Wont rev over 5000 under load.

1985 VF700F. I got it fairly cheap. Guy hurt his back and couldn't ride anymore. He just wanted rid of it. Anywho, It's running and not bad at all. Actually pretty good, but...when I get to 5000 any gear it acts like it hits a rev limiter. If I hold the throttle wide open it'll kinda bog then go, bog then go. You get the picture. I have had the carbs out 5 times looking through them. After the initial cleaning(pulling the jets, unclogging them, blowing air through the passages..etc) it was still running rough and was hard to start. Wouldn't run without choke. So... I pull them back out and take the whole assembly completely apart. I found three torn/dry rotted/old o-rings and replaced them. Put the whole assembly back together and reinstalled it. It ran much better but the plugs read really lean. So I pull the carbs again. Clean again and double check everything. Diaphrams, springs, jets, passages, filters all well and good. I did another bench sync and reinstalled them. Still lean. Then I did a valve adjustment. Yeeesh were they ever tight. Buttoned it up and now it sounds like a sewing maching. You can tell the valves are definitely not where they were before. Bike pulls hard all the way to 5000 now. So... I pull the carbs again and triple check everything. Recheck the valve adjustment and cam timing and surfaces. All good there. At least I hope so on the cam surfaces. The lobes are good but I can see a bit of wear on the bearing surface. No pitting or galling just really light wear. What you guys have been saying about these bikes has me a bit paranoid. BTW, engine has 30k on the clock. Synced the carbs, that job sucks when you don't have the right angle screwdriver doodad. HOT hands!!! Much smoother but still normal nonagressive driving is not getting me past 5000. The other day I took it out and just flogged the crap outta it. Or tried to. Held the throttle open and just said lets see where this takes us. I got it up to 75mph. woopitydo... It didn't impress to say the least. Ive run seafoam through it. I've checked the coils,pulse gens, resistors, plug wires, plugs, ran it without the aircleaner...sheesh, I may have forgotten a few things. Oh, checked the gas flow. Emptied a whole tankful waiting to see if it would stop. What was it? Something like 5 gallons? That was boring. Warm summer day. Peeps piloting their rides all over town and here I sit like some kinda monkey watching gas flow. I checked it by gravity feed but I am running the pump when I ride it. Oh yeah, new fuel filter, air filter, oil filter, oil, etc. I am not taking this into a garage and let some egotistical tech turn a screw, replace a box, overcharge me and imply I'm an idiot. Not how I roll. I've been working on my own bikes since the mid eighties. I'm not about to stop now. Does anyone have any ideas about what else to try. Right now I'm working on prepping for paint, fixing cracks in the bodywork and such just to give myself a break from troubleshooting. I apologize for the length. Any helpful comments are very much appreciated. There are a lotta details I probably missed but I have to get this typed out. I gotta get ready for work. Thank you in advance.

 

this may help...

CV Carb Tuning Procedures

I am no carb expert, but if you havent jetted it or heavily modded, I suspect you may have dirty carbs. I know you may have cleaned, but I would clean them again

 

Hi Boet

The jets for the second stage are clogged. Has the bike been standing a while? Had the same problem on my X vfr400 a while back. Also check for rust or debris in the tank and fuel system.

Cheers, let me know how it goes!

 

Have you checked if the Vacuum Pistons move freely ? Those are the black cylinders which block the carb throats at low speed. They may be gummed-up with varnish, which prevents them from moving. That would limit the air flow severely and cause the problems you are experiencing (including the need for choke during idle).

The Vacuum Pistons should move up and down easily if you push them with your finger. If they are stuck, spray some light oil on, then push it loose.

 

Hi guys and thank you for your input. I will pull the carbs...again...*sigh* I havent been able to work on the engine where its at because its in my utility/laundry room. Wife put down her foot and DEMANDED that I make it look pretty. Enough fussing over the motor already! Women...

