bogging on takeoff/lower rpms

[Guest]

Hi,

This is more of a theory question. I have an 82 GS450T, stock all around. Recently, after completely dipping and rebuilding the bs34 carbs, I upped the main jets from 115 to 120 because it was running lean (both in feel and in spark plugs). The results were much improvement on the pull with full throttle, especially from 4.5k-7k rpm.

However, once giving it full throttle from deadstop, it appears to bog at the lower rpms 2-4.5k Once the engine goes past 4.5k it really pulls quite nicely. Below 4.5k it doesn't pull quite as good.

What would be recommended to improve this portion of the rpm band?

Thanks,
Steve

[BassCliff]

Hi,

You should perform plug chops to confirm which circuits (throttle openings) are performing properly. But off the top of my head I'd say you need to raise the jet needle a little to richen up the midrange.


Thank you for your indulgence,

BassCliff

[pete]

Mate you have CV carbs on there and if what I have read around here is any indication, going to WOT real quick from closed throttle will tend to do some bogging regardless of your jetting setup.

However... Cliff's right that you do need to do plug chops to get it right across the whole throttle opening range.

Adjusting your mixture screws may help in this regard also.

Mine's not exactly stock (K&N pods + free flowing 2 into 1 pipe) and I currently have 137.5 mains, the needle set as rich as it will go, and stock pilots. I get no bogging when I open the throttle but I have also cut just under 20mm off my slide springs to allow them to open faster.

I'm currently thinking I'm still not rich enough at WOT so will try even bigger mains, but I am definitely too rich at idle and am still fine tuning it.

One thing I also haven't done yet is plug chops to confirm everything, but the seat of my pants dyno tells me I'm on the right track.

[bwanna]

Well, I finally got the engine top redone (head cut, new valves, up'd to 500 cyl block). Going to let it settle in for 500 miles, but will resurrect this effort with plug chops and adjustments.

THanks for the feedback and advice!!!

[tkent02]

However, once giving it full throttle from deadstop, it appears to bog at the lower rpms 2-4.5k Once the engine goes past 4.5k it really pulls quite nicely. Below 4.5k it doesn't pull quite as good.

Keep it above 4,500. It's a small motorcycle, not a big block Chevy. Ride it like one.

[pete]

Keep it above 4,500. It's a small motorcycle, not a big block Chevy. Ride it like one.

You know, that's pretty good advice actually... although it still shouldn't "bog" below there, it just won't get up and go...

I've gone up to 150 mains on mine now and she's quite the little goer... but to get her poking along seriously, revs need to be at 5500 - 6000 and I'm confident that that has nothing to do with jetting, just engine design/capacity.