1990 Volvo AQ271C/GM 350 carburetor jetting (stock jet size?)

[Greg68S]

Hey there everyone. I have completed my 1990 Carver 2357 Montego resto project. Now I am looking into why my fuel consumption is so great. It's far to much for a single sbc. My current jets in my Holley 715 cfm dual feed four barrel are as follows. Primary jetting is at 72 and secondary jetting is at 80. Anyone with any ideas as to what should be in there? I'm running richer than I used too and I'm looking for more of a starting point. Thanks guys -Greg

 

[Scott Danforth]

carb 80309 - secondary from factory is one 80, one 90 (originally for an off idle stumble), primaries are 72 with a 2.5 power valve

with my vortec heads, vortec intake and hotter cam, I am currently running 95's for secondaries. I am running 74's for primary

if your running rich, back off on the primaries a bit. I would also replace the power valve - a leaking power valve will make it run ritch. our carbs were before the back-fire blow out prevention check valve, so if you had a lean sneeze, it could have ruptured the power valve.

another note, while some of the documentation calls the carb a 715CFM, most of the stuff I found also calls it a 615CFM

 

[bruceb58]

You using the stock cam? I assume you are close to sea level right?

Float level correct? Mechanical fuel pump? If electric fuel pump, what is your pressure?

Have you done any plug reads? I would run with only primarys open...do a plug read. Once you get them jetted right, run with secondaries open and then do another plug read. Make sure you don't do any idling when you come off plane to do this or you will not get a good reading.

 

[Greg68S]

Going to do a plug read on Friday evening. Stock cam. Carb just had a complete rebuild. Power valve included. Very close to sea level. Approx 410' above. The carb had 70's for primaries. But I replaced them with 72's. I run mostly on my primaries. Is there a way to find out what was put in the carb originally?

 

[Maclin]

If the list# on the airhorn is 80309 then Scott's post has the correct info.

pri=72
Sec= staggered 80 and 90
power valve = 2.5

If your powervalve is much above 4.5 then it may be staying open when cruising, unnecessarily richening the primary mix.

You also may need to change the spring in the vacuum pod that actuates the secondaries.

Make sure your flame arrestor is clean. Restricted airflow can cause the secondaries to actuate sooner, also another reason a different spring may be needed.

 

[Greg68S]

Ok let me go back just a bit because we are now making sense. The original carb that came off of my boat I had rebuilt. It's list number was 80309. I bought another carb from a friend that was the same carb but had a different list number. This is the carb I am using. Initially I thought I carb issues hence the two carbs. I do not have the list of the other carb on me but I will this weekend. I am currently jetted as follows. 72 in the primary's and 80 in the secondaries. If my power valve is anything over 2.5 that could be where my fuel is going. Am I on the correct track?

 

[Scott Danforth]

you are correct, too large a power valve and it will suck fuel and run rich. So would a bad power valve.

what are you pulling for vacuum? at idle? under load? who did the rebuild? some of the small jets require fishing a fine copper wire in them to clean out the goo.

I have also tried a 3.5 power valve, however went back to the 2.5 (didnt see the transition improvement I was looking for) and upped my primary jet size.

 

[Scott Danforth]

on a similar topic, when you do your high speed plug reads, I usually just kill the ignition and then toss the anchor over the side. drink a beer and wait about 10 minutes for the plug to cool a bit. its not a reading thing, its a I hate burning my fingers thing

if your changing jets on the water dont do it in rough water - you may drop a jet in the bilge, then in haste to grab it spill your whole tuning kit (jets, power valves, secondary springs, tools, etc) :facepalm:

 

[Greg68S]

Power valve was a 6.5! OUCH!!!

 

[Greg68S]

Burning much less fuel now. The plugs are still a little dark though. I'm wondering if I re-jet and drop to 70's in the primary's instead of 72's. Thoughts?

 

[Scott Danforth]

cant hurt to try it. I use the teflon gaskets to allow rejetting. still makes a mess trying to catch the fuel, however only takes about 10 minutes to rejet.

I dont idle much, most of my boating is at about 2000 RPM, just on plane about 19-20 MPH (its about 13 miles to the ICW from the boat ramp) I tuned mine for the updated cam and how I use the boat.

 

[Greg68S]

We spend a lot of time at idle. Mostly because we travel the Erie Canal and rivers in between our home port on Cayuga lake and where ever our destination is. Canal speed range from 10mph or no wake. But if we are just on on the lake it's usual a little fuel burning party for about ten minutes. Or as long as it takes to make grinn. Then it's back down to about 20-23 mph and on plane.

 

[Scott Danforth]

with most of your time at idle in the no wake zones, I would try 68's or 70's

FYI - attempting to outrun a storm and traveling 55 miles at WOT in my boat was more than 25 gallons of fuel. I do not recommend it when attempting to save fuel.

 

[Greg68S]

Hey jetting question. I'm set up as follows. Primaries 72 Secondaries 80. By the looks of my plugs I can afford to drop a little. I'm thinking Primaries 70 and Secondaries 76. What do you think?

 

[Scott Danforth]

drop the primaries only, 90% of the time your running on primaries. drop down to 68, check, then adjust from there.

 

[Maclin]

I agree with Scott, change the primary side only.

 

[Greg68S]

69 was the magic number. I'm trying to post a picture

 

[Greg68S]

No Title

 

[Bondo]

Ayuh,.... I think that plug looks Lean at the verge of detonation,....

 

[Greg68S]

Hmmm....I could easily jump to a 70 in the primaries. It's more tan than it seems in the picture. I was considering jumping to a 70 anyways to be safe. I have to pull the carb off to change the secondaries anyways. My plan is to drop to 78's from 80's on the secondaries and see were I am at. Thoughts?