Covering carb vent helps top end..???

[Lupus71]

Hello everyone I have a 65 9.5 johnson that's been giving me a fit trying to get it to run at it's peak. I have replaced a lot of ignition parts and took it out on the river and it was still not reaching its top speed, it's like it needs to rev up some more but never does, so anyway I was messing with it and put my finger over the vent (I'm guessing for the main jet )and it started to pick up a little more speed but after a couple secs it would drop back down. I have already put a new needle, seat, float (bent it even with the old one which was running right),low speed washers and packing, one new orifice plug and soaked it for 30 mins then blew all the jets out. Also it will go a little faster if I screw in the low speed needle a 1/4 turn from closed, I don't know why but it does. Any ideas? Not much of a mechanic, thanks guys!

 

[Daviet]

Re: Covering carb vent helps top end..???

Running at it's peak. What is the rpm of the engine at WOT, need to know so that you know if the engine is running at it's max rpm.

 

[Lupus71]

Re: Covering carb vent helps top end..???

Well I don't have a gauge but I think it's 5000 but have no idea what it running at.

 

[Daviet]

Re: Covering carb vent helps top end..???

I guess what I am trying to say is, If your engine is propped correctly and running at the proper rpm, it's not gonna do any better. The rpm at WOT will tell if you can get any more out of it.
Can you borrow a tach from someone and see what the rpm is?

 

[Lupus71]

Re: Covering carb vent helps top end..???

Don't know anyone with a tach but I do know it will do more than it is now. I think it may be something with the float but I'm not exactly sure what your suppose to bend but I bent the two pieces that hold the float, I bent them right before they touch the float. You don't bend the little tab at the very end right? I know that doesn't say much but don't know how to say it really. Thanks for helping

 

[F_R]

Re: Covering carb vent helps top end..???

Fuel is forced through the jet by atmospheric pressure pressing on the surface of the fuel in the bowl, in relation to the pressure present at the venturi. By blocking the vent, you are mucking up the atmospheric pressure on the fuel. Good or bad, that is a symptom, not a cure. The problem would seem to be the high speed fixed jet (orifice plug). Partially blocked or too small, it will run lean. Oversize and it will run rich. The engineers put in an optimal size to deliver optimal mixture. Perhaps yours has been changed for a different size, or it is dirty, or somebody has reamed it oversize by jamming wires or drills through it.

Smoke inhallation is a notorious problem with those 9.5hp motors. Just a slight whiff of smoke will make it run rich too. Maybe it isn't a carburetor problem at all, but smoke.

 

[Lupus71]

Re: Covering carb vent helps top end..???

Well I've had the motor for about 6 years and I haven't done anything as far as jamming bits in it or anything like that and I have ran it many times without the hood on and it doesn't change. I haven't taken the high speed jet out because I don't have the tool to remove it but I could see light throught it when shining a light in the top of the bowl so I assumed it was clean

 

[5150abf]

Re: Covering carb vent helps top end..???

Grind down a screw driver and get the jet out and clean it properly, after 6 years I gaurantee it is dirty, that you could see light through it means nothing, it needs to be romoved and phsically cleaned, carb cleaner won't do it.

The main in mine looked factory fresh but my engine wouldn't run until I did this, after cleaning it ran like a champ.

Get it out and run a stranded copper wire through it with some Sea Foam, the copper is softer than the jet and won't bugger it up, that is the only way to clean a jet and get the rest of them while you are at it, it simply has to make the engine run better.