Adjusting fuel pressure on a 5.7

[rad1026]

1989 Chaparral 2100 SX, 5.7L with 4 bbl Rochester carb. I just replaced my fuel pump last summer and then had the local shop adjust the fuel pressure. I was at the lake and I could tell the new pump was delivering too much pressure. I got the boat back and they said they adjusted the pump to 7 lbs. Since then I have had a really difficult time starting the engine the first time of the day. I have checked carb choke and everything is working properly. The engine started great before I had the pump replaced. I just had the carb rebuilt and the boat runs great except for the first start up. I still think the 7 lbs is too much. How do I adjust the pressure. Someone told me you have to shim the fuel pump out further from the block. Where do I test the pressure? Do I need to build at T in front of the carb inlet and test it there?

Thanks for the help.

 

[Walt T]

Re: Adjusting fuel pressure on a 5.7

Just install a regulator between the pump and carburetor. Qjets don't really like pressure over 5 psi. Holley makes them about 45 bucks

 

[Bondo]

Re: Adjusting fuel pressure on a 5.7

1989 Chaparral 2100 SX, 5.7L with 4 bbl Rochester carb. I just replaced my fuel pump last summer and then had the local shop adjust the fuel pressure. I was at the lake and I could tell the new pump was delivering too much pressure. I got the boat back and they said they adjusted the pump to 7 lbs. Since then I have had a really difficult time starting the engine the first time of the day. I have checked carb choke and everything is working properly. The engine started great before I had the pump replaced. I just had the carb rebuilt and the boat runs great except for the first start up. I still think the 7 lbs is too much. How do I adjust the pressure. Someone told me you have to shim the fuel pump out further from the block. Where do I test the pressure? Do I need to build at T in front of the carb inlet and test it there?

Thanks for the help.

Ayuh,.... Donno what yer mechanic was talkin' 'bout,... Mechanical fuel pumps Aren't adjustable,...

Yer carb probably is leakin' off, internally,...

Before ya try startin' it again, Pump the throttle a few times, 'n Look to see whether the carb is pumpin' gas,...

If it Don't, it's leakin' into the intake, 'n ya gotta crank the motor over to refill the fuel bowls,...

Quadra-jets are known to leak through the welch plugs in their base castin',...

 

[JustJason]

Re: Adjusting fuel pressure on a 5.7

You don't have to or need to adjust fuel pressure on a carbureted engine. Fuel pump output should be 4 to 7 psi. If it was any higher, the fuel pump would be bad, and you would replace it. Other than that, high fuel pressure would not cause a hard starting issue unless it was so high that it was unseating the needle valve and pushing the float inside of the carburetor down. If this happened, you would see fuel pouring out of the carbs vent hole, as it would be flooding out. And you would hopefully have smelled (or seen) that.

On a carbureted engine, it needs exactly zero psi to start.

 

[rad1026]

Re: Adjusting fuel pressure on a 5.7

I verified with the carb rebuilder that the welch plugs were filled with epoxy, that is part of their process. I will take a look and see if the accelerator pump is working before I start it again. Where is the carb vent hole? is that the clear tube in the front of the carb?

 

[Silly Seville]

Re: Adjusting fuel pressure on a 5.7

When you take your boat back to this "mechanic" again...ask him to inspect your exhaust bearings.
I'm sure he will find that they are worn!

:facepalm:

 

[JustJason]

Re: Adjusting fuel pressure on a 5.7

Look at this picture, I circled it in red.

 

[Bondo]

Re: Adjusting fuel pressure on a 5.7

I verified with the carb rebuilder that the welch plugs were filled with epoxy, that is part of their process. I will take a look and see if the accelerator pump is working before I start it again. Where is the carb vent hole? is that the clear tube in the front of the carb?

Ayuh,... The clear tube should be the fuel pump vent,....

 

[Capt Ken]

Re: Adjusting fuel pressure on a 5.7

Hmmm, something else I can tell the customer other than their prop wash is low and I need to refill it. If it gets low again I may have to search for the leak.

 

[NHGuy]

Re: Adjusting fuel pressure on a 5.7

Guys, let's answer the OP.
So did it start great til the pump was changed or til the carb was redone? Who set the idle mix and idle speed? Carbs must be pumped before cranking and the throttle needs to be at least a bit open, not way open, just a touch above idle.

