Lack of RPM’s in Gear (with video)

[yeahjohn]

Hey friends.

I’m back after some time. It has been a good run of three years with limited issues. That ended. Everything had been working great. We sail twice a week with no issues. Last month we went to start the engine and it had a lack of power in gear. It will not go above 1000 rpm. I guessed main jet and rebuilt the carb. I am no stranger to the carb and it looked great inside. New filters and water separator. New plugs etc. no changes in compression. We are around 80 on 1, 2, and 4 and at 70 on 3. Nothing new for us their. From listening to the engine it sounds like it’s and air issue. Like it’s air starved. What do you think? Thanks!

[YOUTUBE]https://youtu.be/UAuGmXKRtek[/YOUTUBE]

[Dave Neptune]

How is your fuel pressure? Could easily be filters. Also be sure the C-advance is working.

Dave Neptune

[yeahjohn]

Hey Dave! No clue on fuel pressure. I took off house and it’s pumping out gas as normal. Also the problem happened before I cleaned carb and filters. Thanks for the quick response!


John

[zellerj]

prop clean

Don't have to worry about this in Lake Erie, but in CA, that could be the culprit.

[JOHN COOKSON]

Hey friends.
. From listening to the engine it sounds like it’s and air issue. Like it’s air starved. What do you think? Thanks!
[YOUTUBE]https://youtu.be/UAuGmXKRtek[/YOUTUBE]

Since you think it might be an "air issue" is the choke all the way open and is the back flame arrestor clean?
+1 on the fuel pressure gauge.

TRUE GRIT

[sastanley]

Once it is running, there should be little danger/risk in removing the flame arrestor to check both conditions John is talking about. I think you could even loosen the clamp screw prior to start up and easily rock the flame arrestor off to inspect the choke butterfly, and also you'll eliminate the arrestor from the air flow at the same time. Don't run it like this forever, the flame arrestor is there for a reason, but if the engine is running I think it is OK for testing for a few/several minutes while monitoring.

[ndutton]

All good suggestions. My first thought was to get someone over the side and check the prop for fouling and not limited to growth. You may have picked up any sort of debris in your sailing area, plastic bag, kelp, lobster pot warp, who knows?

My second thought Dave already mentioned. Check the advance flyweights for smooth operation and springs intact. When was the last time they were lubed?

A third thought, how warm/hot is the stuffing box underway?

Maybe exhaust restriction? Just guessing.

[sastanley]

I was also thinking the weights, but my personal experience with the weights being stuck is that the engine will run great at WOT, but will try to stall as soon as you throttle down. This depends on where they are stuck..stuck closed..runs like crap except at low throttle..stuck open..only runs good at WOT.

I recall on the VHF to the dockmaster in Cambridge one day, "I am having some motor trouble, it only runs at WOT....do not be alarmed, I'll be coming in hot.."

[yeahjohn]

Thanks guys!
-ran the same with flame arrestor on or off
-choke is open. Closing it kills the engine
-new packing very lose and dripping
-ran with fuel fill open and closed
-new plugs
-exhaust system updated last year

-haven’t check timing
-don’t know what advanced weights are :/
-the engine the same from fuel mixture screw fully in to about a turn out then got progressively worse.

Fuel pump and prop are suspect. When I changed my filter and water separator I feel like the fuel pump took an abnormally long time to get fuel flowing. Like 10min. Then once all the air was out it seemed fine. It could be working at a lower the desired pressure?

The feeling I have had from the begging is the main jet. The carb never seems to transition from idle to primary.

Thanks again!
John

[JOHN COOKSON]

Fuel pump and prop are suspect. When I changed my filter and water separator I feel like the fuel pump took an abnormally long time to get fuel flowing. Like 10min. Then once all the air was out it seemed fine. It could be working at a lower the desired pressure? (YES)
Thanks again!
John

You could have had a blockage in the tank that became a partial blockage Or a blockage at a filter or a weak fuel pump or a carb problem or,or,or ???
Try running off an auxiliary tank. You will find out if there is a tank problem or possibly something after the tank is at fault.
A fuel pressure gauge would tell you if adequate fuel is being delivered to the carb.

TRUE GRIT

[Marian Claire]

Have you checked for air leaks down stream of the venturi? Carb to manifold connection, throttle shaft. Air leak/less suction/less fuel/less RPM.
Dan S/V Marian Claire

[yeahjohn]

Follow up post of shame...

Problem solved. Prop had build up on it. Apparently the diver hadn’t been cleaning the prop. I now have a new diver!

Now we have tons of power and the engine is freshly serviced. Thanks guys!

John

[sastanley]

Yep...that will do it. Although a little slime slows down the boat, I mind it less than a dirty prop. If I have to pick one, I'd pick a clean prop and slimey bottom any day.
The A4 is not happy with our heavy boats with just the least bit of growth on the prop.

[joe_db]

Do you have a vacuum gauge?
It is fairly obvious when the prop is fouled when you see the manifold pressure go to 0 at low RPMs.
As for your other idea about fuel feed, I have a fuel pressure gauge and I can tell you the engine is not particular about pressure. As long as the pressure is >0, it runs fine. You won't get a gradual loss of power, if the fuel feed is inadequate it will lean out and probably quit or barely run. You can get a situation with the fuel feed barely keeping up where a sudden increase in throttle can cause it to stumble or quit.

[zellerj]

Advanced weights

To answer your question posed in post #9...

You will find the timing advanced weights under the distributor plate upon which the points or electronic ignition are mounted. Easy to remove the plate. If you haven't gotten into your distributor in a while, it is worthwhile to take off the plate and clean and oil the advanced fly weights. This helps the engine stay in proper timing as the RPMs increase. Takes about 10 minutes to do.