VHB 29 Tapered Needle Size.

[Tom H]

How do you tell the difference between the V5 and the V9 needle? Do you measure or is the number stamped somewhere?

The V5 is for the 750 and the V9 is for the 850. Does the V5 let less fuel through compared to the V9? If you had a V9 in a 750, would it run rich?

Thank you,
Tom

[Moto]

Here is a table of the dimensions of the V series needles, from http://www.dellortoshop.com/contents/en-us/d65_Dellorto_VHB_VHBT_and_VHBZ_Parts.html:



As you can see, the difference in diameters depends on how far up the needle is drawn through the jet.

I think, but don't recall for sure, that the needle numbers are stamped on them.

Moto

[Tom H]

Thank you for the chart!

I'm not sure if I have v5 or v9 in my 750 and I think it's running rich. Tried the choke slide and it helped at the top end, no more hesitation when whacked to pass on the freeway.

Just still seems sluggish off the line and I thought the needle might be the cause, or a least a place to start as the jets are correct. Maybe the wrong one or worn out. In the 30+ years I've had it, and the carb swaps, it could have anything Now that I have a place to start, I'll check what's in it and scrounge through my boxes of spares.

Thank you,
Tom

[Moto]

Thank you for the chart!

I'm not sure if I have v5 or v9 in my 750 and I think it's running rich. Tried the choke slide and it helped at the top end, no more hesitation when whacked to pass on the freeway.

Just still seems sluggish off the line and I thought the needle might be the cause, or a least a place to start as the jets are correct. Maybe the wrong one or worn out. In the 30+ years I've had it, and the carb swaps, it could have anything Now that I have a place to start, I'll check what's in it and scrounge through my boxes of spares.

Thank you,
Tom

I found that I got much better acceleration off the line (with my T3) after milling about 0.7mm  off the bottom of the slide -- on the longer face. I used a vise, a flat file and careful measurement, after scribing a target cutting line. Reading the Dellorto carburetor tuning guide section on slide cutaways (pp. 16-17 in linked copy below) will explain why this would help in that particular range. Pete Roper suggested this modification. Of course, it is irreversible, so you have to have faith (or a spare set of pricey slides).

http://www.rotaxjetting.com/PDFs/Documents/The%20Old%20Dellorto%20Tuning%20Manual.pdf

[Tom H]

I read about modifying the slides. Before doing anything irreverseable, thought I would look into the needle.

It runs great, but has always been sluggish compared to the 850. Starting up at a light you need to get the revs going a bit first, the 850 is almost throttle and clutch at the same time. 750 needs a bit of throttle first. It's also always smelled a bit rich, so did my 850 until I changed the carbs to a new/used set. That's when I noticed how rich it was running. My mainly freeway ride of 120 miles takes 3.8 US gal. Same for the 850 until the carb change, not it's 2.8-3.1 US gal.

After doing the choke slides and seeing an improvement, now it's time to tinker with the rest. Did around in my parts for some slides and needles and see what I can do.

BTW: Maybe 3000mi on new piston sets, less on new plugs, ect..... So it's not all worn out. Well maybe the carbs 

Thank you,
Tom

[Moto]

My pleasure. Good luck.