First thing, while the motor is cold, take off the flame arrestor, prop open the choke and look down the bore while someone pumps the gas a couple of times. You should see two simultaneous squirts of fuel with each pump. If you don't it's time to redo the carb, or the accelerator pump. If you try this later once the motor has been run and it squirts then but not cold you have the leaky welch plug issue. If you never get a squirt it's the accelerator pump or a clogged pump fluid circuit.
I recently rebuilt my Qjet exactly to OE spec. and it cranks a bit before it cold starts. The reason it won't just start instantly after sitting a couple of days is because the fuel in the intake tract dries up. If you really want to get a quick start after leaving your boat unused for a week or so, pump the throttle about 3 to 5 times. Then open it about 5 to 10% and start. Experiment with it, each is different. After an overnight you can restart it with 2 pumps. Same day, zero to 1 pump.
If it's been really cold and I haven't run it for a few days I will pump it 3 or 4 times and crank, if it doesn't fire quick I continue to crank and pump it from idle to one eighth throttle 2 to 4 times. If it starts and runs rough I let it run a little fast til it smooths, otherwise I run it as slow as possible to let it warm easy.
Also my carb guru claims the welch plug leak problem went away in the early 80's. I tested my carb (1988 build), it did not leak there.
Fuel pressure is not likely the problem.

 

[rad1026]

Re: Adjusting fuel pressure on a 5.7

Thank you NH, Jason and Bondo. Ya know, I probably misunderstood the mechanic. He said the pressure coming off the pump was 7 lbs. I probably assumed, since I was getting frustrated at the starting issue and talking to guys on the beach that the mechanic "adjusted" the pressure to 7 lbs. Seville and Cptn Ken, I hope at least some of the time you spend in here is constructive. If all you do is sit around and criticize the knowledge of others then please refrain from commenting when I need help.

I am replacing my outdirve impeller and as soon as I get that back on the boat and am able to start it up I will see how it goes. I only know that in my attempt to keep the 25 year old boat in great condition I changed out a 25 year old fuel pump. There is no doubt the fuel pump was the original and it had very worn rubber. After the pump was replaced I began having the starting problem so I assumed maybe the fuel pressure was high. I used to be able to pump the throttle 2-3 times and would start right up even after sitting a few weeks. Now when I do that it seems to flood out right away and then it takes a long time to clear the fuel and get started. Maybe I just need to adjust my starting procedure and its going to take some playing with. But it sure is frustrating going from a boat that started easy, to one that is difficult.

 

[Bondo]

Re: Adjusting fuel pressure on a 5.7

Thank you NH, Jason and Bondo. Ya know, I probably misunderstood the mechanic. He said the pressure coming off the pump was 7 lbs. I probably assumed, since I was getting frustrated at the starting issue and talking to guys on the beach that the mechanic "adjusted" the pressure to 7 lbs. Seville and Cptn Ken, I hope at least some of the time you spend in here is constructive. If all you do is sit around and criticize the knowledge of others then please refrain from commenting when I need help.

I am replacing my outdirve impeller and as soon as I get that back on the boat and am able to start it up I will see how it goes. I only know that in my attempt to keep the 25 year old boat in great condition I changed out a 25 year old fuel pump. There is no doubt the fuel pump was the original and it had very worn rubber. After the pump was replaced I began having the starting problem so I assumed maybe the fuel pressure was high. I used to be able to pump the throttle 2-3 times and would start right up even after sitting a few weeks. Now when I do that it seems to flood out right away and then it takes a long time to clear the fuel and get started. Maybe I just need to adjust my starting procedure and its going to take some playing with. But it sure is frustrating going from a boat that started easy, to one that is difficult.

Ayuh,.... So what have you got against Good Humor, 'n Friendly banter,..??

This is an open forum, 'n the posts noted in No way, take away from the useful Info you got,...

It's the Dead of Winter,...
How do you think We all manage to get through the off season, or even the Boatin' season, without a touch of Humor,..??

 

[JustJason]

Re: Adjusting fuel pressure on a 5.7

I hope at least some of the time you spend in here is constructive

This is a free and open forum. Which means that anybody can post what they want to, wether it is right or wrong, good information or bad, wether they are sending you down the right path, or just screwing/trolling with you.

There are other websites out there that will offer you, for a fee, an option to speak with a certified mechanic, either over the internet, or via phone. And I can tell you that that you would have their undivided attention, and treat you in a professional manner helping to guide you through your problem, help provide technical documentation ect. But it does cost money. If you want to know more about that you can either google it, or shoot me a PM and I can explain more about what I mean.

