87' FJ1200 - Loss of Acceleration

vpfjames · April 10, 2011, 04:09:05 PM

Ok guys, bare with me. Im an avid rider, but dont know a think about the mechanics of these machines. Let me tell you whats going on.

Im an avid accelleration freak, top end is nice, but the git up and go is what im all about.
Lately, when gassing my FJ through the gears, around 5 to 6000 RPM, its as if the bike isnt getting enough gas, and starts to studder instead of getting me anywhere close to redline fast. It is doing this throughout every gear. If I ride the bike like a daily driver, there doesnt seem to be a problem, however its quite embarrasing having a 750 take me off the line because my bike isnt pushing at all.

The bike is stock at this point, and I plan on getting many upgrades to it as I get the money (someone mentioned displacement of a hayabusa, muaha) But even at stock, my FJ100 with a Dynojet Stage 3 puts my 1200 to shame.

Could someone tell me whats going on? Bigger engine + less get up and go = A very dissapointed FJ Fan.

James

andyb · April 10, 2011, 04:18:41 PM

Fuel filter added, or any other restriction?
Gas tank venting
hose routing
really, really crappy gas (but it wouldn't idle then either)

Do a WOT plug chop and see what the plugs say. Odds are you're right, just starving it for whatever reason.

rktmanfj · April 10, 2011, 04:23:18 PM

If it's been in winter storage, have a look inside the airbox...

Randy T
Indy

weymouth399 · April 10, 2011, 04:39:28 PM

plus 1 on that

vpfjames · April 10, 2011, 04:43:29 PM

Well, here is the part that has me stumped. I dont believe its related to storage, as ive been riding it for about 2 months now. I know im crazy like that, but love to ride. I just took it in to have the Valve cover gasket replaced as I seen it was leaking a little, and while the guy was in it, I went ahead and had the sparks changed out. This was done about three weeks ago. When it first came out, everything was running great, and no acceleration problems. As far as gas, I guess it could be an issue, but I buy my gas from the same place every time, and only use 93 in my machine. Never had a problem with gas before from there. Yesterday was the first time I noticed that it was 'studdering' around 5 - 6000 RPMs. And today it just seems to be worse then yesterday.

What has me concerned, is when the shop did my Valve cover gasket, to clean all the oil off the outside of the engine, they pressure washed it. Could this have knocked something loose, or put water where water dont belong? If so, why is it just now causing an issue three weeks later?

Any other suggestions?

FJmonkey · April 10, 2011, 06:16:56 PM

I have had a similar problem with my 86' (same bike, different color scheme). My problem only occurred during sustained 5K+ RPM. It would start to cut out and continue to lose power till I was stalled on the side of the road. It would not start till it sat for 5 minutes or so. Did this a few times in the rain, really pissed me off. Turns out my problems only happened with my tank bag on. The gravity feed carbs cannot pull gas from a sealed tank, vacuum lock. I opened up the gas cap and cleaned up all the bits (being very careful not to lose the very tiny bearing). Did the dis-assembly in a bucket, no lost parts. Others have just removed the little flapper valves as posted by Andyb.

vpfjames · April 10, 2011, 06:46:53 PM

I believe you may be on to something FJmonkey. The reason I say this, is because of a high pitched 'Whine' that comes out of the gas tank when I shut it off. It sounds kinda like the whine you get from a cars fuel pump when it is starting to go out. I didnt think much of it, because its my belief the FJ doesnt have a fuel pump, so there wouldnt be one to go out on it. However, after your comment, It dawned on me the same noise may be coming from Air trying to get in the tank, kinda like a whistling sound, if the tank is struggling to let air get in. Would make sense to, at least to me... the higher the RPM the more gas its trying to cyphen out, and if it isnt able to.. voila... Other than the gas cap, is there any other fix to this?

FJmonkey · April 10, 2011, 07:15:21 PM

Quote from: vpfjames on April 10, 2011, 06:46:53 PM
I believe you may be on to something FJmonkey. The reason I say this, is because of a high pitched 'Whine' that comes out of the gas tank when I shut it off. It sounds kinda like the whine you get from a cars fuel pump when it is starting to go out. I didnt think much of it, because its my belief the FJ doesnt have a fuel pump, so there wouldnt be one to go out on it. However, after your comment, It dawned on me the same noise may be coming from Air trying to get in the tank, kinda like a whistling sound, if the tank is struggling to let air get in. Would make sense to, at least to me... the higher the RPM the more gas its trying to cyphen out, and if it isnt able to.. voila... Other than the gas cap, is there any other fix to this?

Maybe a more complicated air pump wired into the ignition system to positive pressure the tank while the engine is on. Switch over to a fuel pump (means changing the carbs to a fuel pump model) I would just modify the gas cap.

rktmanfj · April 10, 2011, 07:18:41 PM

Quote from: vpfjames on April 10, 2011, 06:46:53 PM
I believe you may be on to something FJmonkey. The reason I say this, is because of a high pitched 'Whine' that comes out of the gas tank when I shut it off. It sounds kinda like the whine you get from a cars fuel pump when it is starting to go out. I didnt think much of it, because its my belief the FJ doesnt have a fuel pump, so there wouldnt be one to go out on it. However, after your comment, It dawned on me the same noise may be coming from Air trying to get in the tank, kinda like a whistling sound, if the tank is struggling to let air get in. Would make sense to, at least to me... the higher the RPM the more gas its trying to cyphen out, and if it isnt able to.. voila... Other than the gas cap, is there any other fix to this?

Credit to Klavdy...

http://tinyurl.com/6ym2o65

vpfjames · April 10, 2011, 07:22:41 PM

Ok, you said to modify the gas cap. Bare with my stupidity, but how I would I go about doing that. Does something need to come off, put on, drill holes. lol... im at a loss.

rktmanfj · April 10, 2011, 07:28:48 PM

Um...

I give up...

FJmonkey · April 10, 2011, 07:33:43 PM

Quote from: vpfjames on April 10, 2011, 07:22:41 PM
Ok, you said to modify the gas cap. Bare with my stupidity, but how I would I go about doing that. Does something need to come off, put on, drill holes. lol... im at a loss.

See the pic with the toads? Look for the orange colored thingy in a figure 8 shape of white plastic (between the toads but lower in the pic). Remove your fuel cap from the tank. Cover the tank while the cap is off (eliminate all sources of ignition while the cap is off). Slowly and carefully take the cap apart in while in the bottom of and empty bucket. Have plenty of light to see what you are doing and remember how to reassemble it. The orange flapper is the part that sings to you. Once removed it cannot hinder the pressure in the tank. Them toads are smart buggers.

weymouth399 · April 10, 2011, 07:38:35 PM

My 89 whistles but not my 86, but the cap doesn't close real tight either.

I blame it on the PO it must have been him.

ya it's his fault.

Bob W

Pat Conlon · April 10, 2011, 07:41:41 PM

At a loss?? Did you could read the link that Andy posted in Reply #1 to your original post?

Marsh White · April 10, 2011, 08:49:38 PM

Quote from: Pat Conlon on April 10, 2011, 07:41:41 PM
At a loss?? Did you could read the link that Andy posted in Reply #1 to your original post?

C'mon Pat - give him the link again. Here it is again! (this will fix your problem) http://www.fjowners.com/index.php?topic=2024.0

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87' FJ1200 - Loss of Acceleration

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