Indmar 351W 3000RPM max?

[1000dollabill]

I need help before I send this boat to the bottom of the lake.

1989 Ski Centurion Falcon 20
5.8L Indmar

Brand New:
Holley 80319-1 carb
coil
plugs
wires
distributor
f/w separator
fuel filter on pump

Checked:
135 psi compression on all cylinders
fuel pick-up clean
tank vent clean
all inline filters/screens clean
no fuel in fuel pump rupture line.
pulled anti siphon very difficult to blow through. Attempted to clean with an awl, very easy to blow through now.
all connections clean, all grounds good.
pulled fuel pump no wear or wobble present.
Prop in new condition
firing order checked 35 times
all plugs a nice tan color
no water in oil


had prestolite electronic conversion but put points, condenser, and ballast resistor back in. Points set to .018, plugs set at .035 (autolite 24's), timing set to 10 btdc at 600 rpms.

Idles great, runs great up to around 2900. anything above hesitates and backfires through carb. Will not rev over 3000 under load. original coil would not let it rev over 2500rpms. engine temp is consistent at 160.

the weird part is last outing putting around the lake for about an hour the backfire started occurring at around 2500 rpms under acceleration. maybe an overheated ignition module or coil. Also after putting the points back in there is a noticable popping in the exhaust at 3,000 rpms and above while out of the water running on the hose and bucket.

my best guess now is the fuel pump because it will rev to the moon without load. can a mechanical pump become weak? all gas is new 92 octane (four tanks run through it below 3000 rpms.) could my popping in the exhaust be the dwell incorrect?

Please help me,
Bill

 

[whywhyzed]

Re: Indmar 351W 3000RPM max?

Brand New:
Holley 80319-1 carb

Start with checking the setup and tuning that was done when the new carb went on and check all linkage - especially throttle linkage, check choke operation and such - and check for vacuum leaks around carb base and so forth - proper carb base gasket?

Popping out the exhaust sounds like firing order issue, or something with timing or advance mechanism. Never heard of a fuel pump or fuel delivery issue causing backfiring with no load.

What was wrong with the old distributor?

You know #1 cylinder on a Ford is different than Chevy?

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

Have already checked for vacuum leaks, linkages are working properly. Choke opens fully.

New distributor because timing was erratic. Would change throughout the day.

Firing order is correct with cylinders as shown

4 8
3 7
2 6
1 5
front of motor

not sure the firing order right now but it is on the valve cover and I have double checked it through research.

is .018 correct for the points gap? I do not have a dwell meter.

Popping in the exhaust without load started when the new distributor with points and condenser was installed. it's a very subtle popping not a genuine full out backfire. not noticeable in the water.

suggestions?

this thing is driving me nuts.

Bill

 

[87 bayliner]

Re: Indmar 351W 3000RPM max?

dont worry about firing order. if you had that wrong it would miss continiually. try pulling your timing back to zero and see if there is an improvement. remember, total advance is important. you should have no more than around 37 degrees of total advance.(the mechanical advance weights in the distributor control this.) lets say with dist set to 10 degrees btdc and the mechanical weights kick in and you can end up with a total advance over 40 degrees. (not good). this can cause the carb back fire.
also does your carb have the power valve protection feature ? carb back fire can rupture the power valve membrane and you'll have uncontrolled fuel entering the carb thru the ruptured valve.(although i dont think this is your prob bcuz a ruptured power valve will not affect high speed operation as the excess fuel will be consumed.) at idle a busted power valve will cause an overly rich mixture. check the fuel pump, pressure should be 4- 7 psi. try an inline fuel pressure tester so you can see if pressure drops as you reach the upper rpms.
over all from what you have described im leaning to a fuel delivery issue.

good luck

j

oh yeah what about the air cleaner ? is it plugged ?

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

Yes I do believe my carb has a power valve check ball. Holley states that any carb built by them after 92 has it. My carb is brand spanking new. I replaced it believing it may be the problem but also because it had an automotive carb on it when I bought it. All of the settings, jets, etc. were not calibrated for this motor.

the air cleaner is spotless. Used a whole can of carb cleaner on it.