Other than that. You get what you pay for. And when your paying (as mike tyson would say) in fwree dollar bills, your not going to get much. There is certainly some talent and a wealth of knowledge here on Iboats. But wether you get that, or the sideshow circus, can be a flip of the coin. And since your not paying for it, you kinda have to take things with a grain of salt.

 

[NHGuy]

Re: Adjusting fuel pressure on a 5.7

Since you think it might be flooding check that the choke closes when cold, and as you said, try cold pumping different amounts til it starts best.
Also watch the choke after the motor runs, it should open a little as soon as the motor starts. And then continue to open as the motor warms. It ain't fuel injection so it won't run perfectly til warm. If you work with it a little you can get it darn good though.
When it's fully warm it should idle around 725 with the choke completely open. Your timing should be 8 to 11 degrees BTDC, book says 8.
You can check the idle mix too. It takes a funky carb adjustment tool. They are around $10 or $15 on ebay or at the parts store. I recommend the spring shafted type which is easiest to use.
Once the motor is warm get it to idle speed and turn one mix screw down til the motor stumbles, then out til it seems rough, and finally find a spot between that runs smoothest. On mine it's around half or 2/3 of a turn out from stumbled. Then recheck the idle speed and do the other side and recheck the idle again. Go back and forth til it makes you comfortable.
Don't screw the mixture adjustment down hard, if you feel it seat, stop and back it out.
The "book" says to split the stumble and the "fat" setting, but on my engine it's best a little leaner than that.
High tech guys do this by measuring for maximum intake manifold vacuum, I just mess with it til it works right. Worse thing is I have a vacuum pump & gauge that I could check it with.

 

[rad1026]

Re: Adjusting fuel pressure on a 5.7

Again, thanks to everyone who comes in here to help fellow boaters. I continue to learn every time I ask for help and I greatly appreciate the time, effort and experience sharing this forum provides. That being said, and I know better, I should just let this go, but I'm a little bored today myself.

Why is it okay for people to make fun of my mechanic, who I personally respect, but when I ask that that person refrain from those type of comments I become the bad guy? I did not insult the poster or say anything to them negative, all I said was that I hope they also spend constructive time in here and to please leave those comments out. I became such a bad guy I deserve long comments from two of the most respected members of the forum? Really?

Capt Ken, my apologies. I re-read your post and it is harmless humor. I hope you forgive my comment.

Mr. Seville, I hope we can get off to a better start some time down the road.

 

[JustJason]

Re: Adjusting fuel pressure on a 5.7

Why is it okay for people to make fun of my mechanic, who I personally respect, but when I ask that that person refrain from those type of comments I become the bad guy?

It's because this is free. There are other services out there that are for pay, I do one. And if you want to use a service like that, not only would you have my personal undivided attention, but I would also treat you in the most professional manner I could. After all you would be the customer at that point. But here, being free, there should not be any expectation of professionalism. Nor can you have any expectation of any information you receive even being remotely correct. It's not like everybody here is vetted. Like I said before. Sometimes you get some good "Free" information. And other times you get the circus sideshow. And that's what happens at any of the free forum websites.

 

[Bondo]

Re: Adjusting fuel pressure on a 5.7

Again, thanks to everyone who comes in here to help fellow boaters. I continue to learn every time I ask for help and I greatly appreciate the time, effort and experience sharing this forum provides. That being said, and I know better, I should just let this go, but I'm a little bored today myself.

Why is it okay for people to make fun of my mechanic, who I personally respect, but when I ask that that person refrain from those type of comments I become the bad guy? I did not insult the poster or say anything to them negative, all I said was that I hope they also spend constructive time in here and to please leave those comments out. I became such a bad guy I deserve long comments from two of the most respected members of the forum? Really?

Capt Ken, my apologies. I re-read your post and it is harmless humor. I hope you forgive my comment.

Mr. Seville, I hope we can get off to a better start some time down the road.

Ayuh,.... Nobody, but Nobody is makin' You the Bad Guy,....

Just consider it a Free Education, as to how Free internet advice forums work,...
'n that pretty much includes All, Free internet advice forums,....

Here at iboats, Luckily, there's plenty of posters who actually Know what Good info is, 'n are Quick to correct any truly Bad info offered,...