Jet pump questions

[Camarojoe12]

Hi all, I am new to seadoo’s but have always liked the old school skis so I finally grabbed one. It is a 1990 3 seater gt with reverse, it needs a motor which I picked up to swap out of a good running “parts” ski. I figured while I was replacing the engine I would replace all of the fuel and oil lines as well as power wash everything. I had a few questions about the project maybe some one can answer. 1) will the original dual carb setup work on the single carb motor if I swap the manifold? 2) are the jet pumps the same? The parts ski has a brand new stainless impeller and wear ring that was just installed.

 

[POPPS]

why the swap "down?"

 

[Camarojoe12]

why the swap "down?"

What do you mean by swap down ?

 

[mikidymac]

He is asking why downgrade to a single carb I think?

There is no performance difference between the single and dual carb setup.
However if you have the white engine and yellow engines the white is better. Also you don't want to go to the older round body mikuni carb on the yellow engines.

Pump is the same but impellers will be different.

 

[Camarojoe12]

He is asking why downgrade to a single carb I think?

There is no performance difference between the single and dual carb setup.
However if you have the white engine and yellow engines the white is better. Also you don't want to go to the older round body mikuni carb on the yellow engines.

Pump is the same but impellers will be different.

Ahh I see, should have specified they are both yellow motors. The gt has dual carbs but a bad motor. The parts ski has a good motor but single carb. It also has a rebuilt pump

 

[mikidymac]

Just rebuild the carb on the good engine with Genuine Mikuni parts.

 

[Camarojoe12]

Just rebuild the carb on the good engine with Genuine Mikuni parts.Is

do you know if the throttle cable is the same for a single carb? The ski it is going in had the dual carbs

 

[Camarojoe12]

He is asking why downgrade to a single carb I think?

There is no performance difference between the single and dual carb setup.
However if you have the white engine and yellow engines the white is better. Also you don't want to go to the older round body mikuni carb on the yellow engines.

Pump is the same but impellers will be different.

What would be different about the impeller? The parts ski has a brand new stainless impeller and wear ring, I inspected the impeller and wear ring in the project ski and the wear ring is falling apart. So can I just swap out the entire pump from one ski to the other?

 

[1of500]

Different hull Different pitch

 

[Camarojoe12]

Different hull Different pitch

If Im correct the diameter of the impeller is the same 14”, but the pitch is different for the 1990 gt I am restoring,the pitch is 18.8. The parts ski I have is an sp I’m not 100% sure of the year but according to the impeller chart 1988 sp had 16.5. 1989 had 18.8 1990 had 17.0 and 1991 had 18.8. So let’s just say it’s either a 16.5 or 17 not the 18.8 recommended, into the gt. How would it perform? Is there any way I could confirm the pitch? If it would be a problem? I’m only asking all of these questions due to the fact I already have the parts on hand and they are brand new.

 

[tobytd]

The lower pitch will give a better hole shot. But not as much top end speed. GT is bigger and heavier than the SP. Give What you have a try. It can always be changed later.

 

[Camarojoe12]

The lower pitch will give a better hole shot. But not as much top end speed. GT is bigger and heavier than the SP. Give What you have a try. It can always be changed later.

My thoughts exactly. I’m not even looking for speed. I just want to get to the sand bar and tie off for the day without having to load up the boat

 

[Camarojoe12]

Here they are, just need to swap out the nozzles tomorrow and throw it in

 

[Camarojoe12]

The lower pitch will give a better hole shot. But not as much top end speed. GT is bigger and heavier than the SP. Give What you have a try. It can always be changed later.

While finishing up the engine swap I noticed I have an extra water hose that connects to the water tells. Then realized the engine I installed doesn’t have a nipple in the valve cover to accept it. Do I need to hook it Via swapping the valve cover? Or just by pass it. I also noticed the exhaust manifold is different. The manifold I removed has big open ports and the manifold on the new engine has two little holes with o-rings. Any help is appreciated

 

[Camarojoe12]

While finishing up the engine swap I noticed I have an extra water hose that connects to the water tells. Then realized the engine I installed doesn’t have a nipple in the valve cover to accept it. Do I need to hook it Via swapping the valve cover? Or just by pass it. I also noticed the exhaust manifold is different. The manifold I removed has big open ports and the manifold on the new engine has two little holes with o-rings. Any help is appreciated View attachment 55325

 

[rbowes1]

I dropped a '90 SP motor (with the old round single carb and external fuel pump) in my dual carb '91 XP that had a blown motor (both yellow). I used all of the parts (intake, exhaust, etc.) from the '91 XP, just swapped the motor itself. As far as I can tell all the specs (compression, spark advance, etc.) are the same, just the rotary valve timing is different so I adjusted this. After a carb rebuild it works great. And as everyone says use genuine Mikuni parts, I learned the hard way!

 

[Camarojoe12]

I dropped a '90 SP motor (with the old round single carb and external fuel pump) in my dual carb '91 XP that had a blown motor (both yellow). I used all of the parts (intake, exhaust, etc.) from the '91 XP, just swapped the motor itself. As far as I can tell all the specs (compression, spark advance, etc.) are the same, just the rotary valve timing is different so I adjusted this. After a carb rebuild it works great. And as everyone says use genuine Mikuni parts, I learned the hard way!

Same, I took a motor from a good running 90 sp and put it in my 90 gt. So far the differences I see are, #1 single round carb vs dual. #2 the exhaust manifold from the sp water ports are just round little holes with o rings. The gt is wide open. #3 the head cover from the sp does not have a little water nipple In it. What made you adjust the rotary valve?

 

[rbowes1]

The shop manual for the '91 XP (and the GT) shows the rotary valve opening at 115 degrees BTDC and closing at 65 ATDC. For the '90 SP it is 132 and 52. The rotary valve itself for all of these is the same so it is just slightly rotated on the gear. To be honest it didn't seem to make too much difference performance wise.

 

[Camarojoe12]

I’m not even going to play with it, I know for a fact the engine ran great in the Sp I removed it from. I literally just dropped it in and swapped the pumps. I was just concerned with the cooling lines and how they are slightly different. From what I’ve seen the gt has 2 pisser lines one from the tuned pipe and one from the cylinder cover. The sp only has one coming from the tuned pipe. So I think I will be fine just leaving the one line off

The shop manual for the '91 XP (and the GT) shows the rotary valve opening at 115 degrees BTDC and closing at 65 ATDC. For the '90 SP it is 132 and 52. The rotary valve itself for all of these is the same so it is just slightly rotated on the gear. To be honest it didn't seem to make too much difference performance wise

 

[Camarojoe12]

The shop manual for the '91 XP (and the GT) shows the rotary valve opening at 115 degrees BTDC and closing at 65 ATDC. For the '90 SP it is 132 and 52. The rotary valve itself for all of these is the same so it is just slightly rotated on the gear. To be honest it didn't seem to make too much difference performance wise.

I was able to swap the valve covers out. Only one bolt broke off, but I was able to extract it. Today I tried to start the ski up after priming the oil pump and all the fuel lines, it took a while to start, it won’t idle smoothly and stay running without feathering the throttle. But revs up great and smooth. Any idea what may be the issue? I also noticed the pulse line coming from the block to the fuel pump has fuel in it. Is that normal?

 

[rbowes1]

Shouldn't be fuel in the pulse line. Maybe a bad fuel pump diaphragm - ?
Have you rebuilt the carbs?