Hard starting 4.3LX, normal or not?

[Swedefj40]

So I have a 1998 4.3 LX mercruiser with about 700hrs on it with the weber carb and electric fuel pump.

If it's been sitting for a few days, my normal start up procedure is to give it 3 full throttle pumps and then 1/4 throttle. I'll turn it over for about 5 seconds, let go of the key and listen for the fuel pump to stop priming then turn it over again and it'll usually fire up right away.

If it has been sitting for a few hours, it will take about 1 pump 1/4 throttle and 5 seconds of cranking before it fires up.

If the engine is warm and has been running for a bit and I shut it down for a minute or two, it will start up instantly after I turn the key (throttle in idle position).

I guess my question is, does this sound normal for my application? If not, how can I fix it?

It seems like I'm losing prime. I thought that possibly the fuel is evaporating. I wanted to put in a spacer between the carb and intake to reduce heat transfer to the carb but it has a divorced choke making it a little more involved.

Would an older electric pump cause this? Maybe allowing fuel to drain back to the tank?
I'm not sure if there is an anti siphon valve at the tank either. I'd have to double check on that.

Thoughts?

 

[Scott06]

Seems pretty normal , very similar to what i experience with my relatively new edlebrock 1409 which is essentially the same carb

the long delay in starting after sitting is the carb bowl drying out. unless yours is wired differently the fuel pump runs during cranking getting power off the starter. Just turning igntion on fuel pump is powered through oil pressure switch so wont get power when engine is off.

You just need to get fuel back in the fuel bowl. Of course pumping sets the choke as well as priming with some gas from accelerator pump squirt.

i did use a insulating spacer that edlebrock sells it did help with hot soak where fuel percolates into intake after shut off. Based on what you outline it seems like your hit restart is ok. Mine was long cranking and required opening the throttle due to being flooded somewhat

 

[Swedefj40]

Yeah, you're correct on the wiring setup and I'm going to investigate my choke more closely, but I don't believe it's a flooding issue.

 

[Bondo]

If it's been sitting for a few days, my normal start up procedure is to give it 3 full throttle pumps and then 1/4 throttle. I'll turn it over for about 5 seconds, let go of the key and listen for the fuel pump to stop priming then turn it over again and it'll usually fire up right away.

Ayuh,...... The fuel pump only runs while the starter is engaged, so I don't understand you bein' able to hear the fuel pump,.....

You'll do better by crankin' the motor for 5 seconds or so, Then pump the throttle, to set the choke, 'n prime the motor,.....

If, like most AFB carbs, the bowls are empty at 1st start, yer pumpin' the throttle is only pumpin' air, not gas,....

 

[Lou C]

Yep this is the way electric fuel pumps work on old school engines that originally had mechanical fuel pumps. Powered off the starter till the engine fires then as soon as oil pressure builds it is powered through the oil pressure switch. Make sure all the electrical connections for the fuel pump are clean & tight. With the mechanical pump it usually takes 3 crank overs (5 sec each or so) after winter storage to fill the bowl then it fires off. During the season only one crank over to fire off. I actually prefer the mechanical pump. The only down side to them when you have to replace one is dealing with the push rod. However they rarely go bad.

 

[Prop head]

So I have a 1998 4.3 LX mercruiser with about 700hrs on it with the weber carb and electric fuel pump.

If it's been sitting for a few days, my normal start up procedure is to give it 3 full throttle pumps and then 1/4 throttle. I'll turn it over for about 5 seconds, let go of the key and listen for the fuel pump to stop priming then turn it over again and it'll usually fire up right away.

If it has been sitting for a few hours, it will take about 1 pump 1/4 throttle and 5 seconds of cranking before it fires up.

If the engine is warm and has been running for a bit and I shut it down for a minute or two, it will start up instantly after I turn the key (throttle in idle position).

I guess my question is, does this sound normal for my application? If not, how can I fix it?

It seems like I'm losing prime. I thought that possibly the fuel is evaporating. I wanted to put in a spacer between the carb and intake to reduce heat transfer to the carb but it has a divorced choke making it a little more involved.

