87 DT 140 will not run above 2400 RPMS

[svilla]

OK I know there is an easy answer here that I just can not see. Here is the motor info and trouble shooting steps so far;

1987 DT 140, I have cleaned and rebuilt all carbs, I have replaced the fuel pump and filter.

Boat runs great on the hose, idiles fine in the water, and reves freely in nutral.

as soon as I drop the throttle over the gate she wants to stall. I can keep her running by bumping the throttle. Runs fine at 1500 RPMS.

Once I get her out and push to full throttle the boat will not reve over 2400 RPMS, mostly has problems getting 2000 much less 2400 RPMS.

I tried squizing the primer bulb when under way at 2000 RPMS, the bulb is hard to fill and some times remains flat unless I mess with it, force it back into shape. No noticable change to the RPMS.

I also removed the tank vent hose under way to see if this changed anything. No Joy.

I did not have any premix in a squirt bottle or spare gas tank for futher trouble shooting.

I guess the most logical step to me is, spare known good fuel tank and a bottle of pre-mix.


I there anything else I can check with the boat at home on the hose? I would hate to have to paddle back into the dock.

 

[CmaC1019]

Re: 87 DT 140 will not run above 2400 RPMS

I had the same problem on my dt200 except it wouldnt go over 3000 rpm. I cleaned the carbs and it starting working great. im not sure about the 140 but the 200 has dual throat carbs so there a two jets in the bowl, i missed the 2nd one the first time and there inlied my problem. if that doesnt work check to see if your running on all cylinders, while the engine is running pull the spark plug wires out one at a time (be carefull not to shock yourself, 18000 volts hurts!) if the engine shakes and almost stalls out then that cylinder is ok. if there is no change then that cylinder isnt firing.
good luck

 

[svilla]

Re: 87 DT 140 will not run above 2400 RPMS

I will give that a shot, thank you.

Anyone else have any trouble shooting tips? I am a old C-130 Crew Chief, if it wuz a Herc I would have this bad boy runnin right.

 

[cousinabe]

Re: 87 DT 140 will not run above 2400 RPMS

sure sounds like a fuel restriction from the primer ball back.
do you have a filter between the ball and the tank?
antisiphon valve problem
fuel tank pickup tube problem
i'm assuming your tank vent is good.

definitely try with an auxiliary fuel tank.

 

[James R]

Re: 87 DT 140 will not run above 2400 RPMS

The suggestions so far are very sound. If one cylinder out of four is not functioning then you will have these results. Check the compressions. If one is down badly you have the answer. Try pulling the plug wires one at a time whilst the motor is running and look for the cylinder that makes no difference in running speed. Could be just a plug problem.
In any event a compression check may tell the story.

 

[svilla]

Re: 87 DT 140 will not run above 2400 RPMS

My compresion is ok and with in 10 on all four cylinders, but get this the top two cylinders are not running. Good Spark ( I got zapped ) so off with the top two carbs to be cleaned and looked over.