350 Chevy dying

"My first post - nice site!
I

"My first post - nice site!
I was having problems with both my engines just loosing power after they get warm. I just changed both Holley 600cfm's, and there seemed to be an improvement on one engine. However, after test run today, after running at cruising RPM - about 2800 - for about 20 minutes, I decided to push them down and see what the new carbs would do.
Well, the port engine took power, but starboard engine just bogged right down and quit. I couldn't get it re-started.
After waiting about 1/2 hour, with engine room doors open, starboard engine finally re-started.
I'm thinking something electrical is dropping out upon heating up. Both distributors (Mallory) were rebuilt with Pertronix electronic upgrade kits before I bought the boat. The coils look like stock coils though, and I'm wondering if the coils maybe breaking down, or the module in the distributor.
I'm grasping at straws here. If anybody has any ideas, I'd really appreciate the feedback.
Thanks a lot.

P.S. The engine compression is good all around, and timing is spot on."

I would guess it is a fuel sup

I would guess it is a fuel supply problem. It could be in the fuel pickup or int hte hose connections letting air be sucked in. I assume all the filters have been cleaned or replaced.

Try blowing air back into the tank from the fuel line to clear away any blockage at the pickup.

"Thank you Robert,
I have run

"Thank you Robert,
I have run new fuel lines to carbs, had tank pickup out to examine it, and all new filters. Carbs are also newly rebuilt ones, with all new gaskets."

"Maybe it is a vapor lock. An

"Maybe it is a vapor lock. An electric fuel pump may fix the problem. I copied these defination.

Wikipedia
"Vapor lock is a problem that mostly affects gasoline-fueled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporise due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude. In regions where higher volatility fuels are used during the winter to improve the starting of the engine, the use of "winter" fuels during the summer can cause vapor lock to occur more readily"

Mastertech Marine
"Vapor lock" is loss of power or engine shutdown due to gasoline vaporization in the fuel system. Vaporization prevents the fuel pump from delivering sufficient gasoline to the engine. Factors favoring vapor lock are high eingine compartment temperatures which accompany high power output. Sometimes vaporization occurs after the engine has been intentionally stopped because of the cessation of mechanical cooling and fuel flow. In this case, the hot engine will be difficult to start.""

"Once again Robert, thank you.

"Once again Robert, thank you.
This certainly sounds very interesting. I've never come across an incident of vapour lock before, but since I am desperate, and seeing as the symptoms actually sound convincing, I will definately look into this.
I live in the Bahamas, and it sure is hot right now, so vapour lock might be the culprit."

"William:

Change the igniti

"William:

Change the ignition coil on your starboard engine and see if that helps - it may be that,or your starboard carb dumping too much gas and flooding the engine out,or simply not getting enough gas at all.....

When you changed the Holley carbs did you install same rebuilt or new remans?
Or another brand?

If Holley's make sure of their list numbers and specs.....could be that they have the wrong power valves,jet size,metering plate,diaphragm spring,the power valve might not be fully opening etc.

Vapor locking would more likely occur in both engines same time if that were the problem.

I have a B28 with GM 350's and Holley carbs here in Nassau fyi.
Carb specs:
List #75009-3
M/N 4160
600 cfm
66 Jets Primary
Metering Plate Rear = 59
6.5 Primary Power Valve
31 = Nozzle
Diaphragm Spring = Brown

Good luck."

"Thanks for the input bertram2

"Thanks for the input bertram282.
When I changed the carbs, I put on two newly reman units of the same specs. Carbs actually seemed to improve performance initially, but starboard engine finally seems to be doing the same thing it was before.
It would seem that something is breaking down after engine has run for a while. So I'm thinking heat, and electronic.
Question - does a coil break down partially? Also, what about the electronic components (Pertronix) of the electronic distributor conversions?

Thanks again. I live in Abaco, BTW."

"Oh, I forgot to ask - what co

"Oh, I forgot to ask - what coils should I use with this setup? I was thinking about the Pertronix flame thrower since the distributor conversions are Perronix. Should I use a 1.5 or 3 ohm coil?
Thanks all."

"William:

Glad you are in A

"William:

Glad you are in Abaco - if you were in Freeport I would be wondering about whether their ethanol gas might be an issue as I understand E10 gas is being used by FOCOL there now......and that will become an issue for all fibreglass fuel tank / gas engine boat owners over there........

I use aftermarket universal 12 volt ignition coils,Echlin p/n 1C12 and my distributors are Prestolite electronic p/n IDU 7801 LS 2P.

PerTronix recommend using their 1.5 ohm coils with 8 cylinder 12 volt systems using their Ignitor breakerless ignition.PerTronix 40,000 volt coil p/n 40001,40011 or 40111.

How hot are your ignition coils getting when running?

Mine eventually break down due to the engine compartment heat as far as I can tell.....I carry spares and keep the coils off the intake manifolds as far as possible..... yet still only average 75 -100 hours use out of each coil.

Check how hot your starboard ignition coil is on your next run - and carry a spare to switch to and see if that re-starts you quicker.
Tip:Loosen the ignition coil bracket enough now so you can,with minimum leverage,take the ignition coil out of its bracket to swap it out......

To me this sounds like your ignition coil is overheating causing your starboard engine to shut down.From my experience they either give some short notice by way of power loss / backfiring if at high load,or more usually just give out completely with no warning.

Out of curiousity do you have hi-rise intake manifolds?
Are your carburetors on wedge type adapters?

I'm using standard low profile intake spread bore manifolds with a 7o adapter plate for my Holley carbs,mechanical fuel pumps.Hi-rise intake manifolds were too high for the hatches to close.Base engines are new 350 ci.d. Chevy small blocks installed in 2005.

My B28 is a '76 Flybridge Cruiser.

Good Luck."

"Thanks again, bertram282.
I

"Thanks again, bertram282.
I just ordered two Pertronix epoxy filled, 1.5 ohm coils. From what I can gather, Pertronix says that these coils can be hooked up direct 12v, no resistor needed when using the Pertronix Ignitor conversions. I don't know what coils are on there now, because the labels have long since been torn off.
I have regular low rise intakes with adapter wedge
plates. The intakes are Rochester type, and the carbs are square bolt pattern. I'm not sure how long the engines have been in the boat.
When I get the new coils, I'm gonna post my results after sea trial, so hopefully the info will benefit somebody else. Assuming of course that the coil is the problem. At this point, I'm feeling pretty sure that it is.
In any event, thanks for all of the info, and as soon as I have something new, I'll post it."

"Just a quick update - got my

"Just a quick update - got my Flame Thrower coils today. I hope to put them on and check things out this weekend. As soon as I have some real results to post, I will."

"Just to update -
The flame

"Just to update -
The flame throwers are working okay I think. I'm still having problems with the engines, but I think what happened is that by fixing one problem I created another. So, I'm still tinkering around. Unfortunately I don't have the time to spend on it that I would like.
Thanks again to you all for your input."