Would an older electric pump cause this? Maybe allowing fuel to drain back to the tank?
I'm not sure if there is an anti siphon valve at the tank either. I'd have to double check on that.

Thoughts?

I would check your fuel lines or fittings for cracks and leaks. You may have an air leak. If your sucking air, you are not getting fuel. If you have an air leak and no siphon valve you will lose suction and the fuel will return to the tank. Try inserting a primer bulb in the fuel line and give it some pumps to see if it starts better on an artificial prime or a leak my show itself under the pressure from the fuel. Just a thought. Good luck!

 

[Rinker95]

So I have a 1998 4.3 LX mercruiser with about 700hrs on it with the weber carb and electric fuel pump.

If it's been sitting for a few days, my normal start up procedure is to give it 3 full throttle pumps and then 1/4 throttle. I'll turn it over for about 5 seconds, let go of the key and listen for the fuel pump to stop priming then turn it over again and it'll usually fire up right away.

If it has been sitting for a few hours, it will take about 1 pump 1/4 throttle and 5 seconds of cranking before it fires up.

If the engine is warm and has been running for a bit and I shut it down for a minute or two, it will start up instantly after I turn the key (throttle in idle position).

I guess my question is, does this sound normal for my application? If not, how can I fix it?

It seems like I'm losing prime. I thought that possibly the fuel is evaporating. I wanted to put in a spacer between the carb and intake to reduce heat transfer to the carb but it has a divorced choke making it a little more involved.

Would an older electric pump cause this? Maybe allowing fuel to drain back to the tank?
I'm not sure if there is an anti siphon valve at the tank either. I'd have to double check on that.

Thoughts?

I love this forum. Take a look at achris explanation of the Weber dribble. Search "4.3 cold start issues", particularly March 30, 2021. Elegant.

 

[Swedefj40]

The fuel pump only runs while the starter is engaged, so I don't understand you bein' able to hear the fuel pump,.....

You'll do better by crankin' the motor for 5 seconds or so, Then pump the throttle, to set the choke, 'n prime the motor,.....

If, like most AFB carbs, the bowls are empty at 1st start, yer pumpin' the throttle is only pumpin' air, not gas,....

I think that after cranking the engine for 5 seconds that there is enough oil pressure built up to close the oil pressure switch which is why I can hear it priming. Good info on pumping the gas after the initial crank sequence, thanks.

 

[Swedefj40]

I would check your fuel lines or fittings for cracks and leaks. You may have an air leak. If your sucking air, you are not getting fuel. If you have an air leak and no siphon valve you will lose suction and the fuel will return to the tank. Try inserting a primer bulb in the fuel line and give it some pumps to see if it starts better on an artificial prime or a leak my show itself under the pressure from the fuel. Just a thought. Good luck!

It's not a fuel starvation issue (I don't think) but more of a drain back problem. I will check into the ASV though. Not sure I even have one.

 

[flashback]

I guess you could wire a momentary button to energize the pump and prime the carb before you start cranking.

 

[Scott06]

I think that after cranking the engine for 5 seconds that there is enough oil pressure built up to close the oil pressure switch which is why I can hear it priming. Good info on pumping the gas after the initial crank sequence, thanks.

When the alarm horn goes off the oil pressure is built up. Thats what triggers it during cranking

 

[Swedefj40]

I guess you could wire a momentary button to energize the pump and prime the carb before you start cranking.

Yeah I've thought about doing that.

 

[QBhoy]

Very normal for any I’ve known. Sometimes the choke gets in a fiddle, when the engine is in a certain state of warmth. Just a case of getting to know your engine really. When it’s in that certain state…you can easily get it wrong by pumping and flooding. Sometimes rapid pumping when cranking can just see her fire and if you’re lucky you can catch her on the throttle. A good battery is always helpful.
Personally, I disconnected the chokes on all three of the 4.3 engines I ever had. The Rochester on the VP one was the worst for it, before I did away with the choke.