I pulled the fuel pump again today. I was going to rig an automotive pump on it to test but weather didn't hold out and safety became an issue. But after comparing the new automotive to my current fuel pump I am beginning to wonder. The new pump is much more difficult to operate by hand, also there is very little play in the arm before the diaphram begins to move. The old pump is fairly easy to operate by hand, and nearly a third of the stroke does nothing at all. I am leaning toward a worn out pump right now. But I need to order the correct MARINE pump because my better judgment says rigging this $20 automotive pump on it will be a mistake.

I also rechecked my antisiphon and fuel lines from the tank to the pump. I can blow through the system fairly easily. It also holds pressure so I do not believe it has any leaks. currently the pump is off and I'm leaning towards just ordering a new pump. I know I should do a fuel pressure test however between buying the gauge and all the fittings to put it in the system it's about half the price of a new pump.

Also after changing out the carb, I gained a few hundred RPM's. I am thinking this is because the old carb had larger jets and was using my limited amount of fuel inefficiently.

One of these days this boat will run right. Anybody think I am on the right track?

Any other suggestions?

Thanks,
Bill

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

alright, I've got the new pump, just need to install it for the weekend. Quick question. I've checked for exhaust blockages, however, I have not split the risers from the manifolds. Is this something I should do?

would an exhaust blockage cause an intake backfire?

Again it races up to around 3000 under load holds steady for a minute, then "lobes" for less than a minute, then backfires through the carb. After the first backfire I always let off, mumble obscenities, and get back on my merry way at less than 3000 rpms.

Any help would be greatly appreciated.

Bill

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

How is it that 68 people have read this topic but only two replies? I've done everything suggested so far. I'm going to do Don S's fuel delivery test this weekend. I've been battling this issue for too long.

Suggestions / Experiences?

Thanks,
Bill

 

[Haut Medoc]

Re: Indmar 351W 3000RPM max?

Backfire through the carb is either a lean carb condition or a bad intake valve.......
You can pull your risers & see if a flap is broken off causing a restriction, but it won't cause backfire through the carb.....
Has a compression test been done?.....
Zero compression would indicate a tuliped valve & would fit your scenario.......
I also reccomend performing Don S tests to see if you are running lean.....
Whoops! I missed the 135 on all cylinders......
Something is causing you to run lean, imho.....
How did it run before all of the new stuff?....
Is the order 1-3-7-2-6-5-4-8?.....​

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

It ran the exact same way only I was limited to 2600-2700 RPMS.

I have not run it with the new fuel pump installed. I'm going to try to rule out the fuel system this weekend with dons test as well as a fuel pressure test.

This motor sounds and feels very healthy both at idle and just below where it backfires.

So if the riser is leaking it would not create the intake backfire?

Thanks all,

Bill

 

[mkast]

Re: Indmar 351W 3000RPM max?

Did you check the float setting?
If the float is set too low, engine will backfire through the carb, can't reach WOT.
(Yeah, new carb and all)

 

[1000dollabill]

Re: Indmar 351W 3000RPM max?

yup, checked the floats, needles, and seats in both the new and old carb. According to Holley they should be level across the bowl.

It seems like as soon as the secondaries come on, you hear it sucking loads of air and then *bang*, like the secondaries just ate up the whole fuel supply.

I'm hoping the new pump fixes it.

With all these new parts hopefully I can get a couple years of trouble free service. Then again, it is a B.O.A.T..

Any other ideas before I run it this weekend?

Thanks,
Bill

 

[blingin96]

Re: Indmar 351W 3000RPM max?

I had the same problem with my 1987 ski Centurion trutrack... It was indeed the power valve in the carburator.. It took me about a month to figure it out.. I had the SAME symtoms you have.. I changed it and it started and idled no problem.

It was back fireing through the carb
I could not get it to idle.
I got it to run but over 2500 rpm, nothing under that ... It would just die OR backfire through the carb.

 

[farmboy]

Re: Indmar 351W 3000RPM max?

Is fuel getting to the secondaries and are the new plug wires routed properly?