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Old 11-11-2012, 09:40 AM
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dragray dragray is offline
Motorized Bicycle Elite Member
Join Date: Mar 2012
Location: Indiana
Posts: 278
Default Re: Motor Bogging Out

an o-ring goes inside the carb where it mounts to the intake manifold tube. the o-ring will seal the manifold against the carb.
but, normally if you have an air leak, it will be present all the time, not just at wide open throttle.
normally if an engine runs great up until w.o.t., it's jetted too lean.
you will get a lean bog at w.o.t. if the main jet is too small.
you can get a can of ether (or starting fluid) and spray a TINY amount around the intake manifold where the carb goes on with the engine running.
if you spray an area and the idle goes up, then you have an air leak.(but of corse, if you spray it into the rear of the carb, the idle will go up when the ether is sucked into the carb.)
you want to spray it around areas that shoudl not be allowing air in, and you only need a tiny shot of it to check for a leak.

changing the jet needle setting will not have any effect on w.o.t. issues because at w.o.t., the needle is completely out of the main jets path and the main jet does 100% of the fuel metering at w.o.t.
a lot of people suggest doing this to cure a w.o.t. bog, but the needle jet setting only has an effect from idle to about 3/4 throttle. so unless you are having a problem with a bog or 4 stroking at 3/4 throttle or less, leave the needle right where it is. you can use the needle to fine tune it later if changing the main jet creates a problem at 3/4 throttle or below.

you may need to get some jets, and play around with changing one jet at a time and riding it, until you get the right air-fuel ratio at w.o.t. (no bogging at any point from idle to w.o.t.). changing the main jet is simple, but tuning the carb by changing the jet is time consuming. pull the carb, remove the float bowl, unscrew the main jet, screw the new main jet in, put the float bowl back on and put the carb back on. normally the stock main jet is .70, but they aren't marked. so, you will need to take a guess and go with a jet that's bigger than .70 as a starting point.
start out with a .72. if it runs better at w.o.t. with a .72, pull it out and go to a .74 if it runs even better, pull the .74 out and go to a .76. if it starts 4 stroking and running bad, pull the .74 out and go back to the .72.
but if you put a .72 in it and it runs worse than it did with the stock jet, the stock jet may not be a might be bigger. it's all trial and error, but the time spent is worth the effort.
no 2 engines will run the same on the same jet, so don't let someone tell you "mine runs great with a .68 so you should go with that size." the area that you live in, the altitude, air quality and air temp will all have an effect on what main jet will work best for your engine.
when you start swapping out jets (this is what i do) i get a ziplock baggie for each jet. then, i write the jet size on the baggie and pout that jet in the bag with a note saying that it ran better, worse or whatever. it just helps keep things more organized because you will be pulling and replacing jets, so you don't want to get confused on which ones you already tried and which ones you havent.
plus, if you have to go back and drop a jet size, you'll know how it ran with that particular jet based on your notes.
you might get lucky and only have to make one jet change and cure the problem. but on the other hand, you may have to go through 3-4 different jets until you get it to run right.

what oil-fuel ratio are you running?
if you are going "by the book" and running it at the recomended 16:1, that's too much oil.
you can back it down to 20:1 and it might make a difference and the bog might go away.
once it's broken in you can run it at 32:1 or 40:1.

I'm by no means an expert, this is just my opinion.

Last edited by dragray; 11-11-2012 at 09:54 AM.
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