GT750 CV Carbs and pods filters?

[Vintageman]

Hello,

I have seen a few late model GT750 running stock CV carbs and Pod Filters.

Does that work well?

I have a CB900F and if you go to CB1100F.net forum most people agree you can't get those bikes wont run right with stock CV carbs and pods. I have seen no one get it right...last I looked. It needs the stock air box back pressure to work else go to different carbs like CR or FCR Flat slides.

Well the Honda CB DOHC 750/900/1000/1100 use a CV Keihin and the GT750 has Mikunis.

So my questions, can these GT750 stock CV carbs work well with pods? And better top end performance than stock air box?
Still Nice street bike manners: Small throttle all the way to WOT?

If true what jetting is used?


Thanks

[ja-moo]

CV carbs are a hornets nest. Difficult to tune as there is really no throttle position to work your jetting off of, as the needle position is set by flow velocity and not the throttle cable. You also have 2 extra variables to work with, diaphragm spring tension with is extremely difficult to adjust, or even get alternate springs for. And bleed hole sizing which also effects the position of the needle. You would really need a lot of dyno work to get them to work out of the stock system. Not impossible, but a lot of time and work, I would hate to have been the engineers having to set them up from the factory.

Personally, I would go with some aftermarket carbs and give yourself a chance......

[tz375]

DOHC Hondas and CB350s, 360 and 400 twins have a reputation for being hard to jet for pods. That still appears to be as true today as it was back in the day. The way I look at it is that Keihin used the SU design and Mikuni used a Stromberg design and they are very different.

BS series carbs are used on GT750 triple two strokes and on 4 stroke bikes including XS650 Yamahas and a variety of Suzuki GS/GSX twins.

The next question was if they can be run with pods.
Some cheap pods tend to cover the pressure ports and cause all manner of issues but good pods seem to be used regularly on those 4 strokes and on GT750s.

The third and forth questions were how did they jet them and how good/bad was the performance.
That I can't answer. There are those that claim their bikes run fine and others claim that they will seize at some time. My bike has large UNI filters and very modified 3 into 1 exhaust and on the dyno it showed up as slightly lean but nothing critical. Now I have modified the exhaust further I expect to see a different result.

I'll be using exhaust gas analysis and data logging to see what is actually happening, but not until the next snow storm passes. We'll look at A:F against RPM, throttle position and hopefully (damped) MAP and see if a picture emerges. As JA mentions that may be a costly exercise or at least a frustrating one, but nothing ventured nothing gained.

CV carbs on GSXRs are re-jetted all the time for pods and pipes but they are very different to our old BS carbs. Maybe that's why some Mikuni engineer called them BS

[Vintageman]

Thanks guys,

I would like to see someone else jump in and claim it works better than stock box and with some miles to back it up.

But like you Tz it does seam to work and many people have them on GT750. Must be better top end once jetted there OK, slide sucked all the way up and you ride WOT on butterfly

I had wicked poor luck with CV Keihins / pods and stayed stock on my CB900F.
My GS650E had K&N replacement filter and air box top removed. This has Mikuni CVs. The guy did this when he paid a Suz dealer back in the 80s to put a V&H 4 into 1 and its recommended changes.

After, he basically stopped using and about 25 years later I bought it. After sale he said it never ran right after that was done. I always ask (even after sale) for there is a reason they get parked and stored so long!

Finally found air box cover and went back to factory (maybe a notch or two higher on main don't rememeber). Better, but still ran wierd at times.

Dumped the K&N for stock Air filter and all is perfect, really, day and night.

Yes CVs are dynamic and based on flow and opening

[tz375]

One thing we didn't talk about, but it's important and that's the way that some pod filters tend to obscure the intake ports in the carbs.

On a GT750 there are two air jet inlets plus the larger slide pressure port and some/all pod filters obscure some of those holes.

UNI filters for example are not bad on the 6 inch long straight filters but the 15 degree angled ones are around 3mm smaller and that's enough to block one or more air jets.

With individual filters (and old filter connections) it's important to measure the inner diameter to be 100% sure they are all clear.