 

[H20Rat]

I must be lucky... The two 4.3's I've owned start like they have fuel injection if they have been sitting anywhere from a day to a couple weeks. I don't pump, I don't do anything. Turn the key and it goes. (a '96 and a '03)

Hot starts on the other hand... My current 4.3 hates that! If it sits from around 30 minutes to a couple hours, it has to crank over quite a bit, and kind of acts like it is flooding itself. The choke is definitely over aggressive.

 

[Prop head]

It's not a fuel starvation issue (I don't think) but more of a drain back problem. I will check into the ASV though. Not sure I even have one.

A primer bulb has a one way valve system, Gas can only go one way. it is a easy was to test if you are loosing prime. I had a bad ASV along with an air leak. Boat would start run fine. If I left for a time gas would loose prime and could not start the boat if I primed it with the bulb she would restart no problem. Had air bubbles by the fuel pump not allowing it to pump gas. I put on clear hoses to see fuel flow. Observed air entering the system at the fuel filer. I then watched the gas drain back into the tank after the boat was shut down right past my ASV.

 

[Lou C]

Very normal for any I’ve known. Sometimes the choke gets in a fiddle, when the engine is in a certain state of warmth. Just a case of getting to know your engine really. When it’s in that certain state…you can easily get it wrong by pumping and flooding. Sometimes rapid pumping when cranking can just see her fire and if you’re lucky you can catch her on the throttle. A good battery is always helpful.
Personally, I disconnected the chokes on all three of the 4.3 engines I ever had. The Rochester on the VP one was the worst for it, before I did away with the choke.

Once you've owned a Chevrolet and an Olds with Rochester carbs and that same divorced choke and live in a cold winter climate (like I did in the '70s) you learn how to make those chokes work. The problem with using a divorced choke in marine applications is that the engine runs cooler and takes a lot longer to warm up than the same engine in an auto application with a 195* thermostat. So with my 4bbl Quadrajet on the boat I have it set so it doesn't close all the way, so it opens up reasonably fast.
BTW, with electric chokes, because they open based on a timer set up, sometimes they open too fast. What would have been ideal would have been to rig up a temperature sensor right on the intake manifold that would control the opening of the choke based on actual engine temp. That is exactly how hot air chokes and divorced chokes worked in auto applications, back in the days before throttle body injection and EFI. The reason why you need a choke is that the cold intake manifold causes fuel to condense out of the mixture, and causes stalling and rough running. So you want the choke opening device to accurately sense the temp of the intake manifold. The GM style divorced choke does this, but it could be more sensitive/accurate.
The other idea and I would have done this if I could find a good quality kit with a very long cable is simple manual choke.
The hot soak problems, I have never had and I think it is because if you use the standard gasket with the Quadrajet, it is a thick 1/4" gasket that keeps the carb cool enough not to boil the fuel on a hot day and cause vapor lock. The Weber/Edelbrock are more sensitive to this because the float bowls are right over the hot intake, and I think a carb insulator would help. Holley carbs with the front and rear float bowls are elevated enough over the intake that they don't get that hot.

 

[Bt Doctur]

Some have added a push button to prime the carb . Rochestors have a habit of leaking welch plugs draining the bowls

 

[Swedefj40]

Once you've owned a Chevrolet and an Olds with Rochester carbs and that same divorced choke and live in a cold winter climate (like I did in the '70s) you learn how to make those chokes work. The problem with using a divorced choke in marine applications is that the engine runs cooler and takes a lot longer to warm up than the same engine in an auto application with a 195* thermostat. So with my 4bbl Quadrajet on the boat I have it set so it doesn't close all the way, so it opens up reasonably fast.
BTW, with electric chokes, because they open based on a timer set up, sometimes they open too fast. What would have been ideal would have been to rig up a temperature sensor right on the intake manifold that would control the opening of the choke based on actual engine temp. That is exactly how hot air chokes and divorced chokes worked in auto applications, back in the days before throttle body injection and EFI. The reason why you need a choke is that the cold intake manifold causes fuel to condense out of the mixture, and causes stalling and rough running. So you want the choke opening device to accurately sense the temp of the intake manifold. The GM style divorced choke does this, but it could be more sensitive/accurate.
The other idea and I would have done this if I could find a good quality kit with a very long cable is simple manual choke.
The hot soak problems, I have never had and I think it is because if you use the standard gasket with the Quadrajet, it is a thick 1/4" gasket that keeps the carb cool enough not to boil the fuel on a hot day and cause vapor lock. The Weber/Edelbrock are more sensitive to this because the float bowls are right over the hot intake, and I think a carb insulator would help. Holley carbs with the front and rear float bowls are elevated enough over the intake that they don't get that hot.

