Not running yet

[Uncle Grumpy]

I swapped the Holley marine carb the PO put on for the original rebuilt carb. I started with the idle mixture screw 1.5 turns out. I'm at 6.5 turns and
and that seems pretty far out. Is is this normal? I haven't touched the high idle yet and don't think I need to until I have a low idle. It starts and runs but I have to give it some throttle and keep the rpms up. It dies if I lift the throttle. This is a de-smogged '78 Cali Spec.

Has anyone installed a carb from scratch recently? Do you remember how far you had to back out the idle mixture screw?

 

[charliemeyer007]

Not a Holly guy but 6.5 turns seems like a lot to me for any carb. Not clear - you are now running a OEM carb carb - there should be "stock settings" listed somewhere.

When I see "needs rpms to run" I think vacuum leaks - spray some starting fluid/WD-40 on the intake manifold and carb gasket. Long ago a friend "rebuilt" his jeep carb. Same issue. I found the leak between levels in the carb - he had a gasket backwards and it wouldn't seal ( a vent pipe or something was hanging up. We put it back together correctly and every went normal.

 

[CondeCruiser]

 

[Uncle Grumpy]

Thanks @charliemeyer007 and @CondeCruiser for the replies. I watched the OTRAMM video again before some more tinkering. I reset the idle mixture screw to 3 turns and the idle speed to 1.5 turns (FSM). I previously started at half turns thinking I would get it running and then dial it in. It's actually much finer increments to adjust. I capped all ports except the TP and I used one of the insulator ports for a vacuum gauge. I used a timing light tach for rpm. Without much effort I got it running at 1200 rpm with 15 in Hg. Quick acceleration pulled 20 in Hg. It would run about 1.5 - 2 min at a steady 1100 -1200 rpm and then started to fall off and the motor would die (unless I gave it a little gas.

I used the brief running time to spray the carb with a soapy mixture. I couldn't find anything that looked like a leak and I check from the top of the air horn to the bottom of the insulator plate.

On a whim I covered the air horn as the rpm dropped. It roared back to 1200 rpm. I recall reading in the FSM that the choke should be set to 38 degrees. Mine is straight up and down. The 2F engine FSM I have doesn't cover the Cali Spec carb. I'll poke around and see what I can find to dial in the choke angle.

Thanks for your help,
Michael

 

[middlecalf]

It should stumble/die when you cover the air horn, and you will have fuel on whatever you used to cover it (never a hand). Your situation points to a serious vacuum leak and/or your carb is way out of spec.

 

[Uncle Grumpy]

I should have been more clear, the air horn was only partially covered. I'll have to verify completely covering kills it.

 

[Uncle Grumpy]

After the starting fluid test I have a vacuum leak at the carb base/insulator. These were clean surfaces with new gaskets when installed. Is there a torque spec? I haven't found one.

 

[charliemeyer007]

Good work, soapy water is great for detecting pressure leaks where you can see the bubbles. Clean surfaces are important and they need to be flat too. You can use some sort of gasket compound to help form a seal. If its a any type of fiber gasket, soaking it in warm water for say 1/2 hour will soften them and allow the high spots to dig in so the low spot can seal (old aviation trick from my dad). Sand paper on a pane of glass makes a nice flattening surface, so areas around holes/studs that have been pulled out can be planed off flat, also from dad.

Carb bolts/studs are small, I just choke up on the wrench so I don't strip/brake them off. Anti-seize compound or low strength loctite are my go to items. I think Chilton's has a general torque setting by size when not specified for example head or manifold fasteners.