Was thinking about modifying my carb(dellorto phbl)like is done when you install power-nows or powerblades. It seems that the idle circuit can benefit alot of this. Anyone tried this or done this or has any suggestions why not?

The idea behind is that with slight throttle openings the big venturi avoids good airflow cause of the turbulence. By dividing the venturi with a powernow/blade the venturi is halved so creating better lineair airflow velocties, less turbulence, hence better atomization.

Any comments?

It is easily done by using a sheet of thin alu glued in the middle of the venturi... it is easily withdrawn also

Edited November 24, 200520 yr by gasgas

Harley and Indian used this idea in the '40s and it worked well.

They used a small venturi suspended with struts in the middle of the large venturi...it became known as a "bombsight) venturi and they were bolt-on horsepower.

Although...comparing a GG to a '48 Harley might not be a good idea...

Might be worth an experiment, although from reliable sources in the MX world the Power Now product is 95% marketings and 4.5% myth. I'd think if you were to really make a significant improvement in airflow at low throttle openings you would need to do it at both ends of the carb body. Change the volume of the portion downstream of the slide and you might have something...upstream (as in PowerNow theory) I'm doubtful of.

I ve read all the topics at the mx-forums so am familiar with all the agruments pro and con.

I am not looking for more hp's but more for throttle response although i find my decent at low throttles.

Jtt, the idea of both ends sounds good, i will give it thought.

The whole idea of throttle responce is too avoid lugs and/or swirls where flow is obstructed when you crack open the throttle. Am i right in this thought?

I already modified my reedblock by looking tru it and dremel all the ridges and ledges smooth. From the factory you can see that the reedblock and stuffer have some issues in corresponding to each other. The reedblock is overlapping the stuffer creating a big ledge.

Keep you all informed about any further news....

My understanding of the basic idea was to emulate a smaller bore carb. Without getting into specifics of air flow and such a smaller bore generally produces better throttle response and torque, whereas a larger bore generally makes better top end. Trouble is I don't think you can emulate a smaller bore from the upstream side alone.

My initial thinking is that you are p***ing in the wind by trying to get the idle circuit on a dellorto to respond to anything.

My next thought says why not go to a kiehin carb as it is a better mixer!

Next thought, Mikuni!, why does everyone in trials use Kiehin(except Beta) as an upgrade

After that, why not one of the Korean Kiehin copys that seem exact in every detail and I believe are available in 24 and 26mm sizes that could be perfected for trials use if someone would do it.

As the 4t's progress on the carburated mounts, such a more precise metering device may be required!

Just a couple of thoughts, cheers!

I absolutely agree with everybody that smaller carbs produce better response down low, the fuel signal is much stronger and because of that the mixture will have a better mix

Keihin and Mikuni's what is the diffenrence? Beats me..

The replica's of the keihin, the oko's, yes cld be a good choice for the money spent. Here in holland they sell via the scooters shops a lot. They get good revues.

Well, during these cold days overhere, i like to have something on hand..

So i give the divider a go, I just glue it in the carb for the test and see what happens.

cheers

The difference....

Keihin modern flatslide.

Mikuni old round slide.

Both work well, The Keihin does work well on gassers though.

As for Powerblade - there is a version fo 80 MX bikes that in theory fits Mikuni. However the blade is too far away from slide on a Beta's Mikuni. Its a neat shrink fit & could be a good starting point.

I'm doing the same thing in a Mikuni mounted on my Hodaka custom trialer. Will have the divider plate both in front of the slide and between the slide and the engine. Just be sure there is NO WAY the plates can come adrift and hold the slide from closing. I'll be setting up with approx. 1mm clearance from the plates to the OD of the slide.

Ed

Keep the rubber side down!