97 GTX low on RPM

[cloudmaster_321]

Last year, final test run before winter lay up, ran 7k rpm, approximately 52mph indicated @ 50 degrees out.

This spring, after working some bugs and changing some parts, not getting the same results. I was indicating 6,600 rpm's 52mph indicated @ 75 degrees.

Things I changed this spring:

1. Removed beach house sponsons and installed new OE sponsons
2. Replaced stator with a new OE, and connector replaced (fixed charging issue)
3. Replaced Oil tank with new (fixed oil leak)
4. Unbolted carbs, reset my needles after futzing with them last year to try and figure out my large under rpm issue (turned out to be exhaust hose)

- Low needles set to 1 turn out​

-High needle 0 out on mag, 1/2 turn out on pto (1997 service manual says 0 out for both high needles)​

5. Rerouted pisser to front starboard side so i can see it when running vs out the back. Used 1/4" line and fitting. The route is twice as long as OE. The outlet is 1/4" vs the small 1/8" hole or less out the back. (possibly less backpressure?)

Seems I was approximately 300 rpm's short yesterday. Indicated speed seemed about right though.

​

 

[cloudmaster_321]

Had the ski out last night. Started good cold with choke. Idled around 1,500-1,600 in the water. Initially had decent response from idle. After running the ski for awhile, i'd get an interittent hesitation when pinning it from idle. I tried some choke, i think it helped the low end if i held it out about 1/4", but hard to tell. Seemed if i just came down to idle, and then pinned it, it was fine. Just if i sat at idle for awhile. I'd say it's loading up, but it doesn't feel like a rich hesitation. Also, top rpm's are still around 6,500. A little boggy getting there too. The other thing i noticed, is after getting run for awhile, and having the engine shut off, it would take some throttle to get the engine to fire back off. I couldn't just hit the start button, it wouldn't fire enough to stay running without some throttle. Once it starts, idles like normal. I did some plug checks last night at half throttle and full throttle. I'll attach the pictures. The picture of the plugs together are from the 1/2 throttle test. The pictures of them separately are from the full throttle test. I feel the mag side is slightly lighter than the pto. Currently 1 turn out on the low speed needles, and 0 mag, 1/2 pto high speed needle. I'm considering opening the low speed needles up a bit too. Texted with 2stroke smoke, and his suggestion was to go to 1.5 turns out on the low speed needle, and opening the high speed needles 1/2 turn. I think that concensus is partially due to the fact my compressions are high for some reason. 170/175. Don't know the reason for that, as my Matco gauge seems to read correct on everything else i own. Not sure what the PO did with this engine.

Thoughts?

 

[mikidymac]

You can't hurt anything going richer.
Open the screws and see if it gets better or worse.

 

[cloudmaster_321]

You can't hurt anything going richer.
Open the screws and see if it gets better or worse.

agreed, i'll give it a shot and see what happens

 

[DaddyLoafin]

If you trust your gauge and the compression is higher, are you running higher octane fuel?

 

[cloudmaster_321]

If you trust your gauge and the compression is higher, are you running higher octane fuel?

I've been running 91 no ethanol

 

[DaddyLoafin]

I've been running 91 no ethanol

was just checking. i rebuilt my 787 over winter and had the head cut so it was on my mind lol

 

[cloudmaster_321]

was just checking. i rebuilt my 787 over winter and had the head cut so it was on my mind lol

what are your compression numbers after your rebuild with cut head?

 

[DaddyLoafin]

I haven't checked yet. I've been busy and am still breaking in the engine. Hopefully I can get it done this weekend and ill let you know.