Jetting '90 VFR w/ UniFilter and Staintune

Hi guys

have a 1990 VFR but am fitting 1994 collector and hi mount staintune pipe as well as a UniFilter (foam oiled type).

Any tips on likely jetting required?

Would appreciate advice from others who have been through this kind of exercise. Are jets required (if so is that emulsion tubes plus the main jet that screw into the emulsion tube) or just shim needles? Assuming std needles are not notched. How do you retain the shims without them falling out?

FYI using the std collector, Uni filter and Staintune low mount (this is the current setup before I change out the collector/muffler) it appears to have a flat spot around 5-7k rpm approx. Oh and I also removed the airbox snorkel.

Cheers, Kendrick

 

Best bet is to toss it on a dyno and go from there. That's what I plan on doing here real soon. Even a stock set up could use a bit of tweaking to optimize things.
I'm going to have the same set up once I get my high-mount situation sorted.

 

Hey lucky

Thanks for the advice, agree this seems to be the case to get by Drive By noise requirements (ADRs in Australia).

Meanwhile I did manage to get out the needles without taking the carbs off (had a bit of difficulty getting off the front plastic air blocker). I did two things:

1) I increased pilot screws to 2 turns out from bottom
2) I shimmed the needles up 0.5mm (20thou)

This definitely helped but there is still a flat spot in the upper midrange.

I will try another 1mm perhaps in shims first before getting to the dyno. Clearly it's suboptimal now, I don't really need a dyno run to confirm it as its obvious enough riding it. However once I feel I'm closer to a half reasonable result, I'll give a dyno run a shot (hopefully eddy current type rather than inertial). Not sure who's got that type in Melbourne, Australia.

 

before you reshim the needles, try putting the snorkel back on...you might be too lean. That's easier to do than getting back at the needles and might confirm which direction to go.

 

Hi

I've no doubt that it is lean, that's what I believe is causing the hesitation. As far as I can tell I don't think the main jets need changing - 130s in there already in 36mm carbs. But yeah, putting on the snorkel might be a good stop gap measure to avoid an early (expensive) demise...

 

Updated on jetting VFR750FL

OK

So still had midrange hesitation so got another 8 x 20thou (0.5mm) washers (2 per carb, now totalling 4 washers under each needle) and installed them on the w/e.

This morning's ride was much better, very good part throttle response.

I may put back on the snorkel and see how that goes also.

After that, time for a dyno run.

 

Hi Kendrik,

I just bought an UNI foam filter on ebay for my -91 vfr. It seems that the only way it fits into the air box is with the foam side (and the UNI text) facing down (and the metal grid side facing up), which is opposite to the old OEM filter. It seems a bit odd, but since it is impossible to install it in more than one way (and fits perfectly "up side down"), I wonder if this is the way it should be or if the filter as such has been assembled the wrong way. How does it look on your bike….?

Best regards

Olle D

 

Howdy - Mine came the same way - I just removed the centre section (which comes out for reoiling anyway) and turned it around 180dgs - problem solved. As far as I am aware, the metal mesh should face the carb inlets - that's the way it is on the OEM Honda paper filter.

By the way I have the snorkel back on the airbox now and it runs well - midrange around 5k is very responsive, now just checking fuel mileage etc and trying it in a variety of riding conditions. Without the snorkel it had a noticeable resonance, which if physics serves me correctly, puts more energy into exciting the mechanical resonances of the airbox rather than get air into the carbs. Leave the snorkel on is my suggestion.

Well worth the mod for $40 for the Unifilter and a few dollars for the needle washers from your nearest Honda wrecker. Wish I'd done this 17 years ago when I bought it...

 

Hi,

Thank you for your fast reply. You say "I just removed the centre section (which comes out for reoiling anyway) and turned it around 180dgs", isn't the foam part glued to the filter frame? Did you cut out the foam part and glue it back on the other side, or is the whole section with both the foam part and the metal mesh removable?

/Olle

 

I had the same misconceptions - absolutely not....squeeze the airfilter on the longer sides towards each other. You should be able to see how the insert attaches to the outer 'plate'. Twist it a bit and you can work it out easily. The insert has a U section that locks into the outer plate.

 

Ok, thank you for all your input. I will give it a try tonight and see if I can fix it. I suppose UNI doesn't make two different filters for the same model, so I'll guess that we have the same type. Unfortunately I have already oiled the filter so this can be a bit messy.....

Again, thank you for your help. I will give some feedback when I'm done...

Regards - Olle

 

Some feedback:

You were absolutely right; the filter section could be removed. :thumbsup: Now it’s done and the filter is assembled just as it should...

Thanks for all your help...

/Olle

 

You're most welcome. Try shimming the needles, do a dyno run and let me know the results and what you settled on. It will flow a fair bit more air than the paper element, so don't run it for too long without addressing this - burnt valves, overheating etc are worth avoiding. Oh, and keep the snorkel on - it just doesn't seem to run well without it.

