I'm at a loss.....

minibikin'

minibikin'

Sho-nuff
#1
#1
Well, the Briggs 3.5 on my Cat is giving me trouble. I've never had a pulsa-jet carb that I can't get to work, but this thing is close to getting a for sale sign on it! It will start and idle great at 1.5 turns on the mixture screw. Try giving it some throttle and it bogs/dies as if there is no fuel. The bowl is full in the tank, so I'm figuring the pick up tube is fine. If I open up the mixture 1/2 to 3/4 turn, it will take throttle, but it's not right and loads up under idle. I've had it completely apart, cleaned and blown it out. Everything appears right but???? :confused:
Could I have a bad diaphragm? This one was new when I started the project, but it did sit and I've heard the oxygenated fuel kills them quickly? It's getting to me with all of the time and labor in this bike. I'm ready to fab the new exhaust and can't do much with it like it is. :shrug:
 
jeep2003

jeep2003

#2
#2
how about the seats where the diapram flaps lay. iv seen them corroded away. id pull the tank off and thoroughly check the pickup tube for leaks and flow :shrug:
 
S

supernova

Banned
#3
#3
A diaphram is cheap enough but it does'nt sound like the problem, I'd replace it anyway. Check the air mix body where it screws into the carb and make sure the gasket is intact, it sure sounds like a mixture issue to me.:thumbsup: Good luck!
 
Oldschool

Oldschool

New Member
#7
#7
jeep2003 said:
iv seen 2 or 3 with a split right up the brass part. hard to tell without blowing carb spray up it
Click to expand...
I think its vibration causes the brass to harden and do wierd things like crack OR it shakes and works its way loose from the aluminum castings.

Doesn't happen to engines that are on a machine base just things that vibrate.

No jokes now about cracks and heavy vibration and loosening up things guys......
 
minibikin'

minibikin'

Sho-nuff
#8
#8
It is a brass pick up, but it is in place securely. I sprayed through it and cannot find a crack. As I said, the bowl is full so the fuel should be there. One things I did not think of was to check the timing. I am putting a diaphragm in it whie the carb is off just to eliminate a $2 oversight. I hate to throw parts at something, but $2 is insurace in my mind. If that doesn't sure it, I'm going to check the timing and make sure they keyway hasn't moved.
 
FordGalaxy

FordGalaxy

Member
#9
#9
Check that the diaphragm cover is flat, some times they warp when replacing the diaphragm. Some 400 grit wet/dry, and a flat surface will fix it.
 
Richard Trotter

Richard Trotter

#12
#12
Is your gas cap venting. I had a 5hp briggs with a pulsajet. It kept flooding itself and wouldn't run right. Turns out the gas cap was plugged. Cleared the vent hole and its run great ever since.
 
125ccCrazy

125ccCrazy

Well-Known Member
#14
#14
look for any nicks or imperfections on the needle itself, make sure the tip is not flattened out.... what about the seal on the throttle shaft? carb to tank gasket? intake gasket? an air leak can cause major headaches..
 
minibikin'

minibikin'

Sho-nuff
#15
#15
125ccCrazy said:
look for any nicks or imperfections on the needle itself, make sure the tip is not flattened out.... what about the seal on the throttle shaft? carb to tank gasket? intake gasket? an air leak can cause major headaches..
Click to expand...
I've checked all of that stuff "thrice." I'm normally a pretty savvy trouble shotter, but this has got me over a barrel to this point. I did'nt get out to the garage yesterday so hopefully today.
 
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