SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: Xthaspot on July 01, 2013, 11:18:22 AM

Title: Vacuum leak
Post by: Xthaspot on July 01, 2013, 11:18:22 AM
Well got my boat on the water finally this year. Runs great off idle. I was pushing right around 5 grand on moderate water and that boat is fast. Estimating at least 65-70 mh. Ok so now I have the biggest problem. I have a vacuum leak. I'm pretty sure I have one on the back carb. Couldn't get it to idle no matter what I did. After much frustration trying to set the idle I just bumped the idle up so far that it was dribbling fuel out the primary's to keep it running. I know probably wasn't a good thing but I was trying to salvage my day. I have dual edelbrock 1405 carbs. Using a can of brake cleaner I'm pretty sure that where the top half of the carb meets the bottom half has the vacuum leak. Tightened it down and it helped a little bit still there. Does anybody have any tips for me? This can't be that hard to set. I mean I have set dual carbs before on vw's and had good success.
Title: Re: Vacuum leak
Post by: ka0tyk on July 01, 2013, 11:21:29 AM
id try pulling the carbs off, cleaning all the old gasket off and try new gaskets.   its cheap.  do you have to run multiple gaskets and deal with sandwiching a throttle plate inbetween the carb and intake?  i silicone my throttle plate to the intake and then use a carb gasket between plate and carb.
Title: Re: Vacuum leak
Post by: Xthaspot on July 01, 2013, 11:40:06 AM
id try pulling the carbs off, cleaning all the old gasket off and try new gaskets.   its cheap.  do you have to run multiple gaskets and deal with sandwiching a throttle plate inbetween the carb and intake?  i silicone my throttle plate to the intake and then use a carb gasket between plate and carb.
No I don't have any problem with sandwiching. I will try a new gasket for sure. I did rebuild the front carb and should have done the back carb. Ill try that thanks.
Title: Re: Vacuum leak
Post by: mash on it on July 01, 2013, 03:09:57 PM
On Edelbrock carbs. pull the two mixture screws and check for debris. The one I have, on the wrecker, would do this after sitting for a while, pulled the mixture screws and used compressed air to make sure they were clear, reset at 1.25-1.5 turns out. (fuel tank was full of dirt/mud)

Hope this helps

Dan'l
Title: Re: Vacuum leak
Post by: 1979 hornet on July 01, 2013, 05:56:39 PM
Spray starter fluid around the car and when it idles up you found your leak
Title: Re: Vacuum leak
Post by: ka0tyk on July 01, 2013, 05:59:25 PM
Spray starter fluid around the car and when it idles up you found your leak

unlit propane torch is a little bit safer than spraying liquid all over your engine.
Title: Re: Vacuum leak
Post by: renegade on July 02, 2013, 06:57:09 PM
Inspect insides of carbs could have some shit in there. Todays gas sucks ass, good luck.
Title: Re: Vacuum leak
Post by: Xthaspot on July 03, 2013, 02:29:36 AM
Inspect insides of carbs could have some shit in there. Todays gas sucks ass, good luck.
Yea that's what I initially did but still there. I ordered I gasket kit for the back carb and hoping that's gonna make the fix I need.
Title: Re: Vacuum leak
Post by: renegade on July 03, 2013, 11:17:33 PM
Give it a good blow job in every orfice with compressed air. take the top off carbs. check needle and seat for propper operation.
Title: Re: Vacuum leak
Post by: Xthaspot on July 05, 2013, 06:36:20 PM
Ok got my gasket kit in for the rear carb. Gaskets were hard and old so I got that all changed out. I can get it to idle between 900-1000 rpms. I have no more adjustability for bumping the idle up any hire or it will start dribbling out the primary's. I just have one question. Can your cam profile cause any issues like this? Here is a picture of what cam I have. It will be the JM-25-28 listing.
Title: Re: Vacuum leak
Post by: berkbryan on July 05, 2013, 10:28:02 PM
I can not see a cam causing your problem something is not set right in your carb like the floats

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Title: Re: Vacuum leak
Post by: Xthaspot on July 05, 2013, 10:35:14 PM
Yea I can agree. I did check the floats and there was one way off. After taking care of that and the gaskets and a little tuning I actually got her to idle way better. I think I got both carbs sinked pretty good.   Thanks for your help. 
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