Engines Running Different RPMs
 

Hi Guys,
I have a PQ 290 Enticer with 454 mags. Since I have had it the tachs have read different RPM at similar throttle openings. The port motor will spin to 5050 RPM but the other will only spin 4800 RPM. What could be going on here? The props are identical and have not been damged. Bad sensor/gauge or is this common and just forget about it? Thanks much.

Re: Engines Running Different RPMs
 

switch the props and see if it does the same thing.

Re: Engines Running Different RPMs
 

....or, since they'll be spinning the opposite direction and you'll most likely get a different reading, try switching the gauges. :rolleyes:

Re: Engines Running Different RPMs
 

true, but to eliminate the props, they will still show the different rpm even spinning the opposite direction.

probably not the best approach to diagnose it though
:cool:

Re: Engines Running Different RPMs
 

check you carbs and make sure both carbs are opening all the way.

Re: Engines Running Different RPMs
 

Checked the carbs... both are definatley going wide open throttle... even at part throttle the RPMs are different... so i find myslef trying to keep them at the sam r's rather than the same throttle position...not sure which is better

Re: Engines Running Different RPMs
 

You would need to take the props to a good shop and have them checked to make sure they are identical......i had a set of 23 mirages on my old scarab....had them re-tuned for more pitch....it turns out that all that time before i sent them in, each and evey blade on the props was off!!! They were off by as much as 1 1/2* +/-

See if you can borrow another prop just like yours from a buddy and see if its still not giving you the Rpm's you need...or swap the Tachs and see if it still reads the same...

Re: Engines Running Different RPMs
 

Is there variation all the way through the RPM range, or just at top end?

Is there any chance that the gear ratios are different in the two drives?

Re: Engines Running Different RPMs
 

Don't wast time with your props just yet, you need to get a baseline. Get yourself a Snapon Digital timing light so you can hook it up and read your WOT RPMs. Also, let your ear be your guide, you can hear the difference in RPM if they are that much off.

Then check each plug wire to make sure all cylinders are firing, a different of 300 rpms could be one cylinder down.

If all that is good, then start with props, computer and all that other stuff. Check the simple stuff first. :drink:

Re: Engines Running Different RPMs
 

What if any damage to the power train could happen here? Drives?