qjet secondary plates (hole vs sealed)

[robjen1019]

Ok, went out and got another carb for my volvo 225, which is a 305 gm block. My original carb has 3/8 holes in each of the secondary plates. The other one doesn't have these holes. Does anyone know the reason for these holes? I tried to swap them, and they are just a little different so they don't swap. Wondering if I should drill holes to match on newer carb?

Thanks

 

[jtybt]

Re: qjet secondary plates (hole vs sealed)

I don't understand the reasoning for the holes but the secondaries should have the correct hangars/needles without the need for more air.

 

[robjen1019]

Re: qjet secondary plates (hole vs sealed)

I was doing a little reading on some muscle car forums, and some modders cut transition holes on the back side of the plates to ease the transition from the primaries to the secondary. Im guessing this is what is going on. I am now wondering if the Mercruisiers have the same holes?

 

[jtybt]

Re: qjet secondary plates (hole vs sealed)

...which suggests you didn't have a marine carb.

DO NOT try to copy what a hot rodder, that doesn't know how to adjust a carb, did to make his engine run right., The Q-jet is a 750 CFM carb which is more carb than you'll ever need.

The other BIG danger is running lean. The 305 will never need the secondary upper plates to open all the way.

 

[robjen1019]

Re: qjet secondary plates (hole vs sealed)

99.9 percent sure that it is the original carb for the motor. The paint is an exact match for the motor. the holes look to be factory punched and not drilled. The mods from the other sights showed how to cut out a portion of the blade from the tip. I couldn't find any that drilled holes. Oh well. I'm just going to leave things alone and keep the blades on the respective carbs. I was just wondering more of the why. Ive ran both carbs on the same engine and I can't tell a difference between the two other than the idle circuit on one is a little bit leaner than the other.

 

[45Auto]

Re: qjet secondary plates (hole vs sealed)

Ok, went out and got another carb for my volvo 225,

Ive ran both carbs on the same engine and I can't tell a difference between the two other than the idle circuit on one is a little bit leaner than the other.

Hopefully you didn't buy a new carb because the idle mixture was a little lean. You do know that there are adjustment screws for that?

 

[John_S]

Re: qjet secondary plates (hole vs sealed)

Can you post pictures? I am interested in seeing what you are talking about.

 

[Greg Gessler]

Re: qjet secondary plates (hole vs sealed)

I think the holes you are refering to are in the secondary air valve flaps. The holes or notches (if used) are located above the secondary enrichment orifice (like a secondary accelerator pump) to allow the fuel to start drawing alittle sooner. I would try carb the way it is and not drill any holes in sec. air valves.

 

[dan t.]

Re: qjet secondary plates (hole vs sealed)

some marine q-jets have holes in the secondary air flaps, i dont quite understand the reasoning,but,dont fiddle with them , the carb is calibrated to have them. it seems that the ones with the holes have a tighter air valve setting than the ones without