PDA

View Full Version : Throttle Shaft Vacuum Leak


SugarLake
08-03-2010, 09:49 AM
I think I finally figured out why I am having such a hard time getting my motor to idle correctly. It seems I have found a vacuum leak where the throttle shaft comes out of the throttle body on the choke side of the primaries. Is there anything that I can do for this short of replacing the carb? It is a remanufactured carb that I put on this spring, and I can exchange it under warranty, but I'd rather not have the boat down for 2 - 3 weeks right now. It's a Holley 4160 on an '88 Prostar 351.

oldairboater
08-03-2010, 10:02 PM
Air leaks make it almost impossible to dial in a carb. That is why I don't buy re-manufactured. Someone else may have a quick fix but if it was me I would send it in and try to get one not worn out at the shaft and bushing.

JLeuck64
08-03-2010, 10:52 PM
I fought the same thing once a long while ago... had a Guy in town install new bushings in just the throttle plate assembly. All that did was move the vacuum leak to the other side! New Carb fixed it for good...

SugarLake
08-04-2010, 09:36 AM
Thanks guys. I'm tempted to just go buy a brand new one but I'll probably wait until fall and try once more on a warranty exchange. You'd think the remanufacturers would check tolerances on that stuff, but I doubt it. I wish I had gone new to start with.

jconover
08-04-2010, 12:54 PM
How did you find your vacuum leaks? Carb cleaner around the edges of the carb? I haven't tried this, but my vacuum meter bounces between 5-12 at idle at a schizo-fast rate.

thatsmrmastercraft
08-04-2010, 12:58 PM
How did you find your vacuum leaks? Carb cleaner around the edges of the carb? I haven't tried this, but my vacuum meter bounces between 5-12 at idle at a schizo-fast rate.

Carb cleaner is the best way. Use the provided straw to accurately direct the carb cleaner spray. Just give it smaller and smaller shots and watch the tachometer climb when to find a leak. You must have a serious leak to have such low vacuum.

SugarLake
08-05-2010, 10:04 AM
How did you find your vacuum leaks? Carb cleaner around the edges of the carb? I haven't tried this, but my vacuum meter bounces between 5-12 at idle at a schizo-fast rate.

Exactly as Mr. MC stated, choke cleaner through the straw. At first I wasn't that close when spraying around the base so assumed it was a base gasket leak. Replaced that (twice) and checked the carb and spacer and both were dead flat. Then I realized that I was spraying right where the throttle shaft protruded, and verified it with closer and more directed shots of spray. No mistaking the rev of the engine, it was significant.

jconover
08-05-2010, 12:24 PM
Yeah that's the next project on my rebuild list. I threw a vacuum gauge on my engine once and it just bounced all over; i've since plugged the little vacuum port right next to my carb (it had a brass fitting for a steel line) I haven't rechecked vacuum since I did that, since I ran into a host of other little issues. Thanks for the tips/advice - I wasn't sure how much you'd notice some carb cleaner on an idling 454.