701 throttle Power delay ? help ??

[orangefinger]

Hi ,

I am running an odd engine set up for my back up ski and am having a problem with the throttle response and immediate low end power.

Set up is 61x/Pro tec 61x Cylinder, 650 electrics, coffmans pipe, single SBN 44mm , Westcoast head 25cc domes ( 160 PSI ) we are at very high altitude, jetting 1,5 n&S , 95 g spring 120 low, 130 high. Sparks show good ~!

And this is how it goes in tha water...

At full throttle starting out engine needs to catch up to a certain rev/speed ( no low end power ( till NOS point ) and then suddenly like someone flipped a switch and turned NOS on.... the ski has enourmous power ??? the complete upper powerband is very good..just low end feels like caviatation or slipping clutch.

NOTE: No changes to impeller/pump ( all clean no cavitation ) since last stock 701 61x/61x engine.

- POP OFF ??
- POR TEK Cylinder race ported ? not freestyle suitable ?
- Electrical issue ??

Thank you for any serious advice !

Chris

 

[Matt_E]

How high is your altitude?
Have you tried calling Pro-Tec?

It sounds to me like you got a race ported cylinder that needs racegas compression to get pop off the bottom.

 

[orangefinger]

Altitude is 5500 feet....

I think it is the Cylinder, I have tried all sorts of different jetting specs and no change.....sigh

 

[jakew4]

This problem seems like the one I just fixed on my ski. It was the stator. I replaced it and that "slip" or "dead spot" on the low end disappeared. Might want to check that before ripping into your ski.

 

[Big Kahuna]

sounds like a full race cylinder, at the line you have the RPM's already pulled up, then the band pops and your off........... not much bottom end needed, either that or your popoff and jetting is way off on the bottom

 

[orangefinger]

Stator....mmhh didnt hear that one yet...can you explain ??

 

[keefer]

My money is with the theory that you have a race ported cylinder and a relatively high pop off pressure compounding your problem. The high altitude is also not going to help if you are going for bottom end. Try changing to a 80 gram or maybe even a 65 gram spring and see what happens after retuning the carb.

 

[jakew4]

Stator....mmhh didnt hear that one yet...can you explain ??

My Bendix broke a while back and the shattered pieces tumbled around in the flywheel. During that it damaged the stator, without me seeing the damage. I replaced the bendix, and had the same problem that you are describing (at least I think that what I'm getting from you). Anyways, with troubleshooting and replacing a new flywheel, whole electrical, new carb, and fuel lines, I found that a new stator fixed the problem. I completely got rid of the stutter at the beginning of gripping a handful of throttle. Now it just snaps me back hard, like it should. Might want to check to see if it is damaged in any way. Or check to see if water is getting in through your flywheel cover and disturbing your electrical activity.

I'm not the best with skiis, but have spent the last month diagnosing my problem and yours sounds similar.

Hope this can help in any way.

-Jake

 

[Crab]

Cross had one ported for top end, total dog down low.

 

[keefer]

It is true that a damaged charge coil or pulse coil on the stator can cause the CDI to either not get the proper operating voltage or a flaky pulse. If you want to go to the trouble of ohming it out the you can. I would say that lowering the pop off pressure would be easier. I still say that the race ported cyl is your biggest suspect right now.

 

[Matt_E]

You're getting 160psi on 25cc domes. Even at 5500 ft, that seems indicative of pretty severe race porting.

 

[DaUpJetSkier]

kinda random, had a similar problem last season, take a look at your internal fuel filter in the carb.

 

[orangefinger]

Stator >> The ski is not stuttering, powerband is even just not explosive
Pop-off >> 95 g might be to high will try 65 g or 80 g might help a little
Compression >> was horrible to begin with, * dont forget the 7cc for the headgasket 32cc total, I have to run 30cc for 180 PSI on my other freestyle skis...
Internal and external fuel filters clean >>

My guess race ported cylinder....

QUESTIONS : - once race ported can it be reverted ?

Thank you everyone for all the help !

 

[Matt_E]

Cannot be reverted. Those Pro-Tecs are said to be a race cylinder anyways.

 

[keefer]

I guess you are going to have to get that compression up to 180+ to get it to run better. Maybe a .010 base gasket would help a little, if you can find one.

 

[kevbo]

What prop and nozzle do you have?