RPM increase after engine warms up

[Guest froesefs@mts.net]

86 Venture idles up to 3000 rpm after warm. Has anyone experienced this. Advice appreciated

[Squeeze]

If your haven't worked on the Carbs and splitted them recently, you're most likely chasing Vacuum Leaks.

 

Let the Bike sit on Idle and take something burnable, like Brake Cleaner and carefully spray it on the Manifolds. Where the RpM rises lies the Culprit.

[Snaggletooth]

Hey Squeeze.

 

I gotta ask. My bike has done this since I bought it. The warmer it gets the higher the revs. I recently rebuilt the carbs and while it was down I replaced every vacumn line I could find, epoxied the seams of the chamber and really, really checked the manifolds as completely as I could. They are still soft and pliable and no hard spots at all. When I finished the rebuild the bike still did the same thing. I warmed her up and started to give her little sniffs of starting fluid around the manifolds with nothing resulting in rev increases.

 

I've got the idle down so low now, below 900 rpm that I have to give her a goose now and then to keep her from stalling at a full stop. The idle is a little lumpy like a Jason mod. About a 300 rpm surge.

 

You got any suggestions?

[Black Owl]

86 Venture idles up to 3000 rpm after warm. Has anyone experienced this. Advice appreciated

 

As Squeeze indicated. U are most probably developing a vaccum leak as the engine warms up due to metal expansion.

 

However, I see you live way up in Dauphin. So, given the climatic conditions up there, this should only be a problem like say, one day a year...

 

Seriously though, I suspect a metal expansion induced vaccum leak.

 

If you can't get it resolved before Sept, hook up with the other folks from Manitoba and bring the scoot down to the Pork in the Pines. We could use it as a project bike to find the cause of the problem...

[Squeeze]

I once had a Vmax on the Lift where the same happened. I chased Vacuum Leaks and found nothing. Then i asked the Guy wether he had worked there and splitted the Carbs recently.

 

He answered Yes, so i teared them off and took a deep look. It was simple Thing. The Bolts which hold the Carbs toghter are not guided in any Way. During bolting everything togehter, the Guy tightened the left and right Side in a Manner that the Halves were set at the nearest Point.

 

When the Bike warmed up, the Carbs warmed up also and the Lever which connects both Sides epanded due to the Heat.

 

Now, i'm not saying this might be the Solution to your Problem, but i want to say how Things happen. The Linkage on the right Side Carbs may be a dry and stuck when warm. A Friend of mine tore his Max apart to get the Frame welded and powdercoated, while storaging the Parts, he bent the Linkage of the Carbs and couldn't get them synched or setted down to a normal Idle. He searched everything for Days and found nothing. We talked for Hours over the Phone without Success. Finally, i come to his Garage and 30 Minutes later, i was hooking the Vacuum Gauges on the Manifolds....

 

There are Lot of Things happen ....

[pegscraper]

It's too lean, for whatever reason - vacuum leaks, mixture screws need turned out, pilots too small, something. A lean condition causes problems when the engine is cold and improves when it runs for a bit and warms up. A rich condition does just the opposite.

[86Royale]

I fought this very thing earlier this spring. Turned out to be an old, cracked vacuum line leading up to the baro sensor. I replaced that, took the idle down just a little, no more problem. I had the same thing though, slow, steay advance to 3000 rpm as it got warm, tried looking for vacuum leaks around the carbs, etc. Was really glad it was just an old line. Good luck.