F4i Bogs at WOT. Could use the expertise here
 

Hey guys this is my first real post here. Looking to get some advice on my '01 F4i with 17k miles.

I recently did a valve clearance job, an oil change, spark plug change, coolant flush, air filter (K&N), and throttle body sync and when I buttoned her up for a test ride I was getting hesitation and bogging at about 7k RPM in 4th, 5th, and 6th. The bike reacts slowly with WOT. There's a general lack of top end power. There's also a decent amount of backfire on deceleration. But the bike accelerates fine in first and second.

I switched back the stock air filter and that made a noticeable difference. The backfire was greatly reduced and I gained a lot more throttle response.

I checked the fuel pressure regulator, no dripping fuel when the bike is primed.

I pulled the plugs and they definitely are gas fouled. Here's a picture Attachment 25422.

Timing is verified by myself as I was meticulous trying to get the timing perfect when I reassembled the top end. I double and triple checked the timing marks were aligned with the head when at TDC.

Idle is fairly consistent and smooth at 1300rpm but occasionally requires adjustment while riding (dips lower than 1300)

No fuel leaks that i can find.

Before I go dumping money on the bike I'm looking to get some advice. I've spent a good amount of time researching this problem on forums and I'm thinking it could be a couple of things.



1. FPR still shot
2. Missing/leaking/loose hose connection
3. clogged/malfunctioning MAP sensor (not sure how to check for this)

If you guys have any advice id love to hear it.

The million dollar question is:

Was it doing it before you did the work?

Nope, the bike behaved as normal. I was just doing all this work as periodic maintenance as described in the service manual. Which leads me to believe I either messed up during reassembly or I introduced new issues somehow during the work I did.

I'd have to guess the valves aren't adjusted right [doubtfull] or the throttle body sync didn't go so well. I've never done a sync and I'm at almost 77,000 miles so I have no idea how to screw that up lol.
Having to adjust your idle while riding is a big no no. I'd replace the FPR to elminate that and as insurence since we know they go out eventually and go from there.

Yeah I'm leaning towards a bad FPR even though there's no drip. It might be a slight leak which explains why the issues aren't so bad. What's weird is that it was working just fine before. I have a feeling that when I was siphoning fuel before doing the work (to lighten the gas tank) that I somehow broke a seal or messed something in the tank. Anyone have a similar situation?

It has to be related to the work you did.

Vacuum line off or incorrect
Electrical plug not connected
Fuel return line pinched
Valve clearance off
TB sync off
Cam timing off

You're right. I'll take a look at those items tonight and post an update.

i took a look at electrical connections, vacuum lines, and the fuel return lines. all looked good. One thing I remembered i did incorrectly when removing the tank a month ago was i did not release the tank pressure before removing the fuel rail. Could this have cause damage to the FPR?

I was going to say fuel filter, but I don't know really based on your description. Check out what has been suggested for sure. Seems weird that your idle would drop below 1300... You should go out for a ride, get it nice and hot, and then adjust it from there. If it's dropping off randomly and loping, there's something definitely amiss.

Zealot I've been for a few rides and I'll get it up to temp and it will hold an idle consistently. I just remember having to adjust it once or twice, the throttle body sync went fine. I mean how bad could I have messed up the valve adjustment, I double and triple checked timing to prevent this issue and the valve train sounds smooth as a sailor. It just bogs at WOT. I'm going to pickup an FPR and give it a whirl and see if that makes a difference. I'm also going to verify timing. Will update later tonight.