Revs Trouble Climbing

[DoktorMandrake]

So I'm still fixing my latest VFR up meaning I haven't actually taken her on road yet so these observations are from tickover and so could be nothing at all to worry about. However, when I open the throttle smoothly she climbs without much trouble. She struggles a bit to get passed around the 9k-ish mark but she will climb through the range. Yet if I snap the throttle open she'll get stuck around 9k-ish and have to fight her way to get passed it and if I open the throttle smoothly and let her climb steadily largely unimpeded through the revs if I then snap the throttle shut and then crack it open quickly as she falls passed/around 9k revs there's a lag/struggle/nearly dies before she picks up again. Now I have no idea how she performs when warm after being ridden, and as it's from a standstill and as the temp gauge hasn't even got off blue/cold (never moved the needle even when leaving her with choke on for a bit) I am guessing she could just be cold. However, have a niggling suspicion it could be more than just cold and actually be fuelling. She has a can on her the size of the Dartford tunnel and I have had the carbs off and they were a bugger to get back on so as per another thread on here I am guessing they might not be seated properly. Although, I spent hours with a torch checking and rechecking them and had my fingers down the front of the front two feeling them to make sure and in the other thread it was mentioned a lean mix due to improperly seated carbs will mean the revs hang on the way back down. This is when the throttle is opened. Or rather cracked open hard or opened gently and gradually then shut then cracked open. Like I said, she climbs through the rev range but struggles visibly at around 9k before shooting up again. Just wondered what people's thoughts and opinions were? Know the acid test will be when I get her on the road, get her properly warmed and can see how she responds.

[CMSMJ1]

For starters, don't go trying to max the revs out when the temp gauge has not moved!

let it idle and get warm before doing anything like this. Not good for the moto at all

You'll need to ride it and see how it feels I reckon.

Sounds fuelling to me

[DoktorMandrake]

Cheers for the reply, dude!

I let her tickover for a good while before I began very gradually revving it. Didn't just do it from cold and start wangin' the throttle open. Agree that ideally I should have let it warm right up or taken it for a run, but wanted to see what the revs were like.

However... I have since taken her on a ride, got her up to temp (well between 70 and 90) and still the same probs. As I'd expect from a VFR not much below about 7k but really you can feel her struggling to pull at about 6k right up until after 9k/10k when she shoots up easily to near the red. So seems like the mid-range is effected. Can't tell too much on the low range because as far as I know these bikes are not renowned for having much low range. She feels a wee bit sluggish throughout the rev range though but especially around 6/7k (7k was where you could feel the power band coming in on my old VFR) right through to around 10k where you can feel she's struggling and even reving her at standstill you can see the needle fly up and slow down around 6k and struggle/hesitate/fight it's way through until it shoots up again around 10k). Certainly feels different to my last VFR and that was by no means a pristine example.

She has a straight through Scorpion race can on her (which pops loudly on occasion) so I am guessing that could cause havoc if the carbs weren't jetted accordingly, she has a poss leak from the headers coming off the back two cylinders (where the back right pipe comes off and the back left pipe goes round under/below it whichever it is) where she smokes a lil but I am guessing that could just have been crap on the pipes and I am guessing if it's mid-range it could also be a needle jet problem? Or even improperly seated carbs. Someone in anotehr thread on her mentioned that.

Anyone got any thoughts, ideas or suggestions?

I did whip off one of the carbs and took one float bowl off and that looked pristine - no varnishing, jests looked clear although I didn't remove them as when I tried to remove the main jet it was in v tight got every so slightly mashed with the screwdriver so I left it rather than bugger it up.

Also, after riding when she was hot, if I revved her hard up to around 11k or so or just below the red line and then let go of the throttle as the revs dropped instead of returning to tick over she'd get to her idle rpm and then drop further and she'd just stall/die.


Thoughts would be appreciated people... ta!!

[CMSMJ1]

What jets are in it?

What is the airfilter siutation? Airbox all in one piece?

get it close to standard and then go from there. A pipe won't make it gutless and none revvy as bad as this sounds

[alexwitham]

Had this problem last year. Emulsion tubes were fitted incorrectly, and 1 main jet was blocked.

