Mercruiser 150 inline 6 . 235 ci

[CaptRon66]

I think I have a fuel problem. Boat gets out of the hole fine and then attains wot of 3700 , runs great for 12 seconds and then bogs to 3200 at wot and maintains that rpm . (gauge reads low by approx 200 rpm when compared to more accurate gauge). Idle for a minute and try the same thing with same results. Replaced fuel separator , pump filter and carb filter . Still have the same problem. I was thinking of running on a remote fuel tank to help isolate the problem. Can the mechanical fuel pump cause a lean condition at wot ? Is it the carb ? Am I on the right track?

 

[CaptRon66]

Re: Mercruiser 150 inline 6 . 235 ci

Oops...Mercruiser 150 is 230 ci

 

[Fishermark]

Re: Mercruiser 150 inline 6 . 235 ci

I was thinking of running on a remote fuel tank to help isolate the problem.

Sounds like a good plan. If it solves the problem it will certainly help discover the cause. Could be a number of things from a partially clogged tank vent... to the anti-siphon valve.... etc.

 

[CaptRon66]

Re: Mercruiser 150 inline 6 . 235 ci

Had some time the last 2 days. Did a tune up. Cap,rotor,condenser, and points. Set timing at 6 degrees btdc. Checked to make sure distributor was advancing. Did not compare to curve or max. Ran the boat on a remote fuel tank and the same thing. Had some parts that came off a good running Mercruiser 165 with a leaky block(cracked). Swapped out the coil, fuel pump and carburetor 1 at a time and ran with the same results. Engine acts consistent. Gets up to 3700 rpm surges a little then bogs down 400-500 rpm. Engine has good power out of the hole. The surge/bog begins after about 12 seconds. Compression test after warmed up on cyl 2-5 is between 145 and 150. Cyl 1 is low at 110. What could it be? Burnt valve? What else could be checked?

 

[CaptRon66]

Re: Mercruiser 150 inline 6 . 235 ci

Had some time the last 2 days. Did a tune up. Cap,rotor,condenser, and points. Set timing at 6 degrees btdc. Checked to make sure distributor was advancing. Did not compare to curve or max. Ran the boat on a remote fuel tank and the same thing. Had some parts that came off a good running Mercruiser 165 with a leaky block(cracked). Swapped out the coil, fuel pump and carburetor 1 at a time and ran with the same results. Engine acts consistent. Gets up to 3700 rpm surges a little then bogs down 400-500 rpm. Engine has good power out of the hole. The surge/bog begins after about 12 seconds. Compression test after warmed up on cyl 2-5 is between 145 and 150. Cyl 1 is low at 110. What could it be? Burnt valve? What else could be checked?

 

[Silvertip]

Re: Mercruiser 150 inline 6 . 235 ci

Low compression on one cylinder can be leaky valve, valve lifter adjusted too tight, worn rings, leaky head gasket although that would generally drop compression lower. A bad lobe on the camshaft can cause loss or high end rpm as would a worn bushing in the distributor. Put a dwell meter on the engine and blip the throttle. If dwell changes more that one degree you have bouncy points or a worn distributor. Install a vacuum gauge and check idle and WOT vacuum. Low vacuum at idle means there is an intake leak somewhere (possibly due to a leaky intake valve). Just a few things to consider.