Logo
FULL SITE MENU

Port side engine won't advance past 1800rpm

J

jclays

Regular Contributor
Took my 1966 Californian out today anticipating a good run on flat seas to "Blow" her out. Got to the end of the jetty and started advancing the throttles. She has twin early carburated 350's. Starboard advanced fine Port side would not advance past 1800/1900 rpm. It felt as if someone was holding the propeller the engine just felt bound up. Pushing the throttle past 1800rpms would only generate a notable resistance and a rumbling/vibration type of sensation. With the transmission out of gear the engine freely rev's as high as you want to push the throttle. Tranny problem? Older Velvet Drive model 71 I believe. Never experienced this before.
 
Is the hull clean and free from marine growth?
Are both props clean and free from marine growth?

Before I go into my usual ignition advance suggestions..... which ignition systems do you have?
Are they using a mechanical advancing mechanism?


As for troubleshooting fuel delivery potentials.... since you have twins, you could swap carburetors and either find or eliminate a problem.
It would cost you only two new base gaskets.


.
 
jclays said:
Hull and props clean. Carbs are Edelbrock marine 600cfm. Ignition Prestolite.
Click to expand...
The old Prestoliltes used mechanical advance!
Once you've set BASE or Initial advance, have you looked further at the progressive and total advance?
Rusty flyweights can prevent the progressive advance from functioning as it should.
If the progressive is not doing what it's supposed be doing, performance will suffer.



.
 
Last edited:
jclays said:
Engine revs fine out of gear. Woundnt I experience this problem regardless?
Click to expand...

The short answer is NO.
I could restrict the progressive advance on most any gasoline engine and yet get it to rev up with no load on it.
However, in order to produce any power while under load, it must see the correct progressive advance and the correct total advance.


Since I'm not aware of your engine build, this is an example only ignition advance curve for a Marine SBC.
Look at the spark advance as engine speed increases.
 

Attachments

  • Ignition advance line graph VP 5.7L .jpg
    Ignition advance line graph VP 5.7L .jpg
    81 KB · Views: 57
Will swap carburetors between port and starboard engines. Will change out fuel filters and check counter weights in the distributor. Test run will have to wait until Sunday.
 
jclays said:
Will swap carburetors between port and starboard engines. Will change out fuel filters and check counter weights in the distributor. Test run will have to wait until Sunday.
Click to expand...
Yes.... great ideas!

Un-solicited Tips:

Change fuel filters after you've started the engines (this ensures that the carburetor bowls will be filled).
Pre-fill the cartridges a bit before installing.
If equipped, remove carburetor body filters and inspect, clean or replace.

Let's go back to this for a minute because apparently I missed this earlier:
Pushing the throttle past 1800rpms would only generate a notable resistance and a rumbling/vibration type of sensation.
Click to expand...
Have you checked for:
Bent or damaged propeller on Port side?
Bent prop shaft on Port side?
Excessive marine growth on propeller Port side?
Line wrapped around Port side propeller?


.
 
I was serious about checking the spark advance. Many are the distributors out there with sticky advance mechanisms.

Jeff
 
fastjeff said:
I was serious about checking the spark advance. Many are the distributors out there with sticky advance mechanisms.
Click to expand...
Jeff, I know that you were serious, and I could not agree more with you.
This is all too often over-looked! We set/adjust BASE advance, and we look no further!


You said: "First, put a timing light on that motor and see if the spark advances with the throttle."
I read that post as though I was inexperienced.
I could invision a guy standing there with his timing light aimed at the timing marks, he then advances the throttle, and nothing happens!
Nothing happened, because he forgot to start the engine! :eek:

(must be my rather odd sense of humor!) :D


.
 
Last edited:
Changed the fuel filters, swapped carbs. Checked distributor. Prestolite electronic no weights. Ready for test run on Sunday.
 
..."Prestolite electronic no weights"

Prestolite electronic distributors have centrifugal advance mechanisms hiding under the magnetic sensor plate--and they LOVE to bind.

Were you expecting GM style advance mechanisms located (and obviously) at the top of the distributor?

Jeff
 
Jclays, Jeff is correct! An old Prestolite ignition distributor will use a mechanically advancing system!
If not, it would require EST technology!

In theory.... (if all is working correctly...... and using random ignition advance numbers of let's say 6* Base/26* TA).... we should be able to move the rotor against the flyweights/return springs up to an angle of approximately 10 degrees.
(26* TA minus 6* base = 20* divided by 2 = 10* of actual rotor advance)

This is a crude method, but it may suggest something to you.
Your true test will be when you strobe your markings as you increase engine speed.


.
 
Swapped carbs between engines. Replace fuel filters. Fair amount of water. Bad gas around here lately. Test run this morning. Ran flawless 2700rpm 23knots, 19 mile round trip run.
 
Back
Top