Fuel system issues - help please

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   After having my 79 Nautique carb rebuilt, I have not been able to keep it running below 1500 rpm's ?   After re-installing  the carb, it ran great for about an hour, but  will now only run at  1/4 throttle and up.   I think I've checked all of the basics (new fuel filter, cleaned anti-siphon valve, new fuel pump).  It would seem that something happened with the carb rebuild, but I pulled the carb and it ran good on a dyno-engine at the carb shop.

Can anyone offer troubleshooting advice ? 

Thanks

'79 Nautique, 351 Commander, 4 barrel, Holley D4JL -- 9510, elec choke,   New fuel filer cartridge, new fuel pump (7-9 psi).  

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79ntique Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: July-09-2012 Location: greenwood,in Status: Offline Points: 12	Post Options Post Reply Quote 79ntique Report Post Thanks(0) Quote Reply Topic: Fuel system issues - help please Posted: October-29-2017 at 12:31am
	After having my 79 Nautique carb rebuilt, I have not been able to keep it running below 1500 rpm's ? After re-installing the carb, it ran great for about an hour, but will now only run at 1/4 throttle and up. I think I've checked all of the basics (new fuel filter, cleaned anti-siphon valve, new fuel pump). It would seem that something happened with the carb rebuild, but I pulled the carb and it ran good on a dyno-engine at the carb shop. Can anyone offer troubleshooting advice ? Thanks '79 Nautique, 351 Commander, 4 barrel, Holley D4JL -- 9510, elec choke, New fuel filer cartridge, new fuel pump (7-9 psi).

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10650	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 12:44am
	Sounds like a vacuum leak. Did you replace the gasket between the spacer and the manifold along with the one between the carburetor and the spacer.? Some gaskets don't fit real well between the spacer and manifold leading to a vacuum leak and the symptoms you have.

Duane in Indy Members Profile Send Private Message Find Members Posts Add to Buddy List Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578	Post Options Post Reply Quote Duane in Indy Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 8:30am
	Sound like a candidate for the old ether, or propane leak check. Only us old guys know that trick. Right Pete, and KEN???
	Keep it as original as YOU want it 1978 Mustang (modified)

8122pbrainard Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040	Post Options Post Reply Quote 8122pbrainard Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 8:42am
	Duane, I prefer the propane trick as is less volatile!
	54 Atom 77 Tique 64 X55 Dunphy Keep it original, Pete <

8122pbrainard Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040	Post Options Post Reply Quote 8122pbrainard Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 8:50am
	It's easy: How to check for vacuum leak using a propane torch
	54 Atom 77 Tique 64 X55 Dunphy Keep it original, Pete <

Gary S Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096	Post Options Post Reply Quote Gary S Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 10:05am
	I went through this about a year ago when I put a 4bbl on the Shamrock. If a Commander is the same as a PCM there isn't a aftermarket gasket that will fit a stock iron manifold and the pcv adapter. They are not off by much but enough to cause trouble. You need to use a genuine PCM gasket. If I have them here I will post a picture later, I have extras since they are hard to get. I'm not pulling a Ken and taking it apart.
	69 Mustang HM SS 95 Nautique Super Sport

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10650	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 10:26am
	Here's a picture from the past of the bottom of a PCM spacer. Not a lot of sealing area there and like Gary said it's a tough thing to seal with aftermarket gaskets. Fairly easy to make your own from a piece of gasket material from most any parts store or buy the PCM gasket. Just need to make it bigger around the outside edges Put the spacer on the gasket material and trace around the outside and then cut it about 1/4 inch bigger on the edges Inside can be the original size

79ntique Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: July-09-2012 Location: greenwood,in Status: Offline Points: 12	Post Options Post Reply Quote 79ntique Report Post Thanks(0) Quote Reply Posted: October-29-2017 at 11:45pm
	Thanks guys-- the leaking gasket makes complete sense; I'll test it out in a few days, but I think you are spot on with the fix. I installed a new base gasket, but it was an aftermarket, looked close, but must have failed after an hour of running... I really appreciate your help; after 20 years of tinkering with this thing, I think I know it, but I often prove myself wrong -- thanks again..

Fuel system issues - help please

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