Bogging out at 3500 rpms

[mkbat]

Hello peoples, I have a mercruiser 3.0 alpha 1. She's been running nice this summer until this week. Once I get up to around 3000 rpms or more for 30 seconds it starts to act as if I were running out of gas or coming off the throttle. If I throttle down to about 2000 rpms it runs fine again. Idles beautifully, great for no wake zones but once I get on her it will maintain for about 30 seconds and then starts bogging down again.
I have an in-line fuel/water seperator, have cleaned out the filters at the carb and the bowl on the pump. Even replaced the fuel line in case it was collapsing. Thanks for your time.

 

[Bondo]

Re: Bogging out at 3500 rpms

I have an in-line fuel/water seperator, have cleaned out the filters at the carb and the bowl on the pump. Even replaced the fuel line in case it was collapsing.

Ayuh,.... Did you find any Crap anywhere,..??..??

Did you pull,+ clean the Anti-siphon Valve at the top of the fueltank,..??

 

[mkbat]

Re: Bogging out at 3500 rpms

Yes Sir!!. Some sandy looking particles in the carb filter and a bunch of crap in the bottom of the pump. Looked like rust color junk.
No I have not pulled and cleaned the anti-siphon valve. Is that part of the intake or is it a different part on the top of the tank?
And thanks for the reply!!!

mkbat

 

[mkbat]

Re: Bogging out at 3500 rpms

Mr. Bond-o. I figured out where the anti-siphon is. I did pull that piece. I thought it was just an elbow with the barbed fitting attached. There are no screens or anything that I could see. Should there be something more to this than just an elbow? Thanks

 

[Bondo]

Re: Bogging out at 3500 rpms

Ayuh,...

Usually it's a ball,+ spring Check-valve......Aluminum housing....
There's also Sometimes a small screen on the bottom of the in-tank pickup tube......
The otherside of the same elbow.....

 

[ml8163]

Re: Bogging out at 3500 rpms

mkbat - I have the same exact problem that you have on the same engine. I will try the same as well to see if it fixes the problem. Do you see the problem immediately after you leave the no wake zone from the boat launch, or a little while later afte the engine is good and warm? For me, it is after the engine is good and warm. Also, once while I was out, I had two extra adults in the boat then normal and the boat/engine ran flawlessly at full throttle. Not sure if this was a coinsidence or if having the engine under greater load changed something???

 

[mkbat]

Re: Bogging out at 3500 rpms

Thank you Bond-o. I will see if I can get the part from the merc dealer tomorrow. Or I guess any Marine Shop might have that.
I double checked and it definitely is just an ordinary elbow and no screens either. I will replace and let you know.

I went out just about a half an hour ago and tried leaving the gas cap off like some other threads have mentioned.
Once again it ran fantabulous out the no wake zone (4 minutes) and then up to 4200 (planed out) for about 4 minutes and once again it sounded like it was starving for gas. Slow down to 2000 rpms and runs great.

Ml8163, I had extra bodies in it this weekend and it was a nightmare. No power and extra weight. Quite emberassing!! But I think Bond-o is on to something with the anti-siphon.

Thanks very much!!

 

[ml8163]

Re: Bogging out at 3500 rpms

The extra load must have been a coinsidence then and not a variable to the problem.

I just pulled the anti-siphon valve on mine and from visual inspection, all looks good. I rinsed it out with a little bit of water, blew it out with the air compressor, and made sure the spring loaded ball was working properly. I didn't notice any obstructions or debree. I've re-installed it and will take it out tomorrow and see if there is any difference.

Check out this thread as well, it might be helpful...

http://forums.iboats.com/showthread.php?t=261613&highlight=anti-siphon

Thanks,
ml8163

 

[ml8163]

Re: Bogging out at 3500 rpms

I figured it out! The flame arrestor was extremely dirty and caked in grease/oil from the crankcase ventilation hose, which was not allowing it to breath. While trouble shooting out on the lake I found that if I took the flame arrestor off, the boat ran perfect at wide open throttle. So, I cleaned it in some mineral spirits today and it looks brand new. I'll lake test it this weekend.

Something to think about...