Need serious help with 701...real Pro's help

[orangefinger]

Hi ,

I had a thread a while ago about a ported 701 protec and now I am back, finally got arround to rebuilt the engine and here is whats going on.( ELEV 5500 feet ! ).

- 701 Protec cylinder, new bore & hone, 82,0mm 135 PSI on both.( in my opinion still to low, I want higher compression therefor
- Pro tec head >> will have to be replaced I assume.ANY HIGH COMPR HEADS I WILL PAYPAL IMMEDIATLY !
- Coffmans exhaust
- 44mm SBN ( i have several carbs with different jettings ).
>> ALL FUEL LINES ARE CLEAN,ALL FILTERS EXTERNAL/INTERNAL ARE CLEAN,I HAVE DIFFERENT CARBS WITH DIFFERENT JETTINGS ANYWHERE FROM 2.0-2.5 N&S JETS LOW 120-140 HIGH 135-150, it does not seem to be a fuel problem.
-650 ELECTRICAL,Stator, no cvhanges made.

The Sympton

The ski runs, has no real low end, idle good, gets up to speed but not full speed I can feel it.....no bottom end rip at all.

BUT CHECK THIS

WHEN I JUMP GOING STRAIGHT the SKI SUDDENLY GETS POWER, basically when out of the water, then it somewhat catches on and I have HIGH END but as soon as I let go of the gas and then accelate again nothing.

-CAN THIS BE AN ELECTRICAL PROBLEM ? STATOR ? REV LIMITER ?
-SHOULD I GET THE COMPRESSION HIGER FIRST ?

2 weeks to HAVASU and I need this ski running/

Thank you

Chris

 

[the only couch rider]

seems like you low speed jets are severely fattening the motor which would explain the lack of accel and bottom end, when you jump it out of the water the motor has a chance to rev out w/o a load on it which would explain the pick up on the top end when you get back in the water.....

your low speed should probably be something like a 100-110

 

[norcal ex]

I had this problem on a ported 701 i had. i had a protec pipe on it with stock compression and aftermarket air filters.... switched EVERYTHING and still had same problems. took the protec exaust off and put stock exhaust on and it worked fine.... dont know what the problem was till this day. BTW... i went through THREE different sets of carborators from 46s - 38s and SAME problem!!!

 

[orangefinger]

701 help

- I dont know if the exhaust could be the problem ?

- rejett to 100-110 low ? change N&s TO 1.5 ?

Why does everyone recommend so high jettins then ?

 

[DangerBoy]

You probably have a combination of issues here first your probably jetted to rich for your altitude and do not have enough compression (at 5500 feet) to have good low end punch. You may be overproped for the altitude also.

BUT>>> If you set it up to run corectly at 5500 ft you will have WAY TOO much compression for Havasu

hence you shoud look for a head with interchangeable domes
and get one that is about 4 cc smaller than what you have , and use it at altitude at Havasue your protec head should be about 175

hope this helps

 

[RMBC Freeride]

If it is heavily ported (for top end, race porting) then it will need really high compression to make it work and have some snap. I have dealt with some older pro-tec cylinders years ago that had the same symptoms (especially at altitude)

Are you using a good compression gauge such as a Snap-On?

 

[orangefinger]

701 Help

- I am looking at several heads at them moment and will be purchasing what ever is neccessary this make this work...if I have to take different heads/domes to havasu or lake shast so it wil be no problem.

- I will lower the low end jets, mabey even try it with a stock carb ? who knows....

NOTE : the coffmans pipe was on the 650 in the ski before and against all recommendations of higher jetting I had to keep it low to make it run.

Once the compression is upo to 170-180 do you guys think this will salve the problem ?

C

 

[orangefinger]

701 help

You probably have a combination of issues here first your probably jetted to rich for your altitude

>> jetting will be changed

and do not have enough compression (at 5500 feet) to have good low end punch. You may be overproped for the altitude also.

