Indmar Assault 310 Carb issues

[keehr22]

Just replaced my engine with a new crate motor from GM, got it on the water today and I'm having some carb issues I believe. Anyone here familiar with the Holley 4150?

I adjusted timing with adapter to 10 degrees BTDC, ran the idle air screws out 2 turns each, and set floats so that the fuel is right at bottom of opening.

Issue:

I've got a good idle at 800 rpm, but it's rough with and without load from 1100 up to 3000. Under heavy load I get pinging right around 2800rpm. But then after I wind down from 3000rpm on the water I get a bad surging idle, bouncing from 500 up too 900 for a minute or two.

I tried tuning the idle air screws in a couple turns and back out a couple turns but they have almost no effect on idle surge and roughness between 1100-3000rpm

Any thoughts?

[maxpower220]

Here is what I have done in the past: Start engine, let warm. Adjust idle screw up to 1000-1050 rpm. Turn adjust idle air screws. When adjusting, the engine will increase/decrease in rpm sound. While "searching" with the screws, you will hear the motor go from great to sputtering, move them back to the "sweet spot". Once done, set your idle screw back to factory setting, @ 750 rpm or so.
You may need to reset the float level as the carb changes angles as the boat accels/planes/decels.

Lastly, I would make a slight adjustment on the timing. Timing may be a reason for the ping, but not the surging.

[keehr22]

Totally stumped now...Got on the power valve trip earlier, the machine shop that rebuilt my carb put a 5.5 in it, instead of the 2.5; couldn't find a replacement 2.5 PV in town, so I bought a Holley PV block off, and now I'm even more rich at idle and primary circuit. Doesn't make much sense, never changed the factory 68 jets...any thoughts?

[keehr22]

Edelbrock 1409 ordered. Holley gets an F

[maxpower220]

Smartest move you could make. I am not a Holley fan, once they start having problems.

[rdlangston13]

go fuel injection...

[keehr22]

Yeah, that Holley had a leak somewhere and I just couldn't pin it down. Then I torqued it down a little too hard and cracked the base plate, wasn't worth my time or money to replace it and continue troubleshooting. I just want to get on the lake at this point!
EFI..eh..not worth the money, plus I don't know of any aftermarket company that offers coast guard approved kits.

[keehr22]

Just wanted to post an FYI for future searches, if you replace the Holley with an Edelbrock 1409 you'll need an 8 degree spacer wedge, Summit sells them for about $80. Would have saved me several weeks of frustration trying to tune a rich issue everytime we put it in the water!

[james yarosz]

How does it run now with the Edelbrock and the wedge?

[keehr22]

Runs great with the Edelbrock, no better or worse than a properly tuned Holley I'm sure. I just had so many problems with the Holley that I wanted to try something different. And, the Edelbrock is easier to setup, tune, and clean when the time comes.

[98Roo]

For the record, to properly adjust the mixture screws you need a vacuum gauge. I just had mine rebuilt and used the gauge to set my mixture for maximum vacuum and it runs great. You also want the throttle to rest on the idle screw and have it slightly open or you'll have a hesitation after idle.

[keehr22]

Yep, I drilled and tapped my Holley wedge for a vacuum line connection, still no luck correcting the mixture issues. I believe one of the metering blocks had a blockage of some sort, or I had a leak in the power valve circuit. Didn't have to deal with either in the Edelbrock.

[98Roo]

Oh that sucks, sounds like you certainly had some other issue with the carb. I'll have to remember that if I ever decide to replace my carb. Seems like if the Holley didn't need it then neither would the edelbrock but apparently not. I guess it'd run fine on the trailer but rich in the water?