Stroked311

I have a 87 formula Sr1 with twin 420hp 454s. All of a sudden I'm having a rpm issue. At full throttle my starboard motor is at 5100 rpms and my port side is at 3800- 3900 rpms. Let go of the wheel it pulls to the left a little. If I match them at 4000 it's laser straight. I checked my throttle cables seems to be getting wide open throttle. Boat still runs like a raped ape! Any ideas what's going on

Mr Maine

If wide open on the port side is 38-3900, how do you get it to 4k to match them?
What is the top speed?
Sounds like the port motor is having issues, maybe a tune up and compression check to start

dereknkathy

does it surge like lack of fuel? if so, check the little sock in the tank at bottom of pickup tube. otherwise, back to basics. timing, compression, carb...

Stroked311

Both motors run smooth no fuel surge. When I match the rpms they run great. They idol the same up to a 2000 rpms after that they chance. I just talked to my engine guy he is thinking the carb on the port motor isn't opening the secondaries so I gonna check that

dereknkathy

Could do it. So could lose g spark advance. What distribs? T-bolt 4? If so unlikely. They either run perfect or quit altogether...usually.

mcollinstn

I'm confused.
If wide open throttle results in 3800-3900 rpm on your port motor, then HOW are you matching the revs at 4,000 ?
Are you having MadMax spit nitro down the carb throat?

Help ME understand YOU.

m

Stroked311

It's a mistake I should have put 3900. Either way I match the motors to the rpm so they both rpm the same.

SB

iTrader: (1)

In bold and underline....so your top speed has remained the same since the port motor used to rev at that 5000-5100rpm and now the 3800-3900rpm ?

Stroked311

Yes pretty much. i found the problem rpm gauge is going bad

mcollinstn

Okay, first the boat pulled to one side while tachs showed 3900 port and 5100 stbd yet top speed was no slower than before?
And boat tracked straight when both motors showed 3900.
Am I correct?

But now a bad tachometer is suspected?

How about this..
Run the port motor up to 3700 (slightly less than wide open) and bring the stbd motor up to 3600.
THEN, begin slowly increasing engine speed on the stbd motor while leaving the port motor at 3600.
At some point, you will HEAR the engines get closer to synchronization. The cyclic "pulsation" of the exhaust note will slow more and more until it stops cycling as you increase stbd engine speed. When you go past that point, the cycling will slowly start up again and get faster with more revs. Slow back down until you FIND the spot again where the exhaust note STOPS cycling. THAT is when both motors are spinning the same speed.

If the tachs show something different, then at least one of them is incorrect.

M