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cptskier15
07-21-2010, 03:19 AM
Hi all,

I have a 81 S&S with a ford 351w, with a edelbrock performance intake manifold and a marine holley carburettor 450cfm. Timing is set at 10 degrees.

I am having issues with the engine bogging down under acceleration and am finding that it is under power.

If you have any suggestions on how you would tune the engine and carb, please let me know.

Thanks

1redTA
07-21-2010, 07:42 AM
I have a 600cfm on my 351 with the stock manifold and an ignitorII ignition. Are you running points still? that carb seems small

thatsmrmastercraft
07-21-2010, 09:35 AM
Welcome to Team Talk.

A little more history would be helpful. Did you just install this new intake manifold and carb and are having a hard time getting it set up properly? As with all performance problems, I always start with the basics. Have yo verified that the firing order is correct? Crossed plug wires have done that to me before. As 1redTA suggested, points or electronic ignition - if your points are bad it will do this. The condition of your spark plugs, distributor cap and rotor too.

DBBOOM
07-21-2010, 09:47 AM
Have you verified that the advance is working in the distributor?

thatsmrmastercraft
07-21-2010, 09:52 AM
Also if your engine backfired through the carb (and your carburetor is old enough) it would blow your power valve and cause the same symptom.

cptskier15
07-22-2010, 05:41 AM
It has electronic ignition and the advance is working as it advances when reved to about 30 from 10. The carb is about 3 years old. It did not have this big of a problem with old manifold, but that had to be replaced due to a hole appearing where the exhaust pre heater comes into the intake manifold. The firing order is correct as had plug wires marked. plugs are a year old, not much running though. I emailed holley and they said that the 450 should be fine at low rpm and that would only be a problem at top end, at the moment struggling to pull skiers out the water.

At the moment boat is on trailer and starts easily gets up to temp fine and without any load runs throught the revs fine, but take it to the lake and it struggles under load. we have verified that the secondaries are opening and that they are sucking fuel in.

Feels like a fuel starvation problem but not sure how to correct it as making the mixture richer with idle screws has not helped.

Another issue is that when we get it to temp and turn it off the starter motor finds it really hard if at all possible to crank the motor. Not sure if the two symptoms are related but thought should let you know.

thatsmrmastercraft
07-22-2010, 09:38 AM
Have you checked for vacuum leaks? I always use a can of carb cleaner and spray around the base of the carb and around the intake gasket. Be careful doing this as there is some fire hazard spraying solvent around a running engine.

cptskier15
11-12-2010, 09:26 AM
I am going to check for leaks next weekend. I am currently replacing the cover for the boat as the old one has become a sive and the respray I did last season has been destroyed and there looks to be a lot of corrosion on the carb so will have to check all this before fine tuning again.. Dam winter breaks..

Gamble
11-12-2010, 10:29 AM
for the hard starting, that sounds like heat soak, but it should still crank. I would check the ground and the condition of both your battery cables, paying close attention where the ground cable attaches to the block. My guess is that is where the problem would be. I used to own a S/S and I replaced both cables and it fixed the same problem you're experiencing on cranking after it warms up.

cptskier15
12-10-2010, 10:34 AM
I had had enough with the bogging problem and was certain it was the carb. So I took the entire thing apart this afternoon. I cleared all the internal passages with a can of carb cleaner. I put it all back together. Started up first time and the secondaires opened under acceleration on the trailer! Have not taken it to the lake yet but this is a great start as Thad never done this before! Any way, will keep updated when we take it to the lake

thatsmrmastercraft
12-10-2010, 10:39 AM
Nothing like a gunked up carb to give you running problems. As you seem capable of the job, I would plan on rebuilding the carb sometime in the near future. Make sure that you soak the disassembled carb in cleaner (preferably with an agitator) to make sure you get it thoroughly clean.

Great to hear you are making progress. keep up the good work.

rjracin240
12-10-2010, 03:08 PM
[QUOTE=thatsmrmastercraft;721130]. Make sure that you soak the disassembled carb in cleaner (preferably with an agitator) to make sure you get it thoroughly clean.

Think they only have crocodiles in Africa and no agitators :uglyhamme

thatsmrmastercraft
12-10-2010, 03:17 PM
[QUOTE=thatsmrmastercraft;721130]. Make sure that you soak the disassembled carb in cleaner (preferably with an agitator) to make sure you get it thoroughly clean.

Think they only have crocodiles in Africa and no agitators :uglyhamme

I think the "cold" must be getting to you. That was a real stretch. :D

wheelerd
12-14-2010, 02:21 AM
Don't forget to check all fuel filters (in carb, by the fuel pump, in the tank), water/fuel separator if you have one, and pressure from the fuel pump. These all can cause fuel starvation on hard acceleration.

ctjahn
12-14-2010, 10:35 AM
I agree with Wheelerd....

On more than one occasion I have had similiar issues with clogged fuel pumps/filters... (not on a boat but...in a number of cars) Idle is ok, but as soon as it needs more gas it starves... One can assume there may be a plethora of crud in the lines and/or in the tank and/or in the pump to possibly clog up the works... (Its a heck of a lot easier to change a fuel filter than rebuild a carb?)

on another occasion it was the accellerator pump on the carb (pardon the spelling)

I hope to replace my fuel hose this winter depending on the ability to get to it...

Best wishes on finding the problem...

Cj

cptskier15
03-19-2011, 10:18 AM
Well, we ended up replacing all the piping to tank. In the end there was dirt in the pick up pipe filter in the tank! Did not even know there was a strainer in the tank! PO had used rubber inner tube to make gasket that fell into tank and got sucked up. Hence no fuel..

thatsmrmastercraft
03-19-2011, 06:39 PM
Well, we ended up replacing all the piping to tank. In the end there was dirt in the pick up pipe filter in the tank! Did not even know there was a strainer in the tank! PO had used rubber inner tube to make gasket that fell into tank and got sucked up. Hence no fuel..

One never knows what the previous fiend did. I guess that is part of the fun of a used boat. Not only did you win the battle, you learned a few things along the way. Congrats on a job well done.

Hoosier Bob
03-19-2011, 06:46 PM
Did I miss something? When was a 450 CFM used on a 351? I thought all were 600/650. Also you have now added more flow. Sure no valve work/exhaust work but a performer on a 5.8 and 450cfm? The 450 was on some 302's right?

rsmith_5568
03-24-2011, 08:16 PM
similar problem on 86 last season and after alot of cleaning and checking found a check valve at top of fule tank pick up that was clogged. Ran great for the rest of season

cptskier15
04-03-2011, 04:38 PM
Bob you are right, we had the motor rebuilt by a guy out here and he mistook us for another Mastercraft he had worked on and told us our Motor was a 302 about 3 years ago, hence we ordered a 450cfm. I did e mail holley and ask if this was an issue and they told be that it will only make a difference at WOT. I should still get great acceleration.

We have however found cracks on the distributors rotor arm and are pretty sure that it is not rigid and may be varying the timing! So will try skidim to export to South Africa.

We are having trouble starting her when the motor gets to operating temperatures though, we think the alternator is on its way out. How far to the right should the altimeter go once you start the engine, ours hardly moves of the centre line!

Thanks