tuning carb????

(seansmitty42) · (seansmitty42) **Join Date: Apr 2006** 04-20-2007, 10:42 AM

so my friend just bought a hydrodyne with the mercruiser 350 in it. well he bought it from nick tomsyck on this site and it was in wisconsin. it ran fine when we test drove it there and when we got it here we were cruisin and noticed when u go full throttle it bogs and kind of lunges ??? i dont know if the carb needs to be adjusted for altitude or what any help would be great

(jzd) · (jzd) **Join Date: Jul 2005** 04-20-2007, 12:06 PM

Sounds more like a secondary ignition problem than a fuel problem.

(seansmitty42) · (seansmitty42) **Join Date: Apr 2006** 04-20-2007, 12:19 PM

it almost feels like its running out of gas

(peter_c) · (peter_c) **Join Date: Sep 2001** 04-20-2007, 12:21 PM

What elevation are you at? If you ease into the throttle what happens? Once at wide open throttle, how does it run?

(boarditup) · (boarditup) **Join Date: Jan 2004** 04-20-2007, 12:27 PM

On the Merc, there are a couple of small issues that can cause that problem -most easy:

Fuel filter on the carb.
Carb accelerator pump with bad seal
Float needs replacement
Dirty or corroded contacts in distributer cap

The first and last is a 10-minute job. The middle two are a minor carb rebuild that takes a couple of hours.

(seansmitty42) · (seansmitty42) **Join Date: Apr 2006** 04-20-2007, 12:58 PM

when u ease into it it runs fine until completely wide open but its does the same thing even if u floor it

(olskooltige) · (olskooltige) **Join Date: Mar 2007** 04-20-2007, 2:32 PM

What model carb? Holley? Download a manual and reset it back to original settings. Then make minimal adjustments.

(99_slaunch) · (99_slaunch) **Join Date: Oct 2005** 04-20-2007, 5:35 PM

Check #1 spark plug and you should be able to tell if it's running lean or rich.

(tuffenuff) · (tuffenuff) **Join Date: Aug 2006** 04-20-2007, 6:24 PM

Also check timing and distributor advance. If it is over-advanced, you will sputter and spit because your spark timing is off. Just my 2 cents.

(seansmitty42) · (seansmitty42) **Join Date: Apr 2006** 04-21-2007, 8:19 AM

its a quadrajet carb thanks for all the help

(peter_c) · (peter_c) **Join Date: Sep 2001** 04-21-2007, 9:06 AM

DO NOT rebuild it yourself. Find someone that knows what they are doing. The q-jet is one of the best carbs out there for run ability, but not the easiest to rebuild as they are a few tricks. The shaft may also need to be bored, and sleeved.

You never did answer the questions I asked. Also how does it run at idle and cruising at 2600 RPM or so? Can you better describe lunging?

Take a propane torch with a long hose hooked to it, and when it starts acting up, have someone else induce a little propane. If it cleans up it is lean. There are tons of other tests to run, but first we need to know which direction to go.

(rallyart) · (rallyart) **Join Date: Nov 2006** 04-21-2007, 10:53 PM

Listen to Peter

(seansmitty42) · (seansmitty42) **Join Date: Apr 2006** 04-23-2007, 9:47 AM

ok im not for sure on the tach but i know at about half to 3/4 throttle its runns smoothly. and by lunging it doesnt cut out but rather looses rpm dramatically and quickly then comes back up for a second then looses them again. but this happens after about 5 seconds of being full throttle. so what im saying is, is when you push the throttle lever down it picks up rpm for about 3-5 seconds then starts bogging down and then kicks back up and repeat