 

Uh-oh, gone too far. Addition of 3 x 0.5mm shims (plus the OE x 1 x 0.5mm) has the bike running very rich, to the point it's starting to foul the plugs by the sounds of the bike and some hesitations. Going back to 2 additional shims and will then handover to the dyno guys who know more about what's going on and more importantly can tune with data.

Sorry for any bum steer.

 

you'll never know if you're too rich or too lean until you go too far in that direction..... and then backtrack.

Forget about needle shims for now, cuz "No set up is correct until the BEST MAIN JET is dialed in FIRST"

 

I finally got around to rejet my 93 last weekend. Stock filter, and stock exhaust. I have a shortened D&D end can with a custom hi-mount midpipe that I will be installing soon.
I bought a stage 1 Dynojet kit. It came with 120 and 124 mains, new needles and needle shrouds you install over the needle jet in the intake tract. The stock mains are 130 Keihin mains which translate into a 122 dynojet main.
Install was straight forward and I simply installed the clip/washer on the needle according to the instructions (3rd from the top position). I installed the 124 mains since I will be installing the slip-on soon.
Even as it is right now, it runs great and has no hiccups/flat spots at all. Once I get the slip-on installed, I'll get it on a dyno to fine tune it. I don't know how much better the jet kit by itself is, as I installed a set of 49-state cams at the same time and the bike picked up 10-15hp with the swap.:thumbsup:

 

+1 on the not messing with shims until the best main jet is dialled in.
also taking out the snorkel is good idea, but only with the proper jetting. the snorkel is restriction and essentially increases vacuum inside the air box. with the snorkel out there is less restriction and less vacuum therefore less fuel is being sucked through the stock size jets. with an aftermarket filter and a modded airbox larger mainjets are needed to bring you back to an optimal air/fuel ratio. ideally this should be done on a dyno to see actual a/f ratios, but, if you know what you are doing and can tell the difference between a lean knock and a rich miss you can tune it your self...
good luck!

 

Howdy all - back again.

Have bought a Factory Pro kit which I thought would be a fast track to better midrange. I hear all the recommendations about choosing main jet first, but to be honest, the top end is not the point of interest to me - and it runs fine in that range IMO.

The kit comes with 128 and 132 mains, but I've left in the 130s for the time being because of the above. I started with the jets on second clip from the top and idle screws out 2 turns. This ended up with a way over rich bottom and midrange - very fluffy and a bit harder to start to boot. Not that suprising when you put the jets side by side - check out the difference at the bottom end of the needle! Click Here For Comparison

Then I removed the snorkel (again) from the airbox - this didn't seem to do much except make it sound a bit hornier in the upper mid/top end. Bottom/mid still over rich.

So now I'm trying the top clip position on the needles, and put the idle screws back to 1/3/4 turns out.

Will report back how this went. Cheers.

 

You are going about it the wrong way. You'll never get the needles (not jets) to work properly if you don't have the mains correct, you will be chasing ghosts as you are right now. The folks at FP know a little more about the design of their jet kit that we do...follow their instructions to get it working properly. Needle design is the key thing here, and getting that needle paired up with the correct mainjet is critical. There will be some tweaking with any install due to varying conditions to get it dialed in. But it all starts with the correct mains...get it wrong there and it's wrong everywhere else.

Put the snorkel back on...that is a no-no. Just causing you more difficulties.


I dropped in a DJ stage 1 jet kit about a month ago with stock muffler and filter. Runs like a champ. Still got to get it sniffed on a dyno to fine tune it though. This jet kit stuff is not all that difficult, but if you try to maverick it without knowing what you are doing, you will have all sorts of issues.

 

Despite persisting with the Factory Pro jet/needle kit I have been more than disappointed. Initially I tried the second clip from the top, then the top clip both with and without the snorkel. Appeared to be lean at part throttle (worse when cold) but rich in the top (not very responsive)

In an attempt to get more science into this I visited the dynes to get some real data. Attached is the result both before (above settings top clip position/leanest setting) and after.

Note the 'after' is using the STANDARD needles and minus the std 0.5mm washer. Mains still at 130 and pilots at 40. Idle mixture screw 1.5 turns out - they tried several settings this was the best.

The Factory Pro kit in my opinion has been a total waste of money. Even with the needles on the leanest settings it couldn't pass muster for acceptable air/fuel ratio (around 11:1). I asked the guys whether the 128 mains would bring it back into line, they didn't believe it would help enough.

Looks like there's still potential to run smaller main jets (possibly even smaller pilots) with the std needles, perhaps 125s for the mains to get more optimal air/fuel ratio in the top end (not that I spend much time above 9000rpm though).

Pretty pleased to see 85ps after over 100,000kms though!

Thoughts?