Quadrajet Adjustment

[ChillrMn1]

Hi Woodboat,
Thanks for the input on the 10" pitch. After reading you post, the 11" is probably most appropriate. This is a Pacemaker with semi-hull and seems to propel pretty decently at this RPM, considering the boat itself. Don't want to be less efficient and run higher RPM for same speed considering how my boat is used. Did purchase Doug Roe's book, lot's of Q-Jet info, light on marine specific applications. Will rebuild original 17082403 carb myself and see if I can't do a better job than rebuilder in cleaning out all passageways. Would really like to know which secondary rods was specified in this unit for a Crusader 350 CID. This engine is probably very close to mine. Parts books list same carb I.D. number for both 350 & 454 engines. Don't know which Crusader (350 or 454) this carb was purchased for since this came with boat. One wants to assume the other bought it for the right engine, but you know how assumptions go........... And it's entirely possible the 2 carbs are identical in every way. Would Rochester have built 2 carbs with same I.D. number but with different internals (metering rods, PP Spring, etc.)? Unable to find info this specific.

Have A Good Day!

Bob

If you decide to rebuild the carb. Vacum clean the work benchfor a distance of 5' all around. put down a clean piece of WHITE paper from a supermarket meat room, 6' OK. Wash the tools in a solvent, dry, coat with a thin coat of oil. Have a roll of tape to remove any metal fillings sticking to a tool tip. Read the 1 st take apart set of steps. try to take apart 1 or 2 items and immediatly replace them with new. If you need to stop, mark the last complete step done. My age will now show. If you can not easyly remove a jet, Don't butcher it. Take it to a rebuilder with the instructions. Special tools are sometimes used in the assy. and disassy. He can only refuse. Most will smile, warn you what your into, help you, and give you their bussines card. As far as setting up a car or boat carb for max power. the logic of the book will cover all your questions. Foot to the floor is the same in a car or a boat. Roe's procedure is right. clean-clean-clean!!! Cloth or paper lint strands- barely visable- can get into the metered tunnels and ruin you best efforts. Don't be surprised if it does not run better. This is your first attempt. Pro's turn out duds.-- Compessed air - need a cotton or fuel filter, metal type, to stop grit from your tank, line. Also a pressure regulator set to about 10# max. Good luck, Rich

[gonzo]

Yes, it is true that the camshaft will affect the octane you need. If you don't advance the timing with higher octane, because it burns slower it overheats. It will act like any engine with a retarded ingnition, the fuel will still be burning when the piston is at the bottom. This causes a lot of the energy to become heat instead of force pushing the piston.

[ChillrMn1]

Rebuilt the 174082403 carb. Found main problem was fuel well under secondary jets completely restricted. This took considerable time and patience to clean out by repeated soakings, running a fine wire thru, and flushing with an eye dropper. (This is where the "Professional Carb Rebuilder" failed when I first bought the boat. As soon as the secondary throttle plates and air valve would open, complete bog. Paid $150.00 for this. Gave up on this carb at the time and purchased a generic remanufactured carb off internet, another mistake. Lesson learned).

The engine has never ran so good, since I purchased boat, from idle thru all ranges to WOT. Can't honestly tell if fuel consumption has improved due to the short test run. Flowscan appears to be lower, but could be wishful thinking. Will be able to tell next time out swordfishing.

A tip for first time Q-Jet rebuilders: Upon reassembly of the air horn assembly to the throttle body, lightly snug down with 2 screws. Check the power piston "PP" for free operation. Insert appropriate tool (I used a very small screw driver) thru forward vent stack and lightly press PP down. PP should return back under spring pressure. Mine would not. Found the "retaining spring" for the primary rods to the hanger assembly was interfering with a guide for the PP in the air horn assembly. Take air horn back off and carefully reposition this spring on the hanger. This should now clear the guide of the air horn when you reassemble. Check again. This is very important, Doug Roe in his book states "If the piston sticks down, primary system won't function. If piston sticks up, gas mileage will drop as much as 50%."

I would like to thank everybody for their input, advice, and technical information provided.

Bob

[woodboat]

Anyone got a line on secondary rods and PP springs. I found out why my one engine is such a dog, wrong rods. I need a pair of AV rods with an L hanger.

[ChillrMn1]

Hi Woodboat,
Couldn't find exactly what you're looking for, but try these: http://www.jegs.com/cgi-bin/ncommerc...20&prmenbr=361 and this: http://store.summitracing.com/defaul...239+4294925135 (under edelbrock Q-Jet) . Maybe you can choose a combination that will satisfy your needs. Summit also offers a kit for four different PP springs which cut-in/cut-out at different manifold vacuums.

Bob

[woodboat]

Thanks. I had already called Summit and they were no help. However JEGS helped me out. I needed an AV rod and an L hanger. They didn't have them but had an Ay rod and a K hanger. That has got to be closer than what I had. I also ordered the PP spring assortment.

[crazed chicken]

I have twin 1988 Crusader 270s with 900hrs and Qjets. The engines appear to run great however at the dock idling I notice a gas sheen in the cooling water from both engines. No water in engine oil. The current consensus is the engines are idling rich and the idle mixture screw needs adjustment. Any ideas?

[woodboat]

try adjusting them per specs. Any good manual will give the procedure.

[gonzo]

Are the points, condenser and plugs in good shape?

[ChillrMn1]

The procedure I use knowing all else is OK as mentioned previously "points, plugs, no missing, proper ignition timing, etc.,": Connect vacuum gauge to a port reading true manifold vacuum (not a timed vacuum port), adjust idle speed screw to idle speed RPM per engine specifications, turn idle mixture screws (both & usually clockwise) to know you're running lean, slowly back each screw out until you reach lowest vacuum reading attainable and stop. Gauge needle should not fluctuate more than 1/2 to 1 inch, you may have to adjust each a little at a time, then turn each mixture screw 1/8 - 1/4 turn lean. Keep adjusting your idle speed screw as necessary to maintain specified idle speed RPM. If it's a relatively stock engine, a good steady vacuum at idle speed would be 15 - 19 inches, give or take. Once you start to play with it, you'll get the feel for it.

If you can't get a response by adjusting idle mixture screws at specified idle speed RPM, then you may have a stuck power piston, manifold leak, throttle valve shaft bushings may be worn, leaking fuel well plugs if they haven't already been epoxied, etc.

[crazed chicken]

The plugs, wires, cap and rotor were replaced last summer. It has factory electronic spark. The engines are 100% stock. Revving one of the engines produces slight black smoke and gas odor from exhaust.

[woodboat]

Of course black smoke is bad. That means it is way too rich. If you rebuild the carbs make sure you know everything there is to know about qjets as they are quite complicated.

[crazed chicken]

The black smoke was slight and not continuous. At what point do I decide to rebuild?

[woodboat]

One of my carbs was very rich. It would leave the plugs black, did not make full RPM and burned more fuel. I just redid the power valve spring and metering rods to make it leaner. I did NOT rebuild it as it was functioning correctly but was not set up correctly for efficiency and power. With that said it NEVER was so rich as to puff smoke so I would have been inside the carb way before now.