wont idle and throttle (revs) hangs when i gas it

Hey guys .. in my ongoging journey to get my 3 year build on the road here is my next challenege.

Just put in 120 mains and 20 pilots in my VM29s. I cant get the bike to stay running at idle and when i give it gas the revs hang for at least 10 seconds or so before it comes down. Just put on new throttle cables to.

Where should i check first? I feel like I am starting to go in cirlces checking timing, trying to synch carbs, air screw mixture.

Here are my specs:

75 z1900 bored 1075
410 lift web cams
29 smoothbores (120main 20pilot) - air screw currently out 1 1/2 turns
dyna ignition
vent lines not obstructed
running off a remote tank
vacuum gauges plugged in

When ya give it a twist (not running) watch and make sure the cables arent sticking (on a bind). Also watch and make sure the spring on the carb is pulling back like it should be.

Sounds mechanical to me, but even being new here, I can tell ya others are more experienced.

i double checked the cables and they are definitely snapping closed nicely. I even manualy pushed down the throttle on the carbs when it was hanging (revved) and it still did it.
I know i probably have something stupid i did going on as everything is pretty much new .. manifolds, air filters, cables, jets, cleaned carbs, engine top end, ignition.

I guess i should try taking the cables off and revving it manualy at the carb to make sure it isn't them. Haven't done that yet. Sux having neighbors .. i want to go mess with it right now!!

A fair number of VM29s left the Mikuni factory with the wrong throttle return spring. There are two springs that look similar. One is used on the VM24 and the other the VM26/28. Although they look similar, a side by side comparision will show that the 26/28 springs have heavier gauge steel windings. The 24 spring is just weaker and a hanging idle is the result. Also, remove the air screws and ensure than the orings are still pliable... replace, if they are not. The 29s idle circuit is fussy enough and extra air leaking in in the air screw well will cause the idle to go bonkers... Also make sure the choke plungers are seating by jiggling the choke lever... a poor seat will cause the idle to race.

thanks george!! I'll just go ahead and see if i can get that spring off z1enterprises. One less thing to have to diagnose. The rubbers on air screws looked good but i'll swap those out too.

I was messing with the choke already a bit and i think that seems fine. I'll jump back on after i get the parts and try it.

wiredgeorge wrote:

Although they look similar, a side by side comparision will show that the 26/28 springs have heavier gauge steel windings. The 24 spring is just weaker and a hanging idle is the result.

George .. if i take a picture of my spring would you be able to tell if it is the right one without the other there for comparison?

Nope... they look identical except when compared with each other. They are not much different then except for the 26/28 spring being SLIGHTLY larger gauge. When you go out and ride with the weaker spring, then change to the heavier spring, you definitely feel the difference.

I doubt you will find a spring for sale on a stand alone basis. Buy a junk set of 26 or 28 carbs OR go to the hardware store and see if they have a stout spring. There are three types of springs... compression spring, expansion spring and a both-way type. You need the both-way type. By the way, the words I used may not be correct but a good hardware will all three types.