Good excuse to take your carbs apart and get to know the set-up properly.

And as CMSMJ1 suggested, check the induction hasn't been messed about with as the stock set-up is as good as it gets on a standard bike.

[DoktorMandrake]

First off, cheers ofr ya replies, peeps!! Definitely appreciate ya input.

What jets are in it?

What is the airfilter siutation? Airbox all in one piece?

get it close to standard and then go from there. A pipe won't make it gutless and none revvy as bad as this sounds

It's not bad, but it's not good. It's bad enough where you know something is not right as you can feel the bike struggles and even see it when you watch the rev counter needle. It just ain't running right.

The jets are standard jets as far as I know. Airbox is airtight although the secondary air cleaner (I assume it's some sort of crank breather) has perished. I whacked a straight through can on my old CBR and it did effect it but not very much (increased flat spot here or there and not much improvement performance wise but it sounded sweeter ) however I always thought VFRs were more sensitive to aftermarket enhancements like cans, K&Ns etc. so I thouht I'd throw that one in there if only so you boffins could eliminate nit as a possibility.

Had this problem last year. Emulsion tubes were fitted incorrectly, and 1 main jet was blocked.

Good excuse to take your carbs apart and get to know the set-up properly.

And as CMSMJ1 suggested, check the induction hasn't been messed about with as the stock set-up is as good as it gets on a standard bike.

Right looks like I'm taking em apart then, mate. Did have a check of one carb when I got the bike but after removing the float bowl I found all the jets were in too tight. Went to turn the pilot jet in to make a note of how many turns to set it at and it wouldn't budge and when removing the main jet from the holder I nicked the edge of it slightly and after that I thought best to leave em alone. I hadn't had it running at this stage as it needed plugs so it wasn't as if I definitely knew there was sumat up with the carbs I was just having a nose. Conclusion was that they're only soft brass or whatever and didn't wanna butcher em. Are the emulsion tubes what Haynes refers to as the needle jet holder or am I barking up the wrong tree here?

So how do I check if the emulsion tubes are fitted correctly, what's the best thing to use to clean the carbs/jets with and any other tips/things I should look out for?

Thanks chaps!!

[alexwitham]

Have a read through this - http://www.400greybike.info/newforum/vi ... 24&t=14524" onclick="window.open(this.href);return false;.

My old NC had the 5hole emulsion tubes in the front carbs and 4hole emulsion tubes in the rear (it should be the other way) and I had a lovely bit of grit blocking the front right main jet. God knows how she ran at all to be honest.

When you churned the brass of the jet, did you check if any of the 'shaving' fell into your carb and(or) jet hole?

Alex

[DoktorMandrake]

You're a wealth of good info. Thanks. Pretty nifty step by step guide there.

No there was no swarf when I nicked the main jet. It was just a nick. Enough to make me leave em alone but just a nick. No debris.

When removing/replacing the pilot jets do they need to be a specific number of turns out as the Haynes indicated?

Will crack on with this over the next few days using DataRacer's handy guide. Fingers crossed...

[Neosophist]

Use a socket on the emulsion tube and the jet / tube will come out as one... It's either a 7 or 8mm if I remember correctly.

Compressed air through all the passageways after a liberal soaking in carb cleaner will help to dislodge any crap too.

[DoktorMandrake]

Working on my carbs as I type. Have got the first float bowl off...

Got the emulsion tube out... have one question though...

when replacing the emulsion tube, how many turns out from fully in should it be set at? As I noticed when removing it that it is not screwed all the way in. Are all emulsion tubes for the four carbs set at the same height? So can just check on another carb or is there a set number of turns out they should be? Thanks!!

Also, the Haynes mentioned that the pilot jets are not screwed in fully but set at a number of screws out from fully screwed in. However, the pilot jet I have just removed was fully screwed in. Is this correct or is there a set number of turns out from fully tight they should be? Thanks!!


Oh and found one blocked jet so far... pilot jet. Getting it sorted now.