Thunderbolt ignition problem?

[Chuckd91]

the issue is this 4.3 mercruiser with thunderbolt ignition. After building the engine and running it/setting the base timing at 8 degrees and setting the carb (4barrel holly) it ran great. It would turn less than a full rotation and fire up with no hesitation while at operating temp. Come out to my shop the next day and its barely able to idle. Its running about 500 rpm and very unstable. No carb adjustments will allow rpm increases at all. New plugs and wires as well as cap and rotor and sensor in the distributor base. Rhe choke is not closed. The engine will turn over just a few seconds and fire up but wont idle up at all. Very large amount of unburned fuel in the exhaust. And the timing light (very irratic) shows the timing to be way out around the 20 degree range. I can pull it back and get to the -10 range and it is better sounding but still low speed and unresponsive. Any ideas!?!?

 

[Fun Times]

carb (4barrel holly)

Maybe you have a blown holley power valve.
https://www.jegs.com/p/Holley/Holley...43661/10002/-1

Is the red engine in your avatar the engine you're working on? Though i know you could have painted the engine during rebuild; 'Usually that color red from stock ='s a Volvo penta engine is why I ask plus Volvo mostly used Holley's with the 2.5'' Hg. valve as the most common use.

 

[Chuckd91]

The boat was originally volvo but i rebuilt the boat and engine using mercruiser. Same block and heads though.

 

[Chuckd91]

I just rebuilt the carb and had a major fuel leak at the power valve seal before and couldnt turn the engine over without filling it with fuel and locking it up. And i noticed that with the issues i have currently, if i turn in the idle mixture screws all the way in, the engine still runs like hell but doesnt stall out. Power valve messed up again i guess?

 

[Fun Times]

What is the part number that ought to be on that Merc? electric fuel pump....Do you have a fuel pressure regulator inline of the fuel system going to the carb, etc.? Might be running just a bit to high of fuel pressure....Can you put a fuel psi gauge inline maybe as permanent too ?.

Did the fuel pump come off of the engine listed on top of the flame arrestor cover?

Also is the choke heating electric or?

The spacers under the Holly carb? Not use to seeing any of those being used that I can think of at the moment...Maybe affecting the runnability issues some too....Just a thought.

I'd recheck the power valve at some point too.

 

[Chuckd91]

I dont have a regulator. That is a pump from mercruiser that im using. My setup looks different because i made the engine harness and relocated some of the components. There is a guage attached to the fuel rail of the carb and its a steady 7 psi.

Its an electric choke and ive got it set to open right now for troubleshooting.

I have an adapter and spacer under the carb because the rear bowl will contact the distributor cap without it. Its a quadrajet manifold.

 

[Scott Danforth]

unless the carb is post 1992, if you have a back fire it will rupture the power valve. you can get the check valve kit and add the check valve to the circuit.

https://www.summitracing.com/parts/...MIlvGy8Zix4QIVxVcNCh0d3gGUEAQYAiABEgLi4_D_BwE

the fact that its pouring fuel into the carb with the idle mix screws turned in would lead me to believe the power valve is bad.

7psi is the absolute upper limit of the needle and seat. you may want to consider a regulator.

 

[Chuckd91]

Well the power valve didnt make a difference sadly. I was reading about even and odd fire 4.3 engines and was wondering if ive overlooked something. The block, heads, cam, etc are a 1994 “volvo penta” that came in the boat originally. I installed mercruiser ignition and outdrive during the rebuild/repower.

 

[Muppetman420]

the issue is this 4.3 mercruiser with thunderbolt ignition. After building the engine and running it/setting the base timing at 8 degrees and setting the carb (4barrel holly) it ran great. It would turn less than a full rotation and fire up with no hesitation while at operating temp. Come out to my shop the next day and its barely able to idle. Its running about 500 rpm and very unstable. No carb adjustments will allow rpm increases at all. New plugs and wires as well as cap and rotor and sensor in the distributor base. Rhe choke is not closed. The engine will turn over just a few seconds and fire up but wont idle up at all. Very large amount of unburned fuel in the exhaust. And the timing light (very irratic) shows the timing to be way out around the 20 degree range. I can pull it back and get to the -10 range and it is better sounding but still low speed and unresponsive. Any ideas!?!?

I would take apart the float and clean it and even clean the jets

 

[Muppetman420]

Well the power valve didnt make a difference sadly. I was reading about even and odd fire 4.3 engines and was wondering if ive overlooked something. The block, heads, cam, etc are a 1994 “volvo penta” that came in the boat originally. I installed mercruiser ignition and outdrive during the rebuild/repower.

What kind of oil pressure did u have while it was running I’m wondering if you got the distributor lock that goes to the oil pump backwards therefore throwing off your timing. Try to reset top dead center and your number one plug and check the distributor cap to see if it’s onthe number one plug also. Good way to double check.

 

[Muppetman420]

I’m not sure which one u needed but here’s a few that might help

 

[Muppetman420]

Read that timing page I think that may be your issue