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AQ131 Restriction Plate and Exhaust Manifold Questions

ebacon

ebacon

Contributing Member
"1) Does anyone know why t

"1) Does anyone know why the AQ131 has what looks like a restriction plate between the single barrel Solex carb and the intake manifold?

2) Have any of you experienced decreased AQ131 performance with the Osco exhaust manifold when compared to the OEM VP part?

My AQ131 lost about 10-15% of its peak RPM when I changed the exhaust manifold and removed the plate from between the carb and intake manifold. I'm just wondering if restoring either of those will get her power back.

Thanks,
Ed"
 
No takers?

How about the pl

No takers?

How about the plate between the carb and the intake manifold. Have any of you at least seen it or removed it? If you removed it did you notice any effect?

Thanks
 
"When trouble shooting, it is

"When trouble shooting, it is almost always best to use the P of E (Process of Elimination....) One item, and One Item ONLY at a time as you go down your check list. Likewise, with what you have just done.

El P would be a good one to help you on this, but mean time, I'd suggest re-installing the plate back as it was and give it another test.

."
 
"Ricardo,

Thanks. I will c

"Ricardo,

Thanks. I will certainly replace the plate and try again.

In the meantime if anyone can provide an explanation of what purpose the plate serves I would appreciate it. That plate has me perplexed.

To me it seems like a power robber. If I put it back in and it improves power then I will be at a loss to explain how or why -- maybe it tunes the intake manifold. ::shrug::"
 
"What's its material of co

"What's its material of construction? If non-metallic, maybe it's an insulator to keep (too much) heat from the carburetor."
 
"El P,

The plate fits in th

"El P,

The plate fits in the position of part 14, but it is P/N 856298 which should be mated with the 856126 carb (see item 1 at the top of the parts list).

Mike,

The plate is formed of stamped steel, about 1/8" thick. It is also labeled such that the flat edge of the D-shaped hole points forward toward cyl. 1.


Next week I will report how the engine performs with the plate reinstalled. El P made a good point in the other thread. Perhaps it generates turbulence."
 
"Well yesterday I tried the en

"Well yesterday I tried the engine with the plate reinstalled. In summary, there was no discernible difference of performance. There may have been a small improvement in low end power, but it was hard to tell because the seas and wind were unusually calm. The boat may have pulled onto plane a little more quickly simple because of the calm weather.

Next I will try and find a used OEM Volvo-Penta exhaust manifold. My hunch is that it flows better than the Osco part. If I recall correctly the OEM part has short exhaust runners whereas the Osco part simply dumps the exhaust ports into a plenum. If anyone has the parts to compare side-by-side I would appreciate their comments and/or photos.

Have a safe holiday weekend!"
 
"Well I tried to get my hands

"Well I tried to get my hands on a few VP exhaust manifolds through Craigslist but the sellers never followed through. ::sigh::

The good news is that I managed to eek a few more HP out of the engine. It ends up that the timing curve on the distributor was a little off as the RPM increased. The timing was perfect at idle, but at full throttle it was about 6 degrees retarded from spec. I advanced the timing to spec at full throttle and it really made a difference. The boat gained about 4MPH.

It's still 2 MPH shy of where it was with the original VP manifold, but good enough."
 
"Ed, thanks for the update. Yo

"Ed, thanks for the update. Your experience confirms how important is to have the distributors checked every few years by a specialized shop, especially when there are performance issues."
 
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