FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

[roaker1]

Help! Besides the first 20 problems I just fixed, I am down to my last apparent issue. The boat runs perfect EXCEPT when I punch it to full throttle. From a stand still, it cuts out for a second and then takes off. At full speed it only hits 4000 rpm's and only goes 40mph because it keeps cutting out. Every now and then at full throttle the engine kicks in for a second or 2 and sounds healthy and has a short burst of power. The engine runs perfect except for full throttle. I I just emptied out my fuel tank and replaced it with clean fuel. I changed my fuel filter. I installed a new fuel pump. I had the best guy in Portland completely rebuild the carb, I have new plugs and checked them for fouling and they all look good. The distribuor cap looks good inside. The boat used to go 50mph when we last used it 6 years ago. Carb throat butterfly is 90 degrees open at full throttle as it should be. ANY IDEAS?? ( I did purchase an automotive fuel pump and not a marine pump)

 

[lynnboy021]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

did you check your fuel psi??/ not to sure about an auto pump

 

[John_S]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

( I did purchase an automotive fuel pump and not a marine pump)

Automotive pumps vent to the inside of the compartment. When you have a diaphram failure, you will be in extreme danger from explosion. Replace with marine pump.

 

[mohead1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

OH!!.....yeah.....dump the pump dude......gasoline does some weird stuff to fiberglass......especially when in a fireball....

 

[Raystownboater]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

did you check your fuel psi??/ not to sure about an auto pump

The difference between the auto and marine pump is the marine pump is designed to route fuel back into the carb, rather then into the bilge, if there is a failure

 

[Raystownboater]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

The boat used to go 50mph when we last used it 6 years ago. Carb throat butterfly is 90 degrees open at full throttle as it should be. ANY IDEAS?? ( I did purchase an automotive fuel pump and not a marine pump)

Is this the first time running in six years? You didnt mention a carb rebuild and if the engine has been sitting for that long you may want to put that on the "to do" list.

 

[roaker1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Automotive pumps vent to the inside of the compartment. When you have a diaphram failure, you will be in extreme danger from explosion. Replace with marine pump.

Thanks for your response. I did not mention the full story about my fuel pump. The original marine fuel pump had a bad diaphram and shot fuel up the third venting line into the base of the carb and down into the oil pan so I had to change the oil and some fouled plugs. I went to purchase a marine fuel pump but they wanted $185. I bought an identical fuel pump that had the same third venting line that goes into the base of the carb and it did the same thing. I was told my new fuel pump was defective and changed the oil and plugs yet again. I now purchased a fuel pump that does not have the third venting line coming off of it that goes to the base of the carb. The boat runs perfect with the exception of choking out at full throttle. I received a post from another gentleman telling me to replace it with a marine pump as it will vent into the engine if the diaphram goes bad and could be dangerous.

To answer your question, no I have not checked the fuel pressure yet. What should the fuel pressure be??

Thanks for the help.

 

[roaker1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Oops I almost forgot. I did mention a carb rebuild from a local expert in my post who is the best in town. He boiled it out, replaced the accelerator pump, vacuum pump, etc. I have been very busy with this boat I purchased from my brother.

 

[skideck2]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

fuel water seperator anyone???

 

['77imp]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Not sure if the 88 bayliner with chevy 305 has vacuum advance for the distributor or not, but it sounds like its running retarded in timing at full throttle. Theory: vacuum advance (if that is what is on yours) is designed to advance your timing at high rpm. If it relies on the vacuum from the carb, then check the vacumm line to the distributor, or if its counter weighted like the old days of timing advance, then it might be the weights are sticking in the distributor. Also, one more thing to check...the timing while it's running at idle. If it's too far advanced at idle, when the distributor does advance the timing at high rpm, it will be firing the cylinders way past top dead center (checking engine specs of course first), retard the timing of the distributor to factory settings. I dont think the distributor timing setting is the issue...I think the timing advance via vacuum line or sticky advancing mechanism in the distributor might be your problem.

Hope this helps.

 

[roaker1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Thank you for your help. This is a great forum because of people like you. I appreciate you taking the time to help me.
The boat is at a moorage. I will be taking it out on Sunday. I will look at the distributor to try to take notes or to figure out what kind it is. I believe you are right about the issue not being the timing because 6 years ago it ran perfect and nobody has touched the timing. I noticed today that the accelerator pump has an adjustment. It is on the adjustment that has the shortest throw. Should I place it on the longer throw adjustment? At a dead stop when I punch it it cuts out for about 2 seconds before it sputters and then takes off. Maybe that is because of the vacuum issue that you mentioned. How do I know if there are distributor weights and if they are sticking? Thanks again.

