What if i dont want to use primer on diaphragm carb?

JohnnyTillotson

JohnnyTillotson

#1
#1
Going through all my diaphragm carbs to use on my MTD HS40. The original carb seems to have gone south as i can get it to idle but nothing more. Moving the throttle plate does nothing. What the hell is with that? Two other diaphragm carbs leak like crazy through the hole in the middle underneath.

Anyway, i have this carb but it has a primer tube. Can i block it up or is it going to need air going through while it runs?
 
JohnnyTillotson

JohnnyTillotson

#2
#2
The last carb before this one seems to work great. So ill go with that for now but still would love to know the answer to this in case I use it on something else.
 
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davidlamb78

Member
#4
#4
Are you set on using a diaphragm carb? I had an old Tec carb that was supposed to have a primer bulb, but I used it on a motor that didn't have one. It was fine, and I left it open and unblocked.
 
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davidlamb78

Member
#5
#5
Okay, so I have been working on running a Briggs raptor with a Tec carb, and I finally got it hooked up and running today. It does have a spot for a primer bulb, and it belched gas out of the nipple after running it for a short while. I might have to put a small fuel line on there and plug it.
The other motor I had didn't do this. Not sure what's up with that.
 
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davidlamb78

Member
#8
#8
I just blocked mine off, and it's running fine now. It's weird that I didn't have this problem on my other Tecumseh carb with a primer inlet. I'll block it off too. I just took a short piece of fuel line and stuck a screw in the other end. Works fine.
 
markus

markus

Well-Known Member
#10
#10
Stangrcr1 said:
Just remember you can't do that with a float carb. The primer connection is also the bowl vent.
Click to expand...
probably shouldn't be done a diaphragm carb either...

there are still vent holes in both the diaphragm and bowl carbs, but they are decreased in size to something you can barely see so when you are pumping that primer its actually building up pressure to get the fuel moving. If you take the primer out of the mix and cap them off though the vents are so small they technically are not enough for normal operation, biggest reason would be for them to corrode or clog up easy and cause maybe pressure buildup or vacuum against the diaphragm or in the bowl, causing flooding most likely.

heres the difference on the Dia carbs:



Heres the bowl type (top left I drilled out the small vent hole to the larger size so I could cap the primer inlet off, bottom left is undrilled, right is normal non primer with the larger vent)

 
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JohnnyTillotson

JohnnyTillotson

#12
#12
markus said:
probably shouldn't be done a diaphragm carb either...

there are still vent holes in both the diaphragm and bowl carbs, but they are decreased in size to something you can barely see so when you are pumping that primer its actually building up pressure to get the fuel moving. If you take the primer out of the mix and cap them off though the vents are so small they technically are not enough for normal operation, biggest reason would be for them to corrode or clog up easy and cause maybe pressure buildup or vacuum against the diaphragm or in the bowl, causing flooding most likely.

heres the difference on the Dia carbs:



Heres the bowl type (top left I drilled out the small vent hole to the larger size so I could cap the primer inlet off, bottom left is undrilled, right is normal non primer with the larger vent)
Click to expand...
Oooooh.... See thats exactly why I was asking. So really you may want to keep it on and if everything is ok with it, it shouldn't leak gas anyway no?

I checked out two that were leaking like crazy and I see when I put new diaphragms in I put the diaphragm on first then the gasket. The way the carbs with the F should be done. Surprising. You wouldn't expect a guy of my intelligence to do that. But I did! I have corrected the situation. Tomorrow we'll see if they work.
 
markus

markus

Well-Known Member
#13
#13
JohnnyTillotson said:
Oooooh.... See thats exactly why I was asking. So really you may want to keep it on and if everything is ok with it, it shouldn't leak gas anyway no?

I checked out two that were leaking like crazy and I see when I put new diaphragms in I put the diaphragm on first then the gasket. The way the carbs with the F should be done. Surprising. You wouldn't expect a guy of my intelligence to do that. But I did! I have corrected the situation. Tomorrow we'll see if they work.
Click to expand...
if fuel was to leak out of that fitting the diaphragm has a hole or tear etc, its just an airspace. you could keep a long hose attached to the fitting, that way if the thing does not want to start grab the end of the hose give it a quick blow job, or take the fitting out so you can manually push the diaphragm in like the other type to get some fuel going.
 
JohnnyTillotson

JohnnyTillotson

#14
#14
markus said:
if fuel was to leak out of that fitting the diaphragm has a hole or tear etc, its just an airspace. you could keep a long hose attached to the fitting, that way if the thing does not want to start grab the end of the hose give it a quick blow job, or take the fitting out so you can manually push the diaphragm in like the other type to get some fuel going.
Click to expand...
I'm going to save the one with the primer tip for a 2 cycle. I was just going to use it on my MTD when all other diaphragms where failing me. Now that I know two of them had the gasket in wrong I'm fairly certain the original carbs will do the trick. But yeah I still have the little primer hose. I could just leave it in and give a lil toot when needed.
 
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