older carburetated mercruiser 5.7 hard start

brian3127 · Monday at 6:01 AM

Rochester quadrajet carb.
How many pumps do you give your engine at the throttle to get it started.
I put a spark tester on the engine and the spark wasn't very good so I took the cap off and this is what I found. I ordered a new pickup. I cant get a serial number off the engine it is very tight in the engine compartment.

kenny nunez · Monday at 7:31 AM

With a volt meter on the + side of the coil crank the engine over. You should read 11-12 volts. If it is much lower then the “by pass” circuit from the outer connector on the starter solenoid is the problem.
To further prove out the problem run a jumper wire directly from the + battery to the + side of the coil. If the engine starts easier then the fault is the starter solenoid.

brian3127 · Monday at 7:39 AM

kenny nunez said:
With a volt meter on the + side of the coil crank the engine over. You should read 11-12 volts. If it is much lower then the “by pass” circuit from the outer connector on the starter solenoid is the problem.
To further prove out the problem run a jumper wire directly from the + battery to the + side of the coil. If the engine starts easier then the fault is the starter solenoid.

having trouble understanding, what the starter solenoid has to do with the hard starting. then engine turns over just fine

kenny nunez · Monday at 11:12 AM

When the key is turned and the starter is engaged there is no or very little voltage at the + side of the coil provided from the ignition switch, that is the purpose of the ”by pass” circuit on the starter solenoid to provide voltage at the coil.
Just check the coil to make sure there is 12 volts provided in cranking mode.

brian3127 · Monday at 12:20 PM

kenny nunez said:
When the key is turned and the starter is engaged there is no or very little voltage at the + side of the coil provided from the ignition switch, that is the purpose of the ”by pass” circuit on the starter solenoid to provide voltage at the coil.
Just check the coil to make sure there is 12 volts provided in cranking mode.

ok thanks.

tango13 · Monday at 1:33 PM

my carbed 7.4 w/ TB V ignition was having starting issues (cold and hot), and my pickup looked the exact same.

I swapped out the sensor, cap/rotor, wires, and COIL and it mad a world of difference. Everyone will tell you that the coils never fail but I can tell you that the coil was the last component i changed and my hot start problems essentially went away.

brian3127 · Tuesday at 4:25 AM

tango13 said:
my carbed 7.4 w/ TB V ignition was having starting issues (cold and hot), and my pickup looked the exact same.

I swapped out the sensor, cap/rotor, wires, and COIL and it mad a world of difference. Everyone will tell you that the coils never fail but I can tell you that the coil was the last component i changed and my hot start problems essentially went away.

i bought a new coil when i got the pickup coil too. so when i get a chance i will replace the parts on the motor.

tango13 · Tuesday at 12:50 PM

brian3127 said:
i bought a new coil when i got the pickup coil too. so when i get a chance i will replace the parts on the motor.

assuming your cap and rotor havent been changed, i would do them too

brian3127 · Wednesday at 4:25 AM

tango13 said:
assuming your cap and rotor havent been changed, i would do them too

ok

brian3127 · 2025-06-26T04:29:48-0600

Went to the boat today to replace the pickup and coil. the engine wouldn't start. didn't have a helper to man the key to test the bypass circuit. hopefully it doesnt rain and i can find a helper.

brian3127 · 2025-06-26T04:53:41-0600

Is the starter solenoid built into the starter or is it a seperate part.

Lou C · 2025-06-26T05:07:39-0600

It’s bolted to the starter with 2 bolts.

brian3127 · 2025-06-26T05:14:28-0600

Lou C said:
It’s bolted to the starter with 2 bolts.

That is not what i wanted to hear, but its better than being fully attached to the starter. It will not be fun to get to it. The engine compartment is tight. Hopefully its not bad

cyclops222 · 2025-06-26T05:28:41-0600

REMOVE the cable or cables on ONLY 1 of the battery terminal posts !! Prevent SPARKS !!!!!!!

Tape ALL the disconnected cable & any smaller wires together............ So 1 not accidently slip away and then cause you a ........This does not work now problem. Good Luck

kenny nunez · 2025-06-26T10:16:33-0600

The 2 bolts that mount the solenoid could be 3/8” or phillips head or even 5/16”, hopefully not torx. The copper lead at the bottom of the solenoid going into the starter housing is 5/16“ hex. After the bolts and wires are remove rotate the solenoid 90* to remove it.
Good luck.

tango13 · 2025-06-26T11:12:22-0600

Wouldnt crank or wouldnt fire?

If you swapped the coil, hopefully it was the correct resistance and wires were put back in the correct way, same with the sensor.

Lou C · 2025-06-26T11:41:06-0600

brian3127 said:
That is not what i wanted to hear, but its better than being fully attached to the starter. It will not be fun to get to it. The engine compartment is tight. Hopefully its not bad

In some cases I guess you might be able to get it off the starter without removing it, but you'll just have to do what you have to do to get in there. On my boat I remove the driver side of the rear seat and the wood partitions and then slide the battery backwards and I can get at it.

Looks like fun, eh?

brian3127 · 2025-06-26T12:18:10-0600

tango13 said:
Wouldnt crank or wouldnt fire?

If you swapped the coil, hopefully it was the correct resistance and wires were put back in the correct way, same with the sensor.

wouldnt fire

brian3127 · 2025-06-26T12:20:24-0600

Lou C said:
In some cases I guess you might be able to get it off the starter without removing it, but you'll just have to do what you have to do to get in there. On my boat I remove the driver side of the rear seat and the wood partitions and then slide the battery backwards and I can get at it.
View attachment 409039
Looks like fun, eh?
View attachment 409040

I have dual engines and there is about a foot of space between them

tango13 · 2025-06-26T12:29:44-0600

brian3127 said:
wouldnt fire

Double check your connections on the sensor and the coil. If you still have no spark, put your old coil back on and test. The TB ignitions use a low resistance coil and i found it almost impossible to find the resistance ratings on any amazon/part store coil without testing. I used an MSD 8222 blaster coil because they advertise the primary resistance (0.7ohms), which will work on the TB ignition.

If all else fails, use the TB ignition troubleshoot guide.

older carburetated mercruiser 5.7 hard start

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