Engine Won’t Accelerate

[mestrezat]

A friend has a sailboat with a Perkin engine. Just replaced the transmission. Now when the engine is in gear, it will only accelerate so far and no farther . If in neutral, it accelerates just fine, just not when it’s in gear.
Thoughts?

[StuM]

A different gearbox? If so - gear ratio?

Alternatively, is it the same prop?

[jimbunyard]

If they have a single lever control, could also possibly be a control adjustment or hook up issue.

[mestrezat]

From what I’ve been told, it is the same gear ratio as the old one. They went to the accelerator lever on the engine and when in neutral, it revs up fine but if they put it in gear, it won’t get faster than a certain level of thrust and revs, about 2/3 power. Prop was checked and cleaned so that wasn’t the problem. I’m not with them so I have not seen it in action.
They have read on the internet that it could be the fuel,an algae bloom so they are just sure it is that but if it revs fine in neutral, and it was caused by the “bloom”it shouldn’t rev fine in either case. They changed out all their fuel filters and they are nice and clean after checking the engine and changing them anyhow. Tthe “mechanics” where they are anchored have no clue.

[shakey doug]

Have to generalize without Model Number.
1. Lift pump filter screen. 2. Fuel pump inlet fitting screen. 3. Stop lever not moving to full run position. 4. Throttle lever not moving to 100%. 5. Fuel system requires bleeding. 6. Restricted air intake. 7. Restricted exhaust plumbing. 8. Chocked mixer/ Manifold. 9. Loaded auxiliary drives. Vessel needs to be free running other wise max Rpm can be reduced by up to 20%. All of the above listed, can be indicative of described problem. All easy and cost free.

[jimbunyard]

If everything about the engine remained the same, and it operated correctly before, the first place to check is the connection of the shift cable at both the control and the shift arm on the transmission. There are usually at least two positions on both, and having them in the wrong place can limit the travel of the throttle, though, as far as I know, this is only valid for single lever controls. Why was the gear replaced? More information will probably help...

[sailorboy1]

check/replace the fuel filters!!!!!!!!

[Wotname]

Possibly a fouled prop if it has been some time between removing the old transmission and fitting the new one.

[Lepke]

If the engine was fine before and nothing changed on the engine then the problem is either the cable or the transmission gear ratio.
If a new alignment wasn't done, then it could be a binding condition between the shaft and stern bearing.
With the engine off, put the control full forward. Go look at the stop lever and verify it's full throttle. If necessary remove the cable and move the lever by hand.
Check the shaft alignment.

[sailorboy1]

It runs to full rpm in idle, it not a cable! It’s a fuel problem.

[mestrezat]

I’m here in Mazatlan and motored over to the fuel dock at the marina only to run aground in the mud bottom. I put the engine in reverse and the bow slowly pulled around to port. I put it in forward and we stayed in the mud. I put the engine in reverse again and pushed the throttle forward and the rpms never got above 1500 no matter when I did. I tried in forward with the same response-only would go up to 1500. Top rpms are 2500. Once we got free and we’re moving forward, the rpms went up as high as I could move the throttle with no problem, bot in forward and reverse. Why wouldn’t it do the same when stuck and does this have any bearing on my friends boat?

[Wotname]

Originally Posted by sailorboy1

It runs to full rpm in idle, it not a cable! It’s a fuel problem.

If it runs to full RPM in idle, you have way more problems than fuel. Image what will happen if you open the throttle

[Jason Flare]

I read somewhere, (Probably here at CF,) that the throttle is not connected to the fuel rack but is instead connected to the governor.

Could this be making a difference?