Pressure to Perform Engine Performance Diagnostics, Brake Bleeding, Fluid Transfer, Evacuation, Windshield Repair Jobs​

I use a red Briggs gas filter in the vac line on mine to keep from sucking foreign particles inside. The silverline can be taken apart and cleaned or kitted.

or you can use a $10 blood pressure bulb for pressure only.

 

[skids-stihls]

Thanks Okie,
I tested spark and gap before even pulling it over to start it, but with the existing plug, which doesn’t look bad but can’t beat new I know.
I did see a slight score on the exhaust side of the piston, but not sure if these symptoms refer back to that or not.
I’ll do some more investigation tomorrow and take some pics so I can start a new thread. (Just didn’t want to be the new guy with too many new threads lol) then get told to search as it’s all here, so I looked first and commented on the most recent.
I have some running issues with my ms270 as well as some cool projects (032av and an 08S) on the way to me soon, so the vac and pressure tester was always going to be a necessity, just a matter of when.
Thanks again.
I’ll leave this thread to rest unless replied to. And start a detailed post tomorrow night if still required.
Cheers all.
Stay safe.

 

[Okie]

New with lots of questions is a good thing on this site.

I've seen them little small engine spark plugs cause issues and that can sure make you feel weak upstairs when you have spent several hours working on other things and then find it was just the little measley spark plug, so I always go to the simple easy things first.

If you get a Mityvac 8500 without the carrying case gat a big plastic tool box dedicated just to Vac/pressure fittings and start accumulating fittings. I've got a older model, think maybe it the forerunner of the 8500, maybe a 4500 and they will last forever with just little bit of care. Do not suck brake fluid or liquids into them as it can ruin the little diaphragms check valves. The gauge with mine is not compound type gauge, it only does vacuum on the gauge and use a external automotive compound gauge that costs about $15. The 8500 has a compound gauge.
I use mine for testing lots of things. carbs, automotive vacuum fittings, chainsaws crankcases and fuel and primer bulbs, hose for leaks, etc.

 

[link]

I have worked on many auto, boat, lawn equipment and generator motors etc but I am not
familiar with exactly how or what the primer bulb does. I know what priming means.... in the old
days just squirt fuel into the system to get it ready to run when usually cold. I have one chain saw
that says five squeezes of the bulb for cold start and another that says ten squeezes of the bulb for cold start. From the side of the bulb that would be squirting a massive amount of gas into
the intake guaranteeing flooding so i think something else must be going on. Where does the bulb squirt the fuel ? I dont really know how a chain saw carb works because I dont think
it has a carb bowl and carb float on account if the saw working in all different kinds of positions.

Another useless invention that will certainly desintigrate and crack if the mice don't chew it up, it's primarily a visual thing - looks like the black plague to me.

 

[skids-stihls]

New with lots of questions is a good thing on this site.

I've seen them little small engine spark plugs cause issues and that can sure make you feel weak upstairs when you have spent several hours working on other things and then find it was just the little measley spark plug, so I always go to the simple easy things first.

If you get a Mityvac 8500 without the carrying case gat a big plastic tool box dedicated just to Vac/pressure fittings and start accumulating fittings. I've got a older model, think maybe it the forerunner of the 8500, maybe a 4500 and they will last forever with just little bit of care. Do not suck brake fluid or liquids into them as it can ruin the little diaphragms check valves. The gauge with mine is not compound type gauge, it only does vacuum on the gauge and use a external automotive compound gauge that costs about $15. The 8500 has a compound gauge.
I use mine for testing lots of things. carbs, automotive vacuum fittings, chainsaws crankcases and fuel and primer bulbs, hose for leaks, etc.

That’s good to know, I’ve seen so many sites where new or even existing members get a new bore cut put somewhere unpleasant just because someone else seems to already know the answer, but instead of sharing it, they just shove their well working saw up th OP’s }#%, hence trying search, then to revive and old thread before a new one.

Great idea about a seperate tool box for the vac tester and accumulating fittings and I guess different block off plates ect.

I have to be honest, I’ve been a little naughty lately and spent far to much on buying some really cool projects for collecting and possibly investment value (if that picks up in lil ol NZ)
So I haven’t managed to get a vac tester yet.
I’ve had some progress and problems with the little echo, but I think I’ve found most of the issues, I’ll start that seperate thread for it in the next day or two with the steps taken and results from each, I’ll try to remember to post a link here for yourself and anyone else that may be interested in either helping or learning from someone else’s experience/steps/trial and error.

I’ll also start a new thread to show all these projects that I’ve brought and need to build a shed to hide them from my wife but that might wait a week or 2 till I get them all here, it will make a more impressive thread to start with.

