Forward/Reverse Power?

[george_barringer]

This A4 starts reasonably quickly with a bit of choke then when warmed up and choke off will respond normally to throttle when in neutral from idle up to "redline" (no tach.) and back without pause or stumbling. Develops normal power and usable (normal) rpm in reverse. The trouble is that when put in forward, I can get the engine off idle a few hundred rpm or about a quarter of available throttle and corresponding power but no more. This engine has clean fuel, new filters, clean carburetor, electronic fuel pump, new plugs.

So - power in reverse, no power in forward. I thinking the problem is in the reversing gear only because I can't think of an engine related issue that is consistent with symptoms. Perhaps the brake band is not releasing fully when in neutral or forward? I'm not getting the typical audible signature of the reversing gear in reverse. There is a noticeable neutral band in the shifting lever. Any ideas?

[roadnsky]

George-
Welcome to the forum!

Please check out this FAQ (#15) from Don...

[george_barringer]

Thanks Jerry -

I looked at the FAQ. That all makes sense and will check the plugs etc.

However, the difference in rpm (power?) between forward and reverse is much more than 25%. It can reach a maximum in reverse but only a few hundred rpm above neutral in forward. Much more difference than I would expect for 1.27:1.

Engine has been in the boat and operating ok since last major maintenance a few years ago. The exhaust riser was changed out last summer but I would think if that were the cause then it would affect forward and reverse equally when the gear ratios are taken into account?

[roadnsky]

...The exhaust riser was changed out last summer but I would think if that were the cause then it would affect forward and reverse equally when the gear ratios are taken into account?

Exhaust "back Pressure" could in fact result in your symptom.
I'm not saying it IS your issue, but is worth checking and fairly easy to do so.

Give this thread a gander.
Besides addressing the exhaust there are some other good suggestions and checklists that would apply to you.
See what you think...

[tenders]

Exhaust back pressure was the first thing that came to my mind, too. If you replaced the riser last year, did you replace the hose too? That can collapse from the inside with zero external evidence.