Not sure if the 88 bayliner with chevy 305 has vacuum advance for the distributor or not, but it sounds like its running retarded in timing at full throttle. Theory: vacuum advance (if that is what is on yours) is designed to advance your timing at high rpm. If it relies on the vacuum from the carb, then check the vacumm line to the distributor, or if its counter weighted like the old days of timing advance, then it might be the weights are sticking in the distributor. Also, one more thing to check...the timing while it's running at idle. If it's too far advanced at idle, when the distributor does advance the timing at high rpm, it will be firing the cylinders way past top dead center (checking engine specs of course first), retard the timing of the distributor to factory settings. I dont think the distributor timing setting is the issue...I think the timing advance via vacuum line or sticky advancing mechanism in the distributor might be your problem.

Hope this helps.

 

[gbeltran]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Not sure if the 88 bayliner with chevy 305 has vacuum advance for the distributor or not, but it sounds like its running retarded in timing at full throttle. Theory: vacuum advance (if that is what is on yours) is designed to advance your timing at high rpm. If it relies on the vacuum from the carb, then check the vacumm line to the distributor, or if its counter weighted like the old days of timing advance, then it might be the weights are sticking in the distributor. Also, one more thing to check...the timing while it's running at idle. If it's too far advanced at idle, when the distributor does advance the timing at high rpm, it will be firing the cylinders way past top dead center (checking engine specs of course first), retard the timing of the distributor to factory settings. I dont think the distributor timing setting is the issue...I think the timing advance via vacuum line or sticky advancing mechanism in the distributor might be your problem.

Hope this helps.

I have never seen a boat engine with a vacuum advance, at least not on an outdrive boat. I see them occasionaly on stuff like jet and v drive boats but most of the time the unit is capped off. Vacuum advance on cars is meant to advance the timing during part throttle, at full throttle there is almost no manifold vacuum. An 88 OMC will not have a vacuum advance unit. If it does then then someone stuck an automotive unit in the engine. It is a good idea to check the timing, and do a compression check before chasing down any gremlins. Marine engines are sensitive to total timing, if you look at a timing curve for a boat engine compared to a car engine you will find it is quite conservative. If it was too far advanced it would be firing the cylinder too far BEFORE top dead center, not after.

 

['77imp]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

I see your point gbeltran. I guess I didnt notice the beginning post of it being an outdrive. That eliminates that as an issue.

Sorry roaker1...misled you in the wrong direction. If it ran fine 6 yrs ago, readusting the accelerator pump linkage wouldnt be the answer either. That shouldnt have been touched from the last time you had it running 6 yrs ago. Now, if the mechanic that rebuilt the carb didnt put it back together the same way it was 6 yrs ago...that might be a place to start. Also, if the mechanic that rebuilt the carb damaged the accelerator pump diaphram, that will cause a lower amount of fuel to be discharged through the accelerator nozzles that point into the smaller venturi's. My 76 jeep cherokee has a 4 barrel carb on a v8 and that gave me some of the same symptoms...flat spots when "punching it".

 

[roaker1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Thank for for your help. The carb mechanic is only a carb rebuild specialists. He has been rebuilding carbs for 51 years. He boiled it out, replaced the accelerator pump with a new one, and replaced other parts with new parts. That is why I am a little shy to think he did not do it right but who knows. The timing was never touched from 6 years ago when it was fast and had higher rpm's. This boat actually is a little faster at 3/4 throttle than at full throttle. I was thinking of having a friend ride on the boat with me and at full throttle spraying in a little fuel to see if it accelerates. Maybe that will tell me if it is a fuel problem or not. Any opinions on that idea?

I see your point gbeltran. I guess I didnt notice the beginning post of it being an outdrive. That eliminates that as an issue.

Sorry roaker1...misled you in the wrong direction. If it ran fine 6 yrs ago, readusting the accelerator pump linkage wouldnt be the answer either. That shouldnt have been touched from the last time you had it running 6 yrs ago. Now, if the mechanic that rebuilt the carb didnt put it back together the same way it was 6 yrs ago...that might be a place to start. Also, if the mechanic that rebuilt the carb damaged the accelerator pump diaphram, that will cause a lower amount of fuel to be discharged through the accelerator nozzles that point into the smaller venturi's. My 76 jeep cherokee has a 4 barrel carb on a v8 and that gave me some of the same symptoms...flat spots when "punching it".

 

[roaker1]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

Does anyone think my timing could be the problem? The boat runs and idles perfect up to 3/4 throttle. Full throttle is still choking out a bit. My specs call for 4200-4600 rpm's. I am only hitting 4000 at 3/4 throttle and at a choking out full throttle.

 

[gbeltran]

Re: FULL THROTTLE Problems on my 1988 19' Bayliner Capri with Chev 305 4 barrel carb

If you haven't checked it or done a compression test now would be a good time.