Reed valve questions!! HELP!

[Nisse Järnet]

I think that my reeds is crap, and should really need some help here! :)

Ski set-up: -90 Superjet with 701 cylinders (61X) Wiseco pistons, ADA head, Pro tec pipe, no water box, pro tec CDI, MSD ignition coil, kawasaki 750 intake welded onto the crank, boysen pro series reeds, two 46mm mikunis and riva f/a.

This is how the ski is behaving:
After warm up it runs nearly perfekt, but efter a few minutes it starts to feel very rich att full throttel. And after ca 15min of riding it is going like crap over 60% throttel. The best speed is reached at around 50-60% throttel. I dont think that its the carbs, i have tried to tune them but i wont help. And on top of that, they are brand new (Mikuni 46mm) and the ski is running exactly the same as before. (when i had my old 44 mikunis)

I had Boysen Pro Series reeds on, but i also tested with the stock reeds but it didn´t do any big diffrence. It runs a little bit better, but is harder to start. (None of the reeds seald compleatly against the "reed valve body")

Do you guys think that its the reeds causing this?? And in that case, wich reeds should i buy?

Sry for my bad english.

[sadchapter]

Re: Reed valve questions!! HELP!

There is a pulse pump on your mikuni right?
That goes to intake manifoil right?
I would guess that the pulse is operated by vacuum and pressure from manifoil.
How much leaking reeds affect this Im not sure of but Im pretty sure it does.
It would be much more noticeable in low RPM mayby why you have difficulties starting up.

Tjenare!

[Bill O'Neal2]

Re: Reed valve questions!! HELP!

It is extremely difficult to propery tune a motor with leaky reeds. Have you tried bending the reed stops to put more pressure on the reed petals to hold them tight against the reed cages? But, if that won't work, buy new reed petals or new reeds.

Delta V-Force reeds, or Boyseen reeds are both popular choices.

[Nisse Järnet]

Re: Reed valve questions!! HELP!

Thanks for the answers!! :)

sadchapter: Yes you are right! But with the Boysen reeds i had no starting problems. The starting problems came when i installed the stock reeds about a week ago.

Bill O'Neal2: No i havent! Yet ;) I think im going to buy new reeds anyway, the other ones i have is pretty old i think. How is the Dela Force life time compared to Boysen? Do you have to change them every year?

Thanks again!! This is very helpfull! I want it to get going as soon as possible :)

[wmsky]

Re: Reed valve questions!! HELP!

It really sounds as if you are running just a little too rich. When the engine is cold, the additional gas helps it run better, but as it warms up, the extra gas is choking it.

Are you sure the choke plates on your carbs are opening fully when you turn the choke off? Take the top off your f/a and make sure.

Are you sure the carbs are jetted correctly, and the pop-off pressure is correct for your ski?

[Nisse Järnet]

Re: Reed valve questions!! HELP!

It really sounds as if you are running just a little too rich. When the engine is cold, the additional gas helps it run better, but as it warms up, the extra gas is choking it.

Are you sure the choke plates on your carbs are opening fully when you turn the choke off? Take the top off your f/a and make sure.

Are you sure the carbs are jetted correctly, and the pop-off pressure is correct for your ski?

I thought that too! But now i dont think so? :S

This is the story (short version)
When i bought the ski it had 2 mikuni 44mm and ran really good! But then after half a year or something it started to go a little rich, so i adjusted the carbs. But then it started to go gradually richer (or it felt like that) and last year i didnt really got it right. So this winter i bought 2 new 46mm mikuni just to get rid of the problem once for all, but it ran exactly the same as before! Then i changed the main jets from 150 to 125 but with no big diffrence. I also raised the pop off from ca 16 to ca 22. After this it feels a little lean att low throttels when its cold. It doesnt really matter if i turn the screws all the way out or all the way in.

What do you think? (hope you understand what im saying :))

[wmsky]

Re: Reed valve questions!! HELP!

If you swapped the carbs and it is runs exactly as it did with the other carbs, it may not be the carbs. When was the last time you replaced your plugs. Maybe the plugs have been producing a weaker and weaker spark over time. Could be fouled plugs maybe or old plug wires. Try getting a plug you're pretty certain is good, pull the wire off each of the spark plugs one at a time, hook it to the good plug, ground the plug, crank the engine, and see what kind of spark you get. If you get a good spark, swap that plug with one in the engine, and test again. See if the plug you pulled has as good a spark as the good one you started with.

[Nisse Järnet]

Re: Reed valve questions!! HELP!

If you swapped the carbs and it is runs exactly as it did with the other carbs, it may not be the carbs. When was the last time you replaced your plugs. Maybe the plugs have been producing a weaker and weaker spark over time. Could be fouled plugs maybe or old plug wires. Try getting a plug you're pretty certain is good, pull the wire off each of the spark plugs one at a time, hook it to the good plug, ground the plug, crank the engine, and see what kind of spark you get. If you get a good spark, swap that plug with one in the engine, and test again. See if the plug you pulled has as good a spark as the good one you started with.

Thanks for the answer! Apriciate it alot! But when i put the new carbs on, i also installed a new MSD igition coil with wires and new plugs :S So i dont think its that. Can you measure the coils and pick up on the engine?

[Bill O'Neal2]

Re: Reed valve questions!! HELP!

A service manual will give you resistane ratings for oem coils and ignition pickups.

[wmsky]

Re: Reed valve questions!! HELP!

Thanks for the answer! Apriciate it alot! But when i put the new carbs on, i also installed a new MSD igition coil with wires and new plugs :So i dont think its that. Can you measure the coils and pick up on the engine?

It can't hurt to check for good spark anyway. It'll only take a few minutes and there might be a problem with the CDI.

[Nisse Järnet]

Re: Reed valve questions!! HELP!

Thanks for all the help guys! Im about to order a new set of reeds. Going to do some more checks on the ski this weekend.
Could it have something to do with a relatively big piston to cylinder clearence? I dont think so, but you never know :)