engine starts bogging down at low throttle with HOT engine?
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Speaking from what I know of the F4 carbs, the floats do adjust. They adjust by bending the little tab that stops them from moving up and down. The tab hits a stopper, it's between the two barrels of the float.
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Joined: Jul 2009
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low speeds under 4k rpms? then its your pilots. low speeds 4-8k rpms light throttle may be needles or pilot/needle combo.
Whether to richen or lean is up to you to find out. There are like 3 threads right now with these same problems so I am losing track of what I said where, but it is all the same. Run WFO from 3k up to redline on a cold bike a few times, check for weakness or flat spots... then let the bike get nice and warmed up and do the same test. If the problems get worse hotter then you are rich, if they get a little better hotter then you are lean.
Whether to richen or lean is up to you to find out. There are like 3 threads right now with these same problems so I am losing track of what I said where, but it is all the same. Run WFO from 3k up to redline on a cold bike a few times, check for weakness or flat spots... then let the bike get nice and warmed up and do the same test. If the problems get worse hotter then you are rich, if they get a little better hotter then you are lean.
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Joined: Jul 2009
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From: Pittsburgh, PA
Considering that it doesn't do it when the engine isn't warmed up and as it warms up it starts to sputter more under light throttle. The bike was tuned to run correctly in Washington state, so I'm guessing the pilots were set pretty rich for the cooler denser air up there?
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Joined: Jul 2009
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From: Pittsburgh, PA
So yeah, if your floats have a metal clip on them, it could be bent for more or less float high. I would mess with the pilots first still though. If the floats are a problem, it sucks tackling that issue if you don't have a stock bike which would have an easy to figure out stock float height.
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Joined: Jun 2009
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From: Virginia Beach
You probably are right. I only know the F2 carbs... Maybe they changed it for more adjustability. I am glad my floats can't adjust, makes life more simple.
So yeah, if your floats have a metal clip on them, it could be bent for more or less float high. I would mess with the pilots first still though. If the floats are a problem, it sucks tackling that issue if you don't have a stock bike which would have an easy to figure out stock float height.
So yeah, if your floats have a metal clip on them, it could be bent for more or less float high. I would mess with the pilots first still though. If the floats are a problem, it sucks tackling that issue if you don't have a stock bike which would have an easy to figure out stock float height.
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Joined: Jun 2009
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From: Virginia Beach
So I've got a plan now.
1. Buy a pilot screw adjusting tool with long screwdriver-like shaft
2. Buy and install the correct spark plugs.
3. Warm up bike to temp where low rpm missing begins
4. Install Motion Pro sync tool to identify which plugs have misses.
5. Increase idle screw until miss can be heard consistently.
6. Adjust pilot screw slowly until the miss goes away.
DONE!
1. Buy a pilot screw adjusting tool with long screwdriver-like shaft
2. Buy and install the correct spark plugs.
3. Warm up bike to temp where low rpm missing begins
4. Install Motion Pro sync tool to identify which plugs have misses.
5. Increase idle screw until miss can be heard consistently.
6. Adjust pilot screw slowly until the miss goes away.
DONE!
FYI, I had a similar problem where my cylinder was missing because a plug kept getting fouled. I fixed this using only a sync, never had to adjust the pilot screw. Dissevered will fight you to the death over it, though.
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Joined: Jul 2009
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From: Pittsburgh, PA
Don't hide behind the couch lol... I learn something new from the racing techs, so here goes. Being out of sync can close a throttle plate so much that there is no air getting into the cylinder. A dropping piston still has vacuum though and will pull fuel out of the pilot screw only, which could foul a plug.
So with that said, being out of sync can only foul plugs at idle. Otherwise you just lose power because the pistons don't work in harmony.
A few of the guys I talked to did think however that it is a questionable case because carbs will not go out of sync quickly like yours did. It takes years of vibration to change the adjustments. For example, my bike went without a carb sync for 7 years or more (not sure what the previous owner did) and mine were only very slightly out. I STILL think your bike is too rich Johnny, being out of sync probably just helped finish one of your plugs off.
So with that said, being out of sync can only foul plugs at idle. Otherwise you just lose power because the pistons don't work in harmony.
A few of the guys I talked to did think however that it is a questionable case because carbs will not go out of sync quickly like yours did. It takes years of vibration to change the adjustments. For example, my bike went without a carb sync for 7 years or more (not sure what the previous owner did) and mine were only very slightly out. I STILL think your bike is too rich Johnny, being out of sync probably just helped finish one of your plugs off.