 

You need to either move to a proper house with provisions for a "Man Cave" or get a different wife. :smile: Sounds like a jetting issue, was leaning towards tight valve clearances but you sussed that out. BTW doing the carb synch on a V4 motor sux and you burn the hell out of the back of your hand, payoff is your bike has terrific off idle characteristics for your trouble. I wore mechanix gloves and ended up using a knurled spinner along with this slotted 1/4 socket designed for carburetor tuning, (think its a Snap On tool). All my fancy 90 degree carbs tools I might has well used em as pry bars because they all sucked arse. Good luck figuring out your problem, I got a car issue I am troubleshooting now which just translates into throwing money at it :grin: Its all good though

 

Hey Gents.

I wore mechanix gloves and ended up using a knurled spinner along with this slotted 1/4 socket designed for carburetor tuning, (think its a Snap On tool).--ridervfr

I think I'm gonna mug the snap on guy. My hands cant take that kinda abuse again.

Main jets are too small. Who knows what he previous owner might have done with/to that thing.--tinkerinWstuff

Your probably right. I've been fixing all kinds of little things here and there that the PO had done to this. Actually, I think it was the guy before the guy that I bought it off of. The PO I got it off of didn't really do anything to it. He only rode it three times and hurt his back. Immediately parked it until his wife made him sell it cause she was worried for him. Worried he would succumb to that spring time malady which we all suffer from here. :biggrin:


You need to either move to a proper house with provisions for a "Man Cave" or get a different wife. --ridervfr

I've been trying...Lord I've been trying to get this woman to understand this. And I'm hopelessly addicted to this woman. Whats a guy to do?:crazy:

 

My $.02

First and foremost, a wise man told me : " A happy wife = a happy life" Be smart here.

Secondly: My bike would not rev passed 5k because I mis routed a fuel line into any air vent. Dumbass move.
Point being, triple check everything, go back to stock jetting.
If you have carbs in your hand its a good time to do so.
Check for any fuel obstruction.

My bike would not even start without crankcase vent hooked to airbox. Every vent, hose, vacuum line, fuel line has a job

Have you checked your compression ??

 

Compression test? Not yet. That tool, I fear, got lost in my last move. And my overtime dead and no pay raises in three years I do not have many spare $ for tools. I hope my wife starts a new job soon...

 

Compression test

Hey man, sorry to hear things are going tough for you. You are not alone. Tools are expensive and the theory of "extra" money is a myth!

Earlier this week, I called a local Sport bike mechanic (he previously worked for the local Suzuki dealer, and has since started his own shop) to ask about carb synch and tire mounting.

He offered to let me borrow his carb synch tool! Very cool now I am getting two new tires.

My point is, have you made nice with anyone with tools? I few years ago I left this guy a six pack for helping me press a dirt bike crank. I have always just brought him parts never bikes. Motorcycle people are some of the coolest on the planet.

Does autozone has a loan a tool comp. tester???
But I would look very hard at your carbs and vent hoses.

 

Just in case...where can i get these jets tinker? Or do I have to buy carb kits? I think you are on the right train of thought btw. Me and the wife took a ride today and it seemed more like a fuel starvation issue. I could get it above 6grand pretty easy but around 5 or 6k it was just kinda well...missing a cylinder...like it was going lean. Below that the power is nice. Above that it seemed anemic. Opened Wot and it would only do 75 80ish. Hard to tell when your wife is freaking out on ya. She hates to speed anymore. *sigh*

 

oh! And yes, it will go over 5k now. It had a bad/plugged fuel filter. It was mounted on top of the aftermarket fuel pump. It would flow fuel but I replaced it just cause it was cheap and easy to do. I also rechecked to spark gap with a wire gaper instead of feeler gauges. I would reckon with the feeler gauges it was about .004 larger than the .032 I was shootin for.

 

Great job, glad that you didn't get conned into a rebuild of your engine

How does the fuel flow now with the new filter? I am looking for a reference point to put in the vault.

 

Camo, What are you looking for as a reference? I could put a couple gallons in and report how long it takes to pump said amount through the filter.

 

Quandry
Really no need to do it.

Just wondering if you could see a significant difference in flow.

Mine works now, I could measure how long it would take to fill a gallon. Blocked filter is a good differential diagnosis if it starts runny crappy at speed.

 

The difference was insignificant to the naked eye. It could have something to do with pressure vs flow. I am unsure.

 

I took it from this.



To this.



I'm waiting on decals and then I'm gonna clearcoat it.