Mikuni's making a wierd noise?

[zguitar71]

I have a squeeking, chirping sound comming out from my Mukuni's. It sounds like a belt rubbing but I took the belt off and the sound is still there. I pulled the valve cover and checked everything out and all is good. The sound at 1200 rpm happens about 200 times a minute (I am good with meters, musician and all) and increases as the rpms increase. It does not happen when it is cold only when warm. The sound seems to be comming from the trumpets on the carbs. I have looked at everything I can think of that would make the sound and I am left with the carbs. My racing partner sais he has heard the same sound from carbs like mine before. He seams to think the air rushing in is making the sound. Has anyone experienced this before from a set of tripples. They have very short trumpets (1.5") and no filters yet. Thanks

[Dtsnlvrs]

Yes, this can happen when the ambient conditions are "just right"

[jmortensen]

My friend had that exact problem on his 510. Sounded like a small bird chirping under the hood. In his case he found it to be the throttle plate bushings leaking and the whistle was a vacuum leak. It was only one cylinder which is why it doesn't happen with every intake stroke. Doesn't really matter too much on a car with Mikunis, because once you open the throttle plates no air is going to come in through that small hole. His eventually just went away by itself, the hole must have either closed itself or more likely opened up to the point at which it didn't whistle anymore.

[zguitar71]

Thanks for the info. I did not go through the carbs before I put them on the car, I bet the bushings are bed. The carbs were used on an FP autox car for a couple of seasons then they sat for a few years before I got them and put them on my car. Seems pretty reasonable for bushings to go bad after sitting for a few years.

[Dtsnlvrs]

Thanks for the info. I did not go through the carbs before I put them on the car, I bet the bushings are bed. The carbs were used on an FP autox car for a couple of seasons then they sat for a few years before I got them and put them on my car. Seems pretty reasonable for bushings to go bad after sitting for a few years.

I still stand by what I said earlier, but to rule anything out....spray some starting fluid around the throttle shafts while it is running. If you have a vacuum leak this will cause the rpm to increase.

[zguitar71]

I'll try that, thanks. I believe you about the right conditions but with mine that seems to be any condition as long as it is above 50 degrees or so.

[Dtsnlvrs]

I'll try that, thanks. I believe you about the right conditions but with mine that seems to be any condition as long as it is above 50 degrees or so.

My Webers do the same thing, and it is just one barrel of one carb. Only does it cold at idle. The last Z with webers I had did it all the time on all 6 throats.

[zguitar71]

I sprayed starter fluid on the throttle plate bushing area and all 6 are bad and a couple seem to be worse than the others. The only real problem I see is the attention it draws when I drive down the street, a little embarassing. Thanks for the help.