Odd idle issue with PHBH30's

[v65tt]

My V65TT ( and now V7TT) has always had an odd idle problem, its never caused me any problems but since the V7 Engine has gone in I have decided to dig deeper.

So when its sat idling happily around 1200 rpm I close both fuel taps and the idle goes up to about 1500 slowly, open the taps and it drops back down.  ( prob was same with the v65 engine..!)


any ideas?

[Tom]

Mixture leaning out with less fuel. a guess.

[v65tt]

id figured that bit for myself   ;-)


so smaller main jet , or smaller pilot or alter float height?

[Tom]

Yeah, something like that.  A little experimenting on your part.

[Two Checks]

If your plugs are a nice tan, don't change a thing.

[Triple Jim]

The main jet won't affect idle.  As you know, speeding up as the fuel level in the float bowl drops indicates you're a little on the rich side.  I don't know that carburetor offhand, but adjusting the idle mixture for maximum RPM should do what you want.  If you have air screws, you would open them a little to find the maximum.  If they're fuel screws, you'd close them a little.  If unsure, you'll know as soon as you turn one, since going any richer is sure to slow the engine even more.  If the mixture screws are at maximum lean already, then you'd need to go one or two pilot sizes smaller, but as stated, if you're not blowing black smoke at idle, it may not be worth the trouble.  I bet you can adjust it leaner with the screws though.

I like to set mine slightly rich.  That is, RPM on the edge of dropping if I go any richer, rather than right in the center of the max RPM range.  I find that warmups are easier that way, with less fiddling to keep it running when cold.

[Curtis Harper]

I really have to ask, Why are you concerned with what the idle is when you shut the gas off in the first place?

[jacksonracingcomau]

 

I really have to ask, Why are you concerned with what the idle is when you shut the gas off in the first place?

 :1:

[Chuck in Indiana]

I think he's trying to figure out whether the idle jet is the right size. I go for a *little* big. Helps cold start driveability.

[guzzisteve]

If the mixture screw is 1turn out or under= go smaller
If mixture screw is 3turns out or more= go bigger

This is for the short tip mix screw

I use a Colortune, it's British, get one. Takes out the guess work

[v65tt]

I really have to ask, Why are you concerned with what the idle is when you shut the gas off in the first place?

I only have an 8 litre fuel capacity and as its running too rich I'm hoping to get a fuel economy improvement by sorting out the fueling

[Curtis Harper]

and then I am assuming that you put carbs on the 2014 motor?

[v65tt]

Yes on the 2014 now. Prob was same when on original 650 lump.

Starts well and rides fantastic

[Curtis Harper]

And what is the fuel mileage now?

[v65tt]

hard to be accurate but around 40 miles on 4.5 litres or 80 miles on a tank


Right had afternoon in workshop to compare needles and jets between the 2 V65TT's i have.


My spare white TT has 112 main jet  and a 38 pilot  ( has K&N filers)

My V7TT has 115 main jet and a 40 Pilot.  Put new plugs in this afternoon and they came out 10mins later sooty black.


Compared the 112 to the 115 and the diameter of the hole is huge on the 115.

Got a set of small drill bits and a 1.2mm drill bit falls through the 115's....I think at some point in the past someone has drilled out the mains.

Swapped the 112 and 38 pilots from the white bike's carbs into the V7TT and after 30 miles the plugs are just on the rich side of perfect ( ideal for me) and and the idle is no longer rising as the fuel runs low with the taps off

Will monitor for a few weeks and see how we do!