Lehman Fuel Starvation

I have a DeFever 49 RPH with twin Lehman 135s. Took it for a weekend cruise - only about 30nm each way. On the way back I was having problems with the starboard engine. It would run fine at lower RPM (less than about 1400 RPM) but when I ran the RPM up to between 1600 - 2000 it would run fine for awhile and then bog way down like it was starved for fuel. If I did nothing it would die and then I could restart it. If I grabbed the throttle and pulled way back and worked it up slowly it would come back up to speed and run fine for 15 - 30 minutes and then do it again. Got back to the marina last night and had to drive home for an out of town trip this week so I did not have time to change any filters. I ruled out bad fuel because both engines were drawing from the same tank and I polish it regularly and the port engine was fine. My suspicion is a clogged primary and/or secondary filter or maybe faulty racor ball valve but I thought it could also be fuel pump or injectors. I wanted to check here for input before I made the decision to call a mechanic.

Thanks in advance for any advice or thoughts.

Mike S.

Greetings,
Welcome aboard. Check your fuel supply hose if rubber. As I have mentioned several times I had a problem quite similar to yours and cause was delamination of innermost liner of rubber fuel hose which was sucked closed under lift pump vacuum. OK at lower RPM.

All the time start simple....though we all jump to the worst case scenario because of money calculations...

RTF makes a good point....after filter changes, hose inspections are in order...replace even if you cant find anything and they are more than 5 years old or so. Cheap enough.

Also check you fuel pump (I bought an electric pump just in case and just need some adapters for testing or long term install)....but if you can manually prime your injector pump...it should be OK. You can also rig a fuel source that gravity feeds your injection pump if you don't want to mess with an electric pump.

What RTF said. I had that problem also and changed both the lift pump and flex line.

Lift pumps are a common point of failure. Many who log high miles carry a spare or convert to electric, or both.

Thanks very much for the feedback. I will go back to the boat later next week and will definitely change the filters. I am going to also order a lift pump from American Diesel to have one as a spare or in case. Most of the fuel lines are copper - I know for sure to and from the racor but it might transition to fuel hose before the lift pump. I wiill look at some pics I have around the engines and if it does I will bring some of that with me also. Brian at American Diesel can probably tell me if its fuel hose anywhere.

Mike S.

I had exactly the same symptoms as you on my STB FL135 and a primary filter change fixed it.

Ken