July 15, 2017 at 3:00 pm #16983
On a fishing trip my 470 started and ran perfect 3 days in a row…4th day would not start. Fire, fuel, timing, good, compression a little down when checked cold a little oil in cylinders brings it up. With starting fluid it will try a little, occasional backfire. What can I check next ???July 15, 2017 at 8:42 pm #16984
If you have points, check to see if there is spark with the ignition turned to run and not start. Only if you have points-—remove the dist cap and rotate the engine so the points are closed. pull the coil wire from the cap and hold it close to the engine or anything that is grounded to negative. Turn the ignition to run and open and close the points with a non conductive object, a plastic pen or Popsicle stick. There should be a good spark between the coil wire and engine block. By doing this you are simulating the engine running. The whole point of all this is because there is a bypass in the start circuit that bypasses the resistor wire in the run circuit to give the coil full battery voltage for starting, when you let go of the key the ignition reverts back to the run circuit with the built in resistor. So you might get the engine to fire while trying to start it but as soon as the key is let go the ignition –or lack of same–will not let the engine run.July 15, 2017 at 9:41 pm #16985
Thanks for the quick reply stractor and thanks to all the guys here for helping keep my old merc running good the last few years.
Actually I have Pertronix 2 and flamethrower coil. Plugs (replaced) and wires throwing good spark. Cleaned all grounds and ohmed pertronix mounting plate for good ground as I know they are sensitive. Checked fuel separator for contamination, disconnected fuel line, turned engine, pump is working good, accelerator pump is squirting good fuel. Checked for jumped timing, seems good. Compression is lower than I expected at barely 90 pds avg. cold. A little oil in cylinders and 180+ hopefully that rules out head gasket. Not sure of min. comp to run. Started ran perfect one day natta the next. No over heat (170 max) and oil pressure good. Any and all ideas appreciated. ThanksJuly 16, 2017 at 4:42 am #16986
Might be compression? pull the plugs oil the cylinders and turn the engine a bit to spread the oil, put the plugs back and see what happens. This is one of those problems that is hard to troubleshoot without being there.July 16, 2017 at 4:51 am #16987
Check the engine vacuum if you can find a place to connect the hose to the vacuum gauge. I would do this cold with no oil in the cylindersJuly 18, 2017 at 2:36 pm #16988
Remove the dist cap and rotate engine by hand until the rotor points to where #1 would be if the cap was on. timing marks on front balancer and scale should line up. Just to rule out cam timing due to worn chain/tensioner.July 19, 2017 at 1:24 am #16989
Thanks guys..timing seems good. Today I picked up a leak down tester. Starting to lean towards valves/ head issues. Put a little oil in cylinders to check comp then plugs back in. While spinning it was huffing the oil out the carb.
If it is head issues what do you think about replacing with an aluminum head and going ahead and doing the 4 barrel conversion as I have everything. That is if cylinders look good.July 19, 2017 at 2:49 am #16990
The aluminum head is a nice idea but very expensive $700+ . If you were doing a complete rebuild it might be worthwhile and you intended to keep the boat some time. The 4bbl swap is fun if you can keep your hands off the throttle, sounds great wide open but you can watch the gas gauge go down. Also you really need one of the two original part number Rochester Quadrajet carbs. The carb made for the 470 is a special, with smaller air bleeds and some strange drop in plastic parts. Don’t forget the carb is mounted sideways to normal 4bbl orientation. There were only a finite number of the 4bbl carbs for the 470 made. There are two different serial numbers for the 4bbl. The carbs advertised to fit on the 470 by most of the rebuilders are not original and are made from parts and epoxy and for the most part are to rich for the 470, I know I had one before I wised up. The 470 4bbl secondary air flap (which limits the air flow to the secondary throttle plates) is limited to about 55-60 percent opening, compare that to a chevy marine V8 carbs 85%. I have the 4bbl conversion and at one time had 3 of the original 470 4bbl carbs that I rebuilt .July 22, 2017 at 1:54 am #16999
Up date on the 470…today after doing leakdown test that showed major valve leakage and no head gasket issues I pulled the head. Looks like salt water intrusion caused at least 3 exhaust valve to stick and bend #1 2 3 pushrods. Top side of heads looks new, exhaust port/valve (all 4) area very rusty. Head gasket looks very good no obvious leaks. Not sure if it is a manifold/riser leak or cracked head. I have the early log style manifold. By the way I sure miss all the old posts and good information there (gold).
July 23, 2017 at 8:02 pm #17001
- This reply was modified 6 days, 12 hours ago by kzbryant.
Yes, it would be nice if the archives would come back….good luck
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