Great info Lou C...
FYI, I live in NW BC just south of the Alaska Panhandle and my boating season is usually between April and September. Average temperatures range between 15c - 25c (60f - 77f) so definitely on the cold side.

My routine at the dock is that I'll launch the boat, fire it up and let it idle for a few minutes, then I'll idle out from the dock and then run at about 1500 - 2000 rpm for a few minutes to let everything get up to temp. Then I'll open it up to get it on step and cut it back to a cruising speed of 3800rpm. If I try to speed the sequence up, when I go to put it on step, she'll seem to stumble a little and slightly bog down a bit but then she's good. So looking more into the choke function is definitely a good idea. Maybe swap it to electric?

Just curious, there any form of check valve in the electric fuel pump?

Also, to eliminate confusion, I have the original weber carb.

 

[Lou C]

I would start it up with the flame arrestor off and observe the operation of the choke. Cold engine it should close all the way, or at least almost close all the way. Right after it starts, a vacuum operated valve will pull the choke open a fraction so the carb gets enough air to keep running. When your temp gauge is indicating normal temp (140* or 160* depending on what thermostat you have) the choke should be fully open (the choke blade will be fully vertical). If it opens too slow or too fast you can have stumbling. I think electric chokes are more prone to this because they open independent of the actual engine temp. So they can open too fast.
There is one other aspect that I forgot to mention, as a difference between automotive vs marine applications of automatic chokes...
In an auto applicition you have a fast idle cam that raises the idle speed when the choke is closed, and lowers it in steps as the choke opens, this helps keep the engine from stalling. This can't be used in a marine application because the engine would slam into gear (an outdrive no matter if it is a dog clutch or cone clutch, is either all in gear or out of gear, no automotive clutch or torque converter to smooth engagement) so it would be a safety hazard. So there is the same style of auto choke on a marine engine but NO fast idle cam. You provide the fast idle by setting the idle manually. That's why it doesn't work as well as it does in an auto application.
Not sure about the check valve in the electric fuel pump.

 

[QBhoy]

Once you've owned a Chevrolet and an Olds with Rochester carbs and that same divorced choke and live in a cold winter climate (like I did in the '70s) you learn how to make those chokes work. The problem with using a divorced choke in marine applications is that the engine runs cooler and takes a lot longer to warm up than the same engine in an auto application with a 195* thermostat. So with my 4bbl Quadrajet on the boat I have it set so it doesn't close all the way, so it opens up reasonably fast.
BTW, with electric chokes, because they open based on a timer set up, sometimes they open too fast. What would have been ideal would have been to rig up a temperature sensor right on the intake manifold that would control the opening of the choke based on actual engine temp. That is exactly how hot air chokes and divorced chokes worked in auto applications, back in the days before throttle body injection and EFI. The reason why you need a choke is that the cold intake manifold causes fuel to condense out of the mixture, and causes stalling and rough running. So you want the choke opening device to accurately sense the temp of the intake manifold. The GM style divorced choke does this, but it could be more sensitive/accurate.
The other idea and I would have done this if I could find a good quality kit with a very long cable is simple manual choke.
The hot soak problems, I have never had and I think it is because if you use the standard gasket with the Quadrajet, it is a thick 1/4" gasket that keeps the carb cool enough not to boil the fuel on a hot day and cause vapor lock. The Weber/Edelbrock are more sensitive to this because the float bowls are right over the hot intake, and I think a carb insulator would help. Holley carbs with the front and rear float bowls are elevated enough over the intake that they don't get that hot.

Agree. Just that the way I use the boat…it’s often in that in between stage and can easily flood. Just got rid of it and warmed it up manually really. Always knew where you were then. Can’t disagree with what you’re saying though. Different in a car perhaps.