>> Overproped ? please advice ? I have run the ski with a 650 and coffmans and it felt ok to me...what prop would you recommend.

BUT>>> If you set it up to run corectly at 5500 ft you will have WAY TOO much compression for Havasu

hence you shoud look for a head with interchangeable domes
and get one that is about 4 cc smaller than what you have , and use it at altitude at Havasue your protec head should be about 175

>> right, not to worried about Havasu I know the ski will get scared and run because of all the great mechanix there....


hope this helps

Thank you

 

[DangerBoy]

>> Overproped ? please advice ? I have run the ski with a 650 and coffmans and it felt ok to me...what prop would you recommend.

Just that with that low of compression on a cylinder that is ported for higher rpm your not making enough HP for the prop thats in it
most of your issues should go away with more compression However some ported Protec cylinders have lots of exhaust port duration which than requires lots compression to have any low end punch
they tend to make their power at much higher rpms

also the pipe length could be a bit short if its a 650 pipe

 

[RMBC Freeride]

Without knowing the porting, it is impossible to say if
A) it will solve your problem...
and
B) will it need race gas at 170-180 psi indicated cranking cylinder pressure.. (if the port timing has been raised it likely will)

170-180 psi on a good gauge is only a safe estimate for a non-ported 701

 

[QJS]

It could be that you have a water leak given that you get a surge in power when you unload the pump. Check yhe header pipe is not letting too much water into the exhaust, also the 650 manifold does not match up to the 701 cylinder very well, you probably matched it when you built the engine but it does leave the gasket surface very thin it might be worth checking this area for leaks. Have you pressure ckecked the engine?
Chris.

 

[orangefinger]

701

Exhaust has been matched to Cylinder and so has the gaskets, no leaks !


Here is what I will do...I want to keep this fairly easy if this does not work plan B.

Let me know if you think this makes sense in this order

-I will swap the Head for a High Compression Head that I can get the compression up to 170-180.

-Then change the jetting to lower jets 100-110 LOW , mabey even 1,5-2,0 N&S.

- Last change the impeller, what sort of pitch would you guys recommend.

If this all does not help the Cylinders will be up for sale....my loss ...

I am a rec freestyler and I rather ride then wrench all day, so If this all does not work I am looking for a 701 top end or even a complete engine...

Thank you for all your time and help

Chris

 

[Big Kahuna]

hey, check your pm's

 

[RMBC Freeride]

I think you missed my point... 170-180 compression might be too high for pump gas (91 octane) on that particular cylinder!!!

 

[orangefinger]

701

I missed the point.....

Why would that be to high ?

C

 

[SUPERTUNE]

Aggressive porting can raise the running compression... Start with 125 low jet, stock 1.5 n&s, 95 gram spring and about 130-140 high jet No More..

 

[RMBC Freeride]

^^^^^^ do what he says, he knows way more than me!!!! :hail: ^^^^^

running compression is what I was trying to describe to you Chris

sell some of those 650's, save your cash... have SUPERTUNE build you an engine and you will be amazed!!!!
:bananajump:

 

[sjetrider]

If the exhaust ports are raised at all then 135psi wont work on low end at all. IMO 135 is too low even for stock porting, get smaller domes or aftermarket head. Measure from the top of your exaust port to the top of your cylender (stock 61X is 39mm) let RMBC know what that measurement is and he can tell you what size domes you will need as he knows that altatude.

I would bet the bank this is your problem, as I have been there done that, try to get to aprox 185psi compresion.

OOOPS just noticed this thread was for pros only SORRY

 

[Matt_E]

^^ That will not work on pumpgas. Static compression may be low due to porting, but once the motor is running, the dynamic compression will go through the roof if static is raised higher than it is now.
You can't just take a ported cylinder with raised exhausts, slap a compression gauge on, determine it's too low, and increase compression.

 

[RMBC Freeride]

thanx Matt, exactly what I've been trying to describe to orangefinger!