 

[Vintage Engine Repairs]

If the duckbill valve outer seal isn’t seating properly in its drilling, you can in fact force fuel back into the metering chamber and then out the drillings in the venturi and flood the engine. Make sure you really press that duckbill valve down good and firm if you ever remove it. Like welch plugs, unless they’re faulty, leave well alone

 

[skids-stihls]

I

If the duckbill valve outer seal isn’t seating properly in its drilling, you can in fact force fuel back into the metering chamber and then out the drillings in the venturi and flood the engine. Make sure you really press that duckbill valve down good and firm if you ever remove it. Like welch plugs, unless they’re faulty, leave well alone

I’m not sure who that was for, but I’m still interested.
Not familiar with the “duckbill valve” does it have another name that I may know it as?
I’ve double checked and cleaned the reed valve but I don’t think that’s what you mean? I could be wrong but I can’t see a correlation with that and your post. Again I could be wrong.

I will still start the new thread, but I have pulled the carb apart a couple of times now as it ended up leaking fuel into the carb while purging, I reset the metering lever, still did it, then I recleaned the needle and seat and now it don’t leak when purging, but now starves while full throttling, so I now need to reset the metering lever again, but I also have my doubts about the “pig tail” looking fuel hose as it doesn’t allow the filter to drop to the bottom when the saw was tilted.
All this and more detail of the steps will be in the new thread I dedicated to this repeating lil echo echo echo, bye t just thought I’d reply to you for now anyway.

Will post that link when I do get there.

 

[Okie]

and need to build a shed to hide them from my wife.

Right.
Working on chainsaws inside the house on the kitchen table and storing them in the bedroom and living room is not a good thing with the wiffee.

If mommy not happy no one is happy
and the less the wiffeee or women knows about how many toys you have and are buying/collecting the happier she will remain. So get them hidden good. If she starts seeing such she will start collecting non-useful things like Jewelry, shoes, etc. (she will be spending money that you need for useful things)

 

[Vintage Engine Repairs]

I

I’m not sure who that was for, but I’m still interested.
Not familiar with the “duckbill valve” does it have another name that I may know it as?
I’ve double checked and cleaned the reed valve but I don’t think that’s what you mean? I could be wrong but I can’t see a correlation with that and your post. Again I could be wrong.

I will still start the new thread, but I have pulled the carb apart a couple of times now as it ended up leaking fuel into the carb while purging, I reset the metering lever, still did it, then I recleaned the needle and seat and now it don’t leak when purging, but now starves while full throttling, so I now need to reset the metering lever again, but I also have my doubts about the “pig tail” looking fuel hose as it doesn’t allow the filter to drop to the bottom when the saw was tilted.
All this and more detail of the steps will be in the new thread I dedicated to this repeating lil echo echo echo, bye t just thought I’d reply to you for now anyway.

Will post that link when I do get there.

Hey, sorry it was for the OP, but seems that it has inadvertently related to your current situation.

With carbs that have the purge connected to the carb itself sitting on the metering chamber side, if you take the bulb off there will be a black or orange duckbill valve. These have an outer ring around them that needs to be fully seated. Pull it out, clean inside that area and repress the duckbill valve in firmly and it should sort your issues. Or replace it, they are cheap.

 

[skids-stihls]

and need to build a shed to hide them from my wife.

Right.
Working on chainsaws inside the house on the kitchen table and storing them in the bedroom and living room is not a good thing with the wiffee.

If mommy not happy no one is happy
and the less the wiffeee or women knows about how many toys you have and are buying/collecting the happier she will remain. So get them hidden good. If she starts seeing such she will start collecting non-useful things like Jewelry, shoes, etc. (she will be spending money that you need for useful things)

Haha, too right there,
Back in my firewood days I use to bring them inside for a sharpen and tension up, or change for tomorrow’s needed bars ect, nice n warm in front of the fireplace, but I had no room in the shed then and they were all work saws, not hidden gems/projects, plus I was already doing that when we met, so couldn’t change me too fast. Or middle kid used to ride my 660 making motorcycle noises, then have a morning nap laying next to it with his hand still on the handlebar
But he was saw mad, use to come out with us from 4-5 months old, and once he could talk we had to open the boot when we got home and let him say good night to the saws before I was allowed to take him inside.

Hey, sorry it was for the OP, but seems that it has inadvertently related to your current situation.

With carbs that have the purge connected to the carb itself sitting on the metering chamber side, if you take the bulb off there will be a black or orange duckbill valve. These have an outer ring around them that needs to be fully seated. Pull it out, clean inside that area and repress the duckbill valve in firmly and it should sort your issues. Or replace it, they are cheap.

Ah I get ya now, this one actually has the purge on hoses, so I guessing it’s irrelevant now, but I still learned something, thank you.
Not going to spend too much more time on this carb before I just replace it I think, found a not bad deal today, but out of stubbornness I’